The human body is defined as the entire structure of a human being and comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet. Every part of the body is composed of various types of cells, the fundamental unit of life. The study of the human body involves anatomy and physiology. Human anatomy is primarily the scientific study of the morphology of the human body. Human physiology is the science of the mechanical, physical, bio-electrical, and biochemical functions of humans in good health, their organs, and the cells of which they are composed.
"Systems do not work in isolation, and the well-being of the person depends upon the well-being of all the interacting body systems."
The human body consists of many interacting systems. Each system contributes to the maintenance of homeostasis, of itself, other systems, and the entire body. A system consists of two or more organs, which are functional collections of tissue.
Systems do not work in isolation, and the well-being of the person depends upon the well-being of all the interacting body systems. Some combining systems are referred to by their joint names such as the nervous system and the endocrine system known together as the neuroendocrine system.
The immune system provides a mechanism for the body to distinguish its own cells and tissues from alien cells and substances and to neutralize or destroy the latter by using specialized proteins such as antibodies, cytokines, and toll-like receptors, among many others.
The urinary system consists of the kidneys, ureters, bladder, and urethra. The urinary system removes water from the blood to produce urine, which carries a variety of waste molecules and excess ions and water out of the body.
The musculoskeletal system consists of the human skeleton (which includes bones, ligaments, tendons, and cartilage) and attached muscles. It gives the body basic structure and the ability for movement.
In addition to their structural role, the larger bones in the body contain bone marrow, the site of production of blood cells. Also, all bones are major storage sites for calcium and phosphate. This system can be split up into the muscular system and the skeletal system.
The human circulatory system or cardiovascular system comprises the heart and blood vessels (arteries, veins, and capillaries).
The heart propels the circulation of the blood, which serves as a "transportation system" to transfer oxygen, fuel, nutrients, waste products, immune cells, and signaling molecules (i.e., hormones) from one part of the body to another.
The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and back, as well as the spleen and bone marrow.
The endocrine system consists of the principal endocrine glands: the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads, but nearly all organs and tissues produce specific endocrine hormones as well.
The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function. There is also the exocrine system.
The human respiratory system is a series of organs responsible for taking in oxygen and expelling carbon dioxide.
The respiratory system consists of the nose, nasopharynx, trachea, and lungs. Red blood cells collect the oxygen from the lungs and carry it to the parts of the body where it is needed. During the process, the red blood cells collect the carbon dioxide and transport it back to the lungs, where it leaves the body when we exhale.
The human body needs oxygen to sustain itself. A decrease in oxygen is known as hypoxia and a complete lack of oxygen is known as anoxia.
The brain is the organ of thought, emotion, memory, and sensory processing, and serves many aspects of communication and controls various systems and functions.
The special senses consist of vision, hearing, taste, and smell. The eyes, ears, tongue, and nose gather information about the body's environment.
The digestive system consists of the mouth including the tongue and teeth, esophagus, stomach, gut (gastrointestinal tract, small and large intestines, and rectum), as well as the liver, pancreas, gallbladder, and salivary glands.
The digestive system converts food into small, nutritional, non-toxic molecules for distribution by the circulation to all tissues of the body, and excretes the unused residue.
The integumentary system consists of the covering of the body (the skin), including hair and nails as well as other functionally important structures such as the sweat glands and sebaceous glands.
The skin provides containment, structure, and protection for other organs, but it also serves as a major sensory interface with the outside world.
The human reproductive system consists of the gonads and the internal and external sex organs.
The reproductive system produces gametes in each sex, a mechanism for their combination, and a nurturing environment for the first 9 months of development of the infant.
The main function of the lymphatic system is to extract, transport and metabolize lymph, the fluid found in between cells. The lymphatic system is very similar to the circulatory system in terms of both its structure and its most basic function (to carry a body fluid).
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