Chapter 17

1. Chapter 17 Physiology of the Kidneys and Renal System

2. Composition of Renal System • 2 Kidneys • 2 ureters • 1 • 1

3. 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.

5. 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

6. 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 _______

7. 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 __________

8. 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.

9. 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

10. 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

11. Structure of the Kidney • Outer cortex: • Contains many capillaries. • Dark • Medulla • Lighter colored • Renal pelvis: collects __________ • Transports urine to ureters.

12. 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.

13. 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

15. Nephron Tubules • Glomerular capsule. • Proximal convoluted tubule (PCT). • Descending and ascending limbs of Loop of Henle (LH). • Distal convoluted tubule (DCT). • Collecting duct (CD).

16. 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

17. 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

18. 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

19. Structure of Nephron • Glomerulus is an area of high pressure, therefore, fluid will leak _______ and enter the Bowman’s capsule and flow into the _______________________

20. Proximal Convoluted Tubule • Single layer of cuboidal cells with millions of _________________ • Increase surface area for reabsorption. • PCT functions: • Reabsorption. • Secretion.

21. 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+. • _____________________________.

22. Distal Convoluted Tubule • Contains few microvilli. • Functions: • Secretion. • Reabsorption. • Lies in ____________________ • Many (8 or so) from other nephrons come together • Terminates in Collecting Duct.

23. Collecting Duct • Functions: • Reabsorption. • H20 reabsorption influenced by ______________________ • Secretion. • Collecting ducts combine to empty into _________________________

24. 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

25. Renal Blood Vessels (continued) Insert fig. 17.5

26. Juxtaglomerular Apparatus (continued) Insert fig. 17.25

27. 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.

28. 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

29. 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.

30. Filtration aided by: • 1. Glomeruli (capillaries): • More_____________ than nomal • 2. Efferent arterioles: _________________in diameter than afferent • increases resistance to blood flow out

31. 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!!!!)

32. 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.

33. 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

34. 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.

35. 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.

36. 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

37. 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

38. 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.

39. 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.

40. Salt and Water Reabsorption in Proximal Tubule Insert fig. 17.14

41. Significance of PCT Reabsorption • 65% Na+, Cl-, and H20 reabsorbed across the PCT into the vascular system. • 90% K+ reabsorbed.

42. Osmolality of Different Regions of the Kidney Insert fig. 17.19

43. 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

44. Vasa Recta • Countercurrent exchange. • Recycles NaCl in medulla. • Transports H20 from interstitial fluid. Insert fig. 17.17

45. 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.

46. 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.

47. 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.

48. 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.

49. Kidney Diseases (continued) • Renal insufficiency: • Nephrons are destroyed. • Clinical manifestations: • Salt and H20 retention. • Uremia. • Elevated plasma [H+] and [K+].