Download Digestive System - Biology R: 4(A,C)

Digestion
Section 38-2
Do Now
Discuss the following with your seat partner:
– Remember the last time you sat down to a
dinner of your favorite foods? Recall
everything that you did before you swallowed
your first bite.
1. Why do you cut up your food?
2. What role do your teeth play in eating?
3. Saliva is the fluid that is found in your mouth.
What role do you think it plays in eating?
The Digestive System’s Function
• As food passes through the digestive
system, it gets broken down distributing its
nutrient value to the body
• The function of each organ of the digestive
system is to help convert foods into
simpler molecules that can be absorbed
and used by the cells of the body
The Digestive System Structures
• The digestive system includes:
–
–
–
–
–
–
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
• Major accessory structures that add secretions
to the digestive system include:
– Salivary glands
– Pancreas
– Liver
Figure 38–10 The Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
Mouth & Salivary Glands
• Teeth
– Protected by enamel
– Chewing begins the process of mechanical digestion
= physical breakdown of large pieces of food into
smaller pieces (cutting, tearing, crushing)
• Saliva
– Secreted by salivary glands
– Moisten food making it easier to chew
– Begins the process of chemical digestion = Amylase
(digestive enzyme) chemically breakdown large
starch molecules into smaller sugar molecules
– Lysozyme enzyme fights infection
Pharynx
• Remember from the Respiratory System:
• The pharynx (throat) is a tube in the back
of the mouth that passes both air and food
• Epiglottis (flap of tissue) covers the
trachea to ensure food continue to move
along digestive tract
Esophagus
• Food tube
• Bolus (chewed clump of food) moves along by
contractions of smooth muscle surrounding the
esophagus = peristalsis
• Cardiac sphincter closes esophagus after food
has passed into the stomach preventing
stomach contents from moving back into the
esophagus (heart burn occurs when stomach
acid splashing into the esophagus)
Stomach
• A large muscular sac made of smooth muscle that
mechanically and chemically digests food
• Chemical digestion occurs as gastric glands in the
stomach lining secrete mucus to protect the inner wall
while pepsin and hydrochloric acid break down protein
– Ulcers = a hole in the stomach wall caused by a bacterial
infection that eats away at the lining of the stomach
• Mechanical digestions occurs as the stomach muscles
contract to churn and mix stomach fluids producing a
mixture = chyme
– Pyloric valve opens allowing chyme to flow from the stomach
into the small intestine
Ulcer reading
• Discuss the reading
Duodenum
• More chemical digestion of chyme occurs
in the duodenum (the first part of the small
intestines)
• Chyme mixes with enzymes and digestive
fluids from the pancreas and the liver
(accessory structures)
Pancreas
• A gland that produces hormones that
regulate blood sugar levels
• Produces enzymes that break down
carbohydrates, proteins, lipids, and nucleic
acids
• Produces sodium bicarbonates (a base)
that neutralizes stomach acid
Liver
• Produces bile = “detergent” dissolving fat
droplets
• Bile is stored in the gallbladder
Figure 38–13 The Liver
and the Pancreas
Section 38-2
Liver
Bile duct
Gallbladder
Pancreas
Pancreatic duct
Duodenum
To small intestine
Small Intestine
• Made of three parts: duodenum, jejunum, and
ileum
• Where chemical digestion is completed
• The folded surfaces are covered with villi = small
fingerlike projections that increase the surface
area of the small intestines for greater
absorption of nutrients
• The products of carbohydrate or protein
digestion are absorbed into capillaries in the villi
and microvilli
• Undigested fats are absorbed by lymph vessels
= lacteals
Figure 38–14 The Small
Intestine
Section 38-2
Villus
Small Intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lacteal
Vein
Artery
Activity
• Surface Area Activity
The Digestive Enzymes
Section 38-2
Site
Enzyme
Role in Digestion
Mouth
Salivary amylase
Breaks down starches into
disaccharides
Stomach
Pepsin
Breaks down proteins into large
peptides
Small intestine
(from pancreas)
Amylase
Continues the breakdown of
starch
Trypsin
Continues the breakdown of
protein
Lipase
Breaks down fat
Maltase, sucrase, lactase
Breaks down remaining
disaccharides into
monosaccharides
Peptidase
Breaks down dipeptides into
amino acids.
Small intestine
Large Intestine
• Food entering large intestine is basically
nutrient-free, mainly made of water, cellulose
(fiber), and other indigestible substances
• Removes water left in the chyme by absorbing it
across the large intestine wall
– If water removal is inefficient, diarrhea occurs and can
be dangerous due to the loss of salts and water
• Intestinal bacteria help with digestion
– The appendix is believed to have formerly stored
bacteria to assist with cellulose digestion
• Solid concentrated waste (feces) is excreted
through the rectum