Chapter 28
The Reproductive Systems
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Reproductive System

Primary sex organs (gonads) – testes in males, ovaries in
females
o
Gonads produce gametes (sperms & ova) and secrete
sex hormones

Accessory reproductive organs – ducts, glands and
external genitalia

Sex hormones– testosterone (males), estrogens and
progesterone (females)
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Gamete formation and Meiosis
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Gamete formation is by meiosis, in which the number
of chromosomes is halved (from 2n to n)
Meiosis consists of two nuclear divisions meiosis1 &
meiosis 2
The products of meiosis are 4 daughter cells instead of
two with half the number of chromosomes
Meiosis accomplishes two tasks:
It reduces the chromosome number by half (2n to n)It
introduces genetic variability
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Gamete formation and Meiosis
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Male Reproductive Anatomy

The male gonads are the testes (singular: testis)
o
The ducts of the male reproductive system are
the:
 Epididymis
 Vas deferens (ductus deferens)
 ejaculatory duct
 urethra
o
Accessory reproductive glands are the:
 Seminal vesicles
 Prostate
 Bulbourethral glands
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Male Reproductive Anatomy

The scrotum is a supporting
structure for the testes
o
It consists of a sac of loose
skin and superficial fascia
o
The dartos and
cremaster muscles regulate
the testicular temperature
required for sperm
production
(2-3o below the core temp)
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Male Reproductive Anatomy

The spermatic cord is a supportive
connective tissue structure that
ascends “out of” the scrotum, and
contains:

The Vas deferens

The testicular artery

Veins, lymphatics, and
autonomic nerves
The spermatic cord pass through
the inguinal canal
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Male Reproductive Anatomy

Covered by the tunica vaginalis ( peritoneal layer)

The tunica albuginea forms septae that divide each testis
into lobules
o
Each lobule contains 1-3
seminiferous tubules
where sperm are
produced
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Seminiferous Tubules
Seminiferous tubules are lined by:

Germ cells in various stages of maturation which
give rise to sperms &

Sertoli cells- nourish the germ cells, form fluid for
sperm transport

In between the Seminiferous tubules are
interstitial cells of Leydig
that secrete testosterone
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Descent of Testis

Develop near kidney on posterior abdominal wall

Descends into scrotum by passing through inguinal canal
during 7th month of fetal development

Failure of the testes to descend is called cryptorchidism

Untreated bilateral cryptorchidism results in sterility & a
greater risk of testicular cancer
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Spermatogenesis

Spermatogenesis is the process by which the seminiferous
tubules of the testes produce sperms.

Spermatogenesis begins at puberty

It begins with the diploid spermatogonia (stem cells).

Spermatogonia undergo mitosis to form primary
spermatocytes (also diploid)

Primary spermatocyte undergo meiosis I, to form haploid
secondary spermatocytes ( 23 chromosomes)

Secondary spermatocytes undergo meiosis II to form four
spermatids ( haploid)
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Spermiogenesis: spermatids to sperms

Spermiogenesis – spermatids elongate, lose excess cytoplasm
and form a tail, becoming sperms

Sperms (spermatozoa) have three major regions
o
Head – contains the nucleus has the acrosome cap over
nucleus- contains digestive enzymes to help penetrate oocyte
o
Midpiece – contains mitochondria spiraled around upper
tail
o
Tail – a flagellum
o
Each day about 300 million sperms formed
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Spermatogenesis
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Spermatozoa

The acrosome is a cap-like vesicle filled with enzymes
(hyaluronidase and proteases)
that help a sperm to penetrate
a secondary oocyte to bring about
fertilization

The middle piece contains many
mitochondria which provide
the energy (ATP) for locomotion
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spermatogonia
primary spermatocytes
secondary spermatocytes
spermatids
spermatozoa
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Hormonal Control of Spermatogenesis

At puberty- hypothalamus stimulates anterior pituitary by GnRH
(gonadotropin releasing hormone)

Anterior pituitary produces follicle-stimulating hormone (FSH) and
luteinizing hormone (LH).

