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Processing Food and Nutrition
Lecture Outline
I.
Nutritional styles and adaptations
A. Overview
1. Feeding is the selection, acquisition, and ingestion of food
2. Ingestion is taking food into the digestive cavity
3. Digestion is the process of breaking down food
4. Nutrients are then absorbed into the blood
5. Indigestible food is discharged in a process called egestion or elimination
B. Animals are adapted to their mode of nutrition
1. Herbivores are primary consumers
a) Some herbivores have symbiotic bacteria, which digest the cellulose in
the plant matter
2. Carnivores eat herbivores or other animals
3. Omnivores consume both animal and plant matter
a) Omnivores include suspension feeders that filter food from the water
C. Some invertebrates have a digestive cavity with a single opening
1. Sponges have no digestive systems, but digest trapped food intracellularly
2. Cnidarians and flatworms have gastrovascular cavities with enzymes to
digest food extracellularly
3. Undigested materials are egested through the mouth
D. Most animal digestive systems have two openings
1. Animals with a "tube-within-a-tube" body plan have a digestive tube with
specialized regions
2. The mouth leads to the pharynx, the esophagus, the stomach, the small and
large intestines to the anus
3. Vertebrates have accessory glands that secrete various products into the
digestive tract
II.
The vertebrate digestive system is highly specialized for processing food
A. The wall of the digestive tract has four layers of tissue
1. The mucosa is the inner layer of epithelium and connective tissue
a) The mucosa of the stomach and intestine is greatly folded to increase
the surface area
2. The submucosa is composed primarily of connective tissue, and contains
blood and lymphatic vessels, and nerves
3. The muscular layer consists of two (or three layers) of smooth muscle
4. Below the level of the diaphragm, the outer connective tissue coat of the
digestive tract is the visceral peritoneum
a)
The connective tissue that lines the walls of the abdominal and pelvic
cavities is the parietal peritoneum
b) The visceral peritoneum and parietal peritoneum connect, forming the
peritoneal cavity
B. Food processing begins in the mouth
1. Incisors are adapted for biting, canines for tearing, and premolars and
molars for grinding
2. Enamel covers the tooth, which is primarily composed of dentin
3. Saliva is produced by three pairs of salivary glands, and functions to
moisten food to enable taste and easier swallowing
a) Salivary amylase initiates the enzymatic digestion of starch
C. The pharynx and esophagus conduct food to the stomach
1. The bolus is moved from the mouth into the pharynx and then the
esophagus
2. The epiglottis covers the opening to the airway during swallowing
3. Peristalsis moves the bolus to the stomach
D. Food is mechanically and enzymatically digested in the stomach
1. As the stomach fills with food, the internal folds (rugae) disappear
2. Gastric glands contain parietal cells that secrete HCl and intrinsic factor
(necessary for absorption of vitamin B)
