3. 27-3
Overview of Reproductive System
• Primary sex organs
– produce gametes (testes or ovaries)
• Secondary sex organs – organs other than gonads that
are necessary for reproduction
– male - ducts, glands, penis deliver sperm cells
– female - uterine tubes, uterus and vagina receive sperm
and nourish developing fetus
• Secondary sex characteristics
– Features developed at puberty to attract a mate
• pubic, axillary and facial hair, scent glands, body morphology and
voice changes, in female its distribution of body fat, breast
development, flare of hips, & relatively hairless appearance.
4. 27-4
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 sperm;
• all eggs carry the X chromosome
• Sex of child determined by type of sperm that
fertilizes mother’s egg.
5. 27-5
Androgen-Insensitivity Syndrome
• Genetically male (XY)
• Testosterone secreted
– target cells lack receptors for hormone
• No masculizing effects occur
• External genitalia develop as female, all secondary
characteristics form.
• No ovaries, uterus present.
• Gonadectomy, hormone replacment therapy.
7. Prenatal hormones & Sexual differentation
27-7
Sexual determination depends upon the interaction of
genetics and the hormones produced by the mother
and the fetus.
Up to a point a fetus is sexually undifferentiated
(“noncommittal”).
5-6 weeks the gonads begin to develop as gonadal
ridges, along the side of the primative kidneys
(mesonephros).
8. Prenatal hormones & Sexual differentation
27-8
Adjacent to each ridge are two ducts:
1. mesonephric (wolffian) duct
2. paramesonephric (mullerian) duct
In males: mesonephric duct develops into the
reproductive tract and the paramesonephric duct
degenerates.
In females: the paramesonephric duct develops into
the reproductive tract and the mesonephric duct
degenerates.
10. Prenatal hormones & Sexual differentation
WHY does this happen?
The Y chromosome contain a gene called the SRY
(sex-determining region of the Y) that codes for a
protein called TDF (testis-determining factor).
TDF interacts with genes on other chromosomes,
including the X for androgen receptors, thus
initiating the development of male anatomy.
Testis develop by 8-9 weeks secreting testosterone,
thus stimulating the mesonephric ducts to develop
into the system of male reproductive ducts.
27-10
11. Prenatal hormones & Sexual differentation
Also the testis develop MIF (mullerian-inhibiting
factor) which causes atrophy of the
paramesonephric ducts.
The development of females results from the absence
of androgens and their receptors.
27-11
12. 27-12
Development of External Genitalia
• Even though external genitalia are the defining
characteristics of male & female, they both develop
from identical stuctures.
• By 6 weeks, the embryo has the following:
1. genital tubercle (anterior bud)
• becomes glans of penis
• clitoris
2. pair of urogenital folds
• enclose urethra of male
• form labia minora
3. a pair of labioscrotal folds
• scrotum
• labia majora
Fetus begins to show
sexual differentiation by
the end of the 9th
week &
distinctly shown by the
12th
week.
Since these structures
develop from the same
structure they are
considered Homologous.
13. 27-13
• By 8-9 weeks the fetus
begins to show sexual
differentiation.
• Development is homologous.
• This is more evident in some
abnormalities of sexual
development.
– Excess androgen clitoris
resembles penis
– Ovaries descend as if they were
testes.
14. Descent of the Testes
The testes begin development by the kidneys.
How do they end up in the scrotum?
In the embryo, a CT cord called the gubernaculum
(GN) extends from the gonad to the abdominopelvic
floor.
As the GN grows it will pass into a scrotal swelling. At
the same time (independent) the peritoneum
develops a fold into the scrotum called the vaginal
process.
This creates a path for the descent called the inguinal
canal. 27-14
15. Descent of the Testes
Begins as early as 6 weeks
As they descend they are accompanied by testicular arteries, veins,
lymphatic vessels, nerves, spermatic cord.
The actual mechanism for the descent remains unclear, the descent is
stimulated by testosterone, but unknown how. Reason for it explain later.
27-15
16. Descent of the Testes
Undescended testes called Cryptorchidism.
3% of boys, usually descend within first year, but can
be easily corrected by a testosterone injection or
simple surgery to dilate the inguinal canal and draw
the testis into the scrotum.
Uncorrected can lead to sterility and increase risk of
testicular cancer.
27-16
18. 27-18
Male Reproductive System
Start with the scrotum and testes, continue through the
spermatic ducts and accessory glands associated with
them, and ending with the penis. Sperm formation, transport
and emission.
19. 27-19
Scrotum
The scrotum and the penis constitute the genital of
the male and occupy the perineum.
