Histology of the Urinary System 2010 PDF

HISTOLOGY OF THE URINARY SYSTEM Contents  Kidney * Parts of nephron and structures Juxtaglomerular apparatus Functional aspects Blood circulation  Ureter and urinary bladder General features  Urinary epithelium Urethra * Structure of male and female urethra...

HISTOLOGY OF THE URINARY SYSTEM Contents  Kidney * Parts of nephron and structures Juxtaglomerular apparatus Functional aspects Blood circulation  Ureter and urinary bladder General features  Urinary epithelium Urethra * Structure of male and female urethra  Kidney  Main organ of the excretory system  Kidney is built of billions of little tubes called the nephrons.  At the beginning of each nephron, a web of capillaries releases much water and other molecules into the nephron.  The urine is collected in the urinary bladder and, when it fills up, it is excreted via urethra into the outside environment.  Kidney's Internal Structure  Cortex -- the outer part of the kidney;  Medulla -- the inner portion of the kidney;  Pyramids -- the triangular-shaped divisions of the medulla of the kidney;  Papilla -- narrow, innermost tip of the pyramid;  Pelvis -- the kidney or renal pelvis is an extension of the upper end of the ureter (the tube that drains urine into the bladder);  Calyx -- each calyx is a division of the renal pelvis; opening into each calyx is the papilla of a pyramid.  p h r o n Ne  basic structural and functional unit of the kidney.  Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.  microscopic units of a kidney, have 2 main parts, 1. renal corpuscle (Bowman's capsule with glomerulus) 2. renal tubule.  RENAL CORPUSCLE  glomeruli surrounded by Bowman's capsules.  Bowman's capsule -- the cup-shaped top of a nephron. It is the sack- like Bowmans's capsule that surrounds the glomerulus.  Glomerulus -- a network of blood capillaries tucked into Bowman's capsule. Histology Bowman's capsule  Cells of the outer or parietal layer of Bowman's capsule form a simple squamous epithelium.  Cells of the inner layer, podocytes in the visceral layer, are extremely complex in shape. Small foot-like processes, pedicles, of their cytoplasm form a fenestrated epithelium around the fenestrated capillaries of the glomerulus.  The openings between the pedicles are called filtration slits.  Juxtaglomerular apparatus  The juxtaglomerular apparatus is a microscopic structure in the kidney, which regulates the function of each nephron.  There are three cellular components of the apparatus which are the; 1. macula densa, 2. extraglomerular mesangial cells, 3. juxtaglomerular cells (also known as granular cells).  RENAL TUBULE  Proximal convoluted tubule -- the first segment of a renal tubule, called proximal because it lies nearest the tubule's origin from Bowman's capsule, and convoluted because it has several bends in it.  Loop of Henle -- the extension of the proximal tubule; observe that the loop of Henle consists of a straight descending (directed downward) limb, a loop, and a straight ascending limb (directed upwards). Cont.  Distal convoluted tubule -- the part of the tubule distal to the ascending limb of Henle. It is the extension of the ascending limb of Henle.  Collecting tubule -- a straight (not convoluted) part of a renal tubule; distal tubules of several nephrons join to form a single collecting tubule Histo: proximal tubule  walls - low columnar epithelium.  The eosinophilic cells of the epithelium have a wide brush border and are active in endocytosis.  Histo of Loop of Henle  It is 'U' shaped and has descending and ascending segments.  Thin descending segment has flattened epithelium( squam ous). It is permeable to water but not solutes.  Histo: Distal convoluted tubule  straight part of the DCT is formed by the low cuboidal cells without a brush border. The diameter of the tubule gradually expands to about 35 microns.  convoluted part and comes in contact with the Glomerulus forming the Macula Densa. Nephron structure characteristic Renal corpusle Capillary ball covered by podocyte & surrounded by simple squamous epithelial capsule, capsular space. Proximal convulated Lined with simple cubodial epithelium & prominent brush border Loop of Henle Tubule that form a loop, there are thick & thin ascending & desecnding portion; the most distal part of the loop often extends into the medulla. Thick limb are lined with simple squamous/ cuboidal epithelium Thin limb are lined with simple squamous epithelium Distal convulated Lined with simple cuboidal with only sparse brush border; Ureter The wall of the ureter is made 3 layers. From inside outwards they are : 1. Mucosa- which is made up of epithelium & lamina propria 2. Muscular coat – made of smooth muscles 3. Fibrosa – made of fibrous connective tissue Mucosa- is thrown into folds and thus gives the appearance of star shaped lumen. 1. Transitional epithelium. 3-5 layers thickness. 2. Lamina propria- dense, irregular layer of fibroelastic connective tissue  The epithelium is separated from the lamina propria by a basal lamina.  Muscular layer – Upper 2/3 of the ureter is made of two layers of smooth muscle cells.  Inner longitudinal and outer circular layer( in contrast to the wall of GIT which has inner circular & outer longitudinal !).  Lower 1/3 of the ureter has a third outer layer of longitudinal muscles( inner longitudinal, middle circular, outer loingitudinal ). Fibrous coat – is made up of fibrous connective tissue  Histology of the bladder mucosa of transitional epithelium, Submucosa, and thick muscular layer know as the detrusor muscle The urethra:  Female: relatively short, exits just anterior to the vagina  Male: longer, divided into three sections the prostatic, membranous and spongy urethra. The prostatic urethra is enclosed in the prostate gland. The membranous urethra is a short section that penetrates the urogenital diaphragm. The spongy urethra or penile urethra extends from the membranous urethra to the external urethral orifice (meatus). The urethra:  Histology: In both male and females the urethra starts out as transitional cell but quickly becomes stratified squamous in the female.  The male urethra is more variable but ends up stratified squamous as well.