As you will be required to identify from diagrams of the male reproductive system, specific organs and describe their functions, this and the next series of figures will go over these. The penis * * is an organ for the discharge of urine * and for the deposition of sperm into the vagina of the female during copulation. *
The urethra * * transports urine from the urinary bladder * and sperm and semen * produced by other organs of the male reproductive system. *
The scrotum * * is where the testes are located. Its function is to provide an environment for the testes that is approximately 3 0 Celcius belowthe normal temperature of the body. * Thislower temperature is necessary for the production of viable sperm within the testes. *
You may recall from your dissection of the fetal pig in your A & P I class, that often the testes had not descended completely from the pelvic cavity into the scrotum. The canal through which the testes must descend through to the scrotum is called the inguinal canal. * It not only provides a pathway for the testes but serves as a pathway through which the blood vessels, nerves, muscles and the tube which connects the testes to the urethra are found. *
The testes * * have two primary functions. They produce sperm * and the male hormone, testosterone. *
Each testis is filled with tiny tubules * * called seminiferous tubules. * It is within the seminiferous tubules that sperm are produced through the process of spermatogenesis which occurs from puberty on. *
Shown here * is a cross section through a testis showing the seminiferous tubules. The white spaces * represent the central opening or lumen of each tubule. * In this more highly magnified view of seminiferous tubules, you can visualize the development of sperm cells in the walls of the seminiferous tubules. * By the time the sperm cells are fully developed, they are located in the lumen of the tubule. * Between the seminiferous tubules are groups of cells called interstitial cells. * * These are responsible for the production of the male hormone testosterone within the testes. * *
The seminiferous tubules all eventually lead to the epididymis. * * The sperm are stored within the epididymis,* where they also complete their maturation. *
The vas deferens * *is the duct that connects the epididymis to the urethra. * It provides the passageway for sperm to the urethra. *
A seminal vesicle gland lies on each side of the posterior wall of the bladder. * * These glands produce approximately 60% of the semen. * The semen produced by the seminal vesicle gland is introduced into the vas deferens to form the ejaculatory duct * which connects to the urethra. Semen produced by the seminal vesicle glands is alkaline and contains the sugar fructose which supplies energy for sperm cell movement. *
The single prostate gland encircles the urethra just below the bladder. * * The semen produced by the prostate gland contains enzymes and nutrients which are necessary to activate sperm. * Approximately 1/3 of the semen is produced by the prostate gland. *
The Cowper’s or bulbourethral glands are located below the prostate. * * Their purpose is to produce mucous prior to ejaculation which contains alkaline buffers to neutralize the acidic conditions within the urethra. * *
Reproduction (or procreation) is thebiological process by which new"offspring" individual organisms areproduced from their "parents".Reproduction is a fundamentalfeature of all known life;
Human reproduction• Human reproduction is any form of sexualreproduction• resulting in the conception of a child, typicallyinvolving sexual intercourse between a man anda woman.• During sexual intercourse, the interactionbetween the male reproductive system and thefemale reproductive system results in fertilizationof the womans ovum by the mans sperm,• which after a gestation period is followed bychildbirth.
Function: Transport sperm tourethraVas Deferens
Function: Produce 60% ofalkaline semen includingfructose to provide energy forsperm.SeminalVesiclesEjaculatory Duct
Function: Produces up to 1/3 ofthe semen & includes nutrients& enzymes to activate sperm.Prostate
Function: Secretes mucous &alkaline buffers to neutralizeacidic conditions of urethra.Cowper’s Gland
Male reproductive system• Definition• The male reproductive system is a unionof organs and tissues that producesgametes (reproductive cells known assperm). The male reproductive systemconsists of the penis, testes, scrotum,glands and ductus deferens.
Major Subdivisions• The reproductive functions of the malecan be divided into three majorsubdivisions:1. spermatogenesis, which means simplythe formation of sperm;2. performance of the male sexual act;3. Regulation of male reproductivefunctions by the varioushormones.
