Ch5 Reproduction

• DHT (dihydrotestosterone) stimulates red blood cell production, development of male genital organs, and male behavior
• Testosterone is responsible for the development and maintenance of male genital glands, secondary sexual characteristics, and male genital tract
• Neurotransmitters: Precise action; targets only postsynaptic target cell
• Paracrine hormones/factors: Local action; acts within a tissue
• Inhibin can function as both an endocrine and paracrine hormone
• Reproductive steroids include estradiol, progesterone, and testosterone
• GnRH is released from the hypothalamus and acts through a GPCR-Gs-coupled receptor
• Inhibins inhibit FSH release from the pituitary and gonadal steroids inhibit GnRH release from the hypothalamus
• Inhibin acts through a TGF-β signaling pathway and is an antagonist of the TGF-β receptor ligand activin
• LH and FSH are related glycoprotein hormones with an alpha subunit shared with each other and with TSH
• Chorionic gonadotropin (hCG) from the blastocyst acts like LH and maintains the corpus luteum, progesterone, and estradiol levels during pregnancy.
• Changes in levels of hormones such as estrogens, progesterone, oxytocin, prostaglandins, corticosteroids, and CRH indicate pregnancy in mammals.
• During the menstrual phase, estrogen and progesterone levels fall, leading to the sloughing off of the endometrium.
• During menopause, the ovary becomes refractory to gonadotropins, leading to a drop in estrogen levels and various side effects.
• The timing of birth in humans is influenced by various signals, including stress, mechanical stimulation, administration of prostaglandins, and synthetic oxytocin.
• Humans have continuous reproductive cycling, while sheep have seasonal estrus.
• Lactation is stimulated by hormones such as estrogens, GH, corticosterone, PRL, relaxin, and corticosteroids.
• Uterine cycle: menstruation, proliferation of endometrium, secretory phase (implantation)
• During puberty, FSH stimulates some primary oocytes to form follicles; 2º oocytes arrested at meiotic metaphase II
• High estrogen levels stimulate burst of LH, ovulation
• Proliferative phase: estrogen promotes proliferation of endometrial cells
• Increasing levels of estrogen until critical estrogen level
• Thecal and granulosa cells cooperate to produce estrogens
• FSH stimulates AMH -> formation of primary and secondary follicles
• If no implantation corpus luteum dies, estrogen + progesterone fall, menses
• Proliferation of oogonia (mitosis) occurs in female embryo
• Secretory phase: progesterone suppresses mitosis, promotes secretion of embryotrophic fluid
• Luteal phase of the ovarian cycle: corpus luteum secretes progesterone, limited time (5-8 days)
• LH surge -> cumulus cell oocyte complex growth
• At birth, primary oocytes arrested at meiotic prophase I
• Recruitment and selection of follicles: Many primary follicles are produced, but usually only 1 mature follicle each cycle
• Ovarian cycle: folliculation, ovulation, luteal phase (implantation)
• GDF9 secreted by the oocyte — another TGF β-like ligand
• LH promotes formation of corpus luteum from post-ovulation follicle; estrogen + progesterone
• Corpus luteum formation upon LH surge from granulosa and theca interna cells
• FSH promotes folliculation, synthesis of estrogens
• Pregnancy: formation of placenta — menstruation blocked
• Endocrine disruptors can interfere with reproductive physiology.
• Delayed puberty (females): primary amenorrhea, disorders of HPG axis, low caloric intake (anorexia, athletic training, etc.), secondary amenorrhea, endocrine disorders (e.g. polycystic ovarian syndrome).
• DDT: pesticide, ER and AR binding.