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Chapter 27
Lecture Outline
Male Reproductive System
• The Two Sexes
• essence of sexual reproduction is that it is biparental – offspring receive genes from two parents
– offspring not genetically identical to either one – we will die, but our genes will live on in a different container, our offspring • gametes (sex cells) produced by each parent
• zygote (fertilized egg) has combination of both parent’s genes
• Two Sexes
• male and female gametes (sex cells) combine their genes to form a zygote (fertilized egg )
– one gamete has motility, sperm (spermatozoon)
– other gamete, egg or (ovum) contains nutrients for developing embryo
– males have a copulatory organ (penis) for introducing his gametes into the female
– females have a copulatory organ (vagina) for receiving the sperm
• Overview of Reproductive System
• male reproductive system serves to produce sperm and introduce them into the female body
• female reproductive system produces eggs, receives sperm, provides for the union of the
gametes, harbors the fetus, and nourishes the offspring
• reproductive system consists of primary and secondary sex organs
– primary sex organs (gonads)
– secondary sex organs – organs other than the gonads that are necessary for
• male – system of ducts, glands, penis deliver sperm cells
• female - uterine tubes, uterus, and vagina receive sperm and harbor developing
• Overview of Reproductive System
• external genitalia – located in the perineum
– most are externally visible – except accessory glands of the female perineum • internal genitalia – located mainly in the pelvic cavity
– except tor testes and some associated ducts in the scrotum • secondary sex characteristics – features that further distinguish the sexes and play a role in
– develop at puberty to attract a mate
– both sexes
• pubic and axillary hair and their associated scent glands, and the pitch of the voice • facial hair, coarse and visible hair on the torso and limbs, relatively muscular – female
• distribution of body fat, breast enlargement, and relatively hairless appearance of the • Chromosomal Sex Determination
• our cells contain 23 pairs of chromosomes
– 22 pairs of autosomes – 1 pair of sex chromosomes (XY males: XX females) • males produce half Y carrying sperm and half X carrying sperm • all eggs carry the X chromosome • sex of child determined by type of sperm that fertilizes mother’s egg – X-carrying sperm fertilizes the egg – female – Y-carrying sperm fertilizes the egg - male • Prenatal Hormones and Sex Differentiation
• initially, a fetus is sexually undifferentiated as to which sex it will become
• gonads begin to develop at 5 or 6 weeks as gonadal ridges
• two sets of ducts adjacent to each gonadal ridge
– mesonephric ducts develop into male reproductive system
– paramesonephric ducts (müllerian ducts) develop into female reproductive tract
• SRY gene (sex-determining region of Y chromosome)
– in males, codes for a protein, testes-determining factor (TDF), that initiates development
• begin to secrete testosterone 8 to 9 weeks
• stimulates mesonephric ducts to develop into the male anatomy
• at same time the testes secrete müllerian-inhibiting factor causing degeneration of
• estrogen levels are always high in pregnancy
– if estrogen was the hormone that directed the female development, all fetuses would be • female development occurs in absence of androgen hormones
• Development of Reproductive Tracts
• Descent of Testes
• both male and female gonads initially develop high in the abdominal cavity near the kidneys, and
migrate into the pelvic cavity (ovaries) or scrotum (testes) – in the male, passes between the internal and external abdominal oblique muscles into the
– vaginal process – fold of the peritoneum that extends into the scrotum
– inguinal canal – pathway of low resistance through the groin created by gubernaculum
• most common site of herniation in boys and men – inguinal hernia
• Descent of Testes
• descent of the testes begins as early as 6 weeks
– in 7th month testes abruptly pass through the inguinal canal into the scrotum guided by the
• cryptorchidism – boys born with undescended testes
– occurs in about 3% of male births – most cases the testes descend during the first year of infancy • ovaries descend to lesser extent
– lodge on inferior brim of the lesser pelvis – gubernaculum becomes a pair of ligaments that supports the ovary and the uterus • Descent of Testis
• Male Reproductive System
• The Scrotum and Spermatic Cord
• Scrotum
• external genitalia of the male – scrotum and penis
– occupy the perineum – diamond-shaped area between the thighs
• bordered by the pubic symphysis, ischial tuberosities, and coccyx • scrotum – pouch of skin, muscle, and fibrous connective tissue containing the testes
– left testicle usually descends lower than the right so the two are not compressed against
– skin has sebaceous glands, sparse hair, rich sensory innervation, somewhat darker
– internal median septum divides scrotum into right and left compartments
– perineal raphae – medial seam located on the scrotum extending anteriorly along ventral
• Male Reproductive Anatomy
• Spermatic Cord
• scrotum has three mechanisms to regulate the temperature of the testes
– cremaster muscle – strips of the internal abdominal oblique muscle (skeletal muscle)
• in cold temperatures, contracts and draws testes upward toward body • in warm temperatures relaxes suspending testes further from the body – dartos muscle – subcutaneous layer of smooth muscle
• contracts when it is cold, wrinkling the scrotum, holding testes against warm body • reducing surface area of the scrotum and reducing heat loss – pampiniform plexus – an extensive network of veins from the testes that surround the
• countercurrent heat exchanger – without the pampiniform plexus, warm arterial
blood would heat the testis and inhibit sperm production • removes heat from the descending arterial blood • by the time it reaches the testis, the blood is 1.5° - 2.5° cooler • Countercurrent Heat Exchanger
• Scrotum and Spermatic Cord
• Testis and Associated Structures
• Testes
• testes (testicles) – combined endocrine and exocrine glands that produce sex hormones and
• oval and slightly flattened, 4 cm long x 2.5 cm in diameter – covered anteriorly and laterally by tunica vaginalis • tunica albuginea white fibrous capsule on testes
• connective tissue septa divides testes into 250 to 300 wedge-shaped lobules
• seminiferous tubules
– one to three in each lobule – each tubule lined with a thick germinal epithelium for sperm generation • interstitial (Leydig) cells between tubules produce testosterone
• sustentacular (Sertoli) cells in between germ cells
– protect the germ cells, and promote their development – germ cells depend on them for nutrients, waste removal, growth factors, and other needs • Testis and Associated Structures
• Blood-Testis Barrier (BTB)
• blood-testis barrier - formed by tight junctions between sustentacular cells
– separating sperm from immune system – prevents antibodies and other large molecules in the blood from getting to germ cells – germ cells are immunologically different from body cells and would be attacked by immune • Spermatic Ducts
• spermatic ducts from testis to the urethra
– efferent ductules
• about 12 small ciliated ducts collecting sperm from rete testes and transporting it to – duct of the epididymis (head, body and tail)
• site of sperm maturation and storage (fertile for 40 to 60 days) • contains a single 6 m long coiled duct adhering to posterior of testis • sperm mature as they travel through the duct • if not ejaculated, they disintegrate and epididymis reabsorbs them – ductus (vas) deferens
• muscular tube 45 cm long passing up from scrotum through inguinal canal to • duct widens behind the bladder and widens into the terminal ampulla
• duct ends by uniting with the duct of the seminal vesicle
• thick wall of smooth muscle well innervated by sympathetic nerve fibers
– ejaculatory duct
• 2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra
• Male Duct System
• Male Urethra
• 18 cm long male urethra is shared by the reproductive and urinary systems
• consists of three regions: prostatic, membranous, and spongy (penile) urethra
• Accessory Glands
• there are three sets of glands in the male reproductive system
– seminal vesicles
• pair of glands posterior to bladder • empties into ejaculatory duct • forms 60% of semen – prostate gland
• surrounds urethra and ejaculatory duct just inferior to the bladder • 30 to 50 compound tubuloacinar glands • empty through about 20 pores in the prostatic urethra • thin milky secretion forms 30% of semen – bulbourethral (Cowper) glands
• near bulb of penis • during sexual arousal, they produce a clear slippery fluid that lubricates the head of the penis in preparation for intercourse • protects the sperm by neutralizing the acidity of residual urine • Prostate Diseases
• benign prostatic hyperplasia (BPH) – noncancerous enlargement of the prostate
– compresses urethra and obstructs flow of urine – promotes bladder and kidney infections • prostate cancer
– second most common cancer in men after lung cancer
– tend to be near the periphery of the gland where they do not obstruct urine flow
– go unnoticed until they cause pain
– metastasized to nearby lymph nodes and then to the lungs and other organs
– digital rectal exam (DRE) – palpated through rectal wall to check for tumors
– diagnosed from elevated levels of serine protease (PSA) and acid phosphatase in the
• Penis
• penis serves to deposit semen in the vagina
– half of the penis is an internal root
– half is an externally visible shaft
– external portion 4 in. long when flaccid (nonerect)
– skin over shaft loosely attached allows expansion • extends over glans as prepuce (foreskin)
• removed by circumcision
• smegma – waxy secretion produced by the sebaceous glands in the glans and
• three cylindrical bodies of erectile tissue which fill with blood during sexual arousal and
account for its enlargement and erection – single corpus spongiosum along ventral side of penis
• encloses spongy (penile) urethra
• distal end enlarges and forms the glans penis
• proximal end ends as a dilated bulb ensheathed by bulbospongiosus muscle

– two corpora cavernosa
• diverge like arms of a Y
• each arm called a crus attaches the penis to pubic arch
• covered with ischiocavernosus muscle
• the three cylinders of erectile tissue are spongy – contain many blood sinuses called lacunae
– trabeculae – partitions between lacunae
• Anatomy of Penis
• Puberty and Climacteric
• reproductive system remains dormant for several years after birth
– 10-12 years in most boys and 8-10 years in most girls
– surge of pituitary gonadotropins awakens the reproductive system – onset of puberty
• adolescence – the period from the onset of gonadotropin secretion and reproductive
development until a person attains full adult height • puberty – first few years of adolescence, until the first menstrual period in girls or the first
– typically around age 12 in girls and age 13 in boys • Endocrine Control of Puberty
• testes secrete substantial amounts of testosterone in first trimester (3 months) of fetal
development in levels about as high as they are in midpuberty – then testes becomes dormant until puberty
– from puberty through adulthood, reproductive function is regulated by hormonal links
between the hypothalamus, pituitary gland, and the gonads
• as hypothalamus matures it produces gonadotropin-releasing hormone (GnRH)
– GnRH stimulates anterior pituitary cells (gonadotropes) to secrete:
• follicle stimulating hormone (FSH)
– stimulates sustentacular cells to secrete androgen-binding protein that
binds testosterone keeping it in the seminiferous tubule lumen to stimulate spermatogenesis and raising sperm count • luteinizing hormone (LH) sometimes called interstitial cell-stimulating hormone
– stimulates interstitial cells to produce testosterone
• Other Hormone Effects
• puberty
– enlargement of secondary sexual organs • penis, testes, scrotum, ducts, glands – testosterone stimulates a burst of generalized body growth • limbs elongate, muscle mass increases, and the larynx enlarges – erythropoiesis, basal metabolic rate, and increase in appetite
– pubic hair, scent and sebaceous glands develop in response to dihydrotestosterone (DHT)
– stimulates sperm production and libido (sex drive)
– testosterone sustains the male reproductive tract, sperm production, and libido
– inhibin from sustentacular cells suppresses FSH output from the pituitary reducing sperm
production without reducing LH and testosterone secretion • Hormones and Endocrine Control
• Aging and Sexual Function
• decline in testosterone secretion
– peak secretion at 7 mg/day at age 20 – declines to 1/5 of that by age 80 • decline in the number and activity of interstitial cells (testosterone) and sustentacular • rise in FSH and LH secretion after age 50 produces male climacteric (andropause)
– little or no effect to: – mood changes, hot flashes and “illusions of suffocation” • erectile dysfunction (impotence)– the inability to produce or maintain an erection sufficient for
– 20% of men in 60s to 50% of those in 80s • Meiosis
• Spermatogenesis
• Blood-Testis Barrier
• once the primary spermatocyte undergoes meiosis, it becomes genetically
different and needs to be protected from the immune system • the primary spermatocyte moves towards the lumen of the seminiferous tubule and a new tight junction between sustentacular cells forms behind it
• now protected by the blood-testis barrier closing behind it
• Histology of Testis
• Spermiogenesis
• spermiogenesis - changes that transform spermatids into spermatozoa
– discarding excess cytoplasm and growing tails • Spermatozoon
• Semen
• semen (seminal fluid) – fluid expelled during orgasm
• 2-5 mL of fluid expelled during ejaculation
– 60% seminal vesicle fluid, 30% prostatic fluid, and 10% sperm and spermatic duct • normal sperm count 50-120 million/mL
• lower than 20 to 25 million/mL – infertility
– prostate produces a thin, milky white fluid
• contains calcium, citrate, and phosphate ions • a clotting enzyme • protein-hydrolyzing enzyme called serine protease (prostate-specific antigen) – seminal vesicles contribute viscous yellowish fluid
• contains fructose and other carbohydrates, citrate, prostaglandins, and protein called proseminogelin
• Semen
– stickiness of semen promotes fertilization
• clotting enzyme from prostate activates proseminogelin
• converts it to a sticky fibrin-like protein – seminogelin
• entangles the sperm
• sticks to the inner wall of the vagina and cervix
• ensures that the semen does not drain back into the vagina
• promotes uptake of sperm-laden clots of semen into the uterus
• 20 to 30 minutes after ejaculation, serine protease from prostatic fluid breaks down
• sperm become active • prostaglandins thin the mucus of the cervix, stimulates peristaltic waves in uterus and – two requirements for sperm motility – elevated pH and an energy source
• prostatic fluid buffers vaginal acidity from 3.5 to 7.5 • seminal vesicles provide fructose and other sugars to the mitochondria • Male Sexual Response
• publication of research by William Masters and Virginia Johnson (1966)
– divided intercourse into four recognizable phases
• excitement
• plateau
• orgasm
• resolution
– led to therapy for sexual dysfunction – sexual intercourse is also known as coitus, coition, or copulation
• Anatomy of Male Sexual Response
• innervation of penis
– the glans has an abundance of tactile, pressure, and temperature receptors
– dorsal nerve of penis and internal pudendal nerves lead to integrating center in sacral
– both autonomic and somatic motor fibers carry impulses from integrating center to penis • sympathetics induce an erection in response to input from the special senses and
• parasympathetics induce an erection in response to direct stimulation of the penis
• Excitement and Plateau
• excitement phase is characterized by vasocongestion (swelling of the genitals with blood),
myotonia (muscle tension), and increases in heart rate, blood pressure, and pulmonary ventilation – bulbourethral glands secrete their fluid – initiated by a broad spectrum of erotic stimuli – erection of penis is due to parasympathetic triggering of nitric oxide (NO) secretion – causing dilation of deep arteries and filling of lacunae with blood – vasocongestion can also cause the testicles to be come 50% larger during excitement • plateau phase – the variables such as respiratory rate, heart rate, and blood pressure stay
– marked increased vasocongestion and myotonia – lasts for a few seconds or a few minutes before orgasm • Sexual Response
• parasympathetic signals produce an erection with direct stimulation of penis or perineal organs
• Orgasm and Ejaculation
• orgasm or climax – a short but intense reaction that is usually marked by the discharge of
– lasts 3 to 15 seconds – heart rate, blood pressure, and breathing greatly elevate • ejaculation occurs in two stages:
– emission - sympathetic nervous system stimulates peristalsis which propels sperm
through ducts as glandular secretions are added – expulsion - semen in urethra activates somatic and sympathetic reflexes that stimulate
muscular contractions that lead to expulsion • sympathetic reflex constricts internal urethral sphincter so urine cannot enter the urethra and semen can not enter the bladder • ejaculation and orgasm are not the same • Resolution
• resolution phase – body variables return to pre-excitement state
– sympathetic signals constrict internal pudendal artery and reduce blood flow to penis
– penis becomes soft and flaccid (detumescence)
– cardiovascular and respiratory responses return to normal
• refractory period – period following resolution in which it is usually impossible for a male to
– may last from 10 minutes to a few hours • How Viagra Prolongs Erection
• treatments - Viagra, Levitra, and Cialis
• sexual stimulation triggers nitric oxide secretion, which activates cGMP, which increases blood
– this drugs slow down the breakdown of cGMP by phosphodiesterase type 5 and prolongs
• Sexually Transmitted Diseases
• STDs have an incubation period in which the pathogen multiplies with no symptoms and a
communicable period in which the disease can be transmitted to others
• bacterial STDs
– chlamydia – may cause urethral discharge and testicular pain
– gonorrhea – pain and pus discharge – may result in sterility from pelvic inflammatory
– syphilis – hard lesions (chancres) at site of infection
• disappearance of chancres ends first stage • second stage is widespread pink rash • neurosyphilis is third stage with cardiovascular damage and brain lesions • viral STDs
– genital herpes – most common STD in US
– genital warts – warts on perineal region, cervix, anus
– hepatitis B and C – inflammatory liver disease

Source: http://www3.canyons.edu/faculty/golbertm/205/ChapterOutlines/Chapter27MaleReproductiveSystem.pdf