Hyderabad: This article is in continuation to the previous one focusing on the digestive system, digestion of food, the role of hydrochloric acid and absorption of digested food products. • The mucus along with the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium (pH 7.8) for […]
Hyderabad: This article is in continuation to the previous one focusing on the digestive system, digestion of food, the role of hydrochloric acid and absorption of digested food products.
• The mucus along with the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium (pH 7.8) for enzymatic activities. Sub-mucosal glands (Brunner’s glands) also help in this.
• Proteins, proteoses and peptones (partially hydrolysed proteins) in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice (Trypsin/Chymotrypsin, Carboxypeptidase, etc.,) into Dipeptides.
• Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides.
• Fats are broken down by lipases with the help of bile into di-and monoglycerides.
• Nucleases in the pancreatic juice acts on nucleic acids to form nucleotides and nucleosides.
• Dipeptides convert into the amino acids by the enzyme dipeptidase, maltose converts into the two glucose molecules by the enzyme maltase, lactose converts into one glucose and one galactose molecules by the enzyme lactase, sucrose converts into one glucose and one fructose molecules by the enzyme sucrase. Di and monoglycerides convert into the fatty acids and glycerol by the enzyme lipase.
• The breakdown of biomacromolecules mentioned above occurs in the duodenum region of the small 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.
• No significant digestive activity occurs in the large intestine.
• The functions of large intestine are:
(i) absorption of some water, minerals and certain drugs;
(ii) 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. It is temporarily stored in the rectum till defecation.
• The activities of the gastro-intestinal tract are under neural and hormonal control for proper coordination of different parts.
• The sight, smell and/or the presence of food in the oral cavity can stimulate the secretion of saliva.
• Gastric and intestinal secretions are also, similarly, stimulated by neural signals.
• The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS.
• Hormonal control of the secretion of digestive juices is carried out by local hormones produced by the gastric and intestinal mucosa.
Absorption of digested food products
• Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph.
• It is carried out by passive, active or facilitated transport mechanisms.
• Small amounts of monosaccharides like glucose, amino acids and some electrolytes like chloride ions are generally absorbed by simple diffusion.
• The passage of these substances into the blood depends upon the concentration gradients. However, some substances like glucose and amino acids are absorbed with the help of carrier proteins. This mechanism is called the facilitated transport.
• Transport of water depends upon the osmotic gradient.
• Active transport occurs against the concentration gradient and hence requires energy. Various nutrients like amino acids, monosaccharides like glucose, and electrolytes like Na are absorbed into the blood by this mechanism.
Dr. Modala Mallesh
Palem, Nakrekal, Nalgonda