chapter 28

Copyright © John Wiley & Sons, Inc. All rights reserved.

Chapter 28

The Reproductive Systems


Sexual Reproduction is the process in which

organisms produce offspring by means of

uniting gametes (sperm and egg)

o Male reproductive organs secrete

androgen hormones, produce gametes

(sperm), and facilitate fertilization

o Female reproductive organs secrete

female hormones, produce gametes (ova),

facilitate fertilization and sustain growth of

the embryo and fetus

Reproduction Overview


Urology is the medical specialty that treats

disorders and diseases of the male

reproductive system

Gynecology is the medical specialty that treats

disorders and diseases of the female

reproductive system

o Obstetrics focuses on the care of women

during pregnancy

Reproduction Overview


The genitals are all the structures of

reproduction

o The gonads (the testes in males and ovaries

in females) are the site for gamete

production and hormone secretion

o Various ducts store and transport gametes

o Accessory sex glands produce secretions to

protect and support the gametes

o Supporting structures deliver and/or assist in

joining gametes (penis in male, vagina and

uterus in female)

Male Reproductive Anatomy


The male gonads are the testes (singular:

testis)o The ducts of the male reproductive system

are the:

▪ vas deferens (ductus deferens)

▪ ejaculatory ducts

▪ urethrao Male reproductive

glands are the:

▪ seminal vesicles (2)

▪ Prostate (1)

▪ bulbourethral glands (2)



The scrotum is a supporting structure for the

testes

o It consists of a sac of loose skin and

superficial fascia that hangs from the root of

the penis

o The location and contraction

of muscle fibers (dartos and

cremaster muscles) regulates

the testicular temp to that

required for sperm production

(2-3o below the core temp)



The spermatic cord is a supportive structure

that ascends “out of” the scrotum, and

consists of:

o The vas deferens

o The testicular artery (of course this

is going into the scrotum)

o Veins and lymphatics that

drain the testes and carry

testosterone to the body

o Autonomic nerves



The spermatic cord and ilioinguinal nerve pass

through the inguinal canal, a passageway in

the aponeuroses of the abdominal muscles

(transversus abdominus, internal oblique, and

external

oblique muscles)

o In women, the round

ligament of the uterus and

the ilioinguinal nerve pass

through a very small

inguinal canal



The tunica albuginea (collagen) forms septa

that divide each testis into compartments

called lobules

o Each lobule contains 1-3

seminiferous tubules

where sperm are

produced



Prenatal secretion of testosterone assists

testicular descent and development of male

external genital

Secretion of testosterone at puberty leads to

development of male secondary sexual

characteristics

▪ stimulation of anabolism (musculoskeletal

and protein growth)

▪ hair growth patterns

▪ lowering of the voice

▪ development of libido (sexual drive)

Male Reproductive Physiology


Spermatozoa are produced in the

seminiferous tubules by sperm stem cells

called spermatogonia

At the beginning of puberty, the

anterior pituitary increases secretion

of the gonadotrophs LH and FSH

o Follicle-stimulating hormone

(FSH) stimulates Sertoli cells

and increases the rate of

spermatogenesis

Spermatogenesis


LH stimulates Leydig cells, which are

located between seminiferous tubules, to

secrete the hormone testosterone

(synthesized from cholesterol) Once the degree of spermatogenesis (sperm

formation) required for male reproductive

functions

has been achieved,

Sertoli cells release

inhibin, a hormone

that inhibits FSH

Spermatogenesis


Spermatogenesis


Each day about 300 million sperm complete

the process of spermatogenesis. A sperm

contains several structures that are highly

adapted for reaching and penetrating a

secondary oocyte

o The major parts of a sperm are the head and

the tail

▪ the nucleus contains 23 highly condensed

chromosomes (half the normal

number)

▪ covering the anterior two-thirds of the

nucleus is the acrosome

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

Spermatozoa


Before ejaculation, sperm travel via the

following route:

o Seminiferous tubules

o Rete testis (network)

o Efferent ducts

o Ductus epididymis

o Vas (ductus)

deferens…

Spermatozoa


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

Spermatozoa


The accessory glands contribute greatly to the

constituents of the ejaculate

o Seminal vesicles secrete a viscous,

alkaline fluid (mainly during ejaculation)

which makes up 60% of the total volume. It

contains fructose (for energy), prostaglandins

(to stimulate smooth muscle contractions),

and clotting proteins (fibrinogen)

