Reproductive Lecture

FEMALE REPRODUCTIVE PHYSIOLOGY

2 Major Phases of Female Reproductive Functions 1. Preparation of the female body for conception and gestation. 2. Period of gestation

Female External Genitalia

Female Sexual Organs

Female Sexual Organs

Female Hormonal System

Female Sexual Cycle

Gonadotropin Releasing Hormone (GnRH)      

secreted by the hypothalamus secreted in pulses every 1-3 hours pulsatile nature of GnRH release is essential to its function stimulate the anterior pituitary to release FSH and LH pulsatile release of GnRH causes pulsatile output of LH hypothalamic centers for release of GnRH:  

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mediobasal hypothalamus, esp. the arcuate nuclei (controls most of female sexual activity) preoptic area of anterior hypothalamus

limbic system transmit signals to arcuate nuclei to modify the intensity and frequency of pulsatile GnRH

Gonadotropic Hormones (FSH and LH)  small glycoproteins   

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small glycoproteins secreted by the anterior pituitary target organs: testes in the male; ovary in the female mechanism of action: bind to receptors which activate the cAMP second messenger system in the cell cytoplasm → growth and proliferation of cells cyclic increase and decrease of FSH and LH causes the cyclic ovarian changes characteristic of the the female sexual cycle

FSH and LH Action on the Follicle Unit and Corpus Luteum  FSH     

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initiation of follicle growth induction of aromatase enzyme → increased estradiol induction of FSH and LH receptors acts synergistically with estradiol to increase FSH receptors and granulosa cells stimulation of inhibin production

LH   

initiates luteinization and progesterone production by granulosa cells LH surge stimulates completion of meiotic oocyte division maintains corpus luteum progesterone production

Inhibin 

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secreted by the granulosa cells of the corpus luteum inhibit secretion of FSH by the anterior pituitary and LH to a lesser extent believed to be important in causing the decrease in secretion of FSH and LH at the end of the female sexual cycle

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PUBERTY - period of change which occurs when the anterior pituitary begins to secrete increasing amounts of FSH and LH at about the age of 8 years which later culminates in the initiation of monthly sexual cycles between the ages of 11 and 16 years MENARCH - first menstrual cycle MENOPAUSE 

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period during which the cycles cease and and the female sex hormones diminish to almost none cause is “burning out” of the ovaries: progressive decrease in the number of primordial follicle→ decreased production of estrogen by the ovary → loss of negative feedback inhibition of FSH and LH

Ovarian Hormones (Estrogen and Progestins) ESTROGEN  secreted mostly by the ovaries in normal nonpregnant females  small amount is secreted by adrenal cortices  most important estrogen is estradiol  mainly promote proliferation and growth of specific cells of the body  responsible for development of most of the secondary sexual characteristics of the female

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3 types in estrogens in human female plasma: 1. β-Estradiol - the principal estrogen secreted by the ovaries 2. Estrone - mainly formed in the peripheral tissues from androgens secreted by the adrenal cortices and by the ovarian thecal cells 3. Estriol - weak estrogen converted from estradiol and estrone in the liver estrogenic potency of β-estradiol is 12x that of estrone and 80x that of estriol

Synthesis of Estrogen and Progesterone  both are steroid compounds  synthesized in the ovary mainly from cholesterol and to a slight extent from acetyl coenzyme A  during synthesis, progesterone and testosterone are synthesized first but during the follicular phase of the ovarian cycle almost all of the testosterone and much of the progesterone are converted into estrogen by the granulosa cells  during the luteal phase, far too much progesterone is formed for all of it to be converted to estrogen → increased progesterone secretion

Transport of Estrogen and Progesterone  transported in the blood bound mainly with plasma albumin and specific estrogen- and progesterone- binding globulins Fate of Estrogen  liver conjugates the estrogens to form glucoronides and sulfates  most of these conjugated products are excreted in the urine while 1/5 is excreted in the bile  liver also converts the potent estrogens estradiol and estrone into the impotent estrogen estriol  diminished liver function will increase the activity of estrogen in the body

