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Stomach anatomy and physiology

Anatomy and physiology of Stomach.

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Stomach anatomy and physiology

  1. 1. Gastric Anatomy & Physiology Dr Ashish Tripathi PGY 3, General Surgery ASHISH TRIPATHI, RTIICS11/17/17
  2. 2. Anatomy In adult life, stomach located T10 and L3 vertebral segment Can be divided into anatomic regions based on external landmarks 4 regions Cardia Fundus Corpus (body) Antrum ASHISH TRIPATHI, RTIICS11/17/17
  3. 3. Anatomy Cardia- region just distal to the GE junction Fundus- portion above and to the left of the GE junction ASHISH TRIPATHI, RTIICS11/17/17
  4. 4. Anatomy Corpus- region between fundus and antrum Margin not distinctly external, has arbitrary borders Antrum- bounded distally by the pylorus Which can be appreciated by palpation of a thickened ring of smooth muscle ASHISH TRIPATHI, RTIICS11/17/17
  5. 5. Anatomy Position of the stomach varies with body habitus In general- it is fixed at two points Proximally at the GE juction Distally by the retroperitoneal duodenum ASHISH TRIPATHI, RTIICS11/17/17
  6. 6. Anatomy Anterior- in contact with Left hemi-diaphragm, left lobe and anterior segment of right lobe of the liver and the anterior parietal surface of the abdominal wall Posterior- Left diaphragm, Left kidney, Left adrenal gland, and neck, tail and body of pancreas The greater curvature is near the transverse colon and transverse colon mesentery The concavity of the spleen contacts the left lateral portion of the stomach ASHISH TRIPATHI, RTIICS11/17/17
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  8. 8. Vasculature ASHISH TRIPATHI, RTIICS11/17/17
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  10. 10. Anatomy Nerve Supply Left and Right Vagus Nerves descend parallel to the esophagus within the thorax before forming a peri-esophageal plexus between the tracheal bifurcation and the diaphragm From this plexus, two vagal trunks coalesce before passing through the esophageal hiatus of the diaphragm ASHISH TRIPATHI, RTIICS11/17/17
  11. 11. Anatomy Parasympathetic innervation of Stomach- Vagus Nerve 90% of fiber in vagal trunk is afferent (info transmitting from stomach to CNS) Sympathetic innervation of Stomach- Splanchnic Nerve Derived from spinal segement T5-T10 ASHISH TRIPATHI, RTIICS11/17/17
  12. 12. Anatomy Microscopic Anatomy Glandular portions of stomach Lined by simple columnar epithelium This luminal surface is interrupted at intervals by gastric pits Opening into these gastric pits are one or more gastric glands that have functional significance Mucosa has three types of gastric glands -Cardiac -Oxyntic -Antral ASHISH TRIPATHI, RTIICS11/17/17
  13. 13. Microscopic Anatomy Cardiac Glands Location- Cardia Contain mucous Function- secrete mucous (provides a protective coat for lining of stomach) Oxyntic Glands Most distinctive feature of the stomach Location- Fundus and Corpus Contains many cell types ASHISH TRIPATHI, RTIICS11/17/17
  14. 14. Microscopic Anatomy Parietal cells Location- neck of gastric pit Stimulated by Ach, Histamine and Gastrin Secretes HCl + Intrinsic Factor Chief Cells Location- base of gastric pit Stimulus- Vagal Secretes Pepsinogen (eventually leads to pepsin- digestive enzyme) ASHISH TRIPATHI, RTIICS11/17/17
  15. 15. Microscopic Anatomy Antral Glands Gastrin cells Location- mucosa of distal stomach Stimulus- amino acids Secretion- Gastrin (stimulates HCl production by way of parietal cells) Somatostatin Location- mucosa of distal stomach + Duodenum Stimulus- HCl or low pH in duodenum Actions- Inhibits gastric emptying, Pancreatic secretions, and gallbladder contraction ASHISH TRIPATHI, RTIICS11/17/17
  16. 16. Physiology The stomach contains a number of biologically active peptides in nerves and endocrine cells Ex. Gastrin, somatostatin, vasoactive intestinal peptide (VIP), substance P, and glucagon, etc The two peptides of greatest importance to human disease and clinical surgery are Gastrin Somatostatin ASHISH TRIPATHI, RTIICS11/17/17
  17. 17. Physiology Gastrin Most important stimulus is a meal amino acids that results from proteolysis Fat and carbohydrates are not stimuli for gastrin secretion Gastric distention that occurs from a meal will stimulate cholinergic neurons thereby releasing gastrin Gastrin will then prompt Parietal cell to secrete HCl Once Gastric distention diminishes, VIP-containing neurons are activated causing stimulation of somatostatin, thus attenuating Gastrin secretion Overall, a lumen pH >3.0 will potentiate gastrin release, whereas a pH <3.0 will inhibit its release ASHISH TRIPATHI, RTIICS11/17/17
