URINARY SYSTEM Ján Líška DVM, PhD Institut of Histology and Embryology, Faculty of Medicine, Comenius University Urinary system • The kidneys are the organ with multiple functions: • filtration of the blood • excretion of metabolic waste products and related removal of toxins • maintenance blood volume • regulation of acid-base balance • regulation of fluid and electrolyte balance • production of the hormones The other components of urinary system are accessory. Their function is essentially in order to eliminate urine. Urinary system - anatomy • Kidney are located in the retroperitoneal space • The surface of the kidney is covered by a fibrous capsule of dense connective tissue. • This capsule is coated with adipose capsule. • Each kidney is attached to a ureter, which carries urine to the bladder and urine is discharged out through the urethra. ANATOMIC STRUCTURE OF THE KIDNEY RENAL LOBES CORTEX outer shell columns Excretory portion medullary rays MEDULLA medullary pyramids HILUM Collecting system blood vessels lymph vessels major calyces nerves RENAL PELVIS minor calyces ureter Cortex is the outer layer surrounding the internal medulla. The cortex contains renal corpuscles, convoluted parts of prox. and dist. tubules. Renal column: the renal tissue projection between two medullary pyramids which supports the cortex. Renal pyramids: the conical segments within the medulla. They contain the ductal apparatus and stright parts of the tubules. They posses papilla - having openings through which urine passes into the calyces. Each pyramid together with the associated overlying cortex forms a renal lobe. renal pyramid papilla minor calix minor calyx Medullary rays: are in the middle of cortical part of the renal lobe, consisting of a group of the straight portiones of nephrons and the collec- medullary rays ting tubules (only straight tubules). cortex medulla Kidney cortex (reticular fibers, Lillie) Cortex, medullary ray NEPHRON renal corpuscle the functional unit of the kidney collecting proximal parenchyma tubule tubule Each nephron is composed of an initial filtering component distal tubule - renal corpuscle and renal tubules – specialized for thin reabsorption of utltrafiltrate Henle loop produced by the renal corpuscle limb and secretion. collecting duct Junqueira et al., 1999 RENAL CORPUSCLE Distal tubule Distal tubule Macula densa afferent arteriol efferent arteriol BOWMANN urinary CAPSULE space parietal and vis- ceral layers PODOCYTES Bowman´s capsule visceral layer GLOMERULUS Proximal tubule capillary tuft Gartner and Hiatt, 2003 Glomerular filtration barrier •Fenestrated endothelium •The common basal lamina •Podocyte foot processes The blood filter barrier. consists of : • Thin fenestrated endothelium of glomerular capillaries - the fenestrae lacking membrane • The common basal lamina formed by fusion of the basal laminae of the endothelium and the podocytes • Filtration slits between adjacent secondary foot processes – pedicels of the podocytes The blood filter barrier Diaphragm in the filtration slits between pedicels Pedicles - fused basal laminae – glomeru- lar basal lamina with a central electron - dense layer and on each side electron - lucent layers Fenestrated endothelium - the fenestrae lacking Z. Tonar, 2005 diaphragm Mesangial cells Mesangial cells are similar to pericytes – they contribute to intraglomerular capillary flow. Mesangial cells provide structural support to the glomerular tuft, produce and maintain mesangial matrix. Mesangial cells release also growth factors such as VEGF . Intraglomerular mesangial cells • Fagocytic - cleansing function Mesangial cells are in direct contact with the glomerular endothelium basement membrane NEPHRON podocytes Renal corpuscle - production of primary urine. Proximal convoluted tubule - capillary resorption of 75-80% glomerular filtrate. Henle's loop - in juxtamedular nephron - long with flexion in a Cuboidal epithelium thin segment - resorption of Na and water - hypertonic urine. Cuboidal epithelium with Dist. tubulus - wider lumen, brush border active resorption of Na (aldosterone) and water. Cuboidal epithelium Cuboidal epithelium Squamous epithelium Columnar epithelium R.CIHAK, 1988 Proximal convoluted tubule (PCT) • is lined by simple low columnar epithelium • microvilli on the cell apex, forming a brush border • lateral interdigitations with neighboring cells • the cells have abundant membrane invaginations + concetrated mitochondria in their basal portions and • acidophilic cytoplasm due to the presence of mitochondria • most of the filtrate water and salts are in PCT reabsorbed Proximal tubule cell of nephron - - basal labyrinth concetrated mitochondria in abundant membrane invaginations in the basal portion of cell Kidney – mitochondria in