Human digestive system

 Human digestive system

Food can not go straight to the cells in the different parts of your body. It has to be broken down into smaller substances that can be absorbed into the body cells. Many organs of your body work together to achieve this goal. These organs work together to make up the digestive system and perform digestion. 

Definition of digestion:

The large and complex food particles cannot enter the cell without being broken down by our body into smaller, simpler, and diffusible forms. Digitization is the process of breaking down food into simple and diffusible molecules.

Types of digestion:

There are two types of digestion

1. Physical digestion 

2. Chemical digestion 

Physical digestion:

It is the mechanical breakdown of the food into smaller pieces. This digestion provides a large surface area for enzyme action.

Chemical digestion:

It is the breakdown of the food through enzymes consisting of protein molecules that speed up the rate of chemical reactions.

Steps of digestion:

There are five steps of digestion as follows:

1. Ingestion

2. Digestion 

3. Absorption 

4. Utilization

5. Egestion 

Ingestion: It takes the food inside the mouth.

Digestion: it breaks down the large particles of food into smaller particles.

Absorption: These small particles can easily diffuse through the walls of the alimentary canal into the bloodstream.

Utilization: it utilizes the food for the cell processes.

Egestion: it eliminates the undigested food.

Two groups of organs compose the digestive system

1. The alimentary canal

2. The accessory digestive organs

Alimentary Canal:

The alimentary canal is a continuous tube extending from the mouth to the anu. The length of this tract is about seven meters in a living person. The alimentary canal has a pharynx, esophagus, stomach, mouth, large intestine, small intestine and anus.

Accessory digestive organs:

The accessory digestive organs include the teeth, liver, gallbladder, and pancreas.

Your food usually takes 24 to 30 hours to complete its journey inside your body so when you are having today's lunch that you ate the day before.

Mouth:

The organ of the digestive system in which both chemical and physical digestion takes place in the mouth. The mouth consists of cheeks, lips, teeth, tongue, etc.

Mechanical digestion in the mouth results from chewing, tearing, and crushing by teeth, which helps food to get easily mixed with saliva. The chemical digestion of carbohydrates (starch) starts with saliva. As a result, food is reduced to a soft and flexible semi-solid food called a bolus, easily swallowed by the tongue and moving towards the esophagus.

Oesophagus (food pipe):

The esophagus acts as a pathway and transports food from the pharynx to the stomach. Bolus is pushed from the esophagus by a wave-like pattern movement. No digestion takes place here. 

Pharynx and swallowing:

The pharynx is a funnel-shaped muscular organ that connects the mouth to the esophagus (digestive organ) and the larynx (respiratory organ). The pharynx muscular contraction is used to propel the food firstly into the esophagus and then into the stomach. The act of swallowing food provides the movement of food.

Stomach:

From the esophagus, the bolus enters the stomach. The stomach is a J-shaped muscular bag. The walls of the stomach release gastric juice. This juice contains an acid called hydrochloric acid water and enzymes. The enzyme converts the large protein into the small protein molecules. HCL softens the food and kills the germs that are present in the food of humans. Mechanical digestion in the stomach results from mixing waves, in which the bolus is completely mixed with gastric juice.

Gastric juice starts the chemical digestion of protein. As a result, bolus is converted into a semi-liquid food called chyme. Food remains in the stomach for some hours. Gradually the stomach empties its content into the small intestine. 

Liver and pancreas:

Both the liver and pancreas play a role in digestion. Without their secretion digestion remains incomplete. The liver contains a gallbladder which stores bile. However, the food doesn't pass through these structures that’s why they are not part of the alimentary canal. 

Small intestine:

The small intestine is a long, highly narrow tube of six-meter average length. As the chyme enters into the small intestine it receives bile from the liver and pancreatic juice from the pancreas. Bile is a greenish-brown juice secreted by the liver and stored in the gallbladder. It helps to break down the larger-sized fats into smaller pieces so that fats can be digested faster by enzymes. Pancreatic juice is secreted by the pancreas. This juice contains enzymes that help to digest proteins, fats, and carbohydrates.

The small protein molecules are now broken down into amino acids, a simpler and diffusible form of protein. The semi-digested carbohydrates are converted into diffusible sugar and fat is broken down into glycerol and fatty acids. The muscular action of the small intestine mixes the food with bile and pancreatic juice.

Here the digestion is completed. At the end of the small intestine, the digested soluble and diffusible components of food now diffuse through the walls of the small intestine into the bloodstream. This process is called absorption.  Absorption only occurs in the small intestine as its walls consist of many folds that provide a larger surface area. Its walls are surrounded by capillaries for maximum absorption. The absorbed food is utilized in the body like glucose used in respiration. Amino acid fatty acids and glycerol are used in the formation and growth of cells.

Large Intestine:

The undigested non-discusible and insoluble components of food move towards the last part of the digestive system called the large intestine. It is shorter but much broader than the small intestine. It is a tubular structure that is on average 1.5m long with a large diameter where the water and mineral salts are absorbed. The minerals are absorbed with the help of some friendly bacteria that live here. All the undiscussable components of food move toward the rectum. Here the undigested food is converted into feces which is removed from the body by an opening called anus.