Physiologic Anatomy of the Male Sexual Organs• The testis is composed of upto 900 coiled seminiferoustubules, each averaging onehalf meter long, in which thesperm are formed.• The sperm then empty intothe epididymis, another coiledtube about 6 meters long.• The epididymis leads into thevas deferens, which enlargesinto the ampulla of the vasdeferens immediately beforethe vas enters the body of theprostate gland.
• Two seminal vesicles, onelocated on each side of theprostate, empty into theprostatic end of the ampulla,• The contents from both theampulla and the seminalvesicles pass into anejaculatory duct• leading through the body ofthe prostate gland and thenemptying into the internalurethra.• Prostatic ducts, too, emptyfrom the prostate gland intothe ejaculatory duct and fromthere into the prostaticurethra.• Finally, the urethra is the lastconnecting link from the testisto the exterior.
• The urethra is suppliedwith mucus derivedfrom a large number ofminute urethral glandslocated along its entireextent and even moreso from bilateralbulbourethral glands(Cowpers glands)located near the originof the urethra.
Spermatogenesis• During formation of theembryo, the primordialgerm cells migrate intothe testes and becomeimmature germ cellscalled spermatogoniawhich lie in two or threelayers of the innersurfaces of theseminiferous tubules• The spermatogoniabegin to undergo mitoticdivision, beginning atpuberty,
Steps of Spermatogenesis• Spermatogenesis occurs in theseminiferous tubules during activesexual life as the result ofstimulation by anterior pituitarygonadotropic hormones,• beginning at an average age of 13years and continuing throughoutmost of the remainder of life butdecreasing markedly in old age.• In the first stage ofspermatogenesis, thespermatogonia migrate amongSertoli cells toward the centrallumen of the seminiferous tubule.• The Sertoli cells are very large,with overflowing cytoplasmicenvelopes that surround thedeveloping spermatogonia all theway to the central lumen of thetubule.
Meiosis• Spermatogonia that cross the barrier intothe Sertoli cell layer becomeprogressively modified and enlarged toform large primary spermatocytes• Each of these, in turn, undergoes meioticdivision to form two secondaryspermatocytes.• After another few days, these too divideto form spermatids that are eventuallymodified to become spermatozoa(sperm).• During the change from the spermatocytestage to the spermatid stage, the 46chromosomes (23 pairs ofchromosomes) of the spermatocyte aredivided, so that 23 chromosomes go toone spermatid and the other 23 to thesecond spermatid.• This also divides the chromosomalgenes so that only one half of the geneticcharacteristics of the eventual fetus areprovided by the father, while the otherhalf are derived from the oocyte providedby the mother.• The entire period of spermatogenesis,from spermatogonia to spermatozoa,takes about 74 days.
Sex Chromosomes.• In each spermatogonium, one of the 23 pairs ofchromosomes carries the genetic information thatdetermines the sex of each eventual offspring.• This pair is composed of one X chromosome, which iscalled the female chromosome, and one Y chromosome,the male chromosome.• During meiotic division, the male Y chromosome goes toone spermatid that then becomes a male sperm, and thefemale X chromosome goes to another spermatid thatbecomes a female sperm.• The sex of the eventual offspring is determined by whichof these two types of sperm fertilizes the ovum.
Sperm.• Each spermatozoon is composedof a head and a tail.• The head comprises thecondensed nucleus of the cell withonly a thin cytoplasmic and cellmembrane layer around itssurface.• On the outside of the anterior twothirds of the head is a thick capcalled the acrosome that is formedmainly from the Golgi apparatus.• This contains a number ofenzymes similar to those found inlysosomes of the typical cell,including hyaluronidase (which candigest proteoglycan filaments oftissues) and powerful proteolyticenzymes (which can digestproteins).• These enzymes play importantroles in allowing the sperm to enterthe ovum and fertilize it.
YouTube - Normal Human sperms.flvYouTube - Normal Human sperms.flv
Tail of the sperm• also called the flagellum, hasthree major components:• (1) a central skeletonconstructed of 11microtubules, collectivelycalled the axoneme-thestructure of this is similar tothat of cilia found on thesurfaces of other types ofcells• (2) a thin cell membranecovering the axoneme; and• (3) a collection ofmitochondria surrounding theaxoneme in the proximalportion of the tail (called thebody of the tail).
• Back-and-forth movementof the tail (flagellarmovement) providesmotility for the sperm.• The energy for thisprocess is supplied in theform of adenosinetriphosphate that issynthesized by themitochondria in the bodyof the tail.• Normal sperm move in afluid medium at a velocityof 1 to 4 mm/min. Thisallows them to movethrough the femalegenital tract in quest ofthe ovum.
Hormonal Factors That Stimulate Spermatogenesis• Testosterone, secreted by the Leydig cells located in the interstitium of thetestis, is essential for growth and division of the testicular germinal cells,which is the first stage in forming sperm.• Luteinizing hormone, secreted by the anterior pituitary gland, stimulates theLeydig cells to secrete testosterone.• Follicle-stimulating hormone, also secreted by the anterior pituitary gland,stimulates the Sertoli cells; without this stimulation, the conversion of thespermatids to sperm (the process of spermiogenesis) will not occur.• Estrogens, formed by the Sertoli cells when they are stimulated by follicle-stimulating hormone, are probably also essential for spermiogenesis.• Growth hormone (as well as most of the other body hormones) is necessaryfor controlling background metabolic functions of the testes. Growthhormone specifically promotes early division of the spermatogoniathemselves; in its absence, as in pituitary dwarfs, spermatogenesis isseverely deficient or absent, thus causing infertility.
Maturation of Sperm in the Epididymis• After formation in theseminiferous tubules, thesperm require several days topass through the 6-meter-long tubule of the epididymis.Sperm removed from theseminiferous tubules andfrom the early portions of theepididymis are nonmotile,and they cannot fertilize anovum. However, after thesperm have been in theepididymis for some 18 to 24hours, they develop thecapability of motility, eventhough several inhibitoryproteins in the epididymalfluid still prevent final motilityuntil after ejaculation.
Storage of Sperm.• The two testes of the human adult form up to 120 millionsperm each day.• A small quantity of these can be stored in theepididymis, but most are stored in the vas deferens.• T hey can remain stored, maintaining their fertility, for atleast a month.• After ejaculation, the sperm become motile, and theyalso become capable of fertilizing the ovum, a processcalled maturation.• The Sertoli cells and the epithelium of the epididymissecrete a special nutrient fluid that is ejaculated alongwith the sperm.• This fluid contains hormones (including bothtestosterone and estrogens), enzymes, and specialnutrients that are essential for sperm maturation.
Physiology of the Mature Sperm.• The normal motile, fertile sperm are capable offlagellated movement though the fluid medium atvelocities of 1 to 4 mm/min.• The activity of sperm is greatly enhanced in aneutral and slightly alkaline medium, as exists inthe ejaculated semen, but it is greatly depressedin a mildly acidic medium.• A strong acidic medium can cause rapid deathof sperm• The activity of sperm increases markedly withincreasing temperature, but so does the rate ofmetabolism, causing the life of the sperm to beconsiderably shortened.• life expectancy of ejaculated sperm in thefemale genital tract is only 1 to 2 days.
Function of the Seminal Vesicles• Each seminal vesicle is a tortuous, loculated tube linedwith a secretory epithelium that secretes a mucoidmaterial containing an abundance of fructose, citric acid,and other nutrient substances, as well as large quantitiesof prostaglandins and fibrinogen.• During the process of emission and ejaculation, eachseminal vesicle empties its contents into the ejaculatoryduct shortly after the vas deferens empties the sperm.• This adds greatly to the bulk of the ejaculated semen,and the fructose and other substances in the seminalfluid are of considerable nutrient value for the ejaculatedsperm until one of the sperm fertilizes the ovum.
