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Copyright Pearson Prentice Hall

Biology

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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:mouth (pharynx)esophagusstomachsmall intestinelarge intestine

Other structures add secretions to the digestive system and aid in digestion. (ie. salivary glands, pancreas, and liver)


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Mouth

Salivary glands

Stomach

Pancreas

Large intestine

Small intestine

Pharynx

Esophagus

Liver

Gallbladder

Rectum

The Digestive System


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The Mouth

What is the function of the digestive system?

To convert foods into simpler molecules- these can be absorbed/used by the cells of

the body


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The Mouth

The Mouth

Chewing begins mechanical digestionmechanical digestion- physical breakdown of food into smaller pieces

Teeth:Teeth: cut, tear, and crush food into small pieces

Salivary glands: Salivary glands: secrete saliva- which moistens food and makes it easier to chew


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The Mouth

Saliva:- helps ease the passage of food- begins the process of chemical digestion- contains amylase

- enzyme that breaks down sugars

Saliva also contains lysozyme- an enzyme that fights infection


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The Esophagus

The Esophagus

Food tube which connects mouth to the stomach

Food is moved along by contractions called peristalsis

- these contractions squeeze food into the stomach


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The Esophagus

Peristalsis

Esophagus

Bolus

Stomach

Muscles contracted

The cardiac sphincter:cardiac sphincter: closes the esophagus after food has passed into the stomach.


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The Stomach

The Stomach

Continues mechanical and chemical digestion

Alternating contractions of three smooth muscle layers churn food

Food can stay in stomach 2-6 hours!


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The Stomach

Chemical Digestion

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

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

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

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

Pepsin and hydrochloric acid begin protein digestion


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The Stomach


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The Stomach

Mechanical Digestion

The stomach churns to produce a mixture known as chyme

Chyme flows into the small intestine through the pyloric valve between the stomach and small intestine.


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The Small Intestine

The Small Intestine

Chyme is pushed into the duodenumduodenum

- the first of three parts of the small intestine- where most digestive enzymes enter the intestine

Important Note:Important Note:Most chemical digestion and absorption of food occurs in 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

Accessory Structures of Digestion

Pancreas:Pancreas:

• produces enzymes that break down all foods

• produces sodium bicarbonate- a base that neutralizes stomach acid


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The Small Intestine

Liver:Liver:

• Produces bile.

• Bile dissolves droplets of fat- this helps enzymes to break down fat

• Bile is stored in the gallbladdergallbladder


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Absorption in the Small Intestine


The small intestine is adapted for the absorption of nutrients.

Villi - cover the inner surface of the small intestine - provide enormous surface area for absorption


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The Small Intestine

Small intestine

Circular folds

Villi

Villus

Epithelial cells

Capillaries

Lymph vesselVein Artery



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The Large Intestine

The Large Intestine

- also known as the colon

- removes water from the chyme.

-water is absorbed quickly- leaving undigested materials behind

(feces)(feces)

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 lining- producing a hole in the stomach wall- known as a peptic ulcer- most ulcers are caused by a bacteria( H. pylori

)

Other digestive disorders include diarrhea and constipation

- or -Continue to: Click to Launch:

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38–2

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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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Documents

stomach slide

process of digestion

protein digestion slide

liver slide

infection slide

body slide

stomach mechanical digestion

stomach chemical digestion