Download Chapter 3 – Digestion, Absorption, and Transport

Chapter 3 – Digestion, Absorption, and Transport
Learning Objectives
After completing Chapter 3, the student will be able to:
3.1
3.2
3.3
3.4
H3
a.
Explain how foods move through the digestive system, describing the actions of the organs, muscles, and
digestive secretions along the way.
a. List the segments of the digestive tract in order from the mouth to the colon.
b. Explain the mechanical processes of digestion in order of occurrence in the digestive tract.
c. List the five organs and their secretions which assist in the breakdown of food.
d. List the secretions that break down carbohydrates.
e. List the secretions that break down protein.
f. List the secretions that break down fat.
Describe the anatomical details of the intestinal cells that facilitate nutrient absorption.
a.
Explain the anatomy of the intestinal cells and their role in nutrient absorption
Explain how nutrients are routed in the circulatory systems from the GI tract into the body and identify
which nutrients enter the blood directly and which must first enter the lymph.
a.
Explain the means by which the blood and nutrients travel throughout the circulatory system.
b.
Explain the path of fluid movement through the lymphatic system.
Describe how bacteria, hormones, and nerves influence the health and activities of the GI tract.
a. Identify the hormones involved in digestive and absorptive processes.
Outline strategies to prevent or alleviate common GI problems.
Apply the concepts presented in the chapter to explain
Glossary
Chapter Key Terms
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absorption: the uptake of nutrients by the cells of the small intestine for transport into either the blood or
the lymph.
o absorb = suck in
aorta (ay-OR-tuh): the large, primary artery that conducts blood from the heart to the body’s smaller
arteries. arteries: vessels that carry blood from the heart to the tissues.
bolus (BOH-lus): a portion; with respect to food, the amount swallowed at one time.
o bolos = lump
capillaries (CAP-ill-aries): small vessels that branch from an artery. Capillaries connect arteries to veins.
Exchange of oxygen, nutrients, and waste materials takes place across capillary walls.
cholecystokinin (COAL-ee-SIS-toe-KINE-in), or CCK: a hormone produced by cells of the intestinal wall.
Target organ: the gallbladder. Response: release of bile and slowing of GI motility.
chyme (KIME): the semiliquid mass of partly digested food expelled by the stomach into the duodenum.
o chymos = juice
crypts (KRIPTS): tubular glands that lie between the intestinal villi and secrete intestinal juices into the
small intestine.
digestion: the process by which food is broken down into absorbable units.
o digest = take apart
digestive system: all the organs and glands associated with the ingestion and digestion of food.
gastrin: a hormone secreted by cells in the stomach wall. Target organ: the glands of the stomach.
Response: secretion of gastric acid.
gastrointestinal (GI ) tract: the digestive tract. The principal organs are the stomach and intestines.
o gastro = stomach
o intestinalis = intestine
goblet cells: cells of the GI tract (and lungs) that secrete mucus.
hepatic portal vein: the vein that collects blood from the GI tract and conducts it to the liver.
o portal = gateway
hepatic vein: the vein that collects blood from the liver and returns it to the heart.
o hepatic = liver
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homeostasis (HOME-ee-oh-STAY-sis): the maintenance of constant internal conditions (such as blood
chemistry, temperature, and blood pressure) by the body’s control systems. A homeostatic system is
constantly reacting to external forces to maintain limits set by the body’s needs.
o homeo = like, similar
o stasis = staying
hormones: chemical messengers. Hormones are secreted by a variety of glands in response to altered
conditions in the body. Each hormone travels to one or more specific target tissues or organs, where it
elicits a specific response to maintain homeostasis.
human microbiome: the collection of microbes found in or on the human body.
intestinal ischemia (is-KEY-me-ah): a diminished blood flow to the intestines that is characterized by
abdominal pain, forceful bowel movements, and blood in the stool.
lymph (limf ): a clear yellowish fluid that is similar to blood except that it contains no red blood cells or
platelets. Lymph from the GI tract transports fat and fat-soluble vitamins to the bloodstream via lymphatic
vessels.
lymphatic (lim-FAT-ic) system: a loosely organized system of vessels and ducts that convey fluids toward
the heart. The GI part of the lymphatic system carries the products of fat digestion into the bloodstream.
microbes (MY-krobes): microscopically small organisms including bacteria, viruses, fungi, and protozoa;
also called microorganisms.
