fundamentals
Organ Systems
Organ systems working together
Organ systems often work together to do complicated tasks. For example, after a large meal is eaten, several organ systems work together to help the Overview of the Digestive System obtain more blood to perform its functions. The digestive system enlists the aid of the Communication between organs and organ systems is vital. Communication allows the body to adjust the function of each organ according to the needs of the whole body. In the example above, the heart needs to know when the digestive organs need more blood so that it can pump more. When the heart knows that the body is resting, it can pump less. The Kidneys must know when the body has too much fluid, so that they can produce more urine, and when the body is dehydrated, so that they can conserve water. Homeostasisis the term used to describe how the body maintains its normal composition and functions. Because organ systems communicate with each other, the body is able to maintain stable amounts of internal fluids and substances. Also, the organs neither underwork nor overwork, and each organ facilitates the functions of every other organ. Communications to maintain homeostasis occur by means of the autonomic nervous system and the endocrine system. Special chemicals called transmitters carry out the communications. Overview of the Autonomic Nervous System None Endocrine Glands None (adrenaline). When a person is suddenly stressed or frightened, the brain instantly sends a message to the Overview of the Adrenal Glands , which quickly release Other chemical communications are less dramatic but equally effective. For example, when the body becomes dehydrated and needs more water, the volume of blood circulating through the cardiovascular system decreases. This decreased blood volume is perceived by receptors in the arteries in the neck. They respond by sending impulses through nerves to the Overview of the Pituitary Gland , at the base of the brain, which then produces antidiuretic hormone. This hormone signals the kidneys to concentrate urine and retain more water. Simultaneously, the brain senses thirst, stimulating a person to drink. 