Endocrine System Overview and Comparison

The endocrine system uses chemical signaling via hormones transported in the bloodstream to target cells. This process takes longer than nervous system signaling, but hormones can affect a broad range of target cells.

A chemical messenger secreted by endocrine organs into the bloodstream, causing a response in target cells.

Endocrine signaling uses hormones and takes longer to affect target cells compared to neural signaling, which uses neurotransmitters and is fast. Endocrine signaling is less specific than neural.

The process of maintaining a stable internal environment in the body.

Important endocrine glands include the pineal and pituitary glands in the brain (pituitary is anterior to the thalamus, pineal is posterior to the thalamus) and the thyroid gland in the neck.

The nervous system uses both electrical and chemical signals (neurotransmitters) for faster communication over short distances; its actions affect nearby or specific targets.

Cells with specific receptors that bind to specific hormones and trigger a response. Receptors determine which cells are affected by specific hormones

Gland that releases hormones into the bloodstream to target cells throughout the body; the released hormones travel a long distance to target cells.

Lipid-soluble hormones bind to intracellular receptors, activating genes for protein synthesis.

Water-soluble hormones bind to receptors on the cell membrane, initiating intracellular signaling cascades.

A molecule that relays signals inside a cell in response to a hormone binding to a surface receptor.

An enzyme that phosphorylates proteins to activate or deactivate them, crucial in cell signaling.

The body's control system that maintains stable hormone levels through feedback loops.

A feedback mechanism where a hormone's effect inhibits further hormone release.

The hypothalamus detects hormonal imbalances and triggers the release of hormones from other glands.

A series of hormone releases that eventually trigger a target response.

Hormones produced by the pituitary gland, located at the base of the brain. They regulate various bodily functions, including growth, metabolism, and reproduction.

Pituitary hormones that regulate the activity of other endocrine glands.

A tropic hormone that stimulates the thyroid gland to produce and release thyroid hormones.

A tropic hormone that stimulates the adrenal cortex to produce and release cortisol.

A tropic hormone that stimulates the production of eggs in females and sperm in males.

A tropic hormone that triggers ovulation in females and testosterone production in males.

The thyroid gland is a butterfly-shaped gland located in the neck, anterior to the trachea just inferior to the larynx.

Specialized cells in the thyroid gland that form rings around cavities called follicles, which contain a substance called colloid.

Calcitonin is a hormone produced by the thyroid gland. Its primary function is to decrease blood calcium levels by inhibiting osteoclast activity, increasing osteoblast activity, and reducing intestinal calcium absorption and urinary calcium excretion.

Osteoclasts are bone cells that break down bone tissue, releasing calcium into the bloodstream. Calcitonin inhibits osteoclast activity, reducing the release of calcium.

Osteoblasts are bone cells that build new bone tissue, taking calcium from the bloodstream. Calcitonin stimulates osteoblast activity, increasing calcium uptake from the blood.

Calcitonin decreases calcium absorption from the intestines, reducing the amount of calcium entering the bloodstream.

Calcitonin increases calcium loss in the urine, eliminating excess calcium from the body.

The parathyroid glands are tiny, round structures located near the thyroid gland. They produce and secrete parathyroid hormone (PTH), which is essential for regulating blood calcium levels.

Chief cells are the main functional cells in the parathyroid glands. They produce and release parathyroid hormone (PTH).

Oxyphil cells are another type of cell found in the parathyroid glands, but their function is not fully understood.

The adrenal glands are a pair of endocrine glands located on top of the kidneys. Each gland has an outer cortex and an inner medulla.

The adrenal cortex is divided into three zones: zona glomerulosa, zona fasciculata, and zona reticularis. Each zone produces different types of hormones.

Aldosterone is a mineralcorticoid hormone produced in the zona glomerulosa of the adrenal cortex. It helps regulate mineral balance in the body.

Cortisol is a glucocorticoid hormone produced in the zona fasciculata of the adrenal cortex. It regulates glucose metabolism and is involved in stress response.

The adrenal medulla produces epinephrine and norepinephrine, which are stress hormones that stimulate the sympathetic nervous system.

The adrenal cortex produces steroid hormones like aldosterone, cortisol, and corticosterone. Aldosterone regulates blood sodium levels, while cortisol increases blood glucose levels. These hormones are essential for maintaining homeostasis.

The pineal gland, located near the thalamus in the brain, produces melatonin, an amine hormone. Melatonin regulates sleep-wake cycles and has other functions related to circadian rhythms.

The gonads, testes in males and ovaries in females, produce steroid hormones that regulate sexual development and reproductive processes. Testosterone (testes) promotes male development, while estrogen and progesterone (ovaries) promote female development and pregnancy.

The placenta produces human chorionic gonadotropin (hCG), a protein hormone. hCG supports pregnancy by stimulating progesterone production and suppressing the immune response against the fetus.

The pancreas, primarily an exocrine gland for digestion, also has an endocrine function. It produces insulin and glucagon, hormones that regulate blood glucose levels.

Insulin, produced by the pancreas, helps lower blood glucose levels by promoting glucose uptake into cells.

Glucagon, also produced by the pancreas, helps raise blood glucose levels by promoting glucose release from storage.