welcome everybody today we are diving into the fascinating world of the digestive system this system is crucial for breaking down the food we eat absorbing nutrients and eliminate eliminating waste we'll explore its components functions and the integrate layers that make it all possible so let's get started the digestive system can be broadly divided into two main categories the digestive tract also known as the elementary canal and the accessory organs the digestive tract or elementary canal is the continuous tube through which food passes and this includes the oral cavity the pharynx the esophagus the stomach the small intestine and the large intestine the oral cavity is where digestion begin with the help of the teeth and the tongue the tongue actually is not strictly part of that tube but is essential for its function the pharynx is a common passageway for food and air the esophagus is which the food is transported to the stomach the stomach is where food is further broken down the small intestine is a primary site of nutrient absorption and the large intestine is where water is absorbed and waste is compacted each of these organs plays a vital or role in digestion absorption and secretion and compaction we will dive into these processes in more detail now besides the main elementary canal and the organs along the tube we have accessory organs these organs while not part of the continuous tube are essential for digestion they include the salivary glands which produce enzymes to initiate carbohydrate digestion the liver is where bile is produced for fat emulsification the gallbladder is where the bile is stored and concentrated, and the pancreas is where digestive enzymes and bicarbonate are secreted these organs contribute significantly to the digestive processes and we will explore their specific function later in the lecture. the digestive system performs a series of crucial functions ingestion mechanical processing digestion secretion absorption excretion compaction and defecation ingestion implies the simple act of taking in food and liquids into the mouth mechanical processing involves the physical breakdown of food through chewing or mastication and swallowing digestion is the chemical breakdown of food into its basic wielding blocks carbohydrates into monosaccharides lipids into fatty acids and glycerols, proteins into amino acids and nucleic acids into nucleotides. secretion in the digestive tract and accessory organs they release a variety of substances including enzymes assets and buffers to aid in digestion absorption this is the process by which nutrients move from one from the lumen of the small intestine into the bloodstream excretion involves the removal of waste and waste products from the digestive tract compaction is the progressive dehydration of indigestible materials leading to the formation of solid waste and defecation finally this is the elimination of feces from the body through the anus. understanding these functions is the key to appreciate how the digestive system works as a whole. now let's take a closer look at the microscopic structure of a digestive tract generally it consists of four main layers we'll take a closer look to all the layers from the lumen inward we have the mucosa, the submucosa, the muscular layer or the muscularis externa and the serosa or adventitia. now the mucosa is the inner or the outermost layer which directly lines the lumen it its structure varies depending on the specific organ and function we're looking at. the submucosa is a layer of connective tissue containing blood vessels nerves and lymphatic vessels the muscular layer or muscularis externa is responsible for the movement of the digestive tract such as peristalsis. the serosa or adventitia is the innermost layer which provides a protective covering to the organ. it is important to remember that while these four layers are generally present throughout the digestive tract their specific features can vary significantly between organs reflecting their specialized functions for example the mucosa of the small intestine is highly adapted for absorption while the muscular layer of the stomach is designated for powerful contraction. now let's zoom in and ex and examine the microscopic structures of the digestive tract as we discussed it is organized into four main layers the mucosa sumucosa muscularis externa and cerosa with the mucosa the layer this layer is directly boing the lumen the inside space where food travels the mucosa is essentially a mucus membrane and like most mucus membranes it has three sub layers the mucosa epithelium the lamina propria and the muscularis mucosa the muscular sorry the mucosal epithelial this is the epithelial tissue that lines the lumen its type varies depending on the region's function in areas exposed to abrasion like the oral cavity fernx and esophagus we find a stride esquamos epithelium think of it as a tough protecting layer in on the other hand in regions specialized for secretion and absorption like the stomach and the small intestine we find simple columnar epithelio these taller cells are ideal for these functions then the laminina propria is a layer of loose connective tissue specifically arolar connective tissue containing blood vessels nerves smooth muscle and lymphatic vessels it supports the epithelium and provides nutrients lastly muscularis mucosa this thin layer of smooth muscle is located at the border between the mucosa and sumucosa it is responsible for local movement of the mucosa like creating folds and secreting surface area and increasing surface area sorry moving inward we reach the sumucosa as the layer suggests as a layer name suggests it lies beneath the mucosa this layer is composed of aliolola connective tissue similar to the laminina propria but it also contains larger blood vessels lymphatic vessels and nerve fibers think of it as the support and supply