Regulate chemical composition of body fluids. Controls composition of bloods ion levels and concentration. Help maintain PCO2 & acid/base balance [ph]

Transcription

1 The Urinary System

2 Regulate chemical composition of body fluids Eliminates waste Controls composition of bloods ion levels and concentration Help maintain PCO2 & acid/base balance [ph] Help regulate blood pressure by secreting renin [renin-angiotensin system]

3 Contribute to metabolism detoxify free radicals and drugs [with peroxisomes] gluconeogenesis [during fasting] produce erythropoietin stimulates red blood cell production activation of vitamin D [as calcitrol]

4 Metabolic waste waste substance produced by the body [often lethal] 50% of N containing waste is urea [from protein aa NH 2 ammonia urea [by liver] Uric acid from nucleic acids Creatinine from creatine phosphate

5 BUN typical = mg/dl Too high = azotemia [renal insufficiency] Plasma creatinine increase above 1.5 mg/dl with decreased filtration normal = mg/dl

6 Retroperitoneal in the superior lumbar region. Extend from twelfth thoracic to third lumbar vertebra. Right kidney is lower than left because it is crowded by the liver.

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8 Renal fascia outer layer of dense fibrous connective tissue that anchors the kidney to abdominal wall. Adipose capsule shock absorbing. Renal capsule fibrous cover that prevents kidney infection.

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10 Cortex outer - cortical zone and juxtamedullary zone Medulla renal pyramids [8-18] Renal papillae narrow ends of pyramids Renal columns between pyramids

11 Urine Flow formed in nephrons papillary ducts minor calyx major calyx renal pelvis

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13 ~ one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute. Arterial flow into venous flow out of the kidneys follow similar paths. Figure 25.3c

14 Renal Arteries segmental arteries interlobar arteries arcuate arteries cortical radial arteries afferent arterioles Efferent arterioles also form vasa recta with deep juxtamedulary nephrons Venules cortical radial veins arcuate veins interlobar veins segmental veins renal veins inferior vena cava Figure 25.3c

15 NERVE SUPPLY - Renal plexus of sympathetic division of ANS to afferent & efferent arterioles [vasomotor nerves] - regulate flow and pressure Figure 25.3c

16 Nephrons are the structural & functional units that form urine, consisting of: Renal Corpuscle glomerulus + Bowman s capsule Renal Tubule - PCT, loop of Henle, DCT

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18 BOWMAN S CAPSULE Parietal layer simple squamous epithelium. Capsular space. Visceral layer consists of modified, branching epithelial podocytes.

19 Functions pressure filtration of blood water and small solutes leave blood vascular pole - blood in urinary pole -urine out

20 U P V P

21 Proximal convoluted tubule (PCT) cuboidal epithelium with microvilli & mitochondria

22 Loop of Henle [nephron loop]: Descending limb [thin] simple squamous epithelium permeable to water [out], urea [in]; thick walls Ascending limb [thick] cuboidal to low columnar epithelium; thick at top, then thin

23 Distal convoluted tubule (DCT): Principal cells: Cuboidal cells without microvilli. Help maintain water & salt balance.

24 Collecting Ducts - drains several DCT's Combine to form papillary ducts calyces Cuboidal epithelium, then columnar

25 All nephrons begin in the cortex. Where the loop of Henle reaches to determines type Juxtamedullary nephrons: Have loops of Henle that deeply penetrate medulla. Cortical nephrons 85% of nephrons: Have loops of Henle that only slightly penetrate medulla.

26 Figure 25.5b

27 General Glomerular filtrate - from plasma but with no protein Tubular fluid - from PCT through DCT

28 Endothelium of glomerulus open pores [fenestrations] nm diameter everything but cells and platelets pass through Basal lamina [basement membrane] of glomerulus serves as dialysis membrane blocks large plasma proteins

29 Filtration slits - Endothelium of visceral layer of glomerular capsule podocytes form filtration slits [spaces between pedicels] negatively charged - repel anions -30 nm slit width

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32 Glomerulus blood filtering depends on 3 main pressures 1 promotes, 2 oppose Blood Hydrostatic Pressure [HP G ] about 60 torr forces fluid out of capillaries Capsular Hydrostatic Pressure [HP C ] about -18 torr opposes from fluid already in capsular space

33 Colloidal Osmotic Pressure of blood [OP C ] about -32 torr opposes NFP = HP G [HP C + OP C ] = 55 [15-30]] = about 10 torr outward The positive pressure moves fluid out of the glomerulus into Bowman s capsule.

