Digestive system is the body systems which provides strength and energy to the body. It is the only route through which the foreign material (food) directly enters the body. Hence, the system is designed to make the foreign substance safe and compatible for the body to absorb. Here are the step by step process on how the digestive system works like
Ingestion: Here the food is taken into the digestive system through mouth. This involves eating of solids and drinking of liquids.
The process of ingestion involves
b) Bolus formation
Chewing means mechanical breakdown of food materials by the teeth. The teeth by cutting, tearing, grinding actions breakdown the food into smaller particles.
Bolus formation is mixed with saliva simultaneously with the help of tongue and jaw muscles. This mixing and chewing leads to formation of bolus a small ball like form ready to swallow.
Swallowing involves movement of bolus from mouth into stomach through the esophagus. This occurs by 3 processes.
a) The mouth is closed and the tongue and cheek muscles push the bolus backwards into the pharynx.
b)When the bolus is in oro-pharynx, the involuntary action starts and it pushing the pushing bolus into esophagus. During this process all the routes except for the esophagus route are closed.
c) By the series of peristaltic movement, the bolus in esophagus is propelled into the stomach.
Propulsion: This involves mixing of food with digestive juices and then movement of it through the digestive tract. This propulsion starts from the time the food is in esophagus till it is eliminated from large intestine as feces.
The role of propulsion is to provide better digestion, efficient absorption and excretion of waste. The digestive tract is made up of smooth muscle tissues. There 3 types of muscle tissues present like circular, longitudinal and oblique muscles. The action of these muscles is like churning and squeezing.
Due to this muscle action, the food is mixed well with the digestive juices. Then, the food is moved for better absorption. Since food is exposed to larger surface area of the lengthy intestine, there is sufficient abortion. Finally, this propulsive action leads the undigested waste reach the large intestine.
Digestion: The food is digested by
a) Mechanical crushing of the food by teeth. Due to this, larger food particles are broken down to smaller ones. As you are aware, the smaller the particle size, the greater is the surface area. Greater surface area leads to better enzyme action and absorption.
b) Enzymatic digestion of food into smaller molecules like glucose, amino-acids and fatty acids.
The enzymatic action of food by the digestive juices start from the buccal cavity and seem in the stomach and small intestine.
Digestion in buccal cavity: The saliva in mouth is produced by three pairs of main salivary glands and also other smaller glands. This saliva has amylase enzyme.
This salivary amylase breaks down complex carbohydrates like starch into disaccharide like maltose.The pH for this action is between 5.8 to 7.4. This enzyme action continues till the food reaches the stomach. In the stomach at pH of 1.5 due to the the action of gastric acid the amylase breaks down.
Digestion in stomach: Stomach is the place where some amount of water and alcohol is absorbed directly into blood stream. Hence, we get rid of thirst immediately after drinking water. Even, the effect of alcohol is seen fast due to this gastric absorption.
Further, gastric juice contains enzyme trypsinogen which is activated to trypsin. This trypsin converts proteins to polypeptides.
The acidic content in the stomach converts iron into soluble form for easy absorption.
Digestion in intestine: In intestine all the components of food like carbs, proteins and fats are digested and also absorbed. Intestinal juice has 5 enzymes like
i. Intestinal amylase: Which converts polysacharides from starch into disaccharides.
ii. Trypsinogen: The active form trypsin Converts polypeptides to tripeptides, dipeptides and aminoacids.
iii.Chymotrypsinogen: The active form chymotrypsin acts on polypeptides similar to trypsin.
iv. Lipase: This converts fats into fatty acids and glycerol.
v. Nucleases: Digests DNA and RNA.
Absorption: The digested food material is absorbed through the small intestines which are key organs of digestive system. This is then taken into the blood circulation and lymphatic system. This occurs by processes like diffusion, osmosis, facilitated diffusion and active transport.
Monosacharides, amino acids, water soluble vitamins and minerals pass into the capillaries of villi.
Fatty acids, glycerol and fat soluble vitamins are absorbed through lacteals into lymphatic system.
Even large intestine absorbs some amounts of water, minerals and few vitamins.
Elimination: The undigested food material is removed from the alimentary canal in the form of feces. This is possible due to peristaltic movement of the intestines. These movements force the waste to move towards sigmoid colon and then rectum. From rectum due to intra abdominal pressure, the feces is expelled out.