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Chapter 17. Physiology of the Kidneys and Renal System. Composition of Renal System. 2 Kidneys 2 ureters 1 1. Kidney Function. Regulate ECF (plasma and interstitial fluid) through formation of urine. ________________________. Regulate volume of blood plasma. BP.
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Chapter 17 Physiology of the Kidneys and Renal System
Composition of Renal System • 2 Kidneys • 2 ureters • 1 • 1
Kidney Function • Regulate ECF (plasma and interstitial fluid) through formation of urine. • ________________________. • Regulate volume of blood plasma. • BP. • Regulate [waste products] in the blood. • Regulate concentration of electrolytes. • ____________________and other ions. • Regulate ________________. • Secrete erythropoietin.
Regulation of Blood Flow by the Kidneys • Kidneys produce 180L of filtrate – but we only have 5.5L of blood? What is going on? • Most ____________ is returned to blood • Only pee about _________L per day • 98+% is returned to blood
Regulation of Blood Flow by the Kidneys - ADH • Anitdiuretic Hormone (vasopressin) • Produced by hypothalamus – released by ____ • Increase is plasma ____________ as determined by osmoreceptors in brain • Dehydration or excessive salt intake • ADH stimulates water _________________ from filtrate = decrease urine output • Dilution of blood = decreased osmolality = decreased _______
Regulation of Blood Flow by the Kidneys – Aldosterone • Steroid hormone produced by adrenal cortex • Stimulates _______ retention from kidneys • Indirectly affects retention of ________ • Causes increase in blood volume but not an increase in osmolality = salt and water in proportional amounts • Stimulated during _________deprivation – when blood volume and blood pressure are __________
Regulation of Blood Flow by the Kidneys – Renin-angiotensin- Aldosterone • Juxtaglomerular apparatus – secretes __________ • Renin produces _______________ from angiotensin. • As angiotensin I passes through respiratory system it is converted to angiotensin II • Angiotensin II produces a ______________ blood pressure & blood volume • Due in part to ____________________ and part due to increased blood volume • Triggers _______________centers in hypothalamus = more water ingested • Stimulates aldosterone secretion • High ______________ ingestion = high blood pressure/high blood volume = inhibits _________ etc.
Regulation of Blood Flow by the Kidneys - ANP • Increased blood volume = stimulates Atrial natriuretic peptide • Increases ______________ and water excretion in urine = decrease blood volume • Produced by ___________ of the heart • Decreases secretion of ____________ = vasodilation • Antagonizes angiotensin II
Kidneys: Gross Structure • Horse: ____________shaped • Cow: Cluster of ____________ • Sheep: kidney bean • Pig: small, kidney bean • Usually found amongst a lot of kidney fat, especially in older animals • Sort of a purplish red/brown color • Vary in size depending on breed of animal
Structure of the Kidney • Outer cortex: • Contains many capillaries. • Dark • Medulla • Lighter colored • Renal pelvis: collects __________ • Transports urine to ureters.
Nephron • ____________ of the kidney. • Located in ___________ • Produces ______________ • Humans: @ 1 million/kidney • Cats: 150,000/kidney • Cow: 4 million/kid • Consists of: • Blood vessels: • Vasa recta. • Peritubular capillaries. • Urinary tubules: • PCT. • LH. • DCT. • CD.
2 Types of Nephrons • Cortical nephron: • Originates in outer 2/3 of cortex. • Involved in solute reabsorption. • Juxtamedullary nephron: • Originates in inner 1/3 cortex. • Important in the ability to produce a concentrated urine. • Has longer ______. Insert fig. 17.6
Nephron Tubules • Glomerular capsule. • Proximal convoluted tubule (PCT). • Descending and ascending limbs of Loop of Henle (LH). • Distal convoluted tubule (DCT). • Collecting duct (CD).