3. Chief cells in the gastric glands produce pepsinogen
a) Pepsinogen is converted to the active form (pepsin) when in contact
with HCl
4. After partial digestion in the stomach, the chyme moves through the
pyloric sphincter to the small intestine
5. Helicobacter pylori is implicated in gastric ulcers
E. Most enzymatic digestion takes place inside the small intestine
1. Most chemical digestion takes place in the duodenum
a) Bile from the liver and enzymes from the pancreas empty into the
duodenum via ducts
2. The jejunum and the ilium comprise the rest of the small intestine
3. The foldings of the small intestine are the villi, which act to increase the
surface for digestion and absorption
a) Microvilli on the cells of the mucosa further increase the surface area
F. The digestive function of the liver includes many processes
1. The liver secretes bile, which mechanically digests and aids in the
emulsification of fats
a) Bile is a solution containing dissolved bile salts, pigments, cholesterol,
salts and lecithin
b) Bile is stored and concentrated in the gallbladder
2. The liver aids in homeostasis by removing or adding nutrients to the blood
3. The liver converts glucose to glycogen, which is stored in the liver
4. The liver converts amino acids to fatty acids and urea
5. The liver stores iron and fat-soluble vitamins
6. The liver detoxifies alcohol, drugs, etc.
G. The pancreas secretes digestive enzymes
1. The pancreas produces trypsin and chymotrypsin, which are proteases
2. Pancreatic lipase degrades neutral fats, pancreatic amylase degrades
various carbohydrates (except cellulose) to disaccharides, and ribonuclease
and deoxyribonuclease split RNA and DNA into free nucleotides
H. Enzymatic digestion occurs as food moves through the digestive tract
1. Enzymes from the liver, pancreas, and the small intestine combine to digest
the nutrients in the chyme
2. Carbohydrates are digested to monosaccharides
a) Amylases hydrolyze glycosidic bonds linking glucose units of
polysaccharides
b) These enzymes cannot split the B-glycosidic bonds of cellulose
3. Proteins are digested to amino acids
a) Different proteolytic enzymes break bonds at different points in the
polypeptide chain
b) Trypsin is activated by enterokinase, which then interacts with
chymotrypsin, carboxypeptidase, and more trypsin
c) Chymotrypsin, trypsin, and pepsin digest proteins
d) Dipeptidases produced by the duodenum split dipeptides
4. Fats are digested to fatty acids and monoacylglycerols
a) Pancreatic lipase digests fat droplets at the outer surface
b) Bile salts emulsify fat droplets
c) Fat digestion is incomplete, and undigested fats may be absorbed
without complete digestion
I. Nerves and hormones regulate digestion
1. Gastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide
(GIP) are hormones produced by endocrine cells of the digestive tract
2. Stretch receptors send neural messages to the medulla, indicating the
presence of food
3. Digestive enzymes typically are not produced unless food is present
J. Absorption takes place mainly through the villi of the small intestine
1. Small molecules, such as water, simple sugars, salts, alcohol, and some
drugs are absorbed through the stomach wall
2. The wall of the villus is composed of a single layer of columnar epithelial
cells
a) Absorbed nutrients pass through the epithelial cell and into a capillary
or lymph vessel by diffusion or active transport
b) Absorbed amino acids and glucose are transported to the liver by the
hepatic portal vein, where the blood is processed
c) Lipids combine with bile salts to form micelles
(1) Micelles are absorbed by diffusion into the epithelial cells
(2) Once in the cell, the micelle releases the fats
(3) The fats are processed by the SER and packaged into droplets, the
chylomicrons
(4) Chylomicrons diffuse into the lacteal, the lymph vessel of the
villus
(5) Chylomicrons are transported by lymph vessels and ultimately
enter the blood stream directly
3. Undigested material passes through the ileocecal valve into the large
intestine
K. The large intestine eliminates waste
1. The diameter of the large intestine is larger than that of the small intestine,
but it is shorter in length than the small intestine
2. The cecum is located at the junction of small and large intestines
3. The vermiform appendix is a blind sac projecting from the cecum
a) Appendicitis is inflammation of the appendix
4. The ascending colon is followed by the transverse, descending and sigmoid
colon, the rectum, and the anus
5. The chyme forms the fecal material by dehydration
6. The intestinal flora produce vitamin K and some B vitamins that can be
absorbed
7. The large intestine eliminates digestive wastes and excretes bile pigments
8. Diarrhea and constipation are irregularities in the speed of passage of fecal
material
III.
Adequate amounts of nutrients are necessary to support metabolic processes
L. All animals need carbohydrates, proteins, lipids, vitamins, and minerals for
nutrition
1. Surplus absorbed nutrients are stored or converted into other forms,
typically by the liver
M. Carbohydrates are a major energy source in the omnivore diet
1. Carbohydrates are not considered essential nutrients, as energy can be
obtained from proteins and fats
2. Complex carbohydrates refer to polysaccharides
3. Fiber is a mixture of cellulose and other indigestible carbohydrates
a) Fiber may decrease the risk of colon cancer
4. Excess monosaccharides are converted to glucose, then glycogen by the
liver
a) Continued overconsumption of carbohydrates results in the
conversion of glucose to lipid
N. Lipids are used as an energy source and to make biological molecules
1. Three polyunsaturated fatty acids are essential; from these building blocks,
other lipids may be synthesized
2.