LH stimulates Leydig cells to secrete testosterone ( high
testosterone suppresses LH)

FSH stimulates Sertoli cells to secrete androgen-binding protein
(ABP) that keeps testosterone levels high; testosterone stimulates
spermatogenesis

Sertoli cells release Inhibin to inhibit FSH; control spermatogenesis
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Control of Testosterone Production

Negative feedback system controls
blood levels of testosterone
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Actions of Testosterone

Prenatal effects; male reproductive system development,
assists testicular descent

controls the growth, development, functioning, and
maintenance of sex organs

stimulates development of male secondary sex characteristics

stimulates bone growth, protein anabolism, and sperm
maturation

sexual behavior & libido
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Pathway of Sperm Flow through the Ducts of
the Testis

Before ejaculation, sperm travel via the following route:
o
Seminiferous tubules
o
Rete testis (network)
o
Efferent ducts
o
Epididymis
o
Vas (ductus)
deferens…
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Duct system

Sperm travelogue continued:
o
Vas (ductus) deferens …
o
Ejaculatory duct (within
the prostate gland)
o
Urethra, which has 3
portions to it:
prostatic
membranous
penile
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Duct system: Epididymis

The epididymis lies along the posterior border of the
testis

The epididymis is lined by columnar epithelium having
stereocilia and is the site of sperm maturation ( sperms
become motile)

sperm may remain in storage here for at least a month,
after which they are degenerated and reabsorbed.
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Copyright © John Wiley & Sons, Inc. All rights reserved.
Duct system

The ductus (vas) deferens stores sperm and propels them
toward the urethra during ejaculation

Lined with pseudostratified columnar ciliated epithelium

The ejaculatory ducts are formed by the union of the ducts
from the seminal vesicles and ductus deferens; their function
is to eject spermatozoa into the prostatic urethra

The male urethra serves as a passageway for semen and urine.
The male urethra is subdivided into three portions: prostatic,
membranous, and spongy
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Accessory Glands
o
Seminal vesicles secrete a viscous, alkaline fluid
(mainly during ejaculation) which makes up 60% of
the semen volume.
o
It contains fructose (for energy), prostaglandins
 the alkalinity neutralizes the acidity of the male
urethra and the female reproductive tract
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Accessory Glands

The prostate a donut-shaped gland that secretes about
25% of volume of semen

Prostatic fluid is a milky, slightly acidic solution
containing citric acid (for energy), acid phosphatase,
and proteolytic enzymes (PSA and hyaluronidase)

The bulbourethral (Cowper’s) gland is a pea-sized gland
inferior to the prostate. It secretes a protective &
lubricating alkaline mucus that decreases acidic
environment of the urethra
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Accessory Glands
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Clinical application
Benign prostatic hypertrophy is an enlargement
of the prostate gland in the absence of cancer.
It is a very common affliction as men age, resulting
in obstruction of urine flow and inability to
completely empty the bladder
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Semen

Semen is a mixture of sperm and seminal fluid, a liquid
that consists of the secretions of the seminiferous
tubules, seminal vesicles, prostate, and bulbourethral
glands
o
The volume of semen in a typical ejaculation is 2.5–5
milliliters (mL), with 50–150 million sperm per mL
 when the number falls below 20 million/mL, the
male is likely to be infertile
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The Penis

The penis contains the urethra and is a passageway for
the ejaculation of semen and the excretion of urine
o
It consists of a body, glans penis, and a root
 The body of the penis is composed
of three cylindrical masses of
tissue, each surrounded by
fibrous tissue called the
tunica albuginea
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The Penis

The two dorsolateral masses are the corpora cavernosa
penis, and the smaller midventral mass is the corpus
spongiosum
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The Male Sexual Response

Upon sexual stimulation (visual, tactile, auditory,
olfactory, or imagined), sacral parasympathetic fibers
initiate and maintain an erection
o
Under the influence of nitric oxide released from
parasympathetic neurons (“neurogenic NO”), arteries
that supply the penis dilate and blood enters penile
sinuses in the erectile tissue; erection
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The Male Sexual Response

After an erection, sympathetic stimulation is necessary
for ejaculation
o
The smooth muscle sphincter at the base of the urinary
bladder must close, followed by semen being propelled
into the penile portion of the urethra (emission)
o
Powerful peristaltic contractions culminate in the
release of semen from
the urethra to
the exterior
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Female Reproductive Anatomy

The organs of the female reproductive system include
the ovaries (female gonads); the uterine tubes
(fallopian tubes); the uterus; the vagina; and the external
organs (collectively called the vulva,
or pudendum)
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Ovaries
o
The germinal epithelium covers the surface of the
ovary
o
The ovarian cortex contains the follicles in various
stages of maturation
o
The ovarian medulla
contains blood vessels,
lymphatic vessels
and nerves
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Oogenesis

Is the process of production of oocytes

Before birth:

In the fetal period, oogonia (2n stem cells) multiply by mitosis

Oogonia are transformed into primary oocytes & become
surrounded by a single layer of follicular cells forming
primordial follicles

