Copyright 2010 Pearson Education, Inc. Urinary System

Transcription

1 Urinary System

2 What are the organs that comprise the urinary system?

3 Urinary System Organs Kidneys Urinary bladder Ureters Urethra

4 Hepatic veins (cut) Esophagus (cut) Inferior vena cava Adrenal gland Aorta Iliac crest Renal artery Renal hilum Renal vein Kidney Ureter Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra Figure 25.1

5 Peritoneum Ureter Rugae Detrusor muscle Ureteric orifices Bladder neck Internal urethral sphincter External urethral sphincter Urogenital diaphragm Trigone (b) Female. Urethra External urethral orifice Figure 25.21b

6 Peritoneum Ureter Rugae Detrusor muscle Adventitia Ureteric orifices Trigone of bladder Bladder neck Internal urethral sphincter Prostate Prostatic urethra Urogenital diaphragm External urethral sphincter Membranous urethra Spongy urethra Erectile tissue of penis External urethral orifice (a) Male. The long male urethra has three regions: prostatic, membranous and spongy. Figure 25.21a

7 Urethra Sphincters Internal urethral sphincter Involuntary (smooth muscle) at bladderurethra junction Contracts to open External urethral sphincter Voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor

8 Urinary System In general, what are the functions of the urinary system?

9 Urinary System General Functions Kidneys are major excretory organs Removal of toxins, metabolic wastes, and excess ions from the blood Regulation of blood volume, chemical composition, and ph Endocrine functions of kidney Renin: regulation of blood pressure and kidney function Erythropoietin: regulation of RBC production Activation of vitamin D Urinary bladder is the temporary storage reservoir for urine Ureters transport urine from the kidneys to the bladder Urethra transports urine out of the body

10 What is the composition of urine?

11 Physical Characteristics of Urine Color and transparency Clear, pale to deep yellow (due to urochrome) Drugs, vitamin supplements, and diet can alter the color Cloudy urine may indicate a urinary tract infection

12 Physical Characteristics of Urine Odor Slightly aromatic when fresh Develops ammonia odor upon standing May be altered by some drugs and vegetables

13 Physical Characteristics of Urine ph Slightly acidic (~ph 6, with a range of 4.5 to 8.0) Diet, prolonged vomiting, or urinary tract infections may alter ph Specific gravity to 1.035, dependent on solute concentration

14 Chemical Composition of Urine 95% water and 5% solutes Nitrogenous wastes: urea, uric acid, and creatinine Other normal solutes Na +, K +, PO 4 3, and SO 4 2, Ca 2+, Mg 2+ and HCO 3 Abnormally high concentrations of any constituent may indicate pathology

15 Renal Calculi Kidney stones form in renal pelvis Crystallized calcium, magnesium, or uric acid salts Larger stones block ureter, cause pressure and pain in kidneys May be due to chronic bacterial infection, urine retention, Ca 2+ in blood, ph of urine

16 Location of The Kidneys

17 Kidney Anatomy Retroperitoneal, in the superior lumbar region Right kidney is lower than the left

18 Peritoneum Renal vein Renal artery Body of vertebra L 2 Body wall (a) Anterior Peritoneal cavity (organs removed) Posterior Inferior vena cava Aorta Supportive tissue layers Renal fascia anterior posterior Perirenal fat capsule Fibrous capsule Figure 25.2a

19 anatomy of the kidneys

20 Kidney Anatomy Convex lateral surface, concave medial surface Renal hilum leads to the renal sinus Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum Layers of supportive tissue surround the kidney 1. Renal fascia The anchoring outer layer of dense fibrous connective tissue 2. Perirenal fat capsule A fatty cushion 3. Fibrous capsule Prevents spread of infection to kidney

21 Internal Kidney Anatomy Renal cortex A granular superficial region Renal medulla The cone-shaped medullary (renal) pyramids separated by renal columns Lobe A medullary pyramid and its surrounding cortical tissue Papilla Tip of pyramid; releases urine into minor calyx Renal pelvis The funnel-shaped tube within the renal sinus Major calyces The branching channels of the renal pelvis that Collect urine from minor calyces Empty urine into the pelvis Urine flows from the pelvis to ureter

22 Renal hilum Renal cortex Renal medulla Major calyx Papilla of pyramid Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule (a) Photograph of right kidney, frontal section (b) Diagrammatic view Figure 25.3

23 Blood and Nerve Supply Arterial flow into and venous flow out of the kidneys follow similar paths Nerve supply is via sympathetic fibers from the renal plexus

24 Cortical radiate vein Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Segmental arteries Renal vein Renal artery Renal pelvis Ureter Renal medulla Renal cortex (a) Frontal section illustrating major blood vessels Figure 25.4a

