Reproductive endocrinology studies hormones and neuroendocrine biologically active substances that are produced in and/or affect the tissues of the reproductive system. These tissues include the hypothalamus, anterior pituitary, ovaries, endometrium, and placenta.
Hormones are the products of cellular secretion of endocrine organs, which can affect target tissues distant from the site of secretion by entering the peripheral bloodstream (endocrine secretion).
In reproductive physiology, there are also additional forms of intercellular interaction. Paracrine interaction (typical for ovarian cells) is the transmission of a chemical signal between adjacent cells. Autocrine action occurs when a cell produces biologically active substances that affect its own function.
The action of neurotransmitters released by neurosecretory cells into the bloodstream and transported to other tissues is called neuroendocrine secretion. An example is the secretion of gonadotropin-releasing hormone (GnRH) into the hypophyseal portal vessels, which affects the cells of the anterior pituitary.
The principles of reproductive system regulation can be schematically represented as five levels that interact on the principle of positive or negative feedforward and feedback loops.
The first level of this regulatory system is represented by: the cerebral cortex, limbic system, hippocampus, amygdala, and some other extrahypothalamic structures. In response to the impulses of the external and internal environment, these structures synthesize and secrete neurotransmitters and neuropeptides (norepinephrine, dopamine, gamma-aminobutyric acid - GABA, acetyl-choline, serotonin, etc.), which affect the neural secretory nuclei in the hypothalamus, stimulating the production of releasing hormones.