Copyright © John Wiley & Sons, Inc. All rights reserved. Chapter 28 The Reproductive Systems

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

Chapter 28

The Reproductive Systems


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)


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

Gamete formation and Meiosis


Gamete formation and Meiosis


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

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)



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



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



Seminiferous Tubules Seminiferous

tubules are lined by:

G

erm cells in various stages of maturation which give rise to sperms &

S

ertoli cells- nourish the germ cells, form fluid for sperm transport

I

n between the Seminiferous tubules are interstitial cells of Leydig

that secrete

testosterone


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

Descent of Testis


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)

Spermatogenesis


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


Spermatogenesis


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


spermatogonia

primary spermatocytes

secondary spermatocytes

spermatids

spermatozoa


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

Hormonal Control of Spermatogenesis



Control of Testosterone Production

Negative feedback system

controls blood levels 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

Actions of Testosterone


Before ejaculation, sperm travel via the

following route:

o Seminiferous tubules

o Rete testis (network)

o Efferent ducts

o Epididymis

o Vas (ductus)

deferens…

Pathway of Sperm Flow through the Ducts of the Testis


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

Duct system


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.

Duct system: Epididymis



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

Duct system


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

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

Accessory Glands


Accessory Glands


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


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 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

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; erection

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

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



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

Ovaries


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


Oogenesis 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


Oogenesis


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.

Ovaries; follicular development


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



Ovarian follicles



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

oThe 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



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



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



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)


The vagina is a fibromuscular canal lined with

stratified squamous epithelium It 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 ,and labia minorao Vestibule, the

area between the

labia minora contains urethral &

vaginal orifice



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



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



The breasts (mammary glands) are present in the

anterior thoracic wall Contains 15–20 lobes divided into lobules

o Each lobule is

composed of milk-

secreting glands called

alveoli. The nipple has openings

for the lactiferous ducts &

pigmented area (areola)

around it





Female Reproductive Cycle The female reproductive cycle includes the

ovarian and uterine cycles & the hormonal changes that regulate themo Controlled by monthly hormone cycle of

anterior pituitary, hypothalamus & ovary

Ovarian cycleo changes in ovary during & after

maturation of oocyte and follicles The uterine (menstrual) cycle

o involves changes in the endometriumo preparation of uterus to receive fertilized

ovumo if implantation does not occur, the stratum

functionalis is shed during menstruation


Hormonal Regulation of Reproductive Cycle GnRH secreted by the hypothalamus:

stimulates the release of FSH and LH by the anterior pituitary gland

o FSH initiates growth of follicles that secrete estrogen estrogen maintains reproductive organs

o LH :o stimulates ovulation o romotes formation of the corpus luteum

which secretes progesterone, estrogens, relaxin, inhibins progesterone prepares uterus for

implantation


Overview of Hormonal Regulation


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.

Estrogen: functions


Progesterone is the principal hormone

responsible for maturation of the uterine

endometrium for implantation, as well as an

important player in stimulating breast

development


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

Phases of the Female Reproductive Cycle


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


Preovulatory (proliferative)phase - days 6-

13 In the ovary (follicular phase)o secondary follicles secreting estrogeno One dominant secondary follicle develops into a

Vesicular (Graafian) follicleo The graafian follicle enlarges & bulges at

surface of the ovary & is ready for ovulationo 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


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

Ovulation; day 14


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


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


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


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


Female Reproductive Cycle

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Copyright © John Wiley & Sons, Inc. All rights reserved. Chapter 28 The Reproductive Systems