1. Urinary System
Sanjaya Adikari
Department of Anatomy

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

3. 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 12 6

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
Perinephric fat
Renal capsule
Ureter
Renal vessels
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 Urinary pole Vascular pole (Bowman’s space)
of the visceral layer
Vascular pole

15. Mesangium Glomerulus Bowman’s capsule Supporting connective tissue
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 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. Glomerulus – high power view
E – capillary endothelial cell
M – mesangial cell
MS – mesangeal substance
BM – glomerular basement membrane
P - podocyte

20. 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

21. Proximal convoluted tubule…
PCT
DCT

23. 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

24. Loop of Henle…

25. 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

26. 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

27. 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

28. Collecting ducts…

29. Calyces and renal pelvis
Minor Calyces
Renal Papilla
Calyces and renal pelvis

30. 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

31. 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

32. 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

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

35. 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

36. Transitional epithelium…

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

39. 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

40. Urethra Females are more prone to get urinary tract infections (UTI)
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)

41. Juxtaglomerular apparatus (JGA)

42. 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

43. 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

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

46. Blood supply of the kidney

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

48. 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

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

50. 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.

52. Each segmental artery gives several interlobar arteries.
They ascend between the pyramids of the renal medulla.
At the corticomedullary junction, they branch to form the arcuate arteries.
Arcuate arteries give rise to interlobular arteries.
Afferent arterioles of the glomeruli originate from these interlobular arteries.

53. Efferent arterioles give rise to peritubular capillaries and vasa recta
Vasa recta are found in association with the loops of Henle of juxtamedullary nephrones that extend down into the medulla
The cortical and medullary capillaries drain via interlobular veins to arcuate vein at the corticomedullary junction and through interlobar veins to the renal vein

54. Efferent
arteriole
Peritubular
Capillaries.
Afferent
arteriole

56. Renal Veins The left renal vein receives blood from
The left suprarenal vein
The left gonadal vein
The inferior phrenic vein
The right renal vein collects blood only from its own kidney.

58. Renal artery
Segmental arteries
Renal vein
Interlobar arteries
Interlobar veins
Arcuate arteries
Arcuate veins
Interlobular arteries
Interlobular veins
Afferent arterioles
Peritubular capillaries
Glomerulus
Vasa recta
Efferent arterioles