Animal nutrition

Goals

1. To understand the function of the digestive system on an organismal level, and in terms of individual organs

2. To become familiar with the structure of the components of the digestive system.

Outline

Introduction

To get food (a collection of organic molecules minerals and water) from the environment to our cells we must:

Ingest it -- take it in from the environment, so that we can

Digest it -- break it down both physically and chemically, so that we can

Absorb it -- move it across a surface from the environment to our interstitial fluid. The part of food that cannot be absorbed is eliminated (egested) and returned to the environment.

Digestion

physical digestion -- increases the surface area of food so that it can be broken down chemically

• chewing
• churning
• emulsification.

chemical digestion

Molecules in food are broken down into their components by hydrolysic enzymes, which break polymers into monomers

some are polymers (made up of repeating subunits, or monomers): polymer Æ monomers

Carbohydrates: polysaccharides Æ monosaccharides

Proteins: polypeptides Æ amino acids

Nucleic acids: nucleic acids Æ nucleotides

Fats aren't

Fats: triacylglyceride Æ glycerol + 3 fatty acids

Once digested, the components of large food molecules can be reassembled into our molecules

Oral cavity

function:

ingestion and digestion (chewing)

structure:

tongue, teeth, etc

secretions:

saliva, which contains salivary amylases and mucin

control:

voluntary

absorption:

none

Pharynx (throat)

function:

swallowing, getting the bolus of food down the esophagus without going through the glottis down the trachea

structure:

epiglottis covers the glottis (see diagrams in book)

secretions:

none

control:

involuntary

absorption:

none

Esophagus

function:

get food to stomach from pharynx

structure:

muscular tube with sphincters at either end

secretions:

none

control:

involuntary peristalsis

absorption:

none

Stomach

function:

storage, DIGESTION -- physical and chemical breakdown of food, sterilizes food

proteins, especially collagens, are hydrolyzed here

structure:

muscular sac with sphincters at either end, glandular tissue in epithelium (see pictures in book)

secretions:

HCl, pepsin (as pepsinogen), mucus

Why doesn't the stomach digest itself?....

absorption:

not much; water, salts, some drugs such as aspirin and alcohol

control:

food in stomach stimulates the secretion of gastrin, which stimulates stomach secretions

Small Intestine

function:

DIGESTION and ABSORPTION

structure:

duodenum, jejunum, ileum : a long muscular tube with sphincters at either end (see pictures in book). Large surface area

Pancreas and liver (w/ gall bladder) release secretions via a duct that empties into the duodenum.

secretions:

liver:

bile, an emulsifier -- stored in gall bladder

pancreas:

sodium bicarbonate

hydrolytic enzymes -- amylases, nucleases, lipases, proteases

absorption:

Most small molecules (monomers) are absorbed into blood stream, some fats taken up by lacteals into lymphatic system. Water and ions are also absorbed here.

control:

3 hormones -- secretin, choleocystokinin (CCK) and gastric inhibitory peptide (GIP) -- regulate digestion by the small intestine

Large intestine

function:

ABSORPTION; chyme becomes feces

structure:

muscular tube with sphincters at either end (see pictures in book)

secretions:

none, usually

absorption:

water, ions and vitamins -- dysfunction can cause diarrhea

A large bacterial flora occupies the colon, manufacturing some vitamins (e.g., K), as well as gases...

Note:

some animals such as cows, horses, rabbits and termites use a microbial community in their guts to break down cellulose, etc.

Vocabulary

click here to go to nutrition vocabulary