Gastric acid
Gastric acid is a digestive fluid, formed in the stomach. It has a pH of 1.5 to 3.5 and is composed of hydrochloric acid (HCl) (around 0.5%, or 5000parts per million), and large quantities of potassium chloride (KCl) andsodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes can break down the long chains of amino acids.
Gastric acid is produced by cells lining the stomach, which are coupled to 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. Cells in the beginning of the small intestine, or duodenum, further produce large amounts of bicarbonate to completely neutralize any gastric acid that passes further down into the digestive tract.
The presence of gastric acid in the stomach and its function in digestion was first characterized by U.S. Army surgeon William Beaumont around 1830. Beaumont was able to study the stomach action of fur trapperAlexis St. Martin due to the latter's gastric fistula.
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Physiology
Gastric acid is produced byparietal cells(also called oxyntic cells) in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the gastric acid is secreted into the lumen of the stomach. These cells are part of epithelialfundic glands in the gastric mucosa. The pH of gastric acid is 1.35 to 3.5[1] in the human stomach lumen, the acidity being maintained by theproton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the blood stream in the process, which causes a temporary rise of pH in the blood, known as alkaline tide.
The resulting highly acidic environment in the stomach lumen causesproteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and rennin).HCl activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known asproteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection.
Secretion
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 oxyntic 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.
Chloride and sodium ions are secreted actively from the cytoplasm of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV to -70 mV across the parietal cell membrane that causes potassium ions and a small number of sodium ions to diffuse from the cytoplasm into the parietal cell canaliculi.
The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water to form carbonic acid. This acid immediately dissociates into hydrogen and bicarbonate ions. The hydrogen ions leave the cell through H+/K+ ATPase antiporter pumps.
At the same time sodium ions are actively reabsorbed. This means that the majority of secreted K+ and Na+ ions return to the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions mix and are secreted into the lumen of the oxyntic gland.
The highest concentration that gastric acid reaches in the stomach is 160mM 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,[2] but the acid is diluted in the stomach lumen to a pH between 1 and 3.
There are three phases in the secretion of gastric acid:
- The cephalic phase: Thirty percent of the total gastric acid secretions to be produced is stimulated by anticipation of eating and the smell or taste of food.
- The gastric phase: Sixty percent of the acid secreted is stimulated by the distention of the stomach with food. Plus, digestion produces proteins, which causes even more gastrin production.
- The intestinal phase: The remaining 10% of acid is secreted whenchyme enters the small intestine, and is stimulated by small intestine distention.
There is also a small continuous basal secretion of gastric acid between meals of usually less than 10 mEq/hour.[3]
Regulation of secretion
Gastric acid production is regulated by both the autonomic nervous system and several hormones. The parasympathetic nervous system, via the vagus nerve, and the hormone gastrin stimulate the parietal cell to produce gastric acid, both directly acting on parietal cells and indirectly, through the stimulation of the secretion of the hormone histamine fromenterochromaffine-like cells (ECL). Vasoactive intestinal peptide,cholecystokinin, and secretin all inhibit production.
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.
Nerve endings in the stomach secrete two stimulatory neurotransmitters:acetylcholine and gastrin-releasing peptide. Their action is both direct on parietal cells and mediated through the secretion of gastrin from G cells and histamine from enterochromaffine-like cells. Gastrin acts on parietal cells directly and indirectly too, by stimulating the release of histamine.
The release of histamine is the most important positive regulation mechanism of the secretion of gastric acid in the stomach. Its release is stimulated by gastrin and acetylcholine and inhibited by somatostatin.
Neutralization
In the duodenum, gastric acid is neutralized by sodium bicarbonate. This also blocks gastric enzymes that have their optima in the acid range ofpH. 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 duodenum falls below 4.5 to 5.0. The neutralization is described by the equation:
- HCl + NaHCO3 → NaCl + H2CO3
The carbonic acid instantly decomposes into carbon dioxide and water.
Role in disease
In hypochlorhydria and achlorhydria, there is low or no gastric acid in the stomach, potentially leading to problems as the disinfectant properties of the gastric lumen are decreased. In such conditions, there is greater risk of infections of the digestive tract (such as infection with Vibrio orHelicobacter bacteria).
In Zollinger-Ellison syndrome and hypercalcemia, there are increasedgastrin levels, leading to excess gastric acid production, which can causegastric ulcers.
In diseases featuring excess vomiting, patients develop hypochloremicmetabolic alkalosis (decreased blood acidity by H+ and chlorine depletion).
Pharmacology
The proton pump enzyme is the target of proton pump inhibitors, used to increase gastric pH in diseases that feature excess acid. H2 antagonistsindirectly decrease gastric acid production. Antacids neutralize existing acid.
History
The role of gastric acid in digestion was established in the 1820s and 1830s by William Beaumont on Alexis St. Martin, who, as a result of an accident, had a fistula (hole) in his stomach, which allowed Beaumont to observe the process of digestion and to extract gastric acid, verifying that acid played a crucial role in digestion.[4]
What Is Stomach Acidity?
It is commonly known that excessive secretion of acid leads to hyper acidity. The stomach has a inner lining. If this lining gets damaged or weakened if challenged with certain foods like too much tea, coffee, alcohol or certain medicines like pain relieving drugs. The acidic secretion transverses the stomach and causes pain and discomfort. If this happens repeatedly, it gives rise to gastritis thereby inflaming the lining of the stomach.