o mikros = small
microvilli (MY-cro-VILL-ee or MY-cro-VILL-eye): tiny, hairlike projections on each cell of every villus
that can trap nutrient particles and transport them into the cells; singular microvillus.
peristalsis (per-ih-STALL-sis): wavelike muscular contractions of the GI tract that push its contents along.
o peri = around
o stellein = wrap
pH: the unit of measure expressing a substance’s acidity or alkalinity. The lower the pH, the higher the H+
ion concentration and the stronger the acid. A pH above 7 is alkaline, or base (a solution in which OH– ions
predominate)
prebiotics: food components (such as fibers) that are not digested by the human body but are used as food
by the GI bacteria to promote their growth and activity.
probiotics: living microorganisms found in foods and dietary supplements that, when consumed in
sufficient quantities, are beneficial to health.
o pro = for
o bios = life
reflux: a backward flow.
o re = back
o flux = flow
secretin (see-CREET-in): a hormone produced by cells in the duodenum wall. Target organ: the pancreas.
Response: secretion of bicarbonate-rich pancreatic juice.
segmentation (SEG-men-TAY-shun): a periodic squeezing or partitioning of the intestine at intervals
along its length by its circular muscles.
stools: waste matter discharged from the colon; also called feces (FEE-seez).
subclavian (sub-KLAY-vee-an) vein: the vein that provides passageway from the lymphatic system to the
vascular system.
thoracic (thor-ASS-ic) duct: the main lymphatic vessel that collects lymph and drains into the left
subclavian vein.
veins (VANES): vessels that carry blood to the heart.
villi (VILL-ee, VILL-eye): fingerlike projections from the folds of the small intestine; singular villus.
yogurt: milk product that results from the fermentation of lactic acid in milk by Lactobacillus bulgaricus
and Streptococcus thermophilus.
GI Anatomy Terms
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anus (AY-nus): the terminal outlet of the GI tract.
appendix: a narrow blind sac extending from the beginning of the colon that contains bacteria and lymph
cells.
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duodenum (doo-oh-DEEN-um, doo- ODD-num): the top portion of the small intestine (about “12 fingers’
breadth” long in ancient terminology).
o duodecim = twelve
epiglottis (epp-ih-GLOTT-iss): cartilage in the throat that guards the entrance to the trachea and prevents
fluid or food from entering it when a person swallows.
o epi = upon (over)
o glottis = back of tongue
esophageal (ee -SOF-ah-GEE-al) sphincter: a sphincter muscle at the upper or lower end of the
esophagus. The lower esophageal sphincter is also called the cardiac sphincter because of its proximity to
the heart.
esophagus (ee-SOFF-ah-gus): the food pipe; the conduit from the mouth to the stomach.
gallbladder: the organ that stores and concentrates bile. When it receives the signal that fat is present in the
duodenum, the gallbladder contracts and squirts bile through the bile duct into the duodenum.
ileocecal (ill-ee-oh-SEEK-ul) valve: the sphincter separating the small and large intestines.
ileum (ILL-ee-um): the last segment of the small intestine.
jejunum (je-JOO N-um): the first two-fifths of the small intestine beyond the duodenum.
large intestine or colon (COAL-un): the lower portion of intestine that completes the digestive process. Its
segments are the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.
o sigmoid = shaped like the letter S (sigma in Greek)
lumen (LOO -men): the space within a vessel such as the intestine.
mouth: the oral cavity containing the tongue and teeth.
pancreas: a gland that secretes digestive enzymes and juices into the duodenum. (The pancreas also
secretes hormones into the blood that help to maintain glucose homeostasis.)
pharynx (FAIR-inks): the passageway leading from the nose and mouth to the larynx and esophagus,
respectively.
pyloric (pie-LORE-ic) sphincter: the circular muscle that separates the stomach from the small intestine
and regulates the flow of partially digested food into the small intestine; also called pylorus or pyloric
valve.
o pylorus = gatekeeper
rectum: the muscular terminal part of the intestine, extending from the sigmoid colon to the anus.
small intestine: a 10-foot length of small-diameter intestine that is the major site of digestion of food and
absorption of nutrients. Its segments are the duodenum, jejunum, and ileum.
sphincter (SFINK-ter): a circular muscle surrounding, and able to close, a body opening. Sphincters are
found at specific points along the GI tract and regulate the flow of food particles.
o sphincter = band (binder)
stomach: a muscular, elastic, saclike portion of the digestive tract that grinds and churns swallowed food,
mixing it with acid and enzymes to form chyme.
