Spring 2022 _NU204 Study Guide for Exam 1
Chapter 5 Digestion, Absorption, and Metabolism
What is the difference between mechanical and chemical digestion?
 Mechanical Digestion: GI motility. Muscles in the GI wall produce tonic contractions,
which produce continuous movement. Rhythmic waves (periodic muscle contraction and
relaxation) which mix food mass and move it forward called peristalsis.
 Chemical Digestion: GI secretions. Hydrochloric acid, enzymes, mucus,
water/electrolytes, bile all make chemical digestion possible. Breaks down food into
progressively smaller components and the. Releases its nutrients or absorption.
What is a Calorie?
 The amount of energy in food or the amount that is expended in physical actions.
 Kilocalorie: the amount of heat that is necessary to raise 1kg of water 1 degree Celsius.
What is an essential nutrient?
 Essential nutrients are ones that cannot be synthesized by the body and therefore, must be
supplied from foods. (ex. Protein, fat, carbohydrates, vitamins, minerals, water)
What is the function of HCL, mucus, and bile?
 HCL: produce the correct pH necessary for enzyme activity.
 Mucus: lubricates and protects the GI tract tissues and helps mix the food mass
 Bile: emulsifies fat into smaller pieces to assist fat enzymes
Identify all the organs of the GI tract, and the accessory organs, and state the major
functions of each organ.
 Organs of GI tract:
o Mouth: biting and chewing (mastication) starts to break down food.
o Esophagus: connects mouth to stomach. Gastroesophageal constrictor muscle
relaxes to allow the food to pass and then contracts quickly to prevent
regurgitation or reflux.
o Stomach: storage, mixing, controlled emptying. Muscle waves gradually increase
their kneading and mixing action to move the mass of food and secretions toward
the pyloric valve at the distal end of the stomach. The energy (kcaloric) density,
volume, and composition of a meal influence the rate of stomach emptying.
o Small intestine: Secretes many enzymes specific to the breakdown of
carbohydrate, fat, or protein. Acts as a regulatory center that senses the nutrient
content, pH, and osmolarity of its contents. Completes the final stage of chemical
breakdown. Absorbs nutrients.
o Large intestine: main task is the absorption of water. Important for maintaining
water balance. Fiber is not absorbed but helps with bulking of feces.
o Rectum: excretes waste.
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Accessory organs:
o Salivary glands: sensory stimuli influences secretions  chemical digestion
beginning in mouth via salivary secretions (salivary amylase)
o Liver: secretion of bile (important for lipid digestion), storage of nutrients
o Gall bladder: storage and concentration of bile
o Pancreas: Exocrine cells secrete buffers and digestive enzymes. Endocrine cells
secrete hormones.
For all three macronutrients: Lipids, Carbohydrates, Protein
Describe the mechanical and chemical digestion that occurs in the mouth, including the
enzymes involved.
 Mechanical digestion in the mouth consists of mastication.
 Chemical digestion consists of salivary amylase (ptyalin) in the saliva breaking down
starch (complex sugars in foods)
Describe the mechanical and chemical digestion that occurs in the stomach, including the
enzymes involved.
 Mechanical digestion in the stomach occurs via peristaltic contractions of the smooth
muscle (these are periodic and rhythmic). Under sphincter control, the food enters upper
portion of the stomach (fundus). Stomach muscles knead, store, mix, and propel food
mass forward. By the time food mass reaches the lower portion of the stomach (antrum),
it is a semiliquid acid/food mix called chyme. Pyloric valve slowly releases chyme into
the first section of the small intestine (duodenum)
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Chemical digestion: Hydrochloric acid  the hormone gastrin stimulates parietal cells in
the stomach lining to secrete acid. HCl deactivates salivary amylase while activating
pepsinogen. Mucus  secretions protect the stomach lining from the erosive effect of the
acid and also bind and mix the food mass and help move it along. Enzymes 
pepsinogen is secreted by stomach cells and is activated by HCl to become pepsin, a
protein-splitting enzyme
Describe the mechanical and chemical digestion that occurs in the small intestine, including
the enzymes involved.
 Mechanical digestion: Peristaltic waves push food forward. Pendular movements stir
chyme. Segmentation rings chop food mass into lumps. Longitudinal rotation rolls food
in spiral motion, mixing it and exposing it for absorption. Surface villi motions stir and
mix chyme, which also exposes nutrients for absorption.
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Chemical digestion: The pancreas and gland cells of the small intestine secrete digestive
enzymes that chemically break down complex food molecules into simpler ones. These
enzymes include trypsin (for protein digestion), amylase (for carbohydrate digestion),
and lipase (for lipid digestion).
What are the final end products of digestion for each macronutrient.
 End product of carbohydrates: simple sugars (glucose, fructose, galactose AKA
monosaccharides)
 End product of proteins: reduced into single amino acids
 End product of lipids: reduced into fatty acids and glycerides
Describe the four mechanisms of nutrient absorption (facilitated diffusion, etc) from the
small intestine.
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Simple diffusion is the force by which particles move outward in all directions from an area of
greater concentration to an area of lesser concentration. Small materials that do not need the help
of a specific protein channel to move across the mucosal cell wall use this method.
Facilitated diffusion is similar to simple diffusion, but it makes use of a protein channel for the
carrier assisted movement of larger items across the mucosal cell membrane.
Active transport is the force by which particles move against their concentration gradient. Active
trans port mechanisms usually require some sort of carrier to help transport the particles across
the membrane. For example, glucose enters absorbing cells through an active transport
mechanism that involves sodium as a partner.
Pinocytosis is the penetration of larger materials by attaching to the thicker cell membrane and
being engulfed by the cell
Describe the function of the large intestine.
 Mineral absorption, vitamin absorption, waste elimination, and water absorption (main
task!!)
Identify accessory organs to the digestive system and state their secretions and the functions of
the secretions.
 Salivary glands: Salivary amylase (ptyalin) begins the breakdown of starch (complex
sugars in food).
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Liver: Bile is an emulsifying agent and an important part of fat digestion and absorption. It is
produced by the liver and stored in the adjacent gallbladder, and it is ready for use when fat
enters the intestine.
Gallbladder: as above
Pancreas:
o Pancreatic amylase converts starch to maltose and sucrose.
o Trypsin and chymotrypsin split large protein molecules into small peptide
fragments and eventually into single amino acids; carboxypeptidase removes end
amino acids from peptide chains.
o Pancreatic lipase converts fat to glycerides and fatty acids.
Describe the role of the nervous system in the digestive process.
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Specific nerves regulate muscular action along the GI tract. A complex network of nerves in the
GI wall called the intramural nerve plexus extends from the esophagus to the anus. These nerves
do three things: (1) they control muscle tone in the wall; (2) they regulate the rate and intensity of
the alternating muscle contractions; and (3) they coordinate all of the various movements. When
all is well, these finely tuned move ments flow together like those of a great symphony, without
conscience awareness. However, when all is not well, the discord is felt as pain
State the hormonal stimuli for the various secretions of the GI tract.
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The hormone secretin, which is produced by the mucosal glands in the first part of the
intestine, controls the acidity and secretion of enzymes from the pancreas
The hormone cholecystokinin, which is secreted by intestinal mucosal glands when fat is
present, triggers the release of bile from the gallbladder to emulsify fat.
Hydrochloric acid: the hormone gastrin stimulates parietal cells in the stomach lining to
secrete acid