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Absorption refers to the process through which the products of digestion are absorbed by the blood and then supplied and transported to the rest of the body parts. The human digestive system is a group of organs that help in the breakdown of food into smaller composite particles, which are then absorbed into the bloodstream. Digestive enzymes are proteins that aid the process by catalyzing a series of chemical reactions. Digestion is a complex physicochemical process that breaks down large food particles into smaller, more easily digestible components. Following then, the absorption and assimilation of digested food begin with the alimentary canal's walls. The movement of digested food molecules through the intestinal wall into the blood or lymph is known as absorption. The small intestine is the site of absorption of digested food. The ileum is where the majority of absorption occurs.
Also Read: Difference Between Egestion and Excretion
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Key Terms: Absorption, Assimilation, Intestine, Glycerols, Catalyzing enzyme, Pancreas, Digestive System, Digestion, Organs, Breakdown of Food
What is Absorption?
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The food consumed by an organism must be taken into the bloodstream once it is broken down into smaller and simpler particles as the digested meal can only reach the cells and tissues through the means of blood and the circulatory system. Blood carries simple sugars, glycerol, amino acids, and a few vitamins and minerals to the liver from the digestive organs. All the chemicals are stored and processed in the liver. They're also cleansed here. The process involves the transportation of the nutrients to the rest of the body as and when they are required. Absorption and Assimilation are the terms used to describe the complete process.
Absorption is one of the most vital processes in the digestion of food in which the end products are absorbed into the blood or lymph from the intestinal mucosa. All the passive, active, or assisted transport mechanisms of the human body play an important role in this process. The small intestine is the place in the digestive system where the process of absorption takes place. It has been specially made to do this function. When food particles enter the bloodstream, they are carried to various parts of the body where they are needed. Only smaller, soluble food molecules can pass through the small intestine's walls; larger, insoluble food molecules cannot.
Absorption of Digested Food
Function of Small Intestine in Digestion
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Special cells in the small intestine aid in the absorption of nutrients from the intestinal lining into the circulation. It has several physiological features that help in the absorption process. It is a long, convoluted tube-like organ with a diameter of one inch and a length of roughly 10 feet. The small intestine is surrounded by a thin membrane called the mesentery, which anchors it in place.
The mesentery is home to numerous blood vessels, lymphatic vessels, and nerves. They support the small intestine tissues and help in the transfer of nutrients from the intestines to the rest of the body.
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Parts of Small Intestine
Various parts of the small intestine are:
- Duodenum- It is the first section of the stomach that links to the pyloric sphincter. It is the intestine's shortest section. Here, the chyme is combined with bile and pancreatic juice.
- Jejunum- It is the principal site of nutrient absorption and is located in the middle of the body. This section is approximately 3 feet long.
- Ileum- It is the part of the small intestine that empties into the big intestine at the end. It completes the absorption of the remaining nutrients at a length of 6 feet.
Parts of Small Intestine
Mechanism of Absorption
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During digestion, a network of mucous membranes helps in the transport of digested, soluble food molecules into the bloodstream or lymph. The following are the steps in the absorption process.
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Diffusion
Simple diffusion is the passage of solute particles through a permeable membrane from an area of higher concentration to a region of lower concentration. Monosaccharides such as glucose, ions such as fluoride and chlorides, and amino acids are all carried into the bloodstream by this process, which is based on the concentration gradient across the membranes. This is the initial step in the digestion and absorption process.
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Active Transport
Active transport is the process by which solute particles move from a location of lower concentration to a region of higher concentration by using energy, such as ATP. Active transport aids the diffusion of electrolytes like Na+ ions into the bloodstream against a concentration gradient.
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Facilitated Transport
It is the active transport of solute particles across a permeable biological membrane, which is facilitated by certain carrier proteins. Amino acids, carbohydrates, and glucose are all transported into the bloodstream by facilitated transport.
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Passive Transport
Passive transport is the passage of solute particles across a permeable cell membrane without the use of energy. This is the last step in the digestion process. Passive transport is the process through which simple and soluble food particles are absorbed into the bloodstream after digestion.
Glycerol and fatty acids, for example, cannot be taken into the bloodstream until they have been digested. Micelles, or micellar bodies, are tiny droplets that these molecules adhere to. Chylomicrons are formed from these complexes. Chylomicrons are tiny fat globules with a protein coating.
The chylomicrons are subsequently carried to lymph arteries, where they pass all of the digested food particles into the bloodstream. Food particles that have been digested and absorbed are transported to various cells and tissues where they might be used again. The assimilation of digested food is the last step.
The process of absorption in different parts of the alimentary canal is tabulated below:
| Part | Function |
|---|---|
| Mouth | When certain drugs come in contact with the mucosa of the mouth and lower side of the tongue, they are absorbed into the blood capillaries lining them. |
| Stomach | In the stomach, the absorption of water, simple sugar and alcohol takes place. |
| Small intestine | Glucose, fructose, fatty acids, glycerol, and amino acids are absorbed through the mucosa into the bloodstream and lymph. |
| Large intestine | The Large Intestine is the site of absorption for water, some minerals, and drugs. |
Human Digestive System
Things to Remember
- Absorption refers to the process through which the products of digestion are absorbed by the blood and then supplied and transported to the rest of the body parts.
