april 27, 2022

What are the functions of the small and large intestines?

The small intestine does the following:

- It absorbs nutrients from food, which it sends to the large intestine for elimination.

- It helps digest food by separating water and nutrients into simple forms that can be absorbed in the blood.

- It also egests waste products (like undigested food) into the large intestine, where they are eliminated by normal body functions.

The large intestine does the following:

- It absorbs water and nutrients left over after the small intestine has absorbed them.

- It egests undigested food, waste products, and bacteria into the rectum, where they are eliminated by normal body functions.

Note: The large intestine includes the cecum and colon. The small intestine consists of the duodenum, jejunum, and ileum.

The inner lining of the smallest part of the intestine, the duodenum, secretes digestive juices to break down foods into simpler compounds for absorption into the bloodstream. This process is complicated because it must identify foods that are beneficial to the body and foods that are harmful to it; not all substances are equally digestible or absorbable. Some kinds of food require special enzymes that only certain bacteria produce, and these bacteria live in the large intestine. Without them, the intestinal enzymes are not able to complete their tasks. A look at the chart below will help you understand this process.

With the help of digestive juices from the stomach and small intestines, the proteins from food are broken down into simple substances such as amino acids, carbohydrates, and fats. These substances form a thick solution called chyme (chy-may) which is pumped into the small intestine through tiny tubes that line its walls called ducts. They are lined with fingerlike projections called villi (vee-lee), which create a large surface area to absorb the digested food.

The body is highly efficient when it comes to energy. It can extract from food only what it needs and store the rest of the digested material as fat where it is required. The digestion process also absorbs water from foods, and if this water isn't needed, it is also stored as body fat. Finally, waste products that remain after digestion are eliminated through the intestines in egestion (egz-tee-on).

The shape and function of the small intestine are similar in many respects to that of the human heart. The inner aspect, called the mucosa (mu-kooo-sa), is lined with similar epithelial cells, which are flattened cells covered by a single layer of the cell membrane. Containing no blood vessels, the small intestine has no red blood cells. There are no white blood cells either because their inner lining lacks a barrier to infection and other harmful substances.

The small intestine has one massive active organ: the villus (vee-oo-lus), which forms a fingerlike projection from its cylindrical walls. A villus is a fingerlike projection from a cylindrical wall, which creates a large surface area to absorb and digest the food. Villi are lined by cells called epithelium (ee-tee-lee-um), similar to those in the stomach or small intestine of other animals. These cells secrete digestive juices into the villi, breaking down food and absorbing its nutrients. The villi are joined together by tiny channels called microvilli (mee-koo-vee-li) that increase their surface area and act as tiny brushes to complete the work of digestion. This process is similar to how a blender works, where food is broken into smaller pieces.

The microvilli at the base of villi absorb water and nutrients and help remove waste substances. However, they are also different from intestinal cells in that they don't line the whole length of their base. But instead, they are short stubby structures that extend into the lumen (loom-yoo-en) through which waste products move. If a person could "see" all the villi in his intestine, he would see them as little tree stumps. They form a dense fingerlike projection from each small intestine wall with spaces between each one that fills with fluid and food during digestion.

After a meal, the microvilli absorb as much of the digested food and liquid as possible. The remaining waste products are moved into the spaces between villi and then further into the large intestine, where they gradually transfer through the wall of the small intestines into the bloodstream. This transfer occurs because the intestinal cells have tiny pores in their membranes controlled by a pressure mechanism called "leaky" junctions. They open to allow nutrients to pass through.