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Urinary System

by: Brooke Polinsky

Urinary System BIOL 2510 - 001

Brooke Polinsky

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About this Document

First new material for the final
Human Anatomy & Physiology II
Dr. Shobnom Ferdous
Class Notes
Urinary, system, anatomy
25 ?




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This 5 page Class Notes was uploaded by Brooke Polinsky on Monday April 25, 2016. The Class Notes belongs to BIOL 2510 - 001 at Auburn University taught by Dr. Shobnom Ferdous in Spring 2016. Since its upload, it has received 23 views. For similar materials see Human Anatomy & Physiology II in Anatomy at Auburn University.


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Date Created: 04/25/16
Urinary System Final Exam Notes: • What are the three steps of urine formation? ◦ filtration,secretion,absorption • What is reabsorption? ◦ the movement of substances from filtration the nephron tubule back into blood via peritubular capillaries/ vasa recta • What would happen if reabsorption didn't occur? ◦ much of substances (99%) filtered will be reabsorption and if this didn't occur we would excrete our plasma volume in less than half an hour • What two processes does reabsorption involve? ◦ passive and active transport • Where does reabsorption occur? ◦ occurs at PCT,LOH,DCT,CD,although most reabsorption occurs in the PCT • What is reabsorbed in the PCT? ◦ all glucose and amino acids: Apical- co-transport,Basolateral- facilitated diffusion ◦ 65% of water: Apical-osmosis via aquaporin,Basolateral- osmosis via aquaporin ◦ 65% of Na+: Apical- Co-transport/Facilitated Diffusion,Basolateral- Na+/K+ATPase (1active transport) ◦ 80% HCO3: reabsorption dependent on H+ secretion ◦ 60% Cl and 55% K+: paracellular route- movement between tubule cells due to leaky tight junctions • What is tubular reabsorption? ◦ quickly reclaims most of the tubular contents and returns them to blood • What is the selective transepithelial process? ◦ almost all organic nutrients are reabsorbed ◦ water and ion reabsorption is hormonally regulated and adjusted • What two processes are involved in tubular reabsorption? ◦ active and passive tubular reabsorption • What two routes can substances follow in tubular reabsorption? ◦ transcellular and paracellular route • What is the transcellular route? ◦ solute enters apical membrane of tubule cells ◦ travels through cytosol of tubule cells ◦ exits basolateral membrane of tubule cells (often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces) ◦ enters blood through endothelium of peritubular capillaries by movement of interstitial fluid • What is the paracellular route? ◦ between tubule cells ◦ limited by tight junctions,but leaky in proximal convoluted tubule nephron ‣ water,Ca2+,Mg2+,K+,and some Na+ in the PCT move via this route ◦ movement through the interstitial fluid and into the capillary • What is the tubular reabsorption of Na across the basolateral membrane? ◦ Na+ is most abundant cation in filtrate ◦ transport of Na+ across basolateral membrane of tubule cells is via primary active transport ◦ Na+-K+ATPase pumps Na+ into interstitial space ◦ Na is then swept by the bulk flow into peritubular capillaries • What is the tubular reabsorption of Na across apical membrane? ◦ Na+ enters tubule cell at apical surface via secondary active transport (cotransport) or via facilitated diffusion through channels ‣ Active pumping of Na+ at basolateral membrane results in strong electrochemical gradient within tubule cell • results in low intracellular Na+ levels that facilitates Na+ diffusion • K+ leaks out of cell into interstitial fluid,leaving a net negative charge inside the cell, which also acts to pull Na+ inward • What does primary active transport provide for Na+ reabsorption? ◦ provides energy and means of reabsorbing almost every other substance • What is active secondary transport? ◦ electrochemical gradient created by pumps at basolateral surface give "push" needed for transport of other solutes ◦ organic nutrients reabsorbed secondary active transport are cotransported with Na+ ‣ glucose,amino acids,some ions,vitamins • What is passive