Endocrine System Overview

Organs specialized for hormone production and secretion directly into the bloodstream.

Organs that perform their primary function and also produce hormones.

Pituitary gland, Pineal gland, Thyroid gland, Parathyroid glands, Adrenal glands.

Kidneys, Gonads, GI tract organs, Liver, Pancreas, Lungs, Heart.

Uses electrochemical signals (neurotransmitters) for rapid, localized communication.

Uses chemical signals (hormones) for slower, widespread communication.

Some molecules act as both neurotransmitters and hormones.

Both systems can influence the same target cells and often regulate each other.

Hormones derived from cholesterol, secreted by gonads and adrenal cortex. Examples include sex steroids, glucocorticoids, and mineralocorticoids.

Hormones derived from single amino acids, secreted by the adrenal medulla, pineal, and thyroid glands. Examples include epinephrine, norepinephrine, melatonin, and thyroid hormones.

Hormones made from chains of amino acids, representing the majority of endocrine hormones.

Hormones that dissolve easily in water, like peptide and most monoamine hormones. They travel freely in blood plasma.

Hormones that don't dissolve easily in water, like steroid hormones and thyroid hormone. They need carrier proteins to travel in the bloodstream.

A complex communication network involving the hypothalamus, pituitary gland, and a target endocrine gland. This system regulates various physiological processes through hormone signaling.

The Hypothalamic-Pituitary-Thyroid axis controls thyroid hormone production. Low thyroid hormone triggers the release of TRH from the hypothalamus, which stimulates TSH release from the pituitary. TSH then activates thyroid hormone production.

The Hypothalamo-Pituitary-Adrenal axis controls stress response. CRH from the hypothalamus stimulates ACTH release from the pituitary. ACTH then activates cortisol production in the adrenal glands.

The Hypothalamo-Pituitary-Gonadal axis controls reproductive function. GnRH from the hypothalamus stimulates LH and FSH release from the pituitary. LH and FSH then activate sex hormone production in the gonads.

The Hypothalamo-Pituitary-Liver axis controls growth. GHRH from the hypothalamus stimulates GH release from the pituitary. GH then promotes growth in liver, muscle, and bone.

The hypothalamus produces 8 hormones that regulate the endocrine system, including 2 directly released into the posterior pituitary and 6 regulatory hormones that control the anterior pituitary.

The posterior pituitary stores and releases two hormones: oxytocin and anti-diuretic hormone, which are produced by the hypothalamus.

The anterior pituitary is made of glandular tissue and produces six hormones that control various bodily functions.

The hypothalamus releases regulatory hormones (TRH, CRH, GnRH, GHRH, PIH, GHIH) that control the secretion of hormones from the anterior pituitary.

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are released by the anterior pituitary and target the gonads (testes or ovaries).

FSH stimulates the development of ovarian follicles in females and sperm production in males.

LH triggers ovulation in females and testosterone production in males.

A negative feedback loop exists between FSH and inhibin, a hormone produced by the gonads. When inhibin levels rise, FSH secretion is inhibited.

Hydrophilic hormones, unable to cross cell membranes, bind to membrane-bound receptors. This activates a G protein, leading to a cascade of events involving second messengers like cAMP, ultimately affecting cellular functions.

A signaling pathway triggered by hydrophilic hormones. It involves a series of steps: hormone binding, G protein activation, adenylate cyclase activation, cAMP production, and enzyme regulation.

A group of hormones that utilize the G protein-coupled receptor and cAMP pathway to exert their effects. Examples include ACTH, FSH, LH, PTH, TSH, glucagon, calcitonin, and catecholamines.

Hydrophobic hormones (like steroid and thyroid hormones) directly enter the cell and bind to intracellular receptors. This complex then translocates to the nucleus, directly influencing gene expression.

Hydrophobic hormones bind to receptors inside the cell, forming a complex that translocates to the nucleus. This complex directly regulates gene expression, leading to changes in protein synthesis and cellular function.

A small amount of hydrophilic hormone can trigger a significant cellular response. This is achieved through signal amplification, where one hormone molecule activates multiple enzyme molecules, leading to a potent effect.

Hydrophilic hormones act indirectly, stimulating physiology by activating second messenger systems. Hydrophobic hormones directly enter the cell and influence gene expression, resulting in long-lasting effects.

Hydrophilic hormones bind to cell-surface receptors and activate second messenger systems, while hydrophobic hormones enter cells and bind to intracellular receptors, directly influencing gene expression.

Thyroxine (T4), also known as thyroid hormone, primarily acts as an energy regulator, boosting metabolism and increasing heat production in the body. This metabolic effect is referred to as thermogenic and catabolic.

If a child experiences hyposecretion of thyroxine, they develop cretinism. This condition leads to severe physical and mental developmental delays. The root cause often lies in a maternal iodine deficiency during fetal development.

In adults, hyposecretion of thyroxine results in hypothyroidism. This condition can lead to a range of symptoms like fatigue, weight gain, and sensitivity to cold. Severe cases can even lead to coma, known as myxedema.

Graves' disease is a condition caused by hypersecretion of thyroxine, often due to tumors in the thyroid or other endocrine glands. Symptoms include exophthalmos (protruding eyes), weight loss, anxiety, and tachycardia.

Hyperparathyroidism, usually caused by parathyroid tumors, leads to elevated blood calcium levels. This can cause bone softening and deformities, mood swings, and potential coma.

Hypoparathyroidism, caused by trauma, removal, or genetic absence of the parathyroid glands, leads to low blood calcium levels. This can result in muscle spasms, seizures, and potentially fatal neural and muscular complications.

Aldosterone is a mineralocorticoid produced by the adrenal cortex. It plays a key role in regulating the body's fluid and electrolyte balance, primarily by controlling sodium and potassium levels in the blood.

Cortisol is a glucocorticoid produced by the adrenal cortex. It plays a vital role in the body's response to stress by regulating metabolism, increasing blood sugar levels, and suppressing inflammation.

Cushing syndrome is a condition caused by prolonged exposure to high levels of cortisol. It can lead to weight gain, hyperglycemia, muscle wasting, and characteristic features like a moon face and buffalo hump.

Addison's disease is a condition caused by hyposecretion of cortisol and aldosterone. It can lead to fatigue, weight loss, and a bronze skin pigmentation.

IGF-1 is a hormone primarily produced by the liver, stimulated by growth hormone (GH). It plays a crucial role in promoting growth and development, specifically in tissues like bones and muscles.

Hyposecretion of growth hormone in children leads to pituitary dwarfism. This condition inhibits proper skeletal growth, resulting in short stature.

Hypersecretion of growth hormone in children leads to gigantism, characterized by excessive height due to accelerated bone growth.

Acromegaly is a condition resulting from hypersecretion of growth hormone in adults. It causes abnormal bone thickening and enlargement of hands, feet, and facial features.

The adrenal cortex has three zones: 1) Zona glomerulosa – produces aldosterone (mineralocorticoid); 2) Zona fasciculata – produces cortisol (glucocorticoid); 3) Zona reticularis – produces sex steroids (androgens and estrogens).