34 Pressure remains high throughout length so filtration continues. Especially sensitive to hypertension

35 Amount of filtrate formed in all areas of the renal corpuscles of both kidneys every minute Directly related to pressures that determine NFP Adult rate is about 125 ml/min 180L/day [males]

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37 If the GFR is too high: Needed substances cannot be reabsorbed quickly enough and are lost in the urine. If the GFR is too low: Everything is reabsorbed, including wastes that are normally disposed of.

38 Three mechanisms control GFR: Renal autoregulation (intrinsic system); Neural controls; Hormonal mechanisms (renin-angiotensin system).

39 Renal Autoregulation of GFR - blood flow autoadjustment Myogenic Mechanism Smooth muscle contracts when stretched reduces blood flow which reduces pressure downstream.

40 Tubuloglomerular feedback negative feedback mechanism using the Juxtaglomerular apparatus [respond to NaCl concentration] juxtaglomerular cells - smooth muscle fibers of afferent arterioles mechanoreceptors - dilate or constrict with pressure change & secrete renin.

41 macula densa- chemoreceptors at end of ascending limb tall crowded cells that monitor Na+ and Cl- concentration

42 DC Muller, Johns Hopkins School of Medicine

43 Neural Regulation sympathetic Norepinephrine causes vasoconstriction Affects smooth muscles of vessels low input dilation, high constriction

44 Renin-angiotensin II pathway- JG cells release renin in response to 1 decreased delivery of fluid and NaCl to macula densa 2 decreased stretching of JG cells 3 increased rate of stimulation by renal sympathetic nerves

45 Angiotensin II is the active hormone that produces constriction of arterioles to increase GBHP and raise GFR stimulates secretion of aldosterone, which enhances reabsorption of Na+ [and water] by principal cells in collecting ducts

46 stimulates the thirst center of the hypothalamus stimulates release of ADH which increases water reabsorption increase in blood volume higher BP

47 Every nephron has 2 capillary beds: Glomerulus & Peritubular Each glomerulus is: Fed by an afferent arteriole Drained by an efferent arteriole

48 Peritubular beds are low-pressure, porous capillaries. Vasa recta long, straight efferent arterioles of juxtamedullary nephrons.

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50 99% of materials move from filtrate back into peritubular capillaries or vasa recta Solutes are reabsorbed by active or passive transport Water is reabsorbed by osmosis = facultative water reabsorption Small peptides and proteins are reabsorbed by pinocytosis

51 Most reabsorption occurs in PCT s. Na + reabsorption- by facilitated diffusion, symporters & antiporters. Reabsorption of water Helps establish concentration gradients Promotes reabsorption of other substances

52 Substances reabsorbed in PCT: 100% of filtered glucose, lactate & amino acids 90% of bicarbonate ions 65% of Na + & water 50% of Cl & K +

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54 Transport maximum (T m ): Reflects the number of carriers in the renal tubules available Exists for nearly every substance that is actively reabsorbed When the carriers are saturated, excess of that substance is excreted

55 Removes materials from blood and adds them into filtrate Function to rid body of certain materials and help control blood ph. Except for K +, the PCT is the main site of secretion. Removes urea, uric acid, bile salts catecholamines, prostaglandins, morphine, penicillin, etc.

