Histology Of Urinary System Organs PDF

HISTOLOGY OF URINARY SYSTEM ORGANS Pljushkina Aleksandra Sergeevna MD, PhD, Associate professor  The urinary system includes: Kidneys Ureters Urinary bladder Urethra  Functions of the urinary system Excretion of waste products of...

HISTOLOGY OF URINARY SYSTEM ORGANS Pljushkina Aleksandra Sergeevna MD, PhD, Associate professor  The urinary system includes: Kidneys Ureters Urinary bladder Urethra  Functions of the urinary system Excretion of waste products of metabolism Regulation and maintenance of the fluid volume of the body Regulation of acid-base balance Regulation of salt concentrations and other compounds in body fluid Production of renin, an enzyme that influences blood pressure Production of the erythropoietin Hydroxylation of vitamin D  Kidney Structure Kidney Capsule Lobe The number of lobes in a kidney equals the number of medullary pyramids Cortex Renal Pelvis Medullary Pyramid Ureter  Cortex: outer layer, granular appearance (due to many corpuscles) Medulla: darker striped appearance (due to tubules) ✓ Subdivided into distinct renal pyramids, terminating with a papilla. ✓ Separated by renal columns from the cortex. Pelvis: Expanded proximal part of ureter  Renal lobulations Renal lobe. A medullary pyramid, the surrounding renal column extending to the interlobar vessels, and the overlying cortical tissue Renal lobule. A central medullary ray and the adjacent cortical labyrinth extending to the interlobular vessels  Extrarenal passageways Minor calyx. Funnel-shaped structure (one for each pyramid) into which the point (apex) of a pyramid projects; urine flows from the pyramid into a minor calyx and several minor calyces unite to form a major calyx. Major calyx. Four or five per kidney; formed by the confluence of minor calyces Renal pelvis. Structure formed by the uniting of the major calyces; forms the expanded upper portion of the ureter  Nephron = functional unit of the kidney 1. Renal Corpuscle (Glomerulus + Bowman’s Capsule) 2. Proximal Convoluted Tubule (PCT) 3. Loop of Henle (LOH) 4. Distal Convoluted Tubule (DCT) Production of urine Glomerular filtration Tubular Reabsorption Tubular Secretion  Renal Corpuscle The glomerulus - a tuft of The renal or Bowman’s capsule - a capillaries composed of 10 to 20 double-layered epithelial cup capillary loops The glomerular capillaries are supplied by an afferent arteriole and are drained by an efferent arteriole Endothelial cells have fenestrations (blood cells can’t go through) Vascular pole – a part of glomerulus where aff. arteriole enters and eff. arteriole exits  Renal Corpuscle A-arteriole; b-parietal layer of BC; c-PCT; d-podocyte (visceral layer of BC)  Bowman's capsule Double-walled, epithelial capsule with central space called Bowman's space; surrounds the glomerulus and receives the fluid filtered from the blood Two layers – external (parietal) and internal (visceral) 1. Parietal layer. Outer layer, simple squamous epithelium which is reflected at the vascular pole of the renal corpuscle to become the visceral layer; continuous with the proximal tubule at the urinary pole 2. Visceral layer. Inner layer surrounding the glomerulus. Consists of a single layer of modified epithelial cells called podocytes.  Podocytes a type of epithelial cells: ✓ have long primary processes and interdigitating foot processes (pedicles) which grasp capillaries like fingers ✓ Filtration slits – spaces between the pedicles  Filtration barrier Barrier between blood in glomerular capillary and space of Bowman's capsule 1. Fenestrated Capillary Endothelium 2. Basement membrane 3. Filtration Slits between pedicles of podocytes in the visceral layer of Bowman’s capsule The volume of ultrafiltrate is about 180 L/day Albuminuria (presence of significant amounts of albumin in the urine) or hematuria (presence of significant amounts of red blood cells in the urine) indicate physical or functional damage to the GBM. The renal corpuscle contains an additional group of cells called mesangial cells. Functions: Phagocytosis - remove trapped residues and aggregated proteins from the GBM and filtration slit diaphragm, thus keeping the glomerular filter free of debris. Structural support. Modulation of glomerular distension - Mesangial cells have contractile properties.  