Chapter 27
Lecture
Outline
See PowerPoint Image Slides
for all figures and tables pre-inserted into
PowerPoint without notes.
27-1
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Male Reproductive System
•
•
•
•
•
Sexual reproduction and development
Male reproductive anatomy
Puberty and climacteric
Sperm and semen
Male sexual response
27-2
Essence of Sex
• Reproduction
– one property of a living thing
– great variety of methods
• Sexual reproduction
– each offspring has 2 parents and receives
genetic material from both
– provides genetic diversity
– foundation for survival and evolution of
species
27-3
Two Sexes
• Male and female gametes (sex cells)
combine their genes to form a fertilized
egg (zygote)
– one gamete has motility (sperm)
• parent producing sperm considered male
• has Y chromosome
– other gamete (egg or ovum) contains nutrients
for developing zygote
• parent producing eggs considered female
• in mammals female also provides shelter for
developing fetus (uterus and placenta)
27-4
Overview of Reproductive System
• Primary sex organs
– produce gametes (testes or ovaries)
• Secondary sex organs
– male - ducts, glands, penis deliver sperm cells
– female - uterine tubes, uterus and vagina
receive sperm and nourish developing fetus
• Secondary sex characteristics
– develop at puberty to attract a mate
• pubic, axillary and facial hair, scent glands, body
morphology and low-pitched voice in males
27-5
Role of Sex Chromosomes
• Our cells contain 23 pairs of chromosomes
– 22 pairs of autosomes
– 1 pair of sex chromosomes (XY males: XX females)
• males produce 50% Y carrying sperm and 50% X carrying
• all eggs carry the X chromosome
• Sex of child
determined by type
of sperm that fertilizes
mother’s egg
27-6
Hormones and Sex Differentiation
• Gonads begin to develop at 6 weeks
• 2 sets of ducts
– mesonephric ducts develop into male reproductive
system or
– paramesonephric ducts (müllerian ducts) develop into
female reproductive tract
• SRY gene (Sex-determining Region of Y gene)
– in males, codes for a protein that causes development
of testes 
• secrete testosterone
• secrete müllerian-inhibiting factor  degenerates
paramesonephric ducts
• Female development occurs in absence of
hormones
27-7
Embryonic Development
• External genitals of both sexes begin as a
– genital tubercle
• becomes glans of penis or
• clitoris
– pair of urogenital folds
• enclose urethra of male or
• form labia minora
– a pair of labioscrotal folds
• scrotum or
• labia majora
27-8
Embryonic Development
27-9
Androgen-Insensitivity Syndrome
• Genetically male (XY)
• Testosterone secreted
– target cells lack receptors for hormone
• No masculizing effects occur
27-10
Development of External Genitalia
27-11
Development of External Genitalia
• All 8 week old fetuses have same 3
structures
– by end of week 9, begin to show sexual
differentiation
– distinctly male or female by end of week 12
27-12
Descent of Testes
• Begin development near kidney
– gubernaculum (cordlike structure containing muscle)
extends from gonad to abdominopelvic floor
• it shortens, guides testes to scrotum
– vaginal process
• peritoneum develops fold; extends into scrotum
– create inguinal canal, pass through abdominal wall
• Descent begins in weeks 6-10, finished by 28
– 3% born with undescended testes (cryptorchidism)
• Location outside pelvic cavity essential for low
temperatures needed for sperm production
27-13
Descent of Testis
27-14
Boundaries of Male Perineum
27-15
Male Reproductive System
27-16
Scrotum
• Pouch holding testes
– divided into 2 compartments by median
septum
• Spermatic cord travels up from scrotum
to pass through inguinal canal
– contains testicular artery, vein, nerve and
lymphatics
27-17
Testicular Thermoregulation
• Sperm not produced at core body
temperature
– cremaster muscle = pulls testes close to body
– dartos muscle
• wrinkles skin reducing surface area of scrotum
• lifts it upwards
– pampiniform plexus = veins ascending near
testicular artery
• countercurrent heat exchanger cools arterial blood
entering testis
27-18
Male Inguinal and Scrotal Region
27-19
Countercurrent Heat Exchanger
27-20
Testes
• Oval organ, 4 cm long x 2.5 cm in diameter
– covered anteriorly by tunica vaginalis
• Tunica albuginea
– white fibrous capsule on testes
• Septa divide testes into compartments
containing seminiferous tubules
– each tubule lined with a thick germinal
epithelium for sperm
– interstitial cells between tubules - testosterone
• Sustentacular cells
– promote sperm cell development
27-21
Blood-testis barrier
• Formed by tight junctions between
sustentacular cells -- separating sperm
from immune system
27-22
Testis and Associated Structures
• Seminiferous tubules drain into rete testis
• Low BP of testicular artery results in poor O2
supply
– sperm develop very large mitochondria helping them
survive hypoxic environment of female reproductive
tract
• Testicular veins drain to inferior vena cava
27-23
Spermatic Ducts
• Efferent ductules
– 12 small ciliated ducts collecting sperm from rete
testes and transporting it to epididymis
• Epididymis (head, body and tail)
– 6 m long coiled duct adhering to posterior of testis
– site of sperm maturation and storage (fertile for 60
days)
• Ductus deferens (peristalsis during orgasm)
– muscular tube 45 cm long passing up from scrotum
through inguinal canal to posterior surface of bladder
• Ejaculatory duct
– 2 cm duct formed from ductus deferens and seminal
vesicle and passing through prostate to empty into
27-24
urethra
Male Duct System
27-25
Male Urethra
• Regions: prostatic, membranous and
penile --- totals 20 cm long
27-26
Accessory Glands
• Seminal vesicles
– posterior to bladder