• Pouch holding testes
– Left testis is usually lower than the right so they are not
compressed between the thighs.
– Divided into left and right compartments by an internal
medium septum, protects each testis from infections of
the other (perineal raphe).
20. Scrotum
Spermatic cord (cord of CT) travels up from scrotum to
pass through an opening in the groin called the
inguinal ring.
It contains:
- ducts (vas) deferens (sperm duct),
- blood vessels,
- lymphatic vessels,
- testicular nerves.
Cord is palpable through the scrotum.
27-20
21. 27-21
Scrotum
Sperm cannot be produced in the pelvic cavity due to
the temperature (37o
C) thus they descend to the
scrotum which is 2o
C cooler.
Three mechanisms to ensure a lower temperature:
1. Cremaster muscle = pulls testes close to body;
2. Dartos muscle = subcutaneous smooth muscle layer,
wrinkles skin: drawing scrotum closer to body & reducing
surface area of scrotum ↓ heat loss;
3. Pampiniform plexus (PP) = network of veins (testicular
vein) that surround the testicular artery in the spermatic cord.
W/O the PP arterial blood would heat up the testes and
inhibit spermatogensis.
22. 27-22
The PP prevents the
warming of the testes by
acting as a countercurrent
heat exchanger.
This mechanism removes
heat from the descending
arterial blood, so that by the
time it reaches the testis the
blood is 1.5o
to 2.5o
C cooler
than the core body
temperature.
23. Testes
• Oval organ, 4 cm long x 2.5 cm in diameter
– covered anteriorly by tunica vaginalis
• Tunica albuginea
– white fibrous capsule on testes
• CT septa divide testes into 200- 300 wedge shaped
lobules containing seminiferous tubules (ST),
– Between the ST are interstitial cells (leydig cells) –
source of testosterone
• ST lumen is lined with a thick germinal epithelium,
that contains several layer of germ cells in the process of
becoming sperm; as well as ….
• Sustentacular cells (sertoli cells)
– promote sperm cell development, protect, provide
nutrients, waste removal to germ cells, & produce inhibin.
26. 27-26
The Testes
• Sustentacular cells are form a tight junction between
adjacent sustentacular cells forming a Blood-testis
barrier (BTB);
• Function: separating sperm from immune system;
• Germ cells are genetically different from other cells
of the body;
• Some cases of sterility occur when the BTB fails to
form adequately in adolescence and antibodies are
produced against the germ cells.
28. 27-28
The Testes
Seminiferous tubules lead to a network called the rete testis,
here sperm mature, but do not swim;
Each testis is supplied by:
1 . Testicular artery – arises from the abdominal aorta;
- Low BP of testicular artery results in poor O2 supply
- sperm develop very large mitochondria which may
help them survive hypoxic environment of female
reproductive tract
2. Testicular veins – Rt. TV drains into inferior vena cava, Lt
TV drains into the left renal vein.
3. Testicular Nerves – lead to gonads from T10 spinal
segment mixed nerves (sensory & motor) predominately
sympathetic, some parasympathetic.
29. 27-29
The Spermatic Ducts
After leaving the testis, sperm travel through a series of
spermatic ducts (4) to reach the urethra:
1. Efferent ductules
– 12 small ciliated ducts collecting sperm from rete testes
and transporting it to epididymis;
30. The Spermatic Ducts
2. Duct of the epididymis (head, body and tail)
– 6 m long coiled duct adhering to posterior of testis,
– site of sperm maturation and storage,
– Reabsorbs about 90% of all testis secretion,
– The sperm are physiologically immature when they leave
the testis but after about 20 days of moving through the
epididymis to the tail for storage they become mature,
– They will remain fertile in the tail for 40-60 days after
which time if not released will too old and disintegrate, &
epididymis reabsorbs them.
27-30
31. The Spermatic Ducts
3. Ductus (vas) deferens (peristalsis during orgasm)
– muscular tube 45 cm long passing up from scrotum
through inguinal canal, between the bladder and ureter
and widens into a terminal ampulla; dd will end by uniting
with a gland called the seminal vesicle.
– Thick wall of smooth muscle well innervated by
sympathetic nervous system.
27-31
32. The Spermatic Ducts
4. Ejaculatory duct
– 2 cm duct formed from ductus deferens and seminal
vesicle and passing through prostate to empty into
urethra.
27-32
Male Duct System
33. 27-33
Accessory Glands
Three types of glands:
1. Seminal vesicles:
- pair, associated with each ductus deferens;
- contains smooth muscle;
- empties into the ejaculatory duct;
- constitutes 60% of semen.