Digestive Enzymes
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-ase (ACE): suffix denoting an enzyme. The root of the word often identifies the compound the enzyme
works on. Examples include:
o carbohydrase (KAR-boe-HIGH-drase), an enzyme that hydrolyzes carbohydrates.
o lipase (LYE-pase), an enzyme that hydrolyzes lipids (fats).
o protease (PRO-tee-ase), an enzyme that hydrolyzes proteins.
digestive enzymes: proteins found in digestive juices that act on food substances, causing them to break
down into simpler compounds.
hydrolysis (high-DROL-ih-sis): a chemical reaction in which one molecule is split into two molecules,
with hydrogen (H) added to one and a hydroxyl group (OH) added to the other (from water, H2O). (The
noun is hydrolysis; the verb is hydrolyze.)
o hydro = water
o lysis = breaking
Digestive Glands and Their Secretions
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bicarbonate: an alkaline compound with the formula HCO3 that is secreted from the pancreas as part of
the pancreatic juice. (Bicarbonate is also produced in all cell fluids from the dissociation of carbonic acid to
help maintain the body’s acid-base balance.)
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bile: an emulsifier that prepares fats and oils for digestion; an exocrine secretion made by the liver, stored
in the gallbladder, and released into the small intestine when needed.
emulsifier (ee-MUL-sih-fire): a substance with both water-soluble and fat-soluble portions that promotes
the mixing of oils and fats in a watery solution.
gastric glands: exocrine glands in the stomach wall that secrete gastric juice into the stomach.
o gastro = stomach
gastric juice: the digestive secretion of the gastric glands of the stomach.
glands: cells or groups of cells that secrete materials for special uses in the body. Glands may be exocrine
(EKS-oh-crin) glands, secreting their materials “out” (into the digestive tract or onto the surface of the
skin), or endocrine (EN-doe-crin) glands, secreting their materials “in” (into the blood).
o exo = outside
o endo = inside
o krine = to separate
hydrochloric acid: an acid composed of hydrogen and chloride atoms (HCl) that is normally produced by
the gastric glands.
liver: the organ that manufactures bile. (The liver’s many other functions are described in Chapter 7.)
mucus (MYOO-kus): a slippery substance secreted by cells of the GI lining (and other body linings) that
protects the cells from exposure to digestive juices (and other destructive agents). The lining of the GI tract
with its coat of mucus is a mucous membrane. (The noun is mucus; the adjective is mucous.)
pancreatic (pank-ree-AT-ic) juice: the exocrine secretion of the pancreas that contains both enzymes for
the digestion of carbohydrate, fat, and protein as well as bicarbonate, a neutralizing agent. The juice flows
from the pancreas into the small intestine through the pancreatic duct. (The pancreas also has an endocrine
function, the secretion of insulin and other hormones.)
saliva: the secretion of the salivary glands. Its principal enzyme begins carbohydrate digestion.
salivary glands: exocrine glands that secrete saliva into the mouth.
Highlight Terms
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acid controllers: medications used to prevent or relieve indigestion by suppressing production of acid in
the stomach; also called H2 blockers. Common brands include Pepcid AC, Tagamet HB, Zantac 75, and
Axid AR.
antacids: medications used to relieve indigestion by neutralizing acid in the stomach. Common brands
include Alka-Seltzer, Maalox, Rolaids, and Tums.
belching: the release of air or gas from the stomach through the mouth.
bloating: uncomfortable abdominal fullness or distention.
celiac disease: an intestinal disorder in which the inability to absorb the protein portion of gluten results in
an immune response that damages intestinal cells, also called celiac sprue or gluten-sensitive enteropathy.
colitis (ko-LYE-tis): inflammation of the colon.
colonic irrigation: the popular, but potentially harmful practice of “washing” the large intestine with a
powerful enema machine; also called colonic hydrotherapy.
constipation: the condition of having infrequent or difficult bowel movements.
defecate (DEF-uh-cate): to move the
bowels and eliminate waste.
o defaecare = to remove dregs
diarrhea: the frequent passage of watery bowel movements.
diverticula (dye-ver-TIC-you-la): sacs or pouches that develop in the weakened areas of the intestinal wall
(like bulges in an inner tube where the tire wall is weak).
