Describe the human digestion . Step by step.
Answers
The Human Digestion takes place from stomach to small intestine
In stomach the food is squeezed in HCL to absorb nutrients and sent it to various parts of body
and in the intestine the water from leftover food is sucked out and further Digestion takes place
Answer:
DIGESTION OF FOOD
The process of digestion is accomplished by mechanical and chemical processes.
Digestion of oral cavity
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.
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 the process called deglutition.
The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis.
The salivary juice contains lysozyme and salivary amylase enzymes.
Lysozyme present in saliva acts as an antibacterial agent that prevents infections.
Salivary amylase acts on the starch and splits into a disaccharide maltose.
Digestion in stomach
The mucosa of stomach has gastric glands, which have three major types of cells
mucus neck cells which secrete mucus
peptic or chief cells which secrete the proenzyme pepsinogen
parietal or oxyntic cells which secrete HCl and intrinsic factor.
The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the
The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin.
Pepsin converts proteins into proteoses and peptones.
HCl 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 small intestine
The bile, pancreatic juice and the intestinal juice are the secretions released into the small intestine.
Pancreatic juice and bile are released through the hepato-pancreatic duct.
The pancreatic juice contains inactive enzymes:
trypsinogen
chymotrypsinogen
procarboxypeptidases
amylases
lipases
Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active trypsin.
The bile released into the duodenum contains bile pigments (bilirubin and bili-verdin), bile salts, cholesterol and phospholipids.
Bile helps in emulsification of fats and also activates lipases.
The intestinal mucosal epithelium has goblet cells which secrete mucus.
The secretions of the brush border cells of the mucosa along with the secretions of the goblet cells constitute the succus entericus.
The mucus along with the bicarbonates and Brunner’s glands from the pancreas protects the intestinal mucosa from acid as well
as provide an alkaline medium.
Proteins, proteoses and peptones in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic Juice.
Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides and monosaccharides.
Fats are broken down by lipases with the help of bile into di-glycerides
Nucleases in the pancreatic juice acts on nucleic acids to form nucleotides and nucleosides
The enzymes in the succus entericus act on the end products of all the reactions.
These final steps in digestion occur very close to the mucosal epithelial cells of the intestine.
The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.
The undigested and unabsorbed substances are passed on to the large intestine.
Digestion in large intensine
The functions of large intestine
absorption of some water, minerals and certain drugs
secretion of mucus which helps in adhering the waste (undigested) particles together and lubricating it for an easy passage.
The undigested, unabsorbed substances called faeces enters into the caecum of the large intestine through ileo-caecal valve, which prevents the back flow of the faecal matter.