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Copyright Pearson Prentice Hall

Biology

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38–2 The Process of

Digestion

38–2 The Process of Digestion

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What are the organs of the digestive

system?


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(The digestive system includes the mouth,

pharynx, esophagus, stomach, small

intestine, and large intestine.

Other structures add secretions to the

digestive system, and aid in digestion.

These include the salivary glands,

pancreas, and liver.)


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The Digestive System

Resources/Movies/vahumani.mov


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Mouth

Salivary

glands

Stomach

Pancreas

Large intestine

Small intestine

Pharynx

Esophagus

Liver

Gallbladder

Rectum

The Digestive System

Resources/Movies/vahumani.mov


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The Mouth

What is the function of the digestive

system?


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The Mouth

1. Function:

convert foods into simpler molecules that

can be absorbed and used by the cells.


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The Mouth

2. Mouth

a.Chewing begins mechanical digestion

(the physical breakdown of large pieces of

food into smaller pieces.)


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The Mouth

(The teeth cut, tear, and crush food into small

fragments.

As the teeth cut and grind the food, salivary glands

secrete saliva, which moistens food and makes it

easier to chew.)


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The Mouth

b. Saliva:

1. helps passage of food

2. begins chemical digestion.

3. contains amylase- enzyme that

breaks chemical bonds in

starches and releases sugars.

4. contains lysozyme- enzyme that fights

infection.


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The Esophagus

3. Esophagus

a. food tube

b. Food is moved along to stomach by

contractions of smooth muscle- peristalsis

c. cardiac sphincter-

closes esophagus after food passed into

stomach.


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The Esophagus

Peristalsis

Esophagus

Bolus

Stomach

Muscles

contracted


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The Stomach

4. Stomach

a. continues mechanical and chemical

digestion.

b. Alternating contractions of 3 smooth

muscle layers churn food.


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The Stomach

5. Chemical Digestion

a. stomach lining has millions of gastric glands that release substances into the stomach.

• 1.Some glands produce mucus, which lubricates and protects the stomach wall.

• 2.Other glands produce hydrochloric acid, which makes the stomach contents very acidic.

• 3.Other glands produce pepsin, an enzyme that digests protein.


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The Stomach

(Pepsin and hydrochloric acid begin protein

digestion.

Pepsin breaks proteins into smaller polypeptide

fragments.

Other enzymes are denatured by stomach acid.)


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The Stomach


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The Stomach

6. Mechanical Digestion

a.Chyme- mixture of fluids and food

(After 1–2 hours, the pyloric valve between the

stomach and small intestine opens and chyme

flows into the small intestine.)


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The Small Intestine

7. Small Intestine

a.chyme is pushed through the pyloric valve into

duodenum.

b. most digestive enzymes enter duodenum

c. Most chemical digestion and absorption of food

occurs

(The duodenum is the first of three parts of the

small intestine)


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The Small Intestine

Accessory Structures of Digestion

Liver

Gallbladder

Duodenum

Bile duct

Pancreas

Pancreatic

duct

To rest of small

intestine


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The Small Intestine

8. Accessory Structures of Digestion

a. pancreas.


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The Small Intestine

(During digestion, the pancreas)

• 1.produces enzymes that break down

carbohydrates, proteins, lipids, and nucleic acids.

• 2. produces sodium bicarbonate, that neutralizes

stomach acid so enzymes can be effective.


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The Small Intestine

b. liver: which produces bile.

1. Bile dissolves/disperses droplets of fat

in fatty foods.

2. enables enzymes to break down

smaller fat molecules.

3. stored in gallbladder.


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Absorption in the Small

Intestine

9. Absorption in the Small Intestine

a.villi: folded surfaces, covered with

fingerlike projections

b. provide enormous surface area for

absorption of nutrients


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The Small Intestine

Small intestine

Circular folds

Villi

Villus

Epithelial

cells

Capillaries

Lymph

vessel

Vein

Artery


Intestine


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(Cell surfaces of villi have more projections called

microvilli.

These provide an enormous surface area for the

absorption of nutrient molecules.

Slow, wavelike contractions of smooth muscles move

the chyme along this surface.)


Intestine


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(Nutrient molecules are absorbed into the cells lining

the small intestine.

Most products of carbohydrate and protein digestion

are absorbed into the capillaries in the villi.

Molecules of undigested fat are absorbed by lymph

vessels.)


Intestine


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The Large Intestine

10. Large Intestine or Colon

a. removes water (from the chyme. )

(Water is absorbed quickly, leaving undigested

materials behind.

Concentrated waste material passes through the

rectum and is eliminated from the body.)


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Digestive System Disorders

(Digestive System Disorders

Stomach acids sometimes damage the organ’s

own lining, producing a hole in the stomach wall

known as a peptic ulcer. Most peptic ulcers are

caused by the bacterium H. pylori.

Other digestive disorders include diarrhea and

constipation.)

- or -

Continue to: Click to Launch:

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38–2

Resources/ch38_sectn02_quiz.qtb

Resources/ch38_sectn02_quiz.qtb

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38–2

Food is moved through the esophagus into the

stomach by

a. air pressure.

b. muscle contractions.

c. gravity.

d. swallowing.

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38–2

A gland that has both endocrine and exocrine

functions is the

a. liver.

b. spleen.

c. pancreas.

d. gallbladder.

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38–2

The enzyme in saliva that begins the digestion

of starch is

a. amylase.

b. pepsin.

c. lysozyme.

d. peptidase.

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38–2

Stomach muscles contract to churn and mix

stomach fluids and food, producing a mixture

known as

a. chyme.

b. amylase.

c. bile.

d. acid.

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38–2

Absorption of vitamins, minerals, and digested

food molecules takes place in the

a. stomach.

b. small intestine.

c. large intestine.

d. duodenum.

END OF SECTION

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