Edited by Dr. Stefano Casali
Endocrinology is the discipline that studies the complex system responsible for the transmission of chemical signals and the transfer of information between the different parts of the organism, through which it evokes specific biological effects; it also deals with communication and control in a living organism by means of chemical mediators, called "messengers", the hormones.
Hormones can be synthesized in part or entirely in the living organism. Chemical messengers are hormones defined as endogenous molecules that transfer information within the organism through both extracellular and intracellular communications. The term hormone comes from the Greek όρμάω - "put in motion". In the classical definition, the hormone is a molecule that is synthesized in an organ and is transported through the circulatory system to act on another tissue called "target tissue".
Metabolism is that part of endocrinological science that studies the control of biochemical mechanisms within the body, both anabolic and catabolic. It includes many different activities such as: gene expression, biosynthetic and catalysis pathways, the modification, transformation and degradation of biological substances and the processes by which it obtains, stores and mobilizes the energy substrates. Homeostasis is the condition of internal stability of organisms that must be maintained even when external conditions vary through self-regulating mechanisms. The Endocrine System, as an intersystem and intercellular communication system, integrated with the Nervous and Immune System, presides over the transfer of information by activating stimulatory or inhibitory reactions, modulating specific biological functions. The reciprocal interconnection of the three systems guarantees the adaptation of the organism to external / internal stimuli.
Hormones can have an action Autocrine, which is exerted on the very cells that produce them, an "action Paracrine, which is exerted on neighboring cells, an "activIuxtacrine, which takes place at the interface between two neighboring cells or between the cell and the extracelular matrix, a " Intracrina, which occurs through the conversion, in the cell, of a weakly active hormone into a second hormone that transmits the signal at the cellular level.
Target Cell Concept
Any cell in which a specific hormone binds to its receptor causing or not a biochemical or physiological response. The response of a target cell can vary, it can give different responses to a single hormone.
The response of the Target Cell depends on
- Concentration of the hormone
- Proximity of the target organ to the source
- The binding with specific transport proteins
- Percentage of transformation of an inactive hormone into its active form
- Percentage of clearance of the hormone
Hormone receptors
The target cell is also defined by the ability to specifically bind a hormone by means of a receptor, this is very important as the concentrations of the hormones are very low. The receptors can be divided into cytoplasmic membrane receptors and intracellular receptors, and are characterized by two functional domains, Recognition and Coupling. The first binds the hormone, the second generates the signal that links the hormone to an intracellular function.
Classification of hormones based on their mechanism of action:
Group of hormones that bind to intracellular receptors
- Androgens
- Calcitriol [1,25 (OH) 2D3]
- Estrogen
- Glucocorticoids
- Mineralocorticoids
- Progestogens
- Retinoic Acid
- Thyroid hormones (triiodothyronine and thyroxine)
Group of hormones that bind to receptors on the cytoplasmic membrane
- The second messenger is the Cyclic Adenosine Monophosphate
Catecholamines α2 β2 Adrenergic, Adrenocorticotropic hormone (ACTH) Angiotensin II, Antidiuretic hormone (ADH), Calcitonin, Chorionic gonadotropin, Corticotropin-releasing -hormone (CRH), Follicle-stimulating-hormone (FSH), Glucagonizing-hormone (FSH), Glucagone Hormone (LH), Melanocyte-stimulating-Hormone (MSH), Parathyroid hormone (PTH), Somatostatin, Thyroid stimulating hormone (TSH).
- The second messenger is Cyclic Guanosine Monophosphate
Atriopeptides, Nitric Oxide.
- The second messenger is Calcium or Phosphainositides (or both)
Catecholamines α1 Adrenergic, Acetylcholine (muscarinic), Angiotensin II, ADH, Epidermal Growth Factor (EGF), Gonadotrpin-releasing-hormone, Pletelet-derived growth factor, Thyrotropin-releasing hormone.
- The second messenger is a Cascade Kinase / Phosphatase
Chorionic somatomammotropin, Erythropoietin, Fibroblast growth factor, Growth hormone (GH), Insulin, Insulin-like growth peptids (IGF-1, IGF-II), Nerve growth factor, Oxytocin, Prolactin.
Chemical classification of hormones
Derivatives of amino acids
Tryptophan → Serotonin and Melatonin
Thyroxine → Dopamine; Norepinephrine; Epinephrine; triiodothyronine; Thyroxine
L-Glutamic acid → γ-aminobutyric acid
Histidine → Histamine
Peptides or polypeptides
Thyrotropin release factor
Insulin
Gh
Steroids
Progestogens, Androgens, Estrogens,
Corticosteroids
Derivatives of Fatty Acids
Prostaglandins
Leukotrienes
Thromboxane
Frequency of endocrine disorders
More frequent endocrinopathies
- Diabetes mellitus
- Thyrotoxicosis
- Hypothyroidism
- Non-toxic nodular goiter
- Diseases of the Pituitary
- Disorders of the adrenal gland
Most common endocrinopathies in medical practice
- Diabetes mellitus
- Obesity
- Hyperlipoprotinemias
- Osteoporosis
- Paget's disease
Bibliography
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P.E. Molina; Endocrine Physiology. Lange Physiology Series. Mc Graw & Hill. 2004.
'Diseases of the endocrine system and metabolism"; G. Faglia and P. Beck-Peccoz;
Mc Graw Hill Publisher Fourth edition.
Giusti G., Serio M .; "Endocrinology". USES, Florence, 1988.
Sword A .: "Receptors and receptor pathology in endocrinology"Agg Med 1987.
Endocrinology And Metabolism; Baxter John; Felig Philip; Frohman Lawrence A .; Mc Graw Hill Publisher.