▪ the alkalinity neutralizes the acidity of the

male urethra and the female reproductive

tract

Accessory Glands


The prostate is a chestnut-sized, donut-

shaped gland that secretes about 25% of

ejaculate volume. 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 alkaline mucus that

decreases sperm damage in the urethra

Accessory Glands


Accessory Glands


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

Semen


The penis contains the urethra and is a

passageway for the ejaculation of semen and

the excretion of urine

o It is cylindrical in shape and 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

The Penis


The two dorsolateral masses are the corpora

cavernosa penis, and the smaller midventral

mass is the corpus spongiosum penis

(contains

the spongy urethra and

keeps it open during

Ejaculation)

The Penis


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; NO also causes the

smooth muscle within the erectile tissue to

relax, resulting in widening of the blood

sinuses

The Male Sexual Response


After an erection, sympathetic stimulation

is necessary for the rest of the sexual

response, including 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

The Male Sexual Response


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)

Female Reproductive Anatomy


The histology of the ovaries reveals the

following parts:

o The germinal epithelium covers the surface

of the ovary, but does not give rise to ova –

those cells arise from the yolk sac and

migrate to the ovaries

o The ovarian cortex contains the ovarian

follicles

o The ovarian medulla

contains blood vessels,

lymphatic vessels

and nerves



The primary role of the ovaries are to produce

mature 2o oocytes (female gametes) and

release one (ovulation) during each monthly

ovarian cycle

o another important

function of the ovaries

are to secrete the female

hormones estrogen,

progesterone, inhibin,

and relaxin



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



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)



The broad ligament

is a major support

for the

uterus (provides

side-to

-side and rotation

support)

oOther supportive

ligaments of the

uterus are depicted

in these graphics



The uterus is a pear shaped organ situated

between the urinary bladder and the rectum

o It serves as part of the pathway for sperm

deposited

in the vagina to reach the uterine tubes

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



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



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



The vagina is a fibromuscular canal lined with

mucous membrane that extends from the

exterior of the body to the uterine cervix. It is

composed of both longitudinal and circular

muscle, and has 3 basic functions:o Serve as a passageway

for menstrual flowo Receive spermo Form the lower

birth canal



The vulva (female external genitalia) refers

to the:o Mons pubis (created by adipose tissue)o Erectile tissue of the clitoriso Labia majora (outer limits of

vulva) and labia minora

(covers the vestibule)o Vestibule, the

area between the

labia minorao Vaginal orifice

(opening)



Anterior to the vaginal orifice and posterior to

the clitoris is the opening of the external

urethral orifice

o Mucus-secreting paraurethral glands flank

the orifice (homologous to the prostate gland

in males)

On either side of the vaginal orifice itself are

the greater vestibular (Bartholin’s) glands

which open by ducts into a groove between the

hymen and labia minora. They produce a small

quantity of lubricating mucous during sexual

arousal



The perineum denotes the diamond-shaped

area medial to the thighs and buttocks of

females (and males) – the entire undersurface

of the pelvis

o It contains the external

genitalia and

anus



The breasts (mammary glands) are modified

sudoriferous glands that produce milk: Each

contains 15–20 lobes divided into lobules

o Each lobule is

composed of milk-

secreting glands called

alveoli. The nipple has a

pigmented area (areola)

