question: When laying down or even being upside down, how does our stomach acid not leak into other parts of the body?
comment: There are rings of muscles called sphincters that keep the openings of each end of the stomach tightly closed when nothing is passing in or out.
passages: A fourth phase of acid secretion is known as the basal state which occurs in the times between meals (interdigestive phase). The level of acid secretion during these times is regulated by body weight, individual, number of parietal cells, and time of day. Acid secretion is lowest in the morning before awakening and highest at night.
  
  Section::::Cephalic Phase.
   The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
  
  There is a small continuous basal secretion of gastric acid between meals of usually less than 10 mEq/hour.
  
  There are three phases in the secretion of gastric acid which increase the secretion rate in order to digest a meal:
   A typical adult human stomach will secrete about 1.5 liters of gastric acid daily. Gastric acid secretion happens in several steps. Chloride and hydrogen ions are secreted separately from the cytoplasm of parietal cells and mixed in the canaliculi. Gastric acid is then secreted into the lumen of the gastric gland and gradually reaches the main stomach lumen. The exact manner in which the secreted acid reaches the stomach lumen is controversial, as acid must first cross the relatively pH neutral gastric mucus layer.
   The stomach bed refers to the structures upon which the stomach rests in mammals. These include the pancreas, spleen, left kidney, left suprarenal gland, transverse colon and its mesocolon, and the diaphragm. The term was introduced around 1896 by Philip Polson of the Catholic University School of Medicine, Dublin. However this was brought into disrepute by surgeon anatomist J Massey.
  
  Section::::Structure.:Blood supply.
   The enteric nervous system in humans consists of some 500 million neurons (including the various types of Dogiel cells), 0.5% of the number of neurons in the brain, five times as many as the one hundred million neurons in the human spinal cord, and about 2/3 as many as in the whole nervous system of a cat. The enteric nervous system is embedded in the lining of the gastrointestinal system, beginning in the esophagus and extending down to the anus.
   The gastric chief cell (also known as a zymogenic cell or peptic cell) is a cell in the stomach that releases pepsinogen and chymosin. Pepsinogen is activated into the digestive enzyme pepsin when it comes in contact with acid produced by gastric parietal cells. This type of cell also secretes gastric lipase enzymes, which help digest triglycerides into free fatty acids and di- and mono-glycerides. There is also evidence that the gastric chief cell secretes leptin in response to the presence of food in the stomach. Leptin has been found in the pepsinogen granules of chief cells.
   Gastric chief cell
  
  A gastric chief cell (or peptic cell, or gastric zymogenic cell) is a type of cell in the stomach that releases pepsinogen and gastric lipase and is the cell responsible for secretion of chymosin in ruminants. The cell stains basophilic upon H&E staining due to the large proportion of rough endoplasmic reticulum in its cytoplasm. Gastric chief cells are generally located deep in the mucosal layer of the stomach lining.
   The carbonic acid rapidly equilibrates with carbon dioxide and water through catalysis by carbonic anhydrase enzymes bound to the gut epithelial lining, leading to a net release of carbon dioxide gas within the lumen associated with neutralisation. In the absorptive upper intestine, such as the duodenum, both the dissolved carbon dioxide and carbonic acid will tend to equilibrate with the blood, leading to most of the gas produced on neutralisation being exhaled through the lungs.
  
  Section::::Role in disease.
   Due to the pH of the small intestine, most of the bile acids are ionized and mostly occur as their sodium salts which are then called “primary conjugated bile salts.” In the lower small intestine and colon, bacteria dehydroxylate some of the primary bile salts to form secondary conjugated bile salts (which are still water-soluble). Along the proximal and distal ileum, these conjugated primary bile salts are reabsorbed actively into hepatic portal circulation. Bacteria deconjugate some of the primary and secondary conjugated bile salts back to lipid-soluble bile acids, which are passively absorbed into hepatic portal circulation. Finally, the conjugated bile acids which remained un-ionized conjugated bile acids are passively absorbed.
   The production of gastric acid in the stomach is tightly regulated by positive regulators and negative feedback mechanisms. Four types of cells are involved in this process: parietal cells, G cells, D cells and enterochromaffine-like cells. Besides this, the endings of the vagus nerve (CN X) and the intramural nervous plexus in the digestive tract influence the secretion significantly.
   Gastric chief cells are primarily activated by ACh. However the decrease in pH caused by activation of parietal cells further activates gastric chief cells. Alternatively, acid in the duodenum can stimulate S cells to secrete secretin which acts on an endocrine path to activate gastric chief cells.
  
  Section::::Gastric Phase.
  
