Alimentary - secretion and motility

Question 1

What is exocrine?

Answer 1

Secretes substances into epithelial surface out of the body and requires a duct where products can be held

e.g. salivary, mammary and mucousal

Question 2

What is endocrine?

Answer 2

Secrete substances directly into the blood and does not need a duct

e.g. pancreas, gonads etc.

Question 3

What are the three different modes of cellular secretion?

Answer 3

Merocrine
Apocrine
Holocrine

Question 4

What is merocrine?

Answer 4

The vesicles fuse with the cell membrane and release products into a duct, like exocytosis

e.g. saliva release

Question 5

What is apocrine?

Answer 5

Products released on cell surface in small membrane bound vesicles that enter a duct

e.g. mammary gland

Question 6

What is holocrine?

Answer 6

Products accumulate in secretory cells, which die and release entire cell and products into a duct

e.g. oily products like sebaceous glands

Question 7

What is saliva formed of?

Answer 7

Mucous
Amylase
Lingual lipase
Electrolyte solutions
Proteins and enzymes

Never glucose

Question 8

What controls saliva production?

Answer 8

Vagus nerve under parasympathetic control

Sympathetic control works via vasoconstriction

Question 9

What are the cells of the gastric pits?

Answer 9

G-cells
Parietal cells
Chief cells
Surface mucousal cell
Mucous neck cell

Question 10

What do G-cells do?

Answer 10

Secrete gastrin when stimulated by vagus nerve

Question 11

What does gastrin do?

Answer 11

Stimulates HCl production and growth of mucosal cells

Question 12

What do parietal cells do?

Answer 12

Produce HCl

Question 13

What do Chief cells do?

Answer 13

In lower pH, these secrete pepsinogen, which is converted to pepsin which breaks down proteins (not keratin or mucous)

Question 14

What do mucous cells do?

Answer 14

Secrete mucous to protect the cells of the stomach from the low pH of the stomach

Question 15

What are the three phases of the gastric secretion?

Answer 15

Cephalic
Gastric
Intestinal

Question 16

What is the cephalic phase?

Answer 16

Stimulated by a conditioned reflex e.g. seeing/smelling/tasting food

This is by the NS (CNX), paracrine (histamine) or endocrine (gastrin).

End result is increased stomach motility and HCl/pepsinogen secretion.

Question 17

What is the gastric phase?

Answer 17

The stimulation of chemo and mechano receptors in stomach leads to gastrin/histamine release.

Local negative feedback loop is operated if gastric pH is <3

Question 18

What is the intestinal phase?

Answer 18

The presence of chyme in the duodenum leads to an inhibition of acidic secretion and motility via release of secretin, gastric inhibitor peptide and cholycystokinin.

Question 19

How is HCl produced by the parietal cells?

Answer 19

Water and Carbon dioxide form H2CO3

This spontaneously dissociates into H+ and bicarb. NaCl dissociates to form Cl- and Na2+

Bicarb - blood via anion exchanger (Cl-)
H+ - transported to stomach lumen via H+K+ATPase pump

H+ and Cl- joins in the lumen

Question 20

What is the pathway of the beginning of digestion?

Answer 20

1. Cephalic via sight/smell/taste - HCl and pepsinogen
2. Mechanoreceptors - promote HCl production through gastrin/histamine release
3. Gastric - promotes growth of stomach mucosal

Question 21

What happens when the chyme reaches the duodenum?

Answer 21

CCK and enterglucagon is released - promotes growth of mucosa in intestines and stimulates gall bladder to release bile

Secretin - inhibits gastrin release

Question 22

Small intestine cell types

Answer 22

Exocrine
Endocrine

Question 23

What are the fluids secreted by the SI?

Answer 23

Brunners glands - mucous
Others
-Intestinal secretion
-Enterokinase
-Carboxy- and Animo-peptidases
-Maltase
-Lactase
-Sucrase
-Lipse
-Mucleases

Question 24

What stimulates secretions from the liver?

Answer 24

Presence of food in duodenum
CCK
Return of bile acids

Question 25

What is produced by the liver and what does it do?

Answer 25

Produced - Bile, enzymes, hormones, cholesterol and triglycerides and Amino acids

ACtions - stores glycogen, Vit A, b12, D and K, converts ammonia to urea, regulates blood clotting, breaks down RBCs and removes toxins/drugs

Question 26

How is bile produced?

Answer 26

Smooth ER of hepatocytes using phospholipids and cholesterol in cell membranes.

1. Secrete bile acid, bile pigments and cholesterol into canaliculi
2. Water is drawn into these channels via osmosis
3. This enters the intrahepatic bile duct, draining into the billary tree and transporting it to the bladder and duodenum
4. CKK stimulates release from gall bladder

Question 27

How is fat transported around the body?

Answer 27

Bile aggregates around lipids, forming micelles stopping the lipids from emulsufying

The micelles are transported to brush border where they are absorbed

In the cell they resynthesise into TAG and assimilates with chylomicrons, which are transported in the lymphatic system

At the capillary endothelium the chylomicrons are broken down and fat is absorbed in the tissue

Question 28

What happens to the chylomicron remnants?

Answer 28

Transported back to liver and converted to LDL, VLDL and HDL

VLDL - TAGs from liver to adipose tissue
HDL - return lipids from tissues to liver
LDL - a mix of lipoproteins

Question 29

What is the enterohepatic circulation?

Answer 29

Circulation of bilary acids, bilirubin, drugs or other stubstances from liver to bile, to SI and absorption by enterocytes back to the liver.

Question 30

What do the exocrine cells of the pancreas secrete?

Answer 30

Trypsinogen
Carboxy- and animo-peptidase
Lipase
Amylase
Mucleases
Bicarbonate

Question 31

What stimulates exocrine release?

Answer 31

ACh
CKK
Secretin