Chapter 27Male Reproductive SystemLecture 18Mariebs HumanAnatomy and Physiology

Marieb w Hoehn

*Overview of the Reproductive SystemWe can sum up the reproductive system in just a few words

*Lecture OverviewFunction of the male reproductive systemOverview of the anatomy of the male reproductive systemDescent of the testesStructure of the testesFormation of sperm cellsStructure of sperm cellsMale internal accessory organsMale external accessory organsErection, orgasm, and ejaculationHormonal control of the male reproductive system

*Male Reproductive SystemThere are three main functions of the male reproductive systemProduce and maintain sex cells (sperm)Transport sperm and supplemental fluids to the female reproductive tractSecrete male sex hormonesSex organs can be divided intoPrimary sex organs (gonads) = testes (sperm, hormones)Accessory (secondary) sex organs = internal and external reproductive organs

*Male Reproductive SystemTestis Epididymis Vas (ductus) deferens Ejaculatory duct Urethra Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Male Reproductive Organsposterior viewFigure from: Holes Human A&P, 12th edition, 2010

*Descent of TestesDescent begins 1-2 months before birth under the influence of testosteroneDescent is necessary for sperm productionFailure of testes to descend = cryptorchidismFigure from: Holes Human A&P, 12th edition, 2010

*Structure of the TestisSurrounded by the tunica albuginea a tough, white, fibrous capsule that encloses each testicleSepta divide each testicle into about 250 lobulesEach lobule contains 1-4 highly coiled seminiferous tubules that give rise to spermInterstitial cells (of Leydig) lie in between seminiferous tubules and secrete male sex hormones

Rete TestisFigure from: Holes Human A&P, 12th edition, 2010

*Review of Mitosis and MeiosisFigures from: Martini, Anatomy & Physiology, Prentice Hall, 2001Mitosis production of two identical diploid daughter cellsMeiosis production of four genetically varied, haploid gametes

*Chromosome Crossing Over mixes up traits

different colors represent the fact that one homologous chromosome comes from the individuals father (paternal) and one from the mother (maternal)

the genetic information in sperm cells and egg cells varies from cell to cellTetradFigure from: Holes Human A&P, 12th edition, 2010

*Seminiferous Tubules and Sperm MaturationFigures from: Martini, Anatomy & Physiology, Prentice Hall, 2001Spermatogonium = stem cell

*SpermatogenesisSpermatogonium (2n)Primary spermatocyte (2n)Secondary spermatocyte (n)Spermatid (n)Spermatozoan (n)SpermiogenesisMeiosis IMeiosis IIKnow the order of events below!

*Formation of Sperm CellsSupporting cells are sustentacular cells They:are important in regulating and supporting spermatogenesishelp maintain the blood-testis barrierFigure from: Holes Human A&P, 12th edition, 2010

*Structure of a Sperm CellOnly flagellum in human bodyEnzymes used to penetrate the egg during fertilizationMitochondriaFigure from: Holes Human A&P, 12th edition, 2010

*Male Internal Accessory OrgansFigure from: Holes Human A&P, 12th edition, 2010

*Epididymis- Maintains fluid produced in the seminiferous tubules - Recycles damaged sperm and cellular debris - Store and protects sperm, and aids in their maturationFigures from: Martini, Anatomy & Physiology, Prentice Hall, 2001Takes about 2 weeks for sperm to travel through the epididymis

*Ductus (Vas) Deferens muscular tube about 45 cm long; transports sperm ( can store sperm for several months) extends from epididymis to ejaculatory ductFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Seminal Vesicles attached to ductus deferens near base of bladder

secretes alkaline fluid (60% of the volume of semen)

secretes fructose, prostaglandins, and proseminogelin

begins capacitation of sperm

contents empty into ejaculatory ductFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Prostate Gland surrounds beginning of urethra ducts of gland open into urethra secretes a thin, milky, slightly acidic fluid (20-30% of semen volume) secretion enhances fluid mobility contains seminalplasmin secretes Prostate-specific Antigen (PSA) composed of tubular glands in connective tissue also contains smooth muscleFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Clinical Application - Prostate Enlargement benign prostatic hyperplasia occurs in most men over 50

BPH causes frequent urination

risk factors include a fatty diet, having had a vasectomy(?), or exposure to certain environmental factors

treatments include surgical removal drugs insertion of balloon into urethra freezing of tumor insertion of stent between lobes of prostate to relieve pressure on urethra

*Bulbourethral (Cowpers) Gland inferior to the prostate gland

secretes thick, alkaline mucus - helps lubricate the tip of the penis (glans) and neutralize any urinary acids in urethra

fluid released in response to sexual stimulationFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Semen sperm cells

secretions of seminal vesicles, prostate gland, and bulbourethral glands (seminal fluid)

slightly alkaline (offsets acidity of reproductive tract)

prostaglandins (stimulates contraction in reproductive tract)

nutrients

enzymes (protease, seminalplasmin, fibrinolysin)

20-100 million sperm cells per milliliter

usually about 2-5 ml of fluid per ejaculate

*Male External Reproductive OrgansFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

*Scrotum pouch of skin and subcutaneous tissue dartos muscle smooth muscle in dermis; contracts to cause wrinkling of the scrotum (traps heat) medial septum divides scrotum into two chambers each chamber lined with a serous membrane each chamber houses a testis and epididymisFigure from: Martini, Anatomy & Physiology, Prentice Hall, 2001Cremaster muscle can retract testes

*PenisConnection of penis to body wall (root)

*PenisFigure from: Holes Human A&P, 12th edition, 2010

*PenisPreputial glands in the prepuce (foreskin) produce a waxy material called smegma. This can be a source of bacterial growth if hygiene is poor.Circumcision is the surgical removal of the prepuce.Figure from: Holes Human A&P, 12th edition, 2010

*Erection, Orgasm, and Ejaculation Erection parasympathetic nerve impulses blood accumulates in erectile tissuesOrgasm culmination of sexual stimulation accompanied by emission and ejaculationEmission and Ejaculation emission is the movement of semen into urethra ejaculation is the movement of semen out of the urethra largely dependent on sympathetic nerve impulses

*Mechanism of Penile ErectionBulbospongiosus m.Ischiocavernosus m.

*How Does Viagra (Sildenafil) Work?GTPcGMPGMPSmooth muscle relaxation, dilation of blood vesselsGuanyl cyclasePhosphodiesterase 5 (PDE5)VIAGRANitric Oxide (NO)Parasympathetic stimulation(Required to start cascade)Erotic stimuli(Also Cialis, Levitra)Interior of smooth muscle cell

*Mechanism of Emission and EjaculationFigure from: Holes Human A&P, 12th edition, 2010

*Hormonal Control of Male Reproductive Functions hypothalamus controls maturation of sperm cells and development of male secondary sex characteristics

negative feedback controls concentration of testosteroneFigure from: Holes Human A&P, 12th edition, 2010

*Actions of Testosterone increased growth of body hair

sometimes decreased growth of scalp hair

enlargement of larynx and thickening of vocal cords

thickening of skin

increased muscular growth

thickening and strengthening of the bonesKnow these actions

*ReviewSpermatogenesisSpermatogonia, 1o spermatocyte, 2o spermatocyte, spermatid, spermatozoanIs a result of meiotic divisionUnder the control of FSHIs guided and regulated by sustentacular cellsProduces 4 haploid gametes (spermatozoa)SpermatozoaHead, midpiece, and tailAcrosomal cap enzymes use for fertilizationNon-motile when produced must undergo capacitation

*ReviewMale Accessory OrgansEpididymisMaintains fluid produced in the seminiferous tubulesRecycles damaged sperm and cellular debrisStore and protects sperm, and aids in their maturationVas (ductus) deferens muscular tube for sperm transport and storageSeminal vesicleAlkaline fluid with fructose, prostaglandin, and fibrinogenAbout 60% of semen volume in ejaculate

*ReviewMale Accessory Organs (contd)Prostate glandThin, milky fluid20-30% of semen volume in ejaculateSeminalplasminBulbourethral glandsCowpers glandsThick, mucus-like substanceLubricates glans of penisNeutralizes acids in urethra

*ReviewSemenSperm + seminal fluid20-100 million sperm per ml in ejaculate (2-5 ml)Contains enzymesExternal Reproductive OrgansScrotumContains and separates testesCremaster and dartos muscles regulate temperature of testesPenisRoot, body (shaft), and glans; prepuce (foreskin)Erectile tissues (c. cavernosum, c. spongiosum)Urethra (common pathway for urine and sperm)Prepuce

*ReviewErection, orgasm, emission, and ejaculationErectionFilling of erectile tissues with blood; venous drainage is blockedControlled by parasympathetic NS (nitric oxide)Orgasm - highly pleasurable culmination of the sexual experience, accompanied by emission and ejaculationEmission - movement of semen into urethraEjaculation - movement of semen out of urethraOrgasm, emission, and ejaculation are controlled by the sympathetic NS

*ReviewHormonal control of male reproductive systemFSHMeiosis in primary spermatocytesSecretion of inhibin by sustentacular cellsLH (ICSH)Secretion of androgens (testosterone) by interstitial cellsLevels of FSH and LH inhibit release of GnRH and FSH/LHEffects of androgens

*Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1]Slides 16 38; 50 min [Lecture 2]118 min (38 slides plus review of course Web sites and syllabus)*In order for sexual reproduction to take place, we need: 1) mobile cells, 2) cells that are nutrient laden. These two things are impractical to combine into one cell, so males have sperm (DNA with propellers!!), and females have large, nutrient-laden eggs as their sex cells (gametes).*Major differences between mitosis and meiosis: 1) mitosis produces identical daughter cells, meiosis produces cells with recombined DNA; 2) daughter cells in mitosis have a diploid number of chromosomes whereas in meiosis gametes contain the haploid chromosome number; 3) two daughter cells are produced as a result of mitosis, whereas four cells are produced after meiosis.*It takes about 75 days for a spermatogonium to become mature spermatazoon.*Young men produce about 300,000 sperm per MINUTE, or about 4 million sperm cells per day. *Newly made sperm contain a thick layer of cholesterol over their acrosomal cap. This prevents premature release of enzymes and damage to male reproductive system. (This cholesterol is later leached away by fluids in the female reproductive tract. This allows more Ca2+ to enter the sperm and causes more powerful lashing of the flagellum.) This process is capacitation.*Sperm count below about 20-25 mil/ml is associated with infertility.