GI Anatomy & Physiology [McNeish]

Question 1

List the organisation of the gut wall

Answer 1

Serosa
Longitudinal smooth muscle
Circular smooth muscle
Submucosa
Muscularis mucosa
Laminara propria
Epithelium
Lumen

Question 2

What is the enteric nervous system?

Answer 2

Main control of motility in wall of GI tract
Integrates autonomic nervous system and local signals
Can function independently of any other signals

Question 3

Which parts of the GIT wall are involved with the enteric nervous system?

Answer 3

The myenteric plexus = mainly motility

The submucosal plexus = mainly formation of secretions/blood flow

Question 4

How does the parasympathetic nervous system affect the GI tract?

Answer 4

Increases motility and secretion
ACh acting on muscarinic receptors
Increased salivation and mucosa constriction
(via vagus nerve)

Question 5

How does the sympathetic nervous system affect the GI tract?

Answer 5

The SNS reduces GI function

Noradrenaline relaxes smooth muscle in GIT

Question 6

Which hormones regulate the GIT?

Answer 6

Endocrine hormones: 
Released into bloodstream
Made in mucosal endocrine cells
Paracrine hormones: 
Relatively short distance - local action
Made in cell walls of GIT

Question 7

How do hormones affect the GIT?

Answer 7

Often modulate nerve action

Affect secretion and motility

Question 8

Give 2 examples of endocrine hormones which are present in the GIT

Answer 8

Gastrin

Cholesystokinin (CCK)

Question 9

Give 2 examples of paracrine hormones which are found in the GIT

Answer 9

Histamine

Somatostatin

Question 10

List 3 roles of saliva

Answer 10

Aids swallowing
Begins digestion
Kills bacteria

Question 11

What effect does the parasympathetic nervous system have on saliva production?

Answer 11

Watery saliva

INcreased secretion and blood flow

Question 12

What effect does the sympathetic nervous system have on saliva production?

Answer 12

Mixed response

Increased secretion, reduced blood flow

Question 13

List the 3 stages of swallowing

Answer 13

1st step = voluntary
2nd step = peristalsis - distention triggered under autonomic control, mucous aids movement
3rd step = enters stomach via oesophageal sphincter

Question 14

What is the role of gastric glands and where are they found?

Answer 14

Gastric glands are found in the stomach

They secrete gastric juice

Question 15

Name the 2 types of gastric gland and their specific roles

Answer 15

Parietal cells = secrete acid

Chief cells = produce pepsinogens (and other digestive enzymes)

Question 16

List 5 substances that gastric juice contains

Answer 16

Salts
HCl
Pepsinogens
Water
Intrinsic factor (glycoprotein necessary for the absorption of vitamin B12)

Question 17

List 4 roles of HCl in the stomach

Answer 17

Aids breakdown of tissue
Activates pepsinogen and optimises pepsin function
Allows absorption of calcium and iron
Protects against micro-organisms/pathogens

Question 18

How is stomach acid formed?

Answer 18

Parietal cell:
Carbonic anhydrase generates H+ and HCO3-
Cl- enters parietal cell in exchange for HCO3- and transported out via the K+/Cl- symport
Proton pump H+/K+ ATPase secretes H+ into stomach lumen

Question 19

How is gastrin regulated?

Answer 19

Released from G cell in response to nerve, hormonal and food stimuli
Activates CCK2 receptors on ECL cells stimulating histamine release

Question 20

How is acetylcholine regulated?

Answer 20

ACh released from cholinergic nerves

Stimulates parietal cells

Question 21

How is histamine regulated?

Answer 21

Released from entero-chromaffin like (ECL) cells

Agonist on H2 receptor on parietal cells = stimulates acid secretion

Question 22

What is the role of the gastric mucosa?

Answer 22

Protects stomach wall from acid and gastric enzymes

Gel-like and alkaline

Question 23

What kind of cells does the gastric mucosa contain?

Answer 23

Secretory cells:
Epithelial cells
Neck cells of gastric pits

Question 24

What is the role of prostaglandins in the GIT?

Answer 24

Promote mucosal secretion

by increasing blood supply

Question 25

List 3 disorders associated with increased acid production

Answer 25

Gastro-Oesophageal Reflux Disease (GORD) - heartburn, acid reflux, indigestion
Gastric bleeding - often due to NSAID treatment
Ulceration - may be caused by stress

Question 26

List 4 things that happen in the GIT during vomiting (emesis)

Answer 26

Respiration inhibited (larynx and nasopharynx closed)
Stomach relaxes, duodenum contracts
Diaphragm and abdominal muscles contract powerfully
Gastro-oesophageal sphincter relaxes, gastric contents expelled

Question 27

Which part of the brain controls vomiting?

Answer 27

The medulla of the brainstem

• The chemoreceptor trigger zone (CTZ)
• Vomiting centre

Question 28

What is the main function of the pancreas?

Answer 28

Endocrine: Releases insulin and glucagon into the bloodstream
Exocrine: Releases alkaline fluid (reduces pH in duodenum) and digestive enzymes

Question 29

Which 2 types of digestive enzyme which is released from the pancreas?

Answer 29

Proteolytic enzymes = aid breakdown of proteins

Lipolytic enzymes = aid fat digestion

Question 30

How are monosaccharides and amino acids absorbed in the small intestine?

Answer 30

They are absorbed by Na-dependent co-transport

Question 31

How are fats and fat-soluble vitamins absorbed in the small intestine?

Answer 31

They are absorbed by micelles and bile salts

Question 32

How are water-soluble vitamins absorbed in the small intestine?

Answer 32

They are absorbed by facilitated transport

Question 33

Name 2 disorders of absorption in the small intestine

Answer 33

Coeliac disease

Chrohn’s

Question 34

What happens in the large intestine?

Answer 34

Indigestible food residues are stored before elimination
Mucous secretion aids motility of faeces
Absorbs water and electrolytes
Resident bacteria from some vitamins (riboflavin, vitamin K, vitamin B12)

Question 35

How does dietary fibre increase motility/defecation?

Answer 35

Bulk stimulates movement

Dietary fibre hydrates the bulk allowing greater propulsion and softer faeces