Chapter 19: The Digestive System

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1. Three Main Functions
Chapter 19:
General Structure and Function of the
Digestive System
2. Two Groups of digestive organs
a. Digestive tract-
alimentary canal; tube
from mouth to anus
(trace the pathway on
your diagram sheet)
4. Organs of the Digestive Tract
• Digestion-breakdown of food into
small particles for transport to blood
• Absorption- into bloodstream to take
to cells
• Elimination- removal of waste from
body
2. Two Groups of digestive organs
b. Accessory organs
-organs that assist in
digestion; but not part
of alimentary canal, ie
FOOD DOES NOT GO
THROUGH THEM!
1. The Teeth
A. The Mouth -
Incisors for cutting,
A. also called oral cavity,
processes food by: ,
• Ingestion
• Mastication(chewing)
• Deglutition(swallowing)
Cuspids (fangs) for
tearing,
Molars for grinding;
20 deciduous, 32
permanent (adult)
Bolus – lump of food that
is being swallowed
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b. The Pharynx - Also called the
throat, connects to esophagus
• Soft palate-skin at
back/top of mouth
• Uvula- hangs from soft
palate & covers sinus
when swallowing
• swallowing animation
d. The Stomach - J-shaped pouch that
receives food from esophagus
2 sphincters1. Lower esophageal
sphincter (LES)-top
of stomach
2. 2. Pyloric sphincterleads to small
intestine
• Muscular tube that
leads to stomach, lies
behind the trachea
– Hiatal hernia – weak
diaphragm allows
stomach to protrude
upward through
esophagus
– animation
ii. FUNCTIONS
• 1. Storage of food and liquid
during digestion
• 2. Secrete gastric juice for
digestion
• 3. Secrete mucus while churning
• 4. Rugae – muscular folds allow
for expansion
• 5. Gastric juices – hydrochloric
acid and pepsin to break down
protein
• 6. Chyme – semiliquid mixture
that leaves stomach and goes to
small intestine
e. The Small Intestine - 10 foot long structure,
about 1 inch diameter, begins with duodenum
Function:
Absorption of
nutrients into
bloodstream
c. The Esophagus
• absorption animation
• Mesentery – thin tissue that holds the small
intestine together
• Greater omentum – fatty covering over
intestines under peritoneum
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f. Large Intestine – 5 feet long, 2.5in
diameter
ii. Villi-tiny fingerlike projections provide surface area for absorption
1. blood vessels for
absorption of nutrients;
• Lacteals – specialized
capillaries that absorb
fats
i.
Breaks down
undigested food (using
e-coli bacteria);
ii. Absorbs excess water
4. Accessory Organs for Digestion –
food doesn’t go through them
1. Salivary Glands – 3 pairs release
saliva
a. moistens food and
helps with swallowing
2. Liver – the body’s largest glandular organ
• Manufactures
bile
• Stores glycogen,
• Detoxifies
harmful
substances such
as alcohol &
drugs
• Function of the Liver
• 3. Gallbladder –A sac that stores bile for
digestion of fats
• 4. Pancreas - produces insulin for sugar
absorption, and bicarbonate to neutralize
stomach acid
• Note: all enzymes are released into common
bile duct and then into duodenum
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Digestion Step by Step
5. Enzymes and the Digestive Process
• 1. Enzymes
– A. Enable food molecules to break apart
2. Water – key factor in process of digestion
– About 7 liters secreted into digestive tract each day
• Structure
Enzymes Released What’s broken down
• Mouth
Amylase
• Stomach
Hydrochloric acid, pepsin Protein
starch
• Small intestine intestinal enzymes
fats, proteins,
Pancreatic enzymes carbohydrates,
Bile from liver
amino acids
• Large intestine no enzymes
IV. Absorption – the means by which
nutrients reach the blood
• 1. Fats – absorbed by lacteals into lymphatic
vessels, then digested and returned to blood
• 2. Vitamins and minerals - absorbed directly
into blood from small intestine
8. Hunger and appetite
• Hunger – the need for food, regulated by the
hypothalamus
• Appetite – desire for food, but not necessarily
need; affected by emotions, culture, habits,
memory, etc.
no digestion
V. Control of Digestion – must be
regulated for proper nourishment
• Nervous – by nerves located in intestinal muscle
walls
• Hormonal secretions by digestive organs into blood
aid digestion
9. Eating disorders
• Eating disorders
– Anorexia – chronic loss of appetite due to variety
of issues (drugs, emotions, social)
– Anorexia nervosa – psychological disorder,
obsessive desire to be thin
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10. Effects of Aging
1. taste and smell receptors deteriorate leading to loss
of appetite
2. Decrease in saliva makes swallowing difficult
3. Digestion slows resulting in chronic constipation
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