Endocrine System Comprehensive Review

Flashcards covering the vocabulary of the endocrine system, including gland types, hormone classifications, and specific functions of hormones like CRH, GH, Cortisol, Insulin, and PTH.

Exocrine glands

Glands that secrete their products via ducts into body cavities, lumens, or onto the outer surface of the body, including sweat, sebaceous, and digestive glands.

Merocrine

A mechanism of exocrine secretion where products are expelled from the cell by exocytosis, for example, sweat.

Apocrine glands

Glands that form buds of the cellular membrane which break off into the duct, losing part of the membrane, such as breastmilk-producing mammary glands.

Holocrine glands

Glands where the secretion is released by the cellular membrane rupturing, such as sebaceous glands.

Endocrine glands

Glands that secrete hormones into the extracellular space around the secretory cell, which then diffuse into capillaries and circulate systemically.

Neuroendocrine system

The combined functional unit of the endocrine and nervous systems that coordinates functions of all body systems to maintain homeostasis.

Steroidal hormones

Fat-soluble hormones made up of a ring system including cholesterol that travel through the phospholipid cell membrane to affect gene expression in the nucleus.

Non-steroidal hormones

Water-soluble hormones made from amino acids that travel easily in plasma and bind to cell membrane receptors or protein channels to cause cellular effects.

Corticotropin-releasing hormone (CRH)

A tropic hormone produced by the hypothalamus that coordinates the production and secretion of cortisol from the adrenal glands.

Tropic hormone

A type of hormone that influences the activity of another endocrine gland.

HPA axis

The hypothalamic-pituitary-adrenal axis, which allows for monitoring of levels and maintaining homeostasis, particularly regarding the body's stress response.

Growth Hormone (GH)

A hormone produced by the pituitary gland that stimulates linear bone growth, organ development, protein synthesis, and lipolysis.

IGF-1

Insulin-like growth factor; secreted by the kidneys and liver in response to GH to affect change at target tissues.

Cortisol

The main steroidal glucocorticoid produced by the adrenal glands that mediates the stress response, increases gluconeogenesis, and promotes anti-inflammatory processes.

Suprachiasmatic nuclei (SCN)

Known as the "brain's clock," it controls circadian rhythms, such as the timing of cortisol and melatonin secretion.

Gluconeogenesis

The metabolic process of producing glucose from non-carbohydrate sources, stimulated by hormones like cortisol and glucagon.

DHEA

Dehydroepiandrosterone; an anabolic hormone that mitigates the catabolic effects of cortisol.

HPG axis

The hypothalamic-pituitary-gonadal axis which organizes the secretion of oestrogen, progesterone, and testosterone.

Thyroxine ($T_4$)

An iodinated derivative of tyrosine that constitutes approximately $90\%$ of the hormone produced by the thyroid gland.

Triiodothyronine ($T_3$)

The more active thyroid hormone, most of which is converted from $T_4$ at the local tissue level.

HPT axis

The hypothalamic-pituitary-thyroid axis responsible for the production and regulation of thyroid hormones.

Parathyroid hormone (PTH)

A hormone that increases blood calcium levels by causing bone resorption, calcium reabsorption in kidneys, and synthesis of active vitamin D.

Islets of Langerhans

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

Insulin

A hormone produced by beta cells that binds to GLUT 4 receptors to allow glucose translocation and promotes glycogenesis and lipogenesis.

Glucagon

A hormone produced by alpha cells in the pancreas that managed blood sugar levels in opposition to insulin.

Melatonin

A hormone produced by the pineal gland upregulated by darkness that has antioxidant, neuroprotective, and anti-ageing properties.

Serotonin

The chemical precursor to melatonin.

Hyperthyroidism

A condition resulting in weight loss, increased appetite, and heart palpitations; can be caused by iodine deficiency as the thyroid overcompensates.

Hypothyroidism

A condition resulting in fatigue, weight gain, and cold intolerance; can be the result of a severe iodine deficiency.