Human body
The external human body consists of a head, hair, neck, torso (which includes the thorax and abdomen), genitals, arms, hands, legs, and feet.
Many systems and mechanisms interact in order to maintain homeostasis, with safe levels of substances such as sugar, iron, and oxygen in the blood.
The human body is composed of elements including hydrogen, oxygen, carbon, calcium and phosphorus.
Lining cells regulate what can and cannot pass through them, protect internal structures, and function as sensory surfaces.
[9] Organs, structured collections of cells with a specific function,[10] mostly sit within the body, with the exception of skin.
It is surrounded by the pericardium, which holds it in place in the mediastinum and serves to protect it from blunt trauma, infection and help lubricate the movement of the heart via pericardial fluid.
The primary purpose of the atria is to allow uninterrupted venous blood flow to the heart during ventricular systole.
It then travels to the atrioventricular node, which makes the signal slow down slightly allowing the ventricles to fill with blood before pumping it out and starting the cycle over again.
[18] Cancer can affect the heart, though it is exceedingly rare and has usually metastasized from another part of the body such as the lungs or breasts.
[19] The gallbladder is a hollow pear-shaped organ located posterior to the inferior middle part of the right lobe of the liver.
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.
[24][25][26] The digestive system consists of the mouth including the tongue and teeth, esophagus, stomach, (gastrointestinal tract, small and large intestines, and rectum), as well as the liver, pancreas, gallbladder, and salivary glands.
These molecules take the form of proteins (which are broken down into amino acids), fats, vitamins and minerals (the last of which are mainly ionic rather than molecular).
What remains passes on to the large intestine, where it is dried to form feces; these are then stored in the rectum until they are expelled through the anus.
The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, resulting in variety of changes of function.
[33] The musculoskeletal system consists of the human skeleton (which includes bones, ligaments, tendons, joints and cartilage) and attached muscles.
The brain is the organ of thought, emotion, memory, and sensory processing; it serves many aspects of communication and controls various systems and functions.
The CNS is mostly responsible for organizing motion, processing sensory information, thought, memory, cognition and other such functions.
[46][47] Cancer can affect most parts of the reproductive system including the penis, testicles, prostate, ovaries, cervix, vagina, fallopian, uterus and vulva.
The smooth muscle lining the ureter walls continuously tighten and relax through a process called peristalsis to force urine away from the kidneys and down into the bladder.
The spine at the back of the skeleton contains the flexible vertebral column, which surrounds the spinal cord, which is a collection of nerve fibres connecting the brain to the rest of the body.
This includes the mechanical, physical, bioelectrical, and biochemical functions of humans in good health, from organs to the cells of which they are composed.
These interact to maintain homeostasis, keeping the body in a stable state with safe levels of substances such as sugar and oxygen in the blood.
The nervous system receives information from the body, and transmits this to the brain via nerve impulses and neurotransmitters.
Together, these systems regulate the internal environment of the body, maintaining blood flow, posture, energy supply, temperature, and acid balance (pH).
[63] The 2nd century physician Galen of Pergamum compiled classical knowledge of anatomy into a text that was used throughout the Middle Ages.
[64] In the Renaissance, Andreas Vesalius (1514–1564) pioneered the modern study of human anatomy by dissection, writing the influential book De humani corporis fabrica.
In the 17th century, William Harvey (1578–1657) described the circulatory system, pioneering the combination of close observation with careful experiment.
Claude Bernard (1813–1878) created the concept of the milieu interieur (internal environment), which Walter Cannon (1871–1945) later said was regulated to a steady state in homeostasis.
In the 20th century, the physiologists Knut Schmidt-Nielsen and George Bartholomew extended their studies to comparative physiology and ecophysiology.