Tubular Reabsorption Absorption of water, ions, glucose, amino acids and proteins back to the blood 85% - in the proximal convoluted tubules  Tubular Secretion Some substances (K, H, ammonium, creatinine, some medicine and etc.) exit from surrounding capillaries into the lumen of tubules  Proximal Convoluted Tubule Reabsorbtion: – 65% ions of Na, Cl and water, 80% ions of P and bicarbonate, 80% of Ca, – 100% glucose – 100% protein – 50% urea Secretion: – Н+ и NH4+, creatinine, acetylcholine, dopamine, adrenalin, histamine – Fatty acids, bile acids, penicillin Tubular Epithelium  Loop of Henle Concentration of urine due to reabsorption of water and NaCl ✓ Countercurrent multiplication: Descending part is permeable to water and impermeable to Na+: ✓ Water leaves the tubule into the interstitium ✓ Ascending part is impermeable to water and permeable to Na+: ✓ Na+, Cl-, K+ leave the tubule into the interstitium ✓ The medullary interstitium around the tubules is “salty”. The osmolarity is higher then in the lumen  Distal Convoluted Tubule Reabsorption: 10% ions of Na, Cl, Ca and bicarbonate Kidney Cortex – PCT (P) & DCT (D) P D D P  Collecting ducts Are mainly in the medulla Reabsorption of water (5- 25%) ✓ Aquaporins – special canals for water. ✓ ADH regulates the number of aquaporins and reabsorption of water Cross section of Kidney Medulla Kidney Medulla (Collect tubules and loops)  Blood Supply The kidneys are highly vascular organs; They receive approximately 25% of the cardiac output Cortex Medulla  Two Types of Nephrons Cortical nephrons (85%) located mostly in the cortex of kidney, produce "standard" urine Juxtamedullary nephrons (15%), located close to the medulla - responsive to ADH, can produce concentrated urine due to longer Loops of Henle Kidney Medulla – Vasa Recta (VR) VR  Endocrine functions of the kidney Secretion: - Renin - Erythropoietin Activation: - Vit D  Juxtaglomerular Apparatus Regulates blood pressure by activating the renin–angiotensin– aldosterone system Located near the vascular pole of each renal corpuscle Includes: - macula densa - extraglomerular mesangial cells - juxtaglomerular cells Kidney Juxtaglomerular Complex MD = macula densa JGC = juxtaglomerular cells Renal Corpuscle and Macula Densa JG Cells Renin – Angiotensin – Aldosterone System  Erythropoietin (EPO) Synthesized by endothelial cells of the peritubular capillaries in the renal cortex. Regulates red blood cell formation in the bone marrow in response to decreased blood oxygen concentration.  Excretion of urine Collecting ducts within each renal papilla release urine into minor calyx → major calyx → renal pelvis → ureter →urinary bladder →urethra  Urinary tract Mucosa, submucosa, muscularis externa, adventitia Mucosa – transitional epithelium + lamina propria Transitional epithelium lines minor and major calices, renal pelvis, urether, bladder and proximal part of urethra Transitional epithelium Urethers  Urethers Inner longitudinal muscular fiber Outer circular muscular fibers Contraction of Longitudinal fibers in the proximal part of ureter keeps the lumen open for the passage of urine from the bladder Peristalsis of muscular fibers propels the urine down the ureter Ureter – folded mucus membrane Transitional Epithelium  Urinary Bladder 3 layers in the wall: ✓ Mucosa – transitional epithelium ✓ Muscularis externa (detrusor muscle) 3 layers of smooth muscle (outer longitudinal, circular, inner longitudinal) circular fibers form internal urethral sphincter ✓ Adventitia/ serosa on the superior surface Bladder – Transitional Epithelium Good luck!