Absorption of Digested Foods

Importance of Absorption

The absorption process is the mechanism by which the final digestive products enter the blood or lymph through the intestinal mucosa. In the small intestine, digested molecules of food are absorbed. This means they go into our bloodstream through the membrane of the small intestine. From there, the molecules of the digested food are carried around the body to the necessary location for nourishment. Absorption of food takes place mostly in the small intestine.

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Absorption across a surface happens rapidly and easily if:

  • The surface is thin

  • It has a large area

The internal wall of the small intestines is designed to allow for the easy and efficient crossing of substances:

  • It has a thin wall, just a dense cell

  • There's a lot of small villi to give a larger surface area

With a thick wall and a small surface, the small intestine may hold a large quantity of digested food before it is absorbed. The villi (singular: villus) stands out and gives a larger surface area for absorption. They also contain blood capillaries for absorbing the molecules of food that are ingested.


In the large intestine, excess water is absorbed from the food. What remains is the faecal matter. The faecal matter is stored in the rectum, which is the ending of the large intestine, and it continues to store there till the matter could be ejected out. It then emerges from the rectum in the form of faeces from the anus. This is known as egestion. Make sure that egestion is not confused with excretion. Egestion is the ejection of undigested food, while excretion is the discharge of metabolic waste material.

The digestive system contains several bacteria and bacteria constitute about half the dry weight of the faeces. Bacteria are important in the digestive system. The constituents of the faeces are:

  • Some forms of nutrients, like certain carbohydrates that people can not digest.

  • Dead bacteria.

The transport mechanisms on the apical surface of enterocytes (the absorptive cells of the intestine) absorb most nutrients. Lipid, fat-soluble vitamins and most water-soluble vitamins are exceptions. The dietary fats are emulsified by bile salts and lecithin to form micelles that may bring fatty particles to the enterozyte's surface. The micelles release their fats throughout the membrane of the cell. Fats are then processed into chylomicrons, which are converted into lactates, into triglycerides and combined with other lipids and proteins. Other absorbed monomers move from the villus to the hepatic portal vein from blood capillaries to and from the liver.

What is Meant by Digestion?

Digestion is how your body turns food into nutrients that are used to repair cells, energy and facilitate growth. The food pipe connecting your mouth and stomach, the stomach and the anus together form the digestive tract (or gastrointestinal tract). It consists of a variety of muscles that coordinate food movement and other cells that contain enzymes and hormones. Three other organs, that is, the liver, gallbladder and pancreas, are needed for digestion.

Mechanisms of Absorption

  • Simple diffusion.

  • Active transport

  • Facilitated transport.

  • Passive transport.

Simple Diffusion

Simple diffusion refers to movement through the membrane of the solution from the higher level to the lower level. Some monosaccharides, based on the concentration gradient, diffuse into the blood after digesting. E.g., Glucose, amino acids and chloride ions.

Active Transport

The process of solute movement from lower concentrations to higher concentrations at the cost of energy can be described as active transport. During successful blood flow, electrolytes such as Na (sodium) ions are absorbed.

Facilitated Transport

The process of the movement of solutes across the biological membrane using specific carrier proteins is defined as facilitated transport. This method absorbs certain digested amino acids and glucose into the blood.

Passive Transport

Passive transportation is characterized as the solvent movement process across a cell membrane without the expenditure of energy. After digestion, passive transportation absorbs a simpler food substance into the blood.

The blood can not absorb certain digested products from fats. E.g., Glycerol and fatty acids. These components attach to small droplets and form the micelle complex. The component complexes of this micelle are transformed into chylomicrons. Chylomicrons are fat globules covered with small proteins. The chylomicrons are then moved into the lymph vessels and released into the blood. Eventually, the substance that is digested and ingested enters the fabric to be used. This is how the absorption and assimilation of digested food are done.

FAQ (Frequently Asked Questions)

1. What is Absorption in Biology?

Absorption of food is the process through which the digestion products are absorbed into the blood to be delivered throughout the rest of the body. Once digestion is complete, there are several basic molecules of nutrients that need to be consumed by blood or Lymph from the GI tract in order to be used within the body by the cells. In the stomach and large intestine, a few substances are consumed. For example, in these two organs, water is absorbed, and it is also absorbed in the large intestines along with some minerals and vitamins. In the small intestine, however, nearly 95% of nutrient molecules are absorbed. In the second section of the intestine called the jejunum, the absorption of a majority of these molecules is facilitated.

2. Where is Digested Food Absorbed into the Blood in the Human Body?

The small intestine takes up most digested food molecules, water and minerals, and transfers them for storage or further chemical modification to other parts of the body. Specialized cells allow the absorption of food in the bloodstream via the intestinal lining. The simplicity of sugar, amino acids, glycerol, vitamins and salts in the bloodstream is found in the skin. The fatty acid and vitamins are absorbed in the lymphatic system, a network of vessels spread through the body carrying white blood cells and a fluid called lymph.