Endocrine Physiology: Secretion & Action of Hormones

Vocabulary practice flashcards covering endocrine system concepts, hormone mechanisms, specific endocrine glands and their secretions, homeostatic feedback loops, and clinical endocrine disorders based on the lecture material.

Endocrine System

The body system consisting of glands, tissues, and cells that secrete hormones directly into the bloodstream to regulate physiological processes.

Hormones

Chemical messengers secreted into the bloodstream that stimulate physiological responses in cells of target tissues or organs, often located at a distance.

Lipid-Soluble (Steroid) Hormones

Non-polar hormones derived from cholesterol that can easily diffuse directly through the plasma membrane of target cells (e.g., testosterone, estrogen, aldosterone, cortisol).

Water-Soluble Hormones

Polar peptide or protein hormones made of amino acids that cannot diffuse through the target cell membrane and must bind to surface cell membrane receptors.

Monoamines (Biogenic Amines)

Hormones synthesized from single amino acids like tryptophan or tyrosine, including melatonin, thyroid hormones ($T_3$ and $T_4$), and catecholamines.

Tropic Hormones

Hormones whose primary function is to stimulate the production and secretion of hormones by other endocrine glands (e.g., ACTH, TSH).

Non-Tropic (Direct) Hormones

Hormones that act directly on non-endocrine target cells or organs to elicit a direct physiological response (e.g., prolactin, ADH).

Trophic Hormones

Hormones that exert a nourishment or growth-stimulating effect on the target endocrine tissue (e.g., TSH, FSH).

Hypothalamus

A region of the brain that secretes regulatory hormones to control the activity and hormone production of the pituitary gland.

Infundibulum

The stalk of tissue that suspends the pituitary gland from the hypothalamus.

Adenohypophysis

The anterior lobe of the pituitary gland, comprising the pars distalis, pars tuberalis, and pars intermedia, linked to the hypothalamus via the hypophyseal portal system.

Neurohypophysis

The posterior lobe of the pituitary gland consisting of neural tissue where axons from the hypothalamo-hypophyseal tract release neurohormones directly into circulation.

Thyroid-Stimulating Hormone (TSH)

An anterior pituitary tropic hormone that stimulates the thyroid gland to synthesize and secrete $T_3$ and $T_4$.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone that stimulates the adrenal cortex to synthesize and release glucocorticoids and mineralocorticoids.

Prolactin (PRL)

An anterior pituitary hormone that stimulates milk production in the mammary glands.

Growth Hormone (GH)

An anterior pituitary hormone that enhances cellular protein synthesis, DNA transcription, and amino acid uptake to promote overall tissue and organ growth.

Follicle-Stimulating Hormone (FSH)

An anterior pituitary gonadotropin that stimulates ovarian follicle growth in females and sperm production in males.

Luteinizing Hormone (LH)

An anterior pituitary gonadotropin that triggers ovulation in females and stimulates testosterone secretion in males.

Antidiuretic Hormone (ADH)

A posterior pituitary hormone (also known as vasopressin) that promotes water reabsorption in kidney tubules to reduce urine volume and prevent dehydration.

Oxytocin (OT)

A posterior pituitary hormone that stimulates uterine smooth muscle contractions during childbirth and triggers milk ejection during lactation.

Pineal Gland

An endocrine gland located in the brain behind the corpus callosum that secretes melatonin to regulate circadian rhythms of sleep and wakefulness.

Thymus

A bi-lobed gland in the superior mediastinum above the heart that secretes thymosins to promote T-cell development and immune function.

Thyroid Gland

A butterfly-shaped gland located in the neck below the larynx that absorbs iodine to produce thyroid hormones controlling body metabolism.

Thyroxine ($T_4$) and Triiodothyronine ($T_3$)

Hormones secreted by thyroid follicular cells that elevate basal metabolic rate, promote body heat production, and regulate appetite.

Calcitonin

A hormone produced by thyroid C cells (parafollicular cells) that lowers elevated blood calcium ($Ca^{2+}$) levels by enhancing calcium deposition into bone tissue.

Parathyroid Hormone (PTH)

A hormone secreted by the parathyroid glands that increases blood calcium ($Ca^{2+}$) levels when calcium drops by mobilizing $Ca^{2+}$ from bone and enhancing intestinal and renal absorption.

Adrenal Cortex

The outer layer of the adrenal gland divided into three zones that secrete steroid hormones, including mineralocorticoids, glucocorticoids, and sex steroids.

Aldosterone

A principal mineralocorticoid from the adrenal cortex that regulates electrolyte balance by encouraging renal $Na^+$ reabsorption and $K^+$ secretion.

Cortisol

A glucocorticoid secreted by the adrenal cortex that stimulates gluconeogenesis, fat catabolism, and protein breakdown to regulate energy levels.

Epinephrine and Norepinephrine

Catecholamines secreted by chromaffin cells in the adrenal medulla that mediate sympathetic responses including increased heart rate, blood pressure, and airflow.

Islets of Langerhans

Endocrine cell clusters scattered throughout the pancreas containing alpha ($\alpha$), beta ($\beta$), and delta ($\delta$) cells that regulate blood glucose homeostasis.

Glucagon

A hormone secreted by pancreatic alpha ($\alpha$) cells in response to low blood glucose ($< 80\,\text{mg}\%$) that triggers glycogenolysis and gluconeogenesis in the liver.

Insulin

A hormone produced by pancreatic beta ($\beta$) cells during high blood glucose levels ($> 120\,\text{mg}\%$) that promotes cellular glucose uptake and glycogen storage.

Somatostatin

A hormone produced by pancreatic delta ($\delta$) cells that suppresses glucagon and insulin release while slowing down nutrient digestion.

Diabetes Mellitus

A metabolic disorder characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both.

Synergistic Effect

A type of hormonal interaction where two or more hormones work together to produce an overall response greater than the sum of their individual effects.

Permissive Effect

A hormonal interaction in which the presence of one hormone is required to enhance or enable the target tissue's response to a subsequent hormone.

Antagonistic Effect

A hormonal interaction in which the functional action of one hormone directly opposes or counters the effect of another hormone.

Diabetes Insipidus

An endocrine hyposecretion disorder caused by inadequate ADH secretion or renal resistance to ADH, leading to excessive excretion of dilute urine.

Graves' Disease

An autoimmune hypersecretion disorder where autoantibodies (TRAb) bind to TSH receptors, triggering continuous thyroid hormone production, goiter, and exophthalmos (bulging eyes).