Osmoregulation

Chapter 44

Homeostasis

Homeostasis – maintaining an internal steady state

Osmoregulation – maintaining a water and solute balance; rates of water uptake and loss must balance

Excretion – removing metabolic wastes

Water Balance

Osmolarity

Osmotic pressure or the total solute concentration (expressed in moles of solute/liter of solution)When two solutes are separated by a selectively permeable membrane they will be: isoosmotic, hyperosmotic or hypoosmotic to each other

When comparing two solutions…

To conform or not to conform…

Osmoconformers – does not actively adjust to its internal osmolarity, ectoderms ex: marine animals that are isoosmotic to the water

Osmoregulators – must control their osmolarity because it is not isoosmotic to its surroundings, endotherms ex: freshwater or terrestrial animals

Marine Animals Need Salt Excretory Glands

Most fish are hypoosmotic to the ocean water-therefore they lose water and gain salt from the oceanTo replenish, they drink seawater then remove the salt through their gills or salt glands (in birds)

Freshwater Animals

Consistently gain water and lose salt

They have no need to drink sea water like the marine animals

Therefore they excrete large amounts of water in dilute urine and take up salt through their gills

What about Salmon??

Salmon survive in both marine and freshwater environments. How??

The Nitrogenous Wastes

N wastes come from the metabolism of protein and nucleic acids

The form of N waste the animal removes is influenced by the environment it lives in

The type of excretion

Ammonia – the end product of protein and nucleic acid breakdown, extremely toxic, aquatic animals excrete ammonia into the water (gets diluted immediately) ex: fish

Urea – ammonia gets transformed into urea in the liver then removed through urine ex: mammals

Uric Acid – ammonia gets transformed into uric acid (a paste) to conserve the most water ex: insects and birds

General Excretory

System Function

Filtration – body fluid is filteredReabsorption – important and usable molecules are reabsorbed to the body fluidSecretion – remaining toxins are actively transported into the tubuleExcretion – wastes are removed

Protonephridria - Planarian

Flame bulb has cilia that bring water and solutes into tubules called protonephridia –

Wastes empty into the external environment through nephridiopores

Metanephridia - Earthworm

Cilia metanephridia filters and reabsorbs wastes empty through nephridiopore

Malpighian Tubules - Grasshopper

Insects secrete wastes and salts from hemolymph into Malpighian tubules Water follows by osmosisSalt and water are reabsorbed across rectum and wastes are eliminated with feces

Mammalian Excretory System

Skin

Liver

Kidney (urinary system)

The Urinary System

Urinary System filters blood (excretion) and aids in osmoregulation

Urinary System composed of the kidney, 2 ureters, bladder and urethra

The KidneyPart of the urinary systemSupplied with blood through the renal artery and removed through the renal vein2 regions – outer renal cortex and inner renal medullaFilters blood through nephrons (about 1 million each) – produce urine that is hyperosmotic to body fluids (water conservation)

The Nephron

Surrounded by capillariesGlomerulus – ball of capillariesBowman’s Capsule – cup-shaped end of tubule, surrounds the glomerulus - FILTRATIONProximal Tube, Loop of Henle, Distal Tube – REABSORPTION AND SECRETIONCollecting Duct - EXCRETION

The Mammalian Excretory System

Regional Functions of Nephron 1. Filtrate2. Reabsorption of water by passive transport3. High water content due to passive and active transport of NaCl4. Reabsorption and secretion to regulate pH, NaCl, and K+5. Active reabsorption of salt, causes reabsorption of water

Urine Concentration through a two solute model

High Salt; Low Water

Low Salt; High Water

Hormonal Control of the Kidney

Negative feedbackHigh salt or low water ADH (anti-diuretic hormone) increases water absorptionReduced BP Renin, angiotensinogen, aldosterone increases arteriole constrictionIncreased BP ANF (atrial natriuretic factor) inhibits release of renin

Hormonal Regulation