Osmoregulation Flashcards
What is osmotic pressure?
The pressure that would have to be applied to a pure solvent to prevent it diffusing across a semi-permeable membrane thorough osmosis.
Why do some areas have higher osmotic pressure than others? What kind of property is osmotic pressure?
Osmotic pressure is a colligative property, so it is dependant on the number of osmotically active molecules (effective osmoles) in an area. A molecule will be osmotically active if it cannot pass through the membrane of the area uninterrupted.
Describe tonicity by using osmotic pressures.
Hypertonic solution: the cell shrinks (e), so the surrounding solution must have a higher osmotic pressure than inside the cell.
Hypotonic solution: the cell swells (o), so the surrounding solution must have a lower osmotic pressure than the cell.
Isotonic: the cell neither wells nor shrinks, and the osmotic pressure is in equilibrium inside and outside the cell.
What is colloid osmotic pressure?
Osmotic pressure attributed to the presence of osmotically active proteins.
What are the two types of nephrons? What is the difference and what type of animal would have each one?
Cortical and Juxtamedullary. Cortical nephrons have a shorter Loop of Henle that does not extend into the inner medulla, and their renal corpuscles are in the cortex. Juxtamedullary nephrons have their thin limbs from the Loop of Henle in the inner medulla, with the thick part of the ascending limb starting only in the outer medulla, their renal corpuscles are in the cortex as well. Animals living in drier climates have a higher percentage of juxtamedullary nephrons. Freshwater fish only have cortical nephrons.
Describe the filtration barrier of the Bowman’s Capsule.
The glomerulus capillaries are fenestrated (have gaps), which allows blood to access the basement membrane. After the basement membrane, there are podocyte processes that project into the membrane, increasing the surface area across which water and solutes can be forced out. The basement membrane is made from negatively charged glycoproteins and collagen, thus positively charged molecules are more likely to pass through.
How does water transport across the integumnent occur?
Mainly through transcellular transport mechanisms as there are incredibly tight junctions between cells that limit paracellular transport and thus water loss. Transcellular trasnport occurs through aquaporins.
How does urine formation happen in insects?
Urine forms in the malpighian tubules in insects, luminal cells contain sodium potassium pumps on their basolateral membranes that pump potassium ions into the cell, then the sodium ions pumped out of the cell reenter through NKCC channels along with more potassium ions and chloride ions. The chloride ions then leave the cell through chloride ions channels on the luminal membrane. A proton pump on the luminal membrane generates a proton motive force by pumping protons into the malpighian tubule. A K+/H+ antipoter then uses this electrochemical gradient to pump potassium ions into the lumen and protons back into the cell. The high concentrations of potassium and chloride ions in the tubule make the tubular fluid hyperosmotic to the haemolymph, and water moves into the tubules though paracellular osmosis. Later on, near the rectum, ions are reabsorbed by rectal pad cells, and water follows, leaving an extremley hyperosmotic excreta. The countercurrent mechanism between the malpighian tubules and the rectum also contributes to the low osmolarity of the excretement. [This is the fact that near the anus, there is a higher osmolarity in the malpighian tubules that run parallel to the hidngut, thus water is reabsorbed].
How do freshwater teleost fish produce hypoosomotic urine?
In freshwater:
Chloride cells activley uptake chloride and calcium ions. Low outside concentrations of sodium ions causes paracellular transport channels to close.
Pavement cell uptake sodium ions. Mechanism: Proton pump in luminal membrane pumps protons into freshwater, creates electrochemical gradient, sodium ions move into the cell through sodium ion channels in luminal membrane. Sodium potassium pumps in adluminal membrane pump sodium ions into ECF. Chloride ions responsible for the removal of carbonic acid which is a product of CO2 being used to form protons.
In saltwater:
Chloride cells increase in number and secretory effect, so more calcium, chloride and sodium ions are pumped out of the cells. Paracellular sodium channels open and sodium diffuses into the cells.
Pavement cells decrease in active uptake of sodium ions, the hormones cortisol and GH downregulate the proton pump, thus lowering the electrochemical gradient and the amount of sodium that enters the cell.
What is the osmolarity of elashmobranch’s ECF compared to seawater?
How do elasmobranch rectal glands [and chloride cells] work?
Elasmobranch’s ECF is isoosmotic with seawater.
Elasmobranchs have rectal glands which secrete chloride and sodium ions. They do this through this mechanism:
NKCC channels in the baslateral membrane of luminal cells pump sodium, potassium and chloride ions into the cells. Chloride ions diffuse through chloride ion channels in the luminal membrane into the rectum. Potassium ions diffuse back out through potassium channels in the basolateral membrane. Sodium potassium pumps in the basolateral membrane also pump sodium ions out of the cell and potassium ions back into it. All this creates an electrochemical gradient that results in the paracellular transport of sodium ions from the ECF to the rectum. Due to the hyperosmotic nature of the fluid in the rectum, water follows the sodium and diffuses into the rectum through paracellular transport. This is why elasmobranch’s rectal glands cannot secrete fluid that is hyperosmotic to their blood, it will always be isoosmotic.
