Digestion and Nutrition
Digestion
 The
mechanical and chemical breakdown
of foods and the absorption of the resulting
nutrients by cells
 Mechanical: large pieces into smaller
pieces
 Chemical: food into simpler chemicals
Alimentary Canal

Muscular tube which extends 8 meters from
mouth to anus
 Structure of wall
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Mucosa: protects the tissues beneath it and carries
on secretion and absorption
Submucosa: vessels nourish surrounding tissues and
carry away absorbed materials
Muscular layer: produces movement of the tube
Serosa: secrete fluid which moistens and lubricates
the tube’s outer surface

Movements of the
tube
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Mixing: Smooth
muscles in small
segments contract
rhythmically
Propelling: wavelike
motion called
peristalsis
Mouth
 Receives
food and begins digestion by
mechanically reducing the size of solid
particles and mixing them with saliva
 Cheeks contain muscles for chewing
 Lips judge temp. and texture of foods
 Tongue is mostly skeletal muscle which
mixes food particles and moves food
underneath the teeth for chewing
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Palate forms the roof of
the oral cavity and closes
opening between the
nasal cavity and the
pharynx
Teeth
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20 deciduous (primary)
teeth
32 permanent (secondary)
teeth
Incisors used to bite off
large pieces of food
Cuspids grasp and tear
food
Bicuspids grind food
particles
Molars grind food particles
Salivary Glands
Amylase – enzyme
splits starch and
glycogen molecules
into disaccharides
 Mucus – binds food
particles and
lubricates during
swallowing

Swallowing Mechanism (p. 394)
1.
2.
3.
Food is chewed and mixed with saliva.
Tongue rolls mixture into a mass, or
bolus, and forces it into the pharynx.
Food stimulates sensory receptors
around the pharyngeal opening triggering
the swallowing reflex.
Peristalsis transports the food in the
esophagus to the stomach.
Esophagus
 Straight,
collapsible tube 25 cm long
 Food passageway from the pharynx to the
stomach
 Contains mucous glands
 Just above meeting stomach, cardiac
sphincter prevents stomach contents from
regurgitating into the esophagus
Acid Reflux
 liquid
content of the stomach regurgitates
into the esophagus
 chronic condition
 reflux occurs as frequently in normal
individuals as in patients with GERD
 Contributing factors:
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the lower esophageal sphincter
hiatal hernias
esophageal contractions
emptying of the stomach
Stomach
 Receives
food from the esophagus
 Mixes food with gastric juices
 Initiates protein digestion
 Carries on limited absorption
 Moves food into small intestine
 Pepsin – most important enzyme
Ulcer
 Open
sore in the skin or mucous
membrane resulting from localized tissue
breakdown
 Gastric ulcers occur in the stomach
 Caused by a bacterium
 Treated with antibiotics
Chyme
 Semifluid
paste of food particles and
gastric juice
 Rate at which stomach empties depends
on the fluidity of the chyme and the type of
food present
 Fatty foods may remain in the stomach
from three to six hours
 As chyme enters the duodenum the
pancreas, liver, and gall bladder add their
secretions
Vomiting