25 The Nephron: The Repeated Functional Unit of the Kidney

26 function more in secretion than reabsorption Functions in reabsorption and secretion freely permeable to water function in maintaining the acid-base balance of the body and help maintain the body s water and salt balance

27 Nephrons Cortical nephrons 85% of nephrons; almost entirely in the cortex Juxtamedullary nephrons Long loops of Henle deeply invade the medulla Extensive thin segments Important in the production of concentrated urine

28 Nephrons Structural and functional units that form urine ~1 million per kidney Parts of the nephron glomerulus: a tuft of capillaries renal tubule: begins as cup-shaped glomerular (Bowman s) capsule surrounding the glomerulus renal corpuscle Glomerulus + its glomerular capsule Fenestrated glomerular endothelium Allows filtrate to pass from plasma into the glomerular capsule

29 Renal Tubule Glomerular capsule Parietal layer: simple squamous epithelium Visceral layer: branching epithelial podocytes Extensions terminate in foot processes that cling to basement membrane Filtration slits allow filtrate to pass into the capsular space

30 Cortical nephron Has short loop of Henle and glomerulus further from the corticomedullary junction Efferent arteriole supplies peritubular capillaries Renal corpuscle Kidney Glomerular capillaries (glomerulus) Glomerular (Bowman s) capsule Proximal convoluted tubule Peritubular capillaries Ascending or thick limb of the loop of Henle Cortex Medulla Renal pelvis Ureter Efferent arteriole Arcuate vein Arcuate artery Loop of Henle Descending or thin limb of loop of Henle Juxtamedullary nephron Has long loop of Henle and glomerulus closer to the corticomedullary junction Efferent arteriole supplies vasa recta Cortical radiate vein Cortical radiate artery Afferent arteriole Collecting duct Distal convoluted tubule Afferent arteriole Efferent arteriole Corticomedullary junction Vasa recta (a) Figure 25.7a

31 Vascular Resistance in Microcirculation High resistance in afferent and efferent arterioles Causes blood pressure to decline from ~95 mm Hg to ~8 mm Hg in kidneys

32 A Portion of the Nephron Called the Juxtaglomerular Apparatus

33 Efferent arteriole Glomerular capsule Glomerulus Afferent arteriole Efferent arteriole Parietal layer of glomerular capsule Capsular space Foot processes of podocytes Podocyte cell body (visceral layer) Red blood cell Proximal tubule cell Juxtaglomerular apparatus Macula densa cells of the ascending limb of loop of Henle Extraglomerular mesangial cells Granular cells Afferent arteriole Juxtaglomerular apparatus Renal corpuscle Lumens of glomerular capillaries Endothelial cell of glomerular capillary Mesangial cells between capillaries Figure 25.8

34 Juxtaglomerular Apparatus (JGA) One per nephron Important in regulation of filtrate formation and blood pressure contains renin act as mechanoreceptors that sense blood pressure act as chemoreceptors that sense NaCl content of filtrate

35 The Portion of the Nephron Called the Glomerulus: The glomerular capillaries and filtration membrane

36 Efferent arteriole Glomerular capsular space Afferent arteriole Glomerular capillary covered by podocytecontaining visceral layer of glomerular capsule (a) Glomerular capillaries and the visceral layer of the glomerular capsule Parietal layer of glomerular capsule Proximal convoluted tubule Podocyte cell body Fenestrations (pores) Cytoplasmic extensions of podocytes Filtration slits Glomerular capillary endothelium (podocyte covering and basement membrane removed) Foot processes of podocyte Figure 25.9a

37 Capillary Filtration membrane Capillary endothelium Basement membrane Foot processes of podocyte of glomerular capsule Filtration slit Fenestration (pore) Plasma Filtrate in capsular space Slit diaphragm Foot processes of podocyte (c) Three parts of the filtration membrane Figure 25.9c

38 Filtration Membrane Porous membrane between the blood and the capsular space Consists of 1. Fenestrated endothelium of the glomerular capillaries 2. podocytes with foot processes and filtration slits 3. Gel-like basement membrane 4. glomerular mesangial cells that engulf and degrade macromolecules Allows passage of water and solutes smaller than most plasma proteins Fenestrations prevent filtration of blood cells Negatively charged basement membrane repels large anions such as plasma proteins Slit diaphragms also help to repel macromolecules

39 Kidney Physiology: Mechanisms of Urine Formation

40 General Facts about Urine Formation The kidneys filter the body s entire plasma volume 60 times each day Filtrate Blood plasma minus proteins Urine <1% of total filtrate Contains metabolic wastes and unneeded substances

41 Afferent arteriole Glomerular capillaries Cortical radiate artery Efferent arteriole Glomerular capsule Rest of renal tubule containing filtrate Three major renal processes: Glomerular filtration Tubular reabsorption Tubular secretion Urine Peritubular capillary To cortical radiate vein Figure 25.10

42 Mechanisms of Urine Formation: A three step process 1. Glomerular filtration - passive mechanical process driven by hydrostatic pressure, GFR or glomerular filtration rate is the volume of filtrate formed per minute by the kidneys ( ml/min) 2. Tubular reabsorption Returns all glucose and amino acids, 99% of water, salt, and other components to the blood 3. Tubular secretion Reverse of reabsoprtion: selective addition to urine

43 If hydrostatic pressure drives glomerular filtration (#1 on previous slide), then what is the driving force for reabsorption and secretion (#2 and #3 on previous slide)?