Causes Of Excess Stomach Acid
- Factors responsible for hyper acidity include excessive intake of pungent and sour food, alcoholic beverages and hot food which cause burning sensations.
- Fried, fatty, creamy stuff, chocolate, garlic and onion, coffee, tea and carbonated beverages may also be a reason for increasing acidic levels in your stomach.
- Anger, fear, excessive stress, exposure to sun and fire and irregular meals also contribute to acidity.
How To Reduce Stomach Acid
- Avoid excess salt, oil, pickles, curd, fried food, sour foods like tamarind
- Increase intake of salads and legumes.
- Inculcate proper eating habits:
- Do not eat too fast.
- Maintain an upright posture after eating.
- Do not overeat.
- Dinner should be taken at least three hours before going to bed.
- Avoid bedtime snacks.
- Milk acts as an excellent remedy for acidity.
- Cereals from fresh crops should be avoided.
- Excess intake of sweets also can cause acidity as sugar causes fermentation and produces acid in stomach.
Natural Remedies For Stomach Acid
- Chewing of fennel seeds after a meal, stimulates production of saliva, an alkaline solution that helps soothe and protect the food pipe.
- Two teaspoonfuls of clarfied butter in a glass of warm milk lowers acid levels in your stomach. It also acts as a laxative, which helps flush excess acid from the system.
- Coconut water is one of the best home remedies for acidity.
- Take two spoons of Gooseberry powder three times a day.
- A decoction of sandal if consumed thrice daily, gives good relief from acidity.
Excess Stomach Acid
SELECT A TOPIC
- Symptoms of Excess Stomach Acid
- Causes of Excess Stomach Acid
- Help for Excess Stomach Acid
- Excessive Stomach Acid During Pregnancy
- Excessive Stomach Acid in Babies and Children
- How to Avoid Excess Stomach Acid
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What is Excess Stomach Acid?
When we eat food, our body needs to break it down into usable nutrients and vitamins. The process of this breakdown starts off in the stomach. The stomach secretes an acid that is essential in the digestive process, as this acid helps in breaking down the food during digestion.
Usually, protective mechanisms in the stomach and proximal intestine make sure that the acid levels are in balance. However, when the stomach produces too much acid, it results in a condition known as Acidity, or APD. Excess gastric acid is more prevalent in the morning when the stomach is empty.
Excess stomach acid levels can contribute greatly to:
- Heartburn
- Dyspepsia (often described as a feeling of indigestion, fullness, bloating, flatulence or nausea)
- Duodenal ulcer
- Gastric ulcer
- Peptic ulcer
- Non-ulcer dyspepsia
- Acid Reflux
Causes of excess stomach acid:
Symptoms of Excess Stomach Acid:
- Hair Loss
- Bad Breath (Halitosis)
- Belching
- Nasal Congestion and Phlegm
- Abdominal Pain
- Throat Pain
Excessive Stomach Acid During Pregnancy
There are a couple reasons why pregnant women suffer with excessive stomach acid. One of the main reasons is due to raised hormone levels. When hormones are constantly changing the digestive tract muscles are affected and therefore can result in the way different foods are tolerated. Secondly, a growing baby also crowds the abdomen, pushing acids upwards.
As with many pregnant women, heartburn can be a result of excessive stomach acid. Pregnancy hormones cause the lower esophageal sphincter to relax which allows stomach acid to seep back up into the esophagus, causing acid reflux.
Excessive Stomach Acid in Babies and Children
Just like adults babies and children can suffer from excessive stomach acid too. For growing babies, stomach acid is part of normal digestive system growth. When stomach acid is in excess it can lead to acid reflux in which the stomach acids start to travel up the esophagus thereby resulting in "spitting up" or vomiting. Though many babies suffer from reflux symptoms it can be painful for the child and troubling to parents.
Older children who suffer from excess stomach acid often complain of an upset stomach. Frequently, children who overeat unhealthy foods such as cookies or candy develop excessive stomach acid. Alternatively, nervousness or anxiousness can create tummy acid.
Help for Excess Stomach Acid
Natural Remedies
Many herbal and homeopathic remedies have been formulated with specific ingredients toassist the body in keeping excess gastric acid levels in balance. Mentha Piperita is an herb from the mint family that has been used for many hundreds of years for relief ofindigestion, nausea and heartburn. Its calmative properties relax the muscles of the digestive tract and stimulate the flow of natural digestive juices and bile, thereby assisting healthy digestion.
Nat.Sulph. Is a tissue salt and is known as the 'cell cleanser.' This tissue salt regulates body fluids and helps to promote healthy functioning of the digestive system, thereby preventing nausea as well as the bitter taste in the mouth often associated with acid reflux and regurgitation.
How to Avoid Excess Stomach Acid
- Try to identify foods that contribute to excess stomach acid. Foods that are spicy, salty and acidic should be avoided.
- Smoking and alcohol consumption should be stopped to keep stomach acid levels in the stomach and esophagus in harmony.
- Avoiding stress and moderating your lifestyle to include relaxing techniques can go a long way to prevent excess stomach acid and ulcers, particularly if you are a nervous and emotional person or involved in a high-stress job.
- Avoid non-steroidal anti-inflammatory drugs (NSAIDs). These drugs may predispose a person to excess stomach acid.
- Try to eat regular meals and follow a healthy diet.
- Take extra care when lifting weights, as this puts the abdominal area under added strain and may result in digestion problems.
- If you have a bout of excess stomach acid, try having an organic glass of fat-free or low-fat milk to help normalize the pH in your stomach.
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