Download Summary for Chapter 3 – Digestion, Absorption, and

Summary for Chapter 3 – Digestion, Absorption, and Transport
As Figure 3-1 shows, food enters the mouth and travels down the esophagus and through the upper and lower
esophageal sphincters to the stomach, then through the pyloric sphincter to the small intestine, on through the
ileocecal valve to the large intestine, past the appendix to the rectum, ending at the anus. The wavelike contractions
of peristalsis and the periodic squeezing of segmentation keep things moving at a reasonable pace. Along the way,
secretions from the salivary glands, stomach, pancreas, liver (via the gallbladder), and small intestine deliver fluids
and digestive enzymes.
Summary of Digestive Secretions and Their Major Actions
Organ or Gland
Target Organ
Secretion
Action
Salivary glands
Mouth
Saliva
Gastric glands
Stomach
Gastric juice
Pancreas
Small intestine
Pancreatic juice
Liver
Gallbladder
Intestinal glands
Gallbladder
Small intestine
Small intestine
Bile
Bile
Intestinal juice
Fluid eases swallowing; salivary enzyme breaks down
carbohydrate.
Fluid mixes with bolus; hydrochloric acid uncoils proteins;
enzymes break down proteins; mucus protects stomach cells.
Bicarbonate neutralizes acidic gastric juices; pancreatic
enzymes break down carbohydrates, fats, and proteins.
Bile stored until needed.
Bile emulsifies fat so enzymes can attack.
Intestinal enzymes break down carbohydrate, fat, and protein
fragments; mucus protects the intestinal wall.
The many folds and villi of the small intestine dramatically increase its surface area, facilitating nutrient absorption.
Nutrients pass through the cells of the villi and enter either the blood (if they are water soluble or small fat fragments)
or the lymph (if they are fat soluble).
Nutrients leaving the digestive system via the blood are routed directly to the liver before being transported to the
body’s cells. Those leaving via the lymphatic system eventually enter the vascular system but bypass the liver at first.
A diverse and abundant bacteria population support GI health. The regulation of GI processes depends on the
coordinated efforts of the hormonal system and the nervous system; together, digestion and absorption transform
foods into nutrients.