44 If hydrostatic pressure drives glomerular filtration (#1 on previous slide), then what is the driving force for reabsorption and secretion (#2 and #3 on previous slide)? Passive transport (osmosis) and Active transport (pumps requiring energy such as ATP) as shown in the next slide

45 Osmolality of interstitial fluid (mosm) Active transport Passive transport Water impermeable Filtrate entering the loop of Henle is isosmotic to both blood plasma and cortical interstitial fluid. H 2 O H 2 O H 2 O NaCI NaCI NaCI Cortex The descending limb: Permeable to H 2 O Impermeable to NaCl As filtrate flows, it becomes increasingly concentrated as H 2 O leaves the tubule by osmosis. The filtrate osmolality increases from 300 to 1200 mosm. H 2 O H 2 O H 2 O H 2 O Loop of Henle NaCI NaCI Outer medulla Inner medulla (a) Countercurrent multiplier. The long loops of Henle of the juxtamedullary nephrons create the medullary osmotic gradient. The ascending limb: Impermeable to H 2 O Permeable to NaCl Filtrate becomes increasingly dilute as NaCl leaves, eventually becoming hypo-osmotic to blood at 100 mosm in the cortex. NaCl leaving the ascending limb increases the osmolality of the medullary interstitial fluid. Figure 25.16a

46 What regulates the rate of glomerular fitration (urine production)?

47 Regulation of Glomerular Filtration GFR is tightly controlled by two types of mechanisms Intrinsic controls (renal autoregulation) Act locally within the kidney Extrinsic controls Nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function

48 Intrinsic control for the rate of glomerular fitration (urine production)

49 Intrinsic Control BP constriction of afferent arterioles to drive BP back down and protect glomeruli from damage due to high BP BP dilation of afferent arterioles to drive BP back up

50 Extrinsic control for the rate of glomerular fitration (urine production)

51 Extrinsic Controls: Sympathetic Nervous System Under normal conditions at rest Renal blood vessels are dilated Renal autoregulation mechanisms prevail Under extreme stress Norepinephrine is released by the sympathetic nervous system Epinephrine is released by the adrenal medulla Both cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin

52 So what happens when renin is released?

53 So what happens when renin is released? What happens is several steps which are called the renin-angiotensin mechanism?

54 Renin-Angiotensin Mechanism Triggered when renin is released (by the granular cells of the JGA) angiotensinogen (a plasma globulin) renin angiotensin converting enzyme (ACE) angiotensin I angiotensin II

55 So now what? What is the job of angiotensin II?

56 Effects of Angiotensin II 1. Stimulates the reabsorption of Na + 2. Triggers adrenal cortex to release aldosterone 3. Stimulates the hypothalamus to release ADH and activates the thirst center 4. increases fluid reabsorption 5. decreasing the surface area available for filtration, i.e., decreases filtration

57 SYSTEMIC BLOOD PRESSURE ( ) Blood pressure in afferent arterioles; GFR GFR Granular cells of juxtaglomerular apparatus of kidney Baroreceptors in blood vessels of systemic circulation Stretch of smooth muscle in walls of afferent arterioles Vasodilation of afferent arterioles Filtrate flow and NaCl in ascending limb of Henle s loop Targets (+) Renin Catalyzes cascade resulting in conversion Angiotensinogen Release Angiotensin II (+) (+) Sympathetic nervous system Macula densa cells of JG apparatus of kidney (+) Adrenal cortex Releases (+) Systemic arterioles (+) Release of vasoactive chemical inhibited Aldosterone Targets Vasoconstriction; peripheral resistance GFR Vasodilation of afferent arterioles Kidney tubules Na + reabsorption; water follows Blood volume (+) ( ) Stimulates Inhibits Increase Decrease Systemic blood pressure Myogenic mechanism of autoregulation Tubuloglomerular mechanism of autoregulation Hormonal (renin-angiotensin) mechanism Neural controls Intrinsic mechanisms directly regulate GFR despite moderate changes in blood pressure (between 80 and 180 mm Hg mean arterial pressure). Extrinsic mechanisms indirectly regulate GFR by maintaining systemic blood pressure, which drives filtration in the kidneys. Figure 25.12