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.
I. Anatomy of the digestive tract
Gastrointestinal (GI) tract: the digestive tract. The principal organs are the stomach and intestines
i. Mouth: chews food
ii. Pharynx: swallowed food passes through it
iii. Digestive system: all the organs and glands associated with the ingestion
and digestion of food
iv. Epiglottis: closes off the airway so no choking occurs when swallowing.
v. Bolos: a portion; the amount of food swallowed at one time
b. Esophagus: during the swallow, the upper esophageal sphincter opens.
c. Stomach: retains the bolus for awhile
i. Chyme: the semiliquid mass of partly digested food expelled by the
stomach into the duodenum.
II. The muscular action of digestion
a. Peristalsis: wavelike muscular contractions of the GI tract that push its contents
b. Segmentation: a periodic squeezing of the intestine at intervals along its length by
its circular muscles
c. Sphincter contractions
i. Sphincter muscles periodically open and close allowing the contents of GI
tract to move along at a controlled pace.
ii. Reflux: a backward flow III. The secretions of digestion
a. Salivary glands: secretes enzyme rich saliva into the mouth and begins the
b. Gastric glands: secrete gastric juice, a mixture of water, enzymes, and
hydrochloric acid, which act in protein digestion.
i. Stomach secretes mucus to protect the acid, enzymes from causing harm
c. Pancreatic juice and intestinal enzymes
i. As food leaves stomach, fats, carbs and protein have begun digestion
IV. The final stage
Stools: waste matter discharged from the colon
I. Anatomy of theAbsorptive system
a. Villi: fingerlike projections from folds of the small intestine
b. Microvilli: tiny, hairlike projections on each cell of every villus that can trap
nutrient particles and transport them into the cells.
c. Crypts: tubular glands that lie between the intestinal villi and secrete intestinal
juices into the small intestine.
d. Goblet cells: cells of the GI tract that secrete mucus.
3.3 The circulatory systems
I. The vascular system
a. Aorta: the large, primary artery that conducts blood from the heart to the bod’s
b. Arteries: vessels that carry blood from the heart to the tissues
c. Capillaries: small vessels that branch from an artery. Exchange of oxygen,
nutrients, and waste takes place across capillary walls
d. Veins: vessels that carry blood to the heart
e. Hepatic portal vein: the vein that collects blood from the GI tract and conducts it
to the liver