proximal tubules (IH) chondriom mitochondria Distal convoluted tubule • larger lumen is lined by simple cuboidal epithelium • the cells have less acidophilic cytoplasm • the cells lack the brush border • the cells have basal membrane invagi- nations with concentrated mitochondria and no significant lateral interdigitations mitochondria Kidney - HE glomerulus Specialized cells forming the macula densa of the distal tubule, contact with the extra- glomer. mesangial cells of the glomerulus of the some nephron Juxtaglomerular renin-producing cells of the afferent arterioles JUXTAGLOMERULAR APPARATUS and RENAL CORPUSCLE RENIN – ANGIOTENSIN – ALDOSTERON SYSTEM Renin is produced by juxtaglomerular cells to produce angiotensin I from an inactive precursor angiotenzinogen (liver). Angiotensin I is transformed into lung to vasoconstrictor angiotensin II - stimulates the release of aldosterone – - increase of Na resorption in dist. tubule and collecting duct. Juxtaglomerular cells produce also erythropoietin important factor in the regulation of blood Stevens and Lowe, 2004 production. LOOP OF HENLE U-shaped tubule consists of descending CORTICAL NEPHRON and ascending limb with thick and thin segments Different sections of the loop of Henle have different permeabilities. JUXTAMEDULLAR NEPHRON pars recta in - pars recta placed in medulla the medullary ray In humans, about 15% of the nephrons are juxtamedullary nephrons and about 85% are cortical nephrons. medulla LOOP OF HENLE Active transport of sodium and chloride ions leads to the formation of a concen- tration gradient in medulla - water moves from the tubules into the surrounding vasa recta capillaries. LOOP OF HENLE Simple squamous epithelium lining the thin segment is permeable to water and solute (NaCl and urea). Lumen of thin segment is relatively wide, nuclei protruding into the lumen. The thick segment of ascending limb lined by taller cells has low permeability to water and to urea but actively transports sodium and chloride into the peritubular fluid around both limbs. NEPHRON loop of Henle The interstitial fluid becomes hyperosmotic after active transport of sodium chloride out of the tubular fluid in the thick ascending limb. As a result, water moves passively out of the tubular fluid in the descending limb into the interstitial space. Young et al.2006 Different origin of excretory (nephron) and collecting portions: Metanephric mesoderm (blastema) diferentiates into excretory portion: Bowman´s capsule proximal tubules loops of Henle distal tubules Ureteric bud forms collecting portion: renal pelvis major calyces minor calyces collecting ducts collecting tubule COLLECTING TUBULES and DUCTS - Descend from the medullary rays into the pyramid - smaller - simple cuboidal epithelium - larger - simple collumnar epithelium and distinct cell boundaries COLLECTING DUCTS - transport the urine via the renal papillae into the renal calyx. The final concentration or dilution of the urine occurs in the collecting ducts. Kidney – medulla (iH) collecting ducts vascularKidneys supply receive blood through the renal artery. An interlobar artery extends between the renal lobes in renal column and then branches to form an arcuate artery that runs along the corticomedullary junction. Arcuate artery branches into interlobular arteries that have small branches that become afferent glomerular arterioles, which enter the renal corpuscle and subsequently exit at the vascular pole as efferent glomerular arterioles. Efferent arterioles close to the juxtamedullary region supply the blood for the medullary peritubular capillary network inculding vasa recta. Vascular supply of the kidney Vascular supply of the kidney Efferent arterioles close to the subcapsular region supply vessels surrounding cortical segments of the tubules and give rise to stelate veins. Then continue into the interlobular vein, through arcuate vein and interlobar vein and finaly to the renal vein. Renal hilum: the opening in the middle of the concave medial border for ureter, nerves, lymph and blood vessels to pass into the renal sinus. Renal pelvis: is formed at one end of kidney by the enlarged upper portion of the ureter and at the other end is divided into the major calyces - from these arise the minor calyces. Ureter: passing from the renal pelvis out of the hilus and conducts urine from the kidneys to the urinary bladder by means of peristalsis. The wall: epithelium, lamina propria, muscular layer, adventitia Ureter (Trichrome) urothelium mucosal folds muscular layer adventitia urothelium lamina propria tunica muscularis URETER (blue trichrome)Ureter (HE) URINARY BLADDER (Vesica urinaria) Wall of the urinary bladder - epithelium, lamina propria, muscular layer, adventitia or serous peritoneum(upper part of bladder)