LU4: OSMOREGULATION
Osmolarity: Moles of osmotically active particles per liter of solvent.
Osmoregulation: Control movement of solutes between internal fluids and external environment.
Water and certain solutes must be maintained within narrow limits.
Osmosis: The movement of water across the plasma membrane from high to low concentration gradient.
Osmoconformers: The internal osmolarity of animals that change according to their surroundings.
Eg: Brine shrimp, hagfishes & other marine invertebrates.
Osmoregulators: Animals that able to maintain their internal osmolarity regardless of external salt concentration, & expand energy to control water movement.
Eg: Marine verterbrates, fresh water organisms, humans, & other animals.
Stenohaline (narrow & salt): Fish cannot endure a wide fluctuation in salinity of water.
Eg: Goldfish (freshwater fish) die in high salinity surroundings.
Euryhaline (wide): Opposites of stenohaline thus, able to endure wide range of salinities.
Eg: Salmon, molly, eels, green crab.
Primary regulatory mechanism: Antidiuretic hormone (ADH)
Freshwater fish: Gills actively absorb salt & have large glomerulus to increase NaCl reabsorption & water excretion.
Saltwater fish: Gill actively release Cl-, passively remove Na+, & absence of glomerulus to reduce water excretion.
Edema: Failure to osmoregulate which cause swollen due to excessive fluid build-up.
Synthesized by hypothalamus, stored in pituitary gland, & stimulated by hyperosmotic extracellular fluid (ECF).
Reduce loss of water in urine
Most found in mammals in which diuretic increases rate of urine formation while antidiuretic decreases it.
Water reabsorption (distal tubule & collecting duct) helps to avoid increase in osmolarity.
Secondary regulatory mechanism: Renin-angiotensin-aldosterone system (RAAS)
- Liver secretes Angiotensinogen to form Angiotensin I
- Angiotensin II is produced with the aid of Angiotensinogen Converting Enzyme (from lung & kidney)
- Decrease of blood pressure/blood volume.
- Juxtaglomerular apparatus secrete renin.
Countercurrent Mechanism
Mechanism that used energy to produce concentration gradient
- After filtrate entered the descending limb, it will become more concentrated since it lost water.
- Ascending limb pumps out Na+, K+, & Cl-, & filtrate becomes hyposmotic.
- In vasa recta, blood removes water by leaving loop of Henle.
Renal Clearance
The ability of kidney to remove substances from the plasma.
Formula: Cx = (UxV)/Px
Glucose regulation
Glucose start to appear in urine when reabsorption reaches tubular capacity (Tm glucose).
Tubular reabsorption increase linearly with filtered load.
Glycosuric threshold is the plasma glucose concentration for given glomerular filtration rate (GFR).