Structure and Function of the Endocrine System in Dogs
Dr. Bari Spielman
The hypothalamus is located at the base of the brain.
What Is the Endocrine System?
The endocrine system is composed of several different types of glands and organs that produce the hormones of the body. A hormone is a chemical that is secreted by a gland in one area of the body and is carried by the bloodstream to other organs in the body, where it exerts some effect. Most hormones regulate the activity or structure of their target organs. The overall effect of the endocrine system is to regulate, coordinate and control many different bodily functions. The endocrine system includes the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, part of the gastrointestinal tract, pancreas, kidneys, liver, ovaries and testes.
Where Is the Endocrine System Located?
The endocrine system is scattered throughout the body as follows:
The pituitary gland is located on the base of the brain and is attached to the hypothalamus via a stalk-like structure.
The thyroid gland is located in the neck, below the larynx (voice box).
Two parathyroid glands are located in the neck, closely associated with the thyroid gland.
Two adrenal glands are located in the abdominal cavity directly in front of the
The gastrointestinal (GI) tract is located in the abdominal cavity.
The pancreas is located in the forward part of the abdominal cavity, behind the liver and stomach.
The liver is in the front of the abdomen, just behind the diaphragm and below the stomach.
The ovaries are located in the middle part of the abdominal cavity near the kidneys.
The testes are located in the scrotum.
What Is the General Structure of the Endocrine System?
The endocrine system is made up of a collection of glands distributed throughout the body. The endocrine glands produce hormones and secrete them directly into the internal environment where they are transmitted via the bloodstream. Hormones produce certain effects at different points in the body. Some endocrine glands are directly under the control of the pituitary gland. For example, the adrenal gland is controlled by the pituitary hormone, adrenocorticotropic hormone (ACTH). ACTH causes the adrenal glands to produce cortisone (cortisol), which is also a hormone. Other endocrine glands respond directly or indirectly to concentrations of substances in the blood, such as the insulin-secreting cells of the pancreas responding to the sugar concentration in the blood.
What Are the Functions of the Endocrine System?
The major function of the endocrine system is to regulate numerous bodily functions, using specific hormones as messengers. Some hormones affect nearly all cells, while others regulate and affect only a single organ. Hormones act by regulating cell metabolism, by changing or maintaining enzyme activity in receptor cells, and by controlling growth and development, metabolic rate, sexual rhythms and reproduction.
The amount of hormone produced at any one time is controlled by feedback mechanisms. These feedback mechanisms are interactions between the endocrine glands, the blood levels of the various hormones, and certain activities of the target organ. For example, when the pituitary gland increases the secretion of ACTH, the increased levels are detected by the adrenal gland, and the end result is more production of cortisone hormone by the adrenal glands. As the cortisol levels rise in the bloodstream, the hypothalamus eventually detects these higher levels and sends a message to the pituitary gland. The pituitary gland then turns down its own production of ACTH. As the ACTH levels in the bloodstream subsequently fall, the adrenal gland decreases its production of cortisol to a normal level again. This is called a negative feedback loop.