Human Digestive System

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.

The liver is central to the regulation of cholesterol levels in the body. Not only does it synthesize cholesterol for export to other cells, but it also removes cholesterol from the body by converting it to bile salts and putting it into the bile where it can be eliminated in the feces.

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