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Nutritional Requirements for Animals

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Nutritional Requirements for Animals. for fuel (chemical energy) organic materials used in biosynthesis essential nutrients (substances that animals can’t make for themselves). The 8 essential amino acids must be obtained from food. Essential fatty acids are unsaturated.

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Nutritional Requirements for Animals

  • for fuel (chemical energy)
  • organic materials used in biosynthesis
  • essential nutrients (substances that
  • animals can’t make for themselves)

The 8 essential amino acids must be obtained from food.

  • Essential fatty acids are unsaturated.
  • Vitamins are organic molecules—need small amts
    • There are 13 essential vitamins. B and C are water-soluble. A, D, E, and K are fat-soluble.
  • Minerals are inorganic molecules—need small amts

Food Processing Steps:

1. Ingestion—eating/feeding

2. Digestion—food is broken down mechanically and chemically into small molecules

3. Absorption—small molecules are absorbed

4. Elimination—undigested material is eliminated


Food is processed in specialized compartments.

Intracellular Digestion—After food is engulfed by a cell, food is hydrolyzed by enzymes inside vacuoles

Eg. Sponge

Animal Feeding Mechanisms


Extracellular Digestion— Occurs in a compartment continuous with the outside of the body

Animals without a full digestive tract have a gastrovascular cavity where food is broken down into smaller pieces. Cells can then engulf smaller particles.


Human Digestive System

Alimentary canal = mouth, esophagus, stomach, small intestine, large intestine, rectum, anus

Accessory glands = salivary glands, gall bladder, liver, pancreas

5-10 seconds

2-6 hours

5-6 hours

12-24 hours


Ingestion digestion absorption elimination

Peristalsis is the rhythmic waves of contraction

of smooth muscles that push food along.

Salivary amylase breaks down food in the mouth.

The bolus goes down the esophagus by peristalsis.

(Swallowing is voluntary, but after that, everything’s involuntary.)


The stomach secretes gastric juices (pH 2) that

contain pepsin to digest proteins. HCl (also secreted) converts pepsinogen into pepsin. Pepsin can also



All the stuff


in the

stomach is




The cardiac orifice prevents backflow into the

esophagus. The pyloric sphincter regulates the

flow of chyme into the small intestine.

Small intestine is long! (Small diameter) This is

where most of the digestion & absorption happens.

The duodenum is the first section of the small

intestine—chyme mixes with digestive juices from

the pancreas, liver, gallbladder and intestine.

The liver produces bile that’s stored in the gallbladder.

Bile helps to digest fats.


Macromolecule Digestion

Digestion Animation


Trypsin and chymotrypsin break peptide bonds.

The inactive forms are

secreted from the pancreas


The small intestine has a large surface area for absorption. Villiproject into the lumen. Absorption takes place in the microvilli.


Large intestine—colon, cecum, and rectum

Colon—reabsorbs water

Cecum—ferments ingested material (mostly plants)

Appendix—extension of the cecum—thought to play a minor role in immunity

Rectum—stores feces

Many bacteria live in the human colon. Some produce vitamins that supplement our dietary intake.


Intestinal Adaptations—plants are harder to digest than meat since plant cells have cell walls.


Mutualistic Adaptations—many animals have large populations of microorganisms in their alimentary canals to digest cellulose and other macromolecules. Both the host and the microorganism benefit from the products of this digestion.

Ruminants are herbivores. They have four chambered stomachs to get the most nutrients from their diets.


Regulation of Digestion

Digestion is controlled by the enteric division of the autonomic nervous system. The presence of food stimulates peristalsis in the stomach and intestines.

The endocrine system also controls digestion by regulating energy storage, glucose levels, and appetite.


If energy taken in > needed excess is stored in liver and muscle cells as glycogen. Once glycogen stores are full, additional excess energy is stored in fat in adipose tissue.


The pancreas detects blood glucose levels.

Insulin decreases blood glucose levels.

Glucagon increases blood glucose levels.



Hormonal Control of Digestion

Gastrin stimulates gastric juice secretion when food is present.

Secretin stimulates pancreas to secrete bicarbonate when chyme is in duodenum.

CCK (cholecystokinin) stimulates gallbladder to release bile when aa or fatty acids are in duodenum.


Appetite is regulated by hormones that affect the satiety center of the brain.

Ghrelin triggers feelings of hunger.

Insulin suppresses appetite after eating.

Leptin suppresses appetite when enough body fat is present.

PYY—suppresses appetite after eating (counters ghrelin)


Mutations in the gene for leptin or the leptin receptor have been found to cause obesity in mice.

The mouse on the right lacks a normal leptin receptor.