Download Chapter 3 – Digestion, Absorption, and Transport

Chapter 3 – Digestion, Absorption, and Transport
Digestion: The process by which food is broken down into absorbable units.
Absorption: The uptake of nutrients by the cells of the small intestine for transport into either
the blood or the lymph.
Peristalsis: Continuous wavelike muscular contractions of the GI tract that push its contents
along.
THE GASTROINTESTINAL (GI) TRACT:
1. MOUTH: Where digestion begins. Chewing (mastication) breaks food into smaller
pieces and mixes it with saliva for lubrication.
2. ESOPHAGUS: The tube that carries food from the mouth to the stomach
3. STOMACH: Converts food to a liquid mass by adding hydrochloric acid, mucus, and
enzymes.
4. SMALL INTESTINE: The site of most chemical digestion and where absorption of
nutrients occurs.
 Duodenum: the top portion of the small intestines
 Jejunum: the middle portion of the small intestines
 Ileum: the last segment of the small intestines
5. LARGE INTESTINE (Colon): Reabsorbs water and minerals; makes some nutrients
with the help of intestinal bacteria (biotin, folate, vitamin B6, vitamin B12, vitamin K);
passes waste to the rectum
6. RECTUM: Stores waste prior to elimination
7. ANUS: Holds rectum closed and opens to allow elimination
Other Digestive Organs:

PANCREAS: Manufactures enzymes to digest all energy-yielding nutrients and
releases bicarbonate to neutralize acid

LIVER: Manufactures bile (an emulsifying agent for

GALLBLADDER: Stores
)
until needed
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DIGESTIVE SECRETIONS:
 Digestive Enzymes: Proteins found in digestive juices that act on food substances,
causing them to break down into simpler compounds.

Saliva: Produced by the salivary glands, it contains water, salts, mucus, and enzymes.

Gastric Juice: A mixture of water, enzymes, and hydrochloric acid produced in the
stomach that starts the digestion of
.

Mucus: Coats the stomach lining and protects it from acid and enzymes

Bile: Produced by the liver and stored in the liver, then sent to the small intestines, it
helps with digestion of fat.
ABSORPTION:
Once nutrients are broken down into simplest form, absorption occurs in the small intestines
within
hours after eating.
Water soluble nutrients (carbohydrate and proteins) absorb directly into the bloodstream, but fat
and fat-soluble vitamins enter the lymphatic system first which eventually carries them into the
bloodstream
Villi / microvilli: small, fingerlike projections on the wall of the small intestines that trap
nutrients and transport them into the cells.
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