Transcript for:
Understanding the Digestive System

hey everybody in this video we're going to go through the digestive system we're going to start by going through each organ and then we'll talk about um breakdown of different macro molecules so we're going to start with the digestive um functions so there are essentially um several processes that are happening in the digestive system um that are all going to have to do with you know breaking down food and absor nutrients so the first stage is ingestion this is the selective intake of food this is going to start in the mouth include the ferx the lnx esophagus for swallowing okay then we're going to move on to digestion we have two types of digestion we have mechanical and chemical chemical is going to use um enzymes and the mechanical is going to be done through um uh movement so like chewing or mixing in the stomach the third process then is absorption this is when we actually take the nutrients and put them into the bloodstream um or or into the lymphatic fluid so then we can use them um this is primarily done in the small intestine moving on then we have compaction this is where we're going to absorb water and consolidate that indigestible residue this happens in the large intestine and then finally defecation which is elimination of the feces which goes through through the um rectum and the enus so again let's just talk about mechanical and chemical digestion so mechanical digestion is where we're going to use for me it helps to remember movement so the MS go together um this is where we're going to physically break down the food into smaller particles um so again um chewing turning in the stomach all of this increases the surface area and exposes the food for the digestive enzymes which is part of the chemical digestion so chemical digestion is um hydrolysis reaction so we're basically um adding water that are going to break apart our macro molecules into their monomers so we're going to come back and talk about this a little bit um so this is done by our enzymes okay um the enzymes are going to be produced in the salivary glands the stomach the pancreas and the small intestine Mo most of our enzymes end in this suffix ASE um just a reminder right our polysaccharides are going to become monosaccharides proteins become amino acids fats become monoglycerides and fatty acids and nucleic acids come nucleotides and so these are your um monomers here and then some of our nutrients are present in an already usable form so that's going to be our vitamins amuno acids minerals cholesterol and water so we don't have to break those down any so looking at the anatomy then digestive system is basically divided into two categories the digestive tract in the elementary Canal or the accessory organs and so the digestive tract is that tube that goes from the mouth um all the way through to the large intestine and then the accessory organs are all the other things so we're going to just start um looking at this so again the digestive tract mouth feric esophagus stomach small intestine large intestine rectum anus okay anal Canal anus and then your accessory organs teeth tongue liver gallbladder pancreas um so when we're looking at kind of the layers of the digestive tract the layers of the digestive tract are essentially the same there are a few instances where we have additional lay layers and we'll talk about that but um the main layers we have the mucosa which is um consists of three sub layers so the epithelium the lamin appropriate and the muscularis mucosa we have the sub mucosa and then the muscularis externa which is going to be two smooth muscle layers and inner um circular layers so the muscles run like this and then an outer longitudinal layer where the muscles run um lengthwise and then we have the Sosa which is made up of aerial or tissue and mesothelium and so most of the um digestive tract is going to follow this so you can see if we start on the inside deepest right we have the mucosa so the light pink here is that stratified squamous epithelium and then the gray tan color here is the lamino proii and then the thin pink band is the muscularis mucosa so those three layers make up the mucosa layer and then we have the um sub mucosal which is again is this brown thicker brown gray area and then the muscularis externa which is two smooth muscle layers so the inner circular layer and then the outer longitudinal layer and then we have the Sosa that is covering it um so we can talk about this a little bit bit more so again we're we're going deep to superficial okay so the mucosa lines the Lumen it's the epithelium it's a simple colar epithelium and most of the digestive tract um we do have stratified SOS epithelium in a few special locations mou through the esophagus and the lower anal Canal the lamin appropri in is loose connective tissue and the muscularis mucosa this is a thin thin thin layer of smooth muscle um this is going to create grooves and ridges that increase the surface area this is where we'll also see the mucosa Associated lymphatic tissue or The Malt which we talked about um this is those lymphocytes or lymphoid nodules that are going to be in our digestive tract the sub mucosa then is a layer of um thick uh loose a thicker layer of loose connective tissue um it has blood vessels lymphatic vessels nerves okay we have goblet cells or mucous secreting glands um and The Malt is going to extend into this layer as well and then the muscularis externa okay so again most of the places this is going to be two layers so the inner circular layer and the outer longitudinal layer okay the inner layer also can form these valves or syins that are going to help with regulating movement okay um and so this muscularis externa this is responsible for the M Mo motility that propels the food through the the digestive tract so it's responsible for peristalsis those rhythmics smooth muscle contractions and then the outermost layer is the Sosa this is a thin layer of areolar tissue and then it has simple squalos mesothelium okay and this is going to go from the esophagus just before for the rectum um some organs don't have the Sosa but instead have the naen tiia which is a fibrous connective tissue so the type of connective tissue is different looking at the nerve control then of the digestive tract this is primarily going to be regulated through the inic nervous system or this inic plexus this is a nervous Network in the Esopus stomach intestine it regulates digestive motility secretion and blood flow the cool thing about this is it functions independently of the central nervous system but the central nervous system can also influence his actions um so it is sometimes considered a subdivision of the autonomic nervous system and then it has two networks of neurons so the sub mucosal plexus which is found in the sub mucosa this controls secretions so kind of all the s's go together and then also movement of the M muscularis mucosa then the myenteric plexuses are in that muscularis externa and so this controls peristalsis so remember my is muscle so this is going to do that smooth muscle that controls peristalsis um this also includes Sensory neurons to monitor um tension in the gut wall and conditions in the Lumen as well so we already went through that so the mesentary is a connective tissue sheet that suspend the stomach and intestines from the abdominal wall essentially think of it as it's a way that's going to hold these organs in place okay um it does have some looseness which allows the stomach and intestines to um contract it gives them freedom of movement but it also holds everything in place and in proper relationship to other it also helps prevent the intestines from becoming Twisted when we change body positions and move and the mesentary provides passage for blood vessels and nerves that Supply the digest digestive tract it does contain a lot of lymph nodes and lymphatic vessels to help with um immune function as well um the mesentary is a folded membrane and then the different regions of it so different areas of it have specific names so parietal peronia lines the abdom wall of the abdominal cavity um this will form the posterior mesentary so this is a two- layered membrane that goes into the extends to the digestive tract um these layers will then separate and go around opposite sides of an organ to form the Sosa and then they'll come together again to form the anterior mesentary um and then if you're looking at the anterior extensions of the mesentary there are two kind of big ones that are associated with the stomach so we have the Lesser momentum and the greater momentum so the Lesser extends from the Lesser curvature of the stomach to the liver so the lessers go together and then the greater go together so the greater armentum hangs from the greater curvature of the stomach so it covers it it it sits over the small intestine okay um and it will form this mesocolon which is a portion of that mesentary that anchors your transverse colon to the uh posterior abdominal wall and so this is part of our first line of defense against pathogens and we talk about the perineum um like we'll talk about different regions so we'll talk about intrarenal or retrop peronal and so I just wanted to kind of Define those words so intra paranal is when an organ is enclosed by the mesentary on all sides so this includes the stomach the liver and parts of the small or large intestine we also talk about an organ being retrop peraonal which means that it's against the posterior body wall and it's covered by perenium on its anterior side only um so this would be the dadum of the small intestine or duum the pancreas and then parts of large intestine would be retr parital so again know we talked about all this but now we can kind of visualize it to help us see okay so here's the Lesser curvature of our stomach so we