1. Tony Serino, Ph.D. BIO 201 Misericordia Univ.
Excretory System
Tony Serino, Ph.D.
BIO 201 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. Water Balance Adapted to Specific Habitats
Humans die with as little as 12% water loss

4. Conformer vs. Regulators
Osmoconformers –are isoosmotic with their environment; therefore there is no tendency for the animal to gain or lose water. All osmoconformers are marine and live in water that has a stable composition. Most marine invertebrates are osmoconformers. Note: while these organism are isoosmotic to their environment, their ionic composition may differ considerably from the surrounding environment.
Osmoregulators –maintain their internal osmotic environment independent of the external environment; such as freshwater and terrestrial habitats

5. Osmoregulators in Fresh and Salt Water
Marine species live in strongly dehydrating environment.
Freshwater species live in a hydrating environment and may lose large amounts of salts
Survive by drinking large amounts of sea water and excreting large amounts of salt.
Drink almost no water and excrete large amounts of dilute urine, and replace salt in their food and uptake through their gills

6. Nitrogen Waste Forms
Ammonia is a breakdown product from protein and NA catabolism, highly toxic (NH4+) interferes with mitochondria function
Ammonia must be diluted with large quantities of water for safe levels –accomplished by mainly aquatic species which can allow ammonia to diffuse directly to ext. environ. (highly energy efficient)
Urea –less toxic, can be stored and excreted with minimal water loss; but takes energy to produce
Uric Acid –is relatively non-toxic, fairly insoluable, secreted as dry paste with little water loss, but most costly to make

7. Protonephridia
Network of blind ended tubule connected to an external opening and ending in a flame bulb
Flame bulb: cap cell with cilia and tubule cell. Form a filtration membrane where the cells meet.
The cilia hang inside lumen of tubule forcing fluid down tubule and drawing water through filter
Found mostly in flatworms
Function mostly in water balance; wastes can diffuse directly from cells to exterior because of limited thickness of organism

8. Metanephridia Found in many annelids
Each segment of worm has a pair of metanephridia with its funnel-like end (nephrostome) projecting into the anterior segment
The nephrostome is ciliated, these draw fluid into the tubules
The tubules have a capillary bed and adjustments are made to the concentrations of the fluid.

9. Malpighian Tubules
Found mostly in insects and other terrestrial arthropods
A series of blind ended tubes arising from the midgut
Tube epithelium secrete wastes and salts into tube from hemolymph
Hindgut performs reabsorption
N waste is passed as nearly uric acid crystals

10. Mammalian Urinary System

11. Urinary System

12. 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

13. Urinary Bladder
(Remanent of Allantois)

14. Urethra

15. Anatomy of Kidney

16. Renal Circulation

17. Nephron (two types)

18. Urine Formation Pressure Filtration Reabsorption Secretion
Reabsorption of water d

19. Glomerulus
Bowman’s Capsule

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

21. 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)

22. 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

23. 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

24. 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)

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