Abdomen (less formally called belly or stomach) constitutes the part of the body below the diaphragm (a sheet of internal muscle) which separates the chest cavity from the abdominal cavity, which contains the stomach, the small intestine, the colon, the liver, the gallbladder, the spleen, the pancreas, kidneys and adrenal glands.

Adrenaline is a hormone secreted by the adrenal glands. It has many functions in the body; among them is its involvement in the regulation of blood sugar.

Amylase is an enzyme present in the saliva of humans and some other mammals, where it begins the chemical process of digestion of carbohydrates by breaking them down into smaller units. Plants and some bacteria also produce amylase.

Anabolism is the set of metabolic processes in the human organism which cause building-up of organic substances, cells, and tissues (opposite to catabolism).

Anus is an opening of the digestive track through which we excrete faeces.

Autonomic nervous system (also autonomous or vegetative nervous system) is the part of the nervous system which is spreading out from the spinal cord into the organs of the body. It is involved in automatic (involuntary, subconscious) control of homeostasis, maintaining a regular heartbeat, normal temperature and internal environment compatible with the immediate external surroundings.

Bile is an alkaline liquid that is secreted by the liver, then concentrated and stored in the gall bladder, and discharged when needed into the duodenum, where it enables proper digestion of fats.

Biological molecules (or biomolecules) are very large and complex molecules, such as proteins, carbohydrates and fats, found inside living organisms.

Brain sand (or corpora arenacea or acervuli or corpus arenaceum) are yellow, sand-like granules in the pineal gland and other areas of the brain, composed of calcium phosphate (a family of materials containing calcium and phosphate), calcium carbonate [CaCO3], magnesium phosphate (various forms of salt from magnesium and phosphate), and ammonium phosphate [(NH4)3PO4]. Phosphate is a compound of phosphorus [P] and oxygen [O].

Caecum is a blind-ended pouch at the junction of the small and large intestines.

Catabolism is the set of metabolic processes in the human organism which cause breaking-down of organic substances, cells, and tissues (opposite to anabolism).

Chyle is the substance which is absorbed from the small intestines into the lymphatic circulation via intestinal villi.

Chyme is according to natural science the substance expelled by the stomach, while in spiritual science it denotes the substance after final breakdown processes in the duodenum. It is the semi-fluid mass containing digested food substances, water, and residues of digestive secretions.

Colon is the last part of the digestive system. It extracts water and salt from solid wastes before they are eliminated from the body and is the site in which much bacterial fermentation of unabsorbed material occurs.

Duodenum is the first part of the small intestine, immediately after the stomach (25 to 38 cm long). From the glands in the wall mucus is secreted which creates the proper chemical environment for digestive activities. The cell walls secrete two enzymes which regulate the secretion of bile and pancreatic juice which are the active substances in the chemical breakdown of fats.

Endocrine system is the system of glands, each of which secretes different types of hormones directly into the bloodstream to regulate homeostasis. It consists of the following endocrine glands: pituitary gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pancreas, and sexual glands.

Enzymes are proteins that catalyze biochemical reactions – i.e., they increase the rate of these reactions, but they are not used in them. Enzymes usually catalyze only one specific reaction, either synthesis or breakdown (decomposition).

Erythrocyte is scientific name for the red blood cell. These cells are rich with haemoglobin, an iron containing biomolecules, that can bind oxygen in the lungs and carry it to the body tissues via the blood flow through the circulatory system. These cells originate in the bone marrow and their life span is about 100 -120 days. Approximately a quarter of the cells in the human body are red blood cells.

Faeces or stool contain the waste materials from the digestion of food: indigestible food residues (mainly dietary fibre), intestinal bacteria, dead cells of the walls of the alimentary tracts, and some other residues of the digestion, such as bile, and mucus. Normally it is semi-solid with a mucus coating.

Ganglia (singular: ganglion) are groups of cell bodies of neurons which belong to the peripheral nervous system.

