THE MALE
REPRODUCTIVE
SYSTEM
Learning objectives
• Outline the steps involved in spermatogenesis
• Describe the endocrine regulation of testicular
function: the role of the GnRH pulse generator,
FSH, LH, testosterone, and inhibin.
• Know the general structure of testosterone, and
describe its biosynthesis, transport, metabolism,
and actions.
• List the major target organs and cell types for
testosterone and other androgens.
• Describe the processes involved in regulation of
testosterone secretion
Which of the following is a correct statement about
the production of human sperm?
a. Spermatogonia undergo meiosis
b. Spermatogenesis occurs in the epididymis
c. Normally, 10 to 20 million sperm are produced
daily
d. FSH is required
e. Complete maturation of spermatozoa occurs in
about 1 month
OVERALL CONTROL OF ADULT MALE HORMONAL SECRETION
Leydig cells
• 20% of the adult testis is connective tissue
interspersed with Leydig cells.
• The function of the Leydig cells is synthesis
and secretion of testosterone , the male sex
steroid hormone.
• Testosterone has both local (paracrine) effects
and endocrine effects.
Functions of Sertoli Cells
• Provide nutrition for the development of germinal
cell into spermatozoa and conversion of spermatids
into sperms
• Production of Androgen-Binding Protein thereby
maintain high supply of androgen to the deveolping
germ cells
• Form Blood-Testes Barrier -prevents entry of toxin
• Foetal Sertoli cell produce MIS
• Produce Inhibin which inhibits FSH secretion
• Synthesize estrogen from testosterone by
aromatisation
Functions of the Sertoli cells in the seminiferous
tubules include
a. Secretion of FSH into the tubular lumen
b. Secretion of testosterone into the tubular
lumen
c. Maintenance of the blood-testis barrier
d. Synthesis of estrogen after puberty
e. Expression of surface LH receptors
Spermatogenesis
The process of sperm formation
Hormonal Factors That Stimulate
Spermatogenesis
1. Testosterone
2. Luteinizing hormone
3. Follicle-stimulating hormone
4. Estrogens
5. Growth hormone
STRUCTURE OF SEMINIFEROUS TUBULE
• The tight junctions between Sertoli cells divide the
lumen into a) Basal compartment
b) Luminal or adluminal compart.
• The spermatogonia are located in the basal
compartment
• The spermatocytes develop in the luminal
compartment within the cytoplasmic folds of the
Sertoli cells
The Seminiferous Tubules
Spermatogenesis
divided into three phases:
(1) Mitotic divisions of spermatogonia generate
the spermatocytes, which are destined to become
mature sperm;
(2) meiotic divisions of the spermatocytes, which
decrease the chromosome number and produce
haploid spermatids;
(3) spermiogenesis, in which spermatids are
transformed into mature sperm through the loss of
cytoplasm and the development of flagella
SPERMATOGENESIS- 1st STAGE
• Spermatogonia in the basal comparment of
Seminiferous tubules are called Type A
SPERMATOGONIA.
• These divide 4 times to form slightly more
differentiated cells called Type B
SPERMATOGONIA
SPERMATOGENESIS- 2nd STAGE
• MIGRATION: The Type B spermatogonia migrate
centrally across the tight junctions of the Sertoli cells
into the adluminal compartment
• Having penetrated the barrier they become
enfolded in the cytoplasmic processes of Sertoli cells.
• Further development occurs in association with the
Sertoli cells.
SPERMATOGENESIS- 3rd STAGE
• FORMATION OF PRIMARY SPERMATOCYTE- For a
period averaging 24 hrs the Type B spermatogonium
becomes progressively enlarged and modified to
form the PRIMARY SPERMATOCYTE
• At the end of 24 hrs in the primary spermatocyte the
DNA has replicated and each of the 46 chromosomes
has 2 chromatids bound together at the centromere
SPERMATOGENESIS-4th STAGE
• FIRST MEIOTIC DIVISION & FORMATION OF
SECONDARY SPERMATOCYTE- The Primary
spermatocyte undergoes the first meiotic division
• Each pair of chromosome separate so that each
secondary spermatocyte has 23 chromosomes
• Each of the 23 chromosomes has 2 chromatids
SPERMATOGENESIS- 5th STAGE
• SECOND MEIOTIC DIVISION & FORMATION OF
SPERMATIDS- within 2-3 days a second meiotic
division occurs so that 2 spermatids are formed
• Each spermatid contains 23 chromosomes having 1
chromatid each
• Half of the spermatids have X chromosomes and the
other half Y chromosomes
• Thus the eventual sperm which fertilizes the ovum
provides half the genetic material
SPERMATOGENESIS- 6th STAGE
• SPERMIOGENESIS: CONVERSION OF
SPERMATIDS TO MATURE SPERMATOZOON
• The spermatids have characteristics of epitheloid
cells
• Each spermatid elongates into a sperm composed of
a head & a tail.
• This change requires that the spermatid is in close
association with the Sertoli cell
SPERMIOGENESIS
• From a single spermatogonium 512
sperms are formed.
