28 [chapter 28 the reproductive system]

CHAPTER 28
The Reproductive System
Principles of
Anatomy and
Physiology
14th Edition
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Organs include: testes, ductus deferens,
epididymis, ejaculatory ducts, urethra,
seminal vesicles, prostate, bulbourethral
glands, scrotum and penis.
Male Reproductive System

 Functions of the parts of the system:
 Scrotum: a sac of loose skin and underlying
subcutaneous tissue that contains the testes.
Internally, it is separated into two compartments
by the dartos muscle and a subcutaneous
layer.

 Testes: paired, oval glands in the scrotum
partially covered by the tunica vaginalis.
 Internal to the tunica vaginalis is a
connective tissue capsule, the tunica
albuginea that extends inward to form
septa that create compartments.
 Seminiferous tubules carry sperm
produced within them (spermatogenesis)
out of the testes.

Spermatogenesis begins with
spermatogonia (diploid stem cells) that
differentiate into diploid primary
spermatocytes.

 The primary spermatocyte undergoes
meiosis I to become two secondary
spermatocytes (haploid).
 Meiosis II takes place and the secondary
spermatocytes become four spermatids.

Male
Reproductive
System

 Sperm: designed to reach and penetrate the secondary
oocyte in order to achieve fertilization and create a zygote.
 The head contains a nucleus with 23 chromosomes.
 The acrosome covers the head and contains enzymes to
help with penetration.
 The neck contains centrioles that form the microtubules that
make up the rest of the tail.
 The middle piece contains mitochondria that make ATP for
locomotion of the sperm.
 The principal piece and end piece make up the tail used for
movement.

 Hormones control testicular function. At
puberty gonadotropin releasing
hormone (GnRH) stimulates cells in the
anterior pituitary gland to produce
luteinizing hormone (LH) and follicle
stimulating hormone (FSH).
 LH stimulates cells in the testes to
produce testosterone.
 FSH stimulates spermatogenesis.

Testosterone and dihydrotestosterone
produce several effects:
 Prenatal development
 Development of male sexual characteristics
 Development of sexual function
 Stimulation of anabolism
A negative feedback system controls the
blood level of testosterone.

 There is a system of ducts in the male
reproductive system. Sperm and fluid
travel from the seminiferous tubules to
straight tubules and then to a network of
ducts, the rete testis.
 Efferent ducts carry the sperm to the
epididymis. Sperm mature here and
degenerated sperm are reabsorbed.
 The epididymis propels sperm into the
ductus (vas) deferens.

The ductus (vas) deferens exits the tail of
the epididymis and ascends through the
spermatic cord into the into the pelvis. It
loops over the ureter and passes over the
side and down the posterior surface of the
urinary bladder.

 The spermatic cord ascends out of the
scrotum and contains the ductus
deferens, testicular artery, veins
draining the testes, autonomic nerves,
lymphatic vessels and the cremaster
muscle.
 The spermatic cord and ilioinguinal
nerve pass through the inguinal canal
which originates at the deep inguinal ring
and ends at the superficial inguinal ring.

 The ejaculatory ducts arise from the
junction of the duct from the seminal
vesicle and the ampulla of the ductus
deferens.
 The urethra is the duct shared by the
reproductive and urinary systems. Both
semen and urine pass through it. It passes
through the prostate gland (prostatic
urethra), deep muscles of the perineum
(intermediate or membranous urethra)
and the penis (spongy urethra).

 Accessory glands include:
 Seminal vesicles (glands)—secrete an alkaline,
viscous fluid containing fructose, prostaglandins
and clotting proteins.
 Prostate: a single, donut-shaped gland that
secretes a milky, slightly acidic fluid containing
citric acid, proteolytic enzymes, acid phosphatase
and seminalplasmin.

Bulbourethral (Cowper’s) glands: secrete
an alkaline fluid during sexual arousal that
neutralizes acids from urine and mucus for
lubrication.

 Semen: a mixture of sperm and seminal fluid.
 The volume of an average ejaculate is 2.5-5 ml. with 50–150
million sperm per ml.
 The pH is 7.2–7.7
 Penis: containing the urethra it is a passageway for semen
and urine.
 Composed of 3 cylindrical masses: 2 corpora cavernosa, 1
corpus spongiosum (all erectile tissues).
 Glans: Head of penis covered by the prepuce (foreskin).

 The penis is supported by the fundiform and
suspensory ligaments.
 An erection is brought about by parasympathetic
innervation leading to vasodilation of arterioles in
erectile tissue.
 Large amounts of blood enter the tissue into dilated
blood sinuses.
 Ejaculation is the powerful release of semen due to
sympathetic stimulation. The bulbospongiosus,
ischiocavernosus and superficial transverse
perineal muscles contract to force the semen out.

 Hormonal Control of Male Reproductive Funct
Interactions Animation:
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Organs include: ovaries, uterine (fallopian)
tubes (oviducts), the uterus, the vagina
and external organs.
Female Reproductive System

 Ovaries: paired glands homologous to the
testes. They produce gametes (mature
into ova) and hormones (progesterone,
estrogens, inhibin, relaxin).
 They are supported by the broad
ligament, ovarian ligament and
suspensory ligament.

 Histologically, ovaries consist of:
 The germinal epithelium—covers the surface
 The tunica albuginea—capsule of dense irregular
connective tissue below the germinal epithelium
 The ovarian cortex—below the tunica albuginea.
Consists of ovarian follicles and stromal cells.
 The ovarian medulla—connective tissue, blood
vessels, lymphatic vessels and nerves.

 Ovarian follicles—contain oocytes in
various stages of development, follicular
cells and granulosa cells.
 A mature (graafian) follicle is ready to
rupture and expel the secondary oocyte.
 A corpus luteum develops after ovulation
when the empty follicle produces
progesterone, estrogens, inhibin and
relaxin.

 Formation of gametes in the ovaries is
oogenesis. It begins before a female is born with
the process of meiosis.
 When primordial germ cells migrate from the
yolk sac to the ovaries during fetal development,
they differentiate into oogonia.
 Oogonia divide into germ cells, some of which
become primary oocytes. Each is surrounded
by follicular cells forming a primordial follicle.

Each month after puberty, FSH and LH
stimulate the development of the primordial
follicles. Only one usually reaches maturity.
A few start to grow, developing into primary
follicles.

 In later stages of development, the primary oocyte
is surrounded by several layers of cuboidal and
low-columnar cells (granulosa cells).
 The glycoprotein zona pellucida forms between
the primary oocyte and the granulosa cells.
 As maturation continues, the primary follicle
develops into a secondary follicle.
 The theca folliculi forms from stromal cells.

 In a secondary follicle the theca
differentiates into the theca interna and
theca externa.
 The innermost layer of granulosa cells
becomes the corona radiata.
 The secondary follicle becomes a mature
(graafian) follicle.

 While in the mature follicle, the diploid primary oocyte
completes meiosis I producing a haploid secondary
oocyte (with the majority of the cytoplasm) and a haploid
first polar body.
 At ovulation, both cells and the corona radiata enter the
uterine tube. If sperm are present and fertilization takes
place, the secondary oocyte continues into meiosis II.
 An ovum and a second polar body form. The ovum
becomes a zygote when it unites with the sperm.

Female
Reproductive
System

 Females have two uterine (fallopian) tubes
(oviducts) that extend from the uterus.
 The tubes are the pathway for the sperm to reach
the ovum and for the secondary oocytes and
fertilized ova to travel to the uterus.
 The end of the tube is the infundibulum.
 Fimbriae project from it.
 The ampulla is the widest protion of the tube.

 The uterine tubes have 3 layers: mucosa,
muscularis and serosa.
 The simple ciliated columnar
epithelium of the mucosa contains cilia
that move the fertilized ovum or secondary
oocyte towards the uterus.
 Peg cells in the tube secrete a fluid
providing nourishment for the ovum.

 The uterus is part of the pathway for sperm deposited in the
vagina to reach the uterine tube.
 It is the site of implantation of the fertilized ovum,
development of the fetus during pregnancy and labor.
 The top of the uterus is the fundus.
 The central portion is the body.
 The inferior extension into the vagina is the cervix.
 The isthmus is between the body and the cervix.

 The interior of the body is the uterine
cavity.
 The interior of the cervix is the cervical
canal.
 The opening of the canal into the uterus is
the internal os.
 The opening of the canal into the vagina is
the external os.

 Histologically, there are three layers to the uterus.
 The perimetrium (serosa) is the outermost layer.
 The middle layer is the myometrium consisting of three layers
of smooth muscle.
 The endometrium is the inner layer. Its stratum functionalis
layer is shed each month during menstruation.
 The stratum basalis layer is permanent and gives rise to a new
stratum functionalis after each menstruation.

 Branches of the internal iliac artery
called uterine arterioles supply blood to
the uterus.
 Uterine arteries give rise to arcuate
arteries that feed the myometrium.
 These branch into radial arteries that go
deep into the myometrium.
 Straight arterioles supply the stratum
basalis.

 Secretory cells of the cervix produce
cervical mucus which is chemically more
hospitable to sperm during ovulation
because it is less viscous and more
alkaline.
 It helps nourish sperm
 It may aid in capacitation—functional
changes in sperm that allow them to
fertilize a secondary oocyte.

The vagina: a fibromuscular canal lined with
mucous that extends from the body’s
exterior to the cervix.

The mucosa of the vagina is continuous with
that of the uterus.

 The epithelium and areolar connective tissue of
the vagina lie in a series of transverse folds called
rugae.
 The muscularis is composed of an outer circular
layer and inner longitudinal layer of smooth
muscle.
 This allows the vagina to stretch during
intercourse and childbirth.
 The hymen is a thin fold of vascularized mucous
membrane that partially closes the inferior end of
the vagina.

The vulva (pudendum) refers to the
external genitalia of the female. It includes:
 The mons pubis
 Labia minora
 Labia majora
 Clitoris
 Vestibule (hymen, vaginal orifice, external
urethral orifice, openings of ducts of several
glands)

 Paraurethral (Skene’s) glands secrete mucous and are
embedded in the wall of the urethra. They are homologous to
the prostate.
 Greater vestibular (Bartholin’s) glands produce mucous
during sexual arousal to provide lubrication. They are
homologous to the bulbourethral gland.
 The bulb of the vestibule has two masses of erectile tissue
that engorges during sexual arousal to narrow the vaginal
orifice applying pressure to the penis during intercourse. It is
homologous to the erectile tissues of the penis.

 The mammary glands are located in each
of the two breasts. They are modified
sudoriferous (sweat) glands that
produce milk.
 Mammary glands contain 15–30 lobes.
 Each lobe has lobules containing milk
secreting glands called alveoli.
 Each breast has a nipple containing
lactiferous ducts where milk emerges.
 The skin around the nipple is the areola.

 Nonpregnant females experience cyclical changes in the
ovaries and uterus. Each cycle takes approximately one
month.
 The cycle involves oogenesis and preparation by the
uterus to receive a fertilized ovum.
 The ovarian cycle includes changes that occur during and
after maturation of the oocyte.
 The uterine cycle involves changes in the endometrium
that prepare it for implantation of the developing embryo.
The Female Reproductive Cycle

Gonadotropin-releasing hormone (GnRH)
from the hypothalamus controls both the
ovarian and uterine cycles.

Phases: The cycle generally ranges from
24–36 days. It is divided into 4 phases:
1. Menstrual
2. Preovulatory
3. Ovulation
4. Postovulatory

 Feedback is important in regulating
hormonally controlled cycles.
 The high levels of estrogens during the
last part of the preovulatory phase have a
positive feedback effect on cells
secreting LH and GnRH thus bringing
about ovulation.
 There are many hormonal interactions
between the ovarian and uterine cycles.