and openings for the

lactiferous ducts



During reproductive years, nonpregnant

females normally exhibit cyclical changes in

the ovaries and uterus

o Each cycle takes about a month and involves

both oogenesis (ovarian cycle) and

preparation of the uterus to receive a

fertilized ovum with hormones secreted by

the hypothalamus, anterior pituitary, and

ovaries controling the main events

Female Reproductive Physiology


The hormones secreted in the brain constitute

the part

of the cycle called the

hypothalamic/pituitary cycle. Those

hormones are GnRH, FSH, and LH

oThe reproductive organs in the female pelvis

respond to the brain hormones by cycling at

two “lower” levels

▪ the ovarian cycle occurs in the ovaries

where 1o , 2o and 3o follicles are formed

▪ the uterine cycle refers to the monthly

cycling of

the endometrium when a woman is not

pregnant

The Female Reproductive Cycle


The formation of gametes in the ovaries is

termed oogenesis. In contrast to

spermatogenesis, which begins in males at

puberty, oogenesis is more complex and

begins in females before they are even born

o During early fetal development, primordial

germ cells migrate from the yolk sac to the

ovaries where they differentiate into oogonia

▪ Oogonia are diploid (2n) stem cells that

divide mitotically to produce millions of

germ cells

The Ovarian Cycle


Even before birth, most oogonia degenerate,

though a few develop into larger cells called 1o

oocytes that enter prophase of meiosis I

(during fetal development) but do not

complete it until a fortunate few are called

upon to do so during the reproductive years

o During the interim (an arrested

stage of development), each 1o

oocyte is surrounded by follicular

cells in a primordial follicle

The Ovarian Cycle


At puberty, under the influence of LH and FSH

(the brain gonadotropins), several primordial

follicles will be stimulated each month, although

only one will typically reach the maturity

needed for ovulation

o Maturing oocytes within maturing follicles

undergo a series of developmental stages

which ultimately brings one 2o oocyte within

a 3o follicle to the point of ovulation

▪ the ovulated 2o oocyte will have completed

meiosis I, and so have the haploid number of

chromosomes (1n)

The Ovarian Cycle


As the 1o oocyte is prepared for ovulation, and

receives the signal to complete meiosis I, two

haploid (1n) cells of unequal size are produced –

each with 23 chromosomes

o The smaller cell is called the first

polar body (essentially a packet

of discarded nuclear material)

The Ovarian Cycle

The ovarian cortex with many follicles in different stages of development.

o The larger 2o

oocyte

inherits most

of the

cytoplasm


Be aware that the events depicted in these

graphics depict two separate, yet interrelated

events: Oocyte maturation vs. follicle

maturation

o The follicle

has important

functions beyond

hosting an

oocyte!

The Ovarian Cycle


The Ovarian Cycle


High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

Hypothalamus

Anterior pituitary

Ovary

Corpus hemorrhagicum(ruptured follicle)

Almost mature(graafian) follicle

LH

GnRH

1 High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

Hypothalamus

Anterior pituitary

GnRH promotesrelease of FSHand more LH

Ovary



LH

GnRH

1

2

High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

LH surgebrings aboutovulation

Ovulatedsecondaryoocyte

Hypothalamus

Anterior pituitary

GnRH promotesrelease of FSHand more LH

Ovary



LH

GnRH

1

2

3

Ovulation


At ovulation the 3o follicle (mature Graafian

follicle) ruptures to expel the 2o oocyte into

the pelvic cavity, normally to be swept into the

uterine tube - if not fertilized, it degenerates

o if sperm are

present and

one penetrates

the 2o oocyte,

meiosis II resumes

The Ovarian Cycle


The events of

oogenesis

described thus

far are depicted

in this graphic

o The 2o oocyte is

the cell that

most people

call

“the egg”

The Ovarian Cycle


In the ovary, the mature Graafian follicle has

become a corpus luteum, a temporary

structure essential for establishing and

maintaining pregnancy in females

o It secretes estrogens and progesterone,

which are responsible for the thickening of

the endometrium and its development and

maintenance, respectively

o After approx. 14 days, if the 2o oocyte is not

fertilized, the corpus luteum stops secreting

progesterone and degenerates into a corpus

albicans (just a mass of fibrous scar tissue)

The Ovarian Cycle


Without estrogen, and then with abrupt

progesterone withdrawal, the uterine lining

cannot be maintained and it sloughs (menses) –

more on the uterine cycle shortly

If, on the other hand, 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

The Ovarian Cycle


The window of opportunity for fertilization to

happen is approximately 2 days before

ovulation to 1 day after ovulation (the sperm

can survive 48-72 hrs. in the uterine tube)