Triggered by irritation or distension in the
stomach or intestines
 Steps of vomiting
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Sensory impulses travel to medulla oblongata
Take a deep breath
Raise soft palate (closes nasal cavity)
Close glottis (closes off trachea)
Relax cardiac sphincter
Contract diaphragm
Contract abdominal wall (increase pressure in
stomach)
Pancreas
 Extends
horizontally across the posterior
abdominal wall in the C-shaped curve of
the duodenum
 Pancreatic juice contains enzymes that
digest carbohydrates, fats, nucleic acids,
and proteins
Liver
 Each
lobe divided into lobules
 Metabolizes carbohydrates, lipids, and
protein
 Stores glycogen, iron, and vitamins A, D,
and B12
 Filters blood
 Detoxifies
 Secretes bile
Hepatitis
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Inflammation of the liver
A: spreads by contact with food or objects
contaminated with virus-containing feces
B: spreads by contact with virus-containing body
fluids, such as blood, saliva, or semen
C: transmitted by blood (razors, needles, mother
to fetus)
D: occurs in people already infected by B;
associated with blood transfusions and
intravenous drug use
E: transmitted by water contaminated with feces
G: sudden, severe hepatitis
Gallbladder
 Pear-shaped
sac located in a depression
on the liver’s interior surface
 Stores bile between meals, reabsorbs
water to concentrate bile, and contracts to
release bile into the small intestine
 Cholesterol in bile may precipitate and
form crystals called gallstones
Small Intestine
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Tubular organ that extends from the pyloric
sphincter to the beginning of the large intestine
Receives secretions from the pancreas and liver
Completes digestion of the nutrients in chyme,
absorbs the products of digestion, and
transports the residues to the large intestine
Duodenum, jejunum, ileum
Mesentery suspends portions and supports the
blood vessels, nerves, and lymphatic vessels
that supply the intestinal wall
Inner wall of intestine lined with tiny projections
of mucous membrane called intestinal villi which
aid in the absorption of digestive products
Lactose Intolerance
 Individual
does not produce sufficient
lactase to adequately digest lactose
 Increased osmotic pressure of the
intestinal contents
 Intestinal bacteria metabolize undigested
sugar, producing organic acids and gases
 Overall result is bloating, intestinal
cramps, and diarrhea
Large Intestine
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Diameter greater than small intestine
Ascends on rt. side, crosses obliquely left,
descends into pelvis
Cecum (vermiform appendix below), ascending
colon, transverse colon, descending colon,
rectum, anus
Anus guarded by two sphincter muscles (one
involuntary, one voluntary)
No digestive function
Secretes mucus to protect intestinal wall
Home to 100 trillion bacteria
Hemorrhoids

Enlarged or inflamed branches of the rectal vein
cause itching, sharp pain, and sometimes bright
red bleeding
 Caused by obesity, pregnancy, constipation,
diarrhea, and liver disease
 Eating more fiber-rich foods and drinking lots of
water can usually prevent or cure hemorrhoids
 Warm soaks in the tub, cold packs, external
creams, surgery
Nutrition
 calorie:
amt. of heat required to raise the
temp. of a gram of water by 1°C
 Carbohydrates supply energy for cellular
processes
 Lipids supply energy for cellular processes
and for building structures such as cell
membranes
 Proteins are polymers of amino acids with
a wide variety of functions
Vitamins
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Organic compounds that are required in small amounts
for normal metabolism
See chart p. 417
A: synthesis of visual pigments; found in liver, fish, whole
milk, butter, eggs, leafy green veggies, yellow and
orange vegetables
C: necessary for collagen production, synthesis of
hormones; found in citrus fruits, tomatoes, potatoes
D: promotes absorption of calcium and phosphorus;
produced in skin exposed to UV light, in milk, egg yolk,
fish liver oils
E: antioxidant; found in oils from cereal seeds, salad oils,
margarine, shortenings, fruits, nuts, and veggies
K: synthesis of prothrombin, which functions in blood
clotting; found in leafy green veggies, egg yolk, pork
liver, soy oil, tomatoes, cauliflower
Minerals (p. 419)
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Calcium – milk; milk products; leafy green
veggies
Phosphorus – meats; cheese; nuts; whole-grain
cereals
Potasssium – avocadoes; dried apricots; meats;
nuts; potatoes; bananas
Sulfur – meats; milk; eggs; legumes
Sodium – table salt; cured ham; sauerkraut,
cheese
Chlorine – same as for sodium
Magnesium – milk; dairy products; legumes
Adequate Diets

P. 421
 BMI (body mass index) found by dividing weight
in kg (kg=2.2 lbs) by your height in meters
squared (one ft=0.3 meters)
 <18.5 underweight; 18.5-24.0 normal; 25-29.9
overweight; >30 obese
 Obesity increases risk of developing
cardiovascular disease, type 2 diabetes mellitus,
certain cancers, osteoarthritis, and other health
problems
 http://www.nutrition.gov/
 http://www.webmd.com/diet/calc-bmi-plus
 http://www.kidshealth.org/teen/food_fitnes
s/dieting/weight_height.html