Reproductive Physiology

What will we discuss in this chapter? (Outline) 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

I. Sexual differentiation and formation of genitalia 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.

Human chromosomes

Chromosomes may decide sex

2. Formation of internal genitalia

3. Formation of external genitalia

Origin of mammalian life

Puberty 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.

Maturing sperm come from the testes. Basement Membrane Leydig Cell Spermatozoa Spermatogonia Sertoli Cell The testes are composed of maturing sperm (spermatogonia, spermatozoa), Sertoli cells, and Leydig cells that interact to ensure a continuous production of sperm.

Histology of testes

Histology of testes

Testicle tissue under the microscope

Structure of sperm

Male formation

Male main sexual gland —Testis

Anatomy of male genitalia

Anatomy of male external genitalia

Endocrine regulation of male reproduction sperm

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.

Anatomy of female genitalia

Anatomy of female genitalia

Female internal genitalia

Female main sexual gland —Ovary

Structure of uterine wall Cavity

Synthesis of testosterone, progesterone and estradiol

Endocrine regulation of sexual hormone

Various sexual hormones changes in early to mid-follicular phase

Various sexual hormones changes in early to mid-luteal phase黄体期

Various sexual hormones changes in late follicular phase and ovulation

Various sexual hormones changes in late luteal phase

Mechanism of menstrual cycle induced by the changes in various sexual hormone * Endometrium

Pregnancy and parturition 1. 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.

Effect of the theca and granulose cells of the ovary Granulosa Cells Theca Cells Cholesterol Pregnenolone 17-Hydroxypregnenolone Dehydroepiandrosterone Androstenedione Testosterone Estradiol - - - - & The theca and granulose cells of the ovary interact to ensure adequate production of androgens (androstenedione, testosterone) and estradiol.

Precondition of pregnancy is ovum must combine with sperm

Precondition of pregnancy is ovum must combine with sperm to be zygote

The process of zygote Formation

Ovulation and fecundation

Growth of fetus (10 weeks)

Structure of placenta

Synthesis of the major form of estrogen—estriol during pregnancy Placenta Cholesterol Pregnenolone Estriol Fetal Adrenal DHEA-Sulfate Fetal Liver 16-OH-DHEA-Sulfaye From the maternal blood 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.

2. Parturition

Parturition

Parturition

Expulsion of the placenta after Parturition

Endocrine mechanism of Parturition

V. Mechanism of milk secretion 1. Anatomy of breast 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.

2. Histology of breast

3. Mechanism of milk secretion

VI. Sex Physiology Viripotent representation Changes in physique during puberty (青春期) Genital (生殖器的) development Secondary sexual characters appearance Sex maturation regulation Sexual abnormality during puberty Sexual excitation and sexual behavior Male Female Sexual behavior regulation Nervous regulation Hormonal regulation Sexual dysfunction

Consideration after class 1. Please describe testicular sperm formation and its endocrine function. 2. Please describe ovarian ovum formation and its endocrine function. 3. What is mechanisms of menstrual cycle ? 4. Please describe pregnant maintenance and hormonal regulation. 5. What is phenotype of sex maturation ?