Urinary System Urinary Urinary System - Overview: System Major Functions: 1) Removal of organic waste products Kidney from fluids (excretion) 2) Discharge of waste products into the environment (elimination) 1 3) Regulation of the volume / [solute] / pH 3 of blood plasma Ureter HOWEVER, THE KIDNEY AIN’T JUST FOR PEE’IN… Urinary bladder • Regulation of blood volume / blood pressure (e.g., renin) • Regulation of red blood cell formation (i.e., erythropoietin) 2 • Metabolization of vitamin D to active form (Ca++ uptake) Urethra • Gluconeogenesis during prolonged fasting Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 25.1 Urinary System Renal ptosis: Urinary System Kidneys drop to lower position due Functional Anatomy - Kidney: to loss of perirenal fat Functional Anatomy - Kidney: Pyelonephritis: Inflammation of the kidney Pyramids appear striped due to parallel arrangement Located in the of capillaries / collecting tubes superior lumbar “Bar of soap” region 12 cm x 6 cm x 3 cm Renal cortex 150 g / kidney Renal medulla Renal pyramids Renal papilla Layers of Supportive Tissue: Renal columns Renal fascia: Peritoneal cavity Outer layer of dense fibrous connective Renal hilum Renal pelvis tissue; anchors kidney in place • Entrance for blood vessels / nerves Perirenal fat capsule: Major calyx Fatty mass surrounding kidney; cushions Minor calyx kidney against blows Fibrous capsule: Polycystic Transparent capsule on kidney; prevents kidney disease infection of kidney from local tissues (autosomal dominant Kidneys are located retroperitoneal condition) Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 25.2 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 25.3 Urinary System Nerve supply to the kidney provided Urinary System via the renal plexus (primarily sympathetic) Functional Anatomy - Kidney: Functional Anatomy - Kidney: Nephron: Functional unit of the kidney Blood Supply to Kidney: (Bowman’s capsule) Glomerular (~ 1 million / kidney; urine formation) • 1/4 of cardiac output delivered to kidneys capsule Distal Cortical radiate • Filter ~ 180 L of blood plasma / day • 0.25 x 5 L / min = 1.25 L / min convoluted vein tubule • Produce ~ 1 - 1.5 L of urine / day Arcuate Proximal 99% of filtrate returned vein Aorta Inferior vena cava convoluted to blood tubule Interlobular vein Nephron Anatomy: Renal artery Renal vein Renal vein 1) Glomerulus Segmental artery Interlobar vein Cortex • Network of capillaries • Tightly wound coil ( surface area) Renal artery Interlobar artery Arcuate vein Medulla Segmental Collecting arteries Arcuate artery Cortical radiate vein duct Interlobular artery Loop of Cortical radiate Portal Peritubular Henle Arcuate artery system capillaries artery Cortical radiate Afferent Efferent Glomerulus artery arteriole arteriole 2) Renal tubule (capillary) • Location of filtrate (plasma-derived fluid) Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figure 25.4 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 / 25.7 1 Urinary System Urinary System Renal Corpuscle Functional Anatomy - Kidney: (site of filtration) Functional Anatomy - Kidney: Glomerulus + Glomerular capsule Renal Simple Foot processes Podocyte cell body Filtration Membrane: Efferent corpuscle squamous arteriole epithelium Fenestrated Basement Podocytes endothelium membrane (foot processes) (-) Afferent arteriole (-) Cortex Podocyte Medulla (‘foot cell’) ~ 40 nm ~ 90 nm Filtration slit • Size selectivity (fenestrations / slits) • Charge selectivity (basement membrane) Fenestrated capillaries Glomerular mesangial cells: Degrade macromolecules “hung up” in filtration membrane Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 / 25.9 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 / 25.9 Urinary System Functional Anatomy - Kidney: Proximal Convoluted Tubule (PCT) (major site of filtrate reabsorption) Proximal convoluted tubule Convolutions increase length and enhance filtering ability • Simple cuboidal epithelium Cortex • Dense microvilli ( surface area) • mitochondria ( energy demands) Medulla • Infolded basal membrane ( surface area) Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 Urinary System Urinary System Functional Anatomy - Kidney: Functional Anatomy - Kidney: Distal Convoluted Tubule (DCT) & Loop of Henle Collecting Ducts (site of secretion / selective reabsorption) (site of filtrate concentration) Principal cell Thick Segment Distal convoluted Loop of Henle tubule • Similar in structure to the PCT Thin Segment Intercalated cell • Simple cuboidal epithelium Cortex Cortex • Simple squamous epithelium • Intercalated cells (acid-base balance) • Freely permeable to water • Principal cells (water / Na+ balance) Medulla Medulla • Smaller lumen; number of cells (compared to PCT) Collecting duct Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.5 2 Urinary System Urinary System Cortical Juxtaglomerular nephron nephron Functional Anatomy - Kidney: Functional Anatomy - Kidney: Peritubular Juxtaglomerular Apparatus (JGA) capillary (Regulator of filtration rate / systemic blood pressure) Types of Nephrons: • Region where distal end of loop of Henle / DCT lies against afferent arteriole 1) Cortical Nephrons (85%): feeding glomerulus Short loop of • Located in the upper cortex Henle • Primarily involved in reabsorption Cell Types: 1) Juxtaglomerular (granular) cells 2) Juxtamedullary Nephrons (15%): Extraglomerular Macula densa • Bowman’s capsule in lower cortex; loop mesangial • Modified smooth muscle cells (afferent arteriole) cells cells • Prominent secretory granules (renin) of Henle in medulla • Mechanoreceptors; measure blood pressure • Primarily involved in filtrate concentration Vasa recta 2) Macula densa cells Nephron Capillary Beds: • Line loop of Henle / DCT near renal corpuscle Long loop of • Tall cells; nuclei clustered together 1) Peritubular Capillaries: Henle • Chemoreceptors; measure [osmotic] of filtrate • Arise from efferent arterioles 3) Extraglomerular mesangial cells • Closely associate with PCT / DCT • Cluster between macula densa and JG cells 2) Vasa Recta: • Gap junctions; communication (?) Juxtaglomerular cell • Arise from efferent arterioles • Closely associate with loop of Henle Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.8 Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.7 Costanzo (Physiology, 4th ed.) – Figure 6.10 Urinary System (RBF = Renal blood flow) Urinary System Renal Physiology - Overview: RPF = RBF (1 – hematocrit) Glomerular Filtration: Average GFR = 120 – 125 mL / min In a single day, the kidneys filter 60x the ~ 20% of renal plasma flow (RPF) As in systemic capillaries, the pressures that drive fluid movement is filtered during a pass normal blood plasma volume present across the glomerular capillary wall are Starling pressures • Consume 20 - 25% of all oxygen at rest Starling equation: GFR = Glomerular filtration rate (mL / min) Kf = Hydraulic conductance (mL / min mm Hg) Major processes occurring in kidney: PGC = Glomerular capillary hydrostatic pressure (mm Hg) GFR = Kf [(PGC – PBS) – GC] P = Bowman’s space hydrostatic pressure (mm Hg) 1) Glomerular filtration (glomeruli) GS GC = Glomerular capillary osmotic pressure (mm Hg) Net Filtration Pressure Ultrafiltrate: Since filtration of proteins is negligible, All blood borne solutes except proteins BS is removed from equation (= 0) that cross into the tubule system Beginning of glomerular capillary End of glomerular capillary 2) Tubular reabsorption (Tubular network) • Materials reclaimed from filtrate back into the peritubular capillaries 3) Tubular secretion (Tubular network) • Materials moved from peritubular capillaries out into filtrate Urine: All metabolic waste and unneeded substances; Filtration +16 Results due to change in GC descend collecting ducts to renal pelvis as fluid is filtered out of blood 0 equilibrium Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 25.10 Urinary System Urinary System Changes in PBS (e.g., kidney stones) and GC (e.g., nephronic syndrome) are often For ease of measure, creatinine Glomerular Filtration: linked with pathologies Clinical Application: (endogenous product) also commonly utilized… Changes in the GFR can be brought about by changes in any of the Starling pressures Glomerular filtration rate is measured by the clearance of a glomerular marker GFR = K [(P – P ) – ] • Produced by changes in the resistance of the f GC BS GC afferent and efferent arterioles What makes a good marker? Constriction of efferent arteriole 1) It must be freely filtered across the glomerular capillaries (no size / charge restrictions) Inulin: Less blood enters Fructose polymer glomerulus RPF = PGC = GFR 2) It cannot be reabsorbed or secreted by the (~5000 daltons) renal tubules 3) When infused, it cannot alter the GFR Blood backed up in glomerulus Constriction of afferent arteriole . GFR = Glomerular filtration rate (mL / min) [U]inulin x V [U] = Urine concentration of inulin (mg / mL) GRF = inulin [P]. inulin = Plasma concentration of inulin (mg / mL) RPF = PGC = GFR [P]inulin V = Urine flow rate (mL / min) Costanzo (Physiology, 4th ed.) – Figure 6.11 3 Urinary System Urinary System Q = P / R Glomerular Filtration: Glomerular Filtration: Renal blood flow, and thus glomerular filtration rate, is autoregulated The major hypotheses explaining renal autoregulation