Stomach: Gastric Secretion, Motility and Emptying

Nota:

• Oxyntic Glands area: Body and fundus: Upper 80%, consists of acid secreting parietal cells. Pyloric gland area: Antral Region, Lower 20% Gastrin secreting G-cells.

1. Secretions

   Nota:

   • Acid: Protons or H+ Pepsin: Pepsinogen, activated by acid Mucous and HCo3-: Lubricates and protects against physical damage, maintain near neutral pH at surface  Intrinsic Factor: ileal absorption of vit b12 Gastrin: Regulates acid secretion
   1. Acid

      Nota:

      • Proton pump moves to the cell membrane and pump H+ into lumen and exchange it with K+ Passive K+ channels return it into the lumen and carbonic anhydrase converts water and carbon dioxide to proton and hydrogencarbonate. which is then exchanged with Chloride. and leave trhu apical Cl- channels and combined with proton to make HCl.
      1. Control

         Nota:

         • Control is stimulated by  AChGastrinHistamine (released from enterochromaffin like cells) Reflect a combination of neural, endocrine and paracrine control.
      2. Inhibition

         Nota:

         • Inhibited by somato statin Generated in the D Cells, it is in the anthrum, and it is stimulated by neural and hormonal mechanisms such as gastrin. Somatostatin: Inhibits gastrin release from G cells ECL cells to inhibit histamin Parietal cells inhibited acid.
      3. Regulation

         Nota:

         • 3 receptors senses it: Mechanoreceptors: Monitor state of distention Chemoreceptors: Monitor concentration of substances in lumen Osmoreceptors: Monitor osmolarity of lumen content. integrating centers; CNS ENS Effectors: Include endocrine, exocrine and smooth muscles.
   2. Pepsinogen

      Nota:

      • Control is via pH. Release via ENS and ACh.
   3. Mucous

      Nota:

      • Soluble mucous was produced from mucous neck cells, and stimulated by vagally mediated ACh release, lubricates... Insoluble or surface mucous, produced in response to chemical and mechanical stimuli, forms a protective gel layer to trap hydrogencarbonate and cellular debris

Nota:

• Both hormonal and neural Short vs Long pathways. 3 phases Cephalic, gastric and intestinal phases Cephalic: Vagus Gastric phase: 1. Local nervous secretory reflexes 2. Vagal reflexes 3. Gastrin-histamine stimulation Intestinal: 1. Nervous Mechanisms 2. Hormonal Mechanisms.

1. Cephalic

   Nota:

   • 20-30% max secretory response. Gastric secretion stimulated by thoughts, or sensory. Increased stimulus via parasympathetic activity  to increase plasma gastrin levels.
2. Gastric

   Nota:

   • 50%  Chemoreceptors and mechanoreceptors detect and respond and act via short and long reflexes to increase plasma gastrin.
3. Intestinal

   Nota:

   • Consists of an excitatory and inhibitory event. Excitatory: Low pH and partially digested food stimulates gastrin production Inhibitory: Distension of duodenum causes enterogastric reflex, inhibit local ENS reflex and pyloric sphincter to close/tighten. Enterogastron release: Release CCK (cholecystokinin) and secretin to inhibit gastrin.

Nota:

• Accommodation: Getting and providing temporary storage of food and liquid Mixing: Mix food and liquid with pepsin and acid and other secretory products Grinding: Reduce particle size Regulating the exit

1. Regulation

   Nota:

   • Regulated via reflexes: 1. Receptive relaxation Mechanical stimuli in pharynx 2. Adaptive Relaxation Inhibitory vagal fibre detects ACH and NO and VIP to relax. Or presence of nutrients will distend. 3. Feedback relaxation
2. Contractions and Peristaltic wave

   Nota:

   • Tonic contraction will accumulate chyme and motility will increase with presence of gastrin and decrease under influnece of CCK and secretin
3. Gastric Antrum

Nota:

• Vomiting centre in medulla is activated. Nausea, increased heart rate, sweating and salivation. Retrograde giant contraction and propagates orally thru stomach. Chyme, inhalation closed epiglottis. Diaphragm moves downwards and abdo muscles contract strongly increased in abdominal pressure and closure of pyloric sphincter  and the lower esophagal sphicter and relaation relax. Barf.