Small Intestine

Question 1

What are the three regions of the small intestine?

Answer 1

Duodenum, jejunum, and ileum.

Question 2

Why is absorption in the small intestine selective?

Answer 2

Occurs via specific transporter proteins by diffusion and secondary active transport.

Question 3

What are the two phases of digestion in the small intestine?

Answer 3

1. Luminal - enzymes secreted by salivary glands / pancreas.
2. Membranous - enzymes attached to epithelial surface of intestinal cells.

Question 4

How is the surface area of the small intestine increased?

Answer 4

Mucosal folds, villi, microvilli

Question 5

What are the four types of intestinal epithelial cell?

Answer 5

Goblet cells, enteroendocrine cells, paneth cells and enterocytes

Question 6

Describe the role of goblet cells.

Answer 6

Secrete mucous for lubrication & protection of mucosa and HCO3- for neutralisation of stomach acid.

Question 7

Describe the role of enteroendocrine cells.

Answer 7

Control digestive function via sensory mechanisms and release of hormones.

Question 8

Describe the role of paneth cells.

Answer 8

Possibly involved in defense against microbial penetration.

Question 9

Describe the role of enterocytes (majority of cells).

Answer 9

Responsible for absorption via transporter proteins.

Question 10

What are the two main types of motility in the small intestine?

Answer 10

Segmentation and peristalsis.

Question 11

What is the role of segmentation in the small intestine?

Answer 11

Segmentation involves localised contractions that mix chyme with digestive juices, aiding digestion and maximising contact with absorptive surfaces.

Question 12

What is the role of peristalsis in the small intestine?

Answer 12

Peristalsis involves wave-like contractions that move chyme forward along the small intestine.

Question 13

How does the SI empty?

Answer 13

Ileo-colic sphincter relaxes - empties into colon.

Question 14

How is small intestine motility regulated?

Answer 14

Controlled by interstitial cells of Cajal = pacemaker cells

Question 15

Describe carbohydrate digestion in the luminal digestive phase.

Answer 15

Stach/amylose (amylase) –> maltose
Amylase digestion continues in small intestine with pancreatic amylase

Question 16

Describe carbohydrate digestion in the membranous digestive phase.

Answer 16

Maltose (maltase) –> glucose + glucose
Sucrose (sucrase) –> glucose + fructose
Lactose (lactase) –> glucose + galactose

Question 17

Describe the process of glucose and galactose absorption.

Answer 17

1. Secondary active transport
2. Na+ & glucose / galactose bind to transporter (SGLT1) on luminal side
3. Conformational change in transporter moves Na+ & glucose / galactose into cell and release them into cytosol
4. High levels of Na+ in digestive juice maintain luminal concentration of Na+ high
5. Concentration of glucose / galactose in cytosol high so diffuse down concentration gradient into blood stream via facilitative transporter GLUT2

Question 18

Describe the process of fructose absorption.

Answer 18

Fructose absorbed down concentration gradient by facilitative transporter (GLUT5) –> diffuse out of cytosol down concentration gradient into blood stream via GLUT2.

Question 19

Where are monosaccharides transferred after absorption into the blood?

Answer 19

Transferred to liver via hepatic portal vein –> stored as glycogen or continue in circulation to be metabolised for energy.

Question 20

Describe lactose intolerance.

Answer 20

1. In absence of lactase, lactose accumulates in gut lumen.
2. Osmotic force –> decreased water absorption (diarrhoea)
3. Once reaches large intestine fermented –> lactic acid decreases pH
4. Gas products cause distention resulting in pain / discomfort

Question 21

How are amino acids transported into enterocytes?

Answer 21

Enterocytes via Na+ co-transport similar to monosaccharides (secondary active transport).

Question 22

How are di/tri-peptides transported into enterocytes?

Answer 22

Via H+ co-transport

Question 23

Draw a table to compare carbohydrate and protein digestion.

Answer 23

Look at notes/chat GPT

Question 24

Describe protein digestion in neonates.

Answer 24

Allowed to absorb intact antibodies:
1. Epithelial cells of intestine are permeable to intact protein
2. Stomach produces negligible amounts of HCl
3. Pancreatic enzyme secretion is low
4. Colostrum contains trypsin inhibitors