layer next we have the muscularis externa or muscular layer this layer is responsible for the movements of the digestive tract like paristas which propels food forward it consists of two sub layers of a smooth muscles the circular muscle layer and the longitudinal muscle layer the inner layer is where muscle fibers are arranged circularly around the track the longituino muscle layer is the inner layer where muscle fibers run lengthwise along the track in some areas these muscle layers thickens to form sphincters which act as valves protecting the passage of material finally we have the sarosa the innermost layer this is a serious membrane present on in the peronial cavity which surrounds most of the abdominal organs now even though the fernx esophagus and rectum do not have a cerosa because they don't have they're not in the peronial cavity they have an adventicial layer which is a fibrous layer of collagen fibers to give you a visual let's look at this cross-section of the ilium you can see how the mucosa varies in thickness and structure the sumucosa which with its vessels the distinct circular and longitudinal muscle layers and the outer cerosa or the inner sarosa remember the specific characteristics of the layers can vary slightly throughout the digestive tract reflecting the specialized functions of each organ let's discuss how the digestive tract actually moves food now as you may know food doesn't travel through the digestive tract by gravity the muscularis mucosa and the muscularis externa are responsible for these movements interestingly they contain a specialized cells called the pace setter cells these cells have a unique ability they can initiate muscle contraction without needing a signal from the nervous system much like the pacemakers cells in the heart as a node there are two primary types of muscle contraction paristas and segmentation paristas is the wave movement of the food in the tube paristas leads it involves coordinated contractions of the muscular layers that propel the bolus through the digestive tract the bolus is a small mass of food first the circular muscles contract behind the bolus narrowing the tube and pushing it forward then the longitudinal muscles contract shortening the tubement propelling the the is more like a mixing and churning action um video involves local you can see these rhythmic contractions that break up and in one direction from the mouth towards the in segmentation this is more like a mixing and churning action segmentation involves localized contractions that break up and mix the food with digestive enzymes unlike paristas cementation does not move the bolus in a specific direction instead it is like squeezing and dividing the food mass increasing it increasing its contact with intestinal walls for better absorption like other organ systems the digestive system is protected and organized by a serious membrane called the peritineium the visceral peritinium or cerosa is a layer directly that directly covers the organs of the digestive tract the peritial peritinium is a layer that lines the abdominal cavity walls and the peritineal cavity is a space between these two layers filled with serious flu fluid which lubricates the organs and prevents friction additionally we have the meenties which are double layers of peritinium that helps stabilize the position of the digestive organs these messenties are crucial because the abdominal cavity is packed with organs and they need to be held in place specifically during digestion they also serve as pathways for blood vessels nerves and lymphatic vessels to reach and form the digestive tract think of them as highways of the digestive systems through that support the system remember the digestive system does not work in isolation it needs a network of vessels and nerves to function properly and the messentaries provide that essential infrastructure now let's explore the various messentries which are crucial for organ organizing and supporting the abdominal organs remember meenties are double layers of peritinium that provides a stability and pathways of vessels and nerves messenti proper this large mentary suspends most of the small intestines specifically the jounum and the ilium as you can see here it allows the small intestine to move while still anchoring anchoring it to the posterior abdominal wall the messylon this meant supports the large intestine the transverse messylon specifically holds the transverse colon the sigmoid messylum holds the sigmoid column pushian fascia this anchors the ascending and descending column to the posterior abdominal wall the omena the lesser um connects the stomach to the liver while the greater um is a large fatty fold that drapes over the abdominal organs providing insulation and protection it is like an apron covering the intestines this menter ensures that the abdominal organs stay in the proper position and have access to the necessary blood vessels nerves and lymphatic vessels let's begin our journey through the digestive system starting with the oral cavity or mouth the oral cavity is lined with oral mucosa which consists of non-caratinized stratified squamos epithelial this type of epithelium is well suited to withstand the abrasion of shoeing the roof of the oral cavity has two parts the hard pallet which separates the oral cavity from the nasal cavity and the soft pallet which separates the oral cavity from the nasop ferings the floor of the oral cavity is primarily formed by the tongue the oral cavity is where ingestion and initial mechanical digestion or chewing takes place the salivary glands play a vital role in ingestion by producing saliva saliva is a mixture of w water ions buffers and digestive enzymes these are exocrine glands meaning they secrete their products through dogs not directly into the bloodstream we have three pairs of major salivary glands the paratit gland the sub lingual