Veterinary Histology DVT 10502 #6 PDF

VETERINARY HISTOLOGY DVT 10502 #6 by Dr Abubakar Danmaigoro Senior Lecturer Department of Veterinary Preclinical Sciences Faculty of Veterinary Medicine Universiti Malaysia Kelantan HISTOLOGY OF THE URINARY SYSTEM ...

VETERINARY HISTOLOGY DVT 10502 #6 by Dr Abubakar Danmaigoro Senior Lecturer Department of Veterinary Preclinical Sciences Faculty of Veterinary Medicine Universiti Malaysia Kelantan HISTOLOGY OF THE URINARY SYSTEM  Urinary System Urinary system consists: Histology Glandular organs, Kidneys Excretory passages, the Ureter, the Urinary Bladder The Urethra Basic Unit: Nephron Filtration –by glomeruli of the kidney. Selective resorption and excretion - tubular system of the kidney  KIDNEYS The kidneys are compound tubular It consists of excretory or uriniferous tubules. The Kidneys are embedded in fat and the kidney is covered by a capsule of dense collagenous fibres and a elastic fibres. The glandular part consists of peripheral cortex and an inner Medulla. The Medulla is in the form of renal pyramids whose bases are in contact with the cortex and apices form the renal papillae. The glandular part surrounds a cavity adjacent to the hilus called the renal sinus, the dilated origin of ureter. The renal pelvis divides into primary divisions or Major calyces, which in turn divide into minor calyces.  Cortex The cortex forms the outer zone. The cortical region is subdivided into: Pars convoluta or cortical labyrinth containing convoluted tubules and glomeruli Pars radiata or medullary rays, which are columns of straight tubules The parenchyma of the kidney consists of uriniferous tubules and related blood vessels and collecting tubules. The functional unit is called a nephron. Nephron spherical expansion is known as Bowman’s capsule, which encloses a tuft of capillaries – the glomerulus. The Bowman’s capsule and the glomerulus together form the Renal or Malphigian corpuscle. These are distributed in the pars convoluta of the Cortex.  Bowmans’ capsule the nephron consists of the following segments; Proximal convoluted tubule - a highly tortuous tube in the cortical labyrinth, which passes down into the medulla. Descending limb of Henle which extends for varying distances into the medulla and then forms. Loop of Henle after which it passes up into the cortex, as Ascending limb of Henle. Distal convoluted tubule in the cortical labyrinth. These arched collecting tubules open into straight collecting tubules, reach the apex of the renal pyramid, and form the papillary ducts of Bellini. which opens through the area cribrosa of renal papilla into a minor calyx.  NEPHRON Structural and functional unit of the kidney Consist of: a) Renal corpuscle (RC): Glomerulus + Bowman’s capsule. b)Proximal convoluted tubules (PCT) c) Thin loops of Henle (TH) d)Distal convoluted tubules (DCT) e) Collecting tubules (CT)  Renal Histology Features RENAL CORTEX Cortical labyrinth - Renal corpuscle -Distal and proximal convoluted tubules Medullary rays - Straight tubules - Collecting ducts RENAL MEDULLA - Straight tubules - Collecting ducts  NEPHRON Renal corpuscle Glomerulus consists of a number of separate capillaries connecting an afferent arteriole with an efferent arteriole. The endothelial cells of the glomerular capillaries are extremely thin and the cytoplasm is fenestrated. The Bowman’s capsule consists of two layers of epithelium, a visceral layer closely investing the glomerulus & a parietal layer made up of simple squamous epithelium. The visceral layer of the capsule is made up of cells with their cytoplasm showing numerous foot-like processes, and cells termed as podocytes. These cells exhibit granules demonstrable by special techniques. These are referred to as the Juxta-Glomerular cells or apparatus (JG cells). JG cells secrete a substance (Renin), which acts on hypertensinogen in the blood to form hypertensin (angiotensin), Vaso-constriction of blood vessels , Kidney cell _ Nephron  Neck of the tubule The epithelium is of the cuboidal variety. Proximal convoluted tubules (PCT) It is the longer and broadest portion of the renal tubule. In the pars convoluta goes towards the surface of the cortex and enters medullary ray to pass down into the medulla and runs straight course (termed as the straight or medullary) segment of PCT. The PCT is lined by high pyramidal cells with granular cytoplasm and spherical nucleus located in the basal part with brush border (stereo-cilla), RENAL CORPUSCLE  Distal convoluted tubule (DCT) It is much less convoluted than the PCT It is lined by cuboidal cells with granular cytoplasm stains intensely than the cells of PCT. The cell borders do not show a brush border. In cross sections cells are more numerous, nuclei are placed close and lumen is wider than that of the PCT. Wall of the tubule shows numerous nuclei close together and the cells are also taller and this zone of the tubule is referred as Macula Densa. This DCT terminates the nephron or secretory segment of the renal tubule.  