o divertir = to turn aside diverticulitis (DYE-ver-tic-you-LYE-tis): infected or inflamed diverticula.
o itis = infection or inflammation
diverticulosis (DYE-ver-tic-you-LOH-sis): the condition of having diverticula. Diverticulosis affects more
than 50 percent of adults in later life.
o osis = condition
enema: solution inserted into the rectum and colon to stimulate a bowel movement and empty the lower
large intestine.
flatulence: passage of excessive amounts of intestinal gas.
gastroesophageal reflux: the backflow of stomach acid into the esophagus, causing damage to the cells of
the esophagus and the sensation of heartburn; commonly known as heartburn or acid indigestion.
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Gastroesophageal reflux disease (GERD) is characterized by symptoms of reflux occurring two or more
times a week.
Heimlich (HIME-lick) maneuver (abdominal thrusts): a technique for dislodging an object from the
trachea of a choking person (see Figure H3-2); named for the physician who developed it.
hemorrhoids (HEM-oh-royds): painful swelling of the veins surrounding the rectum.
indigestion: incomplete or uncomfortable digestion, usually accompanied by pain, nausea, vomiting,
heartburn, intestinal gas, or belching.
o in = not
irritable bowel syndrome: an intestinal disorder of unknown cause. Symptoms include abdominal
discomfort and cramping, diarrhea, constipation, or alternating diarrhea and constipation.
larynx (LAIR-inks): the entryway to the trachea that contains the vocal cords; also called the voice box
(see Figure H3-1).
laxatives: substances that loosen the bowels and thereby prevent or treat constipation.
mineral oil: a purified liquid derived from petroleum and used to treat constipation.
peptic ulcer: a lesion in the mucous membrane of either the stomach (a gastric ulcer) or the duodenum (a
duodenal ulcer).
o peptic = concerning digestion
trachea (TRAKE-ee-uh): the air passageway from the larynx to the lungs; also called the windpipe.
ulcer: a lesion of the skin or mucous membranes characterized by inflammation and damaged tissues. See
also peptic ulcer.
vomiting: expulsion of the contents of the stomach up through the esophagus to the mouth.
Lecture Presentation Outline
Key to instructor resource annotations (shown to the right of or below outline topics):
Website
= Available for download from book companion website: HN = student handout
IM
= Included in this instructor’s manual: CS = case study, WS = worksheet, CA = classroom activity
Introductory/whole chapter resources: Test Bank; IM WS 3-1, 3-2, 3-4, CA 3-1, 3-3
I.
Digestion
A. Digestion – Explain the processes of digestion and absorption and describe the challenges associated with
digestion, including:
1. Preventing interference between breathing and eating
2. Foods must pass through the diaphragm to enter the stomach
3. Digestive material must continue to move forward
4. The correct amount of fluid must be added to food to prevent foods from moving too quickly or slowly
through the gastrointestinal system
5. Enzymes must be able to combine with food to break down products into absorbable fragments
6. The walls of the digestive system must be protected from enzymes that break down food
7. Leftover materials must be voluntarily excreted from the gastrointestinal tract
B. Anatomy of the Digestive Tract – Explain and describe the sections of the gastrointestinal (GI) tract
including (Figure 3-1):
IM CA 3-2
1. Mouth
Website HN 3-4
a. Mastication
b. Pharynx
c. Epiglottis
d. Trachea
e. Bolus
2. Esophagus
3. Stomach
a. Chyme
b. Pyloric sphincter
4. Small Intestine
a. Gallbladder
b. Pancreas
c. Duodenum
d. Jejunum
e. Ileum
5. Large Intestine (Colon) (Figure 3-2)
a. Ileocecal valve
b. Rectum
c. Anus
d. Appendix
C. The Muscular Action of Digestion – Explain how the muscular action of digestion is under autonomic
control; define and explain the following:
IM HN 3-1
1. Peristalsis
2. Stomach action: circular, longitudinal, and diagonal muscles (Figure 3-3)
3. Segmentation
4. Sphincter contractions (Figure 3-4)
a. Reflux
D. The Secretions of Digestion – Describe the secretions involved in digestion, including:
1. Digestive enzymes: catalysts in hydrolysis
2. Saliva from the salivary glands (Figure 3-5)
3. Gastric juice
a. Gastric glands
b. Hydrochloric acid
c. pH (Figure 3-6)
4.
