GI Physiology - Hiotology and Cellular Function of Cells in the Small Intestine

Question 1

How long is the average small intestine.

Answer 1

23ft long

Question 2

What are the three structural parts of the small intestine?

Answer 2

The duodenum, jejunum and ileum.

Question 3

What are the four layers of the small intestine?

Answer 3

• Mucosa
• Submucosa
• Muscularis externa
• Adventitia/Serosa

Question 4

Decribe the mucosa.

Answer 4

Contains the epithelium, lamina propria and muscularis mucosae.

Question 5

Describe the submucosa.

Answer 5

Connective tissue layer, which contains blood vessels, lymphatics and the submucosal plexus.

Question 6

Descibe the muscularis externa.

Answer 6

Consists of two smooth muscle layers; the outer longitudinal layer and inner circular layer. The myenteric plexus lies between them.

Question 7

Descibe the adventitia/serosa.

Answer 7

Comprised of loosely arranged fibroblasts and collagen, with the vessels and nerves passing through it.

Question 8

What are the components of the small intestine epithelium?

Answer 8

• Enterocytes
• Goblet cells
• Crypts of Lieberkuhn
• Paneth cells
• Payers patches

Question 9

Describe enterocytes.

Answer 9

Tall columnar cells, which have an absorptive function. They contain brush border enzymes on the surface which have an important digestive function.

Question 10

Describe goblet cells.

Answer 10

Exocrine glands which secrete mucin.

Question 11

Describe the crypts of Lieberkuhn.

Answer 11

The Crypts of Lieberkuhn are glands found in the epithelial lining. They contain numerous cells such as stem cells to produce new cells to replenish the cells lost due to abrasion, as well as enteroendocrine cells to synthesise and secrete hormones.

Question 12

What is the function of paneth cells?

Answer 12

They secrete protective agents to protect from pathogens.

Question 13

What is the funsiton of payers patches?

Answer 13

Peyer’s patches contain mucosal-associated lymphatic tissue (MALT) which house white blood cells and lymphocytes. These cells can produce antibodies to protect the small intestine from infection.

Question 14

What are the four types of enteroendocrine cells?

Answer 14

• I cells
• S cells
• K cells
• enterochromaffin cells

Question 15

What do I cells secrete?

Answer 15

Cholecystokinin (CCK)

Question 16

Cholecystokinin (CCK) is secreted in response to:

Answer 16

The presence of fat in the small intestine.

Question 17

What is the respone to CCK?

Answer 17

CCK stimulates the contraction of the gallbladder (which pushes bile out into the cystic duct) and the release of pancreatic enzymes. Both bile and pancreatic enzymes have a key role in lipid digestion.

Question 18

What do S cells secrete?

Answer 18

Secretin

Question 19

Secretin is secreted in respone to:

Answer 19

The low pH of chyme in the small intestine.

Question 20

What is the repsponse to secretin?

Answer 20

Secretin induces HCO3– secretion from the pancreas and inhibits gastric emptying.

Question 21

What do K cells secrete?

Answer 21

Gastric-Inhibitory Peptide (GIP)

Question 22

Gastric-Inhibitory Peptide (GIP) is secreted in response to:

Answer 22

Chyme entering the small intestine

Question 23

Response to GIP.

Answer 23

GIP has a misleading name as it actually stimulates insulin release, ready to put the newly digested carbohydrates into cells for storage.

Question 24

What do Enterochromaffin cells secrete?

Answer 24

Serotonin

Question 25

Enterochromaffin Cells release serotonin in response to:

Answer 25

The presence of chyme in the small intestine.

Question 26

Function of serotonin from Enterochromaffin cells.

Answer 26

• Acts on the enteric nervous system to activate the cystic fibrosis transmembrane regulators (CFTR).
• This ion channel secretes Cl– ions into the intestinal lumen, with Na+ ions and H2O following. Na+ is required in the lumen for the absorption of a number of nutrients.

Question 27

The common bile duct and pancreatic duct unite to form:

Answer 27

the hepatopancreatic ampulla (also known as the Ampulla of Vater).

Question 28

The major duodenal papilla serves as an important anatomical landmark, as:

Answer 28

it is where the embryonic foregut becomes midgut.

Question 29

The secretions into the small intestine from the hepatopancreatic ampulla are regulated by:

Answer 29

The sphincter of Oddi.

Question 30

nactive enzymes are released from the pancreas as:

Answer 30

zymogens (precursors of the active form) – this prevent the enzymes digesting the pancreas itself.

Question 31

How is Trypsinogen converted to its active form and what is its role?

Answer 31

Trypsinogen is converted to trypsin (active form) in the small intestine by coming into contact with the brush border enzyme enterokinase. Trypsin then converts the remaining inactive proteases to their active form.