Chapter 12—Male
Reproductive System
12-1
Said an ovum one night
to a sperm, “You’re a
very attractive young
germ.
Come join me, my sweet,
let our nuclei meet
And in nine months we’ll
both come to term.”
--Isaac Asimov
12-2
Ch. 12-- Study Guide
1. Critically read:
– (A) pages pp. 239-247 right before Sexual
Differentiation section;
– (B) Negative feedback regulators (pp. 254-255)
right before prepuberty subsection
2. Comprehend Terminology (the text in
bold/italic)
3. Study and understand the text and
corresponding figures.
12-3
12.1. Morphology of the
testes— Leydig cells and
seminiferous tubules
12-4
§ Testes (Fig. 12.2, x)-A
Dimension-- Oval organ; 3 cm (anterior to
posterior) x 2.5 cm (wide) x 4 cm (long)
Each testis is surrounded by two tunics
(C.T.): (From outermost and moving in)
1.Its anterior and lateral surfaces are
covered by tunica vaginalis
2.Tunica albuginea– testis itself has a
white fibrous capsule
12-5


12-6
§ Testicular Thermoregulation
• Sperm cannot be produced at core body
temperature (too warm; 37 degrees Celsius):
– Pampiniform plexus = near testicular artery,
a network of veins– forming countercurrent
heat exchanger that cools arterial blood entering
testis by 1-2 degree Celsius (Fig. x, y)
• When too cold: muscle contraction to:
– Pull testes close to body
– Contract and scrotum becomes taut
– wrinkles skin reducing surface area of scrotum
12-7
12-8
12-9
§ Testes (Fig. 12.1, 12.4)-B
3. Septa divide testes into 250-300 wedgeshaped lobules containing seminiferous
tubules (where sperm are produced);
each tubule lined with a thick germinal
epithelium:
– Several layers of germ cells for sperm
production
– Tall Sertoli (sustentacular) cells;
function?
4. Between the seminiferous tubules are
interstitial (Leydig) cells, the source12-10
of testosterone
See next slide
for details of
germ and
sustentacular
cells
12-11
Lumen of seminiferous tubule
Stages of
sperm
maturation: 
Spermatozoon
Tight
junctions
--see next
slide
Sertoli
cell
Spermatids
Secondary
spermatocyte
Primary
spermatocyte
Spermatogonium
12-12
12.1. Morphology of the
testes— Spermatogenesis
12-13
§ Spermatogenesis--A
1. Def. of spermatogenesis– The
production of sperm cells through a
series of mitotic and meiotic cell
divisions
• Location?
• How long does it take?
• Microscopic examination– two important
cell types (see next slide)
12-14
§ Spermatogenesis--B
2. Two important cell types in
seminiferous tubules
A. Germ cells–
• In various stages of sperm development,
such as spermatogonia, primary
spermatocytes, secondary
spermatocytes
B. Sustentacular (Sertoli) cells– these
cells provide crucial support for
spermatogenesis
Figure x
12-15
12-16
§ Spermatogenesis--C
3.Three major stages—
A. Mitotic proliferation—
• Spermatogonia located in the outermost
layer of the seminiferous tubule, outside the
blood-testis barrier (BTB)
• One of the daughter cells (Type A
spermatogonium) remain at the outer edge of
the tubule; importance?
