Biology 201 Dr. Edwin DeMont St. Francis Xavier University Body Fluid Regulation.

Biology 201Dr. Edwin DeMont

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Body Fluid Regulation

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Osmoregulation

Excretion of is usually associated with the regulation of water and solute (ionic) balance

through a physiological process called osmoregulation.

Osmosis is associated with the movement of water down its concentration gradients.

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Osmosis

Demonstration

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Aquatic animals

Osmoregulation is an important concern for aquatic animals – which are surrounded by water.

Large differences in the process for marine or fresh water animals.

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Osmosis : Marine Animals

WW F F

Water tends to move out of Fish Sugar = ions

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Osmoregulators

Salt water fish

Water tends to move out of Fish

and Ammonia

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Osmosis : Fresh water Fish

FF W W

Water tends to move into Fish Sugar = ions

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Osmoregulators

Fresh water fish

Water tends to move into Fish

and Ammonia

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Invertebrate Excretory Systems

Fresh water flatworm: - Nitrogenous wastes diffuse across body surface

- Flame cells eliminate excess water

Water tends to move into

animal.

Demonstration

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Excretion

Excretion is the elimination of metabolic waste products such as carbon dioxide, water,

nitrogen and ions.

Protein metabolism produces various nitrogenous wastes.

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Nitrogen Metabolism

Amino acid metabolism yields ammonia (NH3)

1. Ammonia or ammonium ions must be highly diluted and rapidly excreted;

2. or be converted to less toxic forms: urea or uric acid.

Interferes with Na+/K+ ATPase transporters of cell membranes by substituting for K+

Ammonium ion can be toxic

Ammonia alters acid-base balance as it binds to protons and becomes ammonium ion (NH4

+)

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Ammonia

Most aquatic animals – including most bony fishes and most invertebrates rely on ammonia excretion, usually via gills.

Most terrestrial animals do not have this option so convert ammonia to urea or uric acid (usually in the

liver) and transport to the excretory organs.

This works because:1. Water outside the animal is plentiful to dilute ammonia

2. Molecule is small and uncharged so readily penetrates most membranes.

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Urea

Urea is the primary nitrogenous waste of most adult amphibians and mammals.

Urea is 10 – 100 times less toxic than ammonia and when it is removed takes two nitrogens per molecule.

Urea is produced from two ammonium ions and a bicarbonate ion using ATP.

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Uric Acid

In other terrestrial animals – insects, birds and most reptiles uric acid is usually the primary

nitrogenous waste.

Production of uric acid is more metabolically expensive to produce than urea but is less

toxic because it is highly insoluble, removes four nitrogens per molecule and is excreted in

a semisolid form.

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Invertebrate Excretory Systems

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Invertebrate Excretory Systems

• Initiated by K+

secretion into lumen

• Fluid more +ve so Cl- attracted

• KCl makes tubule fluid concentrated so water moves in via osmosis.

• Infusion of water generates a bulk flow down the tubule

• Metabolic wastes such as uric acid secreted and transported down system

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Urinary System

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Anatomy: Nephron

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Vertebrate Excretory Systems

Glomerulus – filtration apparatus

Walls of capillaries contain small

perforations that as as filters.

Blood pressure forces fluid through the slits.

The filtrate contains small molecules, ions and the primary nitrogenous wastes either uric acid or urea.

Large proteins and blood cells do not get filtered.

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Physiology: Countercurrent

OsmosisOverview