Digestion is a complicated process that relies on HCl or hydrochloric acid in the stomach, as well as several other organs and digestive juices. There isn't just one function of HCl in the stomach though, but rather several ways that the acid contributes to digestion and keeps you healthy.
Hydrochloric acid helps break down proteins, allows you to absorb certain nutrients and kills off foreign invaders, like bacteria and viruses that can make you sick. To fully grasp how hydrochloric acid works, it's helpful to understand how digestion works, too.
Digestive System Basics
Your digestive system is made up of several organs that come together to form what's called the gastrointestinal, or GI, tract. Your GI tract consists of your mouth, esophagus, stomach, small intestine, large intestine, liver and pancreas. Each organ has a separate job and relies on a series of processes to complete its job.
When you first put food in your mouth, your teeth and saliva start to break down that food. It then travels through your esophagus and into your stomach, where it's mixed with gastric juices that contain a large percentage of hydrochloric acid, also called HCl, stomach acid or gastric acid.
From the stomach, food travels into your small intestine where it's mixed with more digestive juices that come from the liver and the pancreas.
Once the small intestine has finished its job, food moves on to the large intestine where digestion is completed, then waste products travel out of your body through bowel movements. Although every single part of this process is important, the hydrochloric acid in the stomach is a vital component.
Hydrochloric Acid in the Stomach
Hydrochloric acid is a primary component of your stomach acid, accounting for 0.5 percent of its total volume; however, that's not the only important substance. Stomach acid also contains large amounts of potassium chloride and sodium chloride.
Together, these substances give stomach acid a pH of around 1 to 2, which is almost as acidic as you can get on the pH scale. According to the February 2012 issue of ChemMatters, a publication produced by the American Chemical Society, your body makes two to three liters of stomach acid every day.
Even though stomach acid is so acidic, it doesn't cause any harm to your stomach because the body has built-in mechanisms to protect the stomach's lining from being eaten away by the acid.
Mucus cells are the most abundant cells in your stomach lining. These mucus cells release mucus that coats the entire inside of your stomach. The mucus doesn't just form a physical barrier to HCl; it also contains high volumes of bicarbonate, which helps neutralize the acid when it comes into contact with your stomach lining.
Because of this advanced biochemical system, the hydrochloric acid in your stomach is able to perform its jobs without hurting you.
The Breakdown of Protein
One major role of HCl in the stomach is to help break down protein. Your stomach lining contains specialized cells, called parietal cells, that release stomach acid in the presence of food. Other cells in the lining of your stomach, called chief cells, secrete other important substances, one of which is called pepsinogen. When stomach acid comes into contact with pepsinogen, it turns it into an active enzyme called pepsin.
Pepsin is classified as a protease enzyme because it helps break apart the protein from the food you eat into its smaller components, called amino acids. Your body isn't able to absorb whole proteins, but when they're broken down into amino acids, these amino acids can travel through to your small intestine where they're absorbed and used to make other proteins that your body needs to stay healthy.
Without HCl, pepsinogen would never turn into pepsin, and your body wouldn't be able to effectively digest the proteins from the food you eat. On the other hand, without pepsin, HCl also wouldn't be able to break down protein on its own, explains the ChemMatters article.
But protein isn't the only nutrient that relies on the presence of stomach acid — HCl also helps you absorb some vitamins and minerals, too.
Read more: Five Stages of Protein Digestion
Absorption of Nutrients
Another function of HCl in the stomach is to facilitate the absorption of vitamin B12, iron and calcium, according to a report published in November 2014 in Current Opinion in Gastroenterology. Vitamin B12 is an essential nutrient that's found almost primarily in animal-based, protein-rich foods.
In order to absorb vitamin B12, it must be detached from the dietary protein with which it's coupled. In order for your body to do this effectively, it needs to have enough pepsin, which is activated only by HCl.
Iron and calcium both rely on the acidity of hydrochloric acid itself for proper digestion and absorption. A June 2013 report in Therapeutic Advances in Drug Safety notes that iron and calcium both need an acidic environment to dissociate from the foods in which they occur, so that your body can effectively absorb them.
Because hydrochloric acid is such a vital component in nutrient digestion and absorption, people who take proton-pump inhibitors, or medications that reduce the production of stomach acid, have a higher risk of developing vitamin and mineral deficiencies than people who don't.
Prevention of Illness
The Current Opinion in Gastroenterology report also notes that another function of HCl in the stomach is its ability to kill off microorganisms that may otherwise cause infection and disease. Although your stomach is not an official part of your immune system, the acidic environment that HCl creates makes it difficult for bacteria or viruses to survive.
The acid combines with pepsin and lipase, another enzyme that helps your body break down fats, to kill any pathogens that you may have ingested through contaminated food or contact with someone who is sick, thus helping to reduce the risk of getting sick yourself. In addition to warding off foodborne illnesses, Current Opinion in Gastroenterology reports that this may also help prevent:
- Bacterial overgrowth
- Enteric infection
- Bacterial peritonitis
- Certain types of pneumonia
- Mycobacterium tuberculosis infection
So, not only does hydrochloric acid help keep you healthy by allowing you to digest and absorb proteins and other nutrients that your body needs, it also acts as an important defense mechanism.
- National Institute of Diabetes and Digestive and Kidney Diseases: "Your Digestive System and How It Works"
- Colorado State University: "Gastric Secretions"
- Current Opinion in Gastroenterology: "Gastric Secretion"
- Digestive Diseases: "Digestive Function of the Stomach"
- Clinical Education: "The Role of HCL In Gastric Function and Health"
- Therapeutic Advances in Drug Safety: "Proton Pump Inhibitors and Risk of Vitamin and Mineral Deficiency: Evidence and Clinical Implications"
- American Chemical Society: "24 Hours: Your Food on the Move"