GI

Question 1

How does gastrointestinal smooth muscle function as a syncytium?

Answer 1

Gap junctions
Connections between muscle layers

Question 2

What are the 2 types of electrical activity present in GI smooth muscle? Which one is the true action potential that causes contraction?

Answer 2

Slow waves
Spike potentials - true action potential that causes contraction

Question 3

What is the cell that causes slow waves in the gut?

Answer 3

Interstitial cells of Cajal between smooth muscle layers - act as pacemaker

Question 4

What are slow waves in the gut caused by?

Answer 4

Undulating changes in resting membrane potential - vary between 5-15mV

Question 5

When do spike potentials occur?

Answer 5

When slow waves increase membrane potential to >-40

Question 6

What are 2 differences between spike potentials in gut and normal action potentials?

Answer 6

-Depolarisation caused by influx of CALCIUM ions and some sodium ions - Calcium sodium channels
These open and close much more slowly than those on nerves -> longer action potential. Also allow calcium in which generates a contraction

Question 7

What are the 2 neural plexuses controlling the GIT and where are they found? What are their functions?

Answer 7

1. Myenteric plexus (Auerbach’s plexus): stretches whole way along GIT between longitudinal and circular smooth muscle. Controls MOTILITY
2. Submucosal plexus (Meissner’s plexus) in submucosa - local control of secretions, motility, absorption

Question 8

What are the 2 types of gut movement?

Answer 8

Peristalsis - myenteric plexus v important generating this

Mixing movements - local intermittent segmental contractions

Question 9

Name 2 ways to diagnose masticatory myositis.

Answer 9

Type 2M antibodies - >1:100 positive
Histo to specific lab

Question 10

Where is gastrin secreted from (cell and gland)

Answer 10

G cells - pyloric glands in stomach

Question 11

What stimulates gastrin release?

Answer 11

Presence of food (especially digested proteins) in stomach

Question 12

Give 2 actions of gastrin

Answer 12

1. Stimulates HCl by stimulating enterochrommafin like cells to release histamine (also maybe pepsinogen)
2. Causes gastric mucosal growth

Question 13

What inhibits gastrin secretion?

Answer 13

Acid pH <3

Question 14

Where is CCK released from?

Answer 14

I cells in duodenum and jejunum

Question 15

What stimulates CCK release?

Answer 15

Breakdowns of fat digestion in duodenum

Question 16

Give 4 actions of CCK

Answer 16

1. Stimulates gall bladder contraction and duodenal sphincter relaxation
2. Stimulates pancreatic enzyme secretion
3. Inhibits gastric emptying
4. Has trophic effect on exocrine pancreas

Question 17

What stimulates secretin release?

Answer 17

Acidic chyme in the duodenum

Question 18

Where is secretin released from?

Answer 18

S cells of duodenum and jejunum

Question 19

Give 3 actions of secretin.

Answer 19

1. Stimulates pancreatic and biliary epithelial cell bicarbonate secretion to neutralise acid
2. Exocrine pancreatic growth
3. Pepsin secretion

Question 20

Where is GIP released from?

Answer 20

K cells of duodenum and jejunum

Question 21

What stimulates GIP release?

Answer 21

Fatty and amino acids

Question 22

Give 3 actions of GIP?

Answer 22

1. Stimulates insulin release
2. Inhibits motor activity of stomach
3. Inhibits stomach acid secretion

Question 23

Where is motilin secreted from?

Answer 23

M cells in duodenum and jejunum

Question 24

What inhibits motilin release?

Answer 24

Ingestion of food

Question 25

What does motilin do?

Answer 25

Stimulates waves of GI activity and motility in a fasted individual

Question 26

What drug is a motilin agonist?

Answer 26

Erythromycin at subantibiotic doses

Question 27

Parasympathetic innervation to gut - which nerves and where do they act?

Answer 27

Cranial division = VAGUS nerve to upper GI (oesophagus, stomach, pancreas) Sacral division = PELVIC nerve to lower GI (originate S2-S4) -> distal half of large intestine and anus

Question 28

What does lipoprotein lipase do?

Answer 28

Hydrolyses triglycerides in chylomicrons to allow uptake into organs Leaves behind chylomicron remnants which are cleared by the liver

Question 29

What does hormone sensitive lipase do?

Answer 29

Hydrolyses free fatty acids and allows release into the circulation when needed

Question 30

Once fatty acids are hydrolysed from fat, how are they transported?

Answer 30

Combine with albumin to make non-esterified fatty acids

Question 31

Where are lipoproteins made?

Answer 31

liver

Question 32

What is the difference between VLDL and IDL?

Answer 32

VLDL = almost all triglycerides IDL = equal amounts cholesterol, trigs, phospholipids

Question 33

What is the difference between VLDL and LDL?

Answer 33

Almost no trigs in LDL

Question 34

What makes up the highest amount of HDLs?

Answer 34

50% protein

Question 35

What is beta oxidation?

Answer 35

Process of degrading fatty acids to make acetylCoA

Question 36

What is most bilirubin conjugated with?

Answer 36

Glucaronic acid (90%) via glucaronidation

Question 37

What does heme break down into and how are these transported in the blood?

Answer 37

Fe2+ - transported with ferritin Heme oxygenase makes biliverdin then biliverdin reductase makes bilirubin (unconjugated)

Question 38

What is unconjugated bilirubin bound to in blood?

Answer 38

Albumin