Final notes for Renal system
Final notes for Renal system MPP 3202 - 01
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This 6 page Class Notes was uploaded by Mary Hanrahan on Sunday December 6, 2015. The Class Notes belongs to MPP 3202 - 01 at University of Missouri - Columbia taught by Alan Parrish in Fall 2015. Since its upload, it has received 23 views. For similar materials see Elements of Physiology in Medical Technician at University of Missouri - Columbia.
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Date Created: 12/06/15
Study Guide for Renal Physiology, Chapter 17 Lect 1, 11-11/12-2015 1 List the functions of the kidneys. a Reabsorption, secretion, filtration b Regulation of ECF volume and BP c Regulate osmolarity d Produce hormones e Excrete water f Regulate pH 2 What are the three clearly demarcated anatomical regions of the kidneys? Which one receives the most blood flow, and WHY do you think that is…[Hint: the answer to this “why” question is not explicitly spelled out in the lecture slides—it will require some thought about what events occur in portions of the nephron which reside in the cortex]. a Cortex, medulla, papilla b Cortex receives most blood flow; contains the most filtering nephrons 3 What are key features of the renal circulation which make it unique (i.e. the portal system) a Portal system brings blood from body into glomerular bed-> out into peritubular bed-> veins-> heart b All blood filtered through glomeruli c 4 Know the order of blood flow through the vascular network supplying the nephron a Afferent arterioles-> glomerular bed(capillaries)-> efferent arterioles-> peritubular bed-> veins 5 What is the nephron? What are the names of the specific sections of the nephron and what are the major events related to filtration/absorption/secretion occurring in each one? a The nephron is the filtrating functional unit of the kidney b Bowman’s capsule= covers the glomerulus which is a network of capillaries that filter the blood (filtrate) c Proximal convoluted tubules= reabsorption occurs here; needed water, salt, etc are passed from lumen to peritubular bed (reabsorb) d Nephron loop(loop of henle)= fluid passed from convoluted tubule to nephron loop i Down descending loop-> up ascending loop(back in cortex) (secrete) e Distal convoluted tubule= terminates and empties into collecting duct(secrete) f Juxtamedullary nephron= important for producing concentrated urine 6 What are the three basic processes involved in the fate of fluid and solutes as they pass through the nephron and how do the relative balance of these processes affect the extent to which any of these substances are returned to the body versus being excreted in urine? a Ultrafiltration of plasma by glomerulus b Reabsorption of water and solute from ultrafiltrate (proximal tubule) c Secretion of selected solutes into tubular fluid (active, need energy) (proximal tubule) d Needed substances reabsorb into plasma while wastes stay in urine (loop of henle) 7 Explain how Starling forces determine net filtration vs absorption in the glomerular and peritubular capillary beds. Which process predominates in each of these capillary beds? a When pressure in glomerulus increases, favors filtration b Lower pressure in tubules/peritubular caps. bed- favors net reabsoprtion c Higher pressure in tubules/ glomerular caps. Bed- favors net filtration 8 What process if favored if the net filtration pressure (NFP) is positive? How ‘bout when it is negative? a Filtration is favored if NFP is positive b Reabsorption is favored if NFP is negative 9 What does the filtration coefficient represent? a Glomerular Filtration rate 10 Know the micro-anatomical features of the glomerular capillaries which determine what gets filtered and what stays in the blood. a Capillaries fenestrated b Pores allow water and solutes to leave not blood or plasma cell proteins 11 If I give you a substance of given molecular weight (i.e. size) or electrical charge, be able to predict whether it is likely to be filtered in the glomerulus or not. IOW, know the mw cutoffs. a This depends on the weight or charge of a molecule b 52000 ml < freely filtered c 52000-67000 depends on the charge of the molecule d X > 67000 ml it is impermeable to the glomerulus 12 What will happen to plasma oncotic pressure as blood leaves the glomerulus if the filtration fraction goes up vs down? a If the fraction decreases, pressure will decrease b If the fraction increases, the pressure will also increase 13 Understand how changes in renal blood flow and the state of constriction vs dilation of the afferent and efferent arterioles affect GFR. Also, understand how changes in GFR are going to affect the extent of fluid flow through more distal regions (i.e. toward the end of) the tubular system of the nephron. a Constriction of afferent arterioles causes decrease in GFR b Constriction of efferent arterioles can cause either increase or decrease of GFR i This is due to fluid pile up that can and reverse the process. 