GI7 - The Stomach

Question 1

4 basic functions of the stomach

Answer 1

1. ) Receive Food - short term storage facility
   - vagal innervation causes relaxation of stomach,
   - allows food to enter stomach w/out raising intra-gastric pressure too much
   - prevents stomach reflux during swallowing

2.) Disrupt Food - vigorous contractions of the smooth muscle

3. ) Continue/Begin Digestion - via proteins and enzymes
   - acidic conditions helps denature proteins and activate proteases (pepsinogen to pepsin)

4.) Disinfection - via acidic conditions

Question 2

6 features of the basic structure of the stomach

Epithelia Type
Epithelial Cells
Smooth Muscle
Folds
Curvature
Shape

Answer 2

1. ) Epithelia - transition from oesophagus to stomach
   - stratified squamous –> simple columnar (secretion)
2. ) Epithelial Cells - extend to pits/glands
   - mucous cells, parietal cells, chief cells, G cells
3. ) Smooth Muscle - consists of 3 layers:
   - oblique (innermost), inner circular, outer longitudinal
   - contractions mix/move contents along
4. ) Rugae - temporary folds in the mucosa/submucosa
5. ) Curvature - greater (lateral) and lesser (medial)
6. ) Funnel Shape - smaller contents accelerates down to pyloric sphincter, whilst larger contents stay in the body
   - going down, it become narrower and more muscular
   - upper stomach creates basal tone whilst lower stomach has strong peristalsis to mix contents

Question 3

6 features of the anatomical structure of the stomach

Anatomical Position
5 Anatomical Locations

Answer 3

1. ) Anatomical Position - superior aspect of the abdomen between the epigastric and umbilical regions
   - posterior to the diaphragm, greater omentum, gallbladder, and left lobe of the liver
   - anterior to lesser sac, pancreas, transverse mesocolon
2. ) Lower Oesophageal Sphincter - consists of smooth muscle and is attached to the diaphragm
   - prevents retrograde movement of acid and stomach contents into the oesophagus
3. ) Cardia - surrounds superior opening of the stomach
4. ) Fundus - very top of the stomach, often filled w/ gas
5. ) Body - large central portion, inferior to the fundus
6. ) Pylorus - connect the stomach to the duodenum
   - divided into the pyloric antrum, canal, and sphincter
   - sphincter is at the transpyloric plane at level of L1

Question 4

4 features of the blood supply of the stomach

Celiac Trunk
Lesser Curvature
Greater Curvature
Venous Drainage

Answer 4

1. ) Celiac Trunk - comes off the aorta at T12 level
   - supplies the stomach with its branches
   - primary branches are the left gastric artery, splenic artery, and common hepatic artery
2. ) Lesser Curvature - supplied by anastomoses of the the right and left gastric artery
   - left comes directly from the celiac trunk
   - right is a branch of the common hepatic artery

3.) Greater Curvature - supplied by the anastomoses
of the right and left gastroepiploic artery
- right is a terminal branch of the gastroduodenal artery which is a branch of the common hepatic artery
- left is a branch of the splenic artery

4. ) Venous Drainage - drain via respective vessels
   - all the veins drain into the portal vein going to the liver

Question 5

2 types of hormones/signalling

Gut hormone travel path

Answer 5

1. ) Paracrine - effect only in the vicinity of the gland secreting it, diffuse over short distances
   - e.g. somatostatin made by D cell inhibiting the G cell
2. ) Neurocrine - peptides released by neurones in the GI tract
   - e.g. gastrin releasing peptide (GRP) is released from postganglionic fibres of the vagus nerve
3. ) Travel Path - hormones in the gut are released from endocrine cells into the portal circulation
   - pass through the liver to enter the systemic circulation
   - end up close to wherever they started

Question 7

2 hormones in the gastrin family of GI hormones

Function(s)
Secretory Cell
Stimulation

Answer 7

1. ) Gastrin - increases gastric acid secretion
   - secreted by G cells in the antrum of the stomach
2. ) Cholecystokinin (CCK) - stimulates the gallbladder and pancreas to release bile and pancreatic enzymes respectively
   - secreted by I cells in the duodenum and jejunum
   - stimulated by fat (bile) and protein (p enzymes)

Question 7

2 hormones in the secretin family of GI hormones

Function(s)
Secretory Cell
Stimulation

Answer 7

1. ) Secretin - increases HCO3- secretions from the pancreas and gallbladder and decreases gastric acid secretions
   - secreted by S cells in the duodenum
   - stimulated by H+ and fatty acids
2. ) Gastric Inhibitory Polypeptide (GIP) - inhibits gastric acid secretion and also increases insulin
   - secreted by cells in the duodenum and jejunum
   - stimulated by sugars, AAs, and fatty acids