2. Prostate Gland:
- 30 – 50 compound tubuloacinar ducts enclosed by
a fibrous capsule, open through urethral wall;
- thin, milky secretion constitutes 30% of semen.
34. Accessory Glands
3. Bulbourethral (Cowper) glands:
- opens to the penile urethra;
- produces a clear slippery fluid:
- lubricates head in prep for intercourse,
- neutralizes the acidity of residual urine in the
urethra.
27-34
35. 27-35
Penis
Serves to deposit semen
½ of it is situated internally (root), and the other ½ externally
(shaft & glans),
Directional terminology, dorsal side, faces anterior, while the
ventral side faces posterior (due to quadruped anatomy),
3 cylindrical bodies of erectile tissue
– corpus spongiosum along ventral side of penis
• encloses penile urethra,
• Continues distal and fills the entire glans,
– corpora cavernosum (plural, corpora cavernosa) dorsal side
• Each enshealthed in a fibrous tunica albuginea, separated by medium
septum.
Each cylinder of erectile tissue are spongy in appearance and contain tiny
blood sinuses called lacunae, each lacunae are separated by
trabeculae (trabeculae muscle).
36. Penis
The corpus spongiosum terminates internally at the bulb
(ensheathed by the bulbospongiosus muscle),
The corpora cavernosa terminate internally at the Crus, which
attaches the penis to the pubic arch (ensheathed by the
ischiocavernosus muscle).
27-36
37. Puberty & Climacteric
The reproductive system remain dormant for several years after
birth,
Age: 10 – 12 boys, 8 – 10 girls, a surge of pituitary
gonadotrophins awaken the reproductive organs & prepares
them for adult reproduction function,
Adolescence – the period from onset gonadotrophin secretion &
reproductive development until a person reaches full adult
height,
Puberty – the first few years of adolescence, until first menstrual
period in girls or first ejaculation of viable sperm in boys.
Girls – age 12, Boys – age 13
27-37
38. 27-38
Endocrine Control of Puberty
From Puberty to adulthood…
The reproductive functions is regulated by hormonal links
between the hypothalamus, pituitary gland and gonads
called:
Brain-testicular axis
39. Endocrine Control of Puberty
Hypothalamus Testosterone Effects:
Gonadotropin RH
hypophyseal portal system
Anterior pitutary (gonadotrope cells)
interstitial cells
Secrete FSH & LH
Sustentacular cells
Androgen binding protein(ABP)
- which interacts with testosterone to
stimulate spermatogenesis
- thought to raise testosterone levels
27-39
1. stimulates spermatogensis in the
presence of ABP;
2. Inhibits GnRH secretion by
hypothalamus;
3. Stim. Secondary sex characteristics;
4. Causes ducts and accessory glands
to enlarge, frequent erections;
5. Stim. Growth spurt, ↑ muscle mass, ↑
metabolic rate, voice deepens;
6. Stim. Erythropoiesis, ↑ hematocrit &
count;
7. Stim. Libido.
52. 27-52
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
53. 27-53
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 (ED) (Impotence)
– 20% of men in 60s; 50% of those in 80s
54. 27-54
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
56. 27-56
• 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
Spermatogenesis
59. 27-59
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
61. 27-61
Semen or Seminal Fluid
Fluid expelled during orgasm (2-5ml)
Composed of:
- 60% seminal vesicle fluid,
- 30% prostatic fluid,
- 10% sperm
- normal sperm count 50-120 million/mL (<20 – 25 million = infertility).
Prostate contributes: a thin, milky white fluid that contains Ca, citrate,
phosphate ions, clotting enzymes, and serine protease (PSA).
Seminal vesicles contributes a yellowish fluid, last to emerge flushing
remaining sperm from urethra. Contains: fructose, carbohydrates,
prostaglandins, and a protein called proseminogelin.
62. Semen or Seminal Fluid
One property of semen is its stickiness, an adaptation that
promotes fertilization,
This occurs when the clotting enzyme from the prostate
activates proseminogelin, converting it to seminogelin,
Seminogelin entangles the sperm and makes sure it sticks to
the inner wall of the vagina and cervix, preventing loss,
After 30 minutes the serine protease (prostate) breaks down the
seminogelin, the sperm become active and begin crawling up
the mucosa of vagina and uterus,
Prostaglandins (seminal vesicle) thin the mucus of the cervical
canal & stim. peristalic waves in uterus and uterine tubes to
help spread semen through the reproductive tract, 27-62
63. Semen or Seminal Fluid
2 requirements for sperm motility:
1. Elevated pH- the pH of the vagina is 3.5-4.0 and the
male spermatic ducts are also acidic. In this environment
they are inactive,
The prostatic fluid buffers the spermatic ducts and vagina
raising pH to 7.5 thus activating the sperm,
2. Synthesize ATP: need a lot to power motility, energy
from the fructose and other sugars contributed by the seminal
vesicles.
