Why is osmoregulation important?
- It affects internal pH , metabolite concentration, and waste management
- It affects composition of fluids within the body (e.g., interstitial fluid)
- It maintain the cytoplasmic composition within cells
Transport Epithelium
Transport epithelia are layers of epithelial cells that can transport specific amounts of certain solutes in various directions. Each epithelia cell has an 1) apical membrane that faces the lumen of the body cavity, and 2) basolateral membrane that faces the interstitial fluid. Each epithelium also has a basement membrane that anchors basolateral membranes of the epithelial cells. In addition, there are tight junctions between the epithelial cells to prevent solutes from transferring across the membrane.
Transport epthithelial cells actively transport solutes from the lumen to the institial fluid to allow osmosis.
Metabolic Waste
The major metabolic waste products of animals are nitrogenous wastes. These nitrogenous wastes come from the breaking down of protein and nucleic acids. There are three forms of excreted nitrogenous wastes:
- Ammonia: highly toxic but soluble; usually excreted by aquatic organisms because their environment (water) can dilute the ammonia
- Urea: formed by ammonia and water; it requires energey to produce, but is 100000 times less toxic than ammonia. Most mammals and some bony fish excrete urea.
- Uric acid: product of nucleic acid breakdown, and it is very energetically expensive to make. However, it is not toxic at all. Most birds excrete their wastes as uric acid because 1) they have less access to water and 2) their eggs are often impermeable to water, causing urea to be a non-viable option.