gland and the submandibular gland the parotid glands are located near the ears between the mandible and the temporal bone the sublingual glands are located under the tongue and the submandibular glands are located below the mandible saliva helps to moist food initial carbohydrate digestion and lubricate the oral cavity for swallowing let's move to another essential component of the oral cavity the teeth they are vital for mechanical digestion breaking down food into a smaller pieces the structure of the tooth can be divided into three main parts crown neck and root the crown is a visible part of the tooth above the gingiva or the gums it is covered by enamel the hardest substance in the body made of calcium phosphate crystals deep to the enamel is denting a mineralized matrix matrix similar to bone but without living cells the neck is a region between the crown and the root at the gingivival margin the root the portion embedded in the gingiva anchoring the tooth blood vessels and nerves enter through the aical foreman the opening of the to the root tip and travel through the root canal to the pulp cavity the pole cavity located within the crown and root contains a spongy tissue with blood vessels and nerves remember the term gingiva is a technical term for gum adults have different types of teeth each specialized for a specific function incizers canines remolers and mers incizers are located at the front these teeth have sharp edges for clipping and cutting food we have four per jaw canines also known as as cuspetss have have pointed are pointed teeth used for tearing and slashing food we have two per yaw preolars also known as bicospetss are the teeth with flat surfaces for crushing mashing and grinding food we have four per jaw and mers these are large flattened teeth responsible for crushing and grinding food we have between four to six per yaw depending on how many on your um wisdom tooth wisdom teeth so each individual will have a different number of mers these numbers represent the teeth in one jaw upper and lower so an adult has can have a total of 32 teeth or 28 if they don't have any of their wisdom tooth unless you are Freddy Mercury from Quinn which he had I believe two extra incizers humans have two sets of teeth throughout their lifetime the decitious teeth or baby teeth are the first set of teeth typically 20 in total they include central incizers lateral incizers canines and decicitious mers permanent teeth or adult teeth are are replacing the decitious teeth and consists of 32 teeth they include central incizers lateral incizers canines preolars and mers the process of teeth emerging from the gingiva is called eruption in this picture here you can see the skull of a child with their decitious teeth out and the permanent teeth coming from the bottom or the top respectively through demandable we have briefly touched in on the fairings in our discussion of the respiratory system but it is crucial to remember that it is also a shared pathway for the digestive system the fernx serves as a common passageway for both food and air food and liquids travel down the esophagus while air enters the trachea via the larynx the esophagus is a muscular tube that connects the fernx to the stomach it lies posterior to the trachea it contains the upper esophageal sphincter and the lower esophageal sphincter which act as valves to control the passage of food let's take a closer look at the esophagus structure like other parts of the digestive tract it has a four main layers mucosa sumucosa muscularis externa and advanticia instead of the sarosa the esophagus has an adventicia a layer of collagen fibers as its outermost layer you'll notice prominent folds in the mucosa and sub mucosa these folds allow the esophagus to expand and accommodate the passage of food the muscularis externa facilitates paristasis the wavelike contraction that propels food towards the stomach the esophagus structure is designed for efficient transport of food from the fins to the stomach solowing or delutination is a complex process with three distinctive faces the boual phase the ferangeal phase and the esophageal phase the bal phase is voluntary this is initial voluntary phase of swallowing the tongue pushes the bolus of food towards the aura ferings opening the fer feroh the faragen phase once the bolus enters the oro fairings the process becomes involuntary the epiglotus falls down and the larynx elevates this closes the glorus preventing food from entering the trachea and swallowing begins the esophagial phase the upper esophageal sphincter relaxes allowing the bolus to enter the esophagus but estasis the coordinated contraction of the muscular externa propels the bolus down the esophagus the lower esophageal sphincter relaxes allowing the bolus to enter the stomach this is also involuntary phase although we initiate soloing voluntarily the majority of the process is involuntary ensuring the pro the food is efficiently transported to the stomach now let's explore the stomach a vital organ for both mechanical and chemical digestion the stomach transforms food into a semifluid mixture called the kim there are four regions of the stomach the fundus the cardia the body and the pyloric part the fundus is the domeshaped region superior to the gastro esophysial junction the cardia is a region surrounding the gastro gastroesophysial junction where the esophagus enters the stomach the body is the largest region of the stomach extending from the fundus to the pyloric part and then the pylori part is a region connecting the stomach to the diodenum the first part of the small intestine now let's talk about the rugi the gastric folds these are folds in the muscular sorry these are fall in the mucosal layer of the stomach wall they allow the stomach to expand significantly when filled with food think of them like pleats in fabric that allow the stomach to stretch muscle