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Hi guys, present blog will deal with Human Digestive system. So, let's start.

Nutrition is biochemical and physiological process by which an organism uses food to support its life is nutrition. It includes ingestion, digestion, absorption, assimilation and excretion.

<h2 id="content-id-1980-0">Human Digestive system</h2>

Digestion: The process of conversion of complex indiffusible food material into simple and diffusible food by mechanical and biochemical (hydrolysis) processes, is termed as Digestion.

Origin of alimentary canal: The alimentary canal’s tubular structure extends from mouth to anus. It develops from ectoderm & endoderm.

Teeth: We chew food with the help of our sets of teeths. An adult human has 32 permanent teeth which are of four different types (Heterodont esoth dentition), namely, incisors (I), canine( C) premolars (PM) and molars (M). Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which is 2123/ 2123.

Tongue: Plays a major role in swallowing. On the floor of the oral cavity a muscular, flat, fleshy plate-like structure is present which is called tongue.

<h2 id="content-id-1980-1">Digestive glands</h2>

Namely 3 major glands needs to be studied:

<ol>
	<li>Salivary</li>
	<li>Liver</li>
	<li>Pancreas</li>
</ol>

Salivary glands: There are majorly three types of Salivary glands i.e.

<ul>
	<li>Parotid (largest)</li>
	<li>Sub mandibular</li>
	<li>Sublingual</li>
</ul>

These glands are situated just outside the buccal cavity but secrete salivary juice into the buccal cavity.

Liver: Liver is the largest gland of the body weighing about 1.2 to 1.5 kg in an adult human. It is situated in the abdominal cavity, just below the diaphragm and has two lobes. The hepatic lobules are the structural and functional units of the liver containing hepatic cells arranged in the form of lobules. Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gallbladder.

Pancreas: It is a compound gland i.e. both exocrine and endocrine. It secretes hormones, insulin and glucagon.

<h2 id="content-id-1980-2">Digestion of food</h2>

The process of digestion is accomplished by mechanical and chemical processes.

Digestion in mouth: The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The gastro-oesophageal sphincter controls the passage of food into the stomach

Digestion in stomach: The mucosa of the stomach has gastric glands. Gastric glands have three major types of cells namely:

<ol>
	<li>mucous neck cells which secrete mucus</li>
	<li>peptic or chief cells which secrete the proenzyme pepsinogen; and</li>
	<li>parietal or oxyntic cells which secrete HCl and intrinsic factor (factor essential for absorption of vitamin B12). </li>
</ol>

The stomach stores the food for 4-5 hours. The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins into proteoses and peptides (peptides). The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. HCI provides the acidic pH (pH 1.8) optimal for pepsins. Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins.

Digestion in intestine: Various types of movements are generated by the muscularis layer of the small intestine. These movements help in a thorough mixing up of the food with various secretions in the intestine and thereby facilitate reactions to digestion. The bile, pancreatic juice and the intestinal juice are the secretions released into the small intestine.

Hence by studying the digestive system in this blog, we got a general idea of how energy is taken from food in absorbable form from the alimentary canal with the help of several digestive glands.

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