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 Definition
1. What is the biological definition of digestion?
Biologically, digestion is the complex process of breaking down large, insoluble food macromolecules into smaller, water-soluble molecules. These simpler molecules, such as glucose from carbohydrates or amino acids from proteins, are small enough to be absorbed by the body and transported into the bloodstream for energy, growth, and repair.
2. What are the main processes involved in human digestion?
The human digestive process involves six primary stages that occur in a specific sequence:
- Ingestion: The process of taking food into the mouth.
- Propulsion: The movement of food along the digestive tract, primarily through peristalsis.
- Mechanical Digestion: The physical breakdown of food into smaller pieces, starting with chewing in the mouth and continuing with churning in the stomach.
- Chemical Digestion: The chemical breakdown of food by enzymes into its basic building blocks.
- Absorption: The passage of digested nutrients from the small intestine into the blood or lymph.
- Defecation: The elimination of indigestible substances from the body as faeces.
3. What is the difference between mechanical and chemical digestion?
Mechanical and chemical digestion are two distinct but complementary processes. Mechanical digestion is the physical breakdown of food into smaller fragments, which increases the surface area for enzymes to act upon. Examples include chewing (mastication) in the mouth and the churning motion of the stomach. Chemical digestion involves the use of enzymes to break the chemical bonds within food molecules, transforming complex macromolecules into simpler absorbable units. An example is the enzyme amylase breaking down starch into sugars.
4. What is the role of peristalsis in the digestive system?
Peristalsis is the series of wave-like, involuntary muscle contractions that move food through the digestive tract. Its primary role is propulsion. It pushes the food bolus down the oesophagus into the stomach and moves the semi-digested food, known as chyme, through the small and large intestines. This movement is crucial for ensuring food passes through all stages of digestion and absorption efficiently.
5. Why must complex foods like carbohydrates and proteins be digested before absorption?
Our bodies cannot directly use large, complex food molecules like starch (a carbohydrate) or protein. The cells lining the intestine can only absorb very small, simple molecules. Digestion is essential because it breaks down these large macromolecules into their simplest components: carbohydrates into monosaccharides (like glucose), proteins into amino acids, and fats into fatty acids and glycerol. Only in these small forms can nutrients pass through the intestinal wall into the bloodstream to nourish the body's cells.
6. How does the process of digestion in the stomach differ from that in the small intestine?
Digestion in the stomach and small intestine differs significantly in terms of environment and the type of food being broken down. The stomach has a highly acidic environment (due to hydrochloric acid) which kills pathogens and activates the enzyme pepsin to begin protein digestion. In contrast, the small intestine has an alkaline environment. It is the primary site for the final digestion of all major food groups—carbohydrates, proteins, and fats—using a wide range of enzymes secreted by the pancreas and the intestinal wall.
7. What is the relationship between digestion and absorption, and where does each primarily occur?
Digestion and absorption are sequential and interconnected processes. Digestion is the breakdown of food into nutrients, while absorption is the uptake of those nutrients into the body. Digestion must occur before absorption can happen. While some digestion begins in the mouth and stomach, the majority of chemical digestion is completed in the small intestine. Consequently, the small intestine, with its vast surface area due to villi and microvilli, is also the primary site for the absorption of almost all nutrients into the bloodstream.
