Anatomy is the study of the structures associated with the human body.
Physiology is the study of the function(s) of each of these structures.
Pathology is the science of the causes and effects of diseases.

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).

Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention. Urgent medical treatment is required to prevent serious harm or death.

In immunology, an antigen is a molecule or molecular structure that can bind to a specific antibody or T-cell receptor. An antibody is a large, Y-shaped protein used by the immune system to identify antigens such as pathogenic bacteria and then neutralize these foreign entities. The antibody recognizes a unique molecule of the pathogen. According to this scientific view each antibody binds to a specific antigen. This interaction similar to a lock and key forms the basis for the practice of vaccination which supposedly increases the production of specific antibodies that enable the creation of long-term immune memory.

Antiserum is human or nonhuman blood serum containing antibodies that is used to spread passive immunity to many diseases via blood donation. Serum is the fluid and solute component of blood which does not play a role in clotting. It may be defined as blood plasma without the clotting factors, or as blood with all cells and clotting factors removed.

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.

Blood cells are those cells produced in the bone marrow from the same multi-potential stem cells. There are three major types of blood cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Together, these three kinds of blood cells add up to a total 45% of the blood tissue by volume, with the remaining 55% of the volume composed of plasma, the liquid component of blood.

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.

Cardiac arrest is when your heart suddenly stops pumping blood around your body. A cardiac arrest is caused by a dangerous abnormal heart rhythm (arrhythmia). Not all abnormal heart rhythms are life-threatening, but some mean that the heart cannot pump blood around the body.

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.

Coronary heart disease (coronary artery disease) is a common but serious condition where the blood vessels supplying the heart are narrowed or blocked. Coronary heart disease is caused by a build-up of fatty substances in the blood vessels supplying the heart. It's often linked to an unhealthy diet. You can reduce your risk of getting coronary heart disease by making simple lifestyle changes, such as being active and having a healthy diet.

Dementia is a term which includes various types of progressive degeneration and atrophy of the brain that cause gradual impairment of memory, intellect and reasoning. The most common type is Alzheimer's disease.

Dementia praecox (a ‘premature dementia’ or ‘precocious madness’) is a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood.

DNA is DeoxyriboNucleic Acid, a molecule with a twisted double strand of genes which carry genetic instructions for the development and functioning of cells in almost all existing living organisms. In human beings it is stored in the nucleus of the cells. DNA's major task is to act as the template for protein synthesis.

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.

Genome is the complete set of hereditary information of an organism. This information is stored in the form of the extraordinarily long DNA double helix within each cell of the human body, except in the mature red blood cells.

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 the human organism. 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.

Naked virus is a virus that lack an envelope (lipoprotein coat), thus containing only a piece of DNA or RNA chain.

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).

Nucleus is the central part of the cell with the 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.

RNA is RiboNucleic Acid, a molecule with a single strand of genes and smaller in size than DNA. RNA molecules play an active role in the cells by catalysing various biological reactions. All cellular organisms use messenger RNA (mRNA) to carry the genetic information that directs the synthesis of new protein.

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.

In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each.

According to definitions of modern virology [for which there are no indisputable proofs], we have resistant cells that have no functional receptor for a given virus; then we have susceptible cells with receptors which may or may not  support viral replication inside the cell; and then we have permissive cells that have the capacity to replicate viruses, but they may have or not have receptor.

The human being has three skins that border on the outside world. The first and the smallest is the outer skin of our body. The second larger skin surrounds the air-ducts: external auditory canal, nostrils, nasal cavity, throat, windpipe, bronchi and bronchioles (air pipes in the lungs) and alveoli (air sacs in the lungs). The third and the largest skin surrounds our digestive tube: mouth, throat, oesophagus, stomach, small and large intestine and urethra (a separate tube for the elimination of water in the form of urine).

White blood cells or leukocytes are the cells of the immune system that are involved in protecting the body against microbes and other foreign materials. All white blood cells are produced in the bone marrow. They are found throughout the body, including the blood and lymphatic system. They are divided into the five main types: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Lymphocytes are further divided into B and T cells and natural killer cells.