What are the 3 homeostatic processes involved in water & ion balance?
- Osmotic regulation
- Ionic regulation
- Nitrogen excretion
What parameter determines the direction of water movement across biological membranes?
Osmotic pressure (determined by solute concentration on either side of the membrane).
Why do animals rely on solute movement to control water flux across membranes?
Water can't be actively transported; it only moves passively with solutes.
What are the 2 types of transport that allow movement of molecules across epithelial cell membranes?
- Paracellular transport
- Transcellular transport
What 4 basic features do all transport epithelia have in common?
- High surface area
- Abundant mitochondria
- Asymmetric distribution of transporters
- Cell-to-cell interactions
What are the most abundant ions in most animals' extracellular space?
Where do ionoconformers typically live?
What are stenohaline animals?
Aquatic animals that can only tolerate a narrow range of salt concentrations in surrounding water.
What are euryhaline animals?
Aquatic animals that can tolerate a wide range of salt concentrations in surrounding water.
What is metabolic water?
Water molecules formed by oxidative phosphorylation as byproducts of metabolic reactions during digestion.
What are the most common methylamines used by animals as compatible solutes?
- TMAO (trimethylamine oxide)
What are the most common perturbing solutes in animals?
- Inorganic ions (K+, Na+, Cl-, SO42+)
- Organic solutes (charged amino acids)
What are the most common compatible solutes in animal body fluids?
- Polyols (trehalose, glycerol, glucose)
- Uncharged amino acids
How do urea and TMAO act as counteracting solutes?
Urea disrupts hydrophobic interactions and TMAO strengthens them, so they cancel each other out.
What are the most common ions in the cytoplasm of most animals?
What type of animals have the greatest abundance of organic solutes in their body fluids?
What is the difference in water permeability between epithelial cells with and without aquaporins?
Cells with aquaporins can be 100 times more permeable to water than cells without aquaporins.
What 2 factors affect aquaporin levels within a cell membrane?
- Expression of genes encoding aquaporins
- Vesicular traffic pathways transporting aquaporins to the plasma membrane
What is the major function of mucus layers on respiratory and GI tract surfaces?
To reduce water loss across epithelia.
What are keratinocytes?
Epithelial cells in the skin of terrestrial vertebrates that secrete proteins and lipids to form a dense, hydrophobic extracellular matrix to prevent water loss across the skin.
What are corneocytes?
Differentiated keratinocytes that produce a complex protein matrix before undergoing apoptosis, leaving a cornified envelope to protect the underlying keratinocytes.
What is the insect cuticle?
A complex network of hydrophobic molecules that covers all external surfaces of insects.