Digestive System

Any of the temporary first teeth of a young mammal is called milk tooth, baby tooth or primary tooth. The number of baby teeth is 20 (ten at every jaw) that is much less than the number of adult teeth. The primary teeth get replaced at a baby's later age by a set of 32 permanent teeth.

The dental pulp is the part in the centre of a tooth, which is made up of living connective tissues and cells, called odontoblasts.

Ivory is the material from which the teeth and tusks of animals are made. It is also called as enamel. It covers the surface of the tooth or tusk. 

Peristalsis is a distinctive pattern of smooth muscle contractions that propels food distally through the oesophagus and intestines. It is an automatic and important process that moves food through the digestive system.

The soft palate, known as velum or muscular palate is the soft tissue constituting the back of the roof of the mouth in mammals. It is movable, and consists of muscle fibres sheathed in mucous membrane.

The sublingual gland is the smallest of the three glands. It is situated beneath the mucous membrane of the floor of the mouth at the side of the fraenulum, in contact with the sublingual depression on the inner surface of the mandible. It is narrow, flattened, shaped somewhat like an almond and weighs nearly 2 gm.

The stomach when completely full can be stretched to hold about 2 to 3 litres of food. The average time for gastric emptying is about 4 hours that varies according to the quantity and type of food consumed. A light meal can be emptied from the stomach in about 2 hours, while a large heavy meal may require up to 6 hours.

Alimentary canal, called digestive tract is the pathway by which food enters the body and solid wastes are released. The alimentary canal includes the mouth, pharynx, oesophagus, stomach, small intestine, large intestine and anus.

The pylorus is the region of stomach that connects to duodenum. The internal surface of pylorus is covered with a mucous membrane lining that secretes gastric juice.

Amylase is secreted by salivary ducts in the mouth, and helps to digest starch into simple cabohydrates.

Bile or gall is a bitter tasting, dark green to yellowish brown fluid produced by the liver of most vertebrates that aids the process of digestion of lipids in the small intestine. In many species, it is stored in the gallbladder and is discharged into the duodenum during digestion.

Ptyalin or amylase present in saliva catalyses the hydrolysis of starch into maltose and dextrin.

Intestinal villi are small, finger like projections that protrude from the epithelial lining of the intestinal wall. Each villus is approximately 0.5 to 1.6 (millimetres) in length and has many microvilli. The villi increase the surface area of the ileum for absorption.

Rennin is a proteolytic enzyme synthesised by chief cells in the stomach. Its role in digestion is to curdle or coagulate milk in stomach.

It is the function of cement, a bone like structure covering and fixing the root in position. The function of the cement is not only to seal the restoration on the tooth, but also in some cases to support the retention of the restoration.

The vermiform appendix is a small, finger-sized structure found at the end of our small caecum, and it is located near the beginning of the large intestine.

The saliva contains ptyalin or salivary amylase, which starts degrading the starch where the chain is linear. It is an enzyme that breaks the bond joining two sugars together and forms fragments of soluble starches. It then breaks these down further, and the final product is a unit of two glucose molecules known as maltose. This substance is then broken down to glucose in the intestine.

Chyme is a thick semifluid mass of partially digested food and digestive secretion, i.e. formed in the stomach and intestine during digestion. 

Bile does not contain any enzymes for the breakdowm of complex food material. They simply emulsify the fats.

Biliverdin and bilirubin are the pigments that give bile its colour. These are produced by the breakdown of the dead and worn out red blood cells. Biliverdin is a green pigment formed by the catabolism of haemoglobin, and converted to bilirubin in the liver. It may also arise from oxidation of bilirubin.