Reproductive Physiology

Assoc. Prof. Mária Pallayová, MD, [email protected]

Department of Human Physiology, UPJŠ LF

April 28, 2020 (12th week – Summer Semester 2019/2020)

Reproductive Physiology

Human Physiology Course

mailto:[email protected]

Introduction

One of nature's primary goals is perpetuation of the

species. All living organisms must reproduce in some

manner.

Function of the reproductive system is to produce offspring.

Puberty is the age at which the reproductive organs mature

sufficiently to allow reproduction.

Reproductive organs of both the male and female produce

sex cells called gametes.

A combination of the female gamete (ovum) and male

gamete (sperm) is called fertilization.

Sex vs. Gender

Sex - refers to biological characteristics that distinguish

female from male. The distinction may be made on the

basis of chromosomes, gonads, internal and external

morphology, and hormonal status.

Gender - gender identification - refers to the concept

held by the individual (or by those raising the individual)

that the individual is male, female, or ambivalent.

The Male Reproductive

System

♂

The organs of the male reproductive system consist of the

testes and the accessory organs (scrotal sac + penis +

accessory glands).

Pathway of spermatozoa:

– Epididymis

– Ductus deferens (Vas deferens)

– Ejaculatory duct

the male reproductive role is to produce viable sperm, and

to deliver the sperm to the female reproductive system

Male Organs of Reproduction


Testes

– Produce sperm and secrete testosterone causing the

appearance of secondary sexual characteristics

(facial and body hair, deepened voice, increased

muscle mass, thickening of the bones)

Epididymis

– A tube on the surface of each testis that stores the

sperm while they mature

Penis

– Semen and urine are excreted

Seminal vesicles

– Active secretory gland

– Contributes ~60% total volume of semen

– Secretions contain fructose, prostaglandins, fibrinogen

Prostate gland

– Secretes slightly acidic prostate fluid

Bulbourethral glands/COWPER’S GLANDS

– Secrete and add a thick alkaline mucus to the semen

that acts as a lubricant during sexual excitement

Male accessory glands

The primary and secondary

sexual characteristics

THE SECONDARY

SEXUAL

CHARACTERISTICS

The Male: On the average, taller and

heavier than the female. 1. Head hair: may

fall out with age. 2. Facial hair: grows

throughout adult life. 3, Features: more

pronounced, face longer, head (front to

back) longer. 4. Neck: thicker, longer,

larynx one-third larger. 5. Shoulders:

broader, squarer. 6. Chest: larger in every

dimension. 7. Body hair: more evident,

especially on chest and arms. 8. Breasts:

rudimentary in size. 9. Muscles: bigger,

more obvious. 10. Arms: longer, thicker,

"carrying angle" straight. 11. Pubic hair:

growing up to a point, forming triangle. 12.

Hips: narrower. 13. Hands and feet: larger,

fingers and toes stronger and blunter. 14.

Thighs: more cylindrical with bulge of

muscles. 15. Legs: longer, bulging calves.

16. Angle of thigh and leg; as with

"carrying angle" of arm, forming straight

line, thigh to ankle.

THE SECONDARY

SEXUAL

CHARACTERISTICS

The Female: On the average, shorter and

lighter than the male. 1. Head hair: more

lasting. 2. Facial hair: very faint, usually

noticeable only in later years, 3. Features:

more delicate, face rounder, head smaller,

rounder (from top). 4. Neck: shorter, more

rounded, larynx smaller. 5. Shoulders:

more rounded, sloping. 6. Chest: smaller,

narrower. 7. Body Hair: very light and

faint. 8. Breasts: prominent, also well-

developed nipples with large surrounding

rings, 9. Muscles: largely hidden under

layers of fat. 10. Arms: "carrying angle"

bent. 11. Pubic hair: forming straight line

across at top. 12. Hips: wider, more

rounded. 13. Hands and feet: smaller and

narrower. 14. Thighs: wider at top and

shorter in length, 15. Legs: shorter with

smoother contours. 16. Angle of thigh and

leg; as with "carrying angle" of arm,

slightly bent,forming an angle at the knee.

The Male Reproductive System

The testes (testicles) are paired oval glands that descend

into the scrotum.

At the onset of puberty, the testes produce testosterone

(the male sex hormone).

Testosterone stimulates and promotes the growth of the

secondary sex characteristics in the man.

Epididymis is a comma-shaped organ on the top of the

testicle. It stores and propels the sperm toward the urethra

during ejaculation.

