1. Excretory: Disposal & Osmoregulation
Excretion: Disposal of nitrogen-containing wastes
Osmoregulation: Control of gain and loss of water and solutes
Osmoregulation based largely on regulating solutes
Water follows the movement of solutes by osmosis

2. Excretion: Aquatic Animals
Animals must dispose of nitrogenous waste
Metabolism produces nitrogenous wastes from breakdown of proteins and nucleic acids
Most aquatic animals dispose of their nitrogenous wastes as ammonia
Highly soluble in water
Diffuses rapidly across cell membranes

3. Excretory: Saltwater Fish

4. Excretion: Land Animals
Land animals convert ammonia to less toxic compounds
Can be safely stored and transported in the body
Released periodically by excretory system
Requires energy for conversion
Different adaptations and type of reproduction determine excretion as urea or uric acid

5. Excretory: Disposal & Osmoregulation
Urea
Excreted by mammals, most amphibians, sharks, and some bony fishes
Can be stored in concentrated solution but requires water for disposal
Uric acid
Excreted by birds, reptiles, insects, some amphibians
Excreted as solid paste for water conservation
Uses more energy for excretion

6. Excretory

7. Excretory: Waste
Protein and nucleic acid breakdown - nitrogen-containing wastes toxic by-products of
Ammonia poisonous but soluble and easily disposed of
Urea less toxic, easy to store and excrete
Some land animals save water by excreting a virtually dry waste

8. Excretory: Waste in Urine
Urea – from amino acid breakdown
Uric Acid – from nucleic acid breakdown
Creatinine – muscle metabolism waste product

9. Excretory System The excretory system
expels wastes
regulates water and salt balance
Two human kidneys each contain ~ million nephrons
Urine leaves kidneys via ureters
Stored in urinary bladder

10. Excretory Systen

11. Each nephron: folded tubule and associated blood vessels1
Proximal tubule
Bowman’s capsule
Glomerulus
Arteriole from renal artery
Capillaries
Each nephron: folded tubule and associated blood vessels
Arteriole from glomerulus 3
Distal tubule
Branch of renal vein
From another nephron
Collecting duct 2
Loop of Henle with capillary
network
Nephrons extract filtrate from blood
Refine filtrate into much smaller amount of urine
D. DETAILED STRUCTURE OF A NEPHRON
Figure 25.9D

12. LE 25-11 Proximal tubule Distal tubule Bowman’s capsule Nutrients H2O
NaCI
HCO3 –
NaCI
HCO3 –
Blood
Some
drugs
and poisons H+ K+ H+
Filtrate composition
H2O
Cortex
NaCI
Medulla
Collecting
duct
HCO3 – H+
Loop of
Henle
Urea
NaCI
Glucose
Amino acids
Some drugs
NaCI
H2O
Reabsorption
Urea
Secretion
NaCI
H2O
Urine (to renal pelvis)

13. Excretory: Filtration
Filtration (Bowman’s capsule)
Blood pressure forces water and many solutes from blood (glomerulus) into nephron

14. Excretory: Reabsorption / Secretion
Controlled secretion of H+ and reabsorption of bicarbonate ions help regulate blood pH
Secretion also includes active transport of drugs and poisons
Reabsorption of salts and urea allow osmotic reabsorption of water

15. Excretion: Reabsorption / Secretion
PROXIMAL TUBULE
– always reabsorb glucose and amino acid
- sometimes water, sodium, potassium, calcium depending on need
Secretion
urea, creatinine, ions, drugs and toxins

16. Excretory: Reabsorbing Water
LOOP OF HENLE
- much water reabsorbed via active transport of salt
salt concentration in kidney higher in medulla
Longer loop – more water conservation (desert animals)

17. Excretory: Reabsorption/Secretion
DISTAL TUBULE
specialized “Urine fine tuning”
Aldosterone hormone – increases amount of sodium reabsorbed into blood (water follows)

18. Excretory: Water Reabsorption in Collecting Duct
Water reabsorbed
ADH (antidiuretic hormone) – cause collecting walls to be permeable to water to be reabsorbed
Caffeine interferes with ADH (dehydration)

19. Excretory: Regulates Blood Pressure
Releases RENIN when blood pressure low
- enzyme that causes production of chemical (angiotensin II) to constrict blood vessel
- Angiotensin II increase aldosterone production

20. Excretory: Dialysis

21. Homeostasis: Liver It assists the kidneys by making urea from ammonia
breaking down toxic chemicals

22. Liver
Blood from intestines flows through the liver before distribution to the rest of the body
Allows liver to adjust blood’s chemical content