have the Lesser momentum here this is the greater curvature of the stomach and so this is the greater momentum that covers up the small intestine and then you can see the mesentary from the small intestine and the mesocolon that anchors the um transverse colon here in place okay so looking at regulating the digestive tract we're going to look at regulating motility and secretion so motility is moving the food through the digestive tract and then the secretions are necessary for digestion and so this is going to be controlled by uh neural hormone and paracrine mechanism so neural controls we have kind of we have two reflexes here so the short mayic reflex this is going to sense stretch right we've seen myo before okay um or a chemical stimulation this will stimulate paracolic contractions the long or Veo vagal reflexes so the Vegas nerve is parasympathetic so this is going to be parastic Paras parasympathetic stimulation of digestive motility and secretion so remember parasympathetic is going to increase digestion digestive motility and secretions we also have um hormones that can regulate motility and secretions um such as gastrin and secretin and then finally we have paracin which are um secreted and going to stimulate nearby cells okay so we're going to start looking at each organ and talking about its anatomy and its function we're just going to start in the mouth and work our way down the mouth is also called the oral cavity or bual cavity it has many functions which involves ingestion as well as taste chewing chemical digestion swallowing speech and respiration there are lots of parts to the mouth including the cheeks lips pallet and tongue um the oral Fisher is the anterior opening between lips and then the fosies is the posterior opening to the throat this is made up of straide Squam epithelium that lines the mouth um there are both keratinized and non- caroen area so the gums in the hard pallet are keratinized the others are going to be non-c caroen okay so we're looking in the mouth we're going to talk about the cheeks the tongue the lips teeth okay so let's look at the cheek cheeks and lips okay their functions are to hold food into your mouth be able to push it between the teeth um we use them for speech and producing sounds also suckling okay um also here we're going to have the labal frenulum which attaches the lip to the gum and then we have the vegetable which is the space between the cheeks or the lips and the teeth the lips then are divided up into three areas the cutaneous area which is colored like the rest of the face so that's the part between your nose and what you would normally call your lip and then you have the red area which is the hairless region where your lips meet and then you have the labial mu mucosa which is the inner surface where the lips um face the gums and the teeth rub up against the gums and the teeth okay then on the tongue the tongue is a muscle okay so it's muscular and bulky but it's also very sensitive so its functions are to help manipulate food also does taste and texture of food it is nonkeratinized stratified squalos epithelium we have lingual propil which are the bumps and projections where the taste buds are and then your Chong is much longer than you probably real iiz the body is the anterior 2/3 and then you have the root which is a whole other third that goes into the oral fex on the tongue then we have um some different structures so we have the valet pil so valet and V they form a v-shaped row that separates the body from the root of the tongue and then we have a terminal sulcus we've seen sulcus before is a Groove so this is a Groove behind the valet Pilla the lingual frenula so we saw a labial labial fulum um this will attach the tongue to the floor of the mouth and then we have ex intrinsic and extrinsic muscles that are going to be involved with moving the tongue we also have um the lingual glands and the lingual tonsils that are around the tongue so if we look at the tongue here okay so we have the body and then the root okay you have the valet Pilla which make this D shape and then behind that is the terminal suus okay so this is the root and then in front of that is the body on the tongue itself then we have the fungiform Pilla and the foliate Pilla and then you can see in the back also we have our palentine tonsil and our lingual tsils lots of stuff happening with theone you can also here see um intrinsic muscle in the tongue itself and then the extrinsic muscles all of these are involved in movement and of the tongue okay the mouth then is separated from the nasal cavity by the pallet okay the pallet has two parts to it it has the hard pallet which is the anterior portion it's hard because it's made of bone and then we have the soft palette which is the posterior portion it has more of a spongy texture it's skeletal muscle and glandular tissue um we also have the uula of the soft pette which is just at the rear of the mouth helps keep food in the mouth until you're ready to swallow and then we have um muscular things that are going to help with the mouth in kind of separating again separating the oral cavity from the nasal cavity so when we chew food it doesn't squish up we also have in the mouth we also have the teeth which is called your dentition um obviously these are going to be involved in chewing our food which increases surface area right makes them small pieces makes the food easier to swallow exposes them to digestive enzymes so adults we have 32 adult teeth um so 16 and 16 and they follow the same pattern so um two incizors one canine two premolar and then three MERS so two one two three and it goes around each side top and bottom each tooth is embedded in the Alvis which is the socket for the tooth you may remember this is the gomphosis joint which is between the tooth and the bone and then we also have the periodontal ligament um that will anchor the tooth in the alviola so it allows for some flexibility when we bite down but it also holds our teeth in place so if we're looking at our okay so children have 20 teeth again it's the same on the top and the bottom okay adults have 32t so two incizors a k9 two premolars and then three molar so it's the same left to right top and bottom looking more specifically at the tooth then um the gingiva are the gums that cover the Alvar bone and then the tooth kind of has three Re regions the crown which is the part that you call your tooth that's visible above the gum the root um which is below the gum it's in the in the alveolar bone and then the neck which is where the crown root and gum all meet the ginger sulcus then is the space between the tooth and the gum this is where you're flossing this is important for your dental health to floss those Ginger fcus the te tooth itself then has three kind of structural components to it the Dentin is a hard yellowish tissue that actually makes up most of the tooth and then the enamel is on the outside um this is a non- cellular secretion it can't be regenerated this covers the crown and the neck and then the cement covers the root and then deep in we have the root canal that leads to the pulp cavity the pulp cavity contains the blood vessels and nerves occlusion then is the meeting of the teeth when the mouth is closed accusal surfaces of your premolar and MERS have cusps those bumps that are especially there for grinding and chewing your food so looking at our tooth we have the crown above the gum line the neck at the gum line and then the root down into the bone okay we have the pulp cavity with the blood vessels and nerves okay the root canal where the nerves and blood vessels are going to come in and we have the Dentin which is the yellow and then the crown and neck are covered with enamel and the root is covered with cement our teeth will develop beneath our gums and they erupt in a predictable order so you have 20 deciduous or baby teeth um and they erupt from starting six months to six to 30 months um and then they are going to be replaced with permanent teeth starting at age six UPS to 25 years the third MERS are also called your wisdom teeth those are going to erupt from age 17 to 25 um if they erupt at all um many of them actually remain below the gum line and become impacted basically there's not enough room for them to erupt because of the neighboring teeth that's what impacted means and so you can see here in this picture so you have some of the permanent teeth here right growing in the jaw that are going to push up push the ddu or the baby teeth your mouth has a lot of bacteria in it you got over 700 species of microorganisms in your mouth um and so this generates what's called plaque plaque is that sticky residue on the teeth it's made up of bacteria and sugars um the bacteria metabolize the sugar and release acids the acids dissolve the enamel and then that forms Dental cavities um a root Canal may be necessary if the cavity reaches into that deep part of that pulp the plaque also can calfy um and can um penetrate into the gingerful sucus it separates the tooth from the gum and then you can get infection there called gingivitis which can progress to periodontal disease so this is why you go to your six-month dental cleanings so that they can get that calcifi plaque off and make sure that it's not um infecting the gums mastication is our fancy science word for chewing okay this again breaks the food into smaller pieces it's mechanical digestion okay um we're going to use the tongue and all these muscles right to help with chewing and grinding and breaking things up and all of this is to help increase the surface area in our mouth we also we're going to produce the saliva saliva has many important functions it moistens our mouth it's mostly water it's going to begin starch and fat digestion so you're going to have salivary Amala it's going to break down do starch digestion