Ch 19 study questions

9 Pages

Biomedical Physio & Kines
Course Code
BPK 205
Parveen Bawa

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Chapter 19 (Multiple choice and essay type) 1. (a) Draw and explain the structure of a typical nephron all the way to the collecting ducts. [20 minutes, 1 page of writing + one figure] • Afferent arteriole transfers blood to renal corpuscle. Blood travels through glomerulus in the Bowman’s capsule, entering the nephron as filtrate. The glomerulus capillaries join to form the efferent arteriole. • Filtered fluid flows from Bowman’s capsule into proximal tubule o Primary fxn of proximal tubule is bulk reabsorption of isosmotic fluid. Cells transport solutes out of lumen, and water follows by osmosis • then into loop of Henle. o Descending portion of loop: more solute reabsorbed than water. When filtrate leaves loop, it is now hyposmotic relative to plasma • Then it ascends to the distal tubules • From distal tubules to the collecting duct • Filtrate in Collecting ducts travels down from cortex to medulla and drains into renal pelvis o Distal tubules and collecting duct is where fine regulation of salt and water balance takes place under control of several hormones (secretion and reabsorption occurs here in these two regions) (b) Now draw the vascular system related to each part of the nephron. [15 minutes, draw additional parts on the same figure as above] Peritubular capillaries surround both tubules. Vasa recta surrounds loop of henle where it dips into medulla. Passage of solutes and molecules between these two types of capillaries is mediated be interstitial fluid. 2 .What is juxtaglomerular apparatus? What three types of cells/structures comprise the JGA and what are their functions?Draw the corpuscle and indicate where these structures are.[20 minutes, 1 page including figure of the corpuscle]. Juxtaglomerular apparatus is the region where the distal tubule comes in contact with the afferent and efferent arterioles. Macula densa and Granular cells comprise it. • Granular Cells (aka juxtaglomerular cells o Smooth muscle cells in walls of afferent arterioles o Synthesize, store, and release enzyme renin o Renin causes production of angiotensin II for vasoconstriction • Macula Densa o Region of specialized epithelial cells in wall of distal tubule around bowman capsule o Increased NaCl in distal tubules causes constriction of afferent arterioles via paracrine agents 3. Define Glomerular Filtration Rate.What factors does GFR depend on? [20 minutes, 1 page of writingplus figure] Glomerular Filtration Rate: Volume of fluid filtered into Bowman’s Capsule per unit time. Usually around 125 mL/min or 180 L/day. Factors • Pressure o High hydrostatic pressure of blood flowing through glomerular capillaries pushes plasma out o Colloidal osmotic pressure of proteins in capillaries favors fluid back into capillaries o Bowman capsule has fluid that creates fluid pressure. Fluid pressure opposes filtration from capillaries o Net outward osmotic pressure and large pores in fenestrated capillaries allow sufficient plasma volume to filter out into Bowman’s capsule • Filtration coefficient o Determined by surface area available for filtration o Determined by permeability of membranes  Depends on size of filtration slits  Angiotensin II and prostaglandins may act on podocytes and mesangial cells, changing size of filtration slits and permeability of the slits. 4. How does blood pressure and renal blood flow affect GFR?[15 minutes, figure may be used] • Vasoconstriction of afferent arterioles causes decreased renal blood flow, and decreased hydrostatic pressure, and decreased GFR • Increased resistance of efferent arterioles decreases renal blood flow, but increases hydrostatic pressure and GFR • Dialation of afferent arterioles decreases resistance, increases renal blood flow, increases hydrostatic pressure and GFR 5. Explain autoregulation of GFR.What is the range of mean blood pressure during which GFR does not change? Mean arterial pressure goes up  Afferent arteriolar pressure increases  Glomerular filtration rate Pressure increases  increased GFR When Mean Arterial pressure falls drastically, Sympathetic Nervous System decreases diameter of both afferent and efferent arterioles. Vascular resistance increases, which decreases GFR, decreases urine output, conserving water. This is to bring MAP back up. • Intrinsic Control o Myogenic regulation:  Increase in blood pressure would increase GFR, but smooth muscle responds with vasoconstriction which maintains constant GFR  Decrease in blood pressure would decrease GFR but smooth muscles relax causing increased blood flow and maintains constant GFR  Increase in blood pressure stretches mesangial cells that would increase GFR, but mesangial cells response is to contract, reducing surface area available for filtration to keep constant GFR o Tubuloglomerular feedback:  When NaCl in distal tubule increases due to increased GFR, paracrine message is delivered from macula densa to afferent arteriole to constrict. Possible paracrines (ATP, nitrous oxide, adenosine) • Extrinsic Control o Sympathetic nervous system via alpha receptors causes vasoconstriction of arterioles, decreasing blood pressure, and hence GFR o Lowering systemic BP lowers BP in arterioles, which makes granular cells release Renin. Renin increases angiotensin II. Angiotensin II causes vasoconstriction to increase systemic BP. ANG II also helps release aldosterone and ADH. o Prostaglandins (modified fatty acids) are released from damaged tissue and are vasodilators. Range of Mean blood pressure during which GFR doesn’t change is 80-180 mmHg 6. How do hormones and autonomic nervous system affect GFR? 7. Draw and label a typical nephron and associated blood vessels. [ Hint: five parts: (a) Bowman's capsule, (b) prox tubules, (c) Loop of Henle, (d) Distule tubule and (e)collectingtubule].Of which of these five parts is filtration/absorption/secretion controlled by hormones, and which hormones? [20 minutes, 1 page total] • Bowman’s caps
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