14 What is the average GFR per day (i.e., liters/day)? a 180 L/days 15 Describe autoregulation of GFR. a Autoregulation is maintained by a consistant arterial blood pressure which consists between 80 and 180 mm hg 16 How does tubuloglomerular feedback act to regulate GFR when systemic blood pressure is high. How ‘bout when it’s low, e.g. in response to something like severe blood loss? a Maintained by paracrine control b Hormones and autonomic nerves c Changing resistance in arterioles which changes pressure in arteries d Also altering filtration coefficient 17 What is the effect of sympathetic stimulation on the state of constriction in the afferent arteriole? How will that affect GFR? a Diverts blood to heart and muscles b Decreases urine formation to compensate for blood pressure drop c Causes constriction of afferent arterioles -> decrease in GFR Lect 2, 11-13-2015 18 Understand the concept of clearance, and how it can be used to determine GFR. [there WILL be some kind of clearance problem on the exam] a Volume of plasma from which a given substances is cleared by the kidneys/unit time b Every substance in blood has its own clearance value; units expressed as volume of plasma per unit time= mL/min or L/day c Clearance can be used to determine GFR if the substance is freely filterable at the glomerulus, no secreted and reabsorbed by tubules (insulin) 19 Describe the process of tubular reabsorption, what is reabsorbed, and how. a Transcellular reabsorbtion- substances pass apical and basolateral membranes of epithelial cells b Paracellular reabsorptions- substances pass through cell-cell junctions between 2 adjacent cells i Water passive diffusion 1 Volume of tubular fluid decreases as process continues ii Glucose is cotransported over to tubules; limit too how much glucose can be reabsorbed- the rest is sent to urine iii Na+ is reabsorbed through cells with active transport 20 Understand how water and different solutes are reabsorbed or secreted along different parts of the nephron [HINT: the answer to this question relates to the “why” question above for # 2] a Descending limb- highly permeable to H2O; not salt or other substances b Ascending limb- highly permeable to NaCl; not very permeable to water; from ascending limb on, impermeable to urea c Cortical collecting duct- permeable to ADH, Aldosterone, Na+, H2O 21 In what portion of the nephron is the most water reabsorbed? Is the reabsorption itself regulated directly, or not? How might reabsorption here be controlled indirectly? [Hint: think about what controls initial entry of fluid into the tubular system as a whole, i.e. GFR] a Most water is reabsorbed in the descending limb of loop of henle b It is controlled indirectly by the kidneys themselves choosing the concentration of urine based on the amount of water in the body 22 Know what ions are the primary determinants of intra-and extracellular osmolality. Understand how the interaction between the hypothalamo- pituitary control axis and the kidney functions in response to changes in plasma osmolality, and how ADH functions as a critical effector in this process. a Sodium is the main determinant of plasma osmolality b ADH is response of increased plasma osmolality released by the pituitary gland but produced by the hypothalamus c Without ADH the aquaporins would not accept or open up for water 23 Understand how plasma osmolality is regulated through a collaboration between the brain and the kidney, mediated via the hormone, vasopressin (ADH). a ADH is released by the pituitary to attach to aquapores in the collecting duct to reabsorb water 24 What is the role of the Loop of Henle and the countercurrent multiplier in the creation of a hyperosmotic medullary interstitium, and therefore, a concentrated urine? a Countercurrent multiplier is the effect of tuboles and adjacent vessels flowing in opposite direction to excrete or reabsorb substances. b The importance of the loop of henle is to reabsorb sodium and other particles that are excreted by vessels- causing future urine to be hyperosmotic 25 What do the terms, “concentrated urine” or “dilute urine” mean? a Concentrated means containing less water and more particles b Dilute means containing lots of water and partices 26 What does the vasa recta do? a A system of passive exchange capillaries closely associated with the loop of henle i As capillaries descend, solutes diffuse in and water diffused out ii As the capillaries ascend, smaller amount of solutes are contained and more water is present 27 What is the cellular mechanism underlying ADH’s ability to promote water reabsorption? IOW, what specific event is triggered by ADH in the epithelial cells lining the distal collecting duct? a ADH attaches to cells causing a diuretic effect preventing the cells to secrete water b Depends on the interstitial fluid that enters the collecting duct, if it is very dilute than the ADH will not be released if it is concentrated it will be released to reabsorb water Lect 3, 11-16 28 In what portion of the nephron is most sodium and postassium reabsorbed? Is their reabsorption here regulated, or not? a Early on in the nephron, it is not regulated