– empty into ejaculatory duct
• Prostate gland
– below bladder, surrounds
urethra and ejaculatory
duct
– 2 x 4 x 3 cm
• Bulbourethral glands
– near bulb of penis
– empty into penile urethra
– lubricating fluid
27-27
Penis
• Internal root, shaft, and glans
– external portion 4 in. long when flaccid
– skin over shaft loosely attached allows
expansion
• extends over glans as prepuce (foreskin)
• 3 cylindrical bodies of erectile tissue
– corpus spongiosum along ventral side of
penis
• encloses penile urethra
• ends as a dilated bulb ensheathed
by bulbospongiosus muscle
– corpora cavernosa
• diverge like arms of a Y
• each crus attaches to pubic arch
covered with ischiocavernosus muscle
27-28
Anatomy of Penis
Fig. 27.12 a and b
27-29
Puberty and Climacteric
• Reproductive system remains dormant for
years after birth
– surge of pituitary gonadotropins begins
development
• 10-12 in most boys; 8-10 in most girls
• Puberty
– period from onset of gonadotropin secretion
until first menstrual period or first ejaculation
of viable sperm
• Adolescence
– ends when person attains full adult height
27-30
Brain-Testicular Axis
• Hypothalamus produces GnRH
• Stimulates anterior pituitary (gonadotrope
cells) to secrete
– LH
• stimulates interstitial cells to produce testosterone
– FSH
• stimulates sustentacular cells to secrete androgenbinding protein that interacts with testosterone to
stimulate spermatogenesis
27-31
Other Effects of Testosterone
• Enlargement of secondary sexual organs
– penis, testes, scrotum, ducts, glands and
muscle mass enlarge
– hair, scent and sebaceous glands develop
– stimulates erythropoiesis and libido
• During adulthood, testosterone sustains
libido, spermatogenesis and reproductive
tract
27-32
Hormones and Brain-Testicular Axis
27-33
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
• Rise in FSH and LH secretion after age 50
produces male climacteric (menopause)
– mood changes, hot flashes and “illusions of
suffocation”
• Erectile dysfunction
– 20% of men in 60s; 50% of those in 80s
27-34
Mitosis and Meiosis
• Mitosis produces two genetically identical
daughter cells (for tissue repair, embryonic
growth)
• Meiosis produces gametes
– for sexual reproduction
• keeps chromosome number constant from
generation to generation after fertilization
– 2 cell divisions (only one replication of DNA)
• meiosis I separates homologous chromosome
pairs into 2 haploid cells
• meiosis II separates duplicated sister chromatids
into 4 haploid cells
27-35
Meiosis
27-36
Spermatogenesis
• Spermatogonia produce 2 kinds of daughter cells
– type A remain outside blood-testis
barrier and produce more
daughter cells until death
– type B differentiate into
primary spermatocytes
• cells must pass through
BTB to move inward
toward lumen - new tight
junctions form behind
these cells
• meiosis I  2 secondary
spermatocytes
• meiosis II  4 spermatids
27-37
Spermatogenesis
• Blood-testis barrier is formed by tight
junctions between and basement
membrane under sustentacular cells.
27-38
Spermiogenesis
• Changes that transform spermatids into
spermatozoa
– discarding excess cytoplasm and growing
tails
27-39
Spermatozoon
• Head is pear-shaped front end
– 4 to 5 microns long structure containing the nucleus,
acrosome and basal body of the tail flagella
• nucleus contains haploid set of chromosomes
• acrosome contains enzymes that penetrate the egg
• basal body
• Tail is divided into 3 regions
– midpiece contains mitochondria around axoneme of
the flagella (produce ATP for flagellar movement)
– principal piece is axoneme surrounded by fibers
– endpiece is very narrow tip of flagella
27-40
Spermatozoon
27-41
Semen or Seminal Fluid
• 2-5 mL of fluid expelled during orgasm
– 60% seminal vesicle fluid, 30% prostatic, 10% sperm
• normal sperm count 50-120 million/mL
• Other components of semen
– fructose - energy for sperm motility
– fibrinogen causes clotting
• enzymes convert fibrinogen to fibrin
– fibrinolysin liquefies semen within 30 minutes
– prostaglandins stimulate female peristaltic
contractions
– spermine is a base stabilizing sperm pH at 7.2 to 7.6
27-42
Male Sexual Response - Anatomy
• Arteries of penis
– dorsal and deep arteries(brs. of internal pudendal)
– deep artery supplies lacunae of corpora cavernosa
• dilation fills lacunae causing an erection
– normal penile blood supply comes from dorsal a.
• Nerves of penis
– abundance of tactile, pressure and temperature
receptors
– dorsal nerve of penis and internal pudendal nerves
lead to integrating center in sacral spinal cord
– both autonomic and somatic motor fibers carry
impulses from integrating center to penis
27-43
Excitement and Plateau
• Excitement is characterized by
vasocongestion of genitals, myotonia, and
increases in heart rate, BP, and pulmonary
ventilation
• Initiated by many different erotic stimuli
• Erection of penis is due to parasympathetic
triggering of nitric oxide (NO) secretion
– dilation of deep arteries and filling of lacunae with
blood
• Erection is maintained during plateau phase
27-44
Sexual Response
• Parasympathetic signals produce an erection with direct
stimulation of penis or perineal organs
27-45
Orgasm and Ejaculation
• Climax (orgasm) is 15 second reaction that
includes the discharge of semen
(ejaculation)
• Ejaculation
– emission = sympathetic nervous system
propels sperm through ducts as glandular
secretions are added
– expulsion = semen in urethra activates
muscular contractions that lead to expulsion
• Ejaculation and orgasm are not the same
– can occur separately
27-46
Resolution
• 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 (10 minutes to few hours)
27-47
How Viagra Prolongs Erection
27-48