and you're going to have lingual liase that's going to start doing um fat digestion it cleanses the teeth um so you have IG antibodies and inhibits bacterial growth you have l enzymes um which is going to help inhibit bacterial growth and dissolves molecules so that they can stimulate our taste buds without being dissolved in water we can't taste it also will help moisten our food and binds it together into a Bolis once we're ready to swallow it so the Bolis is just the mass of Che up food basically so again your saliva is mostly water okay um it has a pretty neutral pH 6.8 to 7.2 we've talked about these things the mucus will bind and lubric lubricate the food it does have electrolytes in it the Lyme will kill the bacteria the IGA helps cleanse the mouth it's an anti microbial antibody the salivary Amala so it ends an ASC so this is an enzyme this is going to start our starch digestion and lingual lipase is going to start our lipid digestion two types of salivary glands based off of their location intrinsic or extrinsic intrinsic salivary glands are small and they are dispersed among other oral tissues um so you're can to have some in the some in the tongue some in the inside of the lips some in the pallet and some inside the cheeks but then we also have our ex transic or our major salivary glands and there are three pairs um these are much larger so you have the pared glands these are just anterior to each earlobe you have the submandibular gland which are along under and along the mandible and then you have the Su lingual gland which is located under the tongue and the floor of the mouth so looking at our salivary gland here's our pared gland so these are paired okay and then submandibular so this is the mandi's been cut here so under the mandible and then sublingual under the T on the floor of the mouth looking at our salivary glands in the microscopic structure okay you've seen glands like this before in Two of Wands you have mucus Cirrus mixed okay and so these are going to create create all of those enzymes and secretions from the saliva our ex transic salivary glands secrete about one to one and a half liters a day um and again the different cells are going to have different functions so we're going to filter water and electrolytes from the blood add in the Amala muin and Lyme okay um this is going to be regular ated by the medulla oblongata okay and it's going to um stimulate saliva production if we have the odor sight or thought of food the salvatory nuclei are going to this is autonomic this is part of that autonomic nervous system right um and it's G to parasympathetic fibers produce thin enzyme saliva because parasympathetic is going to increase digestion so we need those enzymes to start doing digestion or sympathetic also um is going to do saliva production but now the quantity is going to decrease and it's going to become thicker saliva so it makes our mouth more dry and sticky than parasympathetic where we're preparing for a meal all right that was the m which was a whole lot and we're going to move on to the ferx we've talked about the ferx um because it is also part of our respiratory tract um it connects our oral cavity to our esophagus and the nasal cavity to the Linex okay so it's it's both in our digestive and respiratory tract okay um it does have um a deep layer of longitudinal muscle as well as that superficial layer of circular um that's going to form these constrictors that will help push food down um when we swallow so it does create this upper esophageal sphincter um so that we don't swallow a bunch of air which can make us gassy and uncomfortable okay moving on to the esophagus then the esophagus is a muscular tube um between the FX and the stomach it extends from the fex to the cardiac Orphus of the stomach it does pass through this esophageal Hiatus so it does pass through the diaphragm and we do have this lower esophageal sphincter at the end of the esophagus it's very important because it prevents the um stomach contents from backing up into the esophagus particularly important to help um protect the esophagus from the um hydrochloric acid from the stomach acid which is very acidic and very erosive when this doesn't close all the way and we do get some of the hydrochloric acid it will burn it produces acid reflux in the esophagus and can burn away the esophagus um the esophagus is is going to have non- cariz stod swos epithelium we do have esophageal glands that are going to secrete mucus to help lubricate it does contain m m muscularis externa but this is a little bit different um so the esophagus the upper oneir is skeletal muscle the middle one3 is mixed and then the bottom one third is smooth muscle so as you go down the ES um you lose that conscious voluntary control okay and most of the esophagus has aventia and then the part below the diaphragm is covered with that Sosa instead of the aventia swallowing or deglutition okay is more complex than you think of involves 22 muscles and three organs mouth FX esophagus and this is coordinated by a swallowing Center in the medulla ablang that swallowing Center communicates with all of the muscles to help coordinate all the actions that are necessary for swallowing and so there are kind of there are three phases of swallowing so I want to go over each one kind of briefly so you have the oral phase this is voluntary control the tongue is going to collect the food um pushes it and forms that bolus and and we're going to swallow that b is going to um tip over and cover the Linex so that the food will slide into the loparic and then into the esophagus okay so here's the oral phase the tongue forms the Bolis and pushes it into the loparic the second phase then is the fenal phase this is involuntary this prevents food and drink from re-entering the mouth or going up into the nasal cavity your breathing is temporarily suspended so the LX comes up to meet the epiglottis covers up the l gal opening okay um and the food bowls is driven downward by constriction of those Fair andal constrictors mes the food down instead of up so here is our F andal phase okay the pallet tongue vocal cords everything blocks um the food from going into the Linex or going up into the nasal cavity and then the fal constrictors are going to push the bolus into the esophagus so then the third phase is the esophageal phase also involuntary and this is where we're going to see that peristalsis begin um the muscles are just going to contract above the Bolis and push the Bolis down and we're just going to keep doing this okay um until we get the food moving where we so it's going to go from the esophagus down towards the anus okay um liquid can reach the stomach in one to two seconds a food bowl is takes four to eight seconds when it gets to the end of the esophagus that lower esophageal sphincter is going to relax to let the food go into the stomach so here we see the pistolic contractions the parolis as we move the Bolas down the esophagus and into the stomach when we get to the stomach that lower esophageal sphincter is going to relax to allow the food to go into the stomach so let's move on to the stomach when you think of digestive system probably the first organ that you think of is the stomach um and it is important but it does not do a lot of digestion it's primarily a storage organ um rephrase it does digestion it doesn't do a lot of absorption so it will break up food particles it liquefies the food and does chemical digestion this converts that Bolis into a Kim which is that acidic soupy mixture of semi- digestive food that goes into the small intestine and then that's where absorption is going to occur the stomach has four regions to it so you have the um cardiac region the fundic region the body and the pyloric part the pyloric part is at the end towards the small intestine and so we will also have the pyloric spincter that is going to regulate the movement of time into the small intestine um the stomach has two margins two borders the greater and the Lesser curvature which we already talked about when we talked about the momentum so let's look at the stomach so again here's your lesser curvature and the greater curvature okay the regions so you have the cardiac part the fundus the Dome you have the body okay you have the pyloris and then the pyloric syncer one thing that I want to note about the stomach is that it does have three three muscle layer so you have the longitudinal and the circular muscle that we have in all of the digestive tract but we also have an additional oblique muscle layer and so that allows for increased mixing and turning in the stomach so again you can see the stomach okay so the curvatures greater curvature real big lesser curvature hard fundus body pyloris hyic syncor the stomach does have both sympathetic and parasympathetic fibers so parasympathetic comes from that Vegas nerve and then the sympathetic fibers come from the celc ganglia um it does get branches of blood from the Celiac trunk which you remember is coming off of that um descending aorta and then fluid that or blood that drains from the stomach enters the hepatic portal circulation so it's filtered from the liver before it gets put back into the general circulation the stomach wall has the same tissue layers okay there are some variations um so the mucosa has simple cmer epithelium okay um the mucosa and sub mucosa are flat when the stomach is full but it forms these wrinkles called the gastric rug or R um and then the musculars externa has three layers so remember we have that inner oblique layer that we didn't have in the other digestive organs so if you're looking at the mucosa of the stomach wall okay so this is the Lumen so we have the m musculars mucosa and the sub mucosa so we have pyloric glands and we have gastric gland forms these gastric pits okay we have mucus cells parial cells right