What is the role of the following in the process of digestion in
the human body.
(a) Saliva (b) Gastric juices (c) Trypsin
(ii) Write any three differences between aerobic and anaerobic
respiration.
(iii) Name various plant hormones. mention the role of two plant
hormones
(iv) Differentiate between natural and artificial method of
vegetative propagation in plants.
(
Answers
We all associate the process of digestion with the stomach, right? But what if I told you, the digestive process starts from the mouth itself. There are various other organs involved in the digestion process occurring in the human body. Let us educate ourselves about this process.
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Digestion Process
The digestion process is a series of reactions of food with the digestive hormones and juices. This starts right from the oral cavity.
Why is digestion important?
It is an important process that breaks down the proteins, fats, carbohydrates, vitamins, minerals into simpler forms so that it can be absorbed easily into the body cells. During this process, proteins are converted into amino acids, carbohydrates are converted into simple sugars and fats are broken down into fatty acids and glycerol.
Many digestive enzymes and hormones act on food, at various stages during the process of digestion. The whole process occurs in a sequential manner.
The following table shows the digestive process in a simple format.
Organ
Movement
Digestive juices/enzymes added
Food that is broken down
Mouth Chewing Saliva Starch(Carbohydrate)
Oesophagus Peristalsis —- —-
Stomach Churning Stomach acid and Digestive Enzymes Proteins
Small Intestine Peristalsis Digestive Juices Carbohydrates, proteins, starch
Pancreas —– Pancreatic juice Carbohydrates, Fats, proteins
Liver —– Bile Fats
Large Intestine Peristalsis —- Bacteria act on the remaining food particles.
Mechanism of Digestion
The digestion process can be divided into different stages, such as digestion in the:
Oral cavity
Stomach
Small intestine
Large intestine
Digestion includes a complex combination of mechanical and chemical processes. Some of the activities in the process include ingestion and propulsion of food, mechanical or physical digestion, chemical digestion, absorption, and defecation.
Process of Digestion
Browse more Topics under Digestion And Absorption
Digestive System
Absorption and Assimilation
Disorders of Digestive System
Digestion in the Oral Cavity
When food is taken in through the mouth, chewing and mixing of the food occurs. There is also a chemical breakdown of carbohydrates, due to the action of saliva from the salivary glands. 30% of the starch is hydrolyzed by the action of amylase, which is a salivary enzyme. The other enzyme, lysozyme is an antibacterial agent that prevents infections.
Starch + Salivary amylase → Maltose
Mastication of food and swallowing of food are the important activities that take place here in the oral cavity. Food is broken down into smaller particles by the chewing action of teeth. As saliva is added, it mixes with the food particles, slowly moistening and lubricating the food. This small ball is called a bolus, which is then swallowed. The pharynx helps in the movement of the bolus into the oesophagus, from where it moves to the stomach through the peristaltic movements of the oesophagus.
Learn more about the Human Digestive System here in detail.
Digestion in the Stomach
When food reaches the stomach, it stays for approximately 4 to 5 hours. There are various gastric glands in the mucosa lining of the stomach. The mucus neck cells secrete mucus. The Peptic Cells secrete the proenzyme pepsinogen. The Parietal or Oxyntic Cells secrete HCl (Hydrochloric acid) and intrinsic factor that is essential for vitamin B12 absorption.
Food in the stomach gets mixed thoroughly with the gastric juices through the churning movements of the stomach muscle. This mass of food that is semi-digested, acidic and pulpy is called the chyme. It is mostly the proteins that get digested in the stomach. The mucus and the bicarbonates of the gastric juice help in protecting the mucosal epithelium from the highly acidic HCl. Mucus also helps in lubricating the food.
The different chemical reactions that take place in the stomach are summarised as follows.
Gastric juices and enzymes:
HCl provides the acidic pH.
Pepsinogen(proenzyme) is converted into Pepsin by HCl
Pepsin, in turn, converts protein into peptones & proteoses.
Prorenin (proenzyme) is converted into Renin by HCl.
Casein (milk protein) is converted into peptides by Renin.
After the action of the gastric juices and enzymes, food then enters the small intestine.
Learn more about Disorders of Digestive System here in detail.