Male sexual response Erection is enlargement and stiffening of the penis, resulting from engorgement of the erectile bodies with blood, and innervated by the parasympathetic division of the autonomic nervous system.
Ejaculation is the propulsion of semen from the male duct system, innervated by the sympathetic division of the autonomic nervous system.
Orgasm is a state of muscular andpsychological relaxation andvasoconstriction of the penile arterioles,which allows the penis to become flaccidonce again.
Spermatogenesis Spermatogenesis is the sequence of events in the seminiferous tubules of the testes that leads to the production of male gametes called sperm (spermatozoa). Spermatogenic cells are epithelia from the walls of the seminiferous tubules that give rise to sperm.
Spermatogonia are stem cells that are theoutermost and least differentiated tubulecells, that give rise to type A and Bdaughter cells.
Type A daughter cells remain at thebasement membrane to maintain the germcell line.Type B daughter cells get pushed towardthe lumen, where they become primaryspermatocytes destined to produce foursperm.
Each primary spermatocyte generatedduring the first phase undergoes meiosis I,forming two smaller haploid cells calledsecondary spermatocytes.The secondary spermatocytes proceed tomeiosis II, and their daughter cells, calledspermatids, are small round cells with largenuclei.
Spermatids most undergo a streamliningprocess called spermiogenesis, duringwhich they shed most of their cytoplasmand grow a tail, which results in theformation of a sperm (spermatozoan).
The head of a sperm consists almostentirely of its nucleus.Adhering to the top of the nucleus is anacrosome, which contains hydrolyticenzymes that enable the sperm to penetrateand enter an egg.
The sperm midpiece contains mitochondriaspiraled around the contractile filaments ofthe tail.The tail is a flagellum with an attachedcentriole, that propels the sperm in thefemale reproductive tract.
Descendants of the same spermatogoniumremain closely attached to one another, andare surrounded by and connected tosupporting cells called sustentacular(Sertoli) cells.
The basal compartment is a region of theseminiferous tubule that containsspermatogonia.The adluminal compartment lies internal tothe tight junctions of the seminiferoustubule and includes the meiotically activecells and the tubule lumen.
The tight junctions between thesustentacular cells form the blood-testisbarrier, which prevents the membraneantigens of differentiating sperm fromescaping through the basal lamina into thebloodstream.
The sustentacular cells secrete testicularfluid that provides the transport medium forsperm in the lumen, and dispose of theexcess cytoplasm sloughed off thespermatids as they transform into sperm.
Hormonal regulation of malereproductive function Hormonal regulation of spermatogenesis and testicular androgen production involves interactions between the hypothalamus, the anterior pituitary gland, and testes (brain- testicular axis).
The hypothalamus releases gonadotropin-releasing hormone (GnRH), which controlsthe release of the anterior pituitarygonadotropins, follicle-stimulatinghormone, and luteinizing hormone.
FSH stimulates spermatogenesis in thetestes indirectly by stimulating thesustentacular cells to release androgen-binding protein (ABP), which prompts thespermatogenic cells to bind and concentratetestosterone.
LH, also known as interstitial cell-stimulating hormone, binds to the interstitialcells and stimulates them to secretetestosterone.Testosterone inhibits hypothalamic releaseof GnRH, and acts directly on the anteriorpituitary to inhibit gonadotropin release.
Inhibin is a protein hormone produced bythe sustentacular cells, which is releasedwhen the sperm count is high, inhibitinganterior pituitary release of FSH, and GnRHrelease by the hypothalamus.
Oogenesis The production of female sex cells is called oogenesis. The oogonia are diploid stem germ cells of the ovaries, that multiply rapidly by mitosis and then enter a growth phase, during which they lay in nutrient reserves.
Primordial follicles begin to appear as theoogonia are transformed into primaryoocytes, which begin the first meioticdivision , but become dormant late inprophase I.
One primary oocyte continues meiosis Ieach month, and produces two haploid cells,the smaller of which is called the first polarbody, and the larger, which contains mostof the cytoplasm is called the secondaryoocyte.
If a secondary oocyte is penetrated by asperm, it completes meiosis II, yielding onelarge ovum and a tiny second polar body.
The ovarian cycle The monthly series of events associated with the maturation of an egg is called the ovarian cycle. The follicular phase of the ovarian cycle is the period of follicle growth, and lasts from the first to the fourteenth day of the cycle.
The luteal phase is the period of corpusluteum activity, which occurs during days14-28.Most ovarian cycles repeat every 28 days,with ovulation occurring mid-cycle.
A primary follicle is formed when the cellsof the primordial follicle proliferate, and theoocyte enlarges.When more than one cell layer is present inthe primary follicle, the cells are calledgranulosa cells.
In the next phase, a layer of connectivetissue begins to condense around thefollicle, forming the theca folliculi.The granulosa cells secrete a glycoprotein-rich substance that forms a thick transparentmembrane called the zona pellucida, whichsurrounds the oocyte.
During the next phase, a clear liquidaccumulates between the granulosa cells,and eventually coalesces to form a fluid-filled cavity called the antrum.The antrum isolates the oocyte, along withits surrounding capsule of granulosa cellscalled a corona radiata, on a stalk on oneside of the follicle.
Ovulation occurs when the ballooningovary wall ruptures and expels thesecondary oocyte into the peritoneal cavity.After ovulation and discharge of the antrumfluid, the ruptured follicle collapses, and theantrum fills with clotted blood, which iseventually absorbed.
The hormonal regulation of theovarian cycle At the onset of puberty, the hypothalamus begins to release GnRH, which stimulates the release FSH and LH by the pituitary. Gonadotropin levels continues to increase for a few years, and eventually the adult cyclic pattern is achieved which leads to the initial establishment of menstrual function, called menarche.
The uterine cycle The uterine cycle, also referred to as menstrual cycle, is a series of cyclic changes that uterine endometrium goes through each month as it responds to changing levels of ovarian hormones in the blood.
Events of the three-stage uterinecycle Menstrual phase, days 1-5: The uterus sheds all but the deepest part of its endometrium. Proliferative phase, days 6-14: The basal layer of the endometrium rebuilds itself, under the influence of rising blood levels of estrogen, and generates a new functional layer.
Ovulation occurs in the ovary at the end ofthe proliferative phase in response to thesudden release of LH from the anteriorpituitary.Secretory phase, days 15-28: Theendometrium prepares for implantation ofan embryo.
Female sexual response The female sexual response involves swelling of the clitoris, vaginal mucosa and breasts, increased activity of the vestibular glands, and erection of the nipples, which may ultimately result in orgasm.