PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 25 The Urinary System: Part A
Copyright © 2010 Pearson Education, Inc. Urinary System Organs Kidneys are major excretory organs 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
Copyright © 2010 Pearson Education, Inc. Figure 25.1 Esophagus (cut) Inferior vena cava Adrenal gland Hepatic veins (cut) Renal artery Renal hilum Renal vein Iliac crest Kidney Ureter Urinary bladder Urethra Aorta Rectum (cut) Uterus (part of female reproductive system)
Copyright © 2010 Pearson Education, Inc. Kidney Functions It removes from blood toxins, metabolic wastes, and excess ions It regulates blood volume, blood pressure, blood chemistry and blood pH
Copyright © 2010 Pearson Education, Inc. Kidney Functions Gluconeogenesis during prolonged fasting Endocrine functions Renin: regulation of blood pressure and kidney function Erythropoietin: regulation of RBC production Activation of vitamin D
Copyright © 2010 Pearson Education, Inc. Kidney Anatomy Retroperitoneal, in the superior lumbar region Right kidney is lower than the left 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
Copyright © 2010 Pearson Education, Inc. Figure 25.2a Body wall Perirenal fat capsule Renal artery Renal vein Inferior vena cava Aorta Fibrous capsule Renal fascia anterior posterior Supportive tissue layers Body of vertebra L 2 Peritoneum Peritoneal cavity (organs removed) Anterior Posterior (a)
Copyright © 2010 Pearson Education, Inc. Kidney Anatomy Layers of supportive tissue 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
Copyright © 2010 Pearson Education, Inc. Internal Anatomy Renal cortex A granular superficial region Renal medulla The cone-shaped medullary (renal) pyramids separated by renal columns Lobe (Pyramid) A medullary pyramid and its surrounding cortical tissue
Copyright © 2010 Pearson Education, Inc. Internal Anatomy Papilla Tip of pyramid; releases urine into minor calyx Minor calyx Collects urine from papilla Major calyx The branching channels of the renal pelvis that Collect urine from minor calyces Empty urine into the pelvis
Copyright © 2010 Pearson Education, Inc. Internal Anatomy Renal pelvis The funnel-shaped tube within the renal sinu Urine flows from the pelvis to ureters
Copyright © 2010 Pearson Education, Inc. Figure 25.3 Renal cortex Renal medulla Major calyx Papilla of pyramid Renal pelvis Ureter Minor calyx Renal column Renal pyramid in renal medulla Fibrous capsule Renal hilum (a) Photograph of right kidney, frontal section(b) Diagrammatic view
Copyright © 2010 Pearson Education, Inc. Figure 25.4a Cortical radiate vein Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Segmental arteries Renal artery Renal vein Renal pelvis Ureter Renal medulla Renal cortex (a) Frontal section illustrating major blood vessels
Copyright © 2010 Pearson Education, Inc. Figure 25.4b Aorta Renal artery Segmental artery Interlobar artery Arcuate artery Cortical radiate artery Afferent arteriole Glomerulus (capillaries) Nephron-associated blood vessels (see Figure 25.7) Inferior vena cava Renal vein Interlobar vein Arcuate vein Cortical radiate vein Peritubular capillaries and vasa recta Efferent arteriole (b) Path of blood flow through renal blood vessels
Copyright © 2010 Pearson Education, Inc. Nephrons Structural and functional units that form urine ~1 million per kidney Two main parts 1.Glomerulus: a tuft of capillaries 2.Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus
Copyright © 2010 Pearson Education, Inc. Figure 25.5
Copyright © 2010 Pearson Education, Inc. Nephrons Renal corpuscle Glomerulus + its glomerular capsule Fenestrated glomerular endothelium Allows filtrate to pass from plasma into the glomerular capsule
Copyright © 2010 Pearson Education, Inc. Renal Tubule Renal tubule consists of: Glomerular capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule
Copyright © 2010 Pearson Education, Inc. 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
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Glomerular capsule: parietal layer
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Fenestrated endothelium of the glomerulus Podocyte Basement membrane Glomerular capsule: visceral layer
Copyright © 2010 Pearson Education, Inc. Renal Tubule Proximal convoluted tubule (PCT) Cuboidal cells with dense microvilli and large mitochondria Functions in reabsorption and secretion Confined to the cortex