Functions of Estrogen 1. Effect on the uterus and external genitalia 

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enlargement of the ovaries, fallopian tubes, uterus and vagina enlargement of the external genitalia deposition of fats in the mons pubis and labia majora change vaginal epithelium from cuboidal to stratified type marked proliferation of the endometrial stroma increased development of the endometrial glands

2. Effect on the fallopian tubes proliferation of glandular tissue  increased number of ciliated epithelial cells  increased ciliary activity that helps propel the fertilized ovum towards the uterus 

3. Effect on the the breasts responsible for the characteristic growth and appearance of the mature female breast  development of the stromal tissues of the breast  growth of an extensive ductile system 

4. Effect on the skeleton  

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increased osteoblastic activity causes early union of the epiphyses with the shaft of long bones deficiency of estrogen during menopause can lead to osteoporosis due to: a. decreased osteoblastic activity of bone b. decreased bone matrix c. decreased deposition of bone calcium and phosphate

5. Effect on protein deposition 

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cause slight increase in total body protein→ slightly positive nitrogen balance enhanced protein deposition by testosterone is much more general and much more powerful than

6. Effect on metabolism and fat deposition increase the metabolic rate slightly (only 1/3 as much as that caused by testosterone)  deposition of increased quantities of fats in the subcutaneous tissues  deposition of fats in the thighs and the buttocks 

7. Effect on hair distribution 

do not greatly affect hair distribution

8. Effect on the skin 

development of a thicker but soft and usually smooth skin

9. Effect on electrolyte balance 

cause sodium and water retention by the kidney tubules

10. Intracellular functions of estrogens 

estrogen combine with a cytoplasmic receptor protein and together they will activate specific portions of the chromosomal DNA → initiation of transcription (RNA production) → cell division

PROGESTINS  most important progestin is progesterone  concerned almost entirely with final preparation of the uterus for pregnancy and the breasts for lactation  secreted in minute amounts during the first half of the ovarian cycle by the ovaries and the adrenal cortices  secreted in significant amounts only during the second half of the ovarian

Fate of Progesterone  almost all the progesterone is degraded within minutes of its secretion to other steroids with no progesteronic activity  liver is also important in the metabolic degradation of progesterone  major end product of progesterone

Functions of Progesterone 1. Effect on the uterus promote secretory changes in the uterine endometrium during the second half of the female sexual cycle (most important function of progesterone)  prepares the uterus for implantation of the fertilized ovum  decreases the frequency and intensity of uterine contractions 

2. Effect on the fallopian tubes 

promotes secretory changes in the mucosal lining of the fallopian tubes which are necessary for the nutrition of the fertilized, dividing ovum as it traverses the fallopian tube

3. Effect on the breasts promotes the development of lobules and alveoli in the breast  causes swelling of the breast due to the secretory development in the lobules and alveoli and also due toincreased fluid in the subcutaneous tissue.  does not cause the alveoli to actually 

4. Effect on electrolyte balance progesterone in large quantities can enhance sodium, chloride and water reabsorption in the distal tubules of the kidney  more often causes increased sodium and water excretion than retention due to its competitive antagonism of the effects of aldosterone 

Female Sexual Cycle 

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monthly rhythmical changes in the secretion of the female hormones and the corresponding changes in the ovaries and sexual organs duration of cycle averages 28 days abnormal cycle length is frequently associated with decreased fertility two significant results of the female cycle: 1. only a single ovum is normally released from the ovaries each month so that normally only a single fetus can begin to grow at a time 2. the uterine endometrium is prepared for implantation of the

Female Sexual Cycle

OVARIAN CYCLE   

FOLLICULAR PHASE OVULATION LUTEAL PHASE

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FOLLICULAR PHASE (Ovarian Follicular Growth)