Collecting tubule It starts form the periphery of the medullary ray and reached the apex of pyramid. The diameter progressively increases. The epithelium is cuboidal with clear lightly stained cytoplasm and deeply stained nuclei with definite cell outlines. Papillary ducts of Bellini Columnar cells with clear basophilic cytoplasm line these. Near termination, at the renal papilla the epithelium become two layered it may become transitional as the duct opens into a minor calyx. HISTOLOGICAL STRUCTURE OF RENAL CORPUSCLE Renal corpuscle Histological features Convoluted Forms the central structure of the renal corpuscle capillary tuft Glomerular Separates the endothelial cells on its inner surface from the visceral epithelial Basement cells, or podocytes, which cover its outer surface. membrane Made up of 3 layers : Lamina rara (adjacent to endothelium) Lamina rara externa (adjacent to podocytes) Lamina densa ( in between laminae) Mesangium Provide support outside of the capillary (Mesangial cells) Elongated , irregular cell processes, joint to adjacent mesangial cells by gap junctions Phagocytosis, production of mesangial matrix, maintenance of the coherence of the capillary loops, regulation of blood flow (capillary resistance) Glomerular Surround the glomerulus capsule Space between the visceral and parietal layers is the urinary space (Bowman’s space) (Bowman’s Podocytes (cover the outer surface of the glomerular capillaries) capsule) Foot processes located at the narrow spaces (filtration slit) Podocytes Parietal epithelium (lines the capsule) –simple squamous epithelium  RENAL PELVIS AND CALYCES These are lined by transitional epithelium resting on loose connective tissue proper. The mucularis consists of two ill- defined layers found in each minor calyx at the base of each papilla and at the beginning of the ureter. TUBULES OF NEPHRON a) Proximal convoluted tubule b) Thin loops of Henle c) Distal convoluted tubule d) Collecting tubule HISTOLOGICAL STRUCTURE OF RENAL TUBULES Renal Tubules Histological features and function Proximal Tubules Proximal convoluted tubules : a)Proximal Lined by cuboidal cell with brush border (microvilli) and basal striation. Convoluted tubules The base of these cells are stripped by longitudinally oriented mitochondria. The eosinophilic cells of the (PCT) epithelium have a wide brush border and are active in endocytosis. Descending parts of the straight proximal and intermediate tubules are permeable to water but not to solutes. Thin limbs of Thin loops of Henle (TH): Henle’s Loop (TL Lined by simple squamous epithelium (Passively reabsorbed water) a) Thin descending Epithelial cells in the ascending parts of the intermediate and straight distal tubules cells transport chloride limb (active) and sodium ions (passive) out of the tubular lumen into the surrounding peritubular space. The b) Thin ascending epithelium can not be penetrated by water. Consequently, the transport of ions over the epithelium sets up a limb gradient in osmotic pressure, which serves as driving force in the further concentration of the urine. Distal Tubule Distal convoluted tubules (DC): a) Thick ascending Lined by cuboidal epithelium with basal striation but no brush border (Indistinct border between cells) limb of Henle The straight portion of the distal tubule contacts the glomerulus forming the macula densa. Cells in the distal Loop tubules are sensitive to the hormone aldosterone. Aldosterone stimulates the active resorption of sodium ions b) Distal convoluted and the excretion of potassium ions (Reabsorption of electrolytes) tubules Collecting duct Collecting tubules (CT): Lined by simple cuboidal epithelium Collecting ducts merge to form papillary ducts (of Bellini), which terminate on the tips of the renal papilla and empty into a distended, funnel-shaped part (renal pelvis) of the ureter(Drain urine from the Nephron). URINARY PASSAGES Urine from the collecting ducts of the nephrons enters the papillary ducts and drains from the medulla into either the renal pelvis or renal calyces. Urine is then transported through the ureter, urinary bladder, and urethra.  