we're going to talk about the functions of all of this in just a minute so the stomach does contain you saw those gastric pits so there depressions In the gastric mosa that are lined with colmer epithelium um and then they have the cardiac glands in the cardiac part pyloric glands and the pyloric part and then gastric glands um everywhere else so it kind of looks like this honeycomb shaped thing to me these gastric pits but you can see them how deep they are so let's talk about the different cells and what they produce then because they all have important functions mucosa cells are going to secrete mucus okay um they are going to primarily be in the card and the pyloric gland regenerative stem cells um will divide rapidly and produce new cells to replace the cells that die the parietal cells secrete hydrochloric acid intrinsic factor and grin the chief cells are the most numerous type they secrete gastri gly case and pepsinogen and then we have inner Ino Endocrine cells that secrete hormones and paracrine messagers and there's a variety of those so again looking at the cells so you have the mucus or the neck cells you have the parial cells and then you have the tooth cells the stomach is going to produce 2 to three liters of gastric juice per day it's mostly water hydrochloric acid and pepsin which is going to work on digesting and breaking down proteins so the hydrochloric acid again really acidic truthfully pretty nasty stuff it can jump the pH as low as 2.8 um typically the range is closer to 2 to four but really acidic um the hydrochloric acid is produced by the parietal cells and they do use Carbonic and hydrates we talked about that with our carbon dioxide loading and unloading okay um they also do this chloride shift again we saw this with our um carbon dioxide loading and unloading um we can get if we get an elevated amount of by carbonate it can result in alkaline tide so we're going to get a high pH in the blood leaving the stomach when digestion is occurring okay so this is going to be active during digestion we're using the hydrochloric acid so when we're looking at hydrochloric acid secretion okay so you have the hydrochloric acid you have the um hydrogen potassium atpa pump bicarbonate okay and the chloride shift which can make the blood more alkaline because of the accumulation of the bicarbonate hydrochloric acid while it's pretty nasty has several important functions it activates um our enzymes so pepsin and lingual lipase it also breaks up connective tissues and plant cell walls so it's responsible for liquefying that food to form the time also it converts uh fe+ 3 to fe+ 2 um fe+ 2 is the iron ion that we need to make hemoglobin it also contributes to your um innate immunity because it's too acidic for most pathogens and so it destroys them so let's talk about pepsin for just a minute um pepsin is a zymogen which are digestive enzymes that are secreted as inactive proteins um so zymogens have to be converted to active enzymes through removing some of them amino acids so pepsinogen is the zymogen and it is converted to pepsin um and the conversion is actually done by the hydrochloric acid the hydrochloric acid will remove some of the amino acids from pepsinogen to form pepsin the role of pepsin is that it will digest dietary proteins into shorter peptide so it's going to take those long proteins and make them into shorter proteins so here if you want to look at so the parial cells the chief cells parial cells make the hydrochloric acid we need the chief cells make the pepsinogen the hydrochloric acid cuts off the part of the peptide removed it and that converts pepsinogen xymogen which is inactive to pepsin the active enzyme and then pepsin will break our dietary proteins into smaller peptides gastric liase is secreted by the chief cells okay gastric lipas and lingual lipas play a tiny role in digesting our dietary fats about 10 to 15% of our dietary lipids um digested in the stomach the rest are digested in the small intestine intrinsic factor intrinsic factor is really important um you may have never heard of it before but it is essential to the absorption of vitamin B12 from the small intestine so secretion of intrinsic factor is the only indispensable function of the stomach okay we have to have it so that we can absorb vitamin B12 and make healthy hemoglobin so if your stomach is removed d digestion continues but you got to take B12 supplements because you're not going to be producing intrinsic factor the stomach also will secrete several uh chemical Messengers um and these are mostly hormones that are going to enter the blood um some of them are paracrine but most of them are hormones um we have these gut brain peptides so these are peptides produced in both Digestive and the central nervous system um so things like substance P vasoactive intestinal peptide secreting gastric inhibitory peptide cck neuropeptide y um and these are all chemical Messengers that have to do with uh regulating digestion and motility so looking at gastric motility this is going to be stimulated by swallowing that simulates these mechanical receptors and signals to the medulla the swallowing center of the medulla will signal the stomach to relax the vagus nerve okay we have this receptive relaxation response so it's going to resist stretching but then it will relax to hold more food the stomach is then going to to trigger these pistolic contractions coordinated by an anic pacemaker cell cells so they will um coordinate the rhythm of those paracolic contractions um it's going to start uh constriction every 20 seconds and become stronger at the pyloric part and then they're even stronger after about 30 minutes after consuming a meal and the job of all of this is to turn the food and mix it with the gastric juice which helps liquefy it and expose it to those enes the musculars of the antrum acts as a pump that helps break up that food okay and again this is going to turn and break up so that we liquefy that Kim into small particles then we have to move it out of the stomach and into the dadum OR dadum of the small intestine but we need to do it slowly so we can neutralize the ph and so that pyloric sphincter regulates so that only about 3 Mill of K goes into the Dum at one time again this is really important to help neutralize the stomach acid also it helps us digest the nutrients so it takes a typical meal about 4 hours to be emptied from the stomach it's going to be less if the meal was more liquid and more if it was higher in fat vomiting is another function of the stomach that is a protective reflex um it is the forceful ejection of stomach and intestinal contents from the mouth you do have a nedic center in the medulla oblongata and this is going to trigger the muscles to um initiate vomiting so vomiting can be induced by overstretching chemical irritance visceral trauma um intense pain or psychological or sensory stimuli but it is protective okay um because we haven't absorbed it into the blood then we haven't gotten it into our body so vomiting is usually preceded by um nausea and wretching wretching is when you get thoracic expansion and abdominal contraction and the whole it's got to create this pressure difference to open up the esophagus this will also cause the lower esophageal singer to relax relax so then the Kim is able to enter the esophagus okay um in wretching the Kim does not get past the upper ESOP gal sphincter you're also going to have other physical signs like elevated heart rate sweating increased salivation okay um and then a vom vomiting will occur when the contractions um become strong enough and the pressure is high enough um forces that oper upper esophageal s to open the esophagus in the body of the stomach relaxed and the Kim is driven out of the stomach through that contraction and reverse peristalsis um projectile vomiting is sudden vomiting with no nausea or wretching um shouldn't happen in adults um but it is fairly common in infants um but because their babies we like to call it spit up but it's projectile vomiting okay can be really worse though the projectile vomiting um chronic vomiting is very dangerous um it can result in fluid electrolyte or pH imbalances so individuals who suffer from bulimia um which is a eating disorder the hydrochloric acid in the vomit will erode the tooth enamel um also we could have aspiration or inhalation of the of the hydrochloric acid that destroys the respiratory tract um if you've ever wondered how come you can't eat if you may have surgery if you um and it's because anesthesia can induce nausea um and so we want patients to be fasting so that the stomach and small intestine are empty so that they don't vomit when they're under anesthesia and potentially aspirate on the vomit okay looking at digestion and absorption of the stomach um the salivary and gastric enzymes will partially digest proteins starch and fats um but here's the key thing right most digestion and nearly all absorption occurs in the small intestine okay the stomach does not absorb any significant amounts of nutrients so essentially aspirin alcohol okay um these are going to be so stomach really is a storage organ small intestines are where we're going to do the absorption okay we also need to protect the stomach and the other abdominal organs from the um hydrochloric acid and so there are a couple of ways that we do that so one is we have a mucus coat this is alkaline thick mucus and so that will help neutralize the acid um just on the uh epithelium of the stomach we also have tight Junction so the epithelium cells essentially are cemented together so that hydrochloric acid cannot leak between them and then we also have Epi epithelial cell replacement so those cells only live 3 to six days those are replaced frequently to help um help them so that they they don't live very long they're not exposed to that