Assimilation of food in human body

Assimilation of food

The process by which the body takes in and makes use of the nutrients included in food is known as assimilation. It starts with breaking down complex food molecules into simpler forms that the body’s cells can absorb. There are various processes involved in this process. Ingestion, digesting, absorption, and utilization are the important phases of food assimilation.


Ingestion is the initial stage of the digestive process, where food is taken into the body through the mouth. This process involves the intake of food and liquids, which are then prepared for further digestion. Here are some key aspects of the ingestion process:

  1. Chewing (Mastication): The first step in ingestion is the mechanical breakdown of food in the mouth through chewing or mastication. Teeth play a crucial role in breaking down large pieces of food into smaller, more manageable particles. Chewing not only facilitates the physical breakdown of food but also increases its surface area, making it easier for enzymes to act during the later stages of digestion.

  2. Saliva Production: As food is chewed, saliva is produced by salivary glands in the mouth. Saliva contains enzymes, such as amylase, which begins the chemical breakdown of carbohydrates into simpler sugars. Saliva also helps moisten the food, making it easier to swallow.

  3. Formation of Bolus: The chewed food, mixed with saliva, forms a mass called bolus. The bolus is a soft and partially liquid mixture that can be easily swallowed.

  4. Swallowing (Deglutition): Once the bolus is formed, it is moved to the back of the mouth and swallowed. The process of swallowing, or deglutition, involves the coordinated action of muscles in the tongue, throat, and esophagus. The epiglottis, a flap-like structure, prevents food from entering the windpipe (trachea) during swallowing, directing it to the esophagus.

  5. Transport to the Stomach: The swallowed bolus travels down the esophagus through a series of muscular contractions known as peristalsis. Peristalsis helps move the food toward the stomach.

In summary, ingestion is the process of taking food into the mouth, breaking it down into a more digestible form through chewing and mixing with saliva, and then swallowing the resulting bolus. This prepares the food for further digestion and absorption in the later stages of the digestive system.



Digestion is the process by which the body breaks down food into smaller, more absorbable components. It involves both mechanical and chemical processes and occurs in various stages along the digestive tract. Here is an overview of the digestion process:

  1. In the Mouth:

    • Mechanical Digestion: Chewing breaks down food into smaller pieces, increasing its surface area for better exposure to digestive enzymes.
    • Chemical Digestion: Saliva, produced by salivary glands, contains enzymes (like amylase) that start breaking down carbohydrates into simpler sugars.
  2. In the Stomach:

    • Mechanical Digestion: The stomach muscles contract, churning the food and mixing it with gastric juices, forming a semi-liquid substance called chyme.
    • Chemical Digestion: Gastric juices in the stomach contain enzymes (such as pepsin) and hydrochloric acid. Pepsin breaks down proteins into smaller peptides.
  3. In the Small Intestine:

    • Mechanical Digestion: Contractions of the intestinal walls help mix and propel chyme.
    • Chemical Digestion: Pancreatic enzymes (amylase, lipase, and proteases) and bile from the liver break down carbohydrates, fats, and proteins, respectively, into their basic components.
  4. Absorption in the Small Intestine:

    • The majority of nutrient absorption occurs in the small intestine. The inner surface of the small intestine is lined with villi and microvilli, which increase the surface area for absorption.
    • Nutrients like amino acids, simple sugars, and fatty acids are absorbed through the intestinal wall and transported to the bloodstream.
  5. In the Large Intestine:

    • Water and electrolytes are absorbed from the remaining indigestible material, forming feces.
    • Beneficial bacteria in the colon assist in breaking down certain substances and producing some vitamins (like vitamin K and certain B vitamins).
  6. Elimination:

    • Feces, consisting of water, undigested food particles, bacteria, and waste products, are eliminated from the body through the rectum and anus.

Digestion is a coordinated and complex process that involves the interplay of various organs, enzymes, and physiological mechanisms. Proper digestion is essential for extracting nutrients from food, supporting overall health, and providing the body with energy and essential building blocks.


Absorption is a crucial step in the process of assimilating nutrients from the food we consume. It takes place in the small intestine, where the majority of nutrient absorption occurs. The small intestine has specialized structures called villi and microvilli that increase its surface area, facilitating efficient absorption.

Here’s how absorption occurs in the small intestine:

  1. Intestinal Surface Area: The inner surface of the small intestine is covered with tiny, finger-like projections called villi. These villi, in turn, have even smaller projections called microvilli. This complex structure significantly increases the surface area available for absorption.

