What is human digestive system and how it carries the process of digestion along hormones and enzymes involved in it.

DIGESTIVE SYSTEM

Introduction
For any organism to work and carry out the life sustaining reactions it needs energy and the natural way through food enters in body gets converted into smaller particles and from where eventually through many biochemical reactions energy is extracted from the food in the digestive system. Such as if we discuss digestive system of humans than it is made up of several organs and other supporting organs. digestion is a very complex process. Digestive system is very well designed to convert all the food taken into simple nutrients that are eventually used for various process of the body. The digestive system primarily consist of the digestive or series of some main organs along with the supporting organs from where the food and liquids pass ultimately gets into the blood stream and waste material getting out of the body. Digestion is a very coordinated and a well regulated process. The digestive tract begins with mouth and ends at the anus. The process of digestion is very fascinating as the whole conversion of food into basic nutrients and after that its utilization takes places all the time and along with all of the other process of the body. It takes about 30 - 40 hours for the food to get digested broken down adsorbed till it makes its way to outside of the body. There are also many enzymes and hormones that are involved in the process of digestion that takes place in the digestive system. Such as some the hormones that are involved in the digestive system are as following 
  • Insulin 
  • Glucagon
  • Somatostatin
  • pancreatic polypeptide
  • gastrin 
  • secretin 
  • Cholecystokinin
  • Vasoactive intestinal peptide
  • Motilin
  • Gastric inhibitory polypeptide
  • Ghrelin
  • Amylin
  • Glucagon-like peptide-1
  • Guanylin
along with these hormones there are also many enzymes that are also released in the gastrointestinal system or in the digestive system or during the process of digestion and all of these hormones play vital roles in the process of digestion and some the hormones that are released in the process of digestion and aids in he digestion are as following 
  • Lingual lipase
  • Lysozyme
  • salivary Amylase
  • pepsin
  • gastric lipase
  • Trypsinogen
  • Enteropeptidase
  • Carboxypeptidase
  • Pancreatic lipase
  • Sterol esterase
  • Phospholipase
  • DNAase
  • RNAase
  • Pancreatic amylase
  • enterokinase
  • Erepsin
  • Maltase
  • Lactase
  • Sucrase
in the process of digestion there are other sections also released that aids in the process of digestion such as

  • bile 
  • pancreatic juice



DIGESTION
If we simply want to describe digestion than we can describe it as the conversion of large good particles that cannot be directly taken up the blood into smaller units so that the food taken can ultimately be taken up the blood. This process of digestion starts at the level of the mouth and takes place at various levels such that digestion of different things takes place at different levels of the digestive system and after all the digestion there is diffusion of all the useful  materials into the blood and the waste that is not needed by the body is removed. The different organs that combines with each other to form the digestive system are as following 
  • oral cavity
  • stomach
  • small intestine 
  • large intestine