At the moment of conception, the successful

sperm penetrates the plasma membrane of

the 2o oocyte and the nuclear material of the

two cells unite to reconstitute the normal

number of chromosomes (2n)

o The new diploid cell is called a zygote

The Ovarian Cycle


The events of

oogenesis

and

follicular

development

are

summarized

here

The Ovarian Cycle


Estrogen, progesterone, relaxin, and

inhibin are all secreted by ovaries

(and the placenta during pregnancy)

o Estrogen is responsible for the

presence of secondary sex characteristics

(adipose tissue in the breasts, mons pubis,

abdomen, and hips, voice pitch, and broad

pelvis)

▪ It also lowers blood cholesterol and assists

with fluid and electrolyte balance and

protein anabolism

Ovarian Hormones


Progesterone is the principal hormone

responsible for maturation of the uterine

endometrium, as well as an important player in

stimulating breast development

o It inhibits GnRH and LH through a negative

feedback loop

Ovarian Hormones


Relaxin is released by the corpus luteum; it

relaxes the

myometrium and the pubic

symphysis at the

end of pregnancy

Inhibin is released by

granulosa cells, and then in

large amount by the corpus

luteum; it inhibits FSH

and LH

Ovarian Hormones


In many ways the uterine or menstrual cycle

closely parallels the events happening in the

ovaries

o Under the influence of the ovarian

hormones, the uterine lining undergoes

cyclic events (4 phases) every 28 days (on

average)

▪ Menses marks the beginning of the cycle

▪ This is followed at day 5 by the pre-

ovulatory phase

▪ Ovulation occurs on about day 14, after

which the post-ovulatory phase begins

The Uterine Cycle


The Uterine Cycle


Menses manifests as a degeneration of the

endometrium when levels of progesterone

become insufficient

o Prostaglandin released by the “unsupported”

endometrium causes constriction of

supply arteries causing a reduction in

blood flow: Bloody endometrial tissue

eventually sloughs, and is passed out

through the two uterine os and into the

vagina

▪ Menstruation lasts 1–7 days with 50–150

ml of fluids and cells lost

The Uterine Cycle


Under the influence of estrogens released

from the new developing follicles the pre-

ovulatory (proliferative phase) begins, and

the uterine epithelium is restored

The post-ovulatory (secretory phase) begins

around the time of ovulation. Endometrial

glands increase the secretion of mucous-rich

glycogen and the endometrium reaches

maximum thickness and maturity under the

influence of estrogens and progesterone

The Uterine Cycle


Equivalent structures

during fetal development testes ≈ ovaries sperm ≈ ovum (2o oocyte) scrotum ≈ labia majora spongy urethra and penile

skin ≈ labia minora glans penis ≈ clitoris prostate gland ≈

paraurethral glands bulbourethral glands ≈

vestibular glands

Homologous Structures


As in the male, the initiation of the sexual

response results in stimulation of sacral

parasympathetic fibers and nitric oxide

dilation of the erectile tissues – in this case, of

the clitoris

o Orgasm occurs at the peak of the plateau

phase of the sexual response. Sexual climax

culminates in a sympathetic discharge,

accompanied by quick cycles of muscle

contraction in the lower pelvic muscles and

an intense feeling of euphoria

The Female Sexual Response


The period after orgasm is known as the

refractory period. During this time, release of

the neurohormones oxytocin and prolactin

produce a feeling of relaxation

o Release of these hormones (and others, like

vasopressin) also serves as a reward

mechanism that regulates pair-bonding and

sexual imprinting between the partners

The Female Sexual Response


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

Impotence is the inability to maintain erection

long enough for sexual intercourse

Primary infertility describes couples who have

never been able to become pregnant after at

least 1 year of unprotected sex

Disruptions of Homeostasis


Menstrual Abnormalities

o Amenorrhea is the absence of menstruation

o Dysmenorrhea describes unusual menstrual

discomfort (usually indicates an excess of

prostaglandin secretion)

o Disfunctional uterine bleeding (DUB) is

abnormal uterine bleeding in the absence of

organic disease (usually an

estrogen/progesterone imbalance)

o PMS (premenstrual syndrome) indicates a

mild distress near end of postovulatory

(luteal) phase

Disruptions of Homeostasis

chapter 28

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