PRIMORDIAL FOLLICLE

consist of an ovum surrounded by a single layer of granulosa cells  present at birth and throughout childhood  granulosa cells provide nourishment for the ovum and secrete an oocyte maturation-inhibiting factor  ovum is suspended in the prophase stage of meiotic division 

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PRIMARY FOLLICLES ovum enlarges with growth of additional layers of granulosa cells  occurs after onset puberty when FSH and LH begin to be secreted in increasing amounts by the anterior pituitary  some of the development of the follicle up to this stage can occur even in the absence of FSH and LH but development beyond this point is not possible without FSH and LH 

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ANTRAL FOLLICLES  

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early growth of the primary follicle up to the antral stage is stimulated mainly by FSH alone slight to moderate increase in FSH during the first few days of the menstrual cycle causes accelerated growth of 6 to 12 primary follicles each month effect of FSH:  

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rapid proliferation of granulosa cells → increase in granulosa cell layer spindle cells from the ovarian interstitium form several layers of cells outside the granulosa cell layer to give rise to the theca interna and theca externa

mass of granulosa cells secrete a follicular fluid that contain a high concentration of estrogen accumulation of fluid causes an antrum to appear within the mass of granulosa cells

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VESICULAR FOLLICLE  

larger follicles that results from the accelerated growth of the antral follicle causes of accelerated growth of antral follicles: 

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estrogen secreted into the follicle causes the granulosa cells to form increasing numbers of FSH receptors→ granulosa cells become even more sensitive to the effects of FSH FSH and estrogen combine to increase the number of LH receptors in granulosa cells→LH stimulation of granulosa cells and causes a rapid increase in follicular secretion Estrogen and LH act together to cause proliferation of follicular thecal cells and increase their secretions

ovum diameter increases as much as 10-fold or a mass increase of 1000-fold ovum (still in the primary oocyte stage) remains embedded in a mass of granulosa cells at one pole of the follicle

Development of the Ovum Germinal epithelium of fetal ovary Primordial ova Primordial follicle Primary oocyte At the30th week of gestation, the number of ova reaches about 6 million; only about 2 million are present at birth and only 300,000-400,000 are present at puberty

Development of the Ovum

Development of the Ovum

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MATURATION OF ONLY ONE FOLLICLE  

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before ovulation occurs, one of the follicles will begin to outgrow all the others less developed follicles begin to involute (a process called atresia) and are now called atretic follicles postulated mechanism for the fulldevelopment of only one follicle is the secretion of more estrogen by this highly developed follicle → causes

a positive feedback which increases FSH secretion→increase proliferation of granulosa and theca cells→ increased estrogen production → combination of estrogen and FSH increases FSH and LH receptors in granulosa cells and theca cell→increase stimulation of the these cells → large amounts of estrogen exerts a negative feedback on the hypothalamus→decrease FSH secretion by anterior pituitary→block further growth of less welldeveloped follicles

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process of atresia is important in that it allows only one of the follicles to grow large enough to ovulate

OVULATION 

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occur on the 14th day (midcycle) of a normal 28-days female sexual cycle rupture of a follicle with release of the ovum occurs at a protrusion in the capsule called the stigma released ovum is surrounded by small granulosa cells called the corona radiata

Ovulatory Surge of LH 

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necessary for final follicular growth and ovulation marked and rapid increase in LH secretion by the anterior pituitary (6-10X) which peaks at about 16 hours before ovulation associated with increased FSH (2-3X) which acts synergistically with LH to cause rapid swelling of the follicle before ovulation LH converts the granulosa and theca cells into more progesterone secreting cells and less estrogen secretion → decreased estrogen

Mechanism for Ovulation Luteinizing Hormone Follicular steroid hormone (Progesterone) Proteolytic enzymes (Collagenase)