Primary oocytes begin meiosis 1 but are arrested in prophase 1

At birth upto 2 million primordial follicles are present in the
cortex of the immature ovary
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Oogenesis
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Childhood
ovaries are inactive, and no follicles develop
some primordial follicles regress- by the time a female child
reaches puberty, only about 40,000 primordial follicles
remain
Puberty to menopause
The primary oocytes in the primordial follicles remain
arrested in prophase I until after puberty
Beginning at puberty one primary oocyte completes
meiosis1 producing two haploid cells; the first polar body &
the secondary oocyte
The secondary oocyte arrests in meiosis II and is ovulated
If penetrated by a sperm the secondary oocyte completes
meiosis II, yielding:
o One large ovum (the functional gamete)
o A tiny second polar body
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Oogenesis
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Ovaries; follicular development
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Primordial follicle
Contains a primary oocyte- arrested in the first meiotic
division, surrounded by a single layer flattened follicular cells
Primary follicle
consists of a primary oocyte surrounded by one or more
layers of cuboidal granulosa cells
primary follicles secretes estrogen which stimulates changes
in the uterine lining.
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Secondary follicle
contains a primary oocyte, many layers of granulosa cells & a
fluid-filled space- antrum
 The oocyte is surrounded by the zona pellucida & corona
radiata
 Graafian ( vesicular)–follicle -most mature stage that bulges
from the surface of the ovary
 contains a secondary oocyte and a large, fluid-filled, antrum
 A secondary oocyte has completed meiosis I and is arrested
in meiosis 2.
 one vesicular follicle forms each month.
 Ovulation –rupture of mature follicle with ejection of the
oocyte
 The ruptured follicle gets transformed into a corpus luteum
 secretes sex hormones progesterone and estrogen
 corpus luteum later degenerates to form the
corpus albicans


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Ovarian follicles
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Female Reproductive Anatomy

After receiving the 2o oocyte at the infundibulum the
uterine tubes provide a site for fertilization, and then
transport for
the ovum if
fertilization occurs
o
The uterine
tubes also have
an ampulla and
an isthmus
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Female Reproductive Anatomy

The main anchors for the ovaries are the suspensory
ligaments of the ovary (for pelvic wall attachment), and
the ovarian
ligament
(provides an
attachment to
the side wall of
the uterus)
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Female Reproductive Anatomy

The broad ligament is a
major support for the
Uterus
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Female Reproductive Anatomy

The uterus is a pear shaped organ situated between the
urinary bladder and the rectum
o
It is also the site of implantation of a fertilized ovum,
development of the fetus during pregnancy, and
labor
o
During reproductive cycles when implantation does
not occur, the uterus is the source of menstrual flow
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Female Reproductive Anatomy

Anatomical subdivisions of the uterus include:
o
A dome-shaped superior portion called the fundus
o
A central portion called the body, that tapers to a
narrow isthmus
o
the inferior-most
cervix opens into
the vagina through
the cervical
canal
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Female Reproductive Anatomy

The interior of the body of the uterus is called the
uterine cavity

The cervical canal
has an internal os
and an external os
that opens into
the uterine
cavity and the
vagina, respectively
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Layers of Uterus

Outer perimetrium

middle myometrium

inner endometrium, divided into
 stratum functionalis (shed during
menstruation)
 stratum basalis (gives rise to a new stratum
functionalis after each menstruation)
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Female Reproductive Anatomy

The vagina is a fibromuscular canal lined with stratified
squamous epithelium

It has 3 basic functions:
o
Serve as a passageway
for menstrual flow
o
Receive sperm
o
Form the lower
birth canal
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Female Reproductive Anatomy

The vulva (female external genitalia) refers to the:
o
Mons pubis (created by adipose tissue)
o
Erectile tissue of the clitoris
o
Labia majora ,and labia minora
o
Vestibule, the
area between the
labia minora contains urethral &
vaginal orifice
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Female Reproductive Anatomy

On either side of the vaginal orifice itself are the greater
vestibular (Bartholin’s) glands

They produce a small quantity of lubricating mucous
during sexual arousal
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Female Reproductive Anatomy

The perineum is a diamond-shaped area that is bounded
anteriorly by the pubic symphysis, laterally by the ischial
tuberosities, and posteriorly by the coccyx
o
It contains the external
genitalia and
anus
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Female Reproductive Anatomy

The breasts (mammary glands) are present in the anterior
thoracic wall

Contains 15–20 lobes divided into lobules
o
Each lobule is
composed of milksecreting glands called
alveoli. The nipple has openings
for the lactiferous ducts &
pigmented area (areola)
around it
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Female Reproductive Anatomy
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Female Reproductive Cycle

The female reproductive cycle includes the ovarian
and uterine cycles & the hormonal changes that
regulate them
o Controlled by monthly hormone cycle of anterior
pituitary, hypothalamus & ovary

