Download Different classifications of hormones, and the control of hormone

Different classifications of hormones, and the control of hormone secretion, transport and
metabolism

Synthesis (preprohormone) > packaging (prohormone) > storage and secretion (hormone).

Classifications: (1) Amine, eg catecholamine: E, NE, dopamine (2)
Peptide/Polypeptide/Protein/Glycoprotein, eg insulin, GH (3) Lipids: Eicosanoids (from fatty
acids) & Steroid (from cholesterol), eg cortisol

Steroid hormones are produced from cholesterol by adrenal & gonads & by the placenta during
pregnancy.

Breakdown: Liver, kidneys or target cells. Peptide and catecholamines circulate dissolved in
plasma hence are rapidly removed from the blood, but steroid and thyroid hormones are
removed more slowly because they circulate bound to plasma proteins. Thyroid is bound to
either thyroxine-binding globulin (TBG) / transthyretin (TTR; transports thyroid and retinol) /
albumin.
Intracellular signal transduction pathways that are initiated by hormone binding to a receptor

Recognition: Great majority of steroid and thyroid hormone receptors are inside the target cells,
and function as transcription factors; resulting in increased synthesis of particular proteins.
Intracellular receptors, such as nuclear receptors and cytoplasmic receptors. Typical ligands for
nuclear receptors are lipophilic hormones like the steroid hormones testosterone and
progesterone. To initiate signal transduction, the ligand must pass through the plasma
membrane by passive diffusion. On binding with the receptor, the ligands pass through the
nuclear membrane into the nucleus, enabling gene transcription and protein production.

Relay and amplification: Receptors for peptide and catecholamine hormones are on the plasma
membrane, and activates signal transduction pathways, resulting in altered membrane potential
/ cellular response / intracellular protein activity.

Up- or down-regulation of own or others’ receptors, affect permissiveness and effect.

An activated receptor increases cytosolic [Ca2+] by causing metabotropic or ionotropic Ca2+
channels in plasma membrane and/or ER/SR to open. Ca2+ might bind to intracellular protein,
such as calmodulin, which in turn activates/inhibits protein kinases.
Abnormalities in hormone secretion and/or action that contribute to endocrine disorders

Hypo- or hypersecretion. Primary disorders are those in which the defect is in the cells that
secrete the hormone (autoimmune?). Secondary disorders are those in which there is too much
or too little tropic hormone.