THE REPRODUCTIVE SYSTEMS

The Cell Cycle in the Gonads               

Reproduction is the process by which new individuals of a species are produced and the genetic material is passed from generation to generation.  The organs of reproduction are grouped as gonads (produce gametes), ducts (transport and store gametes), accessory sex glands (produce materials that support gametes), and supporting structures (have various roles in reproduction).  Gametes contain the haploid (n) chromosome number (23), and most somatic cells contain the diploid (2n) chromosome number (46).  Meiosis is the process that produces haploid gametes.  It consists of two successive nuclear divisions called meiosis I and meiosis II.  During meiosis I, homologous chromosomes undergo synapsis (pairing) and crossing-over.  The net result is two haploid daughter cells that are genetically unlike each other and unlike the parent cell that produced them.  During meiosis II, the two haploid daughter cells divide to form four haploid cells.

Male Reproductive System                  

The male structures of reproduction include the testes, ductus epididymis, ductus (vas) deferens, ejaculatory duct, urethra, seminal vesicles, prostate, bulbourethral (Cowper’s) glands, and penis.  The scrotum is a sac that hangs from the root of the penis and consists of loose skin and superficial fascia.  It supports the testes.  The temperature of the testes is regulated by contraction of the cremaster muscle and dartos muscle, which either elevates them and brings them closer to the pelvic cavity or relaxes and moves them farther from the pelvic cavity.  The testes are paired oval glands (gonads) in the scrotum containing seminiferous tubules, in which sperm cells are made; Sertoli cells (sustentacular cells), which nourish sperm cells and secrete Inhibin; and Leydig cells (interstitial endocrinocytes), which produce the male sex hormone testosterone.  The testes descend into the scrotum through the inguinal canals during the seventh month of fetal development.  Failure of the testes to descend is called cryptorchidism. 

Secondary oocytes and sperm, both of which are called gametes, are produced in the gonads.  Spermatogenesis, which occurs in the testes, is the process whereby immature spermatogonia develop into mature sperm.  The spermatogenesis sequence, which includes meiosis I, meiosis II, and spermiogenesis, results in the formation of four haploid sperm (spermatozoa) from each primary spermatocyte.  Mature sperm consist of a head, a midpiece, and a tail.  Their function is to fertilize a secondary oocyte.

At puberty, gonadotropin-releasing hormone (GnRH) stimulates anterior pituitary secretion of FSH and LH.  LH stimulates production of testosterone.  FSH and testosterone stimulate spermatogenesis.  Sertoli cells secrete androgen-binding protein (ABP), which binds to testosterone and keeps its concentration high in the seminiferous tubule.  Testosterone controls the growth, development, and maintenance of sex organs, stimulates bone growth, protein anabolism and sperm maturation, and stimulates development of masculine secondary sex characteristics.  Inhibin is produced by Sertoli cells.  Its inhibition of FSH helps regulate the rate of spermatogenesis.

The duct system of the testes includes the seminiferous tubules, straight tubules, and rete testis.  Sperm flow out of the testes through the efferent ducts.  The ductus epididymis is the site of sperm maturation and storage.  The ductus (vas) deferens stores sperm and propels them toward the urethra during ejaculation.  Each ejaculatory duct, formed by the union of the duct from the seminal vesicle and ampulla of the ductus (vas) deferens, is the passageway for ejection of sperm and secretions of the seminal vesicles into the first portion of the urethra, the prostatic urethra.  The urethra in males is subdivided into three portions: the prostatic, membranous, and spongy (penile) urethra.  The seminal vesicles secrete an alkaline, viscous fluid that contains fructose (used by sperm for ATP production).  Seminal fluid constitutes about 60% of the volume of semen and contributes to sperm viability.

The prostate secretes a slightly acidic fluid that constitutes about 25% of the volume of semen and contributes to sperm motility.  The bulbourethral (Cowper’s) glands secrete mucus for lubrication and an alkaline substance that neutralizes acid.  Semen is a mixture of sperm and seminal fluid.  It provides the fluid in which sperm are transported, supplies nutrients, and neutralizes the acidity of the male urethra and the vagina.  The penis consists of a root, a body, and a glans penis.  Engorgement of the penile blood sinuses under the influence of sexual excitation is called erection.

Female Reproductive System   

The female organs of reproduction include the ovaries (gonads), uterine (Fallopian) tubes or oviducts, uterus, vagina, and vulva.  The mammary glands are part of the integumentary (skin) system and also are considered part of the reproductive system in females.  The ovaries, the female gonads, are located in the superior portion of the pelvic cavity, lateral to the uterus.  Ovaries produce secondary oocytes, discharge secondary oocytes (the process of ovulation), and secrete estrogens, progesterone, relaxin, and inhibin.  Oogenesis (the production of haploid secondary oocytes) begins in the ovaries.  The oogenesis sequence includes meiosis I and meiosis II, which goes to completion only after an ovulated secondary oocyte is fertilized by a sperm cell.

The uterine (Fallopian) tubes transport secondary oocytes from the ovaries to the uterus and are the normal sites of fertilization.  Ciliated cells and peristaltic contractions help move a secondary oocyte or fertilized ovum toward the uterus.  The uterus is an organ the size and shape of an inverted pear that functions in menstruation, implantation of a fertilized ovum, development of a fetus during pregnancy, and labor.  It also is part of the pathway for sperm to reach the uterine tubes to fertilize a secondary oocyte.  Normally, the uterus is held in position by a series of ligaments.  Histologically, the layers of the uterus are an outer perimetrium (serosa), a middle myometrium, and an inner endometrium.

The vagina is a passageway for sperm and the menstrual flow, the receptacle of the penis during sexual intercourse, and the inferior portion of the birth canal.  It is capable of considerable distension.  The vulva, a collective term for the external genitals of the female, consists of the mons pubis, labia majora, labia minora, clitoris, vestibule, vaginal and urethral orifices, hymen, bulb of the vestibule, and three sets of glands: the paraurethral (Skene’s), greater vestibular (Bartholin’s), and lesser vestibular glands.  The perineum is a diamond-shaped area at the inferior end of the trunk medial to the thighs and buttocks.

The mammary glands are modified sweat glands lying superficial to the pectoralis major muscles.  Their function is to synthesize, secrete, and eject milk (lactation).  Mammary gland development depends on estrogens and progesterone.  Milk production is stimulated by prolactin, estrogens and progesterone.  Milk ejection is stimulated by oxytocin.

The Female Reproductive Cycle

The function of the ovarian cycle is to develop a secondary oocyte, whereas that of the uterine (menstrual) cycle is to prepare the endometrium each month to receive a fertilized egg.  The female reproductive cycle includes both the ovarian and uterine cycles.  The uterine and ovarian cycles are controlled by GnRH from the hypothalamus, which stimulates the release of FSH and LH by the anterior pituitary.  FSH stimulates development of secondary follicles and initiates secretion of estrogens by the follicles.  LH stimulates further development of the follicles, secretion of estrogens by follicular cells, ovulation, formation of the corpus luteum, and the secretion of progesterone and estrogens by the corpus luteum.  Estrogens stimulate the growth, development, and maintenance of female reproductive structures, stimulate the development of secondary sex characteristics, and stimulate protein synthesis.  Progesterone works with estrogens to prepare the endometrium for implantation and the mammary glands for milk synthesis.  Relaxin relaxes the myometrium at the time of possible implantation.  At the end of a pregnancy, relaxin increases the flexibility of the pubic symphysis and helps dilate the uterine cervix to facilitate delivery. 

During the menstrual phase, the stratum functionalis of the endometrium is shed, discharging blood, tissue fluid, mucus, and epithelial cells.  During the preovulatory phase, a group of follicles in the ovaries begins to undergo final maturation.  One follicle outgrows the others and becomes dominant while the others degenerate.  At the same time, endometrial repair occurs in the uterus.  Estrogens are the dominant ovarian hormones during the preovulatory phase.  Ovulation is the rupture of the dominant mature (Graafian) follicle and the release of a secondary oocyte into the pelvic cavity.  It is brought about by a surge of LH.  Signs and symptoms of ovulation include increased basal body temperature; clear, stretchy cervical mucus; changes in the uterine cervix; and abdominal pain. 

During the postovulatory phase, both progesterone and estrogens are secreted in large quantity by the corpus luteum of the ovary, and the uterine endometrium thickens in readiness for implantation.  If fertilization and implantation do not occur, the corpus luteum degenerates, and the resulting low level of progesterone allows discharge of the endometrium followed by the initiation of another reproductive cycle.  If fertilization and implantation do occur, the corpus luteum is maintained by placental hCG.  The corpus luteum and later the placenta secrete progesterone and estrogens to support pregnancy and breast development for lactation.

