Digestive System

This is a muscular ring, which is at the end of the large intestine. Its function is to keep the intestine sealed until the need to pass feces arises. 

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

Human canines are the longest and most stable of teeth in the dental arch. Only one tooth of this class is present in each quadrant. Humans have two upper (maxillary) canines and two lower canines. Canines play a vital role in the biting mechanism of the teeth. They touch first when the jaw closes and guide the other teeth into position.

The main function of liver within the digestive system is to absorb nutrients from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs. 

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.

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

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 soft palate also 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 fibers sheathed in mucous membrane. It is responsible for closing off the nasal passages during the act of swallowing and also for closing off the airway. During sneezing, it protects the nasal passage by diverting a portion of the excreted substance to the mouth.

The human anus is the external opening of the rectum. Like other animals, its closure is controlled by sphincter muscles. Feces are expelled from the body through the anus during the act of defecation, which is the primary function of the anus. 

The parotid gland is a salivary gland in humans. It is one of a pair and the largest of the salivary glands. It is wrapped around the mandibular ramus and secretes saliva into the oral cavity to facilitate mastication and swallowing, and to begin the digestion of starches. 

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

Chyme is a thick semi-fluid mass of partially digested food and digestive secretions that is formed in the stomach and intestine during digestion. Other secretions from the pancreas, gallbladder, liver and glands in the intestinal wall add to the total volume of chyme. 

The epithelial cells of the villi transport nutrients from the lumen of the intestine into the capillaries (amino acids and carbohydrates) and lacteals (lipids). 

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 upon eating is discharged into the duodenum.

Pepsin is the principal proteolytic enzyme of vertebrate gastric juice. Its inactive precursor form called pepsinogen is produced in stomach mucosa.

It 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, which receives the most wear such as the tip or the crown. Ameloblasts are responsible for the formation of enamel and are lost after the enamel process is complete. 

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

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

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

Steapsin belongs to the class of digestive enzymes called lipases, and is found in the pancreatic juice that catalyzes the hydrolysis of triglycerides (main constituent in vegetable oils and animal fat) to fatty acids and glycerol.

Defecation is the final action of the digestive system, and the means by which organisms eliminate undigested (mostly indigestible) solid, semi-solid or liquid waste material in the form of faeces from the digestive tract via the rectum, anal canal and finally the anus.

It contains sodium bicarbonate, which neutralizes the acidic material from the stomach. Sodium bicarbonate dissociates into Na⁺ and HCO₃^- in liquids. The Na⁺ component is readily absorbed in the small intestine and enhances water absorption. However, ingestion of this solution raises the pH in the stomach making it alkaline instead of acidic.

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.

Chymosin or rennin is a proteolytic enzyme synthesized by chief cells in the stomach. Its role in digestion is to curdle or coagulate milk in the stomach, a process of considerable importance in the very young animal. If milk were not coagulated it would rapidly flow through the stomach, and miss the opportunity for initial digestion of its proteins.

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

The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones and a digestive organ secreting pancreatic juice containing digestive enzymes that assist the absorption of nutrients, and the digestion in the small intestine. 

Most of the nutrients in food are absorbed by the small intestine and carried to other parts of the body. The walls of the intestine contain tiny blood vessels that transport nutrients first to the liver where any toxins are removed before the nutrients are distributed throughout the rest of the body. On an average, the food spends 4-8 hours in the small intestine.

Pepsin is naturally produced in the stomach. The enzyme pepsin enables the stomach to take filet mignon, and break it down into the same amino acids found in the lowly chuck roast.

The function of the appendix is unknown. One theory is that the appendix acts as a storehouse for good bacteria rebooting the digestive system after diarrheal illnesses. Other experts believe the appendix is just a useless remnant from our evolutionary past. Surgical removal of the appendix causes no observable health problems. 

Diarrhoea usually occurs when fluid cannot be absorbed from the bowel contents, or when extra fluid is secreted into the bowel causing watery faeces. If the waste passes too quickly through the colon and if the colon is irritated by a virus, there is not enough time for the water to be absorbed. This results in diarrhoea. 

Caecum is a pouch like portion of the large intestine. It is located in the lower right side of a person's torso, and marks the intersection of the large intestine, small intestine and appendix. This pouch's chief function is to assist in the digestion of plant based foods.

An ulcer is a discontinuity or break in a bodily membrane that impedes the organ of which that membrane is a part, from continuing its normal functions. 

The pyloric sphincter or valve is a strong ring of smooth muscle at the end of the pyloric canal, which lets food pass from the stomach to the duodenum. It is located at the base of the stomach, and is the contracting ring of muscle that guards the entrance of the small intestine. 

The major components of saliva are water, digestive enzymes and mucus. Mucus is a slimy material that coats many epithelial surfaces, and is secreted into fluids such as saliva. It is composed chiefly of mucins and inorganic salts suspended in water. Mucus is an abundant and important component of saliva giving it virtually unparalleled lubricating properties.

In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. The hepatic portal vein accomplishes two tasks. It supplies the liver with metabolic substrates, and it ensures that substances ingested are first processed by the liver.

The unabsorbed and undigested food then passes from the ileum into the cecum, the beginning of the large intestine. This food residue is full of bacteria. After absorption the remaining undigested matter is squeezed into a bundle called feces. About 30% of the weight of feces is bacteria. These bacteria are good bacteria and billions of them live in our colon all the time.

Saliva is a watery substance secreted by the salivary glands and located in the mouth. Human saliva is composed of 99.5% water while the other 0.5% consists of electrolytes, mucus, glycoproteins, enzymes and antibacterial compounds such as secretory IgA and lysozyme. 

This function is performed by gastric juice. Pepsinogen, an inactive zymogen is secreted into gastric juice from both mucous cells and chief cells. Once secreted, pepsinogen is activated by stomach acid into the active protease pepsin that is largely responsible for the stomach's ability to initiate digestion of proteins. Pepsin breaks down proteins into more easily digestible products.

The last section of the small intestine known as the ileum absorbs amino acids, fat, cholesterol and fat soluble vitamins like vitamins A, D, E and K. 

A lacteal is a lymphatic capillary that absorbs dietary fats bound to a carrier in the villi of the small intestine. This fat is then transported to the subclavian veins where it enters the bloodstream, and can be transported around the body.