Hormones

The endocrine system is made up of a group of organs, called endocrine glands, whose main function is the secretion of hormonal substances.

Hormones are endogenous substances that function as messengers, coordinating the various activities of the organism
The HYPOTALAMUS, the median region of the Central Nervous System, is the coordinating center of the activities of the endocrine system.
It produces release and inhibition factors of the secretion of the pituitary tropins (CRH, TRH, GHRH, somatostatin, GnRH).

The hypophysis, endocrine gland located inside the sella turcica of the sphenoid bone, is composed of an epithelial portion, the adenohypophysis responsible for the secretion of the pituitary tropines, and a nerve, the neurohypophysis responsible for the secretion of vasopressin

HYPOPHYSARY TROPINS are hormones responsible for the control of the endocrine glands, of which they regulate trophism and secretory function.

ACTH: adrenocorticotropic hormone → adrenal → cortisol, adrenal steroids
TSH: thyroid hormone → thyroid → thyroid hormones
GH: somatotropic hormone → IGF-1 → organs and tissues
PROLACTIN: lactotropic hormone → mammary gland and other tissues
LH: luteotropic hormone → gonads → sex hormones
FSH: follicle-stimulating hormone → gonads → sex hormones

Articles on Hormones

MECHANISM OF ACTION OF HORMONES

The biological functions of hormones take place through three different mechanisms:

Endocrine = the hormone produced in the endocrine gland reaches the target tissue via the bloodstream.

Paracrino = the hormone produced in the endocrine gland reaches the target tissue via the extra-cellular fluid.

Autocrine = the hormone produced in the endocrine gland affects the same cells that produced it.

Pheromone = transmitted between cells of different organisms.

Hormones can be secreted

in active form (GH, insulin);

in inactive form à post-secretory activation processes (thyroid hormones, testosterone, vitamin D);

with short / medium / long latency;
starting from very small reserves (peptide hormones) or from large deposits (eg thyroid hormones).

Hormones can be released into the bloodstream

In free form (many protein / water-soluble hormones, catecholamines);

bound to carrier proteins (fat-soluble steroid hormones to SHBG and CBG; thyroid hormones → TBG; plus albumin).

The biological effect determined in a cell by a hormone depends on

hormone concentration;
concentration of receptors;
degree of affinity between hormone and receptors.

The hormone binds a finite number of receptors. The receptor density of the target cell can vary according to the phase of the cell cycle, or to events related to differentiation or to the current metabolic state.
The target cell can regulate the number of receptors according to the hormone concentration: a high hormone concentration corresponds to a reduced receptor density and vice versa.

MEMBRANE RECEPTORS

consisting of an extracellular portion capable of interacting sterically with a specific message, a transmembrane portion and an intracellular portion capable of issuing appropriate messages.

CYTOPLASMATIC AND / OR NUCLEAR RECEPTORS

Nuclear receptors comprise a family of transcription factors that regulate gene expression in a ligand-dependent manner. Members of the nuclear receptor superfamily include receptors for steroid hormones (estrogens, glucocorticoids, androgens, mineralocorticoids), non-ligand receptors. steroids (thyroid hormones, retinoic acid) and receptors that bind various products of lipid metabolism (fatty acids, prostaglandins). Then there are the receptors whose ligands are not yet known, the so-called "orphan receptors", probably recognized by low ligands molecular weight.

Nuclear receptors, with a few exceptions, have a common structure:

a carboxy-terminal domain of interaction with the ligand (ligand binding domain, LBD)
a DNA binding domain
an extremely variable functional amino-terminal domain

ENDOCRINE PATHOLOGIES

Endocrine diseases can be grouped into four broad categories: