The liver is the largest gland in the body. The liver has four lobes. They are the large right lobe, smaller left lobe and caudate and quadrate lobes. Bile juice is secreted by the liver.
Functions of Liver
The production of bile from the pigment of broken down red blood cells.
The removal of toxins that have been absorbed from the intestine.
The storage of simple sugar in the form of glycogen, which is released as needed in the form of glucose.
The storage of certain Vitamins including A,D,E and K.
The manufacture of heparin, which prevents clotting of the blood in the blood vessels.
The formation of antibodies which acts against disease producing organisms.
The production of certain blood plasma proteins such as fibrinogen and albumin.
The removal of a waste product called urea from amino acids.
In the absence of bile, fats are not digested properly which results in fatty diarrhoea. Thus bile is essential for digestion though it does not contain any digestive enzymes. The bile is taken by the hepatic duct and is stored in the gall bladder which is situated on the lower surface of the liver. The bile is concentrated and sent to the duodenum through the cystic duct when chyme from the stomach enters the duodenum. Bile contains bile salt, bile pigment, mucin and water. The two pigments present in the bile are called Bilirubin and Biliverdin. These pigments give colour to the faeces and urine. Due to liver damage or obstruction of the bile duct, bilirubin collects in excess quantities in blood and change the colour of the skin and the eyes. There may be changes in the colour of the urine also. This is called Jaundice.
Functions of Bile Juice
It stimulates the functions of the proteolytic enzymes and Amylase.
It dissolves fatty acid, and glycerol.
It coordinates with lipase to convert the fat into fatty acids.
It helps in the absorption of the fatty acids and glycerol.
With the help of other digestive juices it neutralises the acidic nature of food.
Pancreas is an elongated structure lying across the posterior wall of the abdomen. It is an exocrine as well as an endocrine gland. The pancreas not only produces the pancreatic juice but also secretes hormones e.g. insulin and glucagon. It is released directly in the blood which regulates the blood glucose level. The pancreatic juice contains three enzymes. They are (1) Trypsin (2)
Amylase and (3) Lipase. Besides these enzymes pancreatic juice contains large quantities of sodium bicarbonate which neutralizes the hydrochloric acid present in the gastric juice secreted by the stomach.
Chemical digestion in the small Intestine
When acid chyme passes into the small intestine, it is mixed with pancreatic juice, bile and intestinal juice.
Bile is not primarily a digestive juice because it contains no enzyme but it helps in the digestion of fats. The bile salts emulsifies fats and helps the pancreatic lipase to act and digest it easily. The pancreatic juice contains 3 powerful enzymes. They are:
Pancreatic amylase - Converts carbohydrates - amylase into simple sugars like glucose, fructose and galactose.
Trypsin & Chymotrypsin - Converts peptones into Polypeptides. In the beginning trypsin is present in the form of inactive trypsinogen and Chymotrypsinogen. This trypsinogen is converted into active trypsin by the action of enterokinase which is secreted in the small intestine.
Pancreatic lipase - Converts fats into fattyacids and glycerol.
After pancreatic digestion, the food which is now called chyme proceeds further in the intestine. Here it comes in contact with Succus entericus which is a juice produced by the small intestine. Succus entericus contains three enzymes. They are:
1. Erepsin - It converts polypeptides into amino acids.
Nucleotidases - Converts nucleotide, into nucleosides.
Nucleosidases - Converts nucleosides into pentose, purine
It also contains three sugar splitting enzymes called lactase, maltase and sucrase converting the respective sugars into simple sugars, mostly glucose. It also has lipase which acts on fats and converts them into fatty acids and glycerol.
The final products of digestion of the carbohydrates is glucose, for the proteins are amino acids and fats are fatty acids, and glycerol.
Absorption of Food
Absorption is the process by which water, minerals, vitamins and end products of digestion are absorbed through the mucosa of alimentary canal (especially the small intestines) into blood stream either directly or via lymphatic vessels.
In the stomach there is little absorption. Water, alcohol, glucose, and simple salts are absorbed to a certain degree. The main absorption occurs in small intestine especially in the lower (ileum) part, the upper part of the small intestine is mainly associated with the process of digestion.
The mucous membrane of small intestine is covered with minute fingerlike projections known as villi. About 50 lakhs of villi are found in small intestine. Each villus contains an arteriole, a venule, a capillary network and a lacteal (lymphatic vessel). Nutrients that diffuse through the epithelial cells which cover the villus are able to pass through the capillary walls and the lacteal and enters the blood.
About 90% of all absorption takes place throughout the length of the small intestine. The other 10% occurs in the stomach and large intestine. Both monosaccharides and amino acids are absorbed by a positive pressure gradient between the intestinal content and the blood as well as by an active process involving enzymatic reactions and transported in the blood stream to the liver via the hepatic portal system. The excess amount of glucose is converted into glycogen and stored in the liver, when need arises glycogen is converted into glucose and is utilized by the body.
Fatty acids and glycerol do not enter the blood stream immediately. They are absorbed by the lacteals. So these lymph ducts are seen as white and milky in appearance after a meal of fat. The mineral salts and water soluble vitamin B Complex and C are absorbed via portal blood.
Functions of the Large Intestine
In the large intestine the absorption of water continues until semisolid consistency of faeces is achieved. Mineral salts, vitamins and some drugs are also absorbed into the blood capillaries from the large intestine. The large intestine is heavily colonized by certain types of bacteria which synthesize vitamin K and Folic acid. Unabsorbed carbohydrate undergoes bacterial fermentation and produces gas. These gases pass out of the bowel as flatus. The large intestine exhibits mass movements.
This is the process of emptying the bowels or the passage of faeces. When a mass movement forces the contents of the sigmoid colon into the rectum the nerve endings in the anal walls are stimulated resulting in defaecation.