4a.) Intro to Stomach Flashcards
What do enteroendocrine cells secrete?
What do enterochromafin cells secrete?
- Enteroendocrine: hormones
- Enterochromaffin (like cells): secrete histamine
Describe the general pathway that hormones, produced by organs of the gut, take
- 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
Describe paracrine signalling
Hormone only has an effect in the vicinity of the gland secreting it (act in local environment so only diffuse short distances)
Describe neurocrine secretion
Action potential reaches neurone and causes it to release hormone
Provide an example of a neurocrine hormone in gut
- 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
State the two broad categories/families of gastrointestinal hormones
State two hormones in each category
- Gastrin family: gastrin, cholecystokinin
- Secretin family: secretin, gastric inhibitory peptide
For gastrin hormone, state:
- What stimulates release
- Where it is released from
- What it results in
- Stimulated by peptides/aa, GRP and Ach
- Released from G cells (in antrum of stomach)
- Increases gastric acid secretion
For cholecystokinin (CCK) hormone, state:
- Where it is released from
- What stimulates it’s release
- What the hormone causes
- Released from I cells in duodenum & jejunum
- CCK release stimulated by fats & proteins
- Causes gallbladder contraction
- Pancreas stimulated to increase pancreatic/gallbladder secretions
For hormone secretin, state:
- Where it is released from
- What stimulates it’s release
- What the hormone causes
- Secretin stimulated by H+ and fatty acids
- Secretin released from S cells in duodenum
- Secretin increases HCO3 secretion from pancreas/gallbladder and decreases gastric acid secretion
For gastric inhibitory peptide, state:
- What stimulates release
- Where it is released from
- Actions of the hormone
- Sugars, amino acids & fatty acids stimulate release
- GIP released from cells in duodenum
- Increases insulin secretion and decreases gastric acid secretion
State 4 functions of stomach
- Short term storage
- Disrupt food through contractions of smooth muscle
- Digestion
- Disinfect
What is rugae and why is it beneficial in the stomach?
Rugae= temporary folds in the mucosa of stomach which allow it to distend
Label this image of stomach
State the epithelial transition from lower oesophagus to stomach
- Lower oesophagus: stratified squamous
- Stomach: simple columnar
State the 4 specialist epithelial cells present in the stomach
- Mucous cells
- Parietal cells
- Chief cells
- G cells
How many muscle layers does the stomach have? State the name of each
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
What is the role of stomach acid? (3)
- Helps to unravel proteins creating a larger surface are for enzymes to act on
- Activates proteases in stomach lumen (pepsinogen - pepsin)
- Disinfect stomach contents
Describe the contractions in:
- Upper stomach
- Lower stomach
- Upper stomach: sustained contractions that create basal tone
- Lower stomach: strong peristalsis to mix contents every 20 seconds or so
Describe how the shape of the stomach aids movement of food
Stomach larger at proximal end than distal end meaning:
- Contents are accelerated
- Lumps are left behind
How often is liquid chyme ejected into duodenum?
3 times per minute
Describe the blood supply of the stomach
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
State the venous drainage of the stomach
- 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
Describe receptive relaxation of stomach
- 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
State what each of the following cells in stomach secretes
- Parietal cell
- G Cell
- Enterochromaffin like cell (ECL)
- Chief cell
- D cell
- Muscous cells
Which cells are responsible for acid production in stomach?
What are they stimulated by?
- Parietal cells
- Stimulated by: gastrin, histamine & Ach
State 2 circumstances under which acid production in stomach is increased
- Amino acids/peptides detected
- Stomach is distended
State 2 circumstances under which stomach acid production decreases
- Stomach distension reduces
- Low pH detected
State which each of the following regions of the stomach predominantly secretes
- Cardia
- Fundus/body
- Pylorus
Where are things secreted from in stomach?
What stimulates HCL release from parietal cells in stomach?
- Gastrin
- Ach
- Histamine
State the three phases of digestion
- Cephalic
- Gastric
- Intestinal
Describe HCL production is inhibited when food leaves stomach
- 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
(we know that gastrin, histamine and Ach stimulate parietal cells to secrete acid)
Describe the cephalic stage of digestion
Vagus (parasympathetic) nerve stimulates:
- Parietal cells to secrete gastric secretions before food is swallowed
- GRP release from G cells
Gastric motility also increases
Describe the gastric stage of digestion
- 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
Describe the intestinal phase of digestion
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
What does the stomach secrete, and what cells secrete this, to protect itself?
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
What does the stomch have to buffer acid that has breached the mucus layer?
Gastric mucosa has rich blood supply that can remove and buffer acid that has breached mucus layer. Prostaglandsin promote this process.
State some things that can breach stomach defences
- Alcohol: dissolves mucus layer
- Helicobacter pylori: chronic active gastritis
- NSAIDs: inhibit prostaglandins
Describe how acid in antrum stimulates D cells
- 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
Describe where abouts on abdominal aorta the superior mesenteric artery branches
What does stomach acid do to zymogens?
Activates the unactived enzymes (zymogens)
This image is summary!
Briefly summarise all 3 phases of digestion (including HCl production at each stage)