Follicular hyperemia and Prostaglandin secretion

Weakened follicular wall

Plasma transudation into follicle

Degeneration of the stigma

Follicle swelling

Follicle rupture Evagination of the ovum

LUTEAL PHASE  

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starts shortly after expulsion of the ovum remaining granulosa and theca interna cells change rapidly into lutein cells a few hours after ovulation and form the corpus luteum granulosa and theca cells cells enlarge and become filled with lipid inclusions that give them a yellowish appearance (luteinization) granulosa cells of the corpus luteum form large amounts of the female sex hormones progesterone and estrogen (more progesterone) theca cells form mainly the androgen androstenedione and testosterone → converted to female hormones by the granulosa cells

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corpus albicans - formed 12 days after ovulation when the corpus luteum involute and loses its secretory function as well as its yellowish,lipid characteristics change of granulosa and theca interna cells into lutein cells is mainly dependent on LH luteinization of granulosa cells also depends on the extrusion of the ovum from the follicle luteinization-inhibiting factor in folliclular fluid prevents luteinization

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corpus luteum secretes large amounts of both progesterone and estrogen lutein cells undergo a process of preordained sequence of events: 1. proliferation 2. enlargement 3. secretion 4. degeneration  

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can occur even the absence of LH but will last only 4-8 days presence of LH prolongs the life and secretory function of the corpus luteum up to about 12 days chorionic gonadotropin maintains the life and function of the corpus luteum during the first 2-4 months of pregnancy

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Causes of Involution of the Corpus Luteum 1. negative feedback effect of estrogen (mainly) and progesterone secreted by the corpus luteum on the anterior pituitary → decreased FSH and LH secretion 2. inhibin - secreted by the luteal cells and inhibits anterior pituitary secretions ( esp. FSH secretion) → decreased FSH and LH→corpus luteum degenerate lack of secretion of estrogen, progesterone and inhibin after involution of the corpus luteum removes the feedback inhibition on

ENDOMETRIAL CYCLE PROLIFERATIVE PHASE  under the influence of estrogens  stromal cells and epithelial cells proliferate rapidly  endometrial surface is re-epithelialized within 4-7 days from onset of menstruation  endometrial thickness greatly increase due to proliferation of stromal cells and progressive growth of endometrial glands and new blood vessels (3-4 mm thick at ovulation)  endometrial glands particularly those in the cervical region secrete a thin stringy

SECRETORY PHASE  progestational phase  occurs after ovulation  estrogen cause slight additional cellular proliferation  progesterone causes marked swelling and secretory development of the endometrium  glands increase in tortuosity with increased amounts of secretory substances in the glandular epithelial cells 

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blood supply to the endometrium increase further and blood vessels become highly tortuous purpose of all these endometrial changes is to produce a highly secretory endometrium that contain large amounts of stored nutrients uterine secretions (“uterine milk”) provide nutrition for the fertilized ovum from the time the ovum enters the uterine cavity from the fallopian tubes (3-4 days after ovulation) until the time the ovum implants (7-9 days after ovulation)

MENSTRUATION  results from the sudden reduction of estrogen and specially progesterone secretion due to involution of the corpus luteum at the end of the ovarian cycle  decreased stimulation of the endometrial cells by estrogen and progesterone results in involution of the endometrium  blood vessels become vasospastic presumably due to release of a vasoconstrictor substance (? prostaglandin)  necrosis of endometrium and blood vessels results from the vasospasm

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desquamation of the necrotic superficial outer layer of the endometrium mass of necrotic tissue and blood in the uterine cavity and possibly the contractile effect of prostaglandins initiate uterine contraction that expel the uterine contents during normal menstruation, 40 ml of blood and 35 ml of serous fluid are lost menstrual fluid is normally nonclotting due to the presence of fibrinolysin loss of blood ceases within 4-7 days when the endometrium has reepithelialized tremendous numbers of leukocytes

