Human Body 101 | National Geographic
The human body is a complex network of cells, tissues, and organs that together make life possible. Ten major systems are responsible for the body's functions: skeletal, muscular, cardiovascular, nervous, endocrine, lymphatic, respiratory, digestive, urinary, and reproductive. The skeletal, muscular, cardiovascular, and nervous systems in particular create an infrastructure that facilitates the other systems.
The adult skeletal system is a framework of over 200 bones. They hold the body together, give it shape, and protect its organs and tissues. The skeleton also provides anchor points for the muscular system, which includes three types of muscles: skeletal, smooth, and cardiac. They are found throughout the body and facilitate movement.
Nestled within these muscles is the cardiovascular system, a pipeline that includes the heart, blood vessels, and the blood itself. Also called the circulatory system, the cardiovascular system delivers oxygen, white blood cells, hormones, and nutrients throughout the body. Lastly, the nervous system is a communication network of nerve cells that the body uses to transmit information and coordinate bodily functions.
It's comprised of the brain, the hub of sensory and intellectual activity, the spinal cord, and the many cranial and spinal nerves that emanate from them. This infrastructure created by neurons, blood, muscles, and bones allows three other systems to regulate the body's environment: the endocrine, lymphatic, and urinary systems.
The endocrine system is a series of glands that use information carried by the nervous system to help regulate the body's processes. Thanks to this neural connection, endocrine glands such as the thyroid are aware of the amount of hormones and other chemicals they need to produce. These chemicals are then distributed throughout the body by way of the cardiovascular system.
The cardiovascular and nervous systems are also utilized by the lymphatic system, a collection of lymph nodes and vessels that help regulate the body's defenses. Also called the immune system, the lymphatic system uses neural pathways to transmit information about affected areas of the body and then sends out healing agents like white blood cells via the bloodstream.
Another key regulatory system is the urinary system, which includes the kidneys, ureters, bladder, and urethra. The urinary, or renal, system maintains the body's electrolyte levels and filters wastes from the blood. This waste is sent through the blood vessels into the kidneys and then expelled as urine.
All of these systems require energy to function, and that's where the respiratory and digestive systems come in. The respiratory system is a group of passageways and organs that extracts life-giving oxygen from the air we breathe. Air enters the body through nasal cavities, travels down the throat, and is then transported to the lungs. The lungs extract oxygen for the body to use and then expel a carbon dioxide by-product when we exhale.
Energy can also come in the form of food. The digestive system is an approximately 30-foot series of organs that convert food into fuel. Food enters the system through the mouth, then moves into the esophagus, the stomach, and the intestines. Nutrients are absorbed into the body while solid waste is expelled through the anal canal, the end of the digestive tract.
No matter the size or shape of any of the body systems, each began with the reproductive system. This system is responsible for creating life. The primary organs involved differ between the sexes, with ovaries, fallopian tubes, the uterus, and vagina found in women, and testes and a sperm channel found in men. Together, fertilization may occur, organ systems form, and then a child is born.
Humans are complicated organisms, but when our 10 major organ systems are healthy, they ensure our well-being.