Histology Of The Urinary System PDF

Histology of the Urinary System JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Overview of the function of urinary • Kidneys • Ureters • Urinary Bladder • Urethra Learning Outcomes: LO1. To understand the structure and function of urinary system LO2. To understand...

Histology of the Urinary System JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Overview of the function of urinary • Kidneys • Ureters • Urinary Bladder • Urethra Learning Outcomes: LO1. To understand the structure and function of urinary system LO2. To understand the components of the nephron LO3. To understand the organization of the renal corpuscle and the cells present within it LO4. To understand the organization of the tubules in cortex and medulla LO5. Describe the histological features of ureters, urinary bladder and urethra Overview of the urinary system The urinary system comprises a set of structures which contribute to the elimination of wastes from the body, and the maintenance of homeostasis. Comprises: • • • • 2 kidneys 2 ureters Urinary bladder Urethra LO1. To understand the structure and function of urinary system Function of the Urinary System Remove waste products from the blood Production, storage and voiding of urine Contribute to the regulation of: • Arterial blood pressure • pH of body fluids • Volume and composition of blood • Blood glucose levels (via gluconeogenesis) Production of hormones: - calcitriol (the active form of vitamin D, ↑Ca) - erythropoietin (stimulates the production of erythrocytes) Enzymatic blood pressure regulation (by secreting renin) - cardiovascular + kidneys KIDNEYS 1- Renal cortex 2- Renal medulla Functional unit: Nephron The Nephron The functional unit of the kidney (~1 million), consists of: • Renal corpuscle – filters blood plasma • Glomerulus – capillary network • Glomerular (Bowman’s) capsule – double-walled cup surrounding glomerulus that receives the filtrate • Renal tubule – filtered fluid passes into (reabsorption and secretion): • Proximal convoluted tubule (most reabsorption occurs here) • The loop of the nephron (Henle) (ascending and descending limbs) • Distal convoluted tubule • Nephrons drain into collecting ducts (in renal pyramids of medulla) • Two types: cortical and juxtamedullary LO2. To understand the components of the nephron http://www.dhep.astate.edu/patho/images/nephron.gif The Cortical Nephron The Juxtamedullary Nephron The Cortical Nephron 80 - 85% of nephrons Renal corpuscle in outer portion of cortex and short loops of Henle extend only into outer region of medulla • Thick ascending limb of the loop of Henle. • Tubules receive secretion from peritubular capillaries which also reabsorb some of the filtrate (water and solutes) into blood. LO2. To understand the components of the nephron The Juxtamedullary Nephron 15-20% of nephrons • Renal corpuscle deep in cortex and long loops of Henle extend deep into medulla. • The ascending limb of the loop of Henle has a thin and thick portions. • Tubules receive secretions from peritubular capillaries and vasa recta which also reabsorb some of the filtrate. • Enable kidney to secrete very concentrated urine. Efferent arteriole • Takes filtered blood back into circulation • Thinner – less resistance Afferent arteriole • Brings filtrate towards glomerulus • Thicker than efferent arteriole • Has juxtaglomerular cells (baroreceptors) Once blood is modified by cells of nephron, we call it the TUBULAR FLUID LO2. To understand the components of the nephron Afferent arteriole: - Lined by endothelium and surrounded by smooth muscle and granular cells - Granular (Juxtaglomerular) cells: specialized cells in the wall of the afferent arteriole that release renin in response to decreased perfusion or increased sympathetic tone. Renal Corpuscle • Visceral layer: modified simple squamous e. podocytes (pedicels, filtration slits allow water and small molecules to filter into corpuscle space) • Parietal layer: simple squamous e. • Capsular (Renal/Bowman’s) space. Blood not filtered passes into efferent arteries Renal corpuscle = Glomerular (Bowman’s) capsule + Glomerulus (X300; H&E; Renal corpuscle) • G: glomerulus • CS: capsular space • PL: parietal layer • MD: macula densa • PCT: proximal convoluted tubules • DCT: distal convoluted tubules Proximal Convoluted tubule: • Simple cuboidal ep with microvilli = fuzzy lumen 100% of glucose, amino acids, vitamins and plasma proteins are reabsorbed 60-85% of water reabsorbed • • PCT cells secrete hydrogen into tubular fluid PCT = where filtrate, becomes tubular fluid • • PROXIMAL CONVOLUTED TUBULE (PCT) How to find a PCT: • • • • • • Simple cuboidal epithelium Central