The body consists of billions of cells, which are the smallest building blocks with vital properties, only visible under a microscope. These guarantee internal unity. Depending on their specialization, the cells exhibit very different shapes and functions (e.g., muscle cells, blood corpuscles, neurons, etc.).
Cells that are structured similarly in view of one or several similar functions form associations for certain tasks, namely tissue (e.g., muscle tissue, glandular tissue, nerve tissue, etc.).
Tissues in turn combine by practical associations and in abundant combinations to form organs that are charged with performing certain functions. Tissues and organs combine into systems in which the links are formed by functional complexes, such as digestion, respiration, and so on. All cells for the construction of organs are held together and connected to each other by intercellular fluid.
Nerve tracts and hair blood vessels (capillaries) end freely in the intercellular fluid without having direct cell contact. The intercellular fluid, also called tissue fluid, facilitates microcirculation and thereby the completion of all vital processes. This functional unity of cells, nerves, capillaries, and tissue fluid, called “vegetative ground system” by the researcher A. Pischinger, constitutes an impulse-transmitting system of information in the organism. As a result, every cell in the body is constantly linked indirectly with every other healthy cell. Only cells damaged by irritation, that is, diseased cells, are shut out of this comprehensive information system. Hence, they create a gap in the functional unity and thereby limit organ activity.
The human skeleton determines the shape and form of the body: Its hard and resistant components are the bones and cartilage. Our body is constructed with the purpose of moving it.
4.1.1 Locomotor System
The locomotor system, consisting of muscles and the skeleton, fulfills the task of movement. The framework of the bones is moved in the joints by the muscles. Muscle activities are coordinated through the nervous system. Blood and lymph nourish the locomotor system.
As humans, we express our emotional state with facial muscles and hand movements. Muscle movements allow us to communicate thoughts to others in speaking and writing. Movements facilitate the execution of all other functions that are connected to human life (e.g., changes in location, mechanical influence on the environment).
The body must not only preserve itself and expand by growth, it also needs energy to maintain a stable body temperature and perform chemical and mechanical tasks. This energy has to be supplied to the body through food. The foodstuffs that we absorb by eating are ultimately supposed to reach the individual cells of the organism to guarantee their work. To make this happen, food must be broken down into its chemical components to the point where these become water-soluble. Only then can they penetrate the intestinal wall to enter the blood and be transported to the cells of the organs.
4.1.2 Digestive System
The digestive system has the task of taking the ingested food and breaking it up, liquefying it, and making it absorbable by means of ferments and enzymes. We consider the digestive system to include the oral cavity, the middle and lower sections of the throat, the esophagus, the stomach, the small intestine, the liver and pancreas, the large intestine, the rectum, and the anus.
The nutrients that have been absorbed into the body, for their part, cannot be transformed into energy by the cells without outside assistance. For this process, the body needs oxygen.
4.1.3 Respiratory System
The respiratory system facilitates breathing. By means of our respiratory organs, we inhale the oxygen in the air and exhale carbon dioxide and water vapor. Respiration leads to a step-by-step combustion of carbon and hydrogen, with the help of oxygen. This is a process that supplies energy and is essential for life.
We refer to the gas exchange between the pulmonary alveoli and capillaries of the lung on the one hand and the atmosphere on the other as external respiration. Tissue, or internal, breathing describes the process by which the blood conveys oxygen to the tissue and in its place takes in carbon that has accumulated there. The respiratory passages include the nasal cavity and the upper and middle section of the throat, the larynx, the trachea, the bronchial tubes, and the lungs.
To ensure the constant supply of blood to all parts of the organism, a separate transportation system is necessary.
4.1.4 Circulatory System
The circulatory system consists of blood vessels of different sizes and structures that are in charge of bringing blood into the immediate vicinity of all cells. The heart is the motor of this cycle. It pumps blood that has been replenished with oxygen into the large arteries of the body and pumps used blood that flows in from the large veins of the body back into the lungs.
Blood is one large transport organ that transports nutritive and constructive substances as well as hormones and other active agents to the individual organs and tissues.
The organ systems described here supply the working cell groups of the body with energy-supplying substances and with oxygen. Nevertheless, tissue activity also leads to the formation of substances that the body has no more use for. These must be discharged. The main organs of discharge are the kidneys.
4.1.5 Urinary System
The urinary system performs the vital functions of discharge, especially of substances produced during protein metabolism, but also of water and salts as well as foreign matter, medicinal and recreational drugs, and so on. The urinary system also has the ability to regulate body fluid. It is comprised of the two kidneys, the two ureters, the bladder, and the urethra.
4.1.6 Reproductive Organs
In the human body, its functions also include reproductive capacity. The reproductive organs do not serve the preservation of the body, but the preservation of the species. Their activity produces a new living being of the same genus.
To be able to survive, the human organism must defend itself against a wide variety of pathogens, against extraneous substances of all types (proteins, toxins, etc.), as well as against diseased cells.
4.1.7 Immune System
The immune system enables the organism to recognize and destroy substances that are foreign to the body or have become so. It can be divided into two systems: the humoral (i.e., settled in the bodily fluids) and the cellular (i.e., settled in the cells) immune systems work together and are inseparable because the cells construct the antibodies, and all antibodies in the blood originate in the cells. The cellular immune system is superior to the humoral immune system and directs it.
In addition, the body also contains organs that regulate its relationship with the environment: the sensory organs. These are perceptive organs that are directed toward specific impulses.
4.1.8 Sensory Organs
With special receptors, the sensory organs receive messages (impulses) from the outside and transmit these via neural pathways to the neural central agencies: the brain and the spinal cord.
In humans, we distinguish between the sense of smell, taste, vision, hearing, position, touch, temperature, and balance.
Nature has made ample provisions in the structure of the human body to ensure