The Female
Reproductive
Cycle

The Female Reproductive System
 Phases of the Female Reproductive Cycle
Interactions Animation:
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 Birth control methods are designed to limit
the number of children produced by preventing
conception.
 Complete abstinence is the only 100% reliable
method.
 Other methods include: Surgical sterilization
 Hormonal methods
 Periodic abstinence
 Other than complete abstinence, all methods
have different failure rates.
Birth Control Methods and Abortion

 Surgical sterilization: surgical intervention to render an
individual incapable of reproduction.
 Vasectomy is used in males by removing a portion of the
vas deferens.
 Tubal ligation is used in females to tie closed and then cut
the uterine (fallopian) tubes.
 Non-incisional sterilization employs the insertion of a coil
made of plastic and metal into each uterine tube. Scar
tissue grows and blocks the tubes.

 Hormonal methods include oral
contraceptives that are designed to
prevent pregnancy by inhibiting ovulation.
 There are several types of oral hormonal
methods of contraception.
 Combined oral contraceptives (COC)
contain progestin and estrogens.

 Extended cycle birth control pills
contain progestin and estrogen.
Menstruation occurs every 13 weeks.
 Minipills contain progestin only.
 Progestin thickens cervical mucous.

Non-oral methods include:
 Contraceptive skin patch
 Vaginal contraceptive ring
 Emergency contraception (EC) (oral method,
but only 2 pills are taken—one within 72 hours of
unprotected intercourse; the x = second is taken
12 hours after the first).

Barrier methods employ a physical barrier
to block sperm from gaining access to the
uterine cavity and tubes. These include:
 Male condom
 Vaginal pouch (female condom)
 Diaphragm
 Cervical cap

 Periodic abstinence is employed when the couple has knowledge
of the physiological changes that take place during the female cycle.
 The first method used was the rhythm method. The couple abstains
from intercourse when ovulation is likely to occur.
 The sympto-thermal method may be used to avoid or achieve
pregnancy. It uses normally fluctuating physiological markers such as
temperature and the production of clear, sticky cervical mucous that
is produced at ovulation.

 Abortion is the premature expulsion of the
products of conception from the uterus.
There are several methods employed.
 Mifepristone (RU 486) is a hormone used in
pregnancies 9 weeks or less. It blocks
progestin thus blocking the action of
progesterone. Menstruation occurs.
 Vacuum aspiration (suction) uses suction
to remove the embryo or fetus, placenta and
uterine lining.

 Dilation and evacuation are used
together to dilate the cervix and employ
suction and a forceps to remove the fetus,
placenta and uterine lining.
 Late-stage abortion employs similar
methods to dilation and evacuation or
uses a saline solution or surgical
methods to induce abortion.

The reproductive systems develop from
several structures and require several
chemical substances.
 Gonads develop from intermediate mesoderm
that gives rise to gonadal ridges.
 Mesonephric (Wolffian) ducts develop into the
male reproductive system.
 Paramesonephric (Mullerian) ducts develop
into the female reproductive system.
Development of the Reproductive
Systems

Development
of the
Reproductive
Systems

 Mullerian-inhibiting substance (MIS) causes apoptosis of
cells in the Mullerian ducts in developing males. So, no
structures develop from the ducts in male reproductive
systems.
 Testosterone in developing males secreted by interstitial
cells in the testes stimulates the development of the
mesonephric ducts into the epididymis, vas deferens,
ejaculatory duct and seminal vesicles.
Systems

Before differentiation, all embryos have:
 Urethral (urogenital) folds
 Urethral groove
 Genital tubercle
 Labioscrotal swelling
Systems

Development of
the Reproductive
Systems

 The first decade: reproductive system in
juvenile state
 Age 10: hormone-directed changes
leading to puberty
 Puberty: males begin to produce sperm,
females enter menarche (beginning of
menstruation).
 With age, fertility declines. Between 30–
40, ovarian follicles become exhausted.
Estrogen levels decline.
Aging and the Reproductive Systems

 In males, reproduction is still possible into
the eighties or nineties.
 At around age 55, testosterone levels
decline, sperm levels drop, sexual desire
wanes.
 Most males over 60 experience benign
prostatic hypertrophy where the prostate
enlarges to two to four times its normal
size.
Aging and the Reproductive Systems

Copyright 2014 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this work beyond that
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programs or from the use of the information herein.
End of Chapter 28

28 [chapter 28 the reproductive system]

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28 [chapter 28 the reproductive system]