Water balance and blood pressure Osmoregulation is the maintenance of internal salt and water concentrations in internal fluids despite different concentrations in the external environment Addition of water in the bloodstream = increased blood pressure Less water in the bloodstream = decreased blood pressure

Kidneys Organs for water balance control in vertebrates Eliminate nitrogenous waste Kidneys are the blood’s filtration system Vital for maintaining homeostasis and without kidneys we would only survive a few days

Glomerulus Bowman’s capsule Loop of Henle

Function of nephrons Each kidney contains approx 1 million nephrons! Maintain pH, ion and water balance by excreting excess ions, water, vitamins and hormones in the form of urine Use active transport and passive transport

Antidiuretic Hormone (ADH) Vasopression is an antidiuretic produced by neurosecretory cells in the hypothalamus Secreted when osmoreceptors in the hypothalamus detect a rise in blood solutes (and therefore a decrease in water concentration) Vasopression initiates a feeling of thirst and increases the permeability of the distal tubules in the kidney which helps to re-absorb water into the bloostream

Renin Blood volume decreases with dehydration Pressure sensitive cells detect this this triggers the secretion of renin Renin initiates a chemical reaction that releases aldosterone from the adrenal glands Aldosterone acts on the distal tubules of the nephrons to actively re-absorb sodium ions and increase blood pressure

Nitrogenous waste

Water balance in Amoeba Singled celled organism, relatively simple to maintain water balance Live in aqueous environment with higher concentration of water outside the cell than inside Water permeates the cell membrane via osmosis

Contractile vacuoles accumulate and expel the excess water Waste products are diffused across the membrane

Water balance in fish Freshwater fishMarine (saltwater) fish Tissues hypertonic to surroundingsTissues hypotonic to surroundings Concentration gradient results in a loss of salts and an uptake of water Concentration gradient results in a loss of water and an uptake of salts Fish must counter these changes to maintain homeostasis 1. Does not drink1. Drinks sea water 2. Kidney contains glomeruli and secretes copious amounts of very dilute urine. Tubules actively re-absorb NaCl 2. Minimal urine produced. Kidneys lack glomeruli. Tubules actively secrete MgSO 4 3. Gill membranes permeable to water3. Gill membranes are relatively impermeable to water 4. Gills actively absorb ions. Some ammonia leaves gills at the same time 4. Gills actively secrete sodium from chloride cells; chloride ions follow

 Marine Fresh water 

Water balance in sea birds Water, water everywhere and not a drop to drink Salt glands above the eye excrete a salt solution twice the concentration of sea water out the birds nose Birds with high salt diets have larger salt glands Excrete nitrogenous waste a uric acid

Water balance in reptiles Aquatic reptiles Turtles, crocodiles, alligators etc Lots of water, nitrogenous waste is ammonia or urea

Terrestrial reptiles Lizards, snakes, goannas Need to conserve water Large number of kidney tubules More are active when hydrated and less when dehydrated

Highly convoluted coprodaeum (region between rectum and cloacal opening) to re-absorb water Can also have salt glands to excrete excess salts

Water balance in amphibians Frogs, toads etc Permeable skin allows diffusion of water and salts Produce large quatities of dilute urine and ammonia Actively transport Na and Cl across skin into the body

Biozone Read page 261 “Managing fluid balance on land” and complete the questions of page 262. Due: Monday 5 September