Ureter It has a connective tissue coat externally. The muscular coat consists of an outer circular and an inner longitudinal layer of plain muscle fibers. In the lower third, there is an additional external longitudinal layer. The mucous membrane is thrown into folds and is lined by transitional epithelium. URETER  HISTOLOGICAL STRUCTURE OF URETER Ureter Histological features Mucosa a. Lamina epithelia: Lined with transitional epithelium with a wide variety of cell forms. In the distended ureter all cell appear in section to be narrow spindle. When not distended, give stellate appearance of the lumen. b. Lamina propria: consists mainly of collagen fiber, blood vessels, lymphatics. In horse, it contains tubulo-alveolar mucous glands with wide lumina. The lumen has a star-shaped appearance, that is due to the longitudinal folds of the mucosa. Muscularis mucosa and sub-mucosa- absent Muscularis externa It consists of thin bundles and forms: - An inner longitudinal, - A middle circular - A thin outer longitudinal layer, which may occasionally be interrupted by collagenous bundles. Near the opening into the bladder, the ureter contains only longitudinal muscle fiber. Adventitia Loose adventitia composed of collagen and reticular fiber contains the larger blood vessels and nerves URINARY BLADDER  URINARY BLADDER The anterior part of the bladder is covered by a serous membrane. The muscular coat is very thick and consists of three layers, outer longitudinal, middle circular, and inner longitudinal layers made up of plain muscle. The mucous membrane is lined by transitional epithelium. There is no distinct submucosa. The deeper layers of propria have a looser arrangement HISTOLOGICAL STRUCTURE OF URINARY BLADDER Urinary bladder Histological features Mucosa a. Lamina epithelia – lined with transitional epithelium. b. Lamina propria – the collagenous propria contains few elastic fibers. c. Lamina muscularis mucosa – there is usually a thin layer of longitudinal muscle in between the lamina propria and a loose sub-mucosa. Sub Mucosa Consists of loose connective tissue Muscularis externa It consists of coarse bundle of fibers and are (Detrusor muscle) arranged in : - An inner longitudinal layer - A middle circular (thickest layer) - An outer longitudinal layer The middle circular layer forms the sphincter around the internal urethral orifice, where as outer longitudinal may be modified or absent in some places. Serosa/adventitia A serosa is present on the apex and body of the bladder. At the neck, the muscularis is covered by an adventitia of the same structure as ureter. URETHRA  HISTOLOGICAL STRUCTURE OF URETHRA Urethra Histological features Pelvic Urethra Structure The wall of penile urethra consist of following layers; a. Lamina epithelia – The pelvic urethra is lined by transitional epithelium, surface of the epithelium is irregular. b. Lamina propria – The thin propria is collagenous and poorly vascularized. Corpus cavernosum urethrae – Next to the mucosa lies the stratum vasculature or cavernosum, which is present in all species. It is composed of dense plexus of veins and have the character of erectile tissue. The trabeculae between the veins are rich in smooth musculature. The adjoining glandular layer contains the prostatic tissue (or urethral glands). c. Lamina muscularis mucosa – The next layer is a sheet of thin bundles of smooth muscles, followed by the striated urethral muscle. Extra pelvic The penile urethra has fewer glands but more erectile tissue than the pelvic portion. urethra The folded mucosa bears transitional epithelium, which changes at the urethral opening to stratified squamous epithelium on a papillary body. The cavernous tissue adjoining the mucosa is composed of connective tissue trabeculae which are continuous peripherally with the tunica albuginea that limits the erectile tissue. The trabeculae contain many elastic fibers and blood vessels, and in the horse and bull, longitudinal smooth muscle fibers. Between the trabeculae there are spaces increasing in size towards the albuginea, which are lined with endothelium and usually filled with blood. The cavernosus spaces receive their blood from these veins and from the capillaries of the trabecular system.  Blood Vessels In addition to capillary nets in the muscular coat and propria a rich capillary plexus is seen immediately under the epithelium. Capillaries also enter the epithelium. In the bladder there is a submucosa separated form propria, by bundles of plain muscle running longitudinally. Note: The Urethra will be described with the genital organs. Reading materials and links: https://histology.siu.edu/crr/rnguide.htm https://medicine.nus.edu.sg/pathweb/normal-histology/#system-ug https://youtu.be/NxNtnrz0sNA?si=65lTYHcV5SyI960K https://histology.medicine.umich.edu/full-slide-list THANK YOU