27-63
64. Male Sexual Response
Sexual intercourse unexplored before 1950’s,
By 1966 scientists have come up with 4 phases of
intercourse:
1. excitement
2. plateau
3. orgams
4. resolution
All phases seen in both male and female
27-64
65. 27-65
Anatomical Foundations
Understanding male sexual function, must
understand blood circulation and nerve supply.
Arteries of penis:
- Internal iliac arteries give to internal pudendal (penile) a.
which enters the root of penis and divides into 2:
1. dorsal a.- travels dorsally beneath skin,
2. deep a.- travels through the corpora cavernosa
- supplies lacunae of corpora cavernosa
- dilation fills lacunae causing an erection
Flaccid penis - normal blood supply comes from dorsal a.
66. Anatomical Foundations
Nerves of penis
- Highly innervated by sensory and motor fibers,
-glans - abundance of tactile, pressure and temperature
receptors,
- fibers called dorsal nerve of penis branch to the internal
pudendal nerves lead to the sacral plexus and finally to the
sacral region of the spinal cord,
- both autonomic and somatic motor fibers carry impulses
from integrating center in the spinal cord to penis & other
pelvic organs,
27-66
67. Anatomical Foundations
Sympathetic fibers innervate penile arteries, trabecular
muscles, spermatic ducts, accessory glands.
- dilate penile arteries even when sacral region of spinal
cord is damaged,
- initiate erection in response to input to special senses
and sexual thought,
Parasympathetic fibers are involved in an autonomic
reflex arc:
- cause erection in response to direct stimulation.
27-67
68. 27-68
Excitement and Plateau
Excitement characterized by:
- vasocongestion of genitals,
- myotonia,
- ↑heart rate,
- ↑BP,
- ↑ pulmonary ventilation
Excitement is initiated by many different erotic stimuli
conversely inhibited by emotions,
Erection (obvious manifestation of excitement) is an
autonomic reflex mediated by parasympathetic fibers,
trigger the release of nitric oxide (NO), relaxing the deep
arteries and lacunae, allowing them to fill with blood,
69. Excitement and Plateau
Bulbospongiosus & ischiocavernosus muscle aid in
erection by compressing root and forcing blood
forward into the shaft,
- corpora cavernosa swell and enlarge,
- corpus spongiosum will not swell as much as the
corpora cavernosa, WHY?
Plateau Phase:
- marked by increase vasoconstriction and myotonia,
- respiratory rate, heart rate and BP are maintained at a high
level
27-69
70. 27-70
Orgasm and Ejaculation
Climax (orgasm) is 15 second reaction that includes
the discharge of semen (ejaculation),
Ejaculation - release of semen in to vagina
2 stages:
1. emission = sympathetic nervous system stimulates
peristalsis in smooth muscle of the ductus deferens
which propels sperm from the tail of the epididymus→
ampulla→ prostatic urethra → membranous urethra→
spongy urethra→ creates urgent sensation;
2. expulsion = semen in urethra activates muscular
contractions that lead to expulsion;
71. Orgasm and Ejaculation
During the expulsive phase, sympathetic reflex
constricts the internal urethral sphincter so urine is
unable to enter the urethra and semen cannot enter
the bladder,
Ejaculation and orgasm are not the same. They do
usually occur together, but it is possible to have all
the sensations of an orgasm w/o ejaculation and
visa versa.
27-71
72. Resolution Phase
Immediately following orgasm;
Discharge of the sympathetic nervous system results in the
constriction of the internal pudendal a. decreasing blood flow
into penis, also causes contraction of the trabeculae muscles
which squeeze blood from the lacunae resulting in
detumescence (becoming soft and flaccid);
This phase allows the cardiovascular and respiratory functions
return to normal;
Resolution is followed by a refractory period, (10min – a few
hours) = impossible to attain another erection & orgasm.
27-72
73. Male Sexual Response
Male sexual response requires a tremendous
coordination of the nervous system, from the CNS to
the PNS, sympathetic, parasympathetic, & somatic
fibers all having to work together.
READ INSIGHT 27.5 Sexually transmitted disease
27-73
