Endocrine System Overview

Chemical messengers secreted into the extracellular fluids that affect other glands or tissues.

Hormones are broadly classified as steroids (from lipids/cholesterol) and peptides (proteins, glycoproteins, modified amino acids).

Hormones only affect specific cells or organs, called target cells/organs.

Target cells must have specific protein receptors for hormones to bind.

Hormone binding triggers changes in target cells, including membrane permeability, protein/enzyme synthesis, enzyme activation, etc.

The process by which steroid hormones directly activate genes in the nucleus of a target cell.

A complex formed when a steroid hormone binds to a specific receptor protein in the cytoplasm of a target cell.

The hormone-receptor complex, after entering the nucleus, binds to specific sites on the DNA molecule.

The binding of the hormone-receptor complex to DNA initiates the transcription of specific genes, leading to the production of messenger RNA (mRNA).

The mRNA moves into the cytoplasm and directs the synthesis of specific proteins, which ultimately elicit the cellular response to the hormone.

A signaling pathway where a hormone (first messenger) binds to a membrane receptor, activating an enzyme that produces a second messenger (e.g., cAMP) within the cell, triggering a cascade of events leading to a specific cellular response.

Cyclic adenosine monophosphate, a common second messenger molecule produced by the enzyme adenylyl cyclase. cAMP activates other enzymes within the cell, leading to various cellular responses.

The release of hormones from an endocrine gland is triggered by other hormones. This is a feedback loop where one hormone stimulates the release of another.

Changing blood levels of certain ions (like calcium or glucose) directly stimulate hormone release from endocrine glands.

Nerve impulses directly stimulate hormone release from endocrine glands. This is often controlled by the sympathetic nervous system.

The front lobe of the pituitary gland, responsible for producing and releasing six hormones, including growth hormone and prolactin, which act on non-endocrine targets. It also produces four tropic hormones that stimulate other endocrine glands.

The back lobe of the pituitary gland that stores and releases two hormones: oxytocin and antidiuretic hormone (ADH). These hormones are produced by the hypothalamus and are transported to the posterior pituitary for release.

A hormone produced by the hypothalamus and released by the posterior pituitary. It stimulates the reabsorption of water from the forming urine in the kidneys, reducing urine volume and increasing blood volume.

A hormone produced by the hypothalamus and released by the posterior pituitary. It stimulates contractions of the uterus during labor and milk ejection in nursing women.

A hormone produced by the anterior pituitary. It stimulates protein synthesis, primarily in cartilage, bone, and muscle, promoting growth and development.

A condition caused by inadequate production of growth hormone during childhood, resulting in short stature, but otherwise normal proportions.

A condition caused by excessive production of growth hormone during childhood, resulting in abnormal overgrowth of the long bones and other tissues.

A condition caused by excessive production of growth hormone in adulthood, resulting in thickening of bones, especially in the face, hands, and feet. It also causes enlargement of internal organs.

A hormone produced by the anterior pituitary gland that stimulates and maintains milk production after childbirth. It also plays a role in carbohydrate and fat metabolism.

A hormone produced by the anterior pituitary gland that regulates the endocrine activity of the adrenal cortex, stimulating it to produce its hormones, such as cortisol.

A hormone produced by the anterior pituitary gland that influences the growth and activity of the thyroid gland, stimulating it to produce thyroid hormones.

A hormone produced by the anterior pituitary gland that stimulates follicle development in the ovaries of females and sperm development in the testes of males.

An enlargement of the thyroid gland due to constant stimulation from the anterior pituitary, often caused by the thyroid's inability to produce sufficient thyroid hormones.

Calcitonin is a hormone that lowers blood calcium levels by promoting calcium deposition into bone.

Calcitonin and parathyroid hormone are antagonists, meaning they have opposite effects on blood calcium levels.

The parathyroid glands are small masses found on the posterior (back) side of the thyroid gland.

Parathyroid hormone (PTH) increases blood calcium levels by stimulating osteoclasts (bone-breaking cells), enhancing calcium absorption in the kidneys and intestines.

The adrenal gland has an outer layer called the cortex and an inner layer called the medulla.

Mineralocorticoids, such as aldosterone, are hormones produced by the adrenal cortex that regulate mineral and water balance in the blood, particularly sodium and potassium levels.

Glucocorticoids, including cortisol, are hormones from the adrenal cortex that regulate metabolism, increasing blood glucose levels, controlling inflammation, and reducing pain.

The adrenal cortex produces small amounts of both male sex hormones (androgens) and female sex hormones (estrogens) throughout life.

The adrenal medulla produces epinephrine (adrenaline) and norepinephrine (noradrenaline), which prepare the body for 'fight or flight' responses to stress.

Pancreatic islets, also known as islets of Langerhans, are clusters of endocrine cells within the pancreas that produce hormones like insulin and glucagon.

Insulin and glucagon are antagonistic hormones that work together to regulate blood sugar levels. Insulin lowers blood sugar, while glucagon raises it.

The pineal gland is a small gland located in the brain that produces melatonin, a hormone involved in regulating sleep-wake cycles.

The thymus gland, located in the chest, is important for the development of the immune system by maturing certain types of white blood cells.

The ovaries produce estrogen and progesterone, hormones responsible for female sexual development, reproduction, and the menstrual cycle.