Glycogen is a multibranched polysaccharide that serves as a form of glucose storage primarily in the liver as an integral part of sugar metabolism. Glycogen is similar to starch, and is therefore occasionally referred to as 'animal starch'.

Homeostasis is the ability of the human organism to regulate its internal conditions, the dynamic, ever-changing state of various factors which needs to be kept within narrow limits with the aim to maintain the healthy functions of the body. It includes body temperature, acidity/alkalinity of body fluids, levels of blood sugar, blood pressure, heartbeat, etc. When any of these factors is not properly maintained there is a serious risk to the health of an individual. All the systems of the human body are involved in the maintenance of homeostasis, with particular contributions by the autonomic nervous system, the endocrine system, the respiratory system and the kidney system.

Hormones are substances released by a cell, a gland, or an organ that transports signals to cells in other parts of the organism. Hormones are made mainly from proteins. Although their amounts are extremely small they have a powerful effect on the metabolism of the cells.

Human microbiota or microbiome is the full array of microorganisms that live on and in humans. They populate skin, mouth, nose, lungs, digestive tract, uterus, etc. Bacteria are by far the most numerous members of the human microbiota: the bacterial population alone is estimated at between 75 trillion and 200 trillion individual organisms, while the entire human body consists of about 50 trillion to 100 trillion body cells. The microbes in the body are so small that they make up only about 2 to 3 percent of the total weight of the human body. By some estimates, the human population of microorganisms may consist of a total of 900 different species. The largest populations of microbes, called gut microbiota (formerly called gut flora) reside in the intestine where they play a key role in digesting food we eat, including helping with absorption of existing nutrients and also synthesising new nutrients.

Hydrochloric acid is a clear, colourless solution of hydrogen chloride (HCl) in water. It is a highly corrosive, strong mineral acid, with many industrial uses. It is also the main ingredient of the digestive juice in the stomach (called gastric juice) which enables the breakdown of proteins.

Hypothalamus is a portion of the brain that contains a number of small clusters of neurons with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis).

Intestinal villi (singular villus) are approximately 1 mm long, finger-like projections arising from the lining of the intestinal wall. Villi, together with the folds, increase the internal absorptive area of the intestinal wall up to 200 m2.

Metabolic pathways is a scientific term for the metabolic processes.

Mucus is an important substance in the digestive tract. It is produced by the mucus membrane which lines the digestive tract. It is a slimy, tenacious fluid which can either protect the walls of the digestive tract, or it wraps around the substances to help with their movement through the gut.

Neuron is a nerve cell consisting of a cell body with short branch-like structures called dendrites, and a long string, called axon. Neurons vary considerably in shape and size (up to 100 cm long).

Nucleusis the central part of the cell with the glossary_proteo.html#DNA double helix which directs the activities of the cell. Every cell in the human body has a nucleus, except mature red blood cells.

Peripheral nervous system contains all nerves and ganglia outside of the brain and the spinal cord (i.e., the central nervous system). It is divided into autonomous nervous system and the nerves which are involved in the voluntary movements of the limbs (i.e., the somatic nervous system).

Pineal gland (also pineal body or epiphysis) is a small (about 10 mm long) endocrine gland in the shape of the pine cone in the centre of the human brain. It excretes minute amounts of so-called 'brain sand', a mixture of a few mineral compounds (calcium phosphate, calcium carbonate, etc).

Pituitary gland (or hypophysis) is an endocrine gland in the brain about the size of a pea. It secretes several hormones that regulate homeostasis directly or by regulating the activity of many other endocrine glands.

Ptyalin is an enzyme found in human saliva which enables the breakdown of starches into smaller units.

Solar plexus (also celiac or coeliac plexus) is a complex network of nerves (plexus means a braid of nerves) located in the centre of abdomen (behind the stomach, on the level of the pancreas). The celiac plexus proper consists of the celiac ganglia (also solar ganglia) with a network of interconnecting fibres. These ganglia contain neurons which spread in the stomach, liver, gallbladder, spleen, kidney, small intestine, and the colon.