Copyright © 2010 Pearson Education, Inc. Figure 25.5 MicrovilliMitochondria Highly infolded plasma membrane Proximal convoluted tubule cells
Copyright © 2010 Pearson Education, Inc. Renal Tubule Loop of Henle with descending and ascending limbs Thin segment usually in descending limb Simple squamous epithelium Freely permeable to water Thick segment of ascending limb Cuboidal to columnar cells
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Loop of Henle (thin-segment) cells
Copyright © 2010 Pearson Education, Inc. Renal Tubule Distal convoluted tubule (DCT) Cuboidal cells with very few microvilli Function more in secretion than reabsorption Confined to the cortex
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Distal convoluted tubule cells
Copyright © 2010 Pearson Education, Inc. Collecting Ducts Receive filtrate from many nephrons Fuse together to deliver urine through papillae into minor calyces
Copyright © 2010 Pearson Education, Inc. Collecting Ducts Cell types Intercalated cells Cuboidal cells with microvilli Function in maintaining the acid-base balance of the body
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Intercalated cell Principal cell Collecting duct cells
Copyright © 2010 Pearson Education, Inc. Collecting Ducts Principal cells Cuboidal cells without microvilli Help maintain the body’s water and salt balance
Copyright © 2010 Pearson Education, Inc. Figure 25.5 Fenestrated endothelium of the glomerulus Microvilli Cortex Medulla Podocyte Basement membrane Mitochondria Highly infolded plasma membrane Proximal convoluted tubule Distal convoluted tubule Descending limb Loop of Henle Ascending limb Glomerular capsule Renal corpuscle Glomerulus Thick segment Collecting duct Intercalated cell Principal cell Thin segment Proximal convoluted tubule cells Glomerular capsule: parietal layer Glomerular capsule: visceral layer Distal convoluted tubule cells Loop of Henle (thin-segment) cells Collecting duct cells Renal cortex Renal medulla Renal pelvis Ureter Kidney
Copyright © 2010 Pearson Education, Inc. 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
Copyright © 2010 Pearson Education, Inc. Figure 25.7a Cortical nephron Has short loop of Henle and glomerulus further from the corticomedullary junction Efferent arteriole supplies peritubular capillaries Juxtamedullary nephron Has long loop of Henle and glomerulus closer to the corticomedullary junction Efferent arteriole supplies vasa recta Corticomedullary junction Ureter Renal pelvis Kidney Cortex Medulla (a) Cortical radiate vein Cortical radiate artery Afferent arteriole Collecting duct Distal convoluted tubule Efferent arteriole Vasa recta Loop of Henle Arcuate artery Arcuate vein Peritubular capillaries Glomerular capillaries (glomerulus) Glomerular (Bowman’s) capsule Renal corpuscle Ascending or thick limb of the loop of Henle Descending or thin limb of loop of Henle Efferent arteriole Proximal convoluted tubule
Copyright © 2010 Pearson Education, Inc. Nephron Capillary Beds 1.Glomerulus Afferent arteriole glomerulus efferent arteriole Specialized for filtration Blood pressure is high because Afferent arterioles are smaller in diameter than efferent arterioles Arterioles are high-resistance vessels
Copyright © 2010 Pearson Education, Inc. Nephron Capillary Beds 2.Peritubular capillaries Low-pressure, porous capillaries adapted for absorption Arise from efferent arterioles Cling to adjacent renal tubules in cortex Empty into venules
Copyright © 2010 Pearson Education, Inc. Nephron Capillary Beds 3.Vasa recta Long vessels parallel to long loops of Henle Arise from efferent arterioles of juxtamedullary nephrons Function in formation of concentrated urine
Copyright © 2010 Pearson Education, Inc. Figure 25.7a Cortical nephron Has short loop of Henle and glomerulus further from the corticomedullary junction Efferent arteriole supplies peritubular capillaries Juxtamedullary nephron Has long loop of Henle and glomerulus closer to the corticomedullary junction Efferent arteriole supplies vasa recta Corticomedullary junction Ureter Renal pelvis Kidney Cortex Medulla (a) Cortical radiate vein Cortical radiate artery Afferent arteriole Collecting duct Distal convoluted tubule Efferent arteriole Vasa recta Loop of Henle Arcuate artery Arcuate vein Peritubular capillaries Glomerular capillaries (glomerulus) Glomerular (Bowman’s) capsule Renal corpuscle Ascending or thick limb of the loop of Henle Descending or thin limb of loop of Henle Efferent arteriole Proximal convoluted tubule