tubular reabsorption of water? ◦ movement of Na+ and other solutes creates osmotic gradient for water ◦ water is reabsorbed by osmosis,aided by water-filled pores called aquaporins • What are the two types of reabsorption in aquaporins? ◦ obligatory water reabsorption= aquaporins are always present in PCT ◦ facultative water reabsorption= aquaporins are inserted in collecting ducts only ifADH is present • What is passive tubular reabsorption of solutes? ◦ solute concentration in filtrate increases as water is reabsorbed ‣ creates concentration gradients for solutes,which drive their entry into tubule cell and peritubular capillaries ◦ fat-soluble substances,some ions,and urea will follow water into peritubular capillaries down their concentration gradients ‣ for this reason,lipid-soluble drugs and environmental pollutants are reabsorbed even though it is not desirable • Why is sugar in the urine a symptom of diabetes mellitus? ◦ type 1= body produces little to no insulin ◦ type 2= cells do not respond properly to insulin • What is transport maximum? ◦ limits reabsorption ◦ reabsorption of all substances reabsorbed via transport protein is limited by the number of transport proteins present ◦ if plasma levels of substance exceedsTm,it will be excreted ◦ exists for almost every reabsorbed substance ◦ transport rate at saturation • What is the renal threshold? ◦ plasma concentration at which saturation occurs • Loop of Henle reabsorption includes: ◦ Na+,Cl-,K+:but only from ascending limbs ◦ Water:only from descending limbs • What does DCT and CD reabsorption include? ◦ hormonal control ofADH,adolsterone,ANP ◦ Na+: ‣ increase in adolsterone-->increase Na+ reabsorption (and K+ secretion) ‣ increase inANP-->inhibit Na+ reabsorption at CD,(so decrease BV and BP) ‣ water (increase inADH-->increase in water reabsorption) at CD • What are proximal convoluted tubules? ◦ site of most reabsorption ◦ all nutrients such as glucose and amino acids are reabsorbed ◦ 65% of Na+ and water reabsorbed ◦ many ions ◦ almost all uric acid ◦ about half of urea (later secreted back into filtrate) • What happens in the nephron loop? ◦ descending limb:water can leave,solutes can't ◦ ascending limb:water can't leave,solutes can ‣ thin segment is passive to Na+ movement ‣ thick segment has Na+-K+-2Cl symporters and Na+-H antiporters that transport Na+ into cell • some Na+ can pass into cell by paracellular route in this area of limb • Transcellular transport systems are..... ◦ very specific and limited • What does the transport maximum reflect? ◦ number of carriers in renal tubules that are available ◦ when carriers for a solute are saturated,excess is excreted in urine • What is an example of transport maximum? ◦ hyperglycemia leads to high blood glucose levels that exceedTm,and glucose spills over into urine • Where is the DCT and CD hormonally regulated? ◦ ADH and adolsterone • What isADH? ◦ released by posterior pituitary gland ◦ causes principal cells of CD to insert aquaporins in apical membranes,increasing water reabsorption ◦ increased ADH levels cause an increase in water reabsorption • What is aldosterone? ◦ targets CD (principal cells) and distal DCT ◦ promotes synthesis of apical Na+ and K+ channels,and basolateral Na+-K+ATPase for Na+ reabsorption (water follows) ◦ as a result,little Na+ leaves the body ◦ without aldosterone,daily loss of filtered Na+ would be 2%,which is incompatible with life ◦ increase blood pressure and decrease K+ levels • What is an atrial natriuretic peptide? ◦ reduces blood Na+,resulting in decreased blood volume and pressure ◦ released by cardiac atrial cells if blood volume or pressure elevated • What is the parathyroid hormone? ◦ acts on DCT to increase Ca+ reabsorption • What is the release ofADH caused by? ◦ high blood osmolality ◦ high plasma (Na+) ◦ low systemic BP • What causes the release of aldosterone? ◦ low systemic BP ◦ low plasma (Na+) ◦ High plasma (K+) • What are diuretics? ◦ chemicals that enhance urinary output ◦ ADH inhibitors= alcohol ◦ Na+ reabsorption inhibitors = caffeine or drugs for hypertension or edema ◦ Loop diuretics inhibit medullary gradient formation • What are osmotic diuretics? ◦ substance not