The Human Sexual Response   

The similar sequence of changes experienced by both males and females before, during, and after intercourse is termed the human sexual response.  It occurs in four stages: excitement (arousal), plateau, orgasm, and resolution.  During excitement and plateau, parasympathetic nerve impulses produce genital vasocongestion, engorgement of tissues with blood, and secretion of lubricating fluids.  Heart rate, blood pressure, breathing rate, and muscle tone increase.  During orgasm, sympathetic and somatic motor nerve impulses cause rhythmical contractions of smooth and skeletal muscles.  During resolution, the body relaxes and returns to the unaroused state.

Birth Control Methods and Abortion    

Birth control methods include surgical sterilization (vasectomy, tubal ligation), hormonal methods, intrauterine devices, spermicides, barrier methods (condom, vaginal pouch, diaphragm), periodic abstinence (rhythm and sympto-themal methods), coitus interruptus, and induced abortion.  Contraceptive pills of the combination type contain estrogens and progestins in concentrations that decrease the secretion of FSH and LH and thereby inhibit development of ovarian follicles and ovulation.  An abortion is a spontaneous or induced premature expulsion of the products of conception from the uterus.  RU 486 can induce abortion by blocking the action of progesterone.

Aging and the Reproductive Systems    

Puberty is the period when secondary sex characteristics begin to develop and the potential for sexual reproduction is reached.  The onset of puberty is marked by pulses of GnRH.  The hormone leptin, released by adipose tissue, may signal the hypothalamus that long-term energy stores (triglycerides in adipose tissue) are adequate for reproductive functions to begin.  In females, the reproductive cycle normally occurs once each month from menarche, the first menses, to menopause, the permanent cessation of menses.  Between the ages of 40 and 50, the pool of remaining ovarian follicles becomes exhausted and levels of progesterone and estrogens decline.  Most women experience a decline in bone mineral density after menopause, together with some atrophy of the ovaries, uterine tubes, uterus, vagina, external genitalia, and breasts.  Uterine and breast cancer increase in incidence with age.  In older males, decreased levels of testosterone are associated with decreased muscle strength, waning sexual desire, and fewer viable sperm.  Prostate disorders are common.

DEVELOPMENT AND INHERITANCE

Embryonic Period                    

Pregnancy is a sequence of events that begins with fertilization, proceeds to implantation, embryonic development, and fetal development.  It normally ends in birth.  During fertilization a sperm cell penetrates a secondary oocyte and their pronuclei unite.  Penetration of the zona pellucida is facilitated by enzymes in the sperm’s acrosome.  The resulting cell is a zygote.  Normally, only one sperm cell fertilizes a secondary oocyte because both fast and slow blocks to ployspermy exist.  Early rapid cell division of a zygote is called cleavage, and the cells produced by cleavage are called blastomeres.  The solid sphere of cells produced by cleavage is a morula.  The morula develops into a blastocyst, a hollow ball of cells differentiated into a trophoblast and an inner cell mass.  The attachment of a blastocyst to the endometrium is termed implantation.  It occurs as a result of enzymatic degradation of the endometrium.  After implantation, the endometium becomes modified and is known as the decidua.

The trophoblast develops into the syncytiotrophoblast and cytotrophoblast, both of which become part of the chorion.  The inner cell mass differentiates into hypoblast and epiblast, the bilaminar embryonic disc.  The amnion is a thin protective membrane that develops from the cytotrophoblast.  The exocoelomic membrane and hypoblast form the yolk sac, which transfers nutrients to the embryo, forms blood cells, produces primordial germ cells, and forms part of the gut.  Erosion of sinusoids and endometrial glands provides blood and secretions, which enter lacunar networks to supply nutrition to and remove wastes from the embryo.  The extraembryonic coelom forms within extraembryonic mesoderm.  The extraembryonic mesoderm and trophoblast form the chorion, the principal embryonic part of the placenta. 

