Digestive System

The human digestive system is a systematic mechanism involving various steps . The following  article describes digestion and the digestive system in detail.

What is Digestion?

Digestion is the  process of breaking down food into simpler forms that can be absorbed by body cells. These cells also absorb water, vitamins, minerals and eliminate wastes from the body.

What is a Digestive System?

Organs involved in the breakdown of food are collectively called the digestive system. Such organs include mouth, pharynx, oesophagus, small intestine, large intestine, rectum, and anus. 

There are two groups of organs composing the digestive system:

Gastrointestinal tract: The gastrointestinal tract or alimentary canal is a continuous tube that extends from the mouth to the anus. GI tract includes the mouth, oesophagus, small intestine and large intestine stomach. 

Accessory digestive organs- The accessory structures that contribute to the food processing include the teeth, tongue, salivary glands, liver, gallbladder and pancreas.

The following processes are involved in the process of digestion:

Ingestion-Involves consuming food and liquids. 

Secretion-Release of water, enzymes, buffers into lumen of tract.

Mixing and propulsion-Contractions and relaxations of muscles in the wall of gastrointestinal tract to mix food and propel the food to anus.

What is Digestion?

Mechanical and chemical processes break down ingested food into small molecules. In mechanical digestion, the teeth cut and grind food before it is swallowed, and then muscles of the stomach and small intestine churn the food. As a result, food molecules get dissolved and get mixed with digestive enzymes. In chemical digestion, the large carbohydrates, lipids, protein and nucleic acids molecules in food are split into blood or lymph for distribution to cells.

Parts Of Digestive System:

Mouth: Mouth is referred to as an oral or buccal cavity which formed by cheeks,hard and soft palates and tongue.The mouth is an oval shaped cavity.Parts of mouth include lips, vestibule, hard palate, soft palate, uvula, salivary glands, tongue and teeth .

Mechanical digestion(mastication or chewing) helps in breaking the food into pieces, which mixes with saliva resulting in the formation of bolus. Chemical digestion with the help of amylase breaks down food(starch), as well as through lingual lipase, it breaks down triglycerides into fatty acids and glycerol.

Teeth: Involved in mechanical digestion

Pharynx: When food is first swallowed, it passes from the mouth into the pharynx.

Oesophagus : The oesophagus connects the pharynx to the mouth, by swallowing. Swallowing occurs in 3 stages, namely the Voluntary stage, pharyngeal stage, and esophageal stage. 

In the pharyngeal stage, food moves from pharynx to oesophagus; 

The oesophageal stage begins when bolus enters the oesophagus. Oesophagus contains 2 sphincters (upper esophageal and lower esophageal sphincters). If the lower esophageal sphincter fails to close adequately after food has entered the stomach, the  contents of the stomach can come back into the oesophagus. HCl from the stomach can irritate the esophageal wall and can cause a burning sensation.

Stomach: It’s a j shaped organ, connecting the oesophagus to duodenum. The stomach mixes bolus with gastric juices to turn it into chyme. It has regions like cardia, fundus, and pylorus. As the  food reaches the pylorus, the chyme moves into duodenum through the pyloric sphincter. Most of the chyme is forced back into the body of the stomach where the mixing continues. The forward and backward movements help in mixing the contents in the stomach. The Stomach (parietal cells) also releases HCL which kills microbes in food.

Pancreas: Pancreas produces the correct chemicals in proper quantities at the right time to digest the food. It produces pancreatic juice for digesting the food and contains some enzymes like trypsin etc. The pancreas has two functions: 

Exocrine function that helps in digestion and an endocrine function that regulates blood sugar. 

Pancreas is made up of small clusters of glandular epithelial cells. About 99% of the clusters are called acini, the remaining 1% are pancreatic islets or islets of langerhans. These are:

Alpha cells which secrete glucagon

Beta cells which secrete insulin

Delta cells which secrete somatostatin, and 

F cells which secrete pancreatic polypeptides.

Liver: The liver is the largest and heaviest organ in the body. It is divided into left and right lobes separated by the falciform ligament. Liver weighs 1.4kgs ,and is inferior to the diaphragm. 

It contains specialised cells, called hepatocytes arranged in an irregular manner. The kupffer cells present in the liver destroy the microbes and foreign matter.

Bile which is secreted by hepatocytes enter bile canaliculi that empty into small bile ductules. Bile salts play a role in emulsification, the breakdown of large lipid globules into small lipid globules

Small intestine: It is divided into 3 regions called duodenum, jejunum, ileum. Major events of digestion and absorption take place here, There are villi which increases the cell surface area for proper absorption. 

In the small intestine, the digestion takes place through two processes: segmentations and propulsions. Proteins are digested by pepsin and lipids are digested by gastric lipase

Large intestine: It contains cecum, colon, rectum, and anal canal. Peristalsis quickly moves the contents into rectum. In large intestine, defecation takes place 

Defecation: Elimination of faeces from rectum called defecation. The problems related to defecation are diarrhoea and constipation.

Disorders of digestive system:

Peptic ulcers: These ulcers develop in the mucous membrane of the digestive tract, in areas exposed to gastric juice.

Diarrhoea:  In this condition, water can’t be reabsorbed from the faeces.

Constipation: In this condition, too much water is reabsorbed.

Gastroenteritis: Inflammation of lining of stomach and also intestine caused by bacteria.

Indigestion: It is caused by intolerance to an ingredient of food, defect in stomach, food poisoning, overeating and consumption of spicy food.

Jaundice: Jaundice is a yellowish coloration of sclera, skin and mucous due to a buildup of bilirubin. The main categories of Jaundice are prehepatic, hepatic,and enterohepatic.

Vomiting: Vomiting or emesis is the forcible expulsion of the contents of the upper GI tract through the mouth. The strongest stimulus for vomiting are irritation and distension of the stomach: other stimuli include unpleasant sights, general anaesthesia, dizziness, and certain drugs such as morphine and derivatives of digitalis.

Conclusion

The food you consume takes an implausible journey throughout your body. In the process, the helpful parts of your food are absorbed, providing you energy and nutrients. And when this is achieved, it conveniently wraps up your solid waste, or stool, for clearance when you have a bowel movement.