Bio 288 Lecture 26 Notes 05/09/24 Exam Notes (PDF)

05/09/24 Bio 288 Lecture 26 Notes Announcements - Last day, finishing up our discussion on renal processes - Extra credit points are not added to any particular assignment they are added to the total sum of points - SRTI completion need to have 90% to get extra credit - Deadline is before the exam -...

05/09/24 Bio 288 Lecture 26 Notes Announcements - Last day, finishing up our discussion on renal processes - Extra credit points are not added to any particular assignment they are added to the total sum of points - SRTI completion need to have 90% to get extra credit - Deadline is before the exam - In class activity, if not get to in class it will be due monday 05/13 at 11:59pm - Answer key will be posted tomorrow as part of exam prep - Case study 4 - 2 points of extra credit - Its shorter than a normal case study, most are multiple choice style questions not open response - Due on monday 05/13 at 11:59pm - Will post answer key to it after - Final exam - Thompson 104 on tuesday 05/14/24 at 3:30pm to 5:30pm - The structure is same as the normal ones - 35 multiple choice - 5 true/false - 5 fill in the blank - 2 multi part open responses - Review session - Location is TBD still waiting - Will be recorded and posted after on echo360 - Monday 05/13 3pm-5pm - Will send out a reminder email about this Lecture - Review of loop of henle - Descending loop: fresh primary urine coming in, as it descends water is going to move out b/c the descending loop has aquaporins which makes it permeable to water in response to the osmotic gradient - Outside of descending loop is at a higher osmolarity than inside - Water is going to move out until the osmolarities are the same - Ascending loop: as you move up the loop, solutes diffuse out of the loop which decreases the osmolarity in the lumen - The process continues to happen: it's a continuous cycle - As it continues to go through, the gradients get stronger until we get the static gradient (bottom of loop is around 700mOsm and the top of the ascending is around 300 mOsm) - - - Review of Urea - Generated by liver - Nitrogen elimination - Extremely water soluble - Urea is a solute so movement of urea supports the necessary osmotic gradient that allows for water movement to occur - In nephron, we pump urea into it to allow for appropriate water absorption - Also happens in proximal tubules and loop of henle - With urea, water want to move from loop of henle into interstitial fluid then into the blood - Transport of urea through urea transporter A (UTA) from filtrate to peritubular fluid contributes to approximately 40% of the osmolarity of the gradient Vasa recta in maintaining gradient - Name of capillaries surrounding loop of henle and nephrons is the vasa recta - Right next to loop of henle which allows for the solutes (Na+, Cl-) leaving loop of henle to be absorbed into the blood - Also allows for water to be reabsorbed into blood as well - Vasa recta and loop of henle are moving in opposite directions - Descending loop of henle is next to the ascending vasa recta and vice versa - Prevents the diffusion of water and solutes from dissipating from the gradient - We need to maintain it so we need to keep water and solutes all in one area/system - Descending limb of vasa recta (300 mOsm) - As it descends water leaves capillaries by osmosis and solutes enter by diffusion - Ascending limb of vasa recta (325 mOsm) - Higher osmolarity due to lack of urea transporters - Water moves into plasma and solutes move into interstitial fluid - *don’t need to know exact mOsm concentrations but know that its higher in the ascending limb of vasa recta Iclicker question #1: Which of the following accurately describes the thick ascending limb of the loop of henle? - a) permeable to water in the presence of specific hormones - b) permeable to water and does not contain Na+/K+/Cl- contransporters - Would be correct if the question was about DESCENDING limb of loop of henle - c) impermeable to water and does not contain Na+/K+/Cl- contransporters - d) impermeable to water and does contain Na+/K+/Cl- contransporters - - - - - All moving in same direction - e) permeable to water and does contain Na+/K+/Cl- contransporters Review of water absorption in distal tubule and collecting duct - Regulated water reabsorption happens in distal tubule and collecting duct - Obligatory water loss - Minimum volume of water that must be excreted in urine per day - Were limited in the maximum osmolarity - Max osmolarity urine: 1400 mOsm - Osmosis can only go to equilibrium so the max is based upon that maximum number to reach equilibrium - Dictated by loop of henle - Minimum water loss every day = 440 mL - Necessary to eliminate non reabsorbed solutes - If you change your inputs of water, you have to change your outputs (how much water you lose in the form of urine) Role of the medullary osmotic gradient in water reabsorption - About 70% of water is reabsorbed in proximal tubule which is NOT regulated - About 20% of water is reabsorbed in our distal tubules which is regulated by ADH (antidiuretic hormone) - About 10% of water is reabsorbed in our collecting ducts which is regulated by ADH ADH - As our primary urine moves down the distal tubule to the collecting duct, water can be reabsorbed to match the gradient - However, these channels are not always there because body wants ability to manipulate these - So it is regulated by ADH - Dependant on osmotic gradient established by countercurrent multiplier - Dependant on epithelium permeability to water - Water permeability dependant on water channels - Aquaporin 3: ALWAYS present in basolateral membrane - Aquaporin 