The third week of development is chharacterized by gastrulation, the conversion of the bilaminar (two-layered) disc into a trilaminar (three-layered) embryo consisting of ectoderm, mesoderm, and endoderm.  The first evidence of gastrulation is formation of the primitive streak and then the primitive node, notochordal process, and notochord.  The three primary germ layers form all tissues and organs of the developing organism.  Table 29-1 on Page 1072 summarizes the structures that develop from the primary germ layers.  Also during the third week, the oropharyngeal and cloacal membranes form.  The wall of the yolk sac forms a small vascularized outpouching called the allantois, which functions in blood formation and development of the urinary bladder.  The process by which the neural plate, neural folds, and neural tube form is called neurulation.  The brain and spinal cord develop from the neural tube.

Paraxial mesoderm segments to form somites from which skeletal muscles of the neck, trunk, and limbs develop.  Somites also form CTs and vertebrae.  Blood vessel formation, called angiogenesis, begins in mesodermal cells called angioblasts.  The heart forms from mesodermal cells called the cardiogenic area.  By the end of the third week, the primitive heart beats and circulates blood.

Chorionic villi, projections of the chorion, connect to the embryonic heart so that maternal and fetal blood vessels are brought into close proximity.  Thus, nutrients and wastes are exchanged between maternal and fetal blood.  Placentation refers to formation of the placenta, the site of exchange of nutrients and wastes between the mother and fetus.  The placenta also functions as a protective barrier, stores nutrients, and produces several hormones to maintain pregnancy.  The actual connection between the placenta and embryo (and later the fetus) is the umbilical cord.

Organogenesis refers to the formation of body organs and systems and occurs during the fourth week of development.  Conversion of the flat, two-dimensional trilaminar embryonic disc to a three-dimensional cylinder occurs by a process called embryonic folding.  Embryo folding brings various organs into their final adult positions and helps form the GI tract.  Pharyngeal arches, clefts, and pouches give rise to the structures of the head and neck.  By the end of the fourth week, upper and lower limb buds develop and by the end of the eighth week the embryo has clearly human features.

Fetal Period

The fetal period is primarily concerned with the growth and differentiation of tissues and organs that developed during the embryonic period.  The rate of body growth is remarkable, especially during the ninth and sixteenth weeks.

Prenatal Diagnostic Tests

Several prenatal diagnostic tests are used to detect genetic disorders and to assess fetal well-being.  These include fetal ultrasonography, in which an image of a fetus is displayed on a screen.  Amniocentesis is the withdrawal and analysis of amniotic fluid and the fetal cells within it.  Chorionic villi sampling (CVS) involves withdrawal of chorionic villi tissue for chromosomal analysis.  CVS can be done earlier than amniocentesis, and the results are available more quickly, but it is also slightly riskier than amniocnetesis.  Noninvasive prenatal tests include the maternal alpha-fetoprotein (AFP) test to detect neural tube defects and the Quad AFP Plus test to detect Down syndrome, trisomy 18, and neural tube defects.

Maternal Changes During Pregnancy                

Pregnancy is maintained by human chorionic gonadotropin (hCG), estrogens, and progesterone.  Human chorionic somatomammotropin (hCS) contributes to breast development, protein anabolism, and catabolism of glucose and fatty acids.  Relaxin increases flexibility of the pubic symphysis and helps dilate the uterine cervix near the end of pregnancy.  Corticotropin-releasing hormone, produced by the placenta, is thought to establish the timing of birth, and stimulates the secretion of cortisol by the fetal adrenal gland.  During pregnancy, several anatomical and physiological changes occur in the mother.

Exercise and Pregnancy                                   

During pregnancy, some joints become less stable, and certain maneuvers are more difficult to execute.  Moderate physical activity does not endanger the fetus in a normal pregnancy.

Labor                                                           

Labor is the process by which the fetus is expelled from the uterus through the vagina to the outside.  True labor involves dilation of the cervix, expulsion of the fetus, and delivery of the placenta.  Oxytocin stimulates uterine contractions via a positive feedback cycle.

Adjustments of the Infant at Birth

The fetus depends on the mother for oxygen and nutrients, the removal of wastes, and protection.  Following birth, an infant’s respiratory and cardiovascular systems undergo changes in adjusting to becoming self-supporting during postnatal life.

The Physiology of Lactation                 

Lactation refers to the production and ejection of milk by the mammary glands.  Milk production is influenced by prolactin (PRL), estrogens, and progesterone.  Milk ejection is stimulated by oxytocin.  A few of the many benefits of breast-feeding include ideal nutrition for the infant, protection from disease, and decreased likelihood of developing allergies.

