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)
The Wall of the Digestive Tract
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i.Mucous membrane (mucosa)
• Digestive juice-secreting cells
• Mucus-secreting cells (goblet
cells)
ii.Submucosa
• Contains blood vessels and
nerves that help regulate
digestion
iii.Smooth muscle- moves food
along
• Peristalsis- wavelike action to
move food
iv.Serous membrane – encloses the
tube
• 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!
• Peritoneum - Membrane that lines the
abdominopelvic cavity
• Mesentery – thin tissue that holds the small
intestine together
• Greater omentum – fatty covering over
intestines under peritoneum
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4. Organs of the Digestive Tract
A. The Mouth -
i. Incisors for cutting
A. also called oral
cavity, processes
food by: ,
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ii. Cuspids (fangs) for
tearing,
iii. Molars for grinding;
iv. 20 deciduous, 32
permanent (adult)
Ingestion
Mastication (chewing)
Mixing with saliva
Deglutition (swallowing)
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
• Bolus – lump of food in
mouth that is swallowed
• swallowing animation
d. The Stomach - J-shaped pouch that
receives food from esophagus
2 sphincters- control
entrance of food in &
out of stomach
i. Lower esophageal
sphincter (LES)-top
of stomach
ii. Pyloric sphinctercontrols release of
chyme into
duodenum
1. The Teeth
c. The Esophagus
• Muscular tube that leads
to stomach, lies behind
the trachea
• Esophageal hiatus- where
esophagus ends/meets
stomach
– Hiatal hernia – weak
diaphragm allows stomach
to protrude upward
through esophagus
– animation
ii. FUNCTIONS of the stomach
• 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
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f. The Small Intestine - 10 foot long structure,
about 1 inch diameter, begins with duodenum
Functions:
1. Mucus is secreted to
protect from acid
2. Segmentation –
muscle activity that
moves the food.
3. Absorption of
nutrients into
bloodstream
• absorption animation
ii. Villi-tiny fingerlike projections provide surface area for absorption
1. blood vessels for
absorption of nutrients;
2. Lacteals – specialized
capillaries that absorb
fats
f. Large Intestine – 5 feet long, 2.5in
diameter
i.
4. Accessory Organs for Digestion –
food doesn’t go through them
Teniae coli – coiled bands that
give the puckered
appearance.
Cecum, ascending colon(rt),
transverse colon, descending
colon (lf)
ii.
i.
Appendix-lymphoid tissue
attached to cecum
iii. Functions:
i.
ii.
iii.
iv.
Mucus secretion
Water absorption
Storage of undigested waste
Defecation of waste
1. Salivary Glands – 3 pairs release
saliva in mouth to start digestion
• Moistens food
• Facilitates
mastication and
deglutition
• Helps keep teeth
and mouth clean
2. Liver – the body’s largest glandular organ
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Manufactures bile
Store glycogen, convert to
glucose
Modify fats
Destroy old red blood cells
Synthesize urea
Detoxify harmful substances
Bile is the liver’s main
digestive enzyme
• Function of the Liver
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5. Enzymes and the Digestive Process
• 3. Gallbladder –A sac that stores bile for digestion of
fats
• 4. Pancreas - produces enzymes that digest fats,
proteins, carbs and amino acids
Digestion Step by Step
• Structure
Enzymes Released What’s broken down
• Mouth
Amylase
• Stomach
Hydrochloric acid, pepsin Protein
starch
• 1. Enzymes
– A. Enable food molecules to break apart
– B all enzymes are released into common bile duct and
then into duodenum.
2. Water – key factor in process of digestion
– About 7 liters secreted into digestive tract each day
– Hydrolysis – splitting of molecules using water
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
• Small intestine intestinal enzymes
fats, proteins,
Pancreatic enzymes carbohydrates,
Bile from liver
amino acids
• Large intestine no enzymes
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
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.
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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
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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