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
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 (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 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
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 - changes that transform spermatids into spermatozoa
– discarding excess cytoplasm and growing tails • Spermatozoon
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
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
– 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


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