Inheritance                                               

Inheritance is the passage of hereditary traits from one generation to the next.  The genetic makeup of an organism is called its genotype.  The traits expressed are called its phenotype.  Dominant genes control a particular trait.  The expression of recessive genes is masked by dominant genes.  Many patterns of inheritance do not conform to the simple dominant-recessive patterns.  In incomplete dominance, neither member of an allelic pair dominates.  Phenotypically, the heterozygote is intermediate between the homozygous dominant and the homozygous recessive.  An example is sickle-cell disease.

In multiple-allele inheritance, genes have more than two alternate forms.  An example is the inheritance of ABO blood groups.  In complex inheritance, a trait such as skin or eye color is controlled by the combined effects of two or more genes and may be influenced by environmental factors.

Each somatic cell has 46 chromosomes: 22 pairs of autosomes and one pair of sex chromosomes.  In females, the sex chromosomes are two X chromosomes.  In males, they are one X chromosome and a much smaller Y chromosome, which normally includes the prime male-determining gene, called SRY.  If the SRY gene is present and functional in a fertilized ovum, the fetus will develop testes and differentiate into a male.  In the absence of SRY, the fetus will develop ovaries and differentiate into a female.

Red-green color blindness and hemophilia result from recessive genes located on the X chromosome.  They are sex-linked traits that occur primarily in males because of the absence of any counterbalancing dominant genes on the Y chromosome.  A mechanism termed X-chromosome inactivation (lyonization) balances the difference in number of X chromosomes between males (one X) and females (two Xs).  In each cell of a female’s body, one X chromosome is randomly and permanently inactivated early in development and becomes a Barr body.

A given phenotype is the result of the interactions of genotype and the environment.  Teratogens, which are agents that cause physical defects in developing embryos, include chemicals and drugs, alcohol, nicotine, and ionizing radiation.

REVIEW

Capacitation refers to the functional changes that sperm undergo in the female reproductive tract that allow them to fertilize the secondary oocyte.  Less than 1% of sperm cells introduced into the vagina normally reach the oocyte.  The term syngamy refers to the sperm cell’s penetration of the zona pellucida and entry into a secondary oocyte.  The next event following syngamy is depolarization and release of calcium ions by the oocyte.

At day four after fertilization, the solid ball of cells that has formed is called the morula.  Six days after fertilization the blasotcyst implants.  Implantation usually occurs in the posterior wall of the body or fundus of the uterus.  The enzymes that allow implantation to occur are produced by the syncytiotrophoblast.

The human gestation period is about 38 weeks.  The chorion develops from the trophoblast.  The embryonic disc develops from the inner cell mass.  The fetus is protected from mechanical injury by fluid contained within the amnion.  The embryonic period of development covers the first two months following fertilization.  For fertilization to occur, a sperm must penetrate the corona radiata, the zona pellucida, the granulosa cells, and the clear glycoprotein layer.

The amnion forms from the cytrotrophoblast.  The yolk sac forms from the endoderm of the inner cell mass.  The extraembryonic coelom becomes the ventral body cavity.  The “water” referred to when a woman’s “water breaks” prior to delivery is amniotic fluid released when the amnion ruptures.

In time sequence we see the following: fertilization, zygote, cleavage, blastocyst, implantation, then the development of chorionic villi.  The endometrium is digested by enzymes released from the trophoblast.  Exchange of gases, nutrients, and wastes between maternal and fetal blood takes place between the decidua basalis and chorionic villi.  The decidua basalis is the portion of the endometrium that becomes the maternal portion of the placenta.  Maternal blood only fills intervillous spaces.  The decidua capsularis is the portion of the endometrium that covers the embryo and is located between the embryo and the uterine cavity.

Most materials cross the placenta by diffusion.  Deoxygenated fetal blood is carried to the placenta via the umbilical arteries.  The heart has formed and begun beating by the end of the first month of development.  The corpus luteum is maintained in early pregnancy to keep levels of estrogen and progesterone high enough to maintain the endometrium.  Human chorionic gonadotropin is produced by the trophoblast cells of the chorion.  During early pregnancy, the main function of hCG is to maintain the corpus luteum.  HCG is at its highest levels during the ninth week of pregnancy.  Once hCG levels decrease, estrogen and progesterone are secreted mainly by the placenta.

Peak secretion of hCS occurs late in the third trimester.  In a pregnant woman, decreased utilization of glucose and increased release of fatty acids from adipose tissue are promoted by the hormone hCS.  Early pregnancy tests are based on detection of hCG in the urine. Most pregnancy tests are based on the presence or absence of hCG.

Complete cervical dilation marks the beginning of the stage of expulsion in true labor.  Colostrum is different from true milk because it contains less lactose and virtually no fat. 

The observable characteristics of a person’s genetic makeup are known as the phenotype.  An individual whose alleles for a particular trait are the same is said to be homozygous.  The two alternative forms of a gene that code for the same trait and are at the same locus on homologous chromosomes are called alleles.  A person is heterozygous for a particular trait if they have one dominant allele and one recessive allele for the trait.  If a person’s phenotype is intermediate between homozygous dominant and homozygous recessive then inheritance of this trait is an example of incomplete dominance.  Inheritance of the ABO blood type is an example of codominance.

The normal human has 22 pairs of autosomes.  By doing karyotyping, one can determine the gender of the child because the Y chromosome is much smaller than the X chromosome.  Teratogens are agents that induce physical defects in developing embryos. 

REPRODUCTIVE SYSTEM REVIEW QUESTIONS

Male

1.      What is the function of the cremaster muscle?

2.      What do Sertoli cells produce?

3.      What produces Testosterone?

4.      Where are the Leydig cells located?

5.      What scrotal temperature is required for sperm production?

6.      Why doesn’t the immune system normally attack spermatogenic cells?

7.      What are the cells that result from the equatorial division of spermatogenesis?

8.      What is the process of spermiation?

9.      When does the process of recombination of genes occur?

10.  What is the form (stag) of developing male gamete located nearest to the BM of a seminiferous tubule called?

11.  What undergoes a meiotic division to produce haploid cells during spermatogenesis?

12.  Where does final maturation of sperm cells occur?

13.  Are Primary spermatocytes diploid?

14.  What does the acrosome of a sperm contain?

15.  What is the function of FSH in the male?

16.  What does LH cause in the male?

17.  What is the principal androgen?

18.  What do the Seminal vesicles produce?

19.  What is the normal number of spermatozoa per milliliter of semen?

20.  What is the function of fructose in semen?

21.  Where are the seminal vesicles located?

22.  What manufactures products that become part of semen?

23.  How many chromosomes does a normal mature human spermatozoa contain?

24.  What do Interstitial cells (of Leydig) secrete?

Female

1.      What is the female structure that is homologous to the penis?

2.      What is the glycoprotein layer between the oocyte and the granulosa cells of an ovarian follicle called?

3.      When does the oogenesis begin in females?

4.      What are the secretory cells of an ovarian follicle called?

5.      What helps move the oocyte into and through the uterine tube?

6.      What is the opening between the cervical canal and the uterine cavity called?

7.      What are the folds of the peritoneum attaching the uterus to either side of the pelvic cavity called?

8.      Does the blood flow through the uterine blood vessels via the arcuate arteries, radial arteries, straight arterioles, and the spiral arterioles?

9.      What type of cells form the epithelium of the vaginal mucosa?

10.  What is the female structure that is homologous to the scrotum?

11.  What is the perineum bounded by (landmarks)?

12.  Do estrogens help control fluid and electrolyte balance, promote protein anabolism, help regulate secretion of FSH and promote development and maintenance of female secondary sex characteristics?

13.  What is the part of the female reproductive system that is shed during menstruation?

14.  During the menstrual cycle, when would the endometrium be at its thickest?

15.  During the menstrual cycle, when is LH at its highest levels?

16.  During the menstrual cycle, when is progesterone at its highest levels?

17.  Repair of the endometrium during the preovulatory phase of menstruation is due to rising levels of what?

18.  During the menstrual cycle, what produces progesterone?

19.  What is the main function of progesterone during the menstrual cycle?

20.  What happens to the corpus luteum if fertilization does not occur?

21.  Is the erection of the penis/clitoris during sexual intercourse a sympathetic response, or parasympathetic?  And peristalsis in the ductus deferens, increased blood pressure, contraction of perineal muscles and ejaculation of semen?

22.  What do oral contraceptives for women typically contain?

23.  Is the onset of puberty in both sexes is signaled by increases in levels of LH?

24.  What is the main control center of the female reproductive system?

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