Function of the Prostaglandins• Prostaglandins are believed to aid fertilization intwo ways:• (1) by reacting with the female cervical mucus tomake it more receptive to sperm movement and• (2) by possibly causing backward, reverseperistaltic contractions in the uterus andfallopian tubes to move the ejaculated spermtoward the ovaries (a few sperm reach the upperends of the fallopian tubes within 5 minutes).
Function of the Prostate Gland• The prostate gland secretes a thin, milky fluid thatcontains calcium, citrate ion, phosphate ion, a clottingenzyme, and a profibrinolysin.• A slightly alkaline characteristic of the prostatic fluidmay be quite important for successful fertilization ofthe ovum,• fluid of the vas deferens is acidic due to the presenceof citric acid and metabolic end products of the sperminhibit sperm fertility.• vaginal secretions of the female are acidic (pH of 3.5to 4.0). For optimal motility of sperm the required pHof the surrounding fluids is 6.0 to 6.5.• the slightly alkaline prostatic fluid neutralize the acidityof the seminal fluids during ejaculation, and thusenhances the motility and fertility of the sperm.
Composition of SemenComposition of Semen60 per cent fluid fromthe prostate glandSemen, is composed of the fluid andsperm from the vas deferens10 per cent of the total fluidfrom the seminal vesicles•and small amounts from the mucousglands, especially the bulbourethralglands.The average pH ofsemen is about 7.5
Semen• PH the alkaline prostatic fluid neutralized themild acidity of the semen. 7.5• COLOUR The prostatic fluid gives the semena milky appearance,• Consistency. Fluid from the seminal vesiclesand mucous glands gives the semen amucoid consistency.• Clotting enzyme fibrinogen form a weak fibrincoagulum that holds the semen in the deeperregions of the vagina where the uterine cervixlies.
Life span sperm• sperm live for many weeks in the malegenital ducts, once ejaculated in thesemen, their maximal life span is only 24to 48 hours at body temperature.• At lowered temperatures, however, semencan be stored for several weeks,• and when frozen at temperatures below-100°C, sperm have been preserved foryears.
Capacitation• spermatozoa are said to be"mature" when they leave theepididymis,• their activity is held in checkby multiple inhibitory factorssecreted by the genital ductepithelia.• when first expelled in thesemen, they are unable tofertilizing the ovum.• contact with the fluids of thefemale genital tract, activatethe sperm for fertilization.• These collective changes arecalled capacitation of thespermatozoa.• This normally requires from 1to 10 hours.• these changes are
• The uterine and fallopian tube fluids washaway the various inhibitory factors thatsuppress sperm activity in the male genitalducts.• remain in the fluid of the male genitalducts, spermatozoa are exposed to vesiclecontain cholesterol. This cholesterol isadded to acrosome, toughening thismembrane and preventing release of itsenzymes.• calcium enters the sperm changes theactivity of the flagellum, giving it a powerfulwhiplash motion in contrast to its weakundulating motion.• In addition, the calcium ions causechanges in the cellular membrane of theacrosome, the acrosome release itsenzymes as the sperm penetrates thegranulosa cell ,zona pellucida of theovum itself.Penetrate the Ovum
Acrosome Enzymes "Acrosome Reaction," and Penetration of the OvumAcrosome Enzymes "Acrosome Reaction," and Penetration of the Ovum acrosome contain largeacrosome contain largequantities ofquantities of hyaluronidasehyaluronidaseandand proteolytic enzymesproteolytic enzymes.. HyaluronidaseHyaluronidase depolymerizesdepolymerizesthethe hyaluronic acidhyaluronic acid in thein theintercellular cement that holdintercellular cement that holdthe ovarian granulosa cellsthe ovarian granulosa cellstogether.together. hyaluronidase is especiallyhyaluronidase is especiallyimportant in openingimportant in openingpathways between thepathways between thegranulosa cells so that thegranulosa cells so that thesperm can reach the ovum.sperm can reach the ovum. proteolytic enzymesproteolytic enzymes digestdigestproteins in the structuralproteins in the structuralelements of tissue cells thatelements of tissue cells thatstill adhere to the ovum.still adhere to the ovum.