Female Sexual Cycle

Hormone Feedback Controls in the Female Reproductive Cycle

Female Sexual Act 1. Stimulation of the female sexual act need both psychic stimulation and localsexual stimulation  desire changes during the sexual month and reaches a peak near the time of ovulation  local stimulation may involve massage and othertypes of stimulation of the vulva, vagina and other perineal regions  glans of the clitoris is specially sensitive for initiating sexual sensations  sexual sensory signals are transmitted to the sacral segments of the spinal 

2. Erection and lubrication

parasympathetic signals dilate the arteries of erectile tissues located around the introitus and extending up to the clitoris→ erectile tissue rapidly fills up with blood → introitus tightens around the penis  dilatation of arteries possibly results from release of nitric oxide from nerve endings  erectile tissues are under the control of parasympathetic nerves that pass through the nervi erigentes from the sacral plexus to the external genitalia  parasympathetic signals also pass to the bilateral Bartholin’s gland located beneath the labia minora → secretion of mucus immediately inside the introitus which provides lubrication during sexual 

3. Orgasm (Female Climax)  

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analogous to emission and ejaculation in the male intense sexual sensation pass to the cerebrum and cause intense muscle tension throughout the body may help promote fertilization of the ovum by the following proposed mechanisms:

a. reflex rhythmical contraction of perineal muscle and increase motility of the uterus and fallopian tubes during orgasm may help transport the sperm upwards b. orgasm seem to cause dilatation of the cervical canal for up to 30 minutes thus allowing easy transport of the sperm c. in lower animals, copulation causes the posterior pituitary to secrete oxytocin→increased rhythmical contraction of the uterus→rapid transport of sperm

4. Resolution 

sense of satisfaction characterized by relaxed

Fertile Period of Sexual Cycle 

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ovum remains viable and capable of being fertilized after being expelled from the ovary for up to 24 hours most sperms can remain fertile in the female reproductive tract for no more than 24 hours although a few may remain fertile for up to 72 hours for fertilization to take place, intercourse usually must occur between 1-2 days before ovulation

Rhythm Method of Contraception

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involves avoidance of intercourse near the time of ovulation difficulty with this method is the impossibility of predicting the exact time of ovulation interval from ovulation to onset of the next succeeding menstruation is almost always between 13-15 days avoid intercourse for 4 days before the calculated day of ovulation and 3 days afterward used only when the periodicity of the menstrual cycle is regular

The Pill  

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hormonal suppression of fertility based on the prevention/inhibition of the preovulatory surge of LH secretion by the administration of estrogen and/or progesterone commonly consist of a combination of synthetic estrogen and synthetic progestins since the natural hormones are almost entirely destroyed by the liver within a short time after ingestion usually begun in the early stages of the monthly cycle, continued beyond the time of ovulation then stopped to allow menstruation to occur

MALE REPRODUCTIVE PHYSIOLOGY

PHYSIOLOGIC ANATOMY OF THE MALE SEXUAL ORGAN

PHYSIOLOGIC ANATOMY OF THE MALE SEXUAL ORGAN

PHYSIOLOGIC ANATOMY OF THE MALE SEXUAL ORGAN

Major Subdivisions of Male Reproductive Function 1. SPERMATOGENESIS 2. PERFORMANCE OF THE MALE SEXUAL ACT 3. HORMONAL REGULATION OF MALE REPRODUCTIVE FUNCTIONS

SPERMATOGENESIS

(44XY)

Type A Spermatogonia mitosis Type B Spermatogonia mitosis Primary Spermatocyte

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1st meiotic division Secondary Spermatocyte

(44XY) (44XY)

(22X or Y)

2nd meiotic division Spermatids

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Spermiogenesis Spermatozoa

SPERMATOGENESIS

Spermatogenesis     

formation of sperm occurs in the seminiferous tubules occurs throughout adult life entire period of spermatogenesis, from germinal cells to sperm, takes about 64 days SERTOLI CELLS   

