Neuroendocrine System: Gonads

Made by @agreyr

Testes

Produce sperm cells

Ovaries

Produce ova

Steroid hormones produced by both gonads

Androgens (Testosterone), Estrogens (Estradiol), Progestins (Progesterone)

Gonadotropin releasing hormone (GnRH)

Produced by hypothalamic neuroendocrine cells, secreted into the blood vessels and carried to the anterior pituitary via hypothalamic-pituitary portal system (see Neuroendocrine System: Regions)

Gonadotropins

Released by anterior pituitary following GnRH

Follicle Stimulating Hormone and Luteinizing Hormone

Drive the release of gonadal steroid hormones

Two major effects of sex hormones

Organizational (developmental) and activational

Organizational effects on gonads

Indifferent (primordial) gonads

Presence of a Y chromosome triggers the synthesis of SRY protein at about 6 weeks of development; allows growth of the medulla into the testes while the cortex shrinks away

Organizational effects on internal organs

At 6 weeks, zygote contains two precursor duct systems (Wolffian system and Müllerian system)

Once formed, fetal testes release testosterone and Müllerian-inhibiting hormone (8 weeks of gestation)

Wolffian system

One of the two precursor duct systems present zygote at 6 weeks

Potential to develop into epididymis, vas deferens, and seminal ducts

Müllerian system

One of the two precursor duct systems present zygote at 6 weeks

Potential to develop into fallopian tubes, uterus, and inner vagina

Male reproductive organ development

XY chromosome; Y chromosome being testis-determining factor

Primordial gonads develop into testes; anti-Müllerian hormone and androgens are produced

Defeminization and masculinization occur

Defeminization

Triggered by anti-Müllerian hormone

Müllerian system withers away

Masculinization

Triggered by androgens

Wolffian system develops into vas deferens, seminal vesicles, prostate

Primordial external genitalia develop into penis and scrotum

Female reproductive organ development

XX chromosome

Primordial gonads develop into ovaries; no hormones are produced

Müllerian system develops into fimbriae, fallopian tubes, uterus, inner vagina

Wolffian system, without androgens, withers away

Primordial external genitalia develop into clitoris, labia, outer vagina

Activational effects

Puberty, a time period during which fertility is achieved, growth spurt occurs, and secondary sex characteristics develop; marked by surge in hormone release from the anterior pituitary