Lecture 7 – The Endocrine System

Vocabulary practice flashcards covering the components, classifications, and functions of the Endocrine System based on Lecture 7 notes.

Hormones

Chemical messengers secreted directly into the blood or extracellular fluid that travel until they find cells with specific receptors to trigger metabolic reactions.

Ligand

The general name for any chemical messenger that binds to a specific receptor, of which hormones are one type.

Trophic hormones

Hormones that stimulate growth and secretion in other endocrine glands and are mainly released by the pituitary gland.

Anabolic hormones

Hormones that stimulate the synthesis of new molecules within targeted cells.

Steroid Hormones

Lipid-based molecules built around a steroid nucleus (common framework) from cholesterol that regulate cells by altering gene expression.

Gene expression

The activation of genes, often triggered by steroid hormones to synthesize new proteins.

Non-steroid Hormones

Diverse hormones mostly made from amino acids that are water-soluble and typically activate target cells via second messenger systems.

Second messenger system

A two-stage process where a non-steroid hormone (first messenger) binds to a receptor, initiating chemical reactions that produce an internal molecule to amplify the response.

Prostaglandins (PGs)

Hormone-like lipid molecules produced by enzyme-controlled oxidation of essential fatty acids that regulate cells on a moment to moment basis.

Adenohypophysis

The anterior lobe of the pituitary gland, comprising five types of endocrine cells: somatotrophs, corticotrophs, thyrotrophs, lactotrophs, and gonadotrophs.

Neurohypophysis

The posterior lobe of the pituitary gland, composed of neurosecretory nervous tissue that serves as a storage and release site for ADH and oxytocin.

Somatotropin (Growth Hormone/GH)

A hormone produced by somatotroph cells that speeds up protein anabolism, stimulates fat metabolism, and increases blood glucose levels.

Antidiuretic hormone (ADH)

A hormone released by the neurohypophysis in response to increased osmotic pressure to prevent fluid loss by stimulating kidneys to reabsorb water.

Oxytocin (OT)

A hormone means 'swift child birth' that stimulates uterine contractions and causes breast milk to rush into the ducts.

Infundibulum

The thin stalk that connects the hypothalamus to the pituitary gland.

Melatonin

The main hormone produced by the pineal gland that helps synchronize body functions and biological cycles based on light input.

Thyroxine (T4)

Tetraiodothyronine; the most abundant thyroid hormone, containing 4 iodine molecules, which is mainly converted to T3 inside cells.

Triiodothyronine (T3)

The more potent of the two main thyroid hormones, containing 3 iodine molecules and responsible for regulating metabolic rate.

Calcitonin (CT)

A hormone produced by the parafollicular cells of the thyroid that decreases blood calcium levels by promoting bone deposition via osteoblasts.

Parathyroid hormone (PTH)

A hormone that raises blood calcium levels by stimulating osteoclasts to strip calcium from bone and increasing renal and intestinal absorption.

Thymosin

One of two hormones secreted by the thymus that influences the maturation of lymphocytes into T cells.

Aldosterone

The physiologically important mineralocorticoid that regulates sodium and fluid levels in the blood via the renin-angiotensin mechanism.

Cortisol

A glucocorticoid stress hormone that promotes lipid catabolism, protein breakdown, and increases blood sugar levels.

Catecholamines

A class of hormones including adrenalin and noradrenalin secreted by the adrenal medulla in response to stress.

Islets of Langerhans

Clusters of endocrine cells in the pancreas containing alpha cells (glucagon) and beta cells (insulin).

Glucagon

A hyperglycaemic hormone produced by alpha cells that raises blood sugar by stimulating glycogenolysis in the liver.

Insulin

A hypoglycaemic anabolic hormone produced by beta cells that opens glucose channels in cell membranes to lower blood sugar.

Glycogenesis

The metabolic process of synthesizing glycogen from glucose.

Glycogenolysis

The metabolic process of breaking down glycogen into glucose.

Gluconeogenesis

The production of 'new' glucose from non-carbohydrate sources such as fats and amino acids by the liver.

Normal Blood Glucose Level (BGL)

The physiological range of blood sugar concentration, typically between $4.5-5.6\,mmol/litre$ (or $70-110\,mg/100ml$).

Primary imbalance

A hormonal imbalance caused by a malfunction of the endocrine gland itself.

Secondary imbalance

A hormonal imbalance caused by a malfunction of the gland's controlling systems, such as a lack of regulatory hormones from the pituitary.