• The process takes 74 days on average
• The two testes of the adult form 120
million sperms each day
• STORAGE: A small quantity is stored in
the epididymis, but most in the vas
deferens & ampulla of the vas deferens
Maturation of Sperm in the
Epididymis
• Maturation of Sperm in the Epididymis -capability of
some motility
• Storage of Sperm-up to 120 million sperm each day;
They can remain stored, maintaining their fertility,
for at least a month; After ejaculation, the sperm
become fully motile, and they also become capable
of fertilizing the ovum, a process called maturation.
• Capacitation of the spermatozoa:-uterine and fallopian
tube fluids wash away the various inhibitory factors, it lose much of their
excess cholesterol, becomes much more permeable to calcium ions.
FACTORS AFFECTING SPERMATOGENESIS
• TEMPERATURE: Requires a temperature considerably
lower than interior of body. The testes are
maintained at a temperature of 32 c. They are kept
cool by a heat exchange in a counter-current fasion
between the spermatic arteries and veins.
FACTORS AFFECTING SPERMATOGENESIS
• REDUCED SPERMATOGENESIS AND SPERM COUNTEFFECT OF HIGH TEMPERATURE
1) CRYPTORCHIDISM-testes in the abdomen at high
temp
2)Tight cloth Binders cause degenration of tubular
walls & sterility results
3)Hot baths reduce count
4)Seasonal Variation: Sperm count greater in
winter regardless of scrotal temperature
FACTORS AFFECTING SPERMATOGENESIS
• INFECTION: Mumps causes bilateral orchitis
• STRICTURE OF THE GENITAL DUCT causes
degeneration of tubular epithelium
• GENETIC ABNORMALITIES: Klinefelter’s Syndrome
Adults with bilateral cryptorchidism
• Elevated temperatures
• FSH secretion is elevated, probably as a result
of decreased Sertoli cell production of
inhibins.
• Testosterone secretion by the Leydig cells of
cryptorchid testes also tends to be low, and as
a result, LH secretion of is elevated.
Q. Functions of the Sertoli cells in the
seminiferous tubules include
a. Secretion of FSH into the tubular lumen
b. Secretion of testosterone into the tubular
lumen
c. Maintenance of the blood-testis barrier
d. Synthesis of estrogen after puberty
e. Expression of surface LH receptors
Testosterone
Actions of Androgens on Target Tissues
Mediated by Testosterone
• Differentiation of epididymis,
vas deferens, and seminal
vesicles
• Deepening of voice
• Increased muscle mass
• Pubertal growth spurt
• Spermatogenesis
• Negative feedback on anterior
pituitary
• Libido
• Cessation of pubertal growth
spurt (epiphyseal closure)
Mediated by Dihydrotestosterone
• Differentiation of penis,
scrotum, and prostate
• Male hair pattern
• Male pattern baldness
• Sebaceous gland activity
• Growth of prostate
Age-related changes in LH and testosterone
secretion in the normal male
1. Fetal life
Normal male development requires the presence of
3 hormones:testosterone,dihydrotestosterone,
and the Müllerian inhibiting factor (MIH).
1. (hCG) + LH → Leydig cells → testosterone →
Wolffian ducts
2. testosterone → dihydrotestosterone →
urogenital sinus & genital organs
3. Sertoli cells → MIH → absence of female internal
structures
In order for male differentiation to occur during
embryonic development, testosterone must be
secreted from the testes. What stimulates the
secretion of testosterone during embryonic
development?
A) Luteinizing hormone from the maternal pituitary
gland
B) Human chorionic gonadotropin
C) Inhibin from the corpus luteum
D) Gonadotropin-releasing hormone from the
embryo’s hypothalamus
• Wolffian ducts differentiate into the majority
of male internal structures; namely,
epididymis, vasa deferentia, and seminal
vesicles.
• Dihydrotestosterone induces the urogenital
sinus and genital tubercle to differentiate into
the external scrotum, penis, and prostate
gland.
2. Childhood
Within a few months after birth, LH and testosterone
drop to low levels and remain low until puberty. The
cause of this prolonged quiescence of reproductive
hormone secretion during childhood is not known.
Interestingly, LH secretion remains low in spite of low
testosterone.
3. Puberty
Near the onset of puberty, the amplitude of the LH pulses
becomes greater, driving the mean level of LH higher.
Early in puberty, this potentiation of the LH pulses is
especially pronounced during sleep. This increased LH
stimulates theLeydig cells to again secrete
testosterone.
4. Adult
During adulthood, LH secretion drives testosterone
secretion. Thus, it is not surprising that the relative
levels of the two hormones parallel one another.
5. Aging adult
Testosterone and inhibin secretions decrease with age.
Men in their seventies generally secrete only 60–70%
as much testosterone as do men in their twenties.
Nevertheless, there is no abrupt decrease in testosterone
secretion in men that parallels the relatively abrupt
decrease in estrogen secretion that women experience
at menopause. The loss of feedback will cause an
increase in LH and FSH secretion.
In order for male differentiation to occur during
embryonic development, testosterone must be
secreted from the testes. What stimulates the
secretion of testosterone during embryonic
development?
A) Luteinizing hormone from the maternal
pituitary gland
B) Human chorionic gonadotropin
C) Inhibin from the corpus luteum
D) Gonadotropin-releasing hormone from the
embryo’s hypothalamus
Erection
• Erection is caused by dilation of the blood vessels (a
parasympathetic response) in the erectile tissue of the
penis (the corpora- and ischiocavernous sinuses).
• This dilation increases the inflow of blood so much that
the penile veins get compressed between the engorged
cavernous spaces and the Buck’s and dartos fasciae.
• As a result,for a brief period, inflow of blood to the
penis exceeds outflow.
• Mediators that remove the chronic state of
vasoconstriction are probably vasoactive intestinal
peptide (VIP) and/or nitric oxide (NO). Acetylcholine
may also be involved.
Emission
• Emission is the movement of semen from the
epididymis, vasa deferentia, seminal vesicles, and
prostate to the ejaculatory ducts.
• The movement is mediated by sympathetic
(thoracolumbar) adrenergic transmitters.
• Simultaneously with emission, there is also a
sympathetic adrenergic-mediated contraction of
the internal sphincter of the bladder, which
prevents retrograde ejaculation of semen into the
bladder.
• Destruction of this sphincter by prostatectomy
often results in retrograde ejaculation.
Ejaculation
• Ejaculation is caused by the rhythmic contraction
of the bulbospongiosus and the ischiocavernous
muscles.
• Contraction of these striated muscles that are
innervated by somatic motor nerves causes the
semen to exit rapidly in the direction of least
resistance, i.e., outwardly through the urethra.
• Ejaculation ,is mediated by somatic motor
efferents.
Consequences of deficient testosterone
production
• During second to third month of gestation -ambiguity in the male genitalia and male
pseudohermaphrodism.
• third trimester --leads to problems in testicular
descent (cryptorchidism) along with micropenis.
• Puberty-- to poor secondary sexual development
and overall eunuchoid features.
• Postpubertal --decreased libido, erectile
dysfunction, decrease in facial and body hair
growth, low energy, and infertility
Hormonal Changes in Specific Altered States
Spermatogenesis is regulated by a negative feedback
control system in which follicle-stimulating hormone
(FSH) stimulates the steps in sperm cell formation.
What is the negative feedback signal associated with
sperm cell production that inhibits pituitary formation
of FSH?
A) Testosterone
B) Inhibin
C) Estrogen
D) Luteinizing hormone
Estrogen is required for normal reproductive
function in the male. Where is the principal
site of estrogen synthesis in the male?
A) Leydig cells
B) Osteoblasts
C) Liver cells
D) Prostate cells
A man suffers from a disease that destroyed
only the motor neurons of the spinal cord
below the thoracic region. Which aspect of
sexual function would not be possible?
A) Arousal
B) Erection
C) Lubrication
D) Ejaculation
A “birth control” compound for men has been
sought for several decades. Which of the
following would provide effective sterility?
A) Substance that mimics the actions of
luteinizing hormone
B) Substance that blocks the actions of inhibin
C) Substance that blocks the actions of follicle
stimulating hormone
D) Substance that mimics the actions of
gonadotropin releasing hormone
A man is taking a number of medications, one of
which appears to be interfering with the emission
phase of the sexual act. Which of the following medications
could cause this problem?
A) A medication that prolongs the duration of action
of nitric oxide
B) A medication that blocks the smooth muscle receptors
for nitric oxide
C) A medication that increases the release of nitric
oxide
D) A testosterone-like androgen compound
E) An inhibitor of beta-adrenergic nervous system
receptors
Following ejaculation, arterial blood flow into the
corpora cavernosa decreases back to the normal
resting level resulting in the flaccid state. What is the
best explanation for this decrease in blood flow?
A) Systemic arterial pressure decreases due to absence
of sexual stimulation
B) The level of sympathetic stimulation to the arterioles
supplying the corpora cavernosa decreases
C) Resistance of the arterioles supplying the corpora
cavernosa increases
D) Formation of nitric oxide in the endothelial cells of
the arterioles supplying the corpora cavernosa is
stimulated by the increase in parasympathetic
nervous system activity
E) Resistance of the venules draining the sinuses of the
corpora cavernosa increases
Men who take large doses of testosterone-like androgenic
steroids for long periods are sterile in the reproductive
sense of the word. What is the explanation for
this finding?
A) High levels of androgens bind to testosterone receptors in
the Sertoli cells, resulting in overstimulation of inhibin
formation
B) Overstimulation of sperm cell production results in the
formation of defective sperm cells
C) High levels of androgen compounds inhibit the secretion of
gonadotropin-releasing hormone by the hypothalamus,
resulting in the inhibition of luteinizing hormone and folliclestimulating hormone release by the anterior pituitary
D) High levels of androgen compounds produce hypertrophic
dysfunction of the prostate gland
Which of the following decreases the resistance
in the arteries leading to the sinuses of the
penis?
A) Stimulation of the sympathetic nerves
innervating the arteries
B) Nitric oxide
C) Inhibition of activity of the parasympathetic
nerves leading to the arteries
D) All of the above