1. Osmoregulation and Excretion

2. Osmoregulation
Balances the uptake and loss of water and solutes of the body
Species maintain water balance in 2 ways
Osmoconformer
Isoosmotic with environment
Marine animals
Osmoregulator
Controls internal osmolarity independent of the environment
Can live in environments that are otherwise uninhabitable

3. Adaptations of Osmoregulation
Marine animals
Osmoconformers must actively transport certain solutes
Osmoregulators
Some drink seawater to offset water loss, gills and kidneys are used to rid themselves of salt
Sharks maintain a high urea to keep large amounts of salt from entering. Excess is excreted
Freshwater animals
Drink almost no water and excrete large amounts of dilute urine; salts replenished by eating

4. Adaptations of Osmoregulation
Temporary waters
Animals enter a state of dormancy when waters dry up
Land animals
Body coverings help to prevent dehydration; take in water and solutes by drinking and eating; water is produced via cellular respiration

5. Nitrogenous Wastes
There are a variety of nitrogenous wastes. Animals excrete the nitrogenous waste that best fits its need for water and the availability of energy.
Ammonia
Very toxic; animals need access to large amount of water; most common in aquatic species
Urea
Produced in the vertebrate liver; low toxicity; less water needed; animals must expand energy to produce urea from ammonia
Uric Acid
Relatively nontoxic; does not readily dissolve in water; excreted as a semisolid paste; little water loss

6. Excretory Systems
Systems must be able to handle: filtration, reabsorption, secretion and excretion
Excretory systems will vary widely, but are based on a tubular theme

7. Excretory Systems Protonephridia
A system of dead-end tubules connected to external openings; each branch is capped with a flame bulb which hold cilia – these function in filtration
Includes flatworms, rotifers, some annelids, mullosc larvae, and lancelots
Function in osmoregulation and the excretion of nitrogenous wastes

8. Excretory Systems Metanephridia
Excretory organs that open internally to the coelom with the opening surrounded by a ciliated funnel. The cilia push the fluid into the collecting tubule and eventually into a bladder where it can be released
In worms, each segment consists of 2 metanephridia and both are immersed in the coelomic fluid and surrounded by capillary network. The capillary network works to return solutes that have been reabsorbed.
Most annelids (such as earthworms)
Function in osmoregulation and excretion of nitrogenous wastes

9. Excretory Systems Malpighian Tubules
Extend from dead-end tips immersed in hemolymph to openings in the digestive tract
Filtration does not occur. Transport epithelium lining the tubules secretes solutes and nitrogenous wastes from the hemolymph to the lumen which also draws water via osmosis. Most solutes and water are reabsorbed in the rectum. Nitrogenous waste is excreted in the form of uric acid.
Insects and terrestrial arthropods
Function in osmoregulation and removal of nitrogenous wastes

10. Excretory Systems Kidneys
Kidneys are made of highly organized tubules that are associated with capillaries. These tubules will carry urine out of the kidneys and eventually out of the body
Functions in both osmoregulation and excretion
Site of ultrafiltration – filtration occurs according to size, shape and charge of particles
Pores, the basement membrane and podocytes work to accomplish this
In vertebrates and some chordates

11. Mammalian Excretion
Blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
Permeable to water and small solutes
salts, glucose, amino acids, vitamins, nitrogenous waste
Filtrate will then pass into the regions of the nephron
Proximal tubule, loop of Henle, and distal tubule
Filtrate then passes into the collecting duct where it then can be drained via the ureter

12. Mammalian Excretion Only mammals and some birds have a loop of Henle
In humans
85% of nephrons are cortical
15% of nephrons are juxtamedullary
This allows mammals to make urine that is hyperosmotic to the body and allows for water conservation
Capillaries are associated with the nephrons to aid in reabsorption
The vasa recta and loop of Henle form a countercurrent system that allows for greater effeciency

13. Adaptations of the Vertebrate Kidney
Mammals
Juxtamedullary nephrons with varying sizes of loops of Henle
Dryer environments give rise to L.O.H.s that are much longer/deeper into the nephron
Birds and other reptiles
L.O.H. does not extend as far in birds, but conserve water by producing uric acid
Other reptiles only have cortical nephron, but are able to reabsorb water via the cloaca. Many also excrete uric acid

14. Adaptations of the Vertebrate Kidney
Freshwater fish and amphibians
Conserve salts by reabsorbing ions
Amphibians vary between environments. May conserve water or conserve solutes depending on current conditions
Marine Bony Fish
Do not have distal tubule and many are also missing or have small glomeruli. Filtration rates are low. Main function is to rid excess and unneeded ions

15. Hormones Antidiuretic hormone (ADH) aka vasopressin
Controls the amount of water in urine. An increase in ADH secretion will cause more water to be reabsorbed by the body (less dilute urine). A decrease in ADH will have the opposite effect.