4a.) Intro to Stomach

Question 1

What do enteroendocrine cells secrete?

What do enterochromafin cells secrete?

Answer 1

• Enteroendocrine: hormones
• Enterochromaffin (like cells): secrete histamine

Question 2

Describe the general pathway that hormones, produced by organs of the gut, take

Answer 2

• Hormones released from endocrine cells
• Pass into portal circulation
• Through liver
• Enter systemic circulation
• Travel via systemic circulation to pretty much the place they were produced

Question 3

Describe paracrine signalling

Answer 3

Hormone only has an effect in the vicinity of the gland secreting it (act in local environment so only diffuse short distances)

Question 4

Describe neurocrine secretion

Answer 4

Action potential reaches neurone and causes it to release hormone

Question 5

Provide an example of a neurocrine hormone in gut

Answer 5

• Gastrin releasing peptide

It is released from post ganglionic fibres of the vagus nerve. GRP then acts to increase release of gastrin from G cells

Question 6

State the two broad categories/families of gastrointestinal hormones

State two hormones in each category

Answer 6

• Gastrin family: gastrin, cholecystokinin
• Secretin family: secretin, gastric inhibitory peptide

Question 7

For gastrin hormone, state:

• What stimulates release
• Where it is released from
• What it results in

Answer 7

• Stimulated by peptides/aa, GRP and Ach
• Released from G cells (in antrum of stomach)
• Increases gastric acid secretion

Question 8

For cholecystokinin (CCK) hormone, state:

• Where it is released from
• What stimulates it’s release
• What the hormone causes

Answer 8

• Released from I cells in duodenum & jejunum

1. CCK release stimulated by fats & proteins
2. Causes gallbladder contraction
3. Pancreas stimulated to increase pancreatic/gallbladder secretions

Question 9

For hormone secretin, state:

• Where it is released from
• What stimulates it’s release
• What the hormone causes

Answer 9

1. Secretin stimulated by H+ and fatty acids
2. Secretin released from S cells in duodenum
3. Secretin increases HCO3 secretion from pancreas/gallbladder and decreases gastric acid secretion

Question 10

For gastric inhibitory peptide, state:

• What stimulates release
• Where it is released from
• Actions of the hormone

Answer 10

1. Sugars, amino acids & fatty acids stimulate release
2. GIP released from cells in duodenum
3. Increases insulin secretion and decreases gastric acid secretion

Question 11

State 4 functions of stomach

Answer 11

• Short term storage
• Disrupt food through contractions of smooth muscle
• Digestion
• Disinfect

Question 12

What is rugae and why is it beneficial in the stomach?

Answer 12

Rugae= temporary folds in the mucosa of stomach which allow it to distend

Question 13

Label this image of stomach

Answer 13

Question 14

State the epithelial transition from lower oesophagus to stomach

Answer 14

• Lower oesophagus: stratified squamous
• Stomach: simple columnar

Question 15

State the 4 specialist epithelial cells present in the stomach

Answer 15

• Mucous cells
• Parietal cells
• Chief cells
• G cells

Question 16

How many muscle layers does the stomach have? State the name of each

Answer 16

Remember: 4 layers of GI tract= mucosa, submucosa, muscular layer, serosa. We have already said in basic anatomy FC that muscular layer has two layers: outer longitudinal layer and inner circular layer.

The stomach has an extra oblique layer of muscle to enable it to mix and grind contents as well as move them along

Question 17

What is the role of stomach acid? (3)

Answer 17

• Helps to unravel proteins creating a larger surface are for enzymes to act on
• Activates proteases in stomach lumen (pepsinogen - pepsin)
• Disinfect stomach contents

Question 18

Describe the contractions in:

• Upper stomach
• Lower stomach

Answer 18

• Upper stomach: sustained contractions that create basal tone
• Lower stomach: strong peristalsis to mix contents every 20 seconds or so

Question 19

Describe how the shape of the stomach aids movement of food

Answer 19

Stomach larger at proximal end than distal end meaning:

• Contents are accelerated
• Lumps are left behind

Question 20

How often is liquid chyme ejected into duodenum?