hydrochloric acid um if these break down then we can and get um inflammation and ulcers um ulcers is when we have inflammation of the stomach um and they're going to start to erode the stomach wall most of our ulcers are actually caused by an acid resistant bacteria called H pylor um it is treated with antibiotics um risk factors for UL includes stress um too much acid smoking and use of aspirin or other non-steroid anti-inflammatory drugs so here's a endoscope um so you can see here's a normal esophagus and then here you can see the ulcer like it's all red and irritated and starting to eat a hole through the sage lining looks super painful and then regulation of the of the stomach okay the stomach is um regulated divided up into three phases and the phases are essentially named off of what what organ is controlling it so we have the calic phase the gastric phase and the intestinal phase um these are not necessarily a step by step so they do overlap and can occur simultaneously so in the phase the Vagas nerve will stimulate gastric secretion even before food has been swallowed so the vegus nerve okay in the gastric phase the food stretches the stomach okay activates the myenteric and veal vagal reflexes so this stimulates gastric secretions histamine gastrin stimulates acid and enzyme secretion and then the intestinal phase um intestinal gastrin is going to stimulate the stomach to empty secreton and cck will then inhibit okay this is part of the inog gastric reflex that inhibits gastric secretion so it gives time for the small intestine to process the kind that's already in it um and the sympathetic nerve will also suppress that gastric activity and it that inhibits the vagus nerve as well so this is part of that intestinal phase is going to regulate so we don't get too much time moving into the stomach too quickly along with the pyloric extincter because it only allows a small amount right so calic phase the stomach response to the sight smell taste or thought of food um so we're going to send signals from the hypothalamus to the medulla oonga that activates the vagus nerve to stimulate that inter nervous system a large majority so about 40% of your stomach's acid secretion actually occur in the calic phase before you've even eaten any food the gastric phase then is when you are ingesting and swallowing food and it's getting into the stomach okay um that's ingested food stimulates this by stretching the stomach and increasing the ph and so that's going to tell it that hey there's some food here um and so we're going to need to increase our secretions for digestion so okay gastric secretion In the gastric phase is stimulated by three chemicals so acetylcholine histamine and and gastrin are going to um stimulate gastric secretions the intestinal phase then again is when the Dum or dadum of the small intestine responds to receiving the CT time initially it's going to enhance secretion but then it's going to inhibit it and again we looked at this the reason for that is that we want to um slowly empty the stomach contents so we can neutralize the acid and make sure that we are um able to process the Kim and get the nutrients out of it okay so the Kim is going to stimulate the secreton and cck so that's going to suppress that um gastric secretion okay um and then Intero Endocrine cells also secrete this glucose dependent insulinotropic peptide or a gastron inhibiting peptide um which is going to help stimulate insulin again we're just trying to get secretions for nutrients that are going to be present so we can digest them so when we're looking at the um um gastric secretions it is regulated through feedback so our food in the stomach is going to partially digested hydrochloric acid presence of food is going to increase the the pH that's going to stimulate the G cells the G cells secrete gastron um which stimulates the chief and parietal cells to secrete their um hydrochloric acid pepsinogen so we convert pepsinogen to pepsin which is going to start break bre down the proteins that were in the meal that we ate okay so we're going to pause from the um digestive tract and move to some of the accessory organs so the liver is a reddish brown gland um located just below the diaphragm it is the largest gland weighs about three pounds um huge variety of functions but we're just talking about it in context of digestion so its function is to secrete bile which we're going to need for digestion of lipids um the liver does have four loes so you have right left and then the quadrate and cadate lobe we have some ligaments that are going to separate and hold things in place so the falor ligament separates the left and right lobe and the round ligament is an a remnant of the umbilical vein um with the liver we also have this Porta he heus which is the opening between the quadrate and cadate loes um this allows for our hepatic portal circulation additionally we have the gallbladder on the posterior side of the liver um and we also have this bare area where the liver attaches to the diaphragm so if we look at the liver here from the anterior view you can see the right lobe and the left lobe separated by the fform ligament on the posterior view you have your left lobe your right lobe and then you have the cadate lobe the quadrate lobe the gall bladder here's your Bear area again here is your falor ligament and then the round ligament looking at the microscopic anatomy of the liver then we have these hepatic lobules so these are tiny cylinders um that fill the interior of the liver they have um a central vein that passes down the core and then the hepatocytes which are these cuboidal cells that surround it in in radiating sheets um and so each plate of hepatocytes is one or two cells thick um then we also have these hepatic sinusoids so these are blood filled Chambers or channels um between the plates and then we have the CATE macrophases so macras those are going to be white blood cells that are going to help remove debris and bacteria so if you look microscopic Anatomy you have the central vein and then you have the hepatocytes and then you have the hepatic cyos oids okay so again Central vein and you can see then the hepatocytes you can see here's a hepatic globule see one so here's the hepatocytes okay sinuses Stills the blood all right so that's the microscopic anatomy of the liver um the hepatocytes um will absorb um nutrients from the blood so they're going to get glucose amino acid iron vitamins other nutrients um but then between meals they will break down the stored glycogen the pyes also will remove and break down hormones Toxin biopigment and drugs and then they can secrete into the blood um albumin lipoproteins claing factors angiotensinogen and other products so these hepatocytes again the liver does quite a few things okay um the hepatic lobules are separated by connective tissues and so between the lobules you have that hepatic Triad so Triad is going to be three so it has a bod ductal a branch of the hepatic portal vein and a branch of the hepatic artery so it's going to filter through the sinuses the blood is going to filter through the sinuses and then it's going to be collected in the central vein flows through the hepatic vein so this is that hepatic um circulation that's going to help cleanse the blood we also have bile canicula which are narrow CH channels we're going to where the bile is going to be secreted into um the bile is then going to go um from the canicula into the bile duct does and then into the right and left hepatic ducts and then into the common hepatic duct into the cystic duct and then into the bile duct and the bile duct this is when it's going to be released into the duum OR dadum of the small intestine um near the entrance to the small intestine um we have the hipat pancreatic ampula so this is where um the the uh pancreatic and the bile and the liver secretions are going to come together and then be emptied into the small intestine and it does contain a sphincter so the hipat pancreatic sphincter which regulates the passage of the bile and the pancreatic juices into the Dum or duodenum um so we don't get bile and pancreatic secretions um when we don't need them so look at this so we have the hepatic ducts that drain the bile from the liver the common um hepatic duct bile duct okay and then it comes into and connects with the pancreatic duct and we have our hepato pancreatic stincer and then this widening where the two ducts come together is that hepatic hepatopancreatic ampula so the ampula is the wiing the gall lad then on the posterior side of the liver um it's a pearshaped okay it will concentrate the bile and it does this by absorbing water and electrolytes does have the head which is usually the part that's visible and then the neck which goes to the cystic duct which connects to the bile duct so let's talk about bile um bile is a fluid secreted by the liver it contains minerals cholesterol fats phospholipids biopigments and bio acids so the pigments in color they are yellow green when secreted by the liver and it becomes an intense green when it's concentrated in the gallbladder and the gallbladder is actually typically colored green um because of this the primary biopigment is Billy rubben um and this comes from the hemoglobin breakdown um the bacteria in the large intestine convert the Billy ruin to Euro bilinen um this is going to be re absorbed by the small intestines what isn't reabsorbed the kidneys then convert to eurobin and this is excreted in the urine so this is partially what's responsible for the yellow in the urine the rest of it is converted into the um is converted in the intestines to stero coin which is brown and responsible for the color of the Theses so the the pigments that we see from Billy Ruben come from him come from breaking down hemoglobin and then they are digested or broken down filtered