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35 Cards in this Set
- Front
- Back
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Describe what happens during tubular reabsorption (ie, H2O and solutes move from ____ to ___).
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H2O and solutes move from the tubule lumen into the blood of teh peritubular capillaries or vasa recta
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Describe what happens during tubular secretion (ie, H2O and solutes move from ____ to ___).
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- materials moved from the blood into the filtrate
- allows unnecessary/unwanted materials to be removed from blood |
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Why is the active reabsorption of Na+ so important to the overall process of tubular reabsorption?
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- it is the reabsorption of Na that creates an electrical gradient that favors reabsorption of anions
- anions: bicarbonate (HCO3-), chlorate ion - also establishes osmotic gradient to reabsorb water |
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What is transport maximum Tm? What happens when a solute in the filtrate exceeds its renal threshold?
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- Tm = when the carriers for a solute are saturated, working at there fastest rate; this rate limit is the Tm (mg/min)
- if it exceeds it, then you will pee out that substance, like diabetics with glucose |
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Generally describe the reabsorption and secretion activities in the various regions of teh renal tubule
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- PCT:
-- reabsorbed: sodium, sets up e. chem, virtually all nutrients, Cations (K, Mg, Ca), anions (Cl, HCO3-), water, urea and lipid soluble solutes, small proteins via endocytosis (digested inside PCT cells into AAs, b/c we don't want the osmotic press they create in the filtrate); 65% of filtrate reabsorbed here -- secreted: H+ via Na/H antiporters, small amts of creatinine + urea, ammonium ion - LOH: -- reabsorbed: descending (water can leave thru aquaporin I's, impermeable to solutes); ascending (impermeable to water, Na/K/2Cl symporters reabsorb them actively; also Na/H antiporters, Ca and Mg are passively reabsorbed via paracellular route) -- secretion - none - DCT: -- reabsorption - Na and Cl via Na/Cl symporter, Ca, H2O) -- secreted - H+ can be... - Collecting ducts/late DCT reabsorb: HCO3, K, Na, Cl Secrete: H, HCO3, K |
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Where is the Na+/K+/2Cl- symporter located? why is this important?
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- in the apical membrane of the thick ascending limb
- mean means of Na entry at the luminal surface ot hte thick portion of the ascending limb - works via 2ndary active transport |
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Describe the cotransport process involved in the reabsoprtion of glucose.
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- it's a Na/Glucose cotransport system in the PCT
- it uses secondary active transport to get the energy |
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Describe the process by which bicarbonate ions are reabsorbed in the PCT. What role to Na+/H+ antiporters play in this process?
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- the Na/H transporters allow for the secondary active transport of bicarbonate
- 80% of the filtered bicarbonate is reabsorbed here - via paracellular diffusion driven by electrochemical gradient for Cl - the pump sets up the electrochemical gradient needed |
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What process is involved in water reabsorption?
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- osmosis
- aquaporin I is present in the PCT and parts of the LOH to make the tubule freely permeable to H2O - through aq I, obligatory water reabsorption occurs, where water has to follow the reabsorbed sollutes - aquaporin 2 expressed in DCT, facultative water reabsorption b/c it's affected by ADH levels |
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In what part of the tubule is the greatest amount of water reabsorbed? In what part of the tubule is water reabsorption regulated by ADH?
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- most is reabsorbed in the PCT - the distal part of the tubule - the end of the DCT and the collecting duct
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How does aldosterone help regulate reabsorption in the distal convoluted tubule?
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- aldosterone regulates teh principle cells; makes them reabsorb more sodium and secrete more potassium
- triggered by high K in plasma - it increases the number of Na leakage channels in teh apical surface for the to diffuse into the cell - virtually all of the K was reabsorbed in the PCt, so if the body has too many, we have to secrete it here - due to aldosterone's effects, there is virtually no urinary Na excretion (affects Na and K, not H2O... H2O can only follow if ADH is present) |
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What factors trigger aldosterone release?
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- dec blood volume or BP
- hyponatrimia - hyperkalemia - the Renin-angiotensin system |
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Describe the osmotic gradient in the interstitial fluid of the renal cortex and medulla.
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- the fluid is isotonic near the cortex and becomes more and more hypertonic as it gets closer to the medulla
- this gradient in fluid allows us to keep absorbing H2O in the decending LOH |
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How does the countercurrent mechanism help establish and maintain the renal osmotic gradient?
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- the decending loop is permeable to water; as it goes closer to the medulla, the interstitial fluid becomes more hypertonic, so it keeps drawing the water out of the tubules, even though the tubules themselves are becoming more concentrated
- then it becomes permeable to Na and Cl, so they flow out of the now very concentrated solution in the tubule; as it goes up, tubule= less conc, but so does the medulla, so Na + Cl keep flowing out till the osmotic gradient is the same at the top as when it came in, but w/much less h2o and na and cl |
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What role does the vasa recta play in maintaining the medullary osmotic gradient?
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- need to keep the more hypertonic area towards the cortex in order for the countercurrent mechanism to work
- the vasa recta is a low press cap bed w/permeable walls - can maintain rather than dilute osmo of interstitium - as a result, prevents salts from rapidly diffusing into the vessel and cleansing from the interstitial fluid - basically, because of the hairpin turn, it ballances it's diffusion effects out perfectly |
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How does urea recycling help to establish the medullary osmotic gradient and promote water reabsorption? In what segment of the tubule is urea reabsorbed?
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- urea diffuses out of the collecting ducts deep in the medulla - it helps build up about half of the osmolarity of the medullary interstitial fluid, which allows water to diffuse out of the decending limb. then it reabsorbs into the ascending
- it's deep in the medulla that this happens, b/c the collecting duct is permeable to urea so it can diffuse out, but not permeable to the other things, so the amount of other particles would stay the same in filtrate leaving the nephron |
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How does the medullary osmotic gradient promote the formation of a concentrated urine?
