Urinary System

1. Urinary System Sanjaya Adikari Department of Anatomy

2. Urinary system comprises of • Two kidneys • Two ureters • Bladder • Urethra

3. 12 6 Position and size of the kidneys • Retro-peritoneal • Size 12 x 6 x 3 cm • Weighs about 130 g • Hilum is 5 cm from midline

4. Position and size … Back • Hilum of right Kidney is just below transpyloric plane • Hilum of left Kidney is just above transpyloric plane • Slight movement with respiration

5. Renal fascia Renal vessels Perinephric fat Renal capsule Ureter Renal fascia separates the kidney from the suprarenal gland and surrounding tissues. Limits the spread of a perinephric abscess

6. Structures at the hilum of the kidney • Three structures enter each kidney via the hilum, from front to back • the vein • the artery • the ureter Renal artery Renal vein Ureter

7. Functions of the kidney • Filtration • Selective reabsorption • Secretion • Control of renin-angiotensin-aldosterone mechanism • Secretion of erythropoietin • Production of 1,25-dihydroxycholecalciferol

8. Structure of the kidney • Capsulated • Outer cortex and inner medulla • Medulla is arranged into medullary pyramids • Apices of pyramids are called renal papillae • Papillae project into calyces • Calyces converge to form the renal pelvis

9. Minor Calyces Renal Papilla

10. Structure of the kidney… • Functional unit is the nephron • Approximately 1.3 million nephrons in each kidney • Part of a nephron is in cortex and part in medulla

11. Nephron Glomerulus Renal corpuscle Bowman’s capsule Nephron Proximal convoluted tubule Renal tubule Loop of Henle Distal convoluted tubule Collecting tubule

12. Nephron…cont.

13. Location of nephrons Cortical nephrons Juxtamedullary nephrons

14. Renal corpuscle (Bowman’s space) Urinary pole of the visceral layer Vascular pole

15. Mesangium Supporting connective tissue Glomerulus Coiled network of anastomosing capillaries Bowman’s capsule Single layer of flattened cells resting on a basement membrane

16. Renal corpuscle – microscopic view

17. Glomerular filtration barrier • Capillary endothelium • Contain pores (fenestrations) large enough to permit passage of all non-cellular elements of blood • Common basement membrane (glomerular basement membrane) • Non-fenestrated, continuous layer. Allows passage of molecules <65000 molecular weight. Eg. Free Hb. Albumin with mw of 68000 and other lager molecules are retained • Podocyte layer • Has primary and secondary processes (pedicles). There are slit pores between pedicles. Function of slit pores ?

18. Components of glomerular filter

19. Proximal convoluted tubule (PCT) • Longest section of the tubule • Most convoluted section • Makes up the bulk of cortex • Simple cuboidal epithelium • Brush border fills the lumen • Cytoplasm is pink stained due to mitochondria • >75% of GF is reabsorbed

20. Proximal convoluted tubule… PCT DCT

22. Loop of Henle • Has thin and thick limbs • Descending limb is lined by simple squamous epithelium (thin walled) • Ascending limb is lined by simple cuboidal epithelium (thick walled) • Closely associated with parallel capillary loops called vasa recta (forms a counter-current multiplier system) • Generates a high osmotic pressure in the ECF of medulla

23. Loop of Henle…

24. Distal convoluted tubule (DCT) • Shorter and less convoluted than PCT • Found in the cortex • No brush border • Larger, clear lumen • Cells smaller, so more cells than in PCT in section • Na+ ions absorbed under the influence of aldosterone

25. Collecting tubule • This is the terminal part of the DCT • Opens into collecting ducts • Together with collecting ducts form ‘medullary rays’ • Collecting tubules and ducts are not normally permeable to water • Becomes permeable to water in the presence of ADH • Site of reabsorption of water

26. Collecting ducts • Formed by fusion of collecting tubules • They fuse with adjacent ducts and form larger ducts called ducts of Bellini • Ducts of Bellini convey urine into the calyceal space through renal papillae • Lined by tall, pale stained columnar cells • No brush border • Water reabsorption under ADH control

27. Collecting ducts…

28. Minor Calyces Renal Papilla Calyces and renal pelvis

29. Ureter • About 25cm long • In X-ray seem to lie over the transverse processes of L2 – L5 veterbrae • Comprises the pelvis, abdominal, pelvic and intravesical portions

30. Course of the ureter • Abdominal part lies on medial edge of psoas muscle • Psoas muscle separates it from the tips of transverse processes of L2-L5 • Crosses into the pelvis at the bifurcation of common iliac artery in front of sacroiliac joint • Pelvic part runs on the lateral wall of pelvis towards the ischial spine • At ischial spine turns forwards and medially to enter the bladder • Intravesical part runs obliquely through the bladder wall for 2 cm. This creates a valvular effect

31. Narrow parts in the ureter • Ureter is relatively narrowed at three sites • Junction between the renal pelvis and abdominal part • At the pelvic brim • At the ureteric orifice (narrowest of all) • A ureteric stone can get lodged at one of these places • Usually stones <5mm in diameter tend to pass naturally

33. Ureter… • Lined by transitional epithelium • Muscular tube • Inner longitudinal • Outer circular • Urine is propelled by peristalsis

34. Transitional epithelium • Also called urinary epithelium/ urothelium • Plasma membrane of superficial cells are thicker • Impermeable to urine (potentially toxic) • Prevents water leaking out towards concentrated urine • Allows greater stretching of epithelium

35. Transitional epithelium…

37. Bladder • Lined by transitional epithelium • Wall has three smooth muscle layers (Detrusor muscle)

38. Urethra • In males, has three parts • Prostatic urethra • Membranous urethra • Spongy urethra (penile urethra) • Prostatic urethra is lined by urinary epithelium • Urethral meatus is lined by stratified squamous epithelium • Other parts are lined by stratified or pseudostratified columnar epithelium • External orifice is the narrowest part

39. Urethra Compare the distance between the anus and the urethral opening in male with that of female. In females the urethra opens into the vestibule of vulva where the vagina is also opened. Females are more prone to get urinary tract infections (UTI)

40. Juxtaglomerular apparatus (JGA)

41. Juxtaglomerular apparatus… • Has 3 components: • Juxtaglomerular cells • Derived from smooth muscle cells of afferent arteriole • Macula densa • Modified DCT cells • Lasis cells • Modified extraglomerular mesangial cells

42. Juxtaglomerular cells • Derived from smooth muscle cells of afferent arteriole. Cytoplasm contains granules of enzyme renin. Directly sensitive to BP in the afferent arteriole Macula densa • Modified DCT cells. Closely associated with juxtaglomerular cells. Has taller cells with prominent nuclei. Sensitive to [Na+] within DCT. When [Na+] is low stimulates the release of renin from juxtaglomerular cells

43. Lasis cells • Modified extraglomerular mesangial cells. Lie between macula densa and Bowman’s capsule. Produce the hormone erythropoietin

45. Blood supply of the kidney

46. Anterior view Posterior view Apical Upper Middle Posterior Inferior Five segments of the kidney

47. They are supplied by five segmental branches of the renal artery. • In the region of the hilum, the artery divides into anterior and posterior branches • The posterior branch supplies the posterior segment of the kidney. • The anterior branch further divides into four branches and supply the remaining 4 segments

48. Both renal arteries give off a suprarenal branch and a ureteric branch before they enter the kidneys.

49. The pattern of branching of vessels may vary, but always five segmental arteries are present. • Branches of renal arteries do not have collateral circulations between them.