Answer 20

3 times per minute

Question 21

Describe the blood supply of the stomach

Answer 21

Celiac trunk has 3 branches:

• Left gastric artery
• Splenic artery- short gastric, left gastroepiploic
• Common hepatic- gastroduodenal atery, right gastric & proper hepatic artery. Gastroduodenal gives rise to superior pancreasticoduoenal artery & right gastroepiploic artery

Right and left gastric anastomose= lesser curve

Right and left gastroeplipoic anastomose = greater curve

Question 22

State the venous drainage of the stomach

Answer 22

• Left & right gastric veins directly into portal vein
• Short gastric veins (fundus), left gastro-epiploic/ometnal veins
• Right gastoepilpic vein, left and right pancreaticoduodenal veins drain into superior mesenteric vein

Question 23

Describe receptive relaxation of stomach

Answer 23

• Consume food
• Get vagally mediated relaxation of stomach
  
  • Allows food to enter stomach without increasing intra-gastric pressure too much
  • Prevents reflux of stomach contents during swallowing

Question 24

State what each of the following cells in stomach secretes

• Parietal cell
• G Cell
• Enterochromaffin like cell (ECL)
• Chief cell
• D cell
• Muscous cells

Answer 24

Question 25

Which cells are responsible for acid production in stomach? What are they stimulated by?

Answer 25

* Parietal cells * Stimulated by: gastrin, histamine & Ach

Question 26

State 2 circumstances under which acid production in stomach is increased

Answer 26

* Amino acids/peptides detected * Stomach is distended

Question 27

State 2 circumstances under which stomach acid production decreases

Answer 27

* Stomach distension reduces * Low pH detected

Question 28

State which each of the following regions of the stomach predominantly secretes * Cardia * Fundus/body * Pylorus

Answer 28

Question 29

Where are things secreted from in stomach?

Answer 29

Question 30

What stimulates HCL release from parietal cells in stomach?

Answer 30

* Gastrin * Ach * Histamine

Question 31

State the three phases of digestion

Answer 31

1. Cephalic 2. Gastric 3. Intestinal

Question 32

Describe HCL production is inhibited when food leaves stomach

Answer 32

* Food acts as a buffer, when it leaves stomach pH drops * Low pH activates D cells * D cells release somatostatin * Somatostatin inhibits: * G cells: which then inhibits gastrin * ECL cells: which inhibits histamine ## Footnote *(we know that gastrin, histamine and Ach stimulate parietal cells to secrete acid)*

Question 33

Describe the cephalic stage of digestion

Answer 33

Vagus (parasympathetic) nerve stimulates: * Parietal cells to secrete gastric secretions before food is swallowed * GRP release from G cells Gastric motility also increases

Question 34

Describe the gastric stage of digestion

Answer 34

* Distension of stomach stimulates vagus activity * Vagus nerve stimulates parietal and G cells * AA and smal peptides further stimulate G cells * Presence fo food prevents lowering of pH and removes inhibition on gastrin * Gastrin, along with enteric nervous system, then causes strong smooth muscle contractions

Question 35

Describe the intestinal phase of digestion

Answer 35

First part is about increasing acids production: * Chyme, released into duodenum, **initially** stimulates gastrin secretion which stimulates acid production Second party about reducing acid secretion: * Very quickly get inhibition of G cells * Lipids activate enterogastric reflex which reduces parasympathetic activity to stomach to reduce acid secretion and stomach motility * Chyme stimulates CCK and secretin to further reduce acid secretion

Question 36

What does the stomach secrete, and what cells secrete this, to protect itself?

Answer 36

Foveolar cells secrete mucus to form a mucus layer that adheres to epithelium and prevents it from physical damage. HCO3- is secreted into the mucus to help it act as a barrier against stomach acid

Question 37

What does the stomch have to buffer acid that has breached the mucus layer?

Answer 37

Gastric mucosa has rich blood supply that can remove and buffer acid that has breached mucus layer. Prostaglandsin promote this process.

Question 38

State some things that can breach stomach defences

Answer 38

* Alcohol: dissolves mucus layer * Helicobacter pylori: chronic active gastritis * NSAIDs: inhibit prostaglandins

Question 39

Describe how acid in antrum stimulates D cells

Answer 39

* Acid (H+) stimulates D cells to release somatostatin which inhibits gastrin release from G cells to inhibit too much acid being produced from parietal cells

Question 40

Describe where abouts on abdominal aorta the superior mesenteric artery branches

Answer 40

Question 41

What does stomach acid do to zymogens?

Answer 41

Activates the unactived enzymes (zymogens)

Question 42

This image is summary!

Answer 42

Question 43

Briefly summarise all 3 phases of digestion (including HCl production at each stage)

Answer 43