• The other daughter cell (Type B
spermatogonium) starts moving toward
lumen forming 4 identical primary
12-17
spermatocytes (2N)
§ Spermatogenesis--D
B. Meiosis—
• Each primary spermatocyte (2N) must pass
through BTB (tight junction) and ultimately
yield 4 spermatids (1N)
C. Spermiogenesis—
• Spermatids become extremely
specialized and motile spermatozoa
• Sperm travel lightly
Figure w, x, y, z
12-18
A
B
Meiosis
C
12-19
Spermatogenesis
Stages:
Spermatogonia
Mitosis
Primary
spermatocyte
First meiotic
division
Meiosis Secondary
spermatocyte
Second meiotic
division
Spermiogenesis
Chromosomes:
One daughter cell remains
at the outer edge of the
seminiferous tubule to
maintain the germ cell line
One daughter cell moves
toward the lumen to
produce spermatozoa
46; 2n
(diploid number;
single strands)
46; 2n
(diploid number;
single strands)
46; 2n
(diploid number;
doubled strands)
23; n
(haploid number;
double strands)
Spermatids
23; n
(haploid number;
single strands)
Spermatozoa
23; n
(haploid number;
Single strands)
12-20
Figure 27.16
12-21
12.1. Morphology of the
testes— Male
reproductive tract
12-22
§ Sperm’s journey (male reproductive tract)
1. Testes– sperm-producing organs;
inside the scrotum (skin-covered sac)
2. Routes (spermatic ducts) the sperm
travel: A-Testes  B-Efferent ductules
 C-Epididymis  D-Ductus deferens
 E-Ejaculatory duct  F-Urethra 
Exterior
Fig. x
12-23
Anterior/posterior view?
2. Prostate gland
Urinary bladder
Ureter
1. Seminal
vesicle
3.
Bulbourethral
gland
E
F
Penis
D
C
B
Glans penis
A
12-24
12.2. control of testicular
function— Leydig cells
12-25
§ Leydig cells
1. Principal role of Leydig cells– synthesize
testosterone (& estrogen) in response to LH
2. In the fetus-- initially Leydig cells depend
on chorionic gonadotropin; later on LH
3. After birth– Leydig cells regress and die
until puberty
4. Initial steps of testosterone formation–
similar to adrenal cortex; from cholesterol to
pregnenolone
5. Four other enzymes convert pregnenolone
(21 C) to testosterone (19 C) (Fig. 12.5) 12-26
Pregnenolone
Testosterone
12-27
§ Germinal epithelium (Sertoli cells)
1. Principal role of germinal epithelium
(Sertoli cells)– produce sperm
2. Sertoli cells– only cells known to express
FSH receptors in human males; also have
testosterone receptors
3. FSH, LH, and testosterone all play vital
roles in spermatogenesis. How so for LH
and testosterone?
Fig. 12.6
12-28
CREB– cyclic AMP response
element binding protein
FSH
LH
Sertoli cell
Leydig
cell
12-29
12.3. Testosterone
12-30
§ Secretion and metabolism of T
1. Testosterone (T) is the principal androgen
secreted by the mature testis. In that 5% is from
adrenal cortex.
2. Aging– no sharp drop in T (unlike estrogen in the
postmenopausal woman)
3. In blood 98% of T binds to binding proteins —
albumin, sex hormone-binding globulin (SHBG
also called TeBG; having higher affinity for T), and
ABP (androgen binding protein) in Sertoli cells
4. The other 2% of T can diffuse out of the blood
5. Liver is principal site of degradation of T; T also
can convert to other steroids (Fig. 12.7)
12-31
12-32
§ Mechanism of action by T
1. Nuclear receptors-- Testosterone (T) often
converts to 5alpha-dihydrotestosterone before
binding to their nuclear receptors (Fig. 12.8)
2. T also may bind to membrane receptors-either directly or through the bind of the sex
hormone binding globulin
12-33
12-34
§ Effects of testosterone
1. Testosterone promotes -- growth, differentiation,
and function of accessory organs of reproduction.
2. Maintenance of normal reproductive function
in the adult depends on continued T secretion.
3. T stimulates transport and delivery of sperm
4. On sexual characteristics– during early
adolescence, T stimulates growth of pubic hair,
axillary, and facial hair; lowers the pitch of the
voice
5. T stimulates secretion of the hormone
erythropoietin; T increases sexual drive
(libido) in both men and women .
12-35
12.4. Negative feedback
regulators
12-36
§ hypothalamus-pituitary-testis
1. Hypothalamus GnRH– stimulates secretion of
both LH and FSH
2. Testosterone, which is secreted in response to
LH, acts as a feedback regulator of LH.
3. FSH stimulates the Sertoli cells to synthesize
and secrete inhibin (glycoprotein), which
regulates FSH secretion.
Fig. 12. 17
12-37
Stimulation
Inhibition
Stimulation
12-38