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- in the decending loop, water leaves the filtrate as the interstitial fluid becomes more and more hypertonic
- in the ascending limb, water can't come back in, so instead Na and Cl leave, in order to make the filtrate closer to the hypertonicity of the medullary osmotic gradient. |
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Compare the osmolarity/tonicity of the following solutions: body fluids (blood and interstitial fluid), glomerular filtrate, filtrate in teh PCT, filtrate at the deepest part of the LOH in juxtamedulary nephrons, filtrate in the DCT, urine @ beg of collecting tubule, urine @ end of collecting tubule.
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- body fluids - 300 - they are isotonic to the glomerular filtrate
- glomerular filtrate - isotonic to the body fluids - PCT - increasing as water leaves tubule, all the way up to 1200 - LOH - 1200, the most hypertonic? spot ever - DCT - gets less and less hypertonic till it's isotonic - beg of CT - hypotonic - 100 - end of CT - hypotonic - 100 it isn't permeable, so doesn't change (except to urea) |
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What is the effect of ADH on urine volume and concentration?
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- increases the aquaporin 2 channels in the distal tubule
- promotes water reabsorption into blood of peritubular cap., until the osmolarity of the filtrate - the osmolarity of hte interstitial fluid; depending on level of ADH secretion, urine conc may rise as high as 1200-1400 mOsms (the same as the interstitial fluid deep in the medulla) - less volume, more conc |
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Explain the physiologic mechanisms involved in maintaining homeostasis when the osmolarity of body fluids increases. What happens when the osmolarity decreases?
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too little water in body - ADH and aldosterone are secreted
- aldosterone makes the principle cells in the late DCT absorb more Na and secrete more K. - the ADH causes aquaporin 2 in the collecting duct to make it permeable to water, so it's reabsorbed, as the duct passes through the deep parts of the medulla - too much water? (high osmolarity) - those two are inhibited so the water will leave in the duct and be peed out |
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Describe the composition and pH of urine.
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- clear, pale, slight odor
- pH = 6 (4.5-8) - water (95%) - Solutes: nitrogenous wastes (urea, creatinine, uric acid), electrolytes, other substances (drugs, excess vitamins) - in decreasing conc order: urea, Na, K, phosphate and sulphate ions, creatinine, uric acid |
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What are the metabolic sources of urea, uric acid, and creatinine?
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urea - AA breakdown
creatinine - metabolite of creatine phosphate wich stores e. for ATP regeneration uric acid - nucleic acid breakdown |
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Trace the flow of urine from teh collecting tubules to the point where it leaves the body.
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- collecting tubules
- minor calyx - major calyx - renal pelvis - ureter - bladder - urethra |
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Describe the structure of the ureter
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- no valves @ ureter/bladder jct
weight of bladder as it fills compresses ureters @ this jct to prevent backflow of urine 3 tissue layers: Mucosa - deep one; continuous w/kidney pelvis and bladder; transitional ET w/underlying lamina propria; goblet cells that secrete mucus for protection Muscularis - smooth musc. (internal longitudinal and external circular layers); peristalsis to propel urine to bladder Adventitia - continuous w/fibrous renal capsule and peritoneum |
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How is urine propelled through the ureter to the urinary bladder?
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- 2 layers of smooth muscle (the internal longitudinal and external circular) layers of the middle mucsularis layer contract
- peristalsis |
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Describe the structure of the urinary bladder.
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- retroperitoneal
- 3 openings (2 ureters, 1 urethra; trigone is triangle shaped area b/w openings - 3 layers Mucosa - deep; transitional ET w/underlying lamina propria; rugae present when empty Muscularis - detrusor muscle; 3 sheets of smooth muscle tissue; contract during urination; internal urethral sphincter Adventitia - along inferior/poserior surface Serosa - on anterior surface the last 2 are the superficial layer |
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What is the detrusor muscle? What does it do?
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- found in the middle muscularis layer of the bladder
- composed of 3 sheets of smooth musc - contracts during urination to propell urine |
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Compare and contrast the male and female urethras
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Females: 3-4 cm; directly posterior to pubic symphysis; tightly bound to ant vaginal wall by fibrous CT; anterior to vaginal opening
Males - 20 cm; goes through prostate, urogenital diaphragm andpenis; subdivided into 3 regions (prostatic, membranous, penile); serves as conduit for semen as well as urine |
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Describe the micturation reflex.
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- bladder fills; more than 200 ml causes stimulation of stretch receptor s in wall
- impulses to micturation reflex center in sacral spinal cord - micturation reflex - PNS fibers from S2 and S3: rhythmic contractions of detrusor musc; inhibits contraction of internal urethral sphyncter; interneurons go to brain, decide to let the external urethral sphyncter relax or not - if not, reflex arc triggered atain when 200-300 more ml are in bladder |
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Obligatory water reabsorption
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- through aquaporin I in PCT and parts of LOH;
- if we reabsorb solutes, we HAVE to reabsorb H2O, it's automatic |
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Facultative water reabsorption
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- through aquaporin 2
- we can modify the amt that we absorb using ADH, to vary the number of aq2 that is expressed in the distal portions of the tubule |
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transcellular reabsorption
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- transport across luminal membrane
- diffusion through cytosol - transport across basolateral membrane - movement through interstitial fluid and into capillary |
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paracellular reabsorption
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- movement through leaky tight jct, particularly in the PCT
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erythropoietin
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Also called hematopoietin or hemopoietin, it is produced by the peritubular capillary endothelial cells in the kidney, and is the hormone that regulates red blood cell production.
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diuretic
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- elevates volume of urination
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