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Urinary system


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  • 1. URINARY SYSTEM Assoc. Prof Dr. Karim Al-Jshamy IMS/MSU 2010
  • 2. • The kidneys, ureters, urinary bladder and urethra are the main components of the urinary system. • A function of the urinary system that immediately comes to mind is the excretion of waste products from the body. This is only one of many functions of the system. Others are • elimination of foreign substances • regulation of the amount of water in the body • control of the concentration of most compounds in the extracellular fluid • Most of these tasks are performed in the kidneys. Functionally the processes can be divided into two steps, each of which have their anatomical correlate: • filtration - glomeruli of the kidney • selective resorption and excretion - tubular system of the kidney • In addition, the kidney also functions as an endocrine organ. Fibrocytes in the cortex release the hormone erythropoietin, which stimulates the formation of red blood cells. • Modified fibrocytes of the medulla secrete prostaglandins which are able to decrease blood pressure.
  • 3. Overall Organization of the Kidney Stroma Capsule Dense FECT Myofibroblast layer Interstitial stroma (loose FECT) Parenchyma Nephrons Collecting ducts Vascular components Organized into cortex and medulla
  • 4. Kidney the tubular system  Glomeruli and are both part of the basic functional unit of the kidney, the nephron. The Glomerulus (or renal corpuscle)  The glomerulus is the round (~0.2 mm in diameter) blind beginning of the nephron. It is invaginated by a tuft of capillaries at the vascular pole of the glomerulus.  The tuft of capillaries and other cells in contact with them form the anatomical glomerulus. Glomerulus. The anatomical glomerulus is enclosed by two layers of epithelium, 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.
  • 5. • The openings between the pedicles are called filtration slits. They are spanned by a thin membrane, the filtration slit membrane. • Between the podocytes and the endothelial cells of the capillaries we find a comparatively thick basal lamina, which can be subdivided into an outer lamina rara externa, a middle lamina densa and an inner lamina rara interna. The basal lamina and the slit membranes form the glomerular filtration barrier, • Mesangial cells in the glomerulus form the connective tissue that gives structural support to podocytes and vessels. Blood pressure is the driving force in the formation of about 125 ml of glomerular filtrate per minute. About 124 ml of the glomerular filtrate is reabsorbed in the tubules of the nephron.
  • 6. Kidney Capsule as thin membrane of connective tissue, cortex of the kidney and scan over the tissue, presence of glomeruli (convoluted parts of proximal and distal tubuli). • to identify the vascular pole of a good glomerulus by the attachment of the capillary tuft to the wall of the glomerulus. • The nuclei are located side by side or may even overlap. • Proximal tubules are characterised by their eosinophilic (pink) low columnar cells and by large amounts of fuzzy material, which may fill the entire lumen of the tubulus.
  • 7. The anatomical glomerulus, the parietal blade of Bowman's capsule (squamous cells), podocytes (fairly large and light nuclei ), endothelial cells (smaller and darker nuclei), vascular pole.
  • 8. Tubules of the Nephron • The tubular system can be divided into proximal and distal tubules, which in turn have convoluted and straight portions. • Intermediate tubules connect the proximal and distal tubules. Running from the cortex of the kidney towards the medulla (descending), then turning and running back towards the cortex (ascending), the tubules form the loop of Henle. • The proximal tubule is the longest section of the nephron (about 14 mm). • The convoluted part of the proximal tubules coils close to the glomerulus in the cortex. • The proximal tubules are formed by a low columnar epithelium. The eosinophilic cells of the epithelium have a wide brush border (long microvilli) and are active in endocytosis.
  • 9. • They almost completely resorb substances of nutritional value from the glomerular filtrate (glucose, amino acids, protein, vitamins etc.) • In the proximal tubules the volume of the glomerular filtrate is reduced by about 75%. Sodium ions are actively resorbed from the glomerular filtrate. • hey are followed by passively diffusing chloride ions and the osmotic absorption of water. The straight portion of the proximal tubule descends towards the medulla. • The straight portion of the proximal tubule merges with the intermediate tubule (thin segment of the loop of Henle). • A flattened, only ~1-2 µm high epithelium forms the intermediate tubule, which is only ~15 µm wide. Descending parts of the straight proximal and intermediate tubules are permeable to water but not to solutes.
  • 10. Kidney  The medulla of the kidney, there is a collecting ducts (cuboidal to columnar cells, well-defined boundaries between cells, cytoplasm only weakly stained or unstained, large ducts)  An intermediate (very flat epithelium, nuclei bulge into the lumen of the tubulus, diameter of the duct is small) and distal tubule (cuboidal epithelium, cells stain weakly pink).
  • 11. The Juxtaglomerular Apparatus • The distal tubule contacts the glomerulus forming a specialized section of tubular epithelium, the macula densa. • At the point of contact with the glomerulus, the distal tubule is always in close contact with the efferent and afferent arterioles of the glomerulus. • The juxtaglomerular (JG) apparatus are extraglomerular mesangial cells and the juxtaglomerular cells surrounding the afferent arteriole (modified smooth muscle cells), which produce and secrete renin.
  • 12. • URETER • The urine flows through these structures to the ureter and is channelled to the bladder. • The mucosa is lined with a transitional epithelium , which occurs exclusively in the urinary system. • The lamina propria consists mainly of dense connective tissue, with many bundles of coarse collagenous fibres. • The muscularis usually consists of an inner longitudinal and outer circular layer of smooth muscle cells . • In lower parts of the ureter and the bladder an additional outer longitudinal layer of muscles is added to the first two.
  • 13. “Artifact” Cross Section of a Ureter Lumen
  • 14. Circular smooth muscle Longitudinal smooth muscle
  • 15. Dome cells
  • 16. Transitional epithelia changes depending on how full the urinary bladder is
  • 17. BLADDER Histology of Bladder: mucosa of transitional epithelium, Submucosa, and thick muscular layer know as the detrusor muscle These are retroperitoneal structures. They enter the bladder at an oblique angle which helps to prevent backflow of urine. Smooth muscle in the wall of the ureters rhythmically contracts (peristalsis) to move urine into the bladder
  • 18. Urinary Bladder Mucosa (transitional epithelium)
  • 19. Transitional Epithelium of the U. Bladder – note the different cell shapes
  • 20. The Urethra • Initially, the urethra is lined by a transitional epithelium in males and females. • In males, it is replaced by a pseudostratified or stratified columnar epithelium below the openings of the ejaculatory ducts into the urethra. • The distal parts of the female urethra and the distal end of the male urethra are lined by a stratified squamous epithelium. • The lamina propria contains loose connective tissue. Smooth muscle cells in the muscularis are mainly oriented longitudinally. • They are surrounded, in the middle part of the urethra (below the prostate in males), by striated muscle cells of the sphincter urethrae.