1. The Urinary System

2. Structure It consists of: Kidney Ureter Urinary bladder Urethra

3. Functions Homeostasis Selective absorption of water and solutes Acid base balance Formation of urine Waste elimination Renin production Erythropoietin production Vitamin D3 formation

4. The Kidney It is covered by a dense connective tissue capsule It has a convex lateral border and a concave medial border The hilum were blood vessels, nerves lymphatics, and ureter enter and leave the kidney The ureter is the expanded upper end of ureter The ureter divides into2-3 major calyces which in turn divide into minor calyces The pelvis and calyces are found within renal sinus surrounded by fat

5. The Kidney Cont., The kidney is divided into: An outer cortex Inner medulla It consists of 8-15 conical structures called pyramids Each pyramid and adjoining cortical area is called renal lobe Lobes are separated by cortical extensions called renal columns Kidney consists of one million nephrons (functional unit)

6. The Nephrone Each nephron consists of: Renal corpuscle Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting tubule

7. Renal Corpuscle Glomerulus surrounded by Bowman’s capsule Bowman’s capsule consists of: parietal layer made of simple squamous epithelium visceral layers made of podocytes Afferent and efferent arterioles Glomerular basement membrane Mesangial cells Tubular pole Vascular pole

8. Podocytes Modified visceral layer cells They form primary and secondary pedicles (small foot) that interdigitate with each other surrounding capillaries Area between pedicles are the filtration slits Capillaries are of fenestrated type to facilitate filtration

9. Proximal Convoluted Tubule Lined by cuboidal to low columnar epithelium Acidophilic cytoplasm Brush border due to abundant microvilli Basal invagination Lateral interdigitation It has more profiles than distal one because it is longer

10. Loop of Henle It is the U-shaped structure which consists of: Thick descending Thin descending Thin ascending Thick ascending Thick part is lined by simple cuboidal epithelium Thin part is lined by simple squamous epithelium Juxtamedullary nephron close to medulla 5% Cortical nephron in the cortex 95%

11. Distal Convoluted Tubule Lined by simple cuboidal epithelium Differs from that of the proximal in having smaller cells with less microvilli and less acidophilia The cells have basal invagination and less lateral interdigitation It has fewer profiles than proximal one because it is shorter

12. Collecting Tubules and Ducts Lined by simple cuboidal epithelium Tubules are 40 µm in diameter Cells of tubules increase in height until become columnar Ducts reaches 200 µm in diameter They are weakly stained Intercellular boundary is visible in light microscope Epithelium of collecting ducts is responsive to ADH

13. Juxtaglomerular Apparutus Near the vascular pole of Bowman’s capsule Consists of: 1. Juxtaglomerular cells Modified smooth muscle fibers of afferent arteriole 2. Macula densa cells Modified cuboidal epithelium of proximal part of distal convoluted tubules 3. Lacis cells

14. Blood Circulation

15. Urine Passages Calyces, pelvis, ureter, and bladder have the same structure except that muscle fibers become prominent in lower ureter and bladder All are lined with transitional epithelium Epithelium divides into: 1.Single basal layer 2.Intermediate region of one or more layers of columnar cells 3. Superficial layer of polyhedral (umbrella) cells with dome-shaped appearance with many tight junction

16. ureter Long muscular organ extends from the pelvis to bladder It has longitudinal folds Comsists of: 1. Epithelium of transitional type with lamnia propria 2. Submucosa 3. Muscle layer 4. Adventitia(why)?

17. Urinary Bladder Consists of: Epithelium of transitional type with lamina propria with dense connective tissue Muscularis of three poorly delineated layers layer collectively called (Detrusor muscle). Three layers are distinct at the bladder neck to form bladder sphincter Adventitia the outer most layer. Peritoneum covers the upper surface of the bladder

18. Urethra A comparison between ureter, bladder, and urethra Notice the epithelial folding The lining epithelium varies from transitional at the first part to columnar in middle part to stratified squamous at the end part

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