The endocrine and nervous systems are two major systems involved in the control and regulation of body functions. The endocrine system consists of endocrine glands and endocrine cells in other organs (kidney, placenta, etc.) that secrete biologically active substances called hormones. In contrast to exocrine glands, which have secretory ducts, the endocrine glands are “ductless” and secrete hormones into the blood. Hormones are distant chemical messengers that are transported via the circulating blood to the target cells where they exert their specific effects. Most hormones are derivatives of cholesterol (steroid hormones) or are amino acids (thyroid hormones, adrenaline) and polypeptide derivatives. Depending on the nature and size of the hormone molecule, hormones bind to specific receptors that are either on the surface or in the cytoplasm/the nucleus of target cells, triggering sequences of intracellular changes that produce their physiological effects. The main endocrine glands in the body are the pituitary (hypophysis), thyroid, parathyroid, and adrenal glands, the pancreas, ovaries, and testes. The rate of hormone secretion is often regulated by a homeostatic negative feedback control mechanism. The major hormones and their effects are presented in tables (see picture box).
Male and female reproductive systems
The differences between male and female organisms depend primarily on the sex chromosomes (XY or XX) and a pair of endocrine structures, the testes in the male and the ovaries in the female. The differentiation of gonads in utero is genetically determined, but the formation of male genitalia depends upon the presence of testes, secreting testosterone, and if there is no testicular tissue the development is female. After birth the gonads remain inactive until adolescence when they are activated by gonadotrophins (LH and FSH) from the anterior pituitary. In adolescence, as a result of the action of the gonads-secreted hormones, the secondary sexual characteristics develop and the final maturation of the reproductive system occurs, including mammary development and onset of menstrual cycles in the female.
In both sexes, the gonads have gametogenic (production of germ cells) and endocrine (secretion of sex hormones) functions. Steroid hormones secreted by the gonads (androgens, principally testosterone, from testes and estrogen and progesterone from ovaries) promote the sex-specific physical characteristics and initiate and maintain reproductive function. Androgens are steroid hormones with masculinizing effects and estrogens are steroid hormones with feminizing effects. Both types of sex hormones are normally secreted in males and females, but there are general differences in hormone concentrations between sexes. There is a slow decline in the functions of male reproductive system with advancing age, but the ability to father children persists. The functions of female reproductive system regress after a number of years and the menstrual cycles cease (menopause).
Note: Some hormones reach the target cells by extracellular fluid and have local, paracrine effects (prostaglandins, endothelins, etc.).
Male and female reproductive systems
The differences between male and female organisms depend primarily on the sex chromosomes (XY or XX) and a pair of endocrine structures, the testes in the male and the ovaries in the female. The differentiation of gonads in utero is genetically determined, but the formation of male genitalia depends upon the presence of testes, secreting testosterone, and if there is no testicular tissue the development is female. After birth the gonads remain inactive until adolescence when they are activated by gonadotrophins (LH and FSH) from the anterior pituitary. In adolescence, as a result of the action of the gonads-secreted hormones, the secondary sexual characteristics develop and the final maturation of the reproductive system occurs, including mammary development and onset of menstrual cycles in the female.
In both sexes, the gonads have gametogenic (production of germ cells) and endocrine (secretion of sex hormones) functions. Steroid hormones secreted by the gonads (androgens, principally testosterone, from testes and estrogen and progesterone from ovaries) promote the sex-specific physical characteristics and initiate and maintain reproductive function. Androgens are steroid hormones with masculinizing effects and estrogens are steroid hormones with feminizing effects. Both types of sex hormones are normally secreted in males and females, but there are general differences in hormone concentrations between sexes. There is a slow decline in the functions of male reproductive system with advancing age, but the ability to father children persists. The functions of female reproductive system regress after a number of years and the menstrual cycles cease (menopause).
Crosstalk:
Reproductive and endocrine system
Cannabinoids exert their effects through the activation of two specific receptors located on the surface of the target cells. Recent evidence suggests that multiple endocannabinoid ligands may also play an important role in the maintenance and regulation of early pregnancy and fertility. Furthermore, endocannabinoids are involved in the anterior pituitary and hypothalamic control of sex hormones. Marijuana, tetrahydrocannabinol (THC), and other exogenous cannabinoids exert potent effects on this homeostasis.
In males, cannabis smoking decreases serum LH concentrations. In some studies chronic marijuana use has been shown to be associated with decreased plasma testosterone levels, but other studies have failed to reproduce these findings. Reduced sperm counts in males have been more consistently seen.
In women, acute administration of THC suppresses the secretion of LH in the luteal phase. In chronic users, it shortens the menstrual cycle, the effect being predominately a short luteal phase leading to menstrual irregularities and anovulation. Some data suggest that the decreased release of hypothalamic GnRH into the pituitary is responsible for the suppressed level of LH. The possible mechanism of this effect of THC is modulation of neuronal systems known to inhibit GnRH secretion.
Several experimental and clinical studies have shown adverse effects of marijuana exposure on embryo development and in early pregnancy. In women cannabis use during pregnancy is correlated with low birth weight, prematurity, intrauterine growth retardation, presence of congenital abnormalities and perinatal death.
In males, cannabis smoking decreases serum LH concentrations. In some studies chronic marijuana use has been shown to be associated with decreased plasma testosterone levels, but other studies have failed to reproduce these findings. Reduced sperm counts in males have been more consistently seen.
In women, acute administration of THC suppresses the secretion of LH in the luteal phase. In chronic users, it shortens the menstrual cycle, the effect being predominately a short luteal phase leading to menstrual irregularities and anovulation. Some data suggest that the decreased release of hypothalamic GnRH into the pituitary is responsible for the suppressed level of LH. The possible mechanism of this effect of THC is modulation of neuronal systems known to inhibit GnRH secretion.
Several experimental and clinical studies have shown adverse effects of marijuana exposure on embryo development and in early pregnancy. In women cannabis use during pregnancy is correlated with low birth weight, prematurity, intrauterine growth retardation, presence of congenital abnormalities and perinatal death.