by the body here more so a natural reaction to the body 29 What is aldosterone? How does it affect reabsorption/secretion of Na+/K+? In what portion of the nephron does this occur? a A hormone that is secreted to assess what the body needs and reabsorbs K+ and Na+ in the distal convoluted tubule and collecting duct 30 In the distal tubule/collecting duct, what happens to potassium when sodium reabsorption increases? a Increases in sodium absorption drive extra potassium secretion i Difference in sodium channels whether it be influction or defluction drives the same response for K+ ii Increased flow rates bend cilia on the cells of the distal tubules, resulting in activation of K+ cells 31 How does release of aldosterone respond to an increase in potassium in the plasma? How does it respond to a decrease in plasma sodium? a A rise of blood K+ triggers increased K channels b A decrease in blood K+, causes aldosterone to recede and cause less channels c A fall of blood sodium causes an indirect stimulation of aldosterone via renin-angiotensin-aldosterone system 32 What is the mechanism activated if plasma sodium falls? [Hint: this involves the juxtaglomerular apparatus and activation of the renin-angiotensin- aldosterone system] a Granular Cells secrete renin in afferent arterioles, which converts angiotensinogen into angiotensinogen 2, which is then converted into aldosterone to reabsorb sodium and potassium 33 What factors stimulate renin secretion? Where does renin come from? a Granular cells in juxtaglomerular apparatus 34 How does the renin-angiotensin-aldosterone system respond to changes (up or down) in blood pressure? a In low bp there is usually low salt, the juxtaglomerular apparatus senses this and activated the granular cells to start the system to create aldosterone 35 What hormone is released in response to an elevation in blood pressure, and has the opposite effect on sodium reabsorption as aldosterone? From what tissue is it released? a Secretes renin- secreted from macula densa 36 Explain the feedback mechanism triggered by a low dietary intake of sodium, and how it acts to restore plasma sodium levels. How does this mechanism operate if sodium intake is excessive? a Low pressure in renal artery means there is low NaCl and H2O levels this causes the signal to the juxtaglomerular to secrete renin to fix the levels 37 In general, what happens to water if reabsorption of sodium changes? a When there is more Na+ then water the afferent arterioles are stimulated to prevent and limit filtration 38 Explain how competition between K+ and H+ for the cation (+ charged ions) secretory apparatus in the distal tubule and collecting ducts could affect plasma pH or K+ concentrations—e.g. why might acidosis promote hyperkalemia (excess plasma K+ )? a Reabsorbtion of Na+ causes the release of K+ and H+- competing to be the positive ion b alkalosis also stimulates the release of K+ and inihibites the release H+ c an abundance of K+ can lead to hyperkelamia 39 Understand that overall regulation of body fluids is exerted at two levels: regulation of osmolality via control of water conservation vs excretion (i.e. ADH) and regulation of volume by control of sodium conservation vs excretion (i.e. renin-angiotensin-aldosterone). Also understand that when we say “plasma osmolality,” that that is essentially equivalent to interstitial osmolality, since they are in equilibrium with each other. a 40 Understand how changes in reabsorption vs excretion of sodium at the level of the distal collecting duct is used to control plasma volume, and the respective roles and opposing effects of aldosterone vs atrial natriuretic peptide (ANP) in this process. Be able to describe, say the response to either increases or decreases in volume/blood pressure (a good rule of thumb is that changes in blood volume imply a change in blood pressure). a Aldosterone assess what the body needs and regulates it based on these needs by either reabsorbing k+ and Na+ if needed b ANP is released from the atria in order to decrease blood volume by excreting NaCl and H2O 41 Understand that excretion vs secretion of potassium, especially in the collecting ducts is also controlled by aldosterone, typically in opposition to control of sodium, e.g. when aldosterone is high, sodium is reabsorbed while potassium is secreted, and vice versa. a Reabsorption of sodium causes the secretion of K+ -high aldosterone b When aldosterone is low, sodium is excreted and potassium is absorbed 42 How do kidneys maintain blood pH? a Maintain blood pH by reabsorbing bicarbonate and secreting H+ b Bicarbonate -> H2O + CO2 c CO2 can cross into tubule cells, thus bicarbonate is made again and diffuses in interstitial fluid d Proximal tubule has multiple channels and pumps to excrete Na+/K+/H+ 43 How is acid excreted in urine, and how is bicarbonate reabsorbed? WHERE is bicarbonate reabsorbed? a H+ is continuously secreted to make urine more acidic, and bicarbonate is broken down to h2o and co2 and reabsorbed in the proximal tubule
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