Chapter 12Reproductive Physiology Wang Guoqing Department of Physiology, Medical School, Soochow University, Suzhou 215123, China E-mail:firstname.lastname@example.org Tel:0512-62096158; 13506212030
I. Sexual differentiation and formation of genitalia II. Male reproductive system: function and regulation III. Female reproductive system: function and regulation IV. Pregnancy and parturition V. Mechanism of milk secretion VI. Sex Physiology What will we discuss in this chapter? (Outline)
I. Sexual differentiation and formation of genitalia 1. Sexual Differentiation 性别的分化 • Sexual differentiation is determined at three levels: chromosomes, gonads, and phenotype. • Males have XY and females have XX chromosomes. • Female characteristics develop spontaneously in the absence of the Y chromosome. • Y chromosome contains the gene－sex-determining region (SRY)－that is necessary for the development of male characteristics. • Gonads are composed of three cell types in both males and females: supporting cells (Sertoli or granulosa cells); stomal cells (Leydig or theca cells); and germ cells (spermatogonia or oocytes). • Fetal testes secrete two hormones－antimullerian hormone and testosterone－that are essential for development of the male gonads and internal genitalia; in their absence female gonads and internal genitalia develop. • Dihydrotestosterone is responsible for development of male external genitalia.
Puberty 青春期 • Onset of puberty is marked by pulsatile secretion of GnRH, FSH, and LH (female, age of 6-8 years and male, age of 9-10 years). • In the male, FSH stimulates sperm and Sertoli cell development while LH stimulates Leydig cell proliferation and testosterone secretion. • In the female, FSH stimulates follicle development and, along with LH, the synthesis of estradiol. • Testosterone and estradiol stimulate the development of secondary sex characteristics and a growth spurt in the male and female, respectively.
Male reproductive system: function and regulation • Testes are composed of seminiferous tubules that produce sperm and Leydig cells, which produce testosterone. • Spermatogenesis results from conversion of spermatogonia to mature sperm through mitosis, meiosis, and differentiation. • Sertoli cells of the seminiferous tubules support sperm development as well as surround and isolate developing sperm from the blood supply. • Leydig cells, under the influence of LH, secrete testosterone. • FSH and testosterone acting through Sertoli cells enable spermatogenesis. • Blood levels of testosterone and inhibin feed back to regulate pituitary release of FSH and LH.
Spermatogonia Spermatozoa Sertoli Cell Basement Membrane Leydig Cell Maturing sperm come from the testes.成熟的精子源自睾丸 The testes are composed of maturing sperm (spermatogonia, spermatozoa), Sertoli cells, and Leydig cells that interact to ensure a continuous production of sperm.
sperm Endocrine regulation of male reproduction
III. Female reproductive system: function and regulation • Ovary has three regions: cortex composed of follicles; medulla composed of stromal and hormone-producing cells; and hilum, the point of entry of blood vessels and nerves. • Follicles are composed of three cell types: oocytes, granulosa, thecal. • Initial development of oocytes beings in fetal life, but maturation is delayed until puberty when single oocytes mature and are released monthly for the next 4 decades. • Progesterone and estradiol are main steroid hormones produced by the ovaries –estradiol from granulosa cells and progesterone from many cell types. • Estradiol is released prior to ovulation, progesterone after ovulation; both prepare the uterus for egg implantation. • FSH stimulates monthly development of follicles, LH stimulates monthly ovulation, and both stimulate synthesis and secretion of progesterone and estradiol. • Corpus luteum, the postovulation follicle, secretes estradiol and progesterone to sustain the egg and uterus if fertilization and implantation occur.
Cavity Structure of uterine wall子宫壁的结构
Endocrine regulation of sexual hormone 性激素的内分泌调节
Mechanism of menstrual cycle induced by the changes in various sexual hormone * Endometrium
Pregnancy and parturition1. Pregnancy • Fertilization of the oocyte occurs within 24 hours of ovulation in the distal end of the oviduct. • Fertilized egg completes second meiosis and divides repeatedly to form multicelled blastocyst. • Blastocyst implants in uterine wall within 5 days of ovulation. • After implantation, blastocyst secretes human chorionic gonadotropin (hCG, within 9 days of ovulation), which signals the corpus luteum to continue secreting progesterone and estradiol and is basis of the pregnancy test. • Progesterone is produced from cholesterol by the placenta and estriol through the interaction of the placenta and fetal adrenal cortex and liver. • Progesterone and estriol support development of the fetus as well as maternal breast development. • The mechanism by which parturition is initiated is unclear but involves an interplay between progesterone, prostaglandins, and oxytocin that increase the frequency of uterine contraction.
Theca Cells Granulosa Cells Cholesterol Cholesterol Pregnenolone Pregnenolone - - - - 17-Hydroxypregnenolone Dehydroepiandrosterone Androstenedione Androstenedione Testosterone Testosterone Estradiol Estradiol Androstenedione & Testosterone Effect of the theca and granulose cells of the ovary The theca and granulose cells of the ovary interact to ensure adequate production of androgens (androstenedione, testosterone) and estradiol.
Fetal Adrenal Placenta DHEA-Sulfate From the maternal blood Cholesterol Pregnenolone Fetal Liver Estriol 16-OH-DHEA-Sulfaye Synthesis of the major form of estrogen—estriol during pregnancy Ensuring an adequate production of estriol during pregnancy requires exchange of substances between the maternal blood, the placenta, the fetal adrenal gland, and the fetal liver.
V. Mechanism of milk secretion1.Anatomy of breast 乳房的解剖 Progesterone and estrogen stimulate the development and growth of the mother’s breasts. Estrogen also stimulates prolactin secretion by the anterior pituitary, which participates in breast development. At parturition, the breasts are ready for milk production and release induced by increased prolactin and oxytocin levels brought on by suckling.