Ganong 24e chapter 25 - Overview of GIT (1)

Question 1

Is saliva more alkaline or more acidic than plasma? Why is this useful?

Answer 1

Saliva is more alkaline than plasma. This helps to neutralize any gastric acid reflux in the oesophagus.

Question 2

Name 4 components of saliva and briefly explain their usefulness.

Answer 2

Amylase - digests starch.
IgA and lysozyme - kills bacteria
Mucin - lubricates the bolus

Question 3

Name two secretory cells of the gastric wall glands, and state what they secrete.

Answer 3

Chief cells - Pepsinogen and Gastric lipase

Parietal cells - Hydrochloric acid and Intrinsic Factor

Question 4

What is Gastrin? Where does it come from?

Answer 4

Gastrin is a hormone produced by G cells in the antrum of the stomach. Gastrin stimulates Parietal cells to secrete their secretions (intrinsic factor and HCl). Gastrin also stimulates other cells of the stomach, and stimulates growth of the mucosa of the stomach and intestines.

Question 5

Name three ways that Parietal cells can be stimulated to start secreting.

Answer 5

Gastrin (from G-cells), Histamine (from neighbouring enterochromaffin-like cells), and ACh (from enteric nerve endings and the Vagus nerve). All three bind to specific receptors on the basolateral membrane of the Parietal cell.

Question 6

Name three different cell types of the pancreas and explain what they secrete.

Answer 6

Exocrine cells - secrete zymogens.
Endocrine cells - secete insulin + glucagon.
Duct cells - secrete bicarbonate.

Question 7

What is the approximate pH of the stomach? What is the approximate pH of the jejunum?

Answer 7

Stomach - approx 2-3.

Jejunum - approx 6-7.

Question 8

Name the principle function of secretin.

Answer 8

Stimulates pancreatic duct cells to secrete bicarbonate.

Question 9

What is in bile?

Answer 9

Bile salts, Bile pigments, Cholesterol, Inorganic salts, Fatty acids. But 97% of bile is just water.

Question 10

What is the relationship between the terms “bile salts” and “bile acids” ?

Answer 10

Bile acids are conjugated to glycine or taurine in the liver to form bile salts.

Question 11

What does it mean when you say that bile salts are “amphipathic”?

Answer 11

This means that they have both hydrophilic and hydrophobic domains, and they form micelles.

Question 12

Is bile acidic or alkaline?

Answer 12

Alkaline

Question 13

How much fluid is produced by gastric secretions per day?

Answer 13

2.5L

Question 14

How much fluid is produced by endogenous secretions of the entire GIT per day?

Answer 14

About 7L. Pretty much entirely reabsorbed.

Question 15

How does the colon promote water reabsorption?

Answer 15

It pumps sodium across the apical membrane into the epithelial cells, using a transporter called ENaC (epithelial sodium channel), and water follows by osmosis.

Question 16

Name three principle actions of Cholecystokinin (think about its name!)

Answer 16

1. Stimulates pancreatic enzyme secretion.
2. Stimulates contraction of the gall bladder.
3. Stimulates relaxation of the sphincter of Oddi, to allow bile and pancreatic juice to flow into the duodenum.

Question 17

How do the products of digestion affect CCK?

Answer 17

CCK secretion is increased by the presence of the products of digestion in the small intestine. As the products move away, and as the CCK-releasing peptides are degraded, CCK secretion decreases.

Question 18

Which cells secrete CCK?

Answer 18

I cells in the upper small intestine.

Question 19

Which cells secrete Secretin?

Answer 19

S cells in the upper small intestine.

Question 20

What is Somatostatin? What does it do?

Answer 20

Somatostatin inhibits many features of digestion. It is released in response to gastric acid, and it inhibits the secretion of gastrin, insulin, pancreatic enzymes, and also inhibits motility and absorption.

Question 21

How much blood does the liver receive from the Portal Vein in the fasting state?

Answer 21

1300mL/min

Question 22

Name the essential amino acids.

Answer 22

Private Tim Hall:
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine