Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Block 1: Physiology > Gastric motility and secretion > Flashcards

Gastric motility and secretion Flashcards

1
Q

What are the functions of the stomach?

A 
Food storage
Barrier for harmful bacteria
(Partial) digestion of macromolecules
Regulation of digestion 
Secretion of intrinsic factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does gastric motility allow the stomach to do?

A

Reservoir for large volume of food
Fragment food and mix with gastric secretions
Empty contents into duodenum at controlled rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does receptive relaxation aid gastric motility?

A

Smooth muscle in the orad region relaxes to increase stomach volume to approx. 1.5 litres without increasing pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What mediates receptive relaxation?

A

Parasympathetic input from vagus nerve and enteric plexus

Release of NO and serotonin by enteric neurones mediates relaxation of smooth muscle cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is retropulsion?

A

Closure of the pyloric sphincter as peristaltic wave causes contraction of the antrum - this causes the contents of the antrum to be forced backwards into the body of the stomach

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is peristalsis?

A

Waves of alternating contractions and relaxations of smooth muscle layers that mix and squeeze contents through hollow tubes (i.e. moves bolus along GI tract)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is segmentation?

A

Cycles of contractions that mix contents but do not push them in any one direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are contractions of smooth muscles in the GI tract achieved?

A 
Slow waves (coordinate contractions) 
Action potentials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How are slow waves achieved?

A

Fluctuations in membrane potential spreading to adjacent sections of muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How is gastric emptying achieved?

A

Coordinated contractions of the stomach, pylorus and duodenum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the functions of the pyloric sphincter?

A
  1. Regulation of emptying gastric contents at optimal rate for digestion
  2. Prevents regurgitation of duodenal contents into stomach
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is the pyloric sphincter controlled?

A

Autonomic Nervous System (sympathetic and vagal)

Hormonal control

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What hormones are involved in controlling the pyloric sphincter?

A

Gastrin
Cholecystokinin (CCK)
Gastric Inhibitory Peptide (GIP)
Secretin

[Nb. all elicit contraction of sphincter]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What factors regulate gastric emptying?

A

Nature of duodenal contents (e.g. high in fat, highly acidic or very hypertonic all decrease rate of gastric emptying)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the main components of gastric juice?

A

Hydrochloric acid
Mucus
Enzymes (e.g. pepsinogens, gastric lipase)
Intrinsic Factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where are gastric juices secreted from?

A

Gastric glands in mucosa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Where are parietal cells typically found?

A

Proximal 80% of stomach (oxyntic gland area)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where are gastrin-producing cells typically found?

A

Antrum (pyloric gland area)

19
Q

What are the gastric effects of Gastrin?

A
  1. Stimulation of secretion of acid, pepsinogens, mucus and bicarbonate
  2. Stimulation of gastric motility
  3. Inhibition of gastric emptying
20
Q

What effects does Gastrin have on other areas of the GI tract?

A
  1. Stimulation of pancreatic enzymes and bicarbonate secretion
  2. Stimulation of insulin release
  3. Stimulation of intestinal motility
21
Q

What is Histamine?

A

paracrine agent

22
Q

Where is Histamine secreted from?

A

Enterochromaffin-like Cells (ECL)

23
Q

What are the gastric effects of Histamine?

A
  1. Stimulation of acid secretion

2. Increased local blood flow (supports increased metabolism associated with acid secretion)

24
Q

Where is somatostatin synthesised?

A

D cells (in antrum and body of stomach)

25
Q

What are the gastric effects of Somatostatin?

A
  1. Inhibition of gastrin release

2. Inhibition of acid secretion

26
Q

How are parietal cells specialised?

A

Truncated pyramidal shape
Invaginations of the luminal membrane form canaliculi which are lined with ion pumps
High mitochondrial content

27
Q

How is acid secreted from parietal cells?

A
  1. Hydrogen ions and Bicarbonate produced from CO2 and water
  2. Hydrogen ions secreted into lumen via H+/K+ ATPase pump
  3. Bicarbonate moves across basolateral membrane via antiport with Cl-
  4. Cl- diffuses passively into the lumen via a Cl- channel
28
Q

What physiological agents stimulate gastric acid secretion?

A

Gastrin (hormone)
Acetylcholine (parasympathetic input from CN X)
Histamine (paracrine agent)

29
Q

What hormones inhibit gastric acid secretion?

A

Somatostatin
Prostaglandins (E2 and I2)
Intestinal hormones (Enteric hormones inhibiting Gastrin release)

30
Q

What are prostaglandins?

A

Lipids derived from arachidonic acid made at sites of tissue damage or infection to control processes such as inflammation and blood flow

31
Q

What enzyme catalyses prostaglandin synthesis?

A

Cyclooxygenase Enzyme (COX)

32
Q

What is mucus made up of?

A

Glycoproteins

Glycopolysaccharides

33
Q

Where is mucus secreted from in the stomach?

A

Mucus (neck) cells in the necks of gastric glands

Surface epithelial cells of the stomach

34
Q

What role does mucus play in the stomach?

A

Forms a gastric mucosal barrier that protects the stomach against acid, proteolytic enzymes and mechanical damage

35
Q

How is pepsin secreted?

A

Secreted by chief cells in the form of Pepsinogen

36
Q

What causes pepsinogen to convert to pepsin?

A

Exposure of low pH in the lumen (so pepsin is only active at low pH)

37
Q

What role does pepsin play in the stomach?

A

Accelerates protein digestion

38
Q

What is intrinsic factor?

A

A glycoprotein secreted by parietal cells of the stomach

39
Q

What is the role of intrinsic factor?

A

Essential for absorption of vitamin B12 in the intestines

40
Q

What is Zollinger-Ellison Syndrome?

A

Presence of a gastrin-secreting tumour or hyperplasia of the Pancreatic Islet cells causes increased Gastrin and therefore increased H+ secretion leading to recurrent peptic ulcers

41
Q

Why does Zollinger-Ellison Syndrome cause peptic ulcers?

A

Non-physiological gastrin secretion by a Gastrinoma is not feedback-regulated so gastrin secretion continues even when stomach contents are already very acidic.
Duodenal ulcers can occur as excess H+ load can not be buffered (movement from stomach to duodenum and neutralisation by Bicarbonate)

42
Q

What investigations can be used to diagnose Zollinger-Ellison Syndrome?

A

Endoscopy
Pentagastrin Stimulation Test
Serum Gastrin level
Basal gastric H+ secretion

43
Q

What is a Pentagastrin Stimulation Test?

A

Can be used to identify Zollinger-Ellison Syndrome
In healthy patients, Pentagastrin (a gastrin analogue) would stimulate increased secretion of H+ by parietal cells.
In patients with Zollinger-Ellison (or Gastrinoma), H+ secretion is already maximally stimulated so administration of a gastrin analogue does not increase H+ secretion further.

Block 1: Physiology (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions