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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
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