  18. 18. Physiology Somatostain Like Gastrin, plays an integral role in gastric physiology Also, used for important therapeutic applications in treatment of digestive diseases Main stimulus is a low or acidic (<3.0)luminal pH Many peptides have shown to release somatostatin Ex. Secretin, Cholecystokinin and gastrin In contrast, stimulation of Vagal nerves along with cholinergic neurons inhibit somatostatin Overall, the most important gastric function of somatostatin is to regulate acid secretion and gastrin release ASHISH TRIPATHI, RTIICS11/17/17
  19. 19. Gastric Acid Secretion ASHISH TRIPATHI, RTIICS11/17/17
  20. 20. Gastric Acid Secretion Basolateral membrane of the parietal cell contains specific receptors for the three major stimulants of acid production Histamine Gastrin Acetylcholine Each stimulant has its own 2nd messenger system which allows for stimulation of the parietal cell ASHISH TRIPATHI, RTIICS11/17/17
  21. 21. Gastric Acid Secretion Humans normally secrete 2 to 5 mEq/h of HCl in the fasting state, constituting basal acid secretion Both Vagal tone and ambient Histamine secretion are presumed to regulate basal acid secretion Gastrin is not thought to play a role in basal acid secretion Therefore, a Vagotomy or use of H2 blockers (ex. Cimetidine) will decrease basal acid production ASHISH TRIPATHI, RTIICS11/17/17
  22. 22. Gastric Acid Secretion Stimulated acid secretion begins with Cephalic phase Thought, sight or smell of food stimulates acid secretion Mediated by Vagal stimulation Vagal discharge Directs the cholinergic mechanism for stimulation Can be inhibited by Atropine (anticholinergic) Inhibits release of somatostatin Vagal effects inhibit tonic inhibition that is provided by somatostatin ASHISH TRIPATHI, RTIICS11/17/17
  23. 23. Gastric Acid Secretion Gastric Phase Begins when food enters the stomach The following are responsible for stimulation of acid secretion Presence of partially hydrolyzed food constituents Gastric distention Gastrin is the most important mediator of this phase Ends when Antral muscosa is exposed to acid When luminal pH is <2.0 in the antrum, gastrin release stops Somatostatin release is increased Entry of digestive products into the intestine begins the intestinal-phase inhibition of gastric acid secretion ASHISH TRIPATHI, RTIICS11/17/17
  24. 24. Gastric Acid Secretion Intestinal Phase Also, releases HCl by way of Gastrin Releases secretin to inhibit Gastrin which ultimately decreases Acid production ASHISH TRIPATHI, RTIICS11/17/17
  25. 25. Other Factors Pepsin Secreted from gastric chief cells Contributes to the overall coordination of the digestive process Main function is to initiate protein digestion, usually is incomplete Partially hydrolyzed protein by pepsin are important signals for release of Gastrin Cholecystokinin ASHISH TRIPATHI, RTIICS11/17/17
  26. 26. Other Factors Intrinsic Factor (IF) Located in the parietal cells (oxyntic gland) Main function is to absorb cobalamin (Vitamin B12) form ileal mucosa and then transported to the liver Secretion of IF is similar to acid secretion stimulated Ach Histamine Gastrin ASHISH TRIPATHI, RTIICS11/17/17
  27. 27. Other Factors Bicarbonate Secreted from the gastric mucosa to maintain a neutral pH at the mucosal surface, even if acidic in lumen Cholinergic agonist, vagal nerve stimulation have been shown to increase gastric bicarbonate production ASHISH TRIPATHI, RTIICS11/17/17
  28. 28. Gastric Motility To understand gastric motility the stomach is divided into two functional terms as two different regions which have distinctive smooth muscle Proximal 1/3 3 layers of smooth muscle Outer longitudinal Middle Circular Inner Oblique Distal 2/3 Only a distinctive outer longitudinal layer Gastric smooth muscle ends at the pylorus, a septum of connective tissue marks the change from pylorus to the duodenum ASHISH TRIPATHI, RTIICS11/17/17
  29. 29. Gastric Motility Proximal 1/3 Have prolonged and tonic gastric contractions No action potentials or pacesetter Thus no peristalsis Distal 2/3 In general, gastric smooth muscle exhibit myoelectric activity based on a highly regular pattern, called slow waves Slow waves set a maximum rate at which contrations can occur (3 contractions/min); they do not cause contractions ASHISH TRIPATHI, RTIICS11/17/17
  30. 30. Thanks You 11/17/17 ASHISH TRIPATHI, RTIICS