Excretion and osmoregulation

Universal needs

All cells need aqueous environment

Problems:

Balance water and solutes= osmoregulation

Nitrogenous waste (from proteins) very toxic

Osmolarity: blood: 300 milliosmoles/L

• Seawater: 1,000 milliosmoles/L

Bioenergetics

Osmoconformers: must live in stable environment

Osmoregulators: use energy to maintain homeostasis

Adaptations

Ocean fish:

Gills get rid of NaCl. Active pump Cl- Na+ follows

Kidneys get rid of other solutes (very little water)

Shark:

keeps high concentration of urea.

Will actually take on water and have to urinate

Must soak shark meat in fresh water before eat it

Adaptations

Fresh water animals:

Constantly gain water and lose salts

Make large amounts of dilute urine

Gills actively transport Cl

Anhydrobiosis: life without water: some critters do this in times of dehydration: go into dormant state

Adaptations

Land animals

shell or fur or skin: waxy coat to decrease water loss by evaporation

Eat and drink water

Circulation

Insects and others: open circulation. Hemolymph baths all cells

Closed circulation: cells bathed in interstitial fluid: controlled indirectly by composition of blood.

Transport epithelium

May face the outside environment directly

OR may line channels and tubes.

Control movement of solutes.

Nitrogenous waste

Ammonia: aquatic animals… flush it away

Very soluble

Very toxic

Urea: land animals, sharks, some fish

100,000 times less toxic

Produced in LIVER from ammonia, requires energy

Uric acid: insects, snails, birds

Paste, insoluble in water

Most energy to produce

Making urine

Filtration of blood

Selective reabsoption of water

Secretion of solute

Taxonomy

Flatworms: flame bulb system: protonephridia: tubules throughout body (filtration happens at the ends)

Earthworms (annelids): metanephredia: have 2: have osmoregulation and excretory functions

Mammalian kidney

Liver: makes urea, from ammonia

Kidney – ureter - bladder – urethra

Kidney: filters blood, excretes solutes, reabsorb water

Creates hyperosmotic urine

The Sodium-Potassium pump represents a common

mechanism in maintenance of water and electrolyte

balance

Shark Rectal Gland and NaCl

SecretionOsmoregulatory Activity in Marine and

Freshwater Fish Gill

Mammalian Kidney Function

The ability to form a concentrated urine is critical to the success of animals in terrestrial habitats

The countercurrent multiplier activity of the loop of Henle in the mammalian nephron creates an osmotic gradient for water reabsorption and production of a concentrated urine

.Regulation of water and electrolyte balance is energetically demanding.

Water Conservation

Terrestrial animals must always be concerned with conserving water

The skin is one of the primary water conservation organs - it keeps the water in and prevents evaporation

The kidney, however, also prevents water loss while still filtering the blood

Regulation of Blood Volume and Concentration

The total volume of blood plasma and interstitial fluid is regulated by the degree of filtration and reabsorption in the kidney

The solute concentration and many nutrient levels are also regulated by the excretory system

The loop of Henle has three distinct regions

Descending limb: thin wall the thin-walled: highly permeable to water. Impermeable to solutes As the filtrate travels down the descending loop, water will flow from the loop into the surrounding medium via osmosis. When the filtrate reaches the hairpin turn

Lower portion of the ascending limb: highly permeable to NaCl

Ascending Limb As it travels up into the less-concentrated regions of the medulla, Na+ and Cl- will passively diffuse across the membrane. As the filtrate continues up the thick portion of the loop of Henle, Na+ and Cl- are actively pumped out of the filtrate into the surrounding medium. This requires energy, but helps to maintain the osmotic concentration gradient in the medulla.1200 mosm/L)

NO ADH Present –

Duct is NOT permeable to water

large volume of urine is produced