Process of digestion
Oral cavity that is also known as the buccal cavity is one of the openings of the digestive system from where the food gets in to the digestive system or body and oral cavity is the first point in the whole GIT where digestion starts, Oral cavity consist of following components 
  • teeth
  • cheeks
  • tongue
  • soft palate
  • hard palate
 when food gets into the food it is converted into smaller pieces through the teeth in which cheeks tongue and palates also and this level there is release of enzymes such as salivary amylase Lingual lipase these enzymes starts the digestion of food at the level of the mouth and the mucous and saliva lubricates the food and to some extent helps the teeth in the grinding of food. After mastication grinding  lubrication and partial digestion the food than attains a small of a small ball that is known as the  bolus that this bolus from the oral cavity goes into the stomach where further digestion occurs and the food moves from the oral cavity to the stomach through the esophagus. The most important and the most vital function of the stomach is the breakdown of food into simple components so that it can be consumed by the body to fulfill its need for the energy and the stomach perform this process of digestion of food by  the digestion as well as somewhat absorption and the gastric juice secreted by the stomach play a very major role in the digestion and the microorganism or the unwanted microbes that can be harmful for the body are destroy at the level of the stomach through the hydrochloroic acid. If we talk about the digestion of the food in the stomach than we can describe it as following. As the food that is digested at the level of buccal cavity moves further into the gastrointestinal tract for the further breakdown such that when the food leaves the buccal cavity and enters into the esophagus it is in a small ball shape structure that is known by the name of bolus and that bolus moves through the esophagus by the peristaltic movements of the esophagus and it ultimately reaches the stomach but first it have to pass through a gate that is present between the stomach and the esophagus and that gate is the cardiac sphincter and this sphincter is opened by the peristalsis movements of the esophagus and this sphincter also prevents from the back-flow of partially digested food from the stomach into the esophagus. Once the food in the form of bolus reaches the stomach than in the stomach the process of digestion begins and for the digestion stomach produces a protein digesting enzyme whose active form goes by the name of pepsin and pepsin is responsible for the break down of the protein in the food taken and the stomach contents is mixed with the food by the process of churning and this occurs when stomach muscle contacts and these muscles are known as rugae that are present at the ridges of muscle tissues. Along with the pepsin in the stomach there is HCL that is responsible for the adjustment of the stomach's pH and makes it to about 2-3 which is the pH in which the pepsin works this HCL also softens the food kills microorganisms and coverts inactive pepsinogen into active form pepsin. After the digestion in the stomach the food that was initially in the form of bolus that is converted into a acidic fluid that is known as the chyme and this chyme moves out of the stomach and goes to the duodenum portion of the small intestine by passing through a sphincter that is known as the pyloric sphincter
Along with the digestion of food stomach is also responsible for the somewhat absorption of food and the things absorbed by the stomach. The absorption of food is mainly the function of the intestines but at the level of stomach some absorption also takes place and the absorption that takes place are of following things 
  • a very little amount of water soluble vitamins 
  • caffeine
  • amino acids
  • some medicines such as aspirin
  • water in case of dehydration
there is one thing that is to be cleared at this point and it is that stomach is responsible for the breakdown of the protein part of the food and the stomach is also made up of proteins so why this same proteins digesting enzyme do not digest the walls of the stomach as they are also proteins and if such a conditions occurs and become worse than there can also be formation of pores in the stomach' wall from where the stomach content that are highly acidic can flow out of the stomach and can cause serious problems. Stomach prevents all of this situation by secreting proteins digesting enzyme pepsin in inactive form pepsinogen so that during secretions it does not effect the internal lining of the stomach and than this inactive form pepsinogen is converted into the active form by the hydrochloroic acid that is present in the stomach and the second thing by which the stomach prevents it is that the internal lining of the stomach is also covered by a layer of mucous that prevents it from being digested. Than the food from the stomach goes into the small intestine in the first and second sections of the small intestine that are the duodenum and jejunum respiration further breakdown of food takes place and these are the sections where bile and pancreatic juice is mixed with the food after the digestion the food goes to the third and last section of the small intestine that is the ileum where the absorption of food into the blood stream through the structures known as villi takes place. After the digestion and absorption of food in the small intestine goes into the large intestine and this is mostly water and waste and would be later on removed from the body. All of the chemical digestion and most absorption takes place till the small intestine and in the large intestine there is only adsorption of water and electrolytes along with the temporary storage of the fecal material. 

Diseases related to digestive system
There are also many disease that are related with the digestive system and some of them are following 

  • gastroparesis
  • gastritis
  • zollinger Ellison syndrome
  • peptic ulcer disease
  • gastric ulcers
  • dyspepsia
  • gastro-esophageal reflux
  • pyrosis
  • food poisoning
  • cholecystitis 
  • cholelithiasis   
  • gallstone pancreatitis 
  • gall bladder cancer 
  • choledocholithiasis 
  • common bile duct infection 
  • abscess of gall bladder 
  • gall stone ileus 
  • porcelain gall bladder
  • gall bladder polyps 
  • perforated gallbladder
  • celiac disease
  • Crohn's Disease
  • Ulcerative Colitis
  • Hemorrhoids
  • Diverticulitis

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