BIO 104 5/14/96

Organ System - Excretion (Chapter 42)

problems: excess water and waste products from metabolic processing
A human who lives 70 years will consume 45,000 lbs of food and drink 7,250 gallons of fluid. That is enough fluid to fill a tanker truck.

What is eliminated from the body? Water.

Water by % body mass
The majority of organisms consist of water
Animal % Body Mass

mammals 65

frog 78

jellyfish 95

earthworm 80

flower beetle 59

It is important to know that water is the medium to which all chemical reactions occur.

The majority of organisms consist of water
Water by % body mass
Animal	% Body Mass
mammals	65
frog	78
jellyfish	95
earthworm	80
flower beetle	59

Humans can go a fairly long time without food, but we can only go for a few days without water before death occurs.

Two mechanisms of water balance:

osmoconformers
- They have the same solute concentration as their environment. They are (isotonic)
osmoregulators
- They regulate their water balance

Review of Osmosis: If you insert a animal cell into salt water the cell will shrink up. Why?

Osmosis is the diffusion of water over a semipermeable membrane.

For example

It you have two solutions, and they are separated by a semi-permeable membrane, but one of the solutions has a larger concentration of solute (solutes are particles dissolved in water) then the other: osmosis will occur. The solution with the lower amount of solutes will lose water by diffusion to the solution with the higher solute concentration.

The side, or cell, that receives the water is called Hypertonic.

The side that loses the water is called Hypotonic.

Water always goes from a hypotonic to a hypertonic solution. This is why years ago people used salt to preserve food.The salt not only dried the food, but if there were any bacterial cells on the food, they would die by dehydration.

If a cell is inserted into a hypotonic solution, the cell will dehydrate.
If a cell is inserted into a hypertonic solution, the cell will swell, and possibly burst.

What else do we regulate in our bodies?

Food:

Food contains:
1. proteins
2. carbohydrates
3. lipids
4. nucleic acids

Proteins and nucleic acids contain nitrogen.
We need to continually rid our bodies of excess nitrogen.

If we were to take off the amino acid group off of a protein molecule and add a hydrogen atom: we would end up with ammonia, which is extremely toxic.
Our liver, actually the enzymes in the liver, remove the amino group and combine it with carbon to form urea, which is far less toxic than ammonia.
Despite the fact that urea is less toxic it is still essential to dilute it with water for elimination.

Other animals excrete urea in different ways:

Animals can take the nitrogen and make it into a thick paste of uric crystals. Uric acid is a non-toxic nitrogenous waste product.

Ways of getting Water:

drinking
oxidation water

Animals can either gain or lose water in several different ways:

Where we lose/gain water
Lose Gain
1. evaporation from the lungs (breathing out) 1. water in food

2. evaporation from the skin (perspiration) 2. water in drinking

3. water in feces 3. Oxidation water: make water when consuming food

4. water in urine

Where we lose/gain water
Lose	Gain
1. evaporation from the lungs (breathing out)	1. water in food
2. evaporation from the skin (perspiration)	2. water in drinking
3. water in feces	3. Oxidation water: make water when consuming food
4. water in urine

1 gram of glucose yields 0.6 grams of oxidation water
while
1 gram of fat yields 1.1 grams of oxidation water

Though we need to regulate all of this:

osmoconformers
osmoregulators

1. Osmoconformers

isotonic with their environment
marine vertebrates are osmoconformers

*Sharks are the only vertebrates who are osmoconformers*

do not drink water
retain urea in tissues
- a lot of nitrogen retention
- isotonic with sea water

Difference in how fish treat water: See Figure 42.4 Fish are Osmoregulators.

Fish are osmoregulators. Figure 42.4

Fish would be hypertonic in freshwater, but in salt water, the water will diffuse out of the body.
Fresh water fish do not drink water.
- hypotonic medium
- eliminate water through the kidneys
Marine water fish:
- drink water, but pump salt out of the body by the gills
- they do experience osmotic water loss

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