Osmoregulation and Excretion

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Osmoregulators must expend energy to maintain osmotic gradients. Animals regulate the composition of body fluid that bathes their cells.

Transport epithelia are specialized epithelial cells that regulate solute movement.

They are essential components of osmotic regulation and metabolic waste disposal. They are arranged in complex tubular networks

An example is in salt glands of marine birds, which remove excess sodium chloride from the blood.

Slide 17

How do seabirds eliminate excess salt from their bodies?

Ducts

Nostril

with salt

secretions

Nasal salt

gland

EXPERIMENT

Slide 18

Countercurrent exchange in salt-excreting nasal glands

Salt gland

Secretory

cell

Capillary

Secretory tubule

Transport

epithelium

Direction of

salt movement

Central duct

(a)

Blood

flow

(b)

Secretory

tubule

Artery

Vein

NaCl

NaCl

Salt secretion

Slide 19

An animal’s nitrogenous wastes reflect its phylogeny and habitat

The type and quantity of an animal’s waste products may greatly affect its water balance.

Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids.

Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion.

Slide 20

Nitrogenous wastes

Many reptiles

(including birds),

insects, land snails

Ammonia

Very toxic

Uric acid - not soluble

Urea - less toxic

Most aquatic

animals, including

most bony fishes

Mammals, most

amphibians, sharks,

some bony fishes

Nitrogenous

bases

Amino

acids

Proteins

Nucleic acids

Amino groups

Slide 21

Animals Excrete Different Forms of Nitrogenous Wastes

Ammonia - needs lots of water. Animals release ammonia across whole body surface or through gills / aquatic animals.

Urea - The liver of mammals and most adult amphibians converts ammonia to less toxic urea. The circulatory system carries urea to kidneys, where it is excreted. Conversion of ammonia to urea is energetically expensive; uses less water than ammonia.

Slide 22

Nitrogenous Wastes …

Uric Acid - Insects, land snails, and many reptiles, including birds, mainly excrete uric acid. Uric acid is largely insoluble in water; can be secreted as a paste with little water loss. Uric acid is more energetically expensive to produce than urea.