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considered the primary regulators of spermatogenesis provide physical and nutritional support for the germ cells membranes form a blood-testes barrier that minimizes exposure of germ cells to harmful circulating substances have distinct secretory and endocrine functions

Spermiogenesis 

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complex transformation of spermatids into specialized spermatozoa golgi apparatus, containing hyaluronidase and other proteases, is transformed into the acrosome (caplike structure covering the anterior 2/3 of the sperm head) centrioles and mitochondria are transformed into the flagella (sperm tail) unnecessary cellular organelles and some of its cytoplasm are cast off as residual bodies condensation of the nucleus and chromatin to form a compact head

Hormonal Factors That Stimulate Spermatogenesis  TESTOSTERONE 

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LUTEINIZING HORMONE (LH)  

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secreted by the Leydig’s cells located in the interstitium of the testis essential for growth and division of germinal cells in the formation of the sperm secreted by the anterior pituitary stimulate the Leydig’s cells to secrete testosterone

FOLLICLE STIMULATING HORMONE (FSH)   

secreted by the anterior pituitary stimulate the Sertoli cell stimulation of Sertoli cells by FSH is necessary for spermiogenesis to oocur

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ESTROGEN formed from testosterone by the Sertoli cell when they are stimulated by FSH  probably also essential for spermiogenesis  Sertoli cells also secrete an androgenbinding protein that binds both testosterone and estrogen and carries them into the lumen of the seminiferous tubules to make them available for the maturing sperm 

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GROWTH HORMONE 

promotes early division of the

Maturation of the Sperm in the Epididymis  after formation in the seminiferous tubules, 

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the sperms will have to pass through the epididymis sperm develops the capability for motility after they have been in the epididymis for 18-24 hours but inhibitory proteins in the epididymal fluid prevents actual motility until after ejaculation after ejaculation, the sperm do become motile and they also become capable of fertilizing the ovum (maturation) Sertoli cells and the epithelium of the epididymis secrete a special nutrient fluid that may be important for sperm maturation

Storage of Sperms 

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the 2 testes of a young adult form about 120 million sperms per day most of them stored in the vas deferens and ampulla of the vas deferens a small quantity can be stored by the epididymis sperms can be stored, maintaining their fertility, in the genital tract for at least a month during storage sperms are kept in the inactive state by numerous inhibitory substances in the secretions of the ducts

Physiology of the Mature Sperm  capable of flagellated movement in fluid  

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media at a speed of 1-4 mm/minute tend to travel in a straight line activity of sperm is greatly enhanced in neutral and slightly alkaline media but greatly depressed in mildly acidic media activity of sperm increases with increasing temperature but since rate of metabolism is also increased, lifespan of the sperm is also considerably shortened sperm can live for many weeks in the genital ducts of the testes but lifespan is

Function of the Seminal Vesicle  seminal vesicle is a secretory gland 

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secrete a mucoid material that contain fructose, citric acid, other nutrient and large quantities of prostaglandins and fibrinogen empties its content into the ejaculatory duct during the process of emission fructose and other substances are of considerable nutrient value for the ejaculated sperm prostaglandins are believed to aid fertilization by: 

reacting with cervical mucus to make it more receptive to sperm movement

Function of the Prostate Gland  secrete a thin milky fluid that contains 

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citrate, calcium, phosphate, a clotting enzyme and a profibrinolysin capsule of the prostate gland contracts simultaneously with the contraction of the vas deferens during emission slightly alkaline nature of prostatic fluid may be important for successful fertilization of the ovum because the relatively acidic fluid of the vas deferens and vaginal secretions may help inhibit sperm fertility sperm do not become optimally motile until pH of surrounding fluid increases to about 6.0-6.5