Question 8

6 secretory cells of the stomach

Secretions
Stimulations
Locations

Answer 8

1. ) Mucous Cells - mucous and pepsinogen
   - mucous forms alkaline protective layer w/ HCO3
   - found all over the stomach
2. ) Parietal Cells - HCL and intrinsic factor
   - stimulated by gastrin, vagus nerve (ACh), histamine
   - found mainly in the fundus/body
3. ) Enterochromaffin like Cell (ECL) - histamine
   - stimulated by gastrin and vagus nerve
   - found near parietal cells
4. ) Chief Cells - pepsinogen/pepsin
   - stimulated by gastrin and vagus nerve
   - found mainly in the fundus/body
5. ) G Cells - gastrin into the circulation
   - stimulated by peptides/AAs and also under vagal stimulation (ACh, gastrin releasing peptide)
   - found mainly in the pyloric antrum
6. ) D Cells - somatostatin (inhibits G cell)
   - stimulated by fall in pH
   - found mainly in the pyloric antrum

Question 9

4 features of the control of HCL production

Gastrin
Acetylcholine
Histamine
Inhibition of HCL Production

Answer 9

1. ) Gastrin - binds to CCK receptors on parietal cells
   - causes Ca2+ influx causing vesicular fusion which helps pump H+ ions into the stomach lumen
2. ) Acetylcholine (ACh) - secreted by the vagus nerve
   - directly stimulates the parietal cells
3. ) Histamine - binds to H2 receptors on parietal cells leading to increased vesicular fusion via cAMP
   - secreted in the presence of gastrin and ACh
4. ) Inhibition of HCL Production - inhibition of G cells
   - food leaves stomach –> pH drops –> activates D cells
   - D cells release somatostatin –> inhibits G and ECL cells
   - stomach distension reduces due to reduced vagal act…

Question 10

3 steps in the production of HCL on a molecular level

Answer 10

1. ) Carbonic Anhydrase - CO2 + H2O –> H(+) + HCO3-
   - occurs in the parietal cell
   - H+ ion enters stomach lumen via H-K ATPase on apical membrane
2. ) Anion Exchanger - found on basolateral membrane
   - HCO3- ions exchanged for Cl- ions from ECF
   - Cl- then enters the stomach lumen via Cl- channel on apical membrane
   - efflux of HCO3- causes venous blood leaving the stomach to become more alkaline

3.) H+ and Cl- combine in stomach lumen to make HCL

Question 11

4 features of the cephalic phase of digestion

Answer 11

1. ) Stimulation before food is fully swallowed
2. ) Stimulated by smell, taste, chewing, swallowing action
3. ) Vagus nerve stimulates parietal cells and G cells
4. ) Produces 30% of total HCL

Question 12

6 features of the gastric phase of digestion

Answer 12

1. ) Stomach distension stimulates vagus nerve
2. ) Vagus nerve stimulates parietal cells and G cells
3. ) Presence of AAs and peptides stimulate G cells
4. ) Presence of food removes inhibition of gastrin
5. ) Enteric NS and gastrin cause strong smooth muscle contractions
6. ) Produces 60% of total HCL

Question 13

4 features of the intestinal phase of digestion

Answer 13

1. ) Chyme initially stimulates gastrin secretion
   - partially digested proteins detected in duodenum

2.) Produces 10% of HCL

3. ) However, presence of lipids activate enterogastric reflex which reduces vagal stimulation
   - causes inhibition of G cells

4.) Chyme stimulates CCK and secretin to help suppress secretion

Question 14

6 features of protection of the stomach

Reason
5 Mechanisms

Answer 14

1.) Reason - stomach digests biological material so can digest itself

2. ) Mucin - secreted by foveolar cells
   - forms viscous mucus layer which adheres to epithelium to help prevent physical damage from food
3. ) HCO3 Ions - secreted into mucous layer to provide a barrier against stomach acids
4. ) Rich Blood Supply - can remove and buffer acid that has breached mucus layer
5. ) Prostaglandins - promote all the above processes
6. ) High Turnover - of epithelial cells keep the epithelia intact

Question 15

5 things that can breach stomach defences

Answer 15

1. ) Alcohol - dissolves mucus layer
2. ) Helicobacter Pylori - causes chronic active gastritis
3. ) NSAIDs - inhibits prostaglandins
4. ) Others - physiological stress, smoking