2: only present in apical membrane when ADH is present - ADH stimulates the insertion of aquaporin 2 to apical membrane - Allows for water to be reabsorbed - Maximum urine concentration is now 1400mOsm - Max amount of water absorbed depends of length of loop of henle Diagram 1: - - ADH is a hormone so secreted by pituitary glands and moves through blood Diffuses through blood to bind to receptor on basolateral membrane Hydrophilic (lipophobic) Receptor is g coupled protein receptor so it is metabotropic Causes chain of reactions which allows for aquaporin 2 to be inserted into the apical membrane which allows for water to come through and go through aquaporin 3 (already there) on basolateral membrane which allows for water to get back into the bloodstream Diagram 2: - - - Increased osmolarity of extracellular fluid means less water excretion which allows you to conserve more body water which will result in negative feedback loop to decrease osmolarity - Decrease in MAP (mean arterial pressure) (blood pressure), a baroreceptor senses it which sends signal to neurosecretory cells which allows for increase of ADH secretion which increases water reabsorption and decreases water excretion which causes a conservation of blood volume - If opposite were true in either cause the opposite situation would happen: would send less signals which would cause a decrease in ADH production Iclicker #2: where does ADH primarily act to regulate water reabsorption in the kidney? - a) glomerulus - Capillaries that surround bowman's capsule - Don't absorb water here - b) proximal tubules - Water reabsorption but not regulated - c) ascending loop of henle - Impermeable to water - d) collecting duct Aldosterone - Secretion occurs simultaneously with reabsorption - Sodium balance is critical b/c it dictates our ability to reabsorb water - This is driven by Na+/K+ pumps on the basolateral membrane - When aldosterone is released and binds to CYTOSOLIC receptor (lipophilic/hydrophobic) - Its synthesized by adrenal glands - Increases sodium reabsorption by increasing the number o fNa+/K+ pumps on basolateral membrane - Also supports potassium secretion - Increases of number of open Na+ and K+ channels on apical membrane - Increases water reabsorption due to increase in osmolarity in blood plasma (pumps out 3 Na+ and only 2 K+ in) - Water flow follows the Na+ because of the 3 Na+ pumped out compared to only 2 K+ pumped in - Responds to: - Decreased blood flow - Decreased blood pressure - Renin-angiotensin-aldosterone pathway - Renin (enzyme) is released which converts angiotensin into a usable form which is then converted into aldosterone - - - - Do not need to know specifics of the process - Decreased blood Na+ levels - By regulating water via ADH and aldosterone we can modulate blood pressure - If you're dehydrated you're more likely to release ADH because it directly responds to osmolarity - Aldosterone usually responds to blood pressure Iclicker question #3: What is the primary role of aldosterone in the renin-angiotensin-aldosterone pathway - a) decrease blood pressure - b) promoting sodium and water reabsorption - c) inhibiting renin release - d) stimulating vasodilation - *all other things will decrease blood pressure but aldosterone increases blood pressure Diuretics - Decreases water reabsorption - Examples: - Coffee - Caffeine decreases sodium reabsorption - Since water reabsorption follows solute reabsorption (Na+ is most important factor to dictate water flow) - Caffeine = diuresis - Not severe but short term effects - Alcohol - Alcohol prevents the production of ADH (vasopressin) in pituitary gland - Can't insert aquaporin 2’s which means cannot be absorbed - You urinate it out as fast as you consume it GFR - Normally autoregulated - But you can regulate it as well based on circumstances - If your blood pressure drops below 80mmHg - Decreased GFR - Decrease in water filtered - Decreased in water excretion - If blood pressure increases to more than 160 mmHg - Increase in GFR - Increase in water filtered - Increase in water excretion (dehydration) - - - - - Occurs only in pathological circumstances (injury to one of the urinary organs) Acid-base disturbances - Kidneys get rid of CO2 as well as waste products - CO2 is a source of an acid - CO2 + H20 → H2CO3 (carbonic acid not very stable and does not stay together) → HCO3- (bicarbonate) + H+ - Respiratory acidosis = increased CO2 which increases blood H+ (decrease in pH) - Respiratory alkalosis = decreased CO2 which decreases blood H+ (increase in pH) - Respiratory disturbances are always related back to CO2 b/c dictated by changes in respiration/CO2 Carbon dioxide transport in blood - Carbonic anhydrase - Enzyme that converts CO2 and water to carbonic acid - The equation goes both wats so increasing CO2 causes an increase in bicarbonate and H+ produced Metabolic disturbances - Result of changes in blood pH due to something OTHER than abnormal CO2 - Metabolic acidosis - Excess elimination of alkaline substances (ex: bicarbonate) - Excess production of acid in metabolism (ex: lactic acid production in exercise) - Excess consumption of acid in diet - More likely - Metabolic alkalosis - Excess elimination of acid from the body (ex: vomiting) - Addition of alkaline substances to the blood (ex: IV fluid) - Less common Regulation of acid-base - Three methods - Buffering of hydrogen ions - Binding or releasing of H+ to substances already in the blood - Ex: hemoglobin - Fastest and easiest way to achieve this - Immediate and short term - Respiratory compensation - Immediate and short term - Dictated by changes in ventilation - Renal compensation - Excretion of acid or base substances