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

2. 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

3. Fluid Input & Output

4. Urinary System

5. 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

6. Urinary Bladder
(Remanent of Allantois)

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

8. 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

9. Urethra

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

11. 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

12. 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

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

14. Cortex vs. Medulla
Capsule

15. Anatomy of Kidney

16. Major and Minor Calyx

17. Arterial Supply

18. Venous Drainage

19. Renal Circulation

20. Nephron (two types)

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

22. Glomerulus
Bowman’s Capsule

23. Podocytes

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

25. 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

26. 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)

27. 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

28. 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

29. 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

30. Counter-current Exchange

31. 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)

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