The human body is divided into systems: the skeletal system, muscular system, digestive system, respiratory system, endocrine system, lymphatic system, reproductive system, cardiovascular system, nervous system, and urinary system.
The skeletal system is made up of the bones, cartilage and joints that provide the framework of the body and support it and allow it to move. The skeleton is divided into the axial skeleton and the appendicular skeleton. The axial skeleton comprises the skull, vertebral column and the rib cage. The appendicular skeleton is the skeleton of the body's appendages--the bones of the arms, legs, hands, feet, and the shoulder girdle and pelvic girdle. The skeletal system also serves to protect organs and produce new red blood cells.
The muscular system provides the power for all movement conducted by the human body. There are three types of muscles in the muscular system--skeletal muscles, which are attached to bones and joints and control voluntary movement; smooth muscles, which form organs including the stomach and blood vessels and carry on unconscious body processes; cardiac muscles, which exist only in the heart and pump blood throughout the body.
The digestive system processes the food that enters the human body, and comprises the alimentary canal, which extends from the mouth to the anus. The necessary organs of the digestive system (those involved directly in digestion and absorption of food) include the oral cavity, esophagus, stomach, small intestine, large intestine, and anus. The accessory organs (those that aid digestive processes) include the teeth, tongue, pancreas, liver, gall bladder, and salivary glands.
The endocrine system is the system of glands in the body which secrete hormones that regulate various functions of the human body, such as growth, metabolism, and mood.
The respiratory system controls breathing, or the exchange of gases between the human body and the environment. The respiratory system allows the body to oxygenate blood and excrete carbon dioxide, and includes the lungs, the respiratory passages, bronchioles and alveoli.
The cardiovascular system's function is to circulate blood to all parts of the body, and its components are the heart, the blood vessels (veins and arteries) and the blood itself, which is composed of blood cells and plasma.
The nervous system is made up of the brain, spinal cord, nerves and nerve endings, and is the controlling and coordinating system of the body. It controls how we feel and respond to stimuli, as well as all of our conscious and unconscious activities.
The reproductive system differs in males and females, and controls the functions necessary for sexual human reproduction.
The urinary system and lymphatic system are the drainage systems of the body. The urinary system produces and eliminates urine, and along with it wastes that would be harmful if they remained in the body. The lymphatic system aids the immune system and removes waste from cells and tissues.