Ovarian cycle
o changes in ovary during & after maturation of
oocyte and follicles
The uterine (menstrual) cycle
o involves changes in the endometrium
o preparation of uterus to receive fertilized ovum
o if implantation does not occur, the stratum
functionalis is shed during menstruation

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Hormonal Regulation of Reproductive Cycle

GnRH secreted by the hypothalamus:
 stimulates
o
o
o
o
the release of FSH and LH by the anterior
pituitary gland
FSH initiates growth of follicles that secrete estrogen
 estrogen maintains reproductive organs
LH :
stimulates ovulation
romotes formation of the corpus luteum which secretes
progesterone, estrogens, relaxin, inhibins
 progesterone prepares uterus for implantation
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Overview of Hormonal Regulation
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Estrogen: functions

Promotion of the development and maintenance of female
reproductive structures, secondary sex characteristics

Increase protein anabolism and build strong bones.

Lower blood cholesterol.

Moderate levels of estrogens in the blood inhibit the release
of GnRH by the hypothalamus and secretion of LH and FSH
by the anterior pituitary gland.

Progesterone works with estrogens to prepare the
endometrium for implantation and the mammary glands for
milk synthesis.
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
Progesterone is the principal hormone responsible for
maturation of the uterine endometrium for implantation,
as well as an important player in stimulating breast
development
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Phases of the Female Reproductive Cycle

In many ways the menstrual cycle closely parallels the
events happening in the ovaries

The female reproductive cycle may be divided into (4
phases) every 28 days (on average)

Menstrual phase marks the beginning of the cycle

This is followed by the pre-ovulatory phase

Ovulation occurs on about day 14

after which the post-ovulatory phase begins
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The Menstrual phase; days 1-5

The menstrual phase (menstruation) day 1-5

During this phase, small secondary follicles in each ovary
begin to develop.

the stratum functionalis layer of the endometrium is shed,
discharging blood, tissue fluid, mucus, and epithelial cells as
declining levels of progesterone caused spiral arteries to
constrict
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Preovulatory (proliferative)phase
- days 6-13
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In the ovary (follicular phase)
o secondary follicles secreting estrogen
o One dominant secondary follicle develops into a
Vesicular (Graafian) follicle
o The graafian follicle enlarges & bulges at surface of the
ovary & is ready for ovulation
o increasing estrogen levels trigger the secretion of LH
In the uterus (proliferative phase)
increasing estrogen levels have repaired & thickened the
stratum functionalis to 4-10 mm in thickness
With reference to the ovarian cycle, the menstrual and
preovulatory phases together are termed the follicular phase
because ovarian follicles are developing
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Ovulation; day 14

Ovulation is the rupture of the vesicular ovarian
(Graafian) follicle with release of the secondary oocyte
into the pelvic cavity, usually occurring on day 14 in a
28-day cycle.
o
high levels of estrogen during the last part of the
preovulatory phase exert positive feedback on both
GnRH & LH and to cause ovulation
o
Midcycle LH surge causes ovulation
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Ovulation
GnRH
1 High levels of
estrogens from
almost mature
follicle stimulate
release of more
GnRH and LH
Hypothalamus
2 GnRH promotes
release of FSH
and more LH
LH
Anterior pituitary
3 LH surge
brings about
ovulation
Ovulated
secondary
oocyte
Ovary
Almost mature
(graafian) follicle
Corpus hemorrhagicum
(ruptured follicle) Copyright © John Wiley & Sons, Inc. All rights reserved.
Postovulatory (secretory) - days 15-28

Following ovulation, the ruptured vesicular follicle gets converted
into the corpus luteum, under the influence of LH.

The corpus luteum secretes progesterone & estrogens

This phase is the luteal phase

if fertilization does not occur, then the corpus luteum gets
transformed into the corpus albicans; as progesterone & estrogen
levels drop, secretion of GnRH, FSH & LH rises: follicular growth
resumes

if fertilization does occur, the corpus luteum remains for 3 months
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Phases - Postovulatory - days 15-28

In the uterus (secretory phase)
o
hormones from corpus luteum promote thickening of
endometrium to 12-18 mm
 formation of more endometrial glands &
vascularization
 Increased secretion of glycogen
o
if no fertilization occurs, corpus luteum degenerates ,
loss of hormonal support will begin menstrual phase
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
If pregnancy occurs, the corpus luteum is “rescued” from
degeneration by an LH-like hormone called human
chorionic gonadotrophin (hCG – produced by the
developing embryo)

With hCG support, the corpus luteum goes on to produce
hormones well into the 1st trimester until the placenta can
take over
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Female Reproductive Cycle
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