Human Digestive System

The hepatic portal system is the system of blood vessels that connect the gastrointestinal system and the liver. The nutrients digested by the intestines are transported to the liver, where the excess of carbohydrates is converted into glycogen. The amino acids are broken down and ammonia is released, which is soon converted to urea through the Ornithine cycle. The liver has Kupffer cells that kill the bacteria before the nutrients move out to the different organs of the body.

The process of nourishing or being nourished, especially the process by which a living organism assimilates food and uses it for growth and for replacement of tissues

Gastric acid is a digestive fluid, formed in the stomach. It is composed of hydrochloric acid (HCl) 0.05–0.1 M (roughly 5,000–10,000 parts per million) potassium chloride (KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of amino acids. The highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen, and in infancy rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection. HCl is digestive juice. Fatty acids are digested by bile acids.

Excessive hunger is also associated with Hyperthyroidism and Grave's disease, an autoimmune disease affecting the thyroid. The thyroid functions to increase the metabolic rate, so an overactive thyroid shows symptoms of hyperactivity, insomnia, or constant hunger that is unsatisfied by eating.

Amylase, rennin, and trypsin are all proteins by nature, as all enzymes are globular proteins. They are not all proteolytic (amylase acts on carbohydrates), nor are they all produced in the stomach.

Erepsin, trypsin, pepsin, and rennin are all enzymes involved in the digestion of proteins or protein-related substances (like casein).

Carboxypeptidases (C-terminal) are found in pancreatic juice. Aminopeptidases (N-terminal) are found in intestinal juice (succus entericus).

• Pseudopodia are temporary protrusions that are filled with cytoplasm within the eukaryotic amoeboid cells and unicellular protists. Pseudopodia, also called as "false foot" are majorly used for movement and ingestion of food, nutrients and other particulate matter.
• Villi are the finger-like projections within the small intestine that help in the absorption of nutrients from the digested food by increasing the surface are of intestine walls.
• Lumen is the inside space of the gastrointestinal tract, through which the food is transported while digesting from mouth to anus.

• There are five steps in the process of Nutrition in animals. 

In single-celled organisms like Amoeba, food is ingested through the entire body surface via phagocytosis or endocytosis.

The process in the alimentary canal by which food is broken up physically, as by the action of the teeth, and chemically, as by the action of enzymes, and converted into a substance suitable for absorption and assimilation into the body.

Micelles are formed when bile emulsifies the fat which makes it water soluble and can be absorbed by the intestinal wall. Later on, they convert into chylomicrons by coating them with proteins are absorbed by the lymph vessels which transport it into a blood and then it reaches the cell.