in the digestive system and the kidneys and create pigments that are either yellow or brown which contributes to the color of the urine or the feces in addition the bile also has bile acids or bile salts these are steroids synthesized from cholesterol they they aid in the fat digestion with the lein so bile gets to the gallbladder so it fills the bile duct it overflows into the gallbladder so the liver secretes 500 to 1,000 milliliters of B A Day 80% so a huge portion 80% is reabsorbed and returned to the liver and the hepatocytes then are going to absorb and re secrete them so this is done through that Ino hepatic circulation 20% of the bio acids are excreted in the in the fees um and this is an important way for us to eliminate excess cholesterol gallstones are hard masses that can occur in the gallbladder or the bile dect they are composed of cholesterol calcium carbonate and Billy Rubin um and so they are most common in obese women over 40 but also men and they can be present in children too what happens is they occur when the cholesterol is is too concentrated and so it starts to stick together and crystallize and grows um it does cause a painful obstruction of the ducts and it does result in jaundice or yellowing of the skin you'll also have poor fat digestion and absor and impaired absorption of fat soluble vitamins golf Stones can be removed through laparoscopic surgery so here are some gall stones these are millimeters but those are still pretty pretty big okay then we going to move on to the pancreas um the pancreas is flattened it is retropat Neal gland okay it sits um posterior to the greater curvature of the stomach we have the head the body and the tail it is an endocrine and exocrine gland so we have talked about it before with the endocrine system insulin and glucon okay but that's only a small portion so now we need to look at the exocrine this is 99% of what the pancreas does um which is secrete pancreatic juice so pancreatic juice is exocrine or it does have a duct system so we do have the pancreatic duct that runs the length of the um gland and then we have exess accessory pancreatic ducts which are smaller that Branch off and connect to the panc creatic duct the pancreatic juice is a um alkaline mixture so that's going to help neutralize the pH um so it's water enzymes zymogens sodium bicarbonate and other electrolytes okay um so again the sodium bicarbonate that's the alkaline this is important to um buffer that hydrochloric acid pancreas is also going to release xymogen so again these are inactive enzymes so TR cinogen kind hot cinogen and pro carboxy peptidase um TR cinogen is going to be secreted into the intestine is converted by trip converted by interop peptidase into Tron Tron is the active form okay Tron then is autocatalytic so it's going to convert trinen into more Trion and then Tron also will convert kimot Tri kotri cinogen into kyoten which is the active form and carboxypeptidase which is the active form um other secretions of the pancreatic juice include pancreatic amas to do our starch digestion pancreatic lipase fats ribonuclease and deoy ribonuclease that digest RNA and DNA um these are active enzymes they don't have to be converted like the zonens do so then here's our pancreas we have seen this before um endocrine versus exocrine so here I want to look at triogen chot triogen procarboxypeptidase okay uh kimot cinogen and procarboxypeptidase um are inactive forms okay um trp cinogen is inactive form so the interop peptidase will conver convert trp cinogen to Tron Tron activates this and converts more Tron Tron also will convert the kimot tripsin kyot cinogen to kyoten procarboxypeptidases to carboxypeptidases so trp cinogen and kimot cinogen and procarboxypeptidases are are xogen so those are inactive and then tripen and kimot triin and carb oxy peptidases are active forms of the enzymes the pancreatic secretions are regulated by um three stimuli so we have acetyl choline so from the Vegas AR anic nerves um cctk which is secreted um by the dadum in the in response to the arrival of that and then we also have secreton also released from and this will help raise the pH level okay going back to our digestive strum we're going to pick up again into the small intestine so the small intestine again is the site of all nearly all chemical digestion and our nutrient absorption the small and small intestine refers to the diameter not the length same with the large intes intine okay so when we talk about small and large intestine we're talking about the diameter we're not talking about the length of these organs so looking at our small intestine we have three regions so you have the Dum or dadum the dunum and then the ilium so the dadum or dadum is the smallest portion it's the first portion it's kind of a C shaped okay it it arches around the head of the pancreas um most of this is retrop paranal it's going to receive the kind from the stomach it's going to neutralize the stomach acid mulies fats and activates pepsin this is where we're going to get the bile and the pancreatic enzymes are all going to come in here then we have the dunum which is the first 40% of the small intestine um it has large tall closely spaced circular folds um it has a thick wall That's relatively muscular it's got a rich blood supply so it's going to be bright and red this is where most of our digestion and nutrient absorption occurs is the dunum of the small intestine it's then going to move through the ilium which is going to form the last about 60% of the small intestine um it's thinner and less Mas muscular less vascular so it's going to be a little paler pink we are going to have um lymphoid nodules here um we will also you'll also have the ilocal junction which is the end of the small intestine where it joins the seeum of the small intestine and you'll have the ILO pilli which is um thickened muscularis of the of the ilum the circulation of the small intestine um so most it receives almost all of its blood from the superior mesenteric artery okay um and then it will drain into the superior mesenteric vein looking at the microscopic anatomy of the small intestine um similar to those that we've seen in the esophagus stomach but we do have some specialization for the digestion absorption so we have SIMPLE colmer epithelium the mus extern has a thick inner circular layer and a thinner out um longitudinal layer but the biggest difference is we're going to we want this large internal surface area and so the the the way that this is so that we increase the surface area is we have circular folds we have Villi and we have Micro and so these three characteristics help increase the surface area of the small intestine so the circular Folds these are spiral ridges um and they involve only the mucosa and sub mucosal layers um and they [Music] are they cause the Kim to flow in a spiral path so that they have more contact with the mucosa and so that's going to promote um mixing and nutrient absorption the Villi then are finger-like projections make the makes the Villi look fuzzy okay it looks fuzzy um and they have absorptive and goet cells um and this is going to also be um held together by uh tight junctions so the digestive enzymes don't seep between them so if you look at the Villi here and see and the cells are held together by tight Junction so things can't seep through them and you have goblet cells to produce that produce mucus these are called the brush border microvilli um and you have the Lac teals this our lymphatic system plus blood vessels the microv eye which we were just looking at um and they form this fuzzy brush border and so we'll call the this brush border and they will secrete brush border enzymes um which carry out some of the final stages of digestion they're not released into Lumin they kind of get stuck in that brush border and so we have to have this contact digestion the kind must contact the brush border in order for digestion to occur and the way that we make sure that that happens is through the intestinal turning um we also have those um intestinal CPS that we were looking at um so those are pores um and we have a few penis cells um which are going to secrete Lymes and fosil lipas and defenses these are going to help protect against bacteria pathogens so again you can kind of see here's the Vil and the micro Villi um and so this kind of look like a brush right here's the V and then here are those intestinal CPS okay and then this our muscularis mucosa doal glands and then the musculars externa and then the Sosa the outer layer um so the duol glands in the sub mucosa they will secreted byic carbonate Rich mucus again that's going to help neutralize the stomach acid um and it does have some signaling molec molecules to immune cells so a lot of lymphocytes throughout the lamin propria and sub mucosa so that we can intercept pathogens before they get into the bloodstream the intestinal CPS will secrete about one to two liters of intestinal juice per day um the pH goes back close to neutral so 7.4 to 7.8 contains water mucus but little enzyme remember the enzyme are found in the brush border okay and so we've got to have that contact digestion so looking at the intestinal motility so we have contractions of a small intestine that have three functions so one is to mix the Kim with the intestinal juice bile and pancreatic juice the second is to turn the Kim and bring it in contact to do that contact digestion and then three is movement through the digestive tract towards the large intestine so we'll have peristalsis but we also have segmentation that occurs in the intestine this is where the Rings um we're going to get stationary constrictions appear in several places along the intestine um and so what this segmentation does is it needs and turns the in intestinal contents and so this is going going to allow for that