Biology Class 11 Absorption And Assimilation of Digested Food

In this article, we will discussed how the digested food is absorbed into the blood and utilized by our body cells (absorption and assimilation) from Unit 5, Class 11 Biology. “Absorption and Assimilation of Carbohydrates” we have discussed in last article.

Biology notes for class 11 : Absorption And Assimilation of Digested Food – Once in the small intestine, absorption and assimilation begin. The glucose, fructose, fatty acids, and peptides, amino acids are absorbed through the mucosa of the small intestine and passes into the bloodstream. From there, they reach tissues throughout our body and are assimilated. Assimilation occurs in every cell of the body to help develop new cells.

The food which is not digested or absorbed in the small intestine is then passed into the large intestine where water and minerals are absorbed. Fiber present in the food is indigestible and passes through the gastrointestinal tract without being broken down. Whatever is left is then expelled through the anus. Everything absorbed in the digestive system is used to make substances needed by cells and systems in the body.

Absorption is the process by which the products of digestion are carried into the blood to be supplied to the rest of the body. No absorption takes place in mouth or stomach, practically all food is absorbed in small intestine. Little food remains to be absorbed by the time the contents reach the large intestine. The small intestine offers a large surface area for absorption. The apparent surface area is increased several times (3-12 times) by the presence of finger-like projections called Villi, which project into the lumen of the small intestine. Most absorption takes place through these villi. In the center of each villus (singular of villi), a vessel called lacteal is present which is filled with lymph (a colorless fluid). Around the lacteal, a network of capillaries is present by means of which blood is brought very near to the surface of the membrane of the small intestine.

Absorption is achieved by either of the following mechanisms:

Simple diffusion: Simple diffusion is defined as the movement of solute from the higher concentration to the lower concentration through the membrane. After digestion, a few monosaccharides diffuse into the blood based on the concentration gradient. Example: Glucose, amino acids, and ions like chloride.

Active transport: Active transport may be defined as the process of solute movement from the lower concentration of the higher concentration by the expense of energy. Electrolytes like sodium ions are absorbed by active transport into the blood.

Facilitated transport: Facilitated transport is defined as the process of movement of solutes across the biological membrane with the help of specific carrier proteins. Some digested amino acids and glucose are absorbed into the blood by this method.

Passive transport: Passive transport is defined as the process of solute movement across a cell membrane without a requirement of energy. After digestion, simpler food substances are absorbed into the blood by passive transport.

Some digested products from fats cannot be absorbed into the blood. Example: Fatty acids and glycerol. These components attach to micelles which are small droplets and form a micelle-component complex. This micelle – component complexes are re-formed into chylomicrons. Chylomicrons are a small protein coated fat globules. Then, chylomicrons move into the lymph vessels and release the digested products into the blood. Finally, the digested and absorbed products reach the tissue to be utilized for their activities. This process is called as assimilation.

Assimilation is the movement of digested food molecules into the cells of the body and their utilization. For example, glucose is used in respiration to provide energy. Amino acids are used to build new proteins.

Assimilation of Water

Nutrients aren’t the only thing your body needs to stay healthy. Having enough water is just as important. Water is absorbed in the large intestine or the colon. However, water can’t be moved by a pump in the same way as sugar. So how does the large intestine get water into the blood? The answer is a process called osmosis. Osmosis is the movement of water, from where there is a lower concentration of salt to a higher concentration of salt. This leads water to move out of the intestine and into the blood; the blood needs to have a higher concentration of salt compared to the large intestine. To accomplish this, the epithelial cells of the large intestine actively pump salt from the intestine to the blood. Water follows since there is a greater concentration of salt in the blood compared to the intestine.

In the body assimilation of digested food takes place in the following manner:

The simple sugars absorbed through the intestinal villi, reach the blood and then the body tissues. Simple sugars are necessary for the body as an immediate energy source. The extra sugar is converted into a complex polysaccharide glycogen in the liver. This glycogen is mobilized and utilized during the conditions of stress.
The final product of fat digestion is fatty acids and glycerol which are absorbed into the blood via lacteals. They are again converted to fats and are stored in adipose tissues. This stored fat is utilized by the body when there is a need.
The amino acids that are absorbed from the intestine are utilized to synthesize various types of proteins in the body. The body needs to make various types of proteins for the cells and enzymes that catalyze several reactions of the metabolic pathways inside the cells.

In 11 Science you can visit another notes, NCERT Solutions for biology Class 11

Structure of the small intestine

Pancreas

Digestion in Stomach

Gastrointestinal Hormones

Digestion in Mouth

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