  2. Transport Mechanisms:

    • Simple Diffusion: Some nutrients, such as water and small lipids, can pass through the cell membranes of the intestinal lining directly by simple diffusion.
    • Facilitated Diffusion: Certain nutrients, like some sugars and amino acids, require carrier proteins to facilitate their movement across the cell membranes.
    • Active Transport: This process involves the use of energy to move nutrients against their concentration gradient. It is essential for absorbing ions, amino acids, and glucose.
    • Bulk Transport (Endocytosis): Large molecules, such as certain proteins, are engulfed by the cell membrane and transported into the cell in vesicles through a process called endocytosis.
  3. Specific Nutrient Absorption:

    • Carbohydrates: Digestive enzymes break down complex carbohydrates into simple sugars (glucose, fructose, and galactose), which are then absorbed into the bloodstream.
    • Proteins: Proteins are broken down into amino acids. These amino acids are absorbed by the intestinal cells and transported into the bloodstream.
    • Fats: Fats are broken down into fatty acids and glycerol. These components are absorbed into the cells of the small intestine, where they are reassembled into triglycerides and then packaged into structures called chylomicrons for transport through the lymphatic system and eventually into the bloodstream.
  4. Water and Electrolyte Absorption:

    • Water is absorbed through osmosis, following the movement of solutes.
    • Electrolytes (ions such as sodium, potassium, chloride) are actively transported across the intestinal membrane.
  5. Absorption in the Large Intestine:

    • While the majority of nutrient absorption occurs in the small intestine, the large intestine absorbs water and electrolytes from the remaining undigested material, forming solid feces.

Efficient absorption in the small intestine is vital for ensuring that the body receives the necessary nutrients for energy production, growth, and maintenance of overall health. The absorbed nutrients then enter the bloodstream, which transports them to cells and tissues throughout the body.


In the context of the assimilation of food, the transport phase refers to the movement of nutrients from the digestive system, where they are absorbed, to the various cells and tissues of the body where they are needed. This process is facilitated by the circulatory system, primarily through the bloodstream.

Once nutrients, such as amino acids, simple sugars, and fatty acids, are absorbed into the bloodstream from the walls of the small intestine, they are carried throughout the body to reach cells and tissues. The circulatory system, composed of the heart, blood vessels, and blood, plays a central role in this transport mechanism.

The circulatory system functions as follows:

  1. Heart: The heart pumps blood, which contains nutrients, oxygen, and other essential substances, to different parts of the body. The heart has four chambers—two atria and two ventricles—that work together to circulate blood.

  2. Blood Vessels: Blood vessels form an extensive network throughout the body, comprising arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart, while veins carry deoxygenated blood back to the heart. Capillaries are tiny blood vessels where the exchange of nutrients and oxygen with tissues occurs.

  3. Circulation: Blood is pumped by the heart in a systematic manner, traveling through the arteries to smaller arterioles, then into capillaries where exchange with tissues takes place, and finally, returning through venules and veins to the heart. This circulation ensures that nutrients are delivered to cells and waste products are transported away for elimination.

  4. Transport of Nutrients: Nutrients, along with oxygen, are carried by the bloodstream to various cells and tissues. Each cell takes up the specific nutrients it requires for energy production, growth, and maintenance.

  5. Hormones: The circulatory system also transports hormones, signaling molecules that regulate various physiological processes in the body. Hormones are released by glands and travel through the bloodstream to target cells, influencing their activities.

In summary, the transport phase in the assimilation of food involves the efficient distribution of nutrients through the circulatory system, ensuring that cells receive the necessary elements for their functions. The coordinated efforts of the heart, blood vessels, and blood collectively support this vital process in maintaining overall bodily functions and health.


Elimination is the final stage in the process of digestion and absorption of nutrients, where the body expels undigested and unabsorbed substances as well as waste products. This process is primarily associated with the removal of indigestible material and the by-products of metabolism from the body. The key organs involved in the elimination process are the large intestine, rectum, and anus.

Here is an overview of the elimination process:

  1. Formation of Feces: After the absorption of nutrients in the small intestine, the remaining undigested and unabsorbed substances, along with water and other waste products, move into the large intestine (colon). In the large intestine, water is reabsorbed, and the remaining material is formed into feces.

  2. Bacterial Action: The large intestine is home to a large number of bacteria that play a crucial role in the fermentation of undigested carbohydrates and the production of certain vitamins (such as vitamin K). Bacterial action also contributes to the formation of feces.

  3. Storage in the Rectum: The formed feces are stored in the rectum, the lower part of the large intestine. The rectum serves as a temporary storage site for fecal material before it is ready for elimination.

  4. Defecation: When the rectum is filled with feces, stretch receptors signal to the brain that it’s time for elimination. The anal sphincters (muscles around the anus) relax, and the rectal muscles contract, facilitating the expulsion of feces from the body through the anus. This process is known as defecation.

  5. Elimination of Other Waste Products: Apart from undigested food particles, the body also eliminates waste products from various metabolic processes, such as urea in urine produced by the kidneys.

The elimination process is a crucial aspect of maintaining the body’s internal balance and preventing the accumulation of harmful substances. It ensures that the body gets rid of waste materials in a timely and efficient manner. Regular and healthy bowel movements are indicative of proper elimination and are essential for overall digestive health.

                                       In order to sustain general health and provide the body the energy and components it needs for development, repair, and regular operation, food must be assimilated. To guarantee the body gets the proper nutrients in the right amounts, a diverse and balanced diet is essential.

Scroll to Top