  50-60% of total gastric acid secretion occurs during this phase.
   The second vital secretion of the GI tract is that of digestive enzymes that are secreted in the mouth, stomach and intestines. Some of these enzymes are secreted by accessory digestive organs, while others are secreted by the epithelial cells of the stomach and intestine. While some of these enzymes remain embedded in the wall of the GI tract, others are secreted in an inactive proenzyme form. When these proenzymes reach the lumen of the tract, a factor specific to a particular proenzyme will activate it. A prime example of this is pepsin, which is secreted in the stomach by chief cells. Pepsin in its secreted form is inactive (pepsinogen). However, once it reaches the gastric lumen it becomes activated into pepsin by the high H+ concentration, becoming an enzyme vital to digestion. The release of the enzymes is regulated by neural, hormonal, or paracrine signals. However, in general, parasympathetic stimulation increases secretion of all digestive enzymes.
   Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as peristalsis. The lower esophageal sphincter is a muscular sphincter surrounding the lower part of the esophagus. The junction between the esophagus and the stomach (the gastroesophageal junction) is controlled by the lower esophageal sphincter, which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of this sphincter can lead to heartburn. The esophagus has a mucous membrane of epithelium which has a protective function as well as providing a smooth surface for the passage of food. Due to the high volume of food that is passed over time, this membrane is continuously renewed.
   The largest component of secreted fluids is ions and water, which are first secreted and then reabsorbed along the tract. The ions secreted primarily consist of H, K, Cl, HCO and Na. Water follows the movement of these ions. The GI tract accomplishes this ion pumping using a system of proteins that are capable of active transport, facilitated diffusion and open channel ion movement. The arrangement of these proteins on the apical and basolateral sides of the epithelium determines the net movement of ions and water in the tract.
   The pancreas is a major organ functioning as an accessory digestive gland in the digestive system. It is both an endocrine gland and an exocrine gland. The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The endocrine part releases glucagon when the blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels. The pancreas produces and releases important digestive enzymes in the pancreatic juice that it delivers to the duodenum. The pancreas lies below and at the back of the stomach. It connects to the duodenum via the pancreatic duct which it joins near to the bile duct's connection where both the bile and pancreatic juice can act on the chyme that is released from the stomach into the duodenum. Aqueous pancreatic secretions from pancreatic duct cells contain bicarbonate ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach.
   Section::::Procedure.
  
  Clinical status and relevant medical history are reviewed prior to the studies. Patient consent is required.
  
  Section::::Procedure.:Barium swallow.
   Gastric acid is produced by cells in the lining of the stomach, which are coupled in feedback systems to increase acid production when needed. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring that it does not become too acidic. These cells also produce mucus, which forms a viscous physical barrier to prevent gastric acid from damaging the stomach. The pancreas further produces large amounts of bicarbonate and secretes bicarbonate through the pancreatic duct to the duodenum to completely neutralize any gastric acid that passes further down into the digestive tract.
   In the duodenum, gastric acid is neutralized by sodium bicarbonate. This also blocks gastric enzymes that have their optima in the acid range of pH. The secretion of sodium bicarbonate from the pancreas is stimulated by secretin. This polypeptide hormone gets activated and secreted from so-called S cells in the mucosa of the duodenum and jejunum when the pH in the duodenum falls below 4.5 to 5.0. The neutralization is described by the equation:
   The thoracic duct drains into the left subclavian vein, near its junction with the left internal jugular vein. It carries lymph (water and solutes) from the lymphatic system, as well as chylomicrons or chyle, formed in the intestines from dietary fat and lipids, allowing these to enter the bloodstream; the products of fats and lipids can then be carried by the bloodstream to the hepatic portal vein, and then finally to the liver, making it so that the left subclavian vein plays a key role in the absorption of these fats and lipids.
   Vascular disorders are more likely to affect the small bowel than the large bowel. Arterial supply to the intestines is provided by the superior and inferior mesenteric arteries (SMA and IMA respectively), both of which are direct branches of the aorta.
  
  The superior mesenteric artery supplies:
  
  BULLET::::1. Small bowel
  
  BULLET::::2. Ascending and proximal two-thirds of the transverse colon
  
  The inferior mesenteric artery supplies:
  
  BULLET::::1. Distal one-third of the transverse colon
  
  BULLET::::2. Descending colon
  
  BULLET::::3. Sigmoid colon
   Left gastric vein
  
  The left gastric vein (or coronary vein) is a vein carrying deoxygenated blood that derives from tributaries draining both surfaces of the stomach; it runs from right to left along the lesser curvature of the stomach, between the two layers of the lesser omentum, to the esophageal opening of the stomach, where it receives some esophageal veins.
  
  It then turns backward and passes from left to right behind the omental bursa and drains into the portal vein. Thus, it acts as collaterals between the portal veins and the systemic venous system of the lower esophagus (azygous vein).
   Result 2: if the delta ratio is somewhere between low (<0.4) and high (1–2), then it is usually due to a combination of high anion gap metabolic acidosis and normal anion gap acidosis. For example, a person with cholera may have a normal anion gap acidosis due to diarrhea, but becomes progressively dehydrated and develops a lactic acidosis from shock, and proceeds to develop a high anion gap metabolic acidosis – i.e. a mixed acid-base disorder.
   The biliary tree is normally relatively free of bacteria because of certain protective mechanisms. The sphincter of Oddi acts as a mechanical barrier. The biliary system normally has low pressure (8 to 12 cmHO) and allows bile to flow freely through. The continuous forward flow of the bile in the duct flushes bacteria, if present, into the duodenum, and does not allow the establishment of an infection. The constitution of bile—bile salts and immunoglobulin secreted by the epithelium of the bile duct also has a protective role.
   The cephalic phase is the stage in which the stomach responds to the mere sight, smell, taste, or thought of food. About 30% of total acid secretion occurs before food enters the stomach. These sensory and mental inputs converge on the hypothalamus, which relays signals to the medulla oblongata. Vagus nerve fibers from the medulla stimulate the parasympathetic nervous system of the stomach which, in turn, stimulates gastric secretion (via parietal and G cells).
  
  Section::::Cephalic Phase.:Chain of Events.
   Secondly, patients with acute pancreatitis may present with gastric varices as a complication of a blood clot in the splenic vein. The splenic vein sits over the pancreas anatomically and inflammation or cancers of the pancreas may result in a blot clot forming in the splenic vein. As the short gastric veins of the fundus of the stomach drain into the splenic vein, thrombosis of the splenic vein will result in increased pressure and engorgement of the short veins, leading to varices in the fundus of the stomach.
  