Download Chapter 3 Digestion and Absorption Chapter Outline I. Taste and

Chapter 3
Digestion and Absorption
Chapter Outline
I. Taste and Smell: The Beginnings of Our Food Experience
A. The chemosenses (Figure 3.1)
Key terms: digestion, absorption, chemosenses, olfactory cells, gustatory cells, common
chemical sense, essential fatty acid, cephalic phase responses
II. The Gastrointestinal Tract. *The GI tract is a tube that can be divided into regions: the mouth,
esophagus, stomach, small intestine, large intestine, and rectum.
A. Organization of the GI tract (Figure 3.2). *Digestion and absorption of the nutrients in
foods occur at various sites along the GI tract.
B. A closer look at gastrointestinal structure
Key terms: gastrointestinal tract, excretion, mucosa, submucosa, circular muscle, longitudinal
muscle, serosa
III. Overview of Digestion: Physical and Chemical Processes. *Digestion involves both physical
processes (e.g., chewing, peristalsis, segmentation) and chemical processes (e.g., the hydrolytic
action of enzymes).
A. The physical movement and breaking up of food
B. The chemical breakdown of food
Key terms: sphincter, chyme, peristalsis, segmentation, enzyme, catalyze, hydrolysis
IV. Overview of Absorption. *Absorption is the movement of molecules across the lining of the
gastrointestinal tract and into circulation.
A. The four roads to nutrient absorption (Figure 3.7). *Four mechanisms are involved in
nutrient absorption: passive diffusion, facilitated diffusion, active transport, and endocytosis.
Key terms: lumen, passive diffusion, concentration gradient, amino acid, facilitated diffusion,
active transport, endocytosis, pinocytosis, pragocytosis
V. Assisting Organs. *The pancreas and gallbladder secrete material into the small intestine to
help with digestion.
A. Salivary glands
B. Liver
C. Gallbladder
D. Pancreas
Key terms: emulsifier, salivary glands, liver, bile, enterohepatic circulation, gallbladder,
cholecystokinin (CCK), pancreas
VI. Putting It All Together: Digestion and Absorption
A. Mouth. *In the mouth, food is mixed with saliva for lubrication. Salivary amylase
begins the digestion of starch.
B. Stomach (Figure 3.11). *Secretions from the stomach lower the pH of stomach
contents and begin the digestion of proteins.
1. Nutrient digestion in the stomach
2. Nutrient absorption in the stomach
C. Small intestine (Figure 3.13). *Most chemical digestion and nutrient absorption occur
in the small intestine.
1. Nutrient digestion in the small intestine
2. Absorptive structures of the small intestine (Figure 3.14)
3. Nutrient absorption in the small intestine
D. Large intestine (Figure 3.15). *Electrolytes and water are absorbed from the large
intestine. Remaining material, waste, is excreted as feces.
1. Digestion in the large intestine
2. Nutrient absorption in the large intestine
Key terms: amylase, lingual lipase, bolus, cecum, esophageal sphincter, esophagus, stomach,
hydrochloric acid, pH, mucus, pepsinogen, gastric lipase, triglycerides, intrinsic factor, pyloric
sphincter, small intestine, duodenum, jejunum, ileum, digestive secretions, secretin, villi,
microvilli, lymph, lacteal, ileocecal valve, large intestine, colon, rectum
VII. Regulation of Gastrointestinal Activity. *Both the nervous system and hormonal system
regulate GI tract processes.
A. Nervous system
B. Hormonal system (Figure 3.17)
Key terms: central nervous system (CNS), enteric nervous system, autonomic nervous system,
gastric inhibitory peptide (GIP)
VIII. Circulation of Nutrients
A. Vascular system (Figure 3.18)
B. Lymphatic system
Key terms: vascular system, lymphatic system
IX. Influences on Digestion and Absorption. *Numerous factors affect GI tract functioning,
including psychological, chemical, and bacterial factors.
A. Psychological influences
B. Chemical influences
C. Bacterial influences
Key terms: gastric acid, acrolein
X. Nutrition and GI Disorders (Figure 3.20). *Problems that occur along the GI tract can affect
digestion and absorption of nutrients. Dietary changes are important in the treatment of GI
disorders.
A. Constipation
B. Diarrhea
C. Diverticulosis
D. Heartburn and gastroesophageal reflux
E. Irritable bowel syndrome
F. Colorectal cancer
G. Gas
H. Ulcers
I. Dyspepsia
Key terms: constipation, diarrhea, gastroesophageal reflux, irritable bowel syndrome, flatus,
ulcer, dyspepsia
What About Bobbie?
In this chapter, Bobbie’s fiber and fluid intakes are listed, as both are important for a healthy GI
tract. The following questions could be asked at the close of the chapter in a small group setting:
1. Is there anything else Bobbie can do to boost her fluid intake?
2. Could Bobbie be at risk for digestive problems? Explain why or why not.
Classroom Activities
ACTIVITY 1: GI TRIVIA
TRIVIA QUESTIONS
This initial phase begins the digestive process.
ANSWER: cephalic phase
Starting in the mouth, name the three pairs of salivary glands.
ANSWER: parotid, sublingual, and submaxillary
What is the salivary enzyme called which breaks down starch into small sugar molecules?
ANSWER: salivary amylase (ptyalin)
The cells at the base of the tongue secrete an enzyme that starts fat digestion. What is this
enzyme?
ANSWER: lingual lipase
For the food to be swallowed, it mixes with saliva and other fluids forming a moistened lump of
food. What is this called?
ANSWER: bolus
As the bolus is swallowed, it passes over a valvelike flap of tissue that closes off the air passages.
What is the flap called?
ANSWER: epiglottis
The bolus enters the stomach through the _________.
ANSWER: esophageal sphincter
Now that the bolus is in the stomach, secretions are produced to aid in digestion. Name five
stomach secretions that aid in the digestive process.
ANSWER: HCL, pepsin, gastric lipase, gastrin, instrinsic factor
The next part in the GI tract is where the digestion of protein, fat, and nearly all carbohydrate is
completed and where most nutrients are absorbed.
ANSWER: small intestine
Identify the order in which the parts of the small intestine appear.
ANSWER: duodenum, jejunum, ileum
What structures help absorb the nutrients in the small intestine?
ANSWER: villi
In discussing the small intestine, what part absorbs 85 percent of the water absorbed by the gut?
ANSWER: jejunum
Moving on to the next part of the GI tract, what valve connects the jejunum to the large
intestine?
ANSWER: ileocecal valve
This is the part of the GI tract that contains a large population of bacteria that digest small
amounts of fiber. Minimal nutrient absorption takes place here.
ANSWER: large intestine
Material moves through the large intestine along a portion extending from the cecum to the
rectum. What is this portion called?
ANSWER: colon
This part of the digestive system is the largest glandular organ in the body. It produces and
secretes bile, detoxifies harmful substances, and helps to metabolize carbohydrates, lipids,
proteins, and micronutrients. Before we discuss this organ, can you tell me what it is called?
ANSWER: liver (hepatic is the term referring to the liver)
This part of the digestive system is pear-shaped and stores bile from the liver. What is this sac
called?
ANSWER: gallbladder
This organ secretes enzymes that help break down nutrients and releases hormones, such as
insulin, which regulate metabolism. What is this organ called?
ANSWER: pancreas