Railway Science (Biology – Digestive System)

Calcium phosphate {Ca₃(PO₄)₂} appears as a white amorphous or crystalline powder that is odorless and tasteless. It is found in bones, milk, teeth, and ground.It is also known as Calcium phosphate tribasic or Tricalcium Phosphate. Enamel (Hardest part of teeth) is harder than the bones. Bile is a fluid that is released by the liver and stored in the gallbladder. It helps in digestion.

Liver (largest gland) - Located in the abdominal cavity. It secretes bile juice containing substances like bilirubin, biliverdin, cholesterol, which is stored in gallbladder.
The pancreas is a long and thin organ located in the abdominal region, which is located between the organs of the 'U' shaped duodenum.
Kidneys are reddish brown, bean shaped structures situated between the levels of the last thoracic and third lumbar vertebra.
Functions - Filters blood, urine formation. Stomach - Muscular bag acts as a storage for food. It secretes Mucous, Digestive enzymes and Hydrochloric acid.

Heart - A part of circulatory system. The digestive system of humans is made up of gastrointestinal tract (GI). GI tract is a series of hollow organs joined by a long twisting tube. It comprises mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and the anus. Solid organs of digestive system - Pancreas, liver and gallbladder.

Stomach : Gastric acid (HCl) - Secreted by Parietal or oxyntic cells. Important for activation of pepsinogen and inactivation of ingested microorganisms such as bacteria. Small intestine : Contains three parts (Duodenum, Jejunum, Ileum).
It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water. Large intestine : Absorbing water and electrolytes, producing and absorbing vitamins, and forming and propelling feces toward the rectum for elimination.

The liver performs many important functions, such as processing nutrients, detoxifying harmful substances, and producing bile.These functions are carried out by specialized liver cells called hepatocytes, which are able to carry out numerous biochemical reactions within the liver. The liver's function is not directly dependent on an external force, but rather on the internal biochemical reactions that take place within the organ.

Herbivores have longer small intestines because plant material is harder to digest due to complex carbohydrates like cellulose. The small intestine is distinguishable into three regions, a 'C' shaped duodenum, a long coiled middle portion jejunum and a highly coiled ileum.

Bile juice is stored in the gallbladder. It has pigments like bilirubin and biliverdin, bile salts, and cholesterol. It has two important functions, assists with fat digestion and absorption in the gut.

Bile is a fluid that is made and released by the liver and stored in the gallbladder. Through the process of emulsification, bile acids break down large lipid droplets into smaller ones, increasing the surface area for digestive enzymes. Emulsification is possible due to the amphipathic property of bile salts.

Alveolar Sac (Part of Lungs)- Parts of respiratory system. Human alimentary canal (from mouth to anus): Main Organs - Mouth, Oral Cavity (Palate, Tongue, Teeth), Pharynx, Oesophagus, Stomach, Intestine {Small Intestine (Duodenum, Jejunum, Ileum), Large Intestine (Caecum, Colon, Rectum)}, and Anus.

The secretion of hydrochloric acid by the stomach plays an important role in protecting the body against pathogens ingested with food or water. The hydrochloric acid in the gastric juice breaks down the food and makes the food acidic. The mucus covers the stomach wall with a protective coating. HCl activates pepsinogen into the enzyme pepsin to break down proteins.