5.
Pancreatic Juice & Intestinal Enzymes – Pancreatic juice: enzymes and bicarbonate
Bile
a. Where is it produced
b. Where it is stored
c. Its action as an emulsifier
E. The Final Stage – Explain the final stages of digestion (Figure 3-7)
1. Energy-yielding nutrients
2. Vitamins, minerals, and water
3. Undigested residues
4. Recycling of usable materials
II. Absorption – Describe and explain the process of absorption including:
A. The types of absorption (Figure 3-8)
1. Simple diffusion
2. Facilitated diffusion
3. Active transport
B. Anatomy of the Absorptive System – Describe the anatomical structures involved in absorption
1. Villi (Figure 3-9)
2. Microvilli
3. Goblet cells
C. A Closer Look at the Intestinal Cells
1. Specialized Cells
2. Food Combining
3. Preparing Nutrients for Transport
a. Water-soluble nutrients and small products of fat digestion
b. Fat-soluble vitamins and larger fats
III. The Circulatory System
Website HN 3-3
A. The Vascular System – Explain and describe the vascular system including: consists of arteries, capillaries,
and veins (Figure 3-10)
1. Arteries
2. Capillaries
3. Veins
4. The hepatic portal vein (Figure 3-11)
5. The hepatic vein
B. The Lymphatic System – Explain the lymphatic system including:
1. Lymph fluid
2. The thoracic duct
3. The subclavian vein
IV.
The Health and Regulation of the GI Tract
A. Gastrointestinal Microbiome
1. Bacteria in the GI tract
2. Probiotics
3. Prebiotics
B. Gastrointestinal Hormones and Nerve Pathways
1. Explain hormones including:
a. Gastrin
b. Secretin
c. Cholecystokinin
2. Describe a negative feedback loop (Figure 3-12)
3. Explain how the pancreas is protected by proenzymes or zymogens
IM HN 3-2
C. The System at Its Best – Describe how:
1. A healthy digestive tract is essential
2. Sleep, physical activity, and state of mind impact gastrointestinal health
3. Balance, moderation, variety, and adequacy of meals are important
V. Highlight: Common Digestive Problems
A. Choking (Figure H3-1)
1. Food becomes lodged in the trachea
2. The larynx cannot make sounds
3. The Heimlich maneuver may need to be used (Figure H3-2)
4. Strategies
a. Take small bites
b. Chew thoroughly
c. Don’t talk or laugh with food in the mouth
d. Don’t eat when breathing hard
B. Vomiting
1.
Body’s adaptive mechanism
2.
Dehydration is a concern
3.
May be self-induced as in eating disorders
C. Diarrhea
1. Characterized by frequent, loose, watery stools
2. Many causes, including certain foods or medications, IBS, colitis, & celiac disease
3. Irritable Bowel Syndrome – Bloating, abdominal discomfort, GI motility disturbances
4. Colitis – Inflammation of the large intestine
5. Celiac Disease – Autoimmune disease causing inflammation of the small intestine
6. Treatment
a. Rest
b. Drink fluids
c. Medical help is needed if it persists
D. Constipation
1. Defecation habits are different among people
2. Many causes are possible
3. Hemorrhoids may be a problem
4. Diverticulosis
5. Diverticulitis (Figure H3-3)
6. Laxatives, enemas, and mineral oil
7. Colonic irrigation
8. Strategies
a. High-fiber diet
b. Increased fluids
c. Exercise regularly
d. Respond quickly to the urge to defecate
e. Food and medicinal aides
E. Belching and Gas
1.
Belching – Strategies
a. Eat slowly
b. Chew thoroughly
c. Relax while eating
2.
Intestinal Gas – Strategies
a. Commonly caused by carbohydrate-rich foods
b. Watch bothersome foods
F. Gastroesophageal Reflux (Figure H3-4)
1. Causes
a. Eating or drinking too much
b. Tight clothing
c. Changes in position
d. Medications and smoking
e. Obesity
f. Sphincter defect
2. Indigestion
3. Treatment and complications
G. Ulcers
1.
Peptic ulcers can be gastric or duodenal
2.
Strategies
a. Take prescribed medicine
b. Avoid caffeine- and alcohol-containing foods
c. Minimize aspirin and ibuprofen use
d. No smoking