Urinary System Chapter 25

Urinary System Chapter 25 Filters ~200L of blood Regulates volume of water and total concentration of solutes (osmolality) Regulates concentrations of ions in extracellular fluid Ensures long term acid-base balance Excretes metabolic wastes and other toxins Produces erythopoietin and renin Converts vit D to its active form Gluconeogenesis during prolonged fasting Everyday function Gross Anatomy Gross Anatomy https://youtu.be/lfGYd1wrTgE Urinary System Overview Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct Tuft of capillaries Fenestrated endothelium allows large amounts of solute rich and almost protein free fluid to pass from blood into glomerular capsule Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct AKA Bowman’s capsule 2 layers Parietal layer Simple squamous No part in forming filtrate Visceral layer Clings to capillaries Podocytes terminate in foot processes which have openings called filtration slits Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct Cuboidal Epithelium with large mitochondria Microvilli on apical surface Increases SA for reabsorbing water and solutes Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct AKA the loop of Henle Thick and thin segments Thick=cuboidal Thin=simple squamous Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct Cuboidal epithelium like PCT but thinner and lack microvilli Anatomy of a Nephron Glomerulus Glomerular Capsule Renal Tubule Proximal Convoluted Tubule (PCT) Nephron Loop Distal Convoluted Tubule (DCT) Collecting Duct Collects filtrate from multiple nephrons Fuse together near the renal pelvis and deliver urine into the minor calyces Principal cells Sparse, short microvilli Maintain Na and H2O balance More numerous Intercalated cells Cuboidal with microvilli Type A and B Maintain acid-base balance Anatomy of a Nephron Cortical ~85% of total Almost entirely in the cortex Juxtamedullary Long nephron loop in medulla Important role in concentrating urine Classes of Nephrons Glomerulus Peritubular Capillaries Vasa Recta Juxtaglomerular Complex (JGC) Nephron Capillaries High pressure for filtration Produces large amounts of fluid Afferent arterioles Arise from cortical radiate arteries Efferent arterioles Feed into either peritubular capillaries or vasa recta Glomerulus Cling to adjacent tubules and empty into venules Low pressure and porous Absorb solutes and water from tubules as they are reclaimed from filtrate Service several adjacent nephrons Peritubular Capillaries Supply oxygen and nutrients to local tissue Also play important role in concentrating urine Vasa Recta Point where afferent, efferent and DCT touch Macula densa Chemoreceptors for NaCl in DCT Granular cells Mechanoreceptors for BP in afferent Secretes renin Extraglomerular mesangial cells Lie between MD and GC Communicate with gap junctions Juxtaglomerular Complex Account for ~1% of body weight Consume 20-25% of all body oxygen at rest Filter entire plasma volume over 60 times daily Process about 180L (47 gallons) of fluid ~1.5 L leave as urine, remaining returned to circulation Kidney facts Consists of 3 processes (steps) Glomerular filtration Tubular resorption Tubular secretion Urine Formation Passive process due to hydrostatic pressure Molecules under 5nm pass freely through fenestrations and podocytes Molecules over 5nm (proteins, blood cells) prohibited (maintains colloid osmotic press) Step 1- Glomerular Filtration Step 1- Glomerular Filtration Volume of filtrate formed each minute by combined activity of all glomeruli Expressed in ml/min Directly proportional to the following: Net filtration pressure Hydrostatic pressure in glomerulus most important Total surface area available Glomerular cap have huge SA Mesangial cells can fine tune Filtration membrane permeability Fenestrations provide Glomerular Filtration Rate (GFR) GFR GFR regulation Step 2 – Tubular Resorption Step 3 – Tubular Secretion Countercurrent Mechanism Control of Urine Concentration Slender tubes that take urine from the kidney to the bladder 3 histologic layers Mucosa Continuous with mucosae of kidney pelvis superiorly and bladder medially Muscularis 2 layers of smooth muscle proximal Internal longitudinal layer External circular layer 3rd layer in the distal 1/3 External longitudinal layer Adventitia Fibrous connective tissue Ureters Ureter Histology Storage vessel for urine Muscular layer called detrusor Micturition – act of urinating Trigone – triangular region of bladder base outlined by 3 openings Rugae Capacity 800-1000ml 3 layers Mucosa Muscular Fibrous adventitia (superior cover is peritoneum) Bladder Bladder Muscular tube that drains urine from the bladder to the outside of the body Internal urethral sphincter Involuntary Formed by detrusor muscle Prevents leaking between voiding External urethral sphincter Voluntary skeletal muscle Levator ani muscle also helps with urethral constriction Urethra Medical Testing Blood Urinalysis Abnormal labs Pathology Bladder Stones Can block urine from entering ureter Pain in back with positive Chandelier sign May have blood in urine Treat with lithotripsy Kidney Stones