contact digestion and again this is regulated by the anic pacemaker cells are going to set the Rhythm and rate of this segmentation we still have peristalsis happening okay but peristalsis is going to move the contents from the small intestine towards the colon or the large intestine um so this hormone motilin secreted by the the dadum is going to stimulate pistolic waves okay we also have this migrating Motor complex which is when we have successive overlapping waves um again this is going to move that kind towards um the large intestine and this is actually triggered through this gastro ilal reflex that occurs once food enters the stomach it starts that reflex happening so we can start moving and emptying food so I really just want to make sure that we understand segment ation is going to mix and be responsible for contact digestion peristalsis is moving through the small intestine towards the large intestine so let's look at chemical digestion and absorption then so we're going to look at the macro molecules um and we're going to go through them so we're going to start with carbohydrates so carbohydrates is the um mostly what we're talking about is starch um starch is broken up into oligosaccharides which are eight glucose molecules which are then into disaccharides which are two okay um typically this is maltose maltose is then digested to glucose which is if you remember this is the mono saccharide which is then what's absorbed in the small intestine starch digestion is actually going to use start in the mouth so it actually starts with our salivary amas um that salivary amas works best at that um 6.8 to 7.0 pH once we get to the stomach that pH drops and salivary amales doesn't work um and so amas is denatured and then we'll pick it back up with pancreatic amase um we'll resume start digestion in the intestine with pancreatic amas from the pancreas once we get to the small intestine then um those oligosaccharides are going to be converted to maltose and then our brush border enzymes will continue our carbohydrate digestion so dextrinase gluc amas maltase sucrase lactase okay these are going tobreak down um uh dextrinase gluco amas um break down our aloides and then maltas sucrase and lactase break down our disaccharides um into our monac aides which are then absorbed okay so starch digestion really is going to start in the salivary amas then pancreatic amas right and that's going to break it down into malose and oligosaccharides and then we have maltas dextrinase gluco amas which are going to break down into the monosaccharides glucose and then glucose can be absorbed um 80% of our absorbed sugar is glucose um and it's going to be taken up by these sodium glucose transport proteins um and so the sugar is going to enter the extracellular fluid increases osmolarity water is going to come with it okay so we're going to absorb glucose and water um other monosaccharides um sglt can also absorb glao uh fructose is absorbed through facilitated diffusion so here you can see okay glucose okay fructose is facilitated diffusion and glao is also going to use those sorters so glucose and glao use sorters fructose is facilitated diffusion from the small intestine okay the lactose intolerance incurs in people that do not produce the enzyme lactase and so the lactose sugar goes into the um large intestine which increases the osmolarity of the large intestine because of this High osmolarity we're going to retain water which produces diarrhea the bacteria that live there love the sugar and as they ferment it they produce gas um and so that accounts for the um bloating and gas production uh lactose intolerance is very common um for most people lactose production ceases or declines um after age four um ethnicity does play a role in your likelihood of being lactose intolerant uh yogurt and cheese do not impact people who are lactose intolerant because the bacteria um are already broken down in those products all right let's look at our protein digestion then proteins are broken down by enzymes called proteases these are the digestive enzymes of proteins not in the saliva don't start until the stomach so again we're going to start with pepsin in the stomach this going to break peptide bonds between two amino acids so thyrosine and phenol alanine then this is going to continue in the small intestine um when we get the tripon and kimot tripin right those are going to take those polypeptides and make them into short oligo peptides so eight peptides all right so again we can kind of look at this okay so nothing occurs in the mouth and the stomach then pepsin is is going to hydroly the um specific Bond so we get smaller pieces all right smaller proteins and then the oligopeptides so those eight peptides are going to be broken down forgot what number I was on shoot one two three I think four uh carboxy peptidase removes the amino acids from the carboxy in aminopeptidase removes the amino in and dipeptidase splits our dipeptide bonds um carboxy peptidase is from the pancreas and aminopeptidase and dipeptidase are brush border enzymes okay so mouth nothing and the stomach the pepsin breaks down into shorter right and then trips in and and koton um hydrolize the peptides and break them down into allopeptides okay and then in the small intestine carboxypeptidase removes the carboxy group aminopeptidase removes from the amino group and dipeptidase splits okay until we have the amino acids that we can absorb into blood um amino acids similar to brush border are similar to our carbohydrates so once the brush B enzymes finish breaking it apart then the free amino acids are absorbed into the intestinal epithelial cells using sodium dependent amino acid Transporters um we also use some facilitated diffusion all right lipases lipids lipases are our fat digesting enzymes so we start with lingual lipase from the salivary glands this digests a small amount of of fat while the food is in the mouth but it's more active in the stomach um before digestion in the in the dadum um because we have gastric lipase in the stomach but really it's not doing much 10 to 15% of the of the lipids are digested um so we have to have a better way of doing this and part of the reason the lipids are so difficult to digest is because they are hydrophobic they don't like water um so they're difficult to hydrolized because they don't like water so we don't so we have to do something different um so what we'll have is we'll have anal pumping in the antrum which helps emulsify the fat so it breaks up the Globs so you end up with these emulsification droplets these emulsification droplets go into the small in intestine and are coated with bile and so we get that mixing in the anal part of the of the stomach okay make those little droplets so the droplets then are coated with bile sh how you keep forgetting my number I think this is three four maybe I don't know okay so it's coated with bile that keeps the droplets so they can't stick back together okay um and then pancreatic lipase will act on the triglyceride and remove the first and third so you have a glycerol and you have three fatty acids so pancreatic lipase will you have a glycerol at least this one um and then you have the first and the third Amino um fatty acid so you get two free fatty acids and a monoglyceride I know why I just tried to draw that for you so sorry so here's what this looks like um so you have your fat globule we're going to break it up up right and it is coated with the bile okay and the emulsification and then the pancreatic lipase is going to break our triglycerides into two free fatty acids and the monoglyceride the amono okay and that happens on the emulsification droplets um so then the absorption of the fatty acids the monoglycerides and other depends on the little droplets called the my cells which are made in the liver so they are 20 to 40 bile acid with their um basically it makes a little bubble of bile um and the phospholipids and cholesterol everything goes into the center of it to form the core of the my cells um the My cels then go down the bile duct into the dadum which is where they're going to absorb the um fat soluble vitamins cholesterol free fatty acids monoglycerides and then transport the lipids to the intestines and then the lipids leave the my cells diffus through the plasma membrane because it's lipids they can diffuse through the plasma membrane we don't have to use any kind of active transport the myell and are reused myel are like the little transporter of the lipids right so here's the my cell so it's got the bile acids on the Outside Inside has the lipids and they're going to transport the lipids right into the lymphatic system okay um so they're going to go you saw this in the process but they're G to actually be repackaged as these kyom microns and then those are what will go into the lipids not into the lipids into the lymphatic system okay and then our nucleic acids is our last um macromolecule so we have our nucleases which is the deoxy ribonuclease and ribonuclease from the pancreatic jeice and then we have nucleosidases and phosphatases which are our brush brush border enzymes um that break apart the DNA and RNA into the nucleotides um vitamins vitamins are not digested they are able to be absorbed unchanged as is so we have fat soluble vitamins which are a d e and K they can only be absorbed with lipids um so that is an important part of our diet if we ingest our V vitamins without fat containing food the fat soluble vitamins are going to pass through the species and just be wasted and then we have our water soluble vitamins which is our B complex and vitamin C remember we need intrinsic factor from the stomach to absorb our vitamin B12 mineral absorption minerals are the same thing as our electrolytes these are absorbed throughout the small intestine um we already talked about sodium co-transporters