9 the urinary system nodes quick introduction to this system during metabolism of the essential nutrient monomers required for normal cellular function metabolic wastes that need to be removed from the body are produced excretion is the process of eliminating metabolic wastes from the body and is carried out by the urinary system excretion is different from defecation which is a process of the digestive system and involves the elimination of wastes that were never part of the functioning of the body so some functions of the urinary system first is excretion removal of metabolic wastes most notably the nitrogenous waste so some examples of these nitrogenous wastes are urea this is a byproduct of amino acid metabolism in the liver which produces ammonia which is combined with carbon dioxide to form urea creatine is a byproduct of metabolism of creatine in the muscle tissues and also uric acid is a byproduct of nucleotide metabolism which can crystallize if in high very very high amounts the urinary system will also help maintain ph levels this keeps the ph of body fluids about a ph of 7.4 this can secrete hydrogen ions or reabsorb bicarbonate ion to increase or decrease the ph as needed usually due to acidic foods and diet this results in secretion of hydrogen ions and therefore urine that is acidic another function is to maintain the water salt balance of blood this regulates the concentration of sodium chloride in the blood which controls blood volume due to osmosis and blood pressure due to blood volume also maintains the concentration of ions such as potassium ion bicarbonate ion and calcium ion hormone secretion kidneys assist the endocrine system by secreting renin this causes the release of aldosterone from adrenal glands which increases absorption of sodium ions by kidneys erythropoietin increases the red blood cell production if blood oxygen levels are too low kidneys also help activate vitamin d from the skin to increase calcium ion absorption from the digestive tract did you know that you actually get vitamin d when you go out into the sun organs of the urinary system so here's some anatomy and a bit of physiology first are the kidneys these are the mean excretory organ they help with maintaining homeostasis through the regulation of water and ions our ureters these will transport urine from the kidney to our bladder they also convey urine by peristalsis this is the third time we've seen this we've seen it in our esophagus we've seen our smooth muscle contraction as well in our intestines our urinary bladder this is a hollow muscular sac where urine is stored it's expandable and there are two fingers to control the roots of urine into the urethra which we're pretty happy about urethra a small tube from the bladder to an external opening in males it will also transport semen kidneys the kidneys are bean-shaped organs located at the back of the abdomen they are composed of three main regions and are supplied by specific vessels the first part is the renal cortex this is the outer region of the kidney it's red because of how many capillaries there are next is the medulla renal medulla this is the inner area striped because of the tubules and blood vessels so you'll actually see that it's kind of striped when you look at closer at it we also have the renal pelvis this is the innermost portion where urine collects before leaving the kidney kidneys are made up of about 1 million tiny nephrons a nephron is composed of a system of tubules so here we can see our nephron in green our anatomy of a nephron first we have our bowman's capsule this is also known as the glomerial capsule you should be able to recognize both names it's a cup like structure so it's right here and it surrounds the glomerus a glomerus is part of the blood vessels that we'll get to shortly next we have our proximal convoluted tubule often it is abbreviated to pct remember when you're writing an assessment to always give the full name followed by the abbreviation as it's shown here and then after that point you'll be able to use the abbreviated term the pct is a coboidal epithelial cells with microvilli this is an increased surface area for absorption next we have the loop of hennell or the loop of nephron it is a u-shaped tube so we have our proximal conflated tubule which will go down to the loop of hennell there it dips into the renal medulla so we'll see at this bottom section is actually part of the renal medulla and not the cortex next we have our dct which stands for distal convoluted tubule pretty much like the pct but on the opposite side of the loop of hennell and it lacks microvilli does not have them it's designed for tubular excretion rather than reabsorption and finally are collecting ducts this transports urine through the medulla and delivers it to the renal pelvis it's usually impermeable to water but adh increases it permeability nephrons each nephron has its own blood supply from the renal artery which has high oxygen glucose amino acid and wastes to the afferent arteriole which leads into the glomerus blood leaves the glomerulus via an efferent arteriole it's nearer in size how i like to remember it is a before e so it's afferent arterial to the glomerulus to the effront arterial ab4e the efferent arteriole takes the blood to the peritubular capillary network or also known as the pcn for short these surround the rest of the nephron blood will then go to a renal venule and then a renal vein and back to the vena cava can you guess which vena cava this would be high in carbon dioxide and glucose and amino acids once it goes here to be low in wastes and oxygen the oxygen is going to be diffusing over and the wastes will be excreted via the urinary system so here you can see here is our renal artery the blood's going to flow from our renal artery into our afferent arteriole which is going to go into our glomerulus which is within our bowman's capsule then it's going to flow out through the efferont arteriole and then into our pcn so our parrier tubular capillary network which is the rest of this here once it comes through it will drain into a renal venule and then into the renal vein part two urine formation urine gets rid of wastes ammonia urea uric acid and crinidine and other substances such as vitamins antibiotics histamines found in excess in the blood steps of our urine formation first is our glomerular filtration which is also known as pressure filtration you do need to know both of these terms this is the movement of blood to nephron the blood enters the afferent arterial and then the glomerus this increases the blood pressure at this point so increases the blood pressure in the glomerus because the capillaries are smaller than the arterioles this increased blood pressure forces water and small substances out of the blood and into the bowman's capsule this is the start of the nephron fluid is null called filtrate so once the movement of fluid into the nephron from the glomerus we call that fluid now filtrate the filtrate contains water glucose amino acid salts and nitrogenous waste larger molecules will remain in the now thicker capillaries they are taken away by the effront arterial which is narrower to keep the pressure up in the glomerus for filtration both