56 ph regulation - H+ - by intercalated cells; increasing HCO 3 - reabsorption when ph is low

57 Allows for production of dilute or concentrated urine % Na + & K + 35% Cl - 15% water

58 Variable absorption based on need - 2 cell types Principal cells have infolding of basement membrane maintain water and Na balance. Sensitive to ADH and aldosterone Intercalated Cells - very few lots of mitochondria - can reabsorb K+ and secrete H+ to rid body of excess acid

59 Hormonal Influences Aldosterone - renin angiotensin system ADH - in response to dehydration and high osmolality - acts on collecting ducts,increases water absorption Parathyroid hormone stimulates Ca2+ uptake and increases phosphate excretion

60 Atrial Natriuretic Peptide [increases GFR] Secreted by atria of heart when muscle is stretched [high Bp] Promotes excretion of water and Na+ Inhibits ADH secretion & antagonizes renin system Reduces blood volume and BP

61 By end of DCT 95% of filtrate has been reabsorbed; 90% of water

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63 Dilute Urine is hypotonic to blood plasma. To produce dilute urine just don t remove any water after ascending loop of Henle Dilution occurs in the absence of ADH makes principal cells impermeable to water reabsorption

64 Concentrated urine is hypertonic to plasma. ADH is present water channels [aquaporins] form in principal cell membranes [increase water reabsorption] More Complex than dilution. Solute concentration is maintained by counter current mechanism

65 Based on anatomic arrangement of juxtamedullary nephrons & the vasa recta. Get salinity gradient produced in ECF - very high at base.

66 Countercurrent Multiplier loop of Henle - recaptures Na + and returns it to deep medullary tissues keeping the gradient in place. 1. Descending water leaves, Na + & Cl - enter. 2. Ascending water enters, NaCl leaves.

67 Recycling of urea in renal medulla: gets concentrated in tubules diffuses out at collecting duct into medulla into tubular fluid in ascending loop of Henle - repeats.

68 Countercurrent exchanger Vasa Recta - Blood flows in opposite direction from loop - Maintains a gradient keep removing water and adding salt.

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70 Appearance - clear, colorless to amber [pus, bacteria blood, etc. make cloudy and/or colored Odor - slight - increases with standing due to bacterial ammonia production Specific gravity [water is 1.000]

71 ph Slightly acidic (ph 6) with a range of 4.5 to 8.2 Diet can alter ph Osmolarity mosm/l Composition - 95 water

72 1-2L/da Polyuria - excessive output, Oliguria - low, Anuria none Diabetes - 4 forms - I, II gestational and insipidus. In most - results from high sugar in tubule. Insipidus is from hyposecretion of ADH

73 Diuretics enhance urinary output Osmotic not reabsorbed ADH inhibitors [alcohol] Na+ symporter inhibitors [Lasix]

74 The volume of plasma that is cleared of a particular substance in a given time. Renal clearance tests are used to: Determine the GFR Detect glomerular damage Follow progress of renal disease

75 RC = UV/P RC = renal clearance rate U = concentration (mg/ml) of the substance in urine V = flow rate of urine formation (ml/min) P = concentration of the same substance in plasma

76 1/kidney retroperitoneal, 25 cm inches long Valve-like region as enter bladder prevents backflow 3 layer wall mucosa [transitional epithelium] muscularis longitudinal, outer circular adventitia fibrous coat

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78 Smooth, collapsible, muscular sac that temporarily stores urine. In pelvic cavity Trigone triangular area outlined by openings for ureters and urethra.

79 3 layers: Transitional epithelial mucosa Thick muscular layer Serous coat Storage capacity mL

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81 Muscular tube that drains urine from the bladder & conveys it out of the body. Female much shorter than male. The male urethra has 3 regions: Prostatic Membranous Spongy

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83 Stretch receptors stimulated by mL signal to sacral spinal cord - some to Sympathetic neurons that suppress urination others to Parasympathetic - micturation reflex Voluntary relaxation of external sphincter

84 Renal insufficiency = state in which kidneys cannot maintain homeostasis due to extensive destruction of nephrons Causes - hypertension, infections, trauma, ischemia, poisoning, tubule blockage - protein, etc. atherosclerosis, glomerulonephritis

85 Dialysis - blood is removed and passed through a chamber with a semipermeable membrane - materials are removed from blood by diffusion.