Structure of Nephron • Composed of 2 basic structures 1. _________________ – fluid is filtered from the blood 2. ______________ – filtered fluid is converted into urine on its way to the pelvis • Glomerulus: blood ____________ through afferent arteriole • Blood _____________ through efferent arterioles
Structure of Nephron • _____________ arteriole brings blood into a mass ofcapillaries = glomerulus (glomeruli) • Bowman’s capsules: epithelial cells covering the glomerulus • Lots of blood coming from an area with lots of room, into an area with less room. Stuff will filter out of blood. • Glomerular capillaries are 100 times more permeable than other capillaries
Glomerular Capsule • Bowman’s capsule: • Surrounds the glomerulus. • Location where glomerular filtration occurs. • Filtrate passes into the urinary space into PCT. Insert fig. 17.6
Structure of Nephron • Glomerulus is an area of high pressure, therefore, fluid will leak _______ and enter the Bowman’s capsule and flow into the _______________________
Proximal Convoluted Tubule • Single layer of cuboidal cells with millions of _________________ • Increase surface area for reabsorption. • PCT functions: • Reabsorption. • Secretion.
Loop of Henle • Fluid flows from the proximal tubule to the ______________________ • Loop of Henle travels into the medulla • 2 parts of the L of H • 1. Descending limb (aka thin segment) • H20 reabsorption • 2. Ascending limb (aka thick segment) • Active transport of Na+. • _____________________________.
Distal Convoluted Tubule • Contains few microvilli. • Functions: • Secretion. • Reabsorption. • Lies in ____________________ • Many (8 or so) from other nephrons come together • Terminates in Collecting Duct.
Collecting Duct • Functions: • Reabsorption. • H20 reabsorption influenced by ______________________ • Secretion. • Collecting ducts combine to empty into _________________________
Renal Blood Vessels • Afferent arteriole: • Delivers blood into the ____________________. • Glomeruli: • Capillary network that produces filtrate that enters the _________________________. • Efferent arteriole: • Delivers blood from glomeruli to peritubular capillaries. • Peritubular capillaries: • Deliver blood to ________________________. • Loops of peritubular capillaries that parallel the L of H • Loop down into the medulla from the cortex
Renal Blood Vessels (continued) Insert fig. 17.5
Juxtaglomerular Apparatus (continued) Insert fig. 17.25
Juxtaglomerular Apparatus • Region in each nephron where the afferent arteriole comes in contact with the thick ascending limb LH. • Granular cells within __________________ secrete renin (enzyme that…): • Converts angiotensinogen to angiotensin I. • Initiates the renin-angiotensin-aldosterone system. • Negative feedback. • Macula densa: • Region where ascending limb is in contact with afferent arteriole. • Inhibits renin secretion when blood [Na+] in blood increases.
Juxtaglomerular Apparatus: • Function: • 1. regulate amount of blood flowing to kidney • 2. regulate amount of filtration • HOW: Detects changes in Na and Cl, in the tubular fluid. • When Na and Cl are lowered, the MD sends a signal to the afferent arteriole to dilate (increase in blood and hydrostatic pressure). • = more filtrate
Glomerular Filtration Membrane • Endothelial capillary pores are large • 100-400 times more permeable to H20, and dissolved solutes than capillaries of skeletal muscles. • Pores are small enough to prevent RBCs, platelets, and ____________ from passing through the pores.
Filtration aided by: • 1. Glomeruli (capillaries): • More_____________ than nomal • 2. Efferent arterioles: _________________in diameter than afferent • increases resistance to blood flow out
Glomerular Ultrafiltrate • Fluid that enters glomerular capsule is called ultrafiltrate. • Glomerular filtration: • Mechanism of producing ultrafiltrate under hydrostatic pressure of the blood. • Glomerular filtration rate (GFR): • Volume of filtrate produced by both kidneys each minute. • Averages 115 ml/min. in women; 125 ml/min. in men. • About 1 coke can/3 minutes (that is a lot of pee!!!!)
Regulation of GFR • Vasoconstriction or dilation of the ______________ arterioles affects the rate of blood flow to the glomerulus. • Affects GFR. • Mechanisms to regulate GFR: • Sympathetic nervous system. • Autoregulation.
