Digestion

Introduction:

During digestion, large insoluble food molecules are broken down into smaller water-soluble food molecules, allowing them to be absorbed into the blood’s watery plasma. Certain creatures ingest these tiny chemicals into their bloodstream via the small intestine. This is a type of catabolism that is frequently separated into two processes: mechanical and chemical digestion, depending on how food is broken down. 

Digestive system:

Internal digestion and exterior digestion are fundamentally different. External digestion evolved earlier in evolutionary history, and it is still used by the majority of fungus today. Enzymes are secreted into the environment around the organism, where they degrade an organic material, with some of the products diffusing back to the organism. Internal digestion happens in animals through a tube (gastrointestinal tract), which is more efficient because more of the broken down products can be caught and the internal chemical environment can be better controlled.

Human Digestion Process:

Saliva and its digestive enzymes start the digestion process in the mouth. By mechanical mastication, food is shaped into a bolus and ingested into the oesophagus, from whence it enters the stomach by peristalsis. Gastric juice contains hydrochloric acid and pepsin, which can harm the stomach’s walls, thus mucus and bicarbonates are released to protect them. 

Job of stomach:

More enzymes are released in the stomach, breaking down the meal even more, and this is combined with the stomach’s churning movement. Proteins are primarily digested in the stomach. Partially digested food reaches the duodenum as a thick semi-liquid chyme. Majority of digestion takes place in the small intestine, which is aided by bile, pancreatic juice, and intestinal juice secretions. The intestinal walls are lined with villi, and their epithelial cells are coated with many microvilli to increase the surface area of the intestine and promote nutritional absorption. Bile aids in the emulsification of lipids and also acts as a lipase activator. 

The flow of food is slower in the large intestine to allow for fermentation by the gut flora. Water is absorbed here, and waste is retained as faeces, which is afterwards defecated via the anal canal and anus. 

Breakdown into nutrients:

Protein digestion:

Pepsin from the stomach and trypsin and chymotrypsin from the pancreas break down dietary proteins into polypeptides, which are then broken down into amino acids by various exopeptidases and dipeptidases in the stomach and duodenum. The digestive enzymes, on the other hand, are usually released in the form of their inactive precursors, zymogens. 

Fat digestion:

Some fats can be broken down into diglycerides in the mouth by lingual lipase, which breaks down short chain lipids. Fats, on the other hand, are primarily processed in the small intestine. When fat is present in the small intestine, hormones are released that promote the production of pancreatic lipase from the pancreas and bile from the liver, which aids in the emulsification of lipids for fatty acid absorption. When one molecule of fat (a triglyceride) is completely digested, it produces a mixture of fatty acids, mono- and di-glycerides, and some undigested triglycerides, but no free glycerol molecules. 

Carbohydrate digestion:

Dietary starches in humans are made up of glucose units grouped in long chains termed amylose, which is a polysaccharide. During digestion, salivary and pancreatic amylase break bonds between glucose molecules, resulting in progressively smaller glucose chains. The simple sugars glucose and maltose (2 glucose molecules) are produced, which the small intestine can absorb. 

Digestive hormones:

Mammalian digestive systems are aided and regulated by at least five hormones. There are differences amongst vertebrates, such as in birds. Arrangements are complicated, and new information is frequently uncovered. In recent years, for example, further links to metabolic control (most notably the glucose-insulin system) have been discovered. 

Gastrin:

The arrival of food in the stomach stimulates gastrin secretion. The secretion is stifled when the pH is too low. 

Secretin:

It causes the liver to secrete more bile. The acidity of the chyme triggers the release of this hormone. 

Cholecystokinin (CCK):

Promotes the evacuation of the gallbladder of bile In response to fat in the chyme, this hormone is released.

Gastric inhibitory peptide (GIP):

Reduces stomach churning, which slows the emptying of the stomach. Another function is the induction of insulin secretion.

Motilin:

Increased gastrointestinal motility migrating myoelectric complex component and boosts pepsin synthesis. 

Conclusion:

For the body to utilise food for energy, development, and cell repair, it must be broken down into nutrients. Food and drink must be broken down into smaller nutrition molecules before the circulation absorbs and delivers nutrients to cells throughout the body. The body breaks down food and drink ingredients into carbohydrates, protein, lipids, and vitamins.