Definition and Step by Step Process of Digestion
With regards to digestion definition, it can be defined as the breaking down of large particles of indissoluble food molecules into tiny water dissolving molecules. A body quickly absorbs these small molecules of food into blood plasma.
Also, in some organisms, their small intestine helps in absorbing the small food molecules into blood stream. Moreover, digestion is a kind of catabolism which is often classified into two procedures depending on the breaking down of food. The processes are:
Mechanical Digestion
This process involves physical breakdown of big chunks of food into smaller bits, which the enzymes can digest easily.
Chemical Digestion
In case of chemical digestion, the digestive enzymes break food particles into smaller molecules which the body can utilise.
Do It Yourself
1. Name the organs related to digestive system in humans?
(a) Pancreas and Salivary Glands
(b) Liver and Salivary Glands
(c) Pancreas and Liver
(d) Liver, Pancreas and Salivary Glands
2. Single-cell organisms exhibit a form of digestion referred to as:
(a) Ingestion
(b) Phagocytosis
(c) Absorption
Process of Digestion in Humans
Considering the system of digestion for human beings, mechanical digestion starts as soon as someone eats food and starts mastication (chewing) in the presence of saliva. Furthermore, saliva is a fluid secretion from salivary glands containing salivary amylase. This enzyme aids in digestion of starch present in food.
Moreover, saliva also consists of hydrogen carbonate and mucus. The former one gives suitable pH (alkaline) conditions so that amylase can work, and the latter one helps in lubricating food.
After the actions of starch digestion and mastication, food takes up the shape of tiny circular slurry mass known as a bolus. Next, it moves to the stomach by travelling through the oesophagus with the support of an action called peristalsis.
When food reaches stomach, gastric juices present in it begins the digestion of proteins. It primarily consists of HCL (hydrochloric acid) and pepsin. However, renin is also present in gastric juices in small children like toddlers and infants.
The two chemicals – hydrochloric acid and pepsin can affect and cause damage to the stomach wall. So, stomach secretes mucus which provides a greasy layer against the harming effects of HCL and pepsin. Simultaneously, digestion of protein also occurs where mechanical mixing takes places by the action of peristalsis. Additionally, this process assists in further mixing up of food with digestive enzymes.
Furthermore, the thick fluid which forms after a considerable amount of time (human beings take 1 to 2 hours, cats take 3 to 4 hours, and dogs require 4 to 6 hours) is known as chyme. It moves to duodenum after pyloric sphincter valve opens. Moreover, in duodenum, chyme mixes up with enzymes secreted by pancreas and bile from liver. Then, it travels through small intestine where digestion still continues.
Additionally, when digestion of chyme is fully done, it gets absorbed into blood. Moreover, 95 per cent of absorption of nutrients takes place in small intestine. Also, minerals and water again undergo reabsorption in colon (large intestine), which has pH a bit acidic (5.6 ~ 6.9).
However, bacteria present in colon produces few vitamins like vitamin K and biotin, which also gets absorbed in colon by blood. Finally, waste material eliminates during defecation from rectum.
Digestive Hormones
In general, five hormones help in the digestive system for mammals; they are –
Gastrin.
Secretin.
Cholecystokinin (CCK).
Gastric inhibitory peptide (GIP).
Motilin.
Variations are there over vertebrate organisms like for example in birds.
Did You Know?
Unicellular organisms like the amoeba, exhibit a kind of digestion known as phagocytosis. In this process, phagocytes (here amoeba) ingest food particles with the help of plasma membrane and enables digestion.
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FAQs on Digestion in Humans and Other Organisms
1. What is digestion?
Digestion is the biological process by which complex food substances are broken down into simpler, absorbable molecules. It involves both:
- Mechanical digestion – physical breakdown of food (e.g., chewing in the mouth).
- Chemical digestion – enzymatic breakdown of food using digestive enzymes.
The end products, such as glucose, amino acids, and fatty acids, are absorbed into the bloodstream to provide energy and nutrients for the body.
2. What is the definition of digestion in biology?
In biology, digestion is defined as the enzymatic conversion of complex food molecules into simple, soluble substances that can be absorbed and utilized by cells. It mainly occurs in the alimentary canal and involves organs such as the mouth, stomach, and small intestine.
This process ensures that nutrients are available for cellular respiration, growth, and tissue repair.
3. What are the types of digestion?
The two main types of digestion are mechanical digestion and chemical digestion. These work together to break down food efficiently.
- Mechanical digestion: Physical breakdown of food into smaller pieces (e.g., chewing, churning in the stomach).
- Chemical digestion: Breakdown of food by enzymes such as amylase, protease, and lipase.
Both types increase the efficiency of nutrient absorption in the small intestine.
4. How does digestion work step by step?
Digestion works through a step-by-step process that converts food into absorbable nutrients.
- Ingestion: Food enters the mouth.
- Mechanical digestion: Chewing breaks food into smaller pieces.
- Chemical digestion: Enzymes break down carbohydrates, proteins, and fats.
- Absorption: Nutrients are absorbed in the small intestine through villi.
- Egestion: Undigested waste is eliminated through the anus.
This coordinated process occurs in the digestive system.
5. What is the function of digestion in the human body?
The main function of digestion is to convert food into absorbable nutrients that provide energy and support growth and repair. Specifically, digestion:
- Breaks down carbohydrates into glucose.
- Breaks down proteins into amino acids.
- Breaks down fats into fatty acids and glycerol.
These nutrients are transported by the blood to cells for metabolism and energy production.
6. What is the difference between mechanical and chemical digestion?
The difference between mechanical and chemical digestion is that mechanical digestion physically breaks food apart, while chemical digestion uses enzymes to chemically break down molecules.
- Mechanical digestion: Includes chewing and stomach churning; no chemical change in food.
- Chemical digestion: Involves digestive enzymes that convert complex molecules into simple ones.
Both processes are essential for efficient nutrient absorption.
7. Where does digestion take place in the body?
Digestion takes place mainly in the mouth, stomach, and small intestine of the digestive system. Each organ has a specific role:
- Mouth: Begins mechanical digestion and carbohydrate breakdown with salivary amylase.
- Stomach: Continues digestion using gastric juice and pepsin.
- Small intestine: Completes digestion and absorbs nutrients.
Accessory organs like the liver and pancreas also aid digestion by secreting bile and enzymes.
8. What enzymes are involved in digestion?
Digestion involves specific digestive enzymes that break down different types of food molecules. Key enzymes include:
- Amylase: Breaks down starch into maltose.
- Protease (e.g., pepsin, trypsin): Breaks down proteins into amino acids.
- Lipase: Breaks down fats into fatty acids and glycerol.
These enzymes ensure efficient chemical digestion in the gastrointestinal tract.
9. Why is digestion important for living organisms?
Digestion is important because it provides usable nutrients and energy necessary for survival. Without digestion:
- Cells cannot obtain glucose for cellular respiration.
- Growth and tissue repair cannot occur without amino acids.
- Essential functions cannot be maintained.
Thus, digestion is essential for maintaining homeostasis and supporting life processes.
10. What are the end products of digestion?
The end products of digestion are simple molecules that can be absorbed into the bloodstream. These include:
- Glucose from carbohydrates.
- Amino acids from proteins.
- Fatty acids and glycerol from fats.
These small, soluble molecules are absorbed mainly in the small intestine and used for energy, growth, and repair.
