The Stomach Flashcards
List 4 functions of the stomach
- Temporary storage
- Disinfection
- Continue digestion, mainly proteins
- Disruption of food via vigorous smooth muscle contraction
What are 4 anatomical parts of the stomach
- Cardia (Entrance to stomach, below LOS)
- Fundus (Superior region)
- Body (forms bulk of stomach)
- Antrum (leads to Pyloric sphincter)
How does epithelia change from lower Oesophagus to stomach
Stratified squamous to simple columnar (for secretion)
What are 2 parts of the Lower Oesophageal Sphincter?
Inferior part: Intrinsic smooth muscle of stomach
Superior: Right Crus of Diaphragm
Other than LOS, describe a mechanism that prevents relfux
How are Rugae in the mucosa/ submucosa involved in this?
Receptive relaxation;
- Peristalsis causes reflex relaxation of proximal stomach, allowing Fundus to expand/ distend
- When relaxed, folds called Rugae are present. These allow stomach to expand when needed
What are the layers of muscles in the stomach
What do these muscles do?
Innermost oblique
Inner circular
Outer longitudinal
Mechanical breakdown of food via forceful contractions
How does the shape of stomach influence movement of stomach contents
- Larger fundus breaks down food into larger and smaller chunks
- Smaller chunks accelerate and move faster towards Smaller Antrum
(This helps separate contents)
In the stomach the epithelia extend into the gastric pits/ glands
Name 4 of the cells found in these pits
- Parietal
- Chief (secrete pepsinogen)
- Mucous
- G cells (An enteroendocrine cell)
List 4 secretions of the stomach
- HCL
- Intrinsic Factor
- Pepsinogen
- HCO3- in mucus
Why does the stomach need to be able to protect itself?
Designed to digest biological material so can digest itself
List and describe 4 methods of protection of the stomach
- Mucin secreted by Surface Mucous Cells adheres to epithelia and prevents physical damage from food
- HCO3 ions secreted into mucus layer to provides a pH neutral barrier against acid
- Rich blood supply to gastric mucosa to remove and buffer acid that has breached mucus layer
- High turnover of epithelial cells, so are replaced in only a few days
Of the 4 methods of protection, which 3 are promoted/ sped up by the presence of Prostaglandins?
What drugs can reduce prostaglandin release
- Mucin secretion by Surface Mucous/ Foveolar cells
- HCO3 ion secretion into mucus
- High blood flow to gastric mucosa
- NSAIDS
Name 3 things that can break the stomach’s defences and state what they can cause?
- Alcohol: Dissolves mucus layer
- Helicobacter pylori: Chronic active gastritis
- NSAIDS: Inhibit prostaglandin production
Which cells produce HCl in stomach?
List 8 stimulants for HCl production from these cells?
Parietal cells (by exchanging K+ for H+)
- Gastrin
- Histamine
- ACh
- Sensory triggers
- Stomach stretch
- Amino acid presence
- Food taken in which acts as a buffer, raising pH
- Chyme in duodenum (If continued, inhibits acid production)
How do Parietal Cells produce HCl?
- Tubulovescicles (act as proton pumps, have no K+ permeability stimulated to move towards Canaliculi of Apical membrane
- Apical membrane lined with microvilli and contains K+ channels
State the blood supply of the stomach
Blood supply- Coeliac trunk
Veinous drainage- Portal vein
Identify the secretions from the;
- Cardia
- Fundus/ Body
- Pylorus
Cardia: Mainly mucus
Fundus/ body: Mucus, HCl, Pepsinogen
Pylorus: Gastrin, Somatostatin
Gastrin is secreted from G cells in the Antrum
List 4 stimulants of G cells
- Amino acids/ peptides in stomach
- Vagal stimulation
- ACh
- GRP (Gastrin releasing peptide)
What does an Entero-Chromaffin Like cell release?
What are 2 things that stimulate it?
- Produce histamine (Stimulates parietal cells)
- Vagal stimulation via ACh
- Gastrin via CCK receptor (Same family so can bind)
Describe the Inhibition of HCl production (essentially G Cell inhibition)
- Food leaves stomach-> pH drops-> Activates D cells
- D cells release somatostatin-> Inhibiting G cells and ECL Cells
- Reduced stomach distension due to reduced Vagal activity
List the 3 Phases of Digestion
What percentage of total HCl production comes from each phase?
- Cephalic, 30%
- Gastric, 60%
- Intestinal, 10%
Describe the Cephalic phase of digestion
- Parasympathetic stimuli (Smell/ taste/ chew/ swallow)
- Vagus nerve directly stimulates parietal cells
- Vagus nerve also stimulates G cells (GRP released)
Describe the Gastric phase of digestion
- Stomach distension stimulates vagus nerve-> G and Parietal cell simulation
- Food acts as buffer in stomach removing inhibition on Gastrin production
Describe the Intestinal phase of digestion
- Chyme initially stimulates gastrin secretion as partially digested proteins are detected in duodenum
- Shortly after, G cells inhibited
- Lipid presence activates Enterogastric reflex, reducing Vagal stimulation
- Chyme stimulates CCK and Secretin (Helps suppress secretion)
Describe the chemical basis of how Parietal cells make HCl
- Carbonic Anhydrase catalysts H2O + CO2-> H2CO3 which dissociates into H+ and HCO3-
- HCO3- leaves cell through antiport, while Cl- enters cell through same channel.
- H+ and Cl- leave Apical membrane via their own channels/ pumps and combine-> HCl
What is the Alkaline Tide?
The increase in pH of veinous blood caused by HCO3- accumulation
What are 3 receptors on a Parietal cell?
- Gastrin receptors (Actually a CCK receptor but same family so gastrin can bind)
- Histamine receptors
- Muscarinic receptors
What enzyme is needed to make HCl in the Parietal Cells, once Gastrin binds to a CCK receptor
H+/ K+ ATPase
