Chapter 41

Animal Nutrition

3 Categories of Animals

Omnivores-Consume plants and animals. Humans

Herbivores-Consume plants

Carnivores-eat other animals

Omnivore

Herbivore

Carnivore

Opportunistic Animals

Some animals are considered to be opportunistic.

They feed on food outside of their normal dietary category.

They do this when their foods are not normally available.

The Diet

It doesn’t matter what is eaten, an adequate diet must contain:

1. Chemical energy for work

2. Organic materials for biosynthesis

3. Essential nutrients organisms can’t make itself.

Energy Storage/Use

Most food consumed goes into ATP production.

Any excess energy is stored as glycogen in muscles and liver.

On top of this, excess energy is stored as fat.

Energy Storage/Use

When energy is needed, glycogen gets metabolized from liver and muscle cells.

When this gets used up, fats get oxidized.

Energy Storage/Use

For the most part, if animals have fuel (carbon skeletons) and a nitrogen source (protein and/or amino acids), they can synthesize much of what they need to survive.

Essential Nutrients

Essential nutrients are what an animal needs to obtain in a pre-synthesized form due to their inability to make them from raw materials.

Essential Nutrients

There are 4 classes of essential nutrients:

1. Essential amino acids

2. Essential fatty acids

3. Vitamins

4. Minerals

1. Amino Acids

Animals require 20 amino acids to make protein and most can synthesize about 1/2 of them if given an adequate amount of nitrogen.

Essential amino acids need to be obtained from the environment.

8 aa’s are essential for adults; a 9th, histidine, is essential for infants.

1. Amino Acids

Meat is an excellent source of protein and is “complete” because it provides aa’s in the proper proportions.

Plants are also a good source of aa’s, but they are said to be “incomplete” because they don’t have the proper balance of aa’s.

2. Fatty Acids

Animals can synthesize most fatty acids they need.

The ones they need to obtain are called essential fatty acids.

Most diets provide sufficient amounts of fatty acids.

3. Vitamins

Organic molecules required in relatively small amounts compared to other nutrients.

13 vitamins are deemed essential.

There are 2 categories:– 1. Water soluble– 2. Fat soluble

3. Vitamins

1. Water soluble vitamins are generally considered to be co-enzymes and function in key metabolic processes.

Excess is excreted in the urine.

3. Vitamins

2. Fat soluble vitamins have a wide variety of functions.– Pigmentation, blood clotting, cell

respiration, etc…– Excess is stored in fatty tissue.

4. Minerals

Minerals are simple inorganic nutrients required in small amounts.

They help the organism perform a wide variety of functions in many key processes:– Growth– Maintenance – Metabolic processes

Food Processing

Can be broken into 4 main stages:

1. Ingestion-taking in food-polymers

2. Digestion-breaking down polymers

3. Absorption-taking up small molecules from digestive compartment

4. Elimination-excretion of undigested material from digestive compartment

Food Processing

Animals prevent digestion of themselves by performing these functions in specialized compartments.

There are two general types:

1. Intracellular digestion

2. Extracellular digestion

1. Intracellular Digestion

Food particles get engulfed by phagocytosis and pinocytosis.

Food vacuoles contain hydrolytic enzymes.

These break down food particles without digesting the cell.

Mammalian Digestion

Food enters the oral cavity. Gets chewed, rolled into a bolus and pushed into the esophagus.

Peristalsis squeezes it into the stomach.

In the stomach, food gets mixed with gastric juice (low pH and enzymes) which breaks down the proteins.

2. Extracellular Digestion

Extracellular digestion occurs within a compartment which is continuous with the outside of an animal’s body.

These cavities allow an animal to eat large amounts of food.

2. Extracellular Digestion

Simple animals have a simple digestive tube. Most digestion occurs in the cells.

Most other animals have a complex digestive tract (alimentary canal).

Food moves in one direction and digestive functions can be broken into different parts.

Pepsinogen-Pepsin Reaction

When food enters the stomach, it is stimulated to secrete pepsinogen and HCl.

The HCl converts pepsinogen into pepsin.

The pepsin breaks down the proteins of the food.

Pepsinogen-Pepsin Reaction

As the food leaves the stomach, the parietal cells stop secreting HCl and the chief cells stop secreting pepsinogen.

Also, autodigestion of the stomach is prevented by the mucous lining of the stomach.

Digestion

Enzymatic churning turns the ingested food into chyme.

The small intestine is very long and is where much of the nutrients are absorbed.

It is very specialized for its function.

Digestion

The first part of the small intestine is called the duodenum.More enzymatic digestion occurs here when enzymes from the liver, pancreas, gall bladder, and glands from the intestine mix.The jejunum and ilieum are specialized in food absorption.

The Small Intestine

The surface area is about the size of a tennis court.

The villi and microvilli are the adaptations that increase the absorption of nutrients.

The Small Intestine

Each vilus is penetrated by blood vessels and a lymph vessel (lacteal).

Nutrients are transported to the blood from here.

The Small Intestine

Active and passive transport occur here.

Active transport allows a higher proportion of nutrients to be absorbed than would passive transport.

Fatty Acid and Glycerol Digestion

Glycerol and fatty acids get absorbed by the epithelium and recombined into fats within cells.They are mixed with cholesterol, coated with protein and form small globules called chylomicrons (emulsified fat).They are transported to the lacteals, converge into larger vessels of the lymph system and ultimately into the veins and heart.

Nutrient Digestion

Other nutrients absorbed by the epithelium converge in the hepatic portal vein that leads to the liver.

Further processing of the nutrients occurs here.

Nutrient processing ensures that the blood contains the proper mix of nutrient molecules for the body.

The Large Intestine

Its main function is to absorb water that enters the canal as digestive juice.

90% of the water that enters the alimentary canal is absorbed by the small and large intestine.

The resulting waste is called feces.

The Large Intestine

The large intestine is rich in flora--most commonly the harmless form of E. coli.

The cecum is where the small and large intestine meet.

The rectum is where the large intestine ends.