Fun Facts About the Anatomy and Physiology of the Stomach

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  1. The stomach can hold a lot of food.

When empty, the stomach is pretty small – it is only about the size of your fist. However, it is also capable of stretching to hold up to 4 liters of food – equal to about 8 tubs of Ben & Jerry’s ice cream! This capacity to store food is important: we can eat much faster than we can digest food. It takes anywhere between 6 to 8 hours for food to pass through the stomach and into the intestine, and it can take up to 3 days for food to travel through the entire gastrointestinal tract.

  1. The stomach has many different parts.

Although diagrams of the stomach might make it seem as though it is just a sack, it actually has different parts that perform various functions. The main part of the stomach, the body, is where food is churned and broken down. It is mixed with a cocktail of acidic gastric juices to form a semi-fluid gloopy mass called chyme. The fundus, which forms the upper portion of stomach, is where the air that enters the stomach when we swallow is stored and undigested food is retained before it is mixed in with chyme in the body of the stomach. The lowest part of the stomach is called the pylorus, and it connects the stomach to the small intestine. It prevents the contents of the intestine from rising back up into the stomach when the small intestine contracts.

  1. The acid in our stomach is strong enough to digest most of the organs in the body. It is even strong enough to dissolve some metals!

The cells lining the wall of the upper regions of the stomach secrete hydrochloric acid, which has a pH between 1 and 2. For comparison, that is approximately the pH of the acid in car batteries, and is so acidic that it can dissolve steel. In the body, the hydrochloric acid starts to digest food and kills any microorganisms that might have entered the body along with the food. You might wonder how gastric acid doesn’t digest the stomach itself along with digesting the food it contains. After all, if the acid is strong enough to dissolve steel and cause severe chemical burns if skin were to touch it, the stomach could very well be harmed. The stomach is protected by mucosal cells that secrete a layer of mucus that protect the walls of the stomach. The mucus is 95% water and 5% polymers which give mucus its thick consistency. The mucus contains bicarbonate ions which neutralize some of the hydrochloric acid.

  1. The stomach is the only organ in the digestive system that has three layers of muscles.

Unlike the walls of the rest of the organs in the digestive system, the wall of the stomach is comprised of three layers of muscles. The outer layer is made up of longitudinal muscles, the middle layer is made up of circular muscles, while the inner-most layer – called the oblique layer – has muscles that run diagonally. The outer two layers help in the movement of food down the stomach and into the small intestine, while the inner layer – the layer unique to the stomach –allows the stomach to churn the food and helps in physical digestion. These muscles are why we can digest food even if we are standing on our heads: it is the muscles that move food along the digestive tract, and not gravity!

  1. The stomach is like a small chemical factory.

The stomach secretes a lot of chemicals. As mentioned above, it secretes hydrochloric acid that helps with digestion. It also secretes chemicals that stimulate the secretion of gastric acid. Additionally, it secretes a hormone called ghrelin. Ghrelin is often called the “hunger hormone” because ghrelin levels rise after fasting and make us want to eat!

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