Overarching Function

Food moves from the mouth, through the esophagus to the digestive organs in your body. The digestive system ingests food, breaks it down into nutrients, absorb those nutrients and move them into your blood, and then excrete waste your body cannot process.

Basic structures and functions

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Macroscopic structures

  1. Stomach

    The esophagus leads the food into the stomach. The walls of the stomach are composed of smooth muscle that helps to further break down the food mechanically and mix it with the chemicals secreted by glands that line the inner wall. The environment inside the stomach is very acidic, thanks to an enzyme called pepsin, as described below. Cells in the lining of the stomach secrete mucus to protect damage from such an acidic environment. Some substances, such as alcohol and aspirin, are absorb by cells that line the stomach, whereas most of the absorption happens in the small intestine. Normally, the stomach is about 50 ml. When it is full, it can expand to 2-4 liters.

  2. Small Intestine

    The small intestine helps digest food coming from the stomach. The folds and surfaces of the small intestine increase the area of absorption, which allows more water and nutrients to be absorbed. It also sends waste products to the large intestine.

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Microscopic structures

  1. Pepsin

    Pepsin is an enzyme stored in your stomach that helps break down proteins. It is involved in the chemical digestion process.

  2. Amylase

    Amylase is an enzyme in saliva that breaks down starches into sugars when you chew food. It is involved in the chemical digestion process.

Connection to other systems

The digestive system receives nutrients. Nutrients then get turned into products that the blood can absorb. Blood vessels in the circulatory system absorb the nutrients and carries those nutrients to other parts of the body.

Differences between a frog and human

Frogs do not have strong teeth and instead just swallow the prey without chewing. Chewing, however, is a very important form of mechanical digestion in humans. When frogs shallow, they blink or close their eyes. In addition, frogs have a shorter small intestine with only two parts, the duodenum and ileum. Humans have three parts: the duodenum, jejunum, and the ileum. Frogs absorb nutrients mainly in the ileum, whereas humans absorb them in the jejunum. Since frogs do not have a urethra, the urinary bladder also opens into the cloaca. Humans have a separate urethra for processing urine.