- To function properly, our body needs to extract nutrients from the food we eat.
- The absorption process guarantees that food particles are transported into the bloodstream when they break down into smaller particles.
- Only through the absorption process do digested food particles reach our body's numerous cells, tissues, and organs.
- Sugars and amino acids are transported from the absorbed food into the liver, where they are digested.
- Nutrients are transported from the liver to other regions of the body as needed.
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Previous Year Questions
- The characteristic that is shared by urea... [KCET 2009]
- The primary dentition in humans differs from... [NEET 2015]
- Stool of a person contain whitish grey colour due to... [NEET 2002]
- Food is moved along the alimentary canal by the contraction known as... [JIPMER 2003]
- A baby boy aged two years is admitted to play school and passes through a dental check - up. The dentist observed that the boy had twenty teeth. Which teeth were absent?… [NEET 2017]
- Which cells of "Crypts of Lieberkuhn" secrete antibacterial lysozyme?... [NEET 2017]
- Secretin and cholecystokinin are digestive hormones. They are secreted in….[NEET 2005]
- Which of the following statements is not correct?... [NEET 2015]
- If for some reason the parietal cells of the gut epithelium become partially non-functional, what is likely to happen?... [NEET 2010]
- Jaundice is a disorder of... [NEET 2010]
- Duodenum has characteristic Brunner's gland which secrete two hormones called...[NEET 2004]
- A healthy person eats the following diet-5 gm raw sugar,. 4 gm albumin, 10 gm pure buffalo ghee adultrated with 2 gm vegetable ghee (hydrogenated vegetable oil) and 5 gm lignin. How many calories he is likely to get?...[NEET 2013]
- A person who is eating boiled potato, his food contains the component...[NEET 2000]
- Anxiety and eating spicy food together in an otherwise normal human, may lead to...[NEET 2012]
- Calcium deficiency in the body occurs in the absence of...[NEET 1994]
- Choose the correct enzyme - substrate pair... [NEET 1996]
- Continuous bleeding from an injured part of body is due to deficiency of...[NEET 2002]
- Duct leading from parotid gland and opening into vestibule is...[NEET 1998]
- During prolonged fastings, in what sequence are the following organic compounds used up by the body...[NEET 2003]
- Emulsification of fat is carried out by...[NEET 1990]
Sample Questions
Ques. Why are villi present in the small intestine and not in the stomach? (3 Marks)
Ans. The absorption process is mostly controlled by the small intestine. The absorbing surface area is increased by the villi and microvilli. The stomach, on the other hand, is essentially a storage organ for food and the proteins that are being digested. As a result, the small intestine, not the stomach, has villi.
Ques. How the process of absorption is carried out? (3 Marks)
Ans. The small intestine is where food is absorbed. The molecules of digested food flow past the small intestinal walls and into the circulation. During digestion, a network of mucous membranes aids in the transport of digested, soluble food molecules into the circulation of lymph.
Ques. Why is absorption needed? (3 Marks)
Ans. Food must be absorbed into the bloodstream before oxygen and nutrients can be given to cells for respiration. Carbon dioxide, for example, must be removed from cells and transported into the bloodstream. Tissues have capillary networks that allow these cellular exchanges to take place.
Ques. What happens during absorption? (3 Marks)
Ans. The ingested compounds are delivered to various parts of the body via blood vessels, where they are employed to construct complex substances such as the proteins required by human bodies. The undigested and unabsorbed food is absorbed in the big intestine.
Ques. How do cells absorb nutrients? (3 Marks)
Ans. Small intestine muscles mix food with digestive secretions from the pancreas, liver, and intestine, then push the mixture forward to aid digestion. The digested nutrients are absorbed into the circulation by the small intestine walls. The blood transports nutrients all through the body.
Ques. Where does the body absorb most nutrients? (3 Marks)
Ans. The small intestine absorbs the majority of the nutrients in your meal, which your circulatory system then transports to other parts of your body for storage or usage. Special cells help in the transport of absorbed nutrients through the intestinal lining and into the bloodstream.
Ques. How long does it take your body to absorb nutrients? (3 Marks)
Ans. Individuals both men and women have different digestion times. Food passes through your stomach and small intestine roughly six to eight hours after you eat. Food next reaches your large intestine (colon) for further digestion, water absorption, and undigested food excretion.
Ques. How does absorption take place in the large intestine? (3 Marks)
Ans. Absorption is completed and waste is compacted in the large intestine. Chyme travels from the small intestine to the large intestine's cecum via the ileocecal valve. As peristaltic waves drive the chyme into the ascending and transverse colons, any leftover nutrients and some water are absorbed.
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