Suffixes

Combining Forms

Pituitary Gland

The pituitary (pih TOO ih tare ree) gland, also known as the hypophysis (hye POFF ih sis), is a tiny gland located behind the optic nerve in the cranial cavity. Sometimes called the master gland because of its role in controlling the functions of other endocrine glands, it is composed of anterior and posterior lobes, each with its own functions.

The anterior lobe, or adenohypophysis (add uh noh hye POFF ih sis), is composed of glandular tissue and secretes myriad hormones in response to stimulation by the hypothalamus. The hypothalamus sends hormones through blood vessels, which cause the adenohypophysis either to release or to inhibit the release of specific hormones. The adenohypophysis has a wide range of effects on the body, as Fig. 15-2 and the table above illustrate.

The posterior lobe (neurohypophysis) of the pituitary gland is composed of nervous tissue. The hormones that it secretes are produced in the hypothalamus, transported to the neurohypophysis directly through the tissue connecting the organs, and released from storage in the posterior lobe by neural stimulation from the hypothalamus. The two hormones released by this lobe are antidiuretic hormone (ADH) and oxytocin (OT). See the following table and Fig. 15-2 for the hormones secreted by the neurohypophysis and their effects.

Thyroid Gland

The thyroid gland is a single organ located in the anterior part of the neck. It regulates the metabolism of the body and normal growth and development, and controls the amount of calcium (Ca) deposited into bone. The following table describes the hormones secreted by the thyroid and their effects.

Parathyroid Glands

The parathyroids (pair uh THIGH royds) are four small glands located on the posterior surface of the thyroid gland in the neck. They secrete parathyroid hormone (PTH) in response to a low level of calcium in the blood. When low calcium is detected, the PTH increases calcium by causing it to be released from the bone, which results in calcium reabsorption by the kidneys and the digestive system. PTH is inhibited by high levels of calcium.

Adrenal Glands (Suprarenals)

The adrenal (uh DREE nul) glands, also called the suprarenals, are paired, one on top of each kidney. Different hormones are secreted by the two different parts of these glands: the external portion called the adrenal cortex (uh DREE nul KORE tecks) and an internal portion called the adrenal medulla (uh DREE nul muh DOO lah).

The adrenal cortex secretes three hormones that are called steroids.

The adrenal medulla is the inner portion of the adrenal gland. It produces sympathomimetic hormones that stimulate the fight-or-flight response to stress, similar to the action of the sympathetic nervous system.

Pancreas

The pancreas, located inferior and posterior to the stomach, is a gland with both exocrine and endocrine functions. The exocrine function is to release digestive enzymes through a duct into the small intestines. The endocrine function, accomplished through a variety of types of cells called islets of Langerhans (EYE lets of LANG gur hahnz), is to regulate the level of glucose in the blood by stimulating the liver. The two main types of islets of Langerhans cells are alpha and beta cells. Alpha cells produce the hormone glucagon that increases the level of glucose in the blood when levels are low. Beta cells secrete insulin (IN suh lin) that decreases the level of glucose in the blood when levels are high. Insulin is needed to transport glucose out of the bloodstream and into the cells. In the absence of glucose in the cells, proteins and fats are broken down, causing excessive fatty acids and ketones in the blood. Normally, these hormones regulate glucose levels through the metabolism of fats, carbohydrates, and proteins.

Thymus Gland

The thymus (THIGH mus) gland is located in the mediastinum above the heart. It releases a hormone called thymosin that is responsible for stimulating key cells in the immune response. For more detail, see Chapter 9 on the blood, lymphatic, and immune systems.

Ovaries and Testes

The ovaries and testes, the female and male gonads, also act as endocrine glands, which influence reproductive functions.

Pineal Gland

The pineal (PIH nee ul) gland is located in the center of the brain, functioning to secrete the hormone melatonin, thought to be responsible for inducing sleep.