OSMOREGULATION
Definition of Osmolarity & Osmoregulation
Differentiate between ;
Osmoregulation Mechanism
Counter current mechanism and renal clearance
Osmolarity ; Moles of osmotically active particles per liter of solvent (mOsm/L ) Example : 1M Glucose = 1 Osmolar solution
Osmoregulation
Osmosis ; 2 solutions seperated by membrane differ in osmotic pressure or osmolarity ; water flows from hypo- to hyperosmotic solution .
Hypoosmotic ( Solution with less solute and more water) Hyperosmotic ( Solution with greater concentration of solute than water)
Regulates solute concentrations
Balances the gain and loss of water
Control of movement of solutes between internal fluids and external environment
Water and solutes must be maintained within narrow limits- despite strong chalengges from an animal's external environment)
1) osmoconformers vs osmoregulators
2) stenohaline vs euryhaline
Osmoconformers ; Animals whose internal osmolarity changes in relation to the changes in external environment. Able to equilibrate with the environment , living in a stable environment . Examples ; Marine invertebrates (Hagfishes, brine shrimp)
Osmoregulators ; Animals who can actively maintain their internal osmolarity at a particular level regardless of the external salt concentrations in the environment. They expend energy to control water uptake and loss in a hyper osmotic and hypoosmotic environment. Examples ; Marine vertebrates, Fresh water organisms, Human
Stenohaline ; Animal that can handle only 1 type of environment. " Steno " means narrow. Haline means "salts" . Organism usually cannot tolerate a wide flunctuation in the salinity of water
Euryhaline ; Animal that can handle both type of environment, salt water and freshwater. " Eury" means wide . Organisms can tolerate a wide range of salinities; usually live in coastal estuaries, brackish water and tide pools. Examples ; Salmons, Molly, Eels , Green crab
3) Freshwater fish vs Saltwater fish
Freshwater fish ;
Saltwater Fish ;
The gills actively absorb salts
Plenty of sea water enters via mouth -> Active NaCl secretion; osmotic water loss + Water loss via skin -> Kidney ( Active MgSO4 secretion -> MgSO4 excretion, urea; concentrated urine excretion)
Chloride cells in the gill actively extrude chloride ion while passively remove sodium ions
Have a relatively large glomerulus than salt water fish which increases NaCl reabsorption and water excretion
Reduce/absence of glomerulus which reduce water excretion
Little fresh water enters via mouth -> Active NaCl absorptions; osmotic water enters + Water gained via skin -> Kidney (Active NaCl re-absorption) -> Diluted urine excretion
What happen if FAILED to osmoregulate ? EDEMA (Dropsy) ; Condition where failure to osmoregulate which causes freshwater fish to swell due to excessive fluid build-up
Hormones involved in Osmoregulation of Kidney ; ADH
Hypothalamus (influences water excretion and thirst) synthesized Antidiuretic hormone ADH in pituitary gland
Hyperosmotic ECF ( extracellular fluid stimulates the secretion of ADH. ADH increases water reabsorption in the distal tubules and collecting ducts in of the kidney
Regulate by nervous and hormonal control of water and salt reabsorption in the kidneys
Also known as Vasopressin , can be found in most mammals
Direutic , is an agent that increases urine formation
Important effect of ADH ; Conserving body water by reducing the loss of water in the urine
Hormone was named after the ADH is injected (small amount) into an animal and causes antidiuresis/ decreasd in the formation of urine
2 Osmoregulation Mechanism for kidney function
Primary regulatory mechanism : ADH
Secondary regulatory mechanism : RAAS
Loop of Henle
Decending loop
Ascending loop
Permeable to water (Water diffuses from high conc. to low conc which caused the osmolarity of lumen to increase
Permeable to solute, x impermeable to water (Passive diff of ions, sodium & chlorine)
Water flows from lumen (high concentration) to peritubular fluid (low concentration)
Passive diffusion of solutes diffuse from the tubular fluid to the peritubular fluid
Active reabsorption of Na+ (Ascending thick limb of the loop of Henle)
Definition of Counter-current multiplication= utilization of E to generate osmotic gradient
Renal clearance = measurement of kidney's ability to remove substances from the plasma
Cx = Ux V / Px
Kidney failure
Transport maximum (Tm)
water rentention
acidosis
anemia
increase in blood urea
Maximum rate for reabsorption of substances
according to carrier saturation
Glucose regulation
reabsorption reaches tubular capacity>glucose starts appearing in urine
Glucose & Diabetes Mellitus
Reached when all carrier has become saturated
amt of particular substance excreted directly proportional to the amt filtered by glomerular capsule
Euryhaline organism ; Salmon -most are anadromous fish (born in freshwater, travel and live in salt water and return to freshwater to spawn) Speciality : In sea, they stop drinking sea water & discharge salt through their gills . In freshwater, they stop drinking and produce large volumes of diluted urine, gills take up salts.
When aldosterone is present in the blood, the distal renal tubules increase their re-absorption of sodium and the secretion of potassium. With this action, more water is retained in the body
Aldosterone is secreted by the adrenal glands when the level of the potassium in the blood is increased, as well as the self-regulatory action of the kidneys by means of the renin-angiotensin system.
Concentration of Urine
NaCl and urea contribute to the osmolarity of the extracellular fluid (ECF)> reabsorption of water in the kidney and concentrates the urine > water diffuse out from tubule to interstitial fluid / ECF > tubular fluid concentration increases
Osmolarity increases with distance from the cortex and reach the max in innermost spaces of the medula
Loops of Henle and collecting ducts cooperate and responsible for the osmotic gradient that concentrates the urine
Water leaves descending loop of Henle, osmolarity of the lumen fluid increases
Measurement of GFR
Creatinine clearance
Subtances used must be freely filtered at the glomerulus and X reabsorbed/secreted by tubular epithelium after it enters the nephron
Example; inulin and creatinine
Endogenous, nitrogenous by-product of phosphocreatine
Normal value 0.6-1.2mg/dL
blood pressure or blood volume in the afferent arteriole is decreased > JGA secretes an enzyme called renin into the blood stream> Renin converts and inactive plasma protein angiotensinogen to active angiotensin II. This angiotensin II behaves like a hormone and increase blood pressure and blood volume