Semen  

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fluid ejaculated during the male sexual act compose of fluid and sperm from the vas deferens (10%), fluid from the seminal vesicle (60%), fluid from the prostate gland (30%) and a small amount from the mucous glands particularly the bulbourethral gland bulk of semen is seminal vesicle fluid which is the last to be ejaculated and serves to wash the sperm out of the ejaculatory duct and urethra average pH is 7.5 prostatic fluid gives semen a milky

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clotting enzyme of the prostatic fluid causes the fibrinogen of the seminal vesicle fluid to form a coagulum that holds the semen in the deeper regions of the vagina coagulum subsequently dissolves over the next 15-30 minutes due to lysis by the fibrinolysin from prostatic profibribrinolysin sperm becomes highly motile as soon as coagulum dissolves

Semen Analysis 

Normal semen analysis: 1. Ejaculate volume ≥ 2 ml 2. Sperm concentration ≥ 20 million/ml 3. ≥ 50% of sperm have progressive forward motility 4. ≥ 30% of sperm have normal morphology

Capacitation of the Spermatozoa 

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refers to the multiple changes that occur to activate the sperm for the final process of fertilization usually occurs upon contact of the sperm with the fluids from the female genital tract requires 1-10 hours

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changes that are believed to occur during capacitation: uterine and fallopian tube fluids wash away the inhibitory factors that have suppressed sperm activity in the male genital tract  sperm swims away from the cholesterol vesicles which have deposited and toughened the membrane covering the acrosome and prevented it from releasing its enzymes  membrane of the sperm head becomes highly permeable to calcium; calcium 

Acrosome

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acrosomes of sperms contain large amounts of hyaluronidase and proteolytic enzymes hyaluronidase dissolves the hyaluronic acid polymers in the intercellular cement that binds the granulosa cells together hyaluronidase is specially important in opening pathways between the granulosa cells and ovum sperm must pass through granulosa cell layer, zona pellucida, perivitteline space and membrane of oocyte as soon as anterior membrane of the sperm binds to receptors in the zona pellucida, entire anterior membrane dissolves and all acrosomal enzyme are immediately released

Reasons why only one sperm is able to enter oocyte  only a few the sperm ever gets as far as the 

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zona pellucida within minutes after the first sperm penetrates the zona pellucida, calcium diffuse across the oocyte membrane and cause the release of multiple cortical granules which contain substances that prevent the binding of additional sperms changes in the oocyte membrane after its fusion with the sperm are believed to cause electrical depolarization which tend to fend off subsequent sperms

STAGES OF THE MALE SEXUAL ACT 

ERECTION 

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degree of erection is proportional to the degree of stimulation, whether psychic or physical caused by parasympathetic impulses that pass from the sacral portion of the spinal cord through the pelvic nerve to the penis parasympathetic fiber secrete nitric oxide → relaxes the arteries to the penis as well as the smooth muscle fibers in the erectile tissues of the corpora cavernosa and corpus spongiosum → fills up with blood → penis becomes hard and elongated

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LUBRICATION 

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parasympathetic impulses also causes the urethral glands and the bulbourethral gland to secrete mucus most of the lubrication during coitus is provided by the female sexual organs

EMISSION  

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forerunner of ejaculation initiated by sympathetic impulses from L1 and L2 that pass to the genital organs through the hypogastric and pelvic plexuses begins with contraction of the vas deferens and ampulla which expels the sperm into the internal urethra followed by contraction of the prostate gland then finally contraction of the seminal vesicle

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EJACULATION 

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initiated by filling of the internal urethra which elicits sensory signals that are transmitted to the sacral regions of the cord through the pudendal nerve sensory signals also excite rhythmical contraction of the internal genital organs and cause contraction of the ischiocavernosus and bulbocavernosus muscles that compress the bases of the penile erectile tissue rhythmical, wave-like increases in pressure in the urethra and genital ducts expel the semen from the urethra to the exterior rhythmical contractions of the pelvic muscles cause thrusting movements of the pelvis and the penis which also help propel the semen into the deepest recesses of the vagina

Regulation of Male Hormones