1. Tony Serino, Ph.D. Clinical Anatomy
Excretory System
Tony Serino, Ph.D.
Clinical Anatomy

2. Renal: Topic Objectives
Be able to describe and identify bladder and urethra anatomy and function, including differences between male and female.
Be able to describe micturition reflex.
Be able to describe and identify kidney anatomy, histology and function.
Be able to describe and identify circulation pattern to, from and within the kidney.
Be able to identify parts of the nephron and their functions.
Be able to describe urine formation and predict changes to output with changes in BP, ion pumps, and hydration status.
Be able to describe kidney contribution to acid/base balance and be able to predict kidney response to blood pH changes
Be able to describe hormonal BP control and predict response to low and high BP

3. Excretory System Remove wastes from internal environment
Wastes: water, heat, salts, urea, etc.
Excretory organs include: Lungs, Skin, Liver, GI tract, and Kidneys
Urinary system account for bulk of excretion

4. Fluid Input & Output

5. Urinary System

6. Ureter Histolgy
-about 25 cm long, retroperitoneal, moves urine by peristalsis; volume of urine moved is called a jet (1-5 jets/min) -ureters enter the bladder wall obliquely, allowing them to remain closed except during peristalsis
Adventitia
Mucosa
Muscularis

7. Urinary Bladder
(Remanent of Allantois)

8. Urinary Bladder Histology
Mucosa
Submucosa
Muscularis
(Detrusor Muscle)
(Serosa)

9. Urinary Bladder Filling
Highly distensible
10-600ml normally
Capable of 2-3X that volume
Under normal conditions, the pressure does not significantly increase until at least 300 ml volume is reached

10. Urethra

11. Urethra Histology
-epithelium changes from transitional to stratified squamous along its length -large numbers of mucous glands present

12. Bladder (Storage) Reflex
As urine accumulates, the bladder wall thins and rugae disappear
Innervation (sympathetic) to the sphincter muscles (particularly the internal sphincter) keeps the bladder closed and depresses bladder contraction
Voluntary control

13. Micturition Reflex (Voiding)
Urine volume increases, and the smooth muscle increases pressure in bladder
Stretch receptors in detrusor muscle, increase parasympathetic activity in the splanchnic nerve cause increase bladder contraction and internal sphincter relaxation
Voluntary relaxation of external sphincter by a decrease in firing of the pudendal nerve

14. Kidney Location (x.s.)
(Retroperitoneal)

15. Cortex vs. Medulla
Capsule

16. Anatomy of Kidney

17. Major and Minor Calyx

18. Arterial Supply

19. Venous Drainage

20. Renal Circulation

21. BP in Renal Vessels

22. Nephron (two types)

23. Epithelium of Nephron

24. Urine Formation Overveiw
Pressure Filtration
Reabsorption
Secretion
Reabsorption of water d

25. Glomerulus
Bowman’s Capsule

26. Podocytes

27. Filtration in Glomerulus
Endothelium
Capillary Lumen
Basement Mem.
Pedicels
Slit pores
Glomerular Filtrate
Fenestration

28. Glomerular Filtration
A pressure filtration produced by the BP, fenestrated capillaries of glomerulus, and the podocytes creates the glomerular filtrate
Slit size allows filtration of any substance smaller than a protein
Blood proteins create an osmotic gradient to prevent complete loss of water in blood,
Pressure in Bowman’s capsule also works against filtration
Volume of filtrate produced per minute is the Glomerular Filtration Rate (GFR)
Average GFR = ml/min

29. Forces controlling Glomerular Filtration

30. Tubular Reabsorption 75-85% of glomerular filtrate reabsorbed in PCT
Some of the reabsorption is by passive diffusion
Example: Na+
Much of the reabsorption is active, most linked to the transport of Na+; known as co-transport
The amount of transporter proteins is limited; so most actively transported substances have a maximum tubular transport rate (Tm)

31. Reabsorption

32. Loop of Henle and CD
Provides mechanism where water can be conserved; capable of producing a low volume, concentrated urine
Loop of Henle acts as a counter-current multiplier to maintain a high salt concentration in medulla
CD has variable water permeability and must pass through the medulla
Allows for the passive absorption of water

33. Counter-current Multiplier
Descending is permeable to water but not salt; loss of water concentrates urine in tube
Ascending is permeable to NaCl but not water; Salt now higher in tube than interstitium; first passively diffuses out then near top is actively transported out
Results in a self-perpetuating mechanism; maintaining a high salt concentration in center of kidney

34. Vasa Recta Supply long loops of Henle
Provide mechanism to prevent accumulation of water in interstitial space
Passive diffusion allows the blood to equilibrate with osmotic gradient in extracellular space

35. Counter-current Exchange

36. Tubular Secretion
PCT and DCT both actively involved in secretion (active transport of substances from the blood to the urine)
Both ducts play important roles in controlling amount of H+/HCO3- lost in urine and therefore blood pH
DCT actively controls Na+ reabsorption upon stimulation by aldosterone (controls final 2% of Na+ in urine)

37. Summary Re-absorption Water Re-absorption with ADH present Loses water
Loses NaCl
Selective Secretion & Re-absorption

38. Dehydration & Water Intoxication

39. Thirst Hypertonic, low volume urine Reabsorption of Water in CD
ADH release

40. Juxtaglomerular Apparatus

41. Renin-Angiotensin-Aldosterone
iBP
Decreased Stretch in JG cells
Decreased Na in Urine in DCT
h stimulation of Macula Densa
h Renin Release
Angiotensinogen g Angiotensin I
h arteriolar constriction
Converting Enzyme
h BP
Angiotensin II
h Aldosterone Release
h Na+ reabsorption
h water retention and BV

42. Declining BP Regulation
Stimulates thirst

43. Increase BP Regulation (ANP)

44. Acid/Base Transport