"Acrosome Reaction,"• Within minutes,these enzymes opena penetratingpathway for passageof the sperm headthrough the zonapellucida to theinside of the ovum.
• Within another 30 minutes,the cell membranes of thesperm head and of theoocyte fuse with each otherto form a single cell.• At the same time, thegenetic material of the spermand the oocyte combine toform a completely new cellgenome, containing equalnumbers of chromosomesand genes from mother andfather.
Why does only one sperm enter the oocyte?• The reason is not entirelyknown,• but within a few minutesafter the first spermpenetrates the zonapellucida of the ovum,calcium ions diffuse inwardthrough the oocytemembrane and causemultiple cortical granules byexocytosis from the oocyte• These granules containsubstances that permeate allportions of the zona pellucidaand prevent binding ofadditional sperm,
Abnormal Spermatogenesis and Male Fertility• The seminiferous tubular epithelium can bedestroyed by a number of diseases.• bilateral orchitis of the testes resulting frommumps causes sterility in some affected males.• Also, some male infants are born withdegenerate tubular epithelia as a result ofstrictures in the genital ducts or otherabnormalities.• Finally, another cause of sterility, usuallytemporary, is excessive temperature of thetestes.
Effect of Temperature onSpermatogenesis.• Increasing the temperature of the testes can preventspermatogenesis by causing degeneration of most cellsof the seminiferous tubules besides the spermatogonia.• It has often been stated that the reason the testes arelocated in the dangling (swinging) scrotum is to maintainthe temperature of these glands below the internaltemperature of the body, although usually only about 2°Cbelow the internal temperature. On cold days, scrotalreflexes cause the musculature of the scrotum tocontract, pulling the testes close to the body to maintainthis 2° differential. Thus, the scrotum theoretically actsas a cooling mechanism for the testes (controlledcooling), without which spermatogenesis might bedeficient during hot weather.
Cryptorchidism• Cryptorchidism meansfailure of a testis to descendfrom the abdomen into thescrotum at or near the timeof birth of a fetus.• testes are derived from thegenital ridges in theabdomen.• 3 weeks to 1 month beforebirth of the baby, the testesnormally descend throughthe inguinal canals into thescrotum.• Occasionally this descentdoes not occur or occursincompletely, so that one orboth testes remain in theabdomen, in the inguinalcanal, or elsewhere alongthe route of descent.
Adverse effects of cryptorchid• A testis that remains throughout life in the abdominalcavity is incapable of forming sperm.• The tubular epithelium becomes degenerate, leavingonly the interstitial structures of the testis.• higher temperature in the abdomen cause thisdegeneration of the tubular epithelium and,consequently, sterility,• operations to relocate the cryptorchid testes from theabdominal cavity into the scrotum before the beginningof adult sexual life are frequently performed on boys whohave undescended testes
Effect of Sperm Count on Fertility.• The averages quantity of semen ejaculated during eachcoitus is about 3.5 milliliters,• Each milliliter of semen have about 120 million sperm, in"normal" males• vary from 35 million to 200 million.• 400 million sperm are present in each ejaculate.• When the number of sperm in each milliliter falls belowabout 20 million, the person is likely to be infertile.• Thus, even though only a single sperm is necessary tofertilize the ovum, for reasons not understood, theejaculate usually must contain a tremendous number ofsperm for only one sperm to fertilize the ovum.
Effect of Sperm Morphology and Motility on Fertility.• Occasionally a man has a normalnumber of sperm but is stillinfertile.• When this occurs, sometimes asmany as one half the sperm arefound to be abnormal physically,having two heads,• abnormally shaped heads, orabnormal tails,• At other times, the sperm appearto be structurally normal, but forreasons not understood, they areeither entirely nonmotile orrelatively nonmotile.• Whenever the majority of thesperm are morphologicallyabnormal or are nonmotile, theperson is likely to be infertile, eventhough the remainder of the spermappear to be normal.