HUMAN BODY SYSTEMS Skeletal Muscular Circulatory Lymphatic Digestive Excretory Endocrine Reproductive Skin Respiratory

All the organs in the endocrine system are glands. They are unique from other glands, because they release chemicals known as hormones into general circulation. ENDOCRINE SYSTEM

The organs of the endocrine system are located in widely separated parts of the body: in the cranial cavity, in the neck, in the thoracic cavity, in the abdominal cavity, in the pelvic cavity, and outside the body cavities. The hormones they release are important to body functions. They regulate basic drives and emotions, such as sexual urges, violence, anger, fear, joy, and sorrow. They also promote growth and sexual identity, control body temperature, assist in the repair of broken tissue, and help to generate energy.

The adrenal glands (suprarenal glands) curve over the top of each kidney in the abdomen. Although it appears to be one organ, it is actually two small glands, each weighing about 1/4 ounce (7 grams). The adrenal medulla (inner part) secretes the catecholamines epinephrine and norepinepherine. These hormones help the body reduce stress. The adrenal cortex secretes two hormones: cortisol and aldosterone. They help the body reduce stress and are essential for life.

The pituitary (or hypophysis) is a small gland, no larger than a pea, located at the base of the brain in the small depression of the sphenoid bone called the sella turcica. It is controlled by the hypothalamus to which it is attached and is sometimes referred to as the master gland because its function is to coordinate the nervous system and the endocrine system. This small gland is actually two glands: the anterior pituitary gland (or adenohypophysis) and the posterior pituitary gland (or neurohypophysis). This gland produces several hormones.

Overlying the heart, the thymus is a twin lobed organ consisting largely of developing lymphocytes. Lymph carries white blood cells to this organ, where they multiply and change into special infection-fighting cells. Although the function of the thymus is not fully understood, it is known that it is an important part in developing immunities against various diseases.

The pancreas and spleen lie just behind the lower part of the stomach. The pancreas is responsible for secreting digestive enzymes into the duodenum. The spleen's function is closely related to the cardiovascular and lymphatic systems. The spleen is the only lymphatic organ responsible for filtering blood. It removes worn out blood cells from the bloodstream, converts their hemoglobin to bilirubin, and then releases their iron back into the bloodstream to be used in the manufacture of other blood cells.

The thyroid gland is one of the glands of the endocrine system which lies outside of a body cavity. It is a small gland weighing about 1 ounce (28 grams) and is located in the neck, just below the larynx. This gland secretes two hormones: thyroxine and calcitonin (thyrocalcitonin). Thoroxine affects the growth rate and metabolism of all of the body's cells. It controls reflexes and regulates the rate at which the body produces energy and transforms food into body components. Calcitonin functions to help maintain homeostasis of blood calcium. It prevents a harmful excess of calcium in the blood, called hypercemia, from developing.