Digestion and GI tract

Question 1

What are some of the cells in the gastric gland and what do they secrete?

Answer 1

1. G cells = Gastrin
2. Mucous cells = Mucus and Bicarbonate
3. Parietal cells = Gastric acid (HCl)
4. Chief cells = Pepsinogen and lipases

Question 2

What stimulates secretion of HCl ?

Answer 2

Gastrin, Histamine and neurotransmitters

Question 3

How do parietal cells secrete HCl?

Answer 3

The apical membrane takes K+ ions and releases H+ coming from the breaking down of water. Bicarbonate (HCO3-) is made by reacting OH- (from water) and CO2.
Basolateral membrane releases bicarbonate in blood and intakes Cl- which then is release in stomach lumen.

Question 4

What bacterium causes peptic ulcers?

Answer 4

Helicobacter pylori

Question 5

What are two types of exopeptidases present in villi?

Answer 5

1. Carboxypeptidase (from pancreas)

2. Aminopeptidase (brush border of villi)

Question 6

What are the names of the transporters used for transport of fructose and glucose?

Answer 6

Glucose enters intestinal mucosa with Na+ through SGLUT and fructose by GLUT5. Glucose and fructose are secreted into bloodstream through GLUT2

Question 7

How are lipids transported across intestinal epithelium?

Answer 7

They are covered in bile salts forming micelles which then fuse with pm . The lipids are then covered in proteins forming the chylomicron which is releases by exocytosis into the lacteal and goes to liver and adipose tissue

Question 8

What does the large intestine do?

Answer 8

Absorbs water, electrolytes, vitamin K and B and folic acid

Question 9

What is the hepatic lobule made of?

Answer 9

Irregular hexagon centered around central vein which drains blood in hepatic vein. It is also associated with branches of the hepatic portal vein and hepatic artery , which they all branch inside the lobule (sinusoids). At the sides you also have bile canaliculi which bring bile into bile ductules that run through the liver alongside portal veins.

Question 10

Describe how gastrin helps release of HCl

Answer 10

Gastrin is secreted by G cells when amino acids are detected. It acts as an hormone releasing Histamine which in turns stimulates parietal cells to release HCl

Question 11

What are the 4 layers of the small intestine

Answer 11

1. Mucosa (absorption, secretion,immune system)
2. Submucosa (blood vessels and mucus secretion)
3. Muscularis (peristalsis)
4. Serosa (stops tangling)

Question 12

How is the mucosa subdivided?

Answer 12

1. Epithelium in contact with contents of GI tract
2. Lamina propria: layer of connective tissue containing blood and lymphocytes, macrophages and dendritic cells and vessels for nutrients
3. Muscularis mucosa: smooth muscle

Question 13

Wha do Peyer’s patches contain?

Answer 13

In the lamina propria of mucosa and they contain T cells, B cells and M cells(they actually cover the Peyer’s patch)

Question 14

What is the role of M cells?

Answer 14

Continually sample small samples of antigen using endocytosis from the lumen of GI tract. The antigen is transported to a pocket of lymphoid cells where the B and T cells are

Question 15

What is main antibody class used?

Answer 15

T helper cells activate B cells to convert IgG to IgA

Question 16

What type of movement causes forward movement?

Answer 16

peristalsis

Question 17

How does peristalsis work?

Answer 17

Circular smooth muscles contract behind the bolus and relax at the front causing forward movement

Question 18

What does segmentation do?

Answer 18

Segmentation is the simultaneous contractions of numerous segments and causes the mixing of chyme making sure it is exposed properly to digestive enzymes