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