Railway Science (Biology – Digestive System)

The digestion of carbohydrates begins in the mouth. The salivary enzyme amylase begins the breakdown of food starches into maltose, a disaccharide. Next the disaccharides are broken down into monosaccharides by enzymes called maltases, sucrases, and lactases, which are also present in the brush border of the small intestinal wall. Maltase breaks down maltose into glucose. Other disaccharides, such as sucrose and lactose are broken down by sucrase and lactase, respectively.

Pepsin:- It is secreted in its inactive form “pepsinogen” by pepsin-secreting cells called chief cells. Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH activates pepsin. Trypsin - Enzyme that starts the digestion of protein molecules in the small intestine.

Smooth muscle fibers are located in walls of hollow visceral organs (such as the liver, pancreas, and intestines), except the heart. The basic functions of smooth muscle in the organ systems -
Gastrointestinal tract: Propulsion of the food bolus; Cardiovascular: Regulation of blood flow and pressure via vascular resistance; Renal: The contractile ability of ureteral smooth muscle cells is critical for allowing movement of urine from the kidney to the bladder;
Genital: Contractions during pregnancy, propulsion of sperm; Respiratory tract: Regulation of bronchiole diameter; Integument: Raises hair with erector pili muscle;
Sensory: The iris consists of two sheets of smooth muscle with contrary actions - dilation (expansion) and contraction (constriction). These muscles control the size of the pupil. Smooth muscles are not found in the bone.

A reaction between an acid and base is called neutralisation. Antacids are bases that are used to relieve pain. Antacids neutralize the excess acid. A mild base, Milk of magnesia (magnesium hydroxide), is frequently used for this purpose.

Buccal cavity (Mouth or oral cavity): Mechanical digestion in the oral cavity consists of grinding of food into smaller pieces by the teeth, a process called mastication. Digestive system includes mouth, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, and anus.

Carbohydrates are essential nutrients which include sugars, fibers and starches. They are found in grains, vegetables, fruits and in milk. Enzymes are proteins that help speed up chemical reactions in our bodies.
Proteins are very large molecules composed of basic units called amino acids. Proteins contain carbon, hydrogen, oxygen and nitrogen.

Bile juice kills the germs present in the food. It helps in the absorption of fat after digestion in the small intestine as it Breaks down large fat globules into smaller ones.
It reduces the acid content of the chyme and provides alkaline medium to the food for the action of pancreatic enzymes which Increases the efficiency of the action of pancreatic enzymes.
It also helps in excretion of waste products including bilirubin and excess cholesterol. It facilitates fat absorption.

Parts of tooth - Enamel: Outer covering of the teeth, hardest substance in the human body. Dentine: Tissue that forms the tooth from the dental crown to the tooth root, situated inside the enamel and cementum.
Tooth pulp: Blood vessels and the lymph vessels, as well as nerve fibers, are located in the dental pulp, supplying nutrients to the dentin. Cementum: Tissue covering the surface of the tooth root.

Bile is a complex fluid containing water released by the liver and stored in the gallbladder, electrolytes and a battery of organic molecules including bile acids, cholesterol, phospholipids and bilirubin that flows through the biliary tract into the small intestine.

Villi increases the surface area of the small intestine allowing more nutrients from the lumen to be absorbed in the circulatory system. Gland is an organ that makes one or more substances, such as hormones, digestive juices, sweat, tears, saliva, or milk.
Sphincter is a circular muscle, which often closes the various passageways of the body and opens them when necessary so that the functions of the body go on smoothly. Cilia are hair-like structures present on the surface of all mammalian cells and play a major role in locomotion.