for sugar and amino acids um we've looked at the chloride is exchanged for bicarbonate and that um chloride shift that occurs in the stomach and then potassium is going to be absorbed by simple diffusion um Iron and calcium absorption occurs as needed um so iron absorption is going to be inhibited by hepsin so that we don't get overload the liver um absorptive cells will bind the ferris ions and take them in through active transport we can't absorb the feric f+3 but remember the hydrochloric acid will convert them um and then trans transfer is a protein that transports the iron in the blood to the bone marrow muscles and the liver calcium um again is going to be absorbed throughout the intestine so we can do a trans cellular absorption so this is when um calcium's going to enter the calcium channels okay is going to bind to uh protein so the calcium is going to continue to come in we can also um calcium can also diffuse between the epithelium between the epithelial cells in the dunum and the ilum um most of our absorbed calcium is from meats and dairy lipids slow calcium absorption um also we have our good friends um parathyroid hormone parathyroid hormone can be secreted in response to a reduced calcium level that's going to stimulate the kidneys to synthesize vitamin D and then vitamin D is going to increase our calcium channels so it's going to increase our calcium absorption and so par thyroid hormone is going to increase calcium in the blood digestive system is also involved in water balance so the digestive system gets a significant amount of water gets about nine lers of water per day water is absorbed by osmosis we've talked about this before right it follows the absorption of our salts and organic nutrients diarrhea occurs when the large intestine absorbs too little water what's happening is the feces are passing too quickly um or the feces contain a high concentration of solutes and so we're unable to absorb water the opposite can also occur constipation occurs when the feal movement is too slow and so we reabsorb too much water and the feces becomes hardened and can become impacted so we're moving on now to the large intestine so the large intestine again the large is the diameter not the length um the large intestine is going to begin with the um seeum the appendix attaches to the lower end of the seum and then we have the colon um which has the um ascending colon the right colet flexure the transverse colon left colic fure and the descending colon and the sigmoid colon so we'll look at all those parts of the colon um the large intestine is then going to go into the rectum and the an Al Canal um the rectum has three curves and three infoldings so it has these transverse rectal folds and then the anal Canal is made up of an anal columns and anal sinuses um along the anal Canal we have the hemorrhoidal veins um and this is what's responsible for hemorrhoids when the veins become distended when those humoral veins become distended they protrude into the anal Canal or B outside the anus and that can be um painful so the large intestine is going to look a little bit different um the muscularis externa is a little bit different than the rest of the digestive tract so we have the TNA Kole which are these longitudinal fibers it's these three thicken ribbon likee strips and then we also have Hoster which are pouches in the colon um and and so this is is going to um we're going to see these two characteristics in the large intestine and then the anus is regulated by two sphincter in internal anal sphincter and a external anal sphincter um Additionally the Sosa of the colon often has these momental appendages or appendices which are fat pouches so we'll see these as well so if we're looking at our large intestine Okay so we can see the first portion here is the seeum here is the appendix you can see the pouches so one pouch is a HRA Ostrum you can see the bands which are the ten colle you can see the yellow fat droplets theal appendages okay so seeum ainex and then this is the ascending colon the right colic flexure the transverse colon the left colic flexure the descending colon the s Moy colon the rectum the anal canal and here you can see the external anal sphincter right so that is the large intestin so looking at the rectum and the anal Canal a little bit more so the rectum up here okay with the um rectal valve and then where it Narrows in the anal canal and you have the um anal sign anal um columns and the anal sinuses and then here is your um internal anal sphincter external anal sphincter and here are those hemorrhoidal veins that we were talking about so the circulation to the large intestine is um served by the mesenteric arteries to receive blood flow similar to the small intestine okay and then the superior and inferior mesenteric veins will drain the large intestine as well the large intestine yosa um is simple polymer epithelium um except for the lower half of the anal Canal it does have um nonar stratified spos epithelium in the lower anal Canal there are no circular folds or Villi so this is going to be different from what we saw in our small intestine um intestinal Crypts are deeper than in the small intestine and we've got a lot of goblet cells so we're going to produce mucus the lamina appropriate and some mucos so again we're going to have a lot of lymphoid tissue again this is for protection um from the bacteria that live in the large intestin so looks similar to what we have seen before um but again reduced surface area because we don't have the zilli and the micro Villi that we saw in the um small intestine so let's talk about those bacteria that live there so this is your gut microbiome and this is getting a lot of um interest and research on the importance of our gut microbiome so there are more than 1,000 species of bacteria yeast and virus other microbes that live in large intestine they will digest cellulose pectin other carbohydrates that we are unable to um digest they also help us synthesize vitamins B and K um they are responsible for the flaus or the intestinal gas that is expelled um the average person produces 500 milliliters of gas per day um most of that is actually swallowed air but the bacteria do um add to that and then the hydrogen sulfide andol and skolar what responsible for the odor of the gas um the large intestine abortion and motility this is uh slow it takes about 36 to 48 hours to reduce the residue of a meal to feces most of this time is spent in the transverse colon um remember that we're not chemically changing the residue all we're doing is reabsorbing water and electrolytes feces is still 75% water and 25% Sol solids of those solids about 30% is bacteria 30% is fi undigestible fiber 10 to 20% is fat some mucus protein salt digestive secretions in epithelial cells as well so when we're talking about the motility um the motility in the large intestine we have two types of movement and motility um so we first have hostal contractions those occur every 30 minutes that's when we disend a hostr stimulate it to contract it turns and mixes the residue and and empties it into another hostr the mass movements then are stronger contractions that occur one to three times a day um that's going to um move the residue several centimeters so hostile contractions really are more for that turning and mixing so we can make sure that we're getting the water and salt and then the mass movements are actually going to move the the residue along the digestive tract so then we're going to get into defecation so stretching of the rectum will stimulate the defecation reflex um there are actually two reflexes so we have the intrinsic uh defecation reflex this works within that myenteric plexus and this produces a relatively weak response essentially the stretch signals travel through the plexus to the muscularis caus it to contract and the internal sphincter relaxes the second is the parasympathetic defecation reflex which actually goes to the spinal cord so this is going to be more similar to like our micturation reflex the stretching of the rectum will send the signal to the spinal cord the pelvic nerve Returns the signal which is going to intensify the peristalsis and relaxing of that internal anal spincter so these are reflexes okay those are involuntary control okay that's going to be that internal sphincter um defecation only occurs if the external sphincter and pubo rectus muscles are voluntarily relax um and so this is under volunt voluntary control um abdominal contractions or the dissol maneuver where you kind of hold your breath and and push which increases the abdominal com pressure and pre and compresses the rectum can help with defecation as well so if we look at this okay um so the feces moving into the rectum right stimulate stretch receptors okay um and then the spinal reflex will stimulate contraction of the um rectum and it's going to relax the internal stincer right so this is is involuntary um and then imp from the brain will prevent defecation because they control the external anal sphincter until you're ready and then they're going to allow it to relax and allow for defecation to occur col rectal cancer is cancer of the colon and the rectum um this is serious it's the second most common cause of cancer deaths in the US usually arises from goblet cells in a colon pop um it is one that metastasizes quickly um early signs can be uh persistent diarrhea or constipation abdominal pain blood in the stool weakness fatigue weight loss risk factors include smoking alcohol physical inactivity obesity um ancestry or poor socioeconomic status most cases um involve mutation of this tumor suppressor Gene p53 and the best safeguard is early detection regular screening and early detection okay so here you can see the colon and the col rectal cancer that's present and that is it for the digestive system