nuclei Very acidophilic cytoplasm Many long microvilli: brush border Lumens often fuzzy and hazy. Found in the cortex of the kidney Function of PCT: (X400; H&E; Renal cortex) • G: glomerulus • U: urinary space • P: proximal convoluted tubule • D: distal convoluted tubule • Arrows: peritubular capillaries and draining venules • Reabsorption of all organic nutrients, all proteins, most water, all glucose, and electrolytes • Secretion of of organic anions and cations, H+, and NH4+ • Hydroxylation of vitamin D and release it to the capillaries Nephron Loop (Loop of Henle) • Has descending and ascending limbs with a loop in between • Both limbs have thick and thin segments • Thick = cuboidal lining • Thin = squamous lining Distal Convoluted tubule: • Simple cuboidal ep with short and sparse microvilli = clear lumen • Mainly reabsorption/secretion of NaCl and H2O • DCT is always towards the afferent arteriole…this relationship allows the nephrons to regulate blood pressure • • Intercalated cells = control blood pH Macula densa cells = Chemoreceptors NEPHRON LOOP (Loop of Henle) D: (X160; Mallory trichrome; a medullary renal pyramid) • T: thin descending and ascending limbs • A: thick ascending limbs • CD: collecting ducts Structure: - Composed of two limbs (thick and thin) - Thick limb - Simple cuboidal epithelium with no microvilli, but many mitochondria - Thin Limb: Simple squamous epithelium with few mitochondria Function of Nephron Loop: Passive (thin limb) and active (thick limb) reabsorption of Na+ and Cl– DISTAL CONVOLUTED TUBULE: How to find a DCT: • • • • • • Simple cuboidal epithelium Smaller than PCT Less acidophilic cytoplasm than PCT Short microvilli Lumens clear Found in the cortex of the kidney Function of DCT: • Reabsorption of electrolytes Special features: - MACULA DENSA B: (X120; H&E; Renal cortex) • RS: renal corpuscles • PCT: proximal convoluted tubules • DCT: distal convoluted tubules Macula densa: • Initial, straight part of the distal convoluted tubule in contact with the arterioles • Regulation of the rate of Na+ absorption in DCT: by aldosterone (adrenal glands) • Cells become more columnar and closely packed • Apical nuclei (X400; Mallory trichrome; Juxtaglomerular apparatus) • D: distal tubules • G: glomerulus • MD: macula densa • AA: afferent arterioles • JG: juxtaglomerular granule cells • L: lacis cell • EA: efferent arterioles • P: proximal tubules • US: urinary space (X400; Mallory trichrome; Juxtaglomerular apparatus) • D: distal tubules • G: glomerulus • MD: macula densa • AA: afferent arterioles • JG: juxtaglomerular granule cells • L: lacis cell • EA: efferent arterioles • P: proximal tubules • US: urinary space (X400; Mallory trichrome; Juxtaglomerular apparatus) • DC: distal tubules • G: glomerulus • MD: macula densa • JG: juxtaglomerular granule cells • Pod: Podocytes • BC: Bowmans capsule COLLECTING DUCTS Formed by joining several connecting tubules together Histologic features: • Simple cuboidal epithelium • In the medulla of the kidney • Principal and intercalated (microvilli) cells Function: • Water reabsorption • Carrying the filtrate to a minor calyx Papillary duct (or duct of Bellini) • Formed by merging of several medullary collecting ducts approaching the apex of each renal pyramid • Deliver urine directly into the minor calyx •T: thin descending and ascending limbs •A: thick ascending limbs •CD: collecting ducts •C – Vasa recta containing erythrocytes •I – Interstitium AFTER THIS – TUBULAR FLUID BECOMES URINE Collecting Ducts Principal cells • Most abundant • Cuboidal to columnar • Few organelles • Sparse microvilli • Rich in ADHregulated aquaporins • Pale-staining • Distinct cell membranes • Involved in regulated reabsorption of water & electrolytes Intercalated cells • Few and scattered among the principal cells • Slightly darker staining • More abundant mitochondria • Projecting apical folds • Help maintain acid-base balance (X600; PT staining; collecting ducts) • CD: collecting duct • VR: vasa recta 26_table_01 Intercalated cells secrete H+/absorb HCO3- and therefore adjust the plasma pH Lamina propria Transitional epithelium = urothelium LM of the wall of the ureter in transverse Epithelium section. Urothelium (Ur) lines the star-shaped lumen. The lamina propria is highly vascular and cellular Lumen connective tissue. Interlacing smooth muscle bundles occupy the muscularis externa, which is invested by an outer adventitia. 