Regulation of Reproduction by Dopamine
Nira Ben-Jonathan in Dopamine, 2020
Three elements—chromosomal sex, gonadal sex, and phenotypic sex—must act in coordination for a successful execution of the process of sex determination and sexual differentiation. Chromosomal sex refers to the sex chromosome complement (46XY in males; 46XX in females), which is determined at the time of fertilization. An individual having a normal Y chromosome is destined to develop testes, even in the presence of multiple X chromosomes. Gonadal sex refers to the actual commitment of gonadal tissue as testis or ovary from the bipotential embryonic gonads that can develop into either structure, depending on which genes are expressed at the critical times of organogenesis. Phenotypic sex refers to the type of internal and external genitalia, expression of secondary sex characteristics, and conventional gender-dependent behavior. Abnormalities in any of these elements can result in disorders of sexual development, gender ambiguities, and various degrees of reproductive dysfunctions, as detailed later in this chapter.
Basic medicine: physiology
Roy Palmer, Diana Wetherill in Medicine for Lawyers, 2020
The gonads comprise the ovaries in the female and the testes in the male. Each gonad has a dual function: to produce germ cells, i.e. ova and spermatozoa, and to secrete sex hormones. Pituitary hormones (gonadotropins) cause enlargement of the ovary and testis during childhood, and the resultant release of gonadal hormones brings about the changes of puberty, including the growth spurt and the secondary sexual characteristics of females and males. Oestrogens and progesterone secreted by the ovary cause girls to start their monthly cycle of ovulation and menstruation, while testicular androgens stimulate the production of fertile sperm and seminal fluid. If sexual intercourse takes place during the period following ovulation, when an ovum is shed from the ovary and passes down the female genital tract, then conception may take place as the sperm penetrates the ovum. The developing embryo implants into the wall of the uterus, leading to the formation of the placenta, and placental hormones then sustain the pregnancy. At birth, which occurs around 270 days later, pituitary oxytocin governs the onset of uterine contractions. The breasts have enlarged during pregnancy under the combined actions of oestrogen, progesterone and the pituitary hormone prolactin. After birth lactation is controlled by prolactin combined with oxytocin secreted as a reflex response to suckling by the infant.
Fertility preservation in pediatric and adolescent girls
Joseph S. Sanfilippo, Eduardo Lara-Torre, Veronica Gomez-Lobo in Sanfilippo's Textbook of Pediatric and Adolescent GynecologySecond Edition, 2019
Counseling patients about the fertility risks of gonadotoxic treatments or conditions, or assessing fertility following gonadotoxic therapy, requires some understanding of oogenesis, ovarian reserve, and the hypothalamic-pituitary-ovarian axis. Maximal oocyte number is achieved in utero, with approximately 6–7 million oocytes at 16–20 weeks’ gestational age. Oocyte numbers start to decline via atresia and degeneration soon thereafter, with approximately 500,000 to 2,000,000 oocytes remaining at birth; 300,000–500,000 at the time of puberty; and less than 1000 at menopause (Figure 26.1).10,11 Even in women who are not ovulating, oocytes are continuously being depleted throughout the life span. Gonadal function is important not only for female fertility, but also for the production of sex hormones, important for the maintenance of bone architecture and cardiovascular health. Given that the number of oocytes is fixed at birth, gonadotoxic therapies or surgical removal of the gonads can have lifelong detrimental effects on both fertility and overall health.
The Role of testosterone treatment in patients with metabolic disorders
Published in Expert Review of Clinical Pharmacology, 2021
Giovanni Corona, Giulia Rastrelli, Linda Vignozzi, Arcangelo Barbonetti, Alessandra Sforza, Edoardo Mannucci, Mario Maggi
The testis, the male gonad, is characterized by the production of gametes [spermatozoa] and hormones, from the tubular and interstitial compartments, respectively. Two pituitary hormones mainly control testicular activity: follicular stimulating hormone [FSH] and luteinizing hormone [LH]. The main hormones released by the testis are androgens, and, in particular, testosterone [T], which circulates only in a minor fraction as unbound to some proteins, including albumin and sex hormone-binding globulin [SHBG]. SHBG binds T with high affinity, most probably preventing biological action. In fact, according to the free hormone hypothesis, only unbound [free] T [FT] is able to bind with the androgen receptor [AR]. T concentrations show wide fluctuations over an entire lifespan, with elevated levels in the first postnatal period [mini-puberty] that decline thereafter before surging again during puberty. Several population-based studies have documented that in adult men T levels show a progressive decline as a function of age [1,2]. However, the apparent age-associated decline in serum T is attributable to a range of chronic conditions, which are more frequent with increasing age, including obesity and metabolic derangements. In fact, T levels can remain within the normal range in older healthy men [2]. Obesity-associated reduction of SHBG could partially explain the apparent decline in total T observed in aged subjects [2].
Effects of 1.5-GHz high-power microwave exposure on the reproductive systems of male mice
Published in Electromagnetic Biology and Medicine, 2021
Guofu Dong, Hongmei Zhou, Yan Gao, Xuelong Zhao, Qi Liu, Zhihui Li, Xi Zhao, Jiye Yin, Changzhen Wang
Testosterone is mainly secreted by Leydig cells, a small amount of which comes from the adrenal cortex. It is the most active hormone in androgens. Its main physiological function is to maintain normal gonadal function. In terms of detection results, there was no significant difference between the groups at different times after exposure. It should be noted that the values for the L group at three days and seven days post-exposure were high compared to the values for the other groups, but there was no significant difference between the L group and other groups. This could be because of significant individual differences in serum testosterone levels across the mice. The results showed that 1.5-GHz microwave exposure at 3, 6, and 12 W/Kg for 30 min did not significantly influence the secretion of testosterone in mice (Table 1).
Serum 25-hydroxyvitamin D levels and its relationship with sex hormones, puberty and obesity degree in children and adolescents
Published in Child and Adolescent Obesity, 2020
Liliane Viana Pires, Esther M. González-Gil, Augusto Anguita-Ruiz, Gloria Bueno, Mercedes Gil-Campos, Rocio Vázquez-Cobela, Luis A. Moreno, Ángel Gil, Concepción M. Aguilera, Rosaura Leis
On the other hand, it has been suggested that vitamin D regulates reproductive function in both genders (Blomberg Jensen et al. 2010; Holt et al. 2020). The presence of VDR and enzymes that metabolize vitamin D in the reproductive organs (such as CYP2R1, CYP27B1, and CYP24A1) are related to the participation of this vitamin in the reproductive system (Lorenzen et al. 2017) though the mechanism is poorly understood. Puberty is characterized by the onset of sexual development, involving skeletal height maturity, secondary sexual development, and several hormonal changes. The hypothalamus induces the secretion of Gonadotropin-Releasing Hormone (GnRH), which, along with peripheral factors from the gonads, regulates the production of gonadotropins LH and FSH in the pituitary gland. These hormones induce the maturation of the gonads with consequent ovarian estradiol secretion and testicle testosterone secretion (Loomba-Albrecht and Styne 2012).
Related Knowledge Centers
- Egg Cell
- Hermaphrodite
- Ovary
- Ploidy
- Sperm
- Spermatozoon
- Gamete
- Heterocrine Gland
- Sex Hormone
- Testicle