1.3 Regulation of the GIT: Secretion

Question 1

Describe the structure of an exocrine (out) gland

Answer 1

Secrete substances onto an epithelial surface by way of a duct
- salivary, mammary, mucous

Question 2

Describe the structure of an endocrine (in) gland

Answer 2

Ductless glands of the endocrine system that secrete their products directly into the blood
- pancreas, gonads

Question 3

What is a merocrine gland?

Answer 3

Eccrine - secretory vesicle fuse with the plasma membrane to release their products into a duct

Question 4

What is a apocrine gland?

Answer 4

Secretory products are released at the apical cell surface in small membrane bound vesicles that enter into a duct

Question 5

What is a holocrine gland?

Answer 5

Secretory products accumulate in the secretory cells, which then die and the entire cell and its secretory products are released into a short duct

Question 6

What substances stimulate stomach secretion?

Answer 6

Ach
Gastrin
Histamine

Question 7

Describe the cephalic phase of regulation of gastric secretion

Answer 7

Conditioned reflex or sight/smell/taste of food via vagus (CN X), gastrin secretion and histamine

• increase stomach motility
• increase HCl and pepsinogen secretion

Question 8

Describe the gastric phase of regulation of gastric secretion

Answer 8

Stimulation of chemo and mechano receptors in stomach lead to the release of gastrin and histamine
- local negative feedback loop operates if gastric pH is < 3

Question 9

Describe the intestinal phase of regulation of gastric secretion

Answer 9

Presence of chyme in the duodenum inhibits acid secretion and motility via the release of secretin, Gastric inhibitory peptide (GIP) and choleycystokinin (CKK)

Question 10

Describe the functions of cholecystokinin

Answer 10

Stimulates gall bladder to contract + release through bile salts ducts or bile into duodenum + pancreas

Question 11

What is the function of regulatory peptides in the gut epithelium?

Answer 11

Gastrin = promotes growth of stomach mucosa

Enteroglucagon + cholecystokinin = promote growth of intestinal mucosa

Question 12

How is the regulation of chyme achieved?

Answer 12

Local reflex action in response to chemical and mechanical irritation from the chyme and in response to distention of the intestinal wall

Question 13

What do Brunner’s glands release?

Answer 13

Alkaline mucoid fluid (no enzyme) designed to protect the small intestine mucosa from damage by stomach acid in the first part of duodenum

Question 14

How is bile produced?

Answer 14

Bile acids are produced from cholesterol in smooth ER of hepatocytes (also takes phospholipids and cholesterol from the cell membrane)

Question 15

Describe the composition of bile

Answer 15

Hydrophilic and hydrophobic sides - detergent

• secreted into canaliculi as sodium salts - draws water into bile by osmosis and electrolytes
• bicarbonate is secreted from duct cells into bile
• bilirubin excreted through duct cells into the blood

Question 16

Define entero-hepatic circulation

Answer 16

Circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver

Question 17

Name enzymes secreted (exocrine) by the pancreas

Answer 17

Trypsinogen 
Chymotrypsinogen 
Carboxy and aminopeptidase 
Lipase 
Amylase 
Maltase 
Nucleases

Question 18

Name enzymes secreted (endocrine) by the pancreas

Answer 18

Via splenic artery

• insulin
• glucagon