Hormone Regulation

Hormone levels are controlled by a feedback loop: a body mechanism that turns hormone production off and on to maintain stable concentrations. Most hormones are secreted in response to negative feedback, in which a decrease in hormone levels stimulates the releasing gland. Disorders of the endocrine system most often result from overproduction or underproduction of certain hormones.


Pituitary Gland

OVERVIEW
HORMONES RELEASED

The pituitary is a gland connected to the hypothalamus in the brain and regulates the function of many endocrine glands. The pituitary is divided into three lobes: the anterior lobe, intermediate lobe and posterior lobe.

• Antidiuretic hormone (ADH)
• Oxytocin
• Somatotropin (growth hormone)
• Prolactin
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Luteinizing hormone (LH)
• Interstitial cell-stimulating hormone (ICSH)
• Follicle-stimulating hormone (FSH)

Hypothalamus

OVERVIEW
HORMONES RELEASED

The hypothalamus serves as a pathway for releasing hormones that stimulate and inhibit secretions from the pituitary gland.

• Thyrotropin-releasing hormone (TRH)
• Corticotropin-releasing hormone (CRH)
• Gonadotropin-releasing hormone (GnRH)
• Growth hormone-releasing hormone (GHRH)
• Somatostatin
• Dopamine

Thyroid Gland

OVERVIEW
HORMONES RELEASED

The thyroid gland is located in the lower portion of the neck in front of the trachea, or “windpipe”. The thyroid concentrates iodine from food and uses it to make hormones commonly referred to as T4 and T3, which regulate the body’s metabolic rate. Another thyroid hormone called calcitonin maintains stable calcium levels in bones.

• Tetraiodothyronine (T4)
• Triiodothyronine (T3)
• Calcitonin

Parathyroid Glands

OVERVIEW
HORMONES RELEASED

The parathyroid glands are small, bean-shaped and are located behind the thyroid. These glands secrete parathormone, a hormone that maintains stable calcium levels in the bloodstream. To do so, parathormone activates vitamin D, which causes an increase in calcium absorption within the digestive tract.

• Parathyroid hormone (PTH)

Thymus Gland

OVERVIEW
HORMONES RELEASED

The thymus gland is located in the upper chest, close to the heart and aids in developing specialized cells of the immune system.

• Thymosin
• Thymopoietin
• Thymic humoral factor
• Thymostimulin
• Factor thymic serum

Pineal Gland

OVERVIEW
HORMONES RELEASED

The pineal gland is located in the brain and secretes melatonin, which aids in regulating sleep cycles and mood.

• Melatonin

Adrenal Glands

OVERVIEW
HORMONES RELEASED

The adrenal glands are located above the kidneys. The adrenal glands are made up of an outer portion, called the adrenal cortex and an inner portion, called the adrenal medulla. The cortex is responsible for making and releasing glucocorticoids and mineralocorticoids, also known as corticosteroids; and a small amount of androgenic sex hormones. Glucocorticoids such as cortisol, can affect body metabolism, suppress inflammation and help the body withstand stress. Mineralcorticoids maintain water and electrolyte balances. Derivatives of adrenal androgens, such as anabolic steroids, promote the development of muscle mass and masculine characteristics. The adrenal medulla secretes epinephrine and norepinephrine, two hormones that are released in response to stress or to facilitate the “fight-or-flight” response.

Medulla:
• Epinephrine (adrenaline)
• Norepinephrine

Cortex:
• Corticosteroids
• Glucocorticoids
• Mineralcorticoids
• Gonadocorticoids

Pancreas

OVERVIEW
HORMONES RELEASED

The pancreas is located below the stomach and secretes the hormones insulin, glucagon and somatostatin. Insulin lowers blood sugar levels when it rises above normal limits. Glucagon raises blood sugar levels by stimulating a chemical reaction in the liver that produces glucose. Somatostatin helps maintain a constant blood sugar level by inhibiting the release of insulin and glucagon.

• Insulin
• Glucagon

Ovaries and Testes

OVERVIEW
HORMONES RELEASED

The ovaries, female sex glands and testes, male sex glands are important in the development of secondary sex characteristics and development of ovum and sperm. The female ovaries produce the reproductive hormones, estrogen and progesterone; and the male testes are the main source of testosterone, a hormone involved with the development and maintenance of male secondary sex characteristics, such as a deep voice and facial hair.

Ovaries:
• Estrogens
• Progesterone

Testes:
• Androgens (testosterone)