Most lipids in the diet are triacylglycerols, which may be saturated,
monounsaturated, or polyunsaturated
3. Stored fatty acids may be chemically changed to form acetyl coenzyme A
and utilized in the citric acid cycle
a) This transformation, beta-oxidation, takes place in the liver
b) Ketone bodies are the form that acetyl coenzyme A takes for transport
from the liver
(1) High levels of amino acids cause the blood to become acidic
4. Omega-3 fatty acids decrease LHL levels and play other protective roles in
decreasing the risk of coronary heart disease
5. Trans fatty acids increase LDL cholesterol and lower HDL levels
O. Proteins serve as enzymes and as structural components of cells
1. Essential amino acids are those required to synthesize the remainder
required for nutrition
2. Complete proteins, which contain the appropriate distribution of amino
acids necessary for human nutrition, are primarily those of animal origin
3. Excess amino acids are deaminated by liver cells, which produce ammonia
as a by-product
P. Vitamins are organic compounds essential for normal metabolism
1. Vitamins are necessary in small amounts, typically functioning as
coenzymes
2. Water-soluble vitamins are the B and C vitamins
3. Fat-soluble vitamins are vitamins A, D, E, and K
Q. Minerals are inorganic nutrients
1. Na, Cl, K, Ca, P, Mg, and S are required in amounts of 100 mg or more per
day
2. Other elements such as Fe, Cu, I, F, and Se are trace elements and are
required in amounts of less than 100 mg per day
a) Iron deficiency is one of the most common nutritional deficiencies
R. Antioxidants protect against oxidants
1. Cell processes requiring oxygen produce oxidants
2. Oxidants are highly reactive molecules such as free radicals, peroxides, and
superoxides
3. Oxidants can cause damage to the cell
4. Cells have antioxidants that destroy free radicals and other reactive
molecules
S. Phytochemicals play important roles in maintaining health
1. Chemicals found in fruits and vegetables include the flavonoids, which
function as antioxidants
2. Diets high in phytochemicals may prevent different types of cancers
IV.
Energy metabolism is balanced when energy input equals energy output
T. Metabolic rate is the amount of energy required by the body per unit time
1.
The BMR (basal metabolic rate) is the rate of energy required during
resting, post-digestive conditions
2. The total metabolic rate represents the BMR plus the energy required for
activities
U. Undernutrition can cause serious health problems
1. Severe protein deficiencies may lead to kwashiorkor
V. Obesity is a serious nutritional problem
1. Body mass index (BMI) may be used as a measure of body size, and is
calculated by dividing the square of the width in kilograms by the height
in meters (equivalent is 4.89 x body weight in lb., divided by the square of
the height in ft.)
2. Recent research has identified a gene product, leptin, which produces
weight loss
a) When leptin levels and food intake are low, the hypothalamus
increases secretion of neuropeptide Y, which increases appetite and
slows metabolism
Research and Discussion Topics

Investigate the causes, symptoms, and treatments of colon cancer. Where do most
cancers of the colon occur? How do tests like the occult blood test, or
sigmoidoscopy, detect cancer of the colon?

What are the stages and prognoses of relatively common cancers such as that of
colon cancer, pancreatic cancer, breast cancer, prostatic cancer?

What vitamin or mineral deficiencies might be more common in vegetarians? What
foods might vegetarians try to include in their diets to avoid these deficiencies?

Trace the path of a lipid molecule from ingestion to deposition in an adipose cell.