Forces that affect filtration: • 1. Constriction of afferent arteriole (decrease in GFR) • 2. Dilation of afferent arteriole (increase in GFR) • 3. Constriction of efferent arteriole (increase GRF) • 4. Increase glomerular capillary colloidal osmotic pressure (decrease GFR) • 5. Sympathetic nerve stimulation (decrease GRF) • 6. Constriction of both afferent and efferent arterioles
Renal Autoregulation of GFR • Ability of kidney to maintain a constant GFR under systemic changes. • Achieved through effects of locally produced chemicals on the afferent arterioles. • When MAP drops to 70 mm Hg, afferent arteriole dilates. • When MAP increases, vasoconstrict afferent arterioles. • Tubuloglomerular feedback: • Increased flow of filtrate sensed by macula densa cells in thick ascending LH. • Signals afferent arterioles to constrict.
Reabsorption of Salt and H20 • Return of most of the molecules and H20 from the urine filtrate back into the ___________ capillaries. • About 180 L/day of ultrafiltrate produced; however, only 1–2 L of urine excreted/24 hours.
Tubular Reabsorption: • 97-99% of water and solutes are filtered and put back into the body • Reabsorption sites: ________________, __________________, ________________ • Reabsorption processes: ________, ___________, ________ transport (glucose, amino acids, some electrolytes) • Glucose and amino acids are especially reabsorbed via their association with Na in the proximal tubules
Tubular Reabsorption: • Chloride: reabsorbed in the thick segments of the ascending limb of the loop of Henle • Glucose: if threshold exceeded – some loss in urine (diabetes mellitus) • Electrolytes: absorbed by active transport and some by diffusion • Na: by active transport in many parts, goes into peritubular capillaries and then increases osmotic pressure, is an increase in concentration of Na around the tissues of the nephrons
Proximal Convoluted Tubule • Reabsorption of H20 by osmosis, cannot occur without active transport: • PCT epithelial cells have lower [Na+]. • Low permeability of plasma membrane to Na+. • Active transport of Na+ out of the cell by Na+/K+ pumps. • Favors [Na+] gradient: • Na+ diffusion into cell.
PCT (continued) • Na+/K+ ATPase pump extrudes Na+. • Creates potential difference across the wall of the tubule • Electrical gradient causes Cl- movement towards higher [Na+]. • H20 follows by osmosis.
Salt and Water Reabsorption in Proximal Tubule Insert fig. 17.14
Significance of PCT Reabsorption • 65% Na+, Cl-, and H20 reabsorbed across the PCT into the vascular system. • 90% K+ reabsorbed.
Osmolality of Different Regions of the Kidney Insert fig. 17.19
Countercurrent Multiplier • What happens when you eat pizza or foods with lots of salt? • Why? Because osmolality is disrupted, to much salt, not enough water • What happens when you drink lots of water? • _________________________ • Why? Because osmolality is disrupted, to much water, not enough salt • Must control how much salt is in your body as well as how much water
Vasa Recta • Countercurrent exchange. • Recycles NaCl in medulla. • Transports H20 from interstitial fluid. Insert fig. 17.17
Collecting Duct • Medullary area impermeable to high [NaCl] that surrounds it. • The walls of the CD are permeable to H20. • H20 is drawn out of the CD by osmosis. • Permeable to H20 depends upon the presence of ADH.
Secretion • Secretion of substances from the ___________ capillaries into interstitial fluid. • Then transported into lumen of tubule, and into the urine. • Allows the kidneys to rapidly eliminate certain potential toxins.
Atrial Natriuretic Peptide • Produced by atria (heart) due to stretching of walls. • Antagonist to aldosterone. • Increases Na+ and H20 excretion. • Acts as an endogenous diuretic.
Kidney Diseases • Acute renal failure: • Ability of kidneys to excrete wastes and regulate homeostasis of blood volume, pH, and electrolytes impaired. • Rise in blood [creatinine]. • Decrease in renal plasma clearance of creatinine. • Glomerulonephritis: • Inflammation of the glomeruli. • Autoimmune disease by which antibodies have been raised against the glomerulus basement membrane. • Leakage of protein into the urine.
Kidney Diseases (continued) • Renal insufficiency: • Nephrons are destroyed. • Clinical manifestations: • Salt and H20 retention. • Uremia. • Elevated plasma [H+] and [K+].