layers the stomach has three layers of muscle of a smooth muscle which are unique within the digestive tract we have the oblique layer the circular layer and the longitudinal layer the oblique layer is the innermost layer with fibers running diagonally circular layer the middle layer with the fibers encircling the stomach and the longitudinal layer the outermost layer with fibers running lengthwise these layers work together to churn and mix food aiding in mechanical digestion understanding these regions and features is crucial for appreciating how the stomach functions in digestion let's examine the microscopic structure of the stomach the stomach lining is composed of simple columnar epithelium specialized for secretion and some absorption key structures within the stomach lining include gastropits and gastric glands the gastric pits are indentations in the mucosa that lead to gastric glands gastric glands are located at the base of the gastric pits these glands contain various secrettory cells these glands are the main site of gastric secretion the cells of the gastric glands are responsible for secretreting different products vericial cells ship cells and GC cells are important cells found within these gastric glands like the rest of the digestive tract the stomach has the sumucosa muscularis externa and the cerosa layers the stomach's hisytologology reflects its primary function to secrete digestive juices and begin the chemical breakdown of food now let's move on to the small intestine the primary site of digestion and absorption the small intestine is divided into three regions duodenum yunum and the ilium the duodenum is a far the first and shortest segments approximately 10 in long here shown in bluish the yojenum is a middle segment about 8 ft long and here colored in purplish and the ilium is a final segment about 12 feet long connecting to the large intestine and here represented in orange the small intestine length and specialized structures are crucial for maximizing nutrient absorption like other parts of the digestive tract the small intestine has a four basic tissues layers mucosa sumucosa muscularis externa and cerosa however it is the mucosa's adapt adaption adaptations that make it uniquely suited for absorption to increase surface area the small intestine has three main features the ple circulares or circular folds the vi or vi the microilli ovi the prickly circulares are large permanent holes in the mucosa and sumucosa creating a spiral pathway for kim the vi are fringinger like projections of the smucosa that extends into the lumen the microvilli is a are tiny projections on the surface of the epithelial cells lining the vi creating a brush border now it is important not to mix the vi with a microvi the vi are extensions of the layer mucosa while the microvilli are extensions of the cell membrane of each individual cell these structures work together to dramatically increase the surface area available for absorption you can see how the plea circulares creates folds the vi projects from these folds and the microvi covers the individual epithelial cells the epithelial cells lining the vi are simple columnar epithelium suitable for both secretion and absorption the duodenum plays a crucial role in receiving secretions from the gallbladder and pancreas which aid in digestion the gallbladder stores and releases bile produced by the liver which emulsifies fats pancreas they secrete digestive enzymes and buffers such as bicarbonate to neutralize stomach acids these secretions enter the diodenum through a common pathway the bile duct from the gallbladder merges with the pancreatic dock from the pancreas they form the hippatop pancreatic ampula or diodeno ampula a chamber that opens into the diodenum via the diodeno papilla you can see the vile duct and prancotic dot joining at the ampula and emptying into the diodenum through the papilla the pancreas functions as both an endocrine and an and an exocrine gland in this context we are focusing on its exocrine function where digestive enzymes are secreted into dots the diodeno papila appears as a small mound with an opening on the diodeno wall now let's explore the large intestine which plays a crucial role in water absorption and waste compaction the large intestine consists of three main regions the secum the column and the rectum the secum is initial pouch like region where the ilium the last part of the small intestine connects the ilioal valve controls the flow of the kime from the ilium to the seeum the appendix or the vermy form appendix is a small wormlike projection that extends from the seeum the column is the largest region divided into four parts the ascending column the transverse column the descending column and the isphenoid I mean sorry and the sigmoid column the ascending column travels upwards on the right side of the abdomen the transverse column crosses the abdom the abdomen horizontally the descending column travels downward on the left side of the abdomen and the sigmoid column is the Sshaped portion that connects to the rectum the right collic flexure or hypatic flexure and the left colleague flexure or the splenic flexure are the turns between these segments then finally we have the rectum the final segment leading to the anis contrary to popular belief the large intestine is shorter than the small intestine 5t versus 20 ft the large refers to the to its diameter 3 in versus one to 1.5 in the column frames the small intestine within the wall the abdominal cavity its primary function are water and vitamin absorption and waste compaction the column features the house strap a pouch-like structure that allows for this distension and increased surface area for absorption the hstra are like expandable pockets that accommodate the increasing volume of waste as water is reabsorbed or absorbed like other parts of the digestive tract the large intestine has