filtrate and blood are isotonic at this point remember isotonic means they will approximately have the same concentration of solutes moving from nephron to blood happens during our tubular reabsorption which is also known as our selective reabsorption so first we're moving from the blood to nephron and now we're moving from nephron back to blood this is going to happen in our peritubular capillary network and it occurs mainly in our proximal convoluted tubule of our nephron cells contain lots of protein carriers and mitochondria for active transport there are microvilli for increased surface area for absorption glucose amino acids some salts a little water returned to the blood by active transport by carrier proteins sodium ion is actively reabsorbed and chlorine ion is passively follows reabsorption of salts increases the osmolarity of blood compared to the filtrate the water moves passably from tubule into blood so what this means is once we have some ions moving we can have some passive following of this at the proximal convoluted tubule we have reabsorbed filtrate components so most water nutrients required salts all amino acids and glucose non-reabsorbed filtrate components some water most nitrogenous wastes and excess salts so the reabsorbs filtrate components this means that this is moving to the blood the non-reabsorbed remains in the nephron now we're at the loop of henle and this is descending so we'll see at one point it's descending it's moving down and the other part of the loop of panel is called the ascending it's moving up so the descending down limb of the loop of hennell passively reabsorbs water water moves out for two reasons first as a solute at is reabsorbed water follows by osmosis into the peritubular capillary network the loop of henel is in the renal medulla which is very salty the extracellular fluid is full of sodium's chloride and urea so water moves to establish equilibrium by the end of the descending loop here we can see the descending loop of hennell much water has been reabsorbed filtrate is very concentrated so what this means is water has been reabsorbed into the blood and the filtrate the fluid that is left in the nephron is going to be very concentrated so now we're going to see that the filtrate is hypertonic to the blood at the loop of panel ascending which is from this section upwards this is going to be where salts are reabsorbed for example sodium chloride first passively and then actively this is permeable to salts only not water by the time filtrate reaches the distal convoluted tubule it is isotonic to blood again step is tubular secretion or tubular excretion this is movement from blood back to the nephron and this is going to occur in our distal convoluted tubule or dct by active transport excess substances in blood enter the filtrate so cranine drugs penicillin or hydrogen ions the ph of blood is maintained by adjusting hydrogen ion levels now into the collecting deck some urea slips out and adds to the solute concentration of the renal medulla this causes more water to diffuse out of collecting duct into the renal medulla if adh is present urine urine is a filtered substance and substance is not reabsorbed in secreted substances this is brought to the urinary bladder via the ureter urination stretch receptors in wall of bladder this is going to send impulses when the bladder fills up to about 250 milliliters motor impulses from the spinal cord so bladder contraction the fingers will relax and urine will be excreted out of the body part three urine regulation adh stands for anti-diuretic hormone antidiuresis is a decrease in urine volume when adh is present this is released from the posterior pituitary gland which is made by the hypothalamus this is going to regulate the reabsorption of water by increased permeability of the collecting dot so when adh is present more water is moving into the blood which is going to increase blood pressure and decrease urine volume if a person does not drink much water in a given day posterior pituitary releases adh causing more water to be reabsorbed and less urine to be formed osmoreceptors in our hypothalamus detect changes in osmotic pressure this is the amount of water if low adh is released water is reabsorbed and blood volume increases no more adh this is a negative feedback loop so essentially we make sure that we don't lose too much water if we're not taking in enough water by not excreting excess water alcohol inhibits adh so need to urinate frequently occurs there's water loss which leads to dehydration this causes a hangover symptom aldosterone this is a hormone produced by the adrenal cortex of the adrenal glands on top of the kidneys the same place where epinephrine is created this regulates blood pressure by adjusting the blood at volume by increasing the sodium ion reabsorption at the distal convoluted tubule this causes water to move out by osmosis so blood volume and blood pressure increases so what this means is aldosterone is going to increase the sodium ion reabsorption back into the blood which is going to cause the water to follow by osmosis blood pressure sensors in the glomerular apparatus this is the region of contact between the afferent arterial and the distal convoluted tubule you can see from this photo this detects low blood pressure at the glomerus blood pressure too low to promote filtration the juxtapolaria apparatus secretes renin which is a hormone due to low blood pressure this causes constriction of blood vessels and release of aldosterone from the renal cortex aldosterone increases sodium reabsorption followed by the reabsorption of water out of the nephron and into the blood this overall increases blood pressure and blood volume anh atrial network hormone the hormone produced from the atria of the heart and it inhibits renin's secretion which then stops aldosterone this increases the excretion of sodium ion in the bowman's capsule ph balance remember homeostasis is the maintenance of normal internal conditions of an organism by self-regulation for example blood ph should be maintained at 7.4 the body has three levels of ph regulation we have our hydrogen ion and bicarbonate buffer system in our blood we have a respiratory center and kidneys our kidneys will act to regulate ph if levels are beyond the control of the first two levels if the blood is too acidic hydrogen ion and bicarbonate ions are secreted or reabsorbed as needed they're motion between the blood and urine if blood is acidic in the following diagram so if blood is too acidic we're going to see so the hydrogen ions moving from the blood to the urine as hydrogen ions increase acidity and we're going to have more bicarbonate ion move from the urine to the blood in order to help buffer in the urine it's going to go with ammonia to form ammonium and this is the end of our urinary system please take the time to go through the handouts there's a lot of complicated information a lot of new words a lot of words that are very similar in this unit so make sure to go through the handouts because it helps organize and gives a lot of information about how to put it all together in case you're a little confused thanks for listening and i'll see you for our last unit the reproductive system next