75×. H&E. Muscle layers Ureters Adventitia or serosa Lamina propria - Function: tubes that transport urine from renalTransitional pelvis to urinary bladder Smooth epithelium in contracted muscle state of viscus - Follow an arrangement of layers Ø Transitional epithelium in distended state of viscus Ur Smooth muscle Mucosa (Transitional epithelium & lamina propria); LM of the ureter in transverse section. The irregular stellateLumen contracted lumen is lined by urothelium, which rests on a lamina propria of loose connective tissue. Two layers of loosely arranged smooth muscle Adventitia are easily seen in the upper part of the ureter; three layers occur in its lower part. An adventitia surrounds the ureter externally. 37×. H&E. § Cuboidal or low columnar cells: an intermediate region containing from one to several layers of cells § Umbrella cells: a superficial layer of Higher magnification LM of the mucosa of the large bulbous or ellipticalureter cell; details of the multilayer urothelium. sometimes binucleated Surfaceshowing cells of the epithelium appear rounded when the Lamina propria Adventitia Lumen ureter is contracted (empty) and flattened when it is distended with urine. The richly cellular lamina propria has many small blood vessels. 340×. H&E. Ø Muscularis Externa (Inner longitudinal, outer circular – opposite of GIT) Ø Adventitia 16.20 Urothelium HISTOLOGY OF THE URETERS AND URINARY BLADDER The ureters and urinary bladder follow a common histologic plan, with walls made of four concentric layers. First, a urothelium (transitional epithelium) lines the lumen and is expandable. Epithelium in the upper part of the ureter consists of two or three cell layers; it gradually changes to four or five layers in the lower ureters and bladder. Third, a muscularis externa consists of smoot muscle arranged in layers that are opposite in orientation to thos in the digestive tract wall. An outer oblique layer is found, espe propria but it is irregularly arranged, so it is not we cially Lamina in the bladder, defined. The fourth, outer layer is an adventitia (or serosa), whic consists mostly of loose connective tissue with autonomic nerve and plexuses, blood vessels, and lymphatics. Transitional epithelium = urothelium Transitional epithelium Urinary Bladder - Follow an arrangement of layers Ø Mucosa (transitional epithelium & lamina propria) (urothelium) Lamina propria Section through the ureter. Urothelium Longitudinal muscle Circular muscle Adventitia Muscularis Externa (Inner longitudinal, middle circular, and amina propria outer longitudinal – opposite of GIT) Muscle layers Ø ansitional epithelium dventitia or serosa(superior part of urinary Ø Serosa bladder)/adventitia (inferior part of urinary bladder) Transitional epithelium in contracted state of viscus Lumen Transitional epithelium in distended state of viscus Lamina Propria Mucosa Section through the urinary bladder. Lumen LM LM of the mucosa of the bladder at high magnification. In of thethe wall o ma transverse empty bladder the urothelium has an increased thickness—up to 8-10 section mu of distention, cell layers. The lamina propria is highly fibrous with scattereddegree connective longitudinal folds cre tissue cells and a few capillaries. 420×. H&E. muscle in the muscu of the ureter. The sup externally by a seros adventitia, the usual The serosa consists pl 16.22 HISTOLOGY OF THE URINARY BLADDER externally by thin, sim of a continuous layer pl Layers of the urinary bladder wall are basically the same as those Smooth muscle this magnification). 1 of the lower part of the ureter: urothelium, lamina propria, three de layers of smooth muscle, and adventitia or serosa. The epithe- th lium thickness varies according to the degree of distention of the th organ. In the contracted (empty) bladder, the urothelium is six to ur eight cell layers thick, and the most superficial cells are round to bl pear-shaped. Surface cells of this stratified epithelium can change T shape and position by sliding over each other, so that when the lo bladder is distended, the cells are in only three or four layers and of Serosa the cells become flattened. Electron microscopy shows apical of Epithelium Lumen Urethra Carries the urine from the bladder to the exterior In females: 3- to 5-cm-long tube In males: 1- Prostatic urethra: 2- Membranous urethra: 3- Spongy urethra: Male urethra 1- Prostatic urethra: • 3-4 cm long • Extends through the prostate gland • Lined by urothelium 2- Membranous urethra: • A short segment • Passes through an external sphincter of striated muscle • Lined by pseudostratified columnar epithelium 3- Spongy (penile) urethra: • About 15 cm in length • Enclosed within erectile tissue of the penis • Lined by pseudostratified columnar epithelium with stratified squamous epithelium distally Female urethra • Lined initially with transitional epithelium which then transitions to nonkeratinized stratified squamous epithelium distally.