the four basic tissue layers mucosa sumucosa muscularis externa and cerosa however the muscularis externa has a unique feature the the longitudinal layer of the muscularis externa is reduced to three distinct bands called tenoli this teni coli runs along the length of the colon but they are shorter than the colon itself this creates a pokering effect forming the hostra imagine a long tube where you cinch certain sections this creates pockets which is essential how the tenny colli form the hostra this unique muscle arrangement is essential for the large intestines ability to compact waste and absorb water the final part of the large intestine is the rectum which temporarily stores feces before elimination the very last portion of the rectum is the anal canal which ends at the anus the external opening two sphinctters control the vication the internal anal sphiner and the external anal sphinter the internal anal sphiner is composed of a smooth muscle and it is involuntary the external ano espinter is composed of a skeletal muscle and it is voluntary allowing for conscious control of our movements during pi training you actually reach control of your of your external and inal sphiner understanding the function of these sphincters is key to understanding the process of defecation now let's move on to the accessory digestive organs starting with the liver the largest visceral organ in the body the liver performs numerous crucial functions including regulating metabolism and blood composition and producing bile essential for fat digestion the liver is located in the upper right quadrant of the abdomen beneath the diaphragm the liver is divided into four segments based on the topography this was done many many many years ago however this may not be very helpful for modern surgery but we still going to be focusing on these four segments we have the posterior segment which is only visible through the posterior view or from the posterior view the anterior segment which is visible from the anterior view the medial segment located in the center hence medial and the lateral segment which is located located on the right side of the screen this segmentation is critical for surgical planning and understanding liver function the microscopic structure of the liver is organized into lobules exogonal functional units each lobule is separated by an interlobular septa at the center of each lobule is a central vein hepatocytes are liver cells remember anything related to the liver usually has a HEPA before it these hepatosytes radiate outward from the central vein hepatocytes produce bile which is secreted into the bile canali then into the interlobular bile dot the liver's unique blood supply is crucial for its function the liver receives blood from two main sources hpatic artery proper and the hippatic portal vein the hippatic artery proper delivers oxygenated blood like to any other organ the hippatic portal vein delivers nutrientrich blood from the digestive system this blood is rich in absorbed nutrients which the liver processes and stores this is the hpatic portal system blood from the hippatic portal vein and the hippatic artery proper flows through the lobules past the hpatocytes which process the blood the blood then drains into the central vein which leads to the hpatic vein and back into the systemic circulation the hippatic portal system allows a liver to act as a filter and processing center for nutrients absorbed from the digestive tract portal triads are located at the corner of each lobio the portal triad consists of the interlobular bile dot branch of the hippatic portal vein and the interlobular artery understanding the hisystologology of the liver is vital for appreciating the role in digestion and metabolism let's move on to the pancreas an organ with both exocrine and endocrine functions the pancreas is located posterior to the stomach it has three main regions the head the body and the tail the pancreatic duct is crucial for its exocrine function transporting digestive enzymes to the diodenum you can see the pancreatic dog delivering enzymes to the diodenum right here the pancreas consists of two main types of cells the pancreatic asinar cells and the pancreatic eyelet cells or the eyelets of lunger hands the pancreatic asinar cells make up the majority of the pancreas and are responsible for its exocrine function they are organized into acini clusters of cells that secrete digestive enzymes the pancreatic eyelet cells are scattered throughout the pancreas and are responsible for its endocrine function they secrete hormones like insulin and glucagon into the bloodstream remember exocrine glands secrete their products into ducts while endocrine glands secrete hormones directly into the bloodstream finally let's discuss the effects of aging on the digestive system unlike some other organ systems that experience a clear breakdown the digestive system primarily experiences commumulative damage the key changes include gradually loss of teeth accumulation of toxins declining stem cells production reproduction and decrease smooth muscle tone gradual loss of teeth affects mastication and initial digestion accumulation of toxins can impair liver and other organs functions declining stem cell reproduction leads to decreased tissue repair and increased tissue fragil fragility and decreased smooth muscle tone results in reduced motility and increased constipation reduced smooth muscle tone affects paristasis a segment and segmentation leading to a slower movement of food through the digestive tract this can contribute to constipation as waste material remains in the colon for longer periods all right so this is the end of the lecture for the digestive system make sure that you re um review all the notes and make sure that you redo the quizzes as the uh the questions in case you had some mistakes if you have any questions just let me know bye