Railway Science (Biology – Digestive System)

The function of the Liver - Absorption of Bilirubin, Production of Bile, Supporting Blood Clots, Metabolisation of Fats, Carbohydrate Metabolisation, Storage of Vitamins and Minerals, Filtering Blood, Immunological Function, Albumin Production, Angiotensinogen Synthesis.

Hydrochloric acid (HCl) - It is secreted from gastric glands (Parietal cells) in the stomach. Function - It helps to digest food and also essential for absorption of Vitamin B12 (necessary for functioning and maintaining RBCs and Nervous tissues). It lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin.

Pepsin is secreted as a proenzyme of pepsinogen which is activated in pepsin when exposed to acid in the stomach. Ptyalin is a kind of amylase enzyme that is secreted by the salivary glands in the buccal cavity; begins the digestion process and breaks down carbohydrates into simple sugars.
Amylase is an enzyme that catalyzes the hydrolysis of starch into sugars; present in the saliva of humans and some other mammals. Lipase is a family of enzymes that catalyzes the hydrolysis of fats.

The small intestine is longer in a herbivore than in a carnivore or any other type because herbivores eat only grass which is full of cellulose. The digestion of cellulose takes a long time that is why herbivores require a long small intestine, but carnivores don't need a long small intestine for digestion as it consumes only the flesh of herbivores.

Bile juice - secreted by the liver, contains bile salts, helps in emulsification of fats in which big molecules of fats are broken down into smaller molecules. Fats are present in the intestine in the form of large globules, so it is difficult for enzymes to act on them. Bile salts reduce the size of large fat globules, allowing enzymes (such as lipase) to work more effectively.

Connects different organs in the human body. Adipose tissue - A connective tissue that extends throughout the body. It's found under the skin (subcutaneous fat), between the internal organs (visceral fat) and even in the inner cavities of bones (bone marrow adipose tissue).
Epithelial Tissue - A type of body tissue that forms the covering on all internal and external surfaces of the body, lines body cavities and hollow organs and is the major tissue in glands. Muscular tissue - A specialized tissue in animals which applies forces to different parts of the body by contraction.

The inner surface of the small intestine is folded. Lining of the folds are tiny finger-like projections called villi. They have very thin walls, a network of thin and small blood vessels close to the surface, and they are finger-like projections that enable the villi to absorb digested food. Villi do not have pores for absorption.

It is a glucose-polymer cleavage enzyme that is produced by the salivary glands for digestion of dietary starches and fats. Enterokinase - enzyme for intestinal digestion of proteins. Peptidases - catalytically active proteins (enzymes) that cleave peptide bonds in proteins and peptides by hydrolysis.

In the diagram, (a) represents trachea. The trachea is the long tube that connects our larynx (voice box) to our bronchi. It has nothing to do with digestion. Here, (b) represents the Villi.
These are tiny hair-like projections that line the inside of the small intestine. They contain blood vessels and help absorb nutrients. (c) represents the small intestine.
The length of the small intestine depends upon the food eaten by the organism.(d) represents the liver. The emulsification of fats takes place in the liver in which the larger fat molecules are converted into smaller fat globules.

Lymph is a colorless fluid that circulates throughout the lymphatic system. The main role of the lymphatic system is to act as a filter against microbes, organic wastes, toxins and other debris.
Functions of lymph - Absorption of fats from the small intestine occurs through lymphatic vessels. Drains excess fluid from extracellular space back into blood. It transports antibodies and lymphocytes to the blood.