Copyright © 2010 Pearson Education, Inc. 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
Copyright © 2010 Pearson Education, Inc. Vascular Resistance in Microcirculation Resistance in afferent arterioles Protects glomeruli from fluctuations in systemic blood pressure Resistance in efferent arterioles Reinforces high glomerular pressure Reduces hydrostatic pressure in peritubular capillaries
Copyright © 2010 Pearson Education, Inc. Juxtaglomerular Apparatus (JGA) One per nephron Important in regulation of filtrate formation and blood pressure Involves modified portions of the Distal portion of the ascending limb of the loop of Henle Afferent (sometimes efferent) arteriole
Copyright © 2010 Pearson Education, Inc. Juxtaglomerular Apparatus (JGA) Granular cells (juxtaglomerular, or JG cells) Enlarged, smooth muscle cells of arteriole Secretory granules contain renin Act as mechanoreceptors that sense blood pressure
Copyright © 2010 Pearson Education, Inc. Juxtaglomerular Apparatus (JGA) Macula densa Tall, closely packed cells of the ascending limb Act as chemoreceptors that sense NaCl content of filtrate
Copyright © 2010 Pearson Education, Inc. Figure 25.8 Glomerulus Glomerular capsule Afferent arteriole Efferent arteriole Red blood cell Podocyte cell body (visceral layer) Foot processes of podocytes Parietal layer of glomerular capsule Proximal tubule cell Lumens of glomerular capillaries Endothelial cell of glomerular capillary Efferent arteriole Macula densa cells of the ascending limb of loop of Henle Granular cells Extraglomerular mesangial cells Afferent arteriole Capsular space Renal corpuscle Juxtaglomerular apparatus Mesangial cells between capillaries Juxtaglomerular apparatus
Copyright © 2010 Pearson Education, Inc. Filtration Membrane Porous membrane between the blood and the capsular space Consists of 1.Fenestrated endothelium of the glomerular capillaries 2.Visceral membrane of the glomerular capsule (podocytes with foot processes and filtration slits) 3.Gel-like basement membrane (fused basal laminae of the two other layers)
Copyright © 2010 Pearson Education, Inc. Figure 25.9a Glomerular capillary covered by podocyte- containing visceral layer of glomerular capsule Glomerular capillary endothelium (podocyte covering and basement membrane removed) Proximal convoluted tubule Parietal layer of glomerular capsule Afferent arteriole Glomerular capsular space Fenestrations (pores) Efferent arteriole Podocyte cell body Foot processes of podocyte Filtration slits Cytoplasmic extensions of podocytes (a) Glomerular capillaries and the visceral layer of the glomerular capsule
Copyright © 2010 Pearson Education, Inc. Filtration Membrane 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
Copyright © 2010 Pearson Education, Inc. Filtration Membrane Glomerular mesangial cells Engulf and degrade macromolecules Can contract to change the total surface area available for filtration
Copyright © 2010 Pearson Education, Inc. Figure 25.9c (c) Three parts of the filtration membrane Fenestration (pore) Filtrate in capsular space Foot processes of podocyte Filtration slit Slit diaphragm Capillary Filtration membrane Capillary endothelium Basement membrane Foot processes of podocyte of glomerular capsule Plasma
Copyright © 2010 Pearson Education, Inc. Kidney Physiology: Mechanisms of 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 non-essential substances
Copyright © 2010 Pearson Education, Inc. Mechanisms of Urine Formation 1.Glomerular filtration 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
Copyright © 2010 Pearson Education, Inc. Figure Cortical radiate artery Afferent arteriole Glomerular capillaries Efferent arteriole Glomerular capsule Rest of renal tubule containing filtrate Peritubular capillary To cortical radiate vein Urine Glomerular filtration Tubular reabsorption Tubular secretion Three major renal processes:
Copyright © 2010 Pearson Education, Inc. Glomerular Filtration Passive mechanical process driven by hydrostatic pressure The glomerulus is a very efficient filter because Its filtration membrane is very permeable and it has a large surface area Glomerular blood pressure is higher (55 mm Hg) than other capillaries Molecules >5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the blood
Copyright © 2010 Pearson Education, Inc. Net Filtration Pressure (NFP) The cumulative pressure responsible for filtrate formation (10 mm Hg)
