|
LECTURE OBJECTIVES
1. Identify the basic nutrients found in our food.
2. Discuss how food is physically and chemically broken down in the digestive
organs.
3. Describe how peristalsis moves food as well as how neural and hormonal
systems regulate this process.
4. Explain the neural and hormonal mechanisms regulating digestion in the
stomach and small intestine.
5. Describe the molecular mechanisms by which sugars, amino acids, and fats
are assimilated in the small intestine.
6. Explain the importance of the liver in digestion.
7. Discuss how assimilated nutrients are then used or stored in the body.
8. Describe the regulatory systems that maintain constant blood glucose
during and following a meal.
9. Elaborate on how ions, bile, and water are recycled by the small intestine.
10. Establish how the stomach, pancreas, and small intestine are in biochemical
balance.
LECTURE OUTLINE
I. INTRODUCTION 
A. Food as a source of energy is central to homeostasis
B. Five general functions of the digestive system
1. Motility
2. Secretion
3. Digestion
4. Absorption (Assimilation)
5. Storage and elimination of solid waste
C. Primary and accessory digestive organs
1. Cross-sectional structure of the gut
2. Basics on how food is processed
a. Carbohydrate, protein, and fat digestion
D. Peristalsis
1. Review of single-unit smooth muscle
a. Myogenic
b. Forms a functional syncytium
2. Slow wave potentials
3. Stretch
4. Other factors influencing gut motility
a. Autonomic nervous system
b. Plexus
c. Hormones
II. MOUTH AND ESOPHAGUS
A. Chewing, wetting of the food, but limited digestion
III. STOMACH
A. Gross anatomy of stomach
B. Functions of the stomach
1. How are these processes regulated?
C. Gastric pit and digestion
1. Structure/function of the gastric pit
a. Mucous cells
b. Partietal cells
1) Hydrochloric acid formation
c. Chief cells
D. Dysfunction in the stomach
1. Ulcers (stress or H. pylori infection)
2. Heartburn
III. PANCREAS AND LIVER: ACCESSORY DIGESTIVE ORGANS
A. Pancreas has a number of digestive functions
1. Secretes enzymes for digestion of DNA/RNA, protein, fats,
and carbohydrates
2. Pancreatic secretions are high in bicarbonate (pH is basic)
B. Liver also plays a role in digestion and absorption
1. Bile salts enhance fat digestion
a. Micelles self assemble
b. Recyclng bile salts (Animation)
2. Other liver functions
3. Liver disease
a. Hepatitis
b. Cirrhosis of the liver
c. Gall stones
C. Overview: Hormonal regulation of digestion
1. Roles of Secretin, Cholecystokinin (CCK) and
Glucose-dependent insulinotropic peptide (GIP;
=Gastric Inhibitory Peptide in text)
IV. SMALL INTESTINE
A. Gross anatomy of small intestine
B. Anatomy of the small intestine
1. Villi and microvilli
a. Epithelial brush border to increase surface area
b. Tight junctions
2. Capillary and lacteal systems
C. Final digestion and assimilation of foods in small intestine
1. Role of pancreatic enzymes in the lumen
2. Roles of fixed enzymes on the brush border
a. Multiple enzymes have a number of functions
b. Final digestion and assimilation of sugars
1) Co-transport with Na+ (Animation)
c. Final digestion and assimilation of peptides
d. Final digestion and assimilation of fatty acids
3. Absorption of iron and vitamins
D. Fate of assimilated foods
1. Summary: Storage and conversion of assimilated nutrients
V. LARGE INTESTINE
A. Gross anatomy
B. Storage of waste and reabsorption of NaCl and water
1. Mechanism of water reabsorption
2. Role of bacteria in the large intestine
3. Dysfunction in the large intestine
a. Constipation and diarrhea
b. Refried beans and gas (=flatus)
1) Unique oligosaccharides
Reading Assignment.
Please read Chapter 22 for the next lecture. Skip pages 728-739--the section
entitled Homeostatic Control of Metabolism.
STUDY
QUESTIONS ON DIGESTION (CHAPTER 21)
BASIC FACTS AND TERMS
- List in order the major organs of the digestive system.
- What are the functions of the stomach? small intestine? large intestine?
See Figure 21-22.
- What is peristalsis? What is the mechanism? How does the autonomic
nervous system affect peristalsis? Review the roles of the parasympathetic
and sympathetic nervous systems in salivation and digestion. Also, review
the physiology of single-unit smooth muscle.
- What is the enteric nervous system and how does it work?
- What is the functional importance of bicarbonate ion in the pancreatic
juice?
- Why is important that our diet contains indigestible material (=fiber)?
- Outline the general enzymatic processes by which basic foods (carbohydrate,
protein, and fats) are digested? Where does each process happen in the
digestive system?
- What is the composition of bile and what is its role in digestion?
How is secreted bile retrieved to the liver for re-use? What waste
products appear in the bile?
- How are hormones involved in the regulation of food digestion? List
these hormones and give their function. See Table 21-1.
- Define and give the physiological significance (how or why it is important) for the following
terms:
- Micelle
- "Housecleaning" contractions
- Peristalsis
- Segmentatal contractions
- Chylomicron
- Lacteal
- SGLT symporter
- GLUT transporter
- GALT
- Parietal cell
- Chief cell
- Enterokinase
- Villi and microvilli
- What is the composition of the digestive juices in the mouth, stomach,
and small intestine? What hormonal and neural factors control secretion
of these digestive juices?
- Digestive enzymes are often secreted in an inactive form. What activates them?
List the enzymes of the stomach. How do they function? List the enzymes of the small
intestine. How do they function?
- What waste products are excreted in the feces?
CONCEPTS
- How are amino acids, dipeptides, and monosaccharides assimilated?
How is the basic mechanism similar between the two? --different?
- How are fatty acids and monoglycerides assimilated? How are they
packaged in the cell and transported to the cells of the body? Contrast
these processes with monosaccharide and amino acid/dipeptide assimilation.
- By what process does the large intestine compact solid waste?
- How are the acids/bases produced by the stomach, pancreas, and small
intestine ultimately balanced so that major shifts in blood pH do not
occur as a result of digestion?
- How is hydrochloric acid formed in the stomach mucosal lining?
How does the body protect against the acidic conditions.
What is an ulcer? What are its causes?
- The digestive system recycles critical substances. How are dietary
iron (Review Figure 16-7) and bile salts absorbed and recycled?
- Read about the many functions of the liver. See Figure 21-10.
REASONING AND PROBLEM SOLVING
- If our saliva lacked amylases, would their absence have a major
effect on carbohydrate digestion in the gut? Defend your answer.
- Na+ co-transport is part of assimilation. What is the source of
the Na+ for this co-transport? It is in the small intestine that most
of the water is absorbed from the chyme. Why here and by what process?
[Hint: Think about the proximal tubule in the nephron]
- Obesity is a growing problem in the United States.
Currently, over one-third of adults have a body mass index over 30%,
which is indicative of high fat deposition. Currently, about nine
drug companies are in clinical trials testing the effectiveness of
their drug for weight reduction. Each of these drugs acts differently
to physiologically reduce body weight in obese people. This question
has two parts: 1) Propose four different physiological mechanisms
by which a drug could limit either a) appetite or b) the processing
of fat that is ingested. Each mechanism has to be specific and agree
with existing knowledge on weight regulation. 2) Drugs can often have
side effects. Choose one of your four mechanisms, and in a sentence
or two discuss one possible side effect of the chosen drug.
Last revised: April 9, 2008 |