reabsorbed,so water remains in urine;for example,in a diabetic patient,high glucose concentration pulls water from body • What is secretion? ◦ movement of substances from blood in peritubular capillaries to nephron tubule ◦ disposes of waste in peritubular capillaries ◦ eliminates substances that were passively reabsorbed but not needed by body • What are important secretions? ◦ K+(DCT,CD) ‣ aldosterone increases K+ secretion ‣ coupled with reabsorption of Na+ via Na/K pump ◦ H+ (PCT,CD) ‣ is blood too acidic,increase in H+ secretion ‣ if blood is too basic,decrease in H+ secretion • What are four abnormalities in acid-base balance? ◦ respiratory acidosis- high blood PCO2,due to hypoventilation ◦ respiratory alkalosis- low blood PCO2,due to hyperventilation ◦ metabolic acidosis- low blood pH and HCO3 ‣ cause= consuming too much alcohol,loss of HCO3 due to diarrhea,lactic-acid build up ◦ metabolic alkalosis- high blood pH and HCO3 ‣ cause= vomitting,consuming excess base in food (taking too many antacids) • What is an important function of the kidneys? ◦ maintain water and ion balance in body fluids • What is osmolality? ◦ number of solute particles per kg of water ◦ units are milliosmol/kg (mOsm) ◦ blood plasma= 300 mOsm • What are concurrent mechanisms? ◦ fluid flows in opposite directions through adjacent segments of the same tube ◦ work together to maintain and establish medullary osmotic gradient from renal cortex through medulla ◦ ascending/descnding loop of henle and vasa recta ◦ gradient runs from 300 mOsm in cortex to to 1200 mOsm at bottom of medulla • What does the kidney due in response to dehydration and over hydration? ◦ dehydration= produce small amounts of urine ◦ over hydration= produce dilute urine ◦ accomplish this through countercurrent mechanism • What are the two types of counter current mechanisms? ◦ countercurrent multiplier= interaction filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons ‣ creates gradient ◦ countercurrent exchange= blood flow into ascending/descending limbs of vasa recta ‣ preserves gradient • Countercurrent Multiplier depends on? ◦ filtrate flow in opposite directions (ascending/descending) ◦ difference in permeabilities between descending nephron loop and ascending loop ◦ active transport of solutes out of ascending limb ◦ limbs of nephron loop are not in direct contact but are close enough to influence each other's exchanges with surrounding interstitial fluid • How does LOH establish medullary osmotic gradient? ◦ 1.filtrate entering LOH isometric blood plasma and interstitial fluid ◦ 2.Along descending limb,H2O passes out of filtrate by osmosis ‣ filtrate becomes more concentrated ◦ 3.along ascending limb,NaCl leaves filtrate ‣ NaCl contribute to osmolality of interstitial fluid ‣ filtrate becomes more dilute • How does the vasa recta maintain gradient and take up reabsorbed water? ◦ 1.blood flowing deeper into medulla becomes more concentrated ◦ 2.blood flowing towards cortex picks up H2O and loses salt • How is urine concentrated? ◦ action ofADH on collecting duct ◦ osmoreceptor in hypothalamus detect changes in osmolality of extracellular fluid ◦ even slight changes in osmolality activates osmoreceptors and changes ADH release from pituitary • What happens in the body when someone is over hydrated? ◦ decreases blood ECF osmolality ◦ lowersADH secretion from posterior pituitary ◦ lowers number of aquaporins in CD ◦ decrease H2O reabsoprtion from CD ◦ dilute urine produced ( and decreases blood volume) • What happens in the body if your dehydrated? ◦ increase osmolality of extracellular fluid ◦ increaseADH release from posterior pituitary ◦ increase number of aquaporins in CD ◦ more H2O reabsorption from CD ◦ concentration urine produced and increases blood volume • How does the movement urea helps to concentrate urine? ◦ urea is a nitrogenous waste product but can enter ascending limb by diffusion ◦ ADH increase urea diffusion out of CD,which then enters ascending LOH to make filtrate entering CD even more concentrated (more H2O absorbed) • Why is frequent urination a symptom of diabetes insipidus? ◦ caused by lack ofADH orADH receptors in CD


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