Copyright © 2010 Pearson Education, Inc. Net Filtration Pressure (NFP) Determined by Glomerular hydrostatic pressure (HP g ) the chief force Two opposing forces: Colloid osmotic pressure of glomerular blood (OP g ) Capsular hydrostatic pressure (HP c ) NFP = HP g – (OP g + HP c )
Copyright © 2010 Pearson Education, Inc. Figure Glomerular capsule Afferent arteriole 10 mm Hg Net filtration pressure Glomerular (blood) hydrostatic pressure (HP g = 55 mm Hg) Blood colloid osmotic pressure (Op g = 30 mm Hg) Capsular hydrostatic pressure (HP c = 15 mm Hg)
Copyright © 2010 Pearson Education, Inc. Glomerular Filtration Rate (GFR) Volume of filtrate formed by the kidneys (120–125 ml/minute) Governed by (and directly proportional to) Total surface area available for filtration Filtration membrane permeability NFP
Copyright © 2010 Pearson Education, Inc. 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
Copyright © 2010 Pearson Education, Inc. Intrinsic Controls Maintains a nearly constant GFR when MAP is in the range of 80–180 mm Hg Two types of renal autoregulation Myogenic mechanism (Chapter 19) Tubuloglomerular feedback mechanism, which senses changes in the juxtaglomerular apparatus
Copyright © 2010 Pearson Education, Inc. Intrinsic Controls: Myogenic Mechanism BP constriction of afferent arterioles Helps maintain normal GFR Protects glomeruli from damaging high BP BP dilation of afferent arterioles Helps maintain normal GFR
Copyright © 2010 Pearson Education, Inc. Intrinsic Controls: Tubuloglomerular Feedback Mechanism Flow-dependent mechanism directed by the macula densa cells If GFR increases, filtrate flow rate increases in the tubule Filtrate NaCl concentration will be high because of insufficient time for reabsorption
Copyright © 2010 Pearson Education, Inc. Intrinsic Controls: Tubuloglomerular Feedback Mechanism Macula densa cells of the JGA respond to NaCl by releasing a vasoconstricting chemical that acts on the afferent arteriole GFR The opposite occurs if GFR decreases.
Copyright © 2010 Pearson Education, Inc. Extrinsic Controls: Sympathetic Nervous System Under normal conditions at rest Renal blood vessels are dilated Renal autoregulation mechanisms prevail
Copyright © 2010 Pearson Education, Inc. Extrinsic Controls: Sympathetic Nervous System 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
Copyright © 2010 Pearson Education, Inc. Extrinsic Controls: Renin-Angiotensin Mechanism Triggered when the granular cells of the JGA release renin angiotensinogen (a plasma globulin) resin angiotensin I angiotensin converting enzyme (ACE) angiotensin II
Copyright © 2010 Pearson Education, Inc. Effects of Angiotensin II 1.Constricts arteriolar smooth muscle, causing MAP to rise 2.Stimulates the reabsorption of Na + Acts directly on the renal tubules Triggers adrenal cortex to release aldosterone 3.Stimulates the hypothalamus to release ADH and activates the thirst center
Copyright © 2010 Pearson Education, Inc. Effects of Angiotensin II 4.Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption 5.Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration
Copyright © 2010 Pearson Education, Inc. Extrinsic Controls: Renin-Angiotensin Mechanism Triggers for renin release by granular cells Reduced stretch of granular cells (MAP below 80 mm Hg) Stimulation of the granular cells by activated macula densa cells Direct stimulation of granular cells via 1- adrenergic receptors by renal nerves
Copyright © 2010 Pearson Education, Inc. Figure Stretch of smooth muscle in walls of afferent arterioles Blood pressure in afferent arterioles; GFR Vasodilation of afferent arterioles GFR Myogenic mechanism of autoregulation Release of vasoactive chemical inhibited 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. Tubuloglomerular mechanism of autoregulation Hormonal (renin-angiotensin) mechanism Neural controls SYSTEMIC BLOOD PRESSURE GFR Macula densa cells of JG apparatus of kidney Filtrate flow and NaCl in ascending limb of Henle’s loop Targets Granular cells of juxtaglomerular apparatus of kidney AngiotensinogenAngiotensin II Adrenal cortexSystemic arterioles (+) Renin Release Catalyzes cascade resulting in conversion (+) Kidney tubules Aldosterone Releases Targets Vasoconstriction; peripheral resistance Blood volume Na + reabsorption; water follows Systemic blood pressure (+) (–) Increase Decrease Stimulates Inhibits Baroreceptors in blood vessels of systemic circulation Sympathetic nervous system (+) (–) Vasodilation of afferent arterioles