Digestion

Question 1

What layers does the stomach have?

Answer 1

• mucosa
• submucosa
• muscularis
• serosa

Question 2

What is the in the mucosa layer of the stomach?

Answer 2

Epithelium, lamina propria and muscularis mucosa

Question 3

What is the in the submucosa layer of the stomach?

Answer 3

Blood vessels

Question 4

What is the in the muscular layer of the stomach?

Answer 4

oblique, circular and longitudinal

Question 5

How do carbohydrates enter the digestive system?

Answer 5

Disaccharides and polysaccharides

Question 6

How are carbohydrates absorbed?

Answer 6

Monosaccharides

Question 7

What are polysaccharides?

Answer 7

These are long chains of monosaccharides. Examples are starch and glycogen. Food examples are oats, legumes and beans.

Question 8

What are disaccharides?

Answer 8

These are two monosaccharides joined. These include maltose, sucrose and lactose. Food examples can be seen in the dairy foods.

Question 9

Give some examples of monosaccharides

Answer 9

Glucose, Fructose, pentose and galactose

Question 10

What is the first enzyme involved in carbohydrate digestion?

Answer 10

Salivary amylase and this breaks down alpha-1,4-glycosid bonds. This enzyme will break done polysaccharides into monosaccharide and disaccharides.

Question 11

What is the function of pancreatic amylase?

Answer 11

This has the same function as salivary amylase.

Question 12

What is the function of disaccharidases?

Answer 12

These are brush-border enzymes that are responsible for converting disaccharides into monosaccharides.
Examples include
- Maltase: breaks down maltose into glucose
- Sucrase: sucrose into glucose and fructose
- Lactase: lactose into glucose and galactose

Question 13

What are the three ways in which monosaccharides can be absorbed?

Answer 13

• passive diffusion (high to low with no energy)
• facilitated diffusion (high to low with carrier protien)
• active transport (low to high with ATP and carrier protein)

Question 14

What are the transporters for glucose?

Answer 14

Sodium dependant and sodium independent

Question 15

Explain how Sodium dependant transporters of glucose work

Answer 15

Sodium binds to a receptor and causes a shape change, allowing glucose to bind. Sodium and glucose are then transported through. They both go into the proximal cell.
Sodium is then pumped out by ATP via the sodium/potassium pump and glucose will diffuse into the interstitum down its concentration gradient.

Question 16

Why can glucose not diffuse through the membrane by itself?

Answer 16

It is a polar molecule

Question 17

Explain how Sodium independent transporters of glucose work

Answer 17

This is facilitated diffusion. Examples include GLUT1, GLUT2, GLUT5.

Question 18

Where does protien digestion start?

Answer 18

Stomach

Question 19

What chemical starts off the process of protien digestion?

Answer 19

Pepsin. Pepsinogen is activated by HCL.

Question 20

What four enzymes are secreted by pancreatic juice and that are involved in protien digestion?

Answer 20

Trypsinogen
Proelastase
Carboxypeptidase
Chymotrypsinogen

Question 21

How is Trypsinogen activated and what affect does this have on the other enzymes?

Answer 21

This is activated by enterokinase on the border of the duodenum. This will then cause the activation of the other zymogens.

Question 22

What do the following break down in protien?
 Trypsinogen
Proelastase
Carboxypeptidase
Chymotrypsinogen

Answer 22

These form small polypeptides and dipeptides.

Question 23

What enzymes complete protein digestion and what are some examples?

Answer 23

• dipeptidases: hydrolyses dipeptides
• aminopeptidases: hydrolyses at amino end
• tripeptidases: acts on tripeptides

Question 24

How are amino acids absorbed?

Answer 24

Amino acids are absorbed via a Sodium cotransporter, in a similar mechanism to the monosaccharides. They are then transported across the basolateral membrane via facilitated diffusion. Di and tripeptides are absorbed via separate H+ dependent cotransporters and once inside the cell are hydrolysed to amino acids.

Question 25

What is the first enzyme involved in fat digestion?

Answer 25

Lingual lipase: this breaks down TAGs into DAGs

Question 26

What happens to lipids in the small intestine?

Answer 26

The remainder of the lipids are digested in the small intestine. Here, bile aids digestion by emulsifying the fat goblets into smaller chunks, called micelles, which have a much larger surface area.
Pancreatic lipase, phospholipase A2 and cholesterol ester hydrolase (3 major enzymes involved in lipid digestion) hydrolyse the micelles, breaking them down into fatty acids, monoglycerides, cholesterol and lysolecthin.

Question 27

What are the three products of lipid digestion?

Answer 27

Lysolecthin, monoglycerides and fatty acids

Question 28

How are lipids absorbed?

Answer 28

The products from digestion are released at the apical membrane and diffuse into the enterocyte. Inside the cell, the products are re-esterified to form the original lipids, triglycerides, cholesterol and phospholipids. The lipids are then packaged inside apoproteins to form a chylomicron. The chylomicrons are too large to enter circulation, so they enter lymphatic system via lacteals.

Question 29

What are the layers of the muslce, inner to outer?

Answer 29

Inner: circular
Outer: longitudinal
CILO

Question 30

What produces intrinsic factor?

Answer 30

Parietal cells

Question 31

What does Sucrase break down?

Answer 31

Sucrose into fructose and glucose

Question 32

What does Maltase break down?

Answer 32

Maltose into glucose

Question 33

What does Lactose break down?

Answer 33

Lactose into glucose and galactose