The tissues unite to form the organs which perform a specific function. The internal organs are located inside the body and they unite to form the various systems which perform a large function. Each organ system is made up of different organs.
Nervous system: The nervous system is divided into a central nervous system and a peripheral nervous system. Central nervous system includes the brain and the spinal cord. Brain is located inside the skull or cranium. The spinal cord is contained within the spine, extending from the base of the skull to the second lumbar vertebra at the base of the spine.
Circulatory system: The circulatory system helps in the transport of nutrients and oxygen. It includes the heart and the blood vessels. The heart is located in the thoracic cavity between the lungs.
Digestive system: It helps in digestion of food materials. It includes the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus.Esophagus is in the cervical region and in the posterior mediastinum. The stomach, small intestine, large intestine etc. are located in the abdominal cavity.
Respiratory system: it helps in the exchange of CO2 accumulated in the blood for oxygen in the airways. It includes the nostril, pharynx, trachea, bronchus, bronchioles and alveolus and the lungs. They are located in the thoracic cavity.
Urinary system: It is responsible for the excretion of waste materials and to maintain proper ionic balance. It includes the kidneys, ureter, urinary bladder and urethra. They are located in the abdominal cavity. Kidneys are located on either side of the vertebral column on the back.
Reproductive system: It is involved in the production of male and female gametes and by fusion produce the next generation. Most of the male reproductive organs are located outside the body around the pelvic region. Female reproductive system is located in the pelvis region.