6. Digestion

Question 1

Name all the structures (e.g. stomach) involved in digestion and their role.

Answer 1

1. mouth - ingestion and chewing
2. esophagus - swallowing
3. stomach - killing pathogens and protein digestion
4. gall bladder - stores bile
5. liver - secretes bile
6. pancreas - secretes digestive enzymes
7. small intestine - digestion and absorption
8. large intestine - absorption of water
9. anus - egestion of faeces

Question 2

Draw and label the cross sectional structure of the small intestines.

Answer 2

outside to in:

• circular muscle layer
• longitudinal muscle layer
• submucosa
• mucosa
• villi

Question 3

How does food move through the small intestine?

Answer 3

• waves of muscle contraction, called peristalsis, pass along the intestine

Question 4

Explain how circular muscle contraction and longitudinal muscle contraction moves food through the small intestine.

What additional effect do these contractions have?

Answer 4

• contraction of circular muscle behind the food constricts the gut to prevent food from being pushed back towards the mouth
• contraction of longitudinal muscle where the food is located moves it on along the gut
• mixes food with enzymes in the small intestine

Question 5

What is the role of enzymes in digestion?

Answer 5

enzymes digest most macromolecules in food into monomers in the small intestine

Question 6

Give examples of some macromolecules that enzymes digest in the small intestine.

Answer 6

proteins, starch, glycogen, lipids, and nucleic acids

Question 7

Give an example of a macromolecule that enzymes in the small intestine cannot digest.

Answer 7

cellulose

Question 8

Name three types of enzyme the pancreas secretes to digest macromolecules.

Answer 8

• lipase
• endopeptidase
• amylase

Question 9

Where does the pancreas secrete its enzymes?

Answer 9

into the lumen, the top part of the small intestine

Question 10

What is lipase? What does it break down? What are the products of this reaction?

Answer 10

• an enzyme
• lipids
• fatty acids + glycerol

Question 11

What is endopeptidase? What does it break down? What are the products of this reaction?

Answer 11

• an enzyme
• polypeptides
• shorter peptides

Question 12

What is amylase? What does it break down? What are the products of this reaction?

Answer 12

• an enzyme
• starch
• maltose

Question 13

State the two types of molecule in starch.

Answer 13

• amylose

- amylopectin

Question 14

Compare amylose and amylopectin.

Answer 14

• molecules of starch
• polymers of a-glucose
• linked by 1,4 bonds

Question 15

Contrast amylose and amylopectin.

Answer 15

• amylose: 1,4 bonds therefore chains are unbranched

- amylopectin: 1,4 bonds and has some 1,6 bonds that make the molecule branched

Question 16

How does amylase break 1,4 bonds? Comment on the significance of this?

Answer 16

• in chains of four or more glucose monomers

- it can digest amylose into maltose but not glucose

Question 17

What does the specificity of the active site of amylase mean?

Answer 17

amylase can break 1,4 bonds, but cannot break 1,6 bonds in amylopectin

Question 18

What are dextrins?

Answer 18

fragments of the amylopectin molecule containing a 1,6 bond that amylase cannot digest

Question 19

What is digestion of starch completed by?

Answer 19

enzymes in the membranes of microvilli on villus epithelium cells. The enzymes are maltase and dextrinase that digest maltose and dextrins into glucose

Question 20

What else, apart from the enzymes maltase and dextrinase, are in the membranes of microvilli in the small intestine?

Answer 20

protein pumps that cause the absorption of the glucose produced by digesting starch

Question 21

Outline the path glucose takes on its way to being stored, once it is in the blood.

Answer 21

• blood carrying glucose and other products of digestion flows through villus capillaries to venules in the submucosa of the wall of the small intestine
• blood in these venules is carried via the hepatic portal vein to the liver, where excess glucose can be absorbed by liver cells and concerted to glycogen for storage