From the epididymis, sperm enters the vas deferens

(ductus deferens) that transports sperm to the urethra.


The reproductive glands in the male serve to produce

fluids that are added to the sperm to form SEMEN.

These secretions are vital for keeping the sperm cells

alive and motile (able to move).

The SPERM are cells that have a tail, head, and neck.

The sperm are produced in the TESTICLES.

The testes produce sperm throughout the life of the

male. (Unlike the female, who are born with all the eggs

they will ever have.)


During its trip toward the outside world, sperm picks up

fluids from the glands. When the sperm and fluid join

together, it is then called SEMEN.

COWPER’S GLANDS add a thick mucus to the semen

that acts as a lubricant during sexual excitement.

The PENIS is the male sex organ that transports the

semen into the vagina. A slightly enlarged region at the

tip of the penis is called the GLANS.

The glans of the penis is covered by a fold of skin called

the PREPUCE or FORESKIN.


The Structure of the Testes

The Epididymis

The D

uctu

s D

efe

rens

an

d A

cce

sso

ry G

lan

ds

The Penis

Typical ejaculate = 2-5 ml fluid

– Contains between 20 – 100 million spermatozoa per ml

Seminal fluid

– A distinct ionic and nutritive glandular secretion

Contents of Semen

Testes are formed in abdomen and descend

into scrotum at 7th month of development

Temperature in scrotum is slightly lower than

in body

Spermatogenesis (formation of sperm)

sperm-forming cells

Sertoli cells

interstitial cells-produce testosterone

Process takes about 9-10 weeks

Notes

It takes approximately 65 to 70 days to develop

spermatozoa from the earliest stages of spermatogonia.

Because the production of sperm depends on LH and

FSH, a lack of GnRH (Kallmann’s syndrome) will reduce

the production of LH, FSH, and sperm.

Temperature is important in regulating sperm production.

Optimal sperm production occurs at 2 to 3 degrees C

lower than body temperature.

Testes produce mature spermatozoa

Sperm enter epididymis

– Elongated tubule with head, body and tail regions

– Monitors and adjusts fluid in seminiferous tubules

– Stores and protects spermatozoa

– Facilitates functional maturation of spermatozoa

Male reproductive tract

Seminiferous tubules

– Contain spermatogonia

Stem cells involved in spermatogenesis

– Contain sustentacular cells

Sustain and promote development of sperm

Spermatogenesis

The Seminiferous Tubules

The Seminiferous Tubules

Sp

erm

ato

ge

ne

sis

Spermiogenesis and Spermatozoon Structure

Spermatazoa in testes are not yet capable of fertilization

Epididymis- is actually over 20 feet long!

spermatazoa complete maturation

as they move through epididymis

(about 2 weeks)

Ductus deferens (vas deferens)

Ejaculatory duct

Ejaculatory duct

Sperm

Seminal fluid

secretions from prostate

seminal vesicles

bulbourethral glands (Cowper’s glands)

Activate sperm

Provide nutrients

Contractions help move sperm

Buffers

Control of erection

Hypothalamus (conscious control)

Parasympathetic nerves

neurotransmitter- nitric oxide?

promotes blood flow into penis

(sildenafil-Viagra promotes vasodilation)

Control of emission and ejaculation

sympathetic nerves- muscle contraction

Puberty is the time of life when sexual maturation occurs.

Greatly increased testosterone secretion during puberty

stimulates the growth of the penis and the testes.

Testosterone also brings about and maintains the male

secondary sex characteristics that develop during puberty,

including the growth of a beard, axillary (underarm) hair,

and pubic hair.

Regulation of Male Hormone

Levels


Levels

At the time of puberty, the sex organs mature, and then

changes occur in the physique of males.

The cause of puberty is related to the level of sex

hormones in the body, as regulated by the negative

feedback system.

This feedback system functions long before puberty, but

the level of hormones is low because the hypothalamus is

supersensitive to feedback control.

At the start of puberty, the hypothalamus becomes less

sensitive to feedback control and begins to increase its

production of gonadotropin-releasing hormone, which

stimulates the anterior pituitary to produce the gonadotropic

hormones.

– Two gonadotropic hormones, FSH (follicle-stimulating

hormone) and LH (luteinizing hormone), are named for

their function in females but exist in both sexes,

stimulating the appropriate organs in each.


Levels

Gonadotropic hormones

FSH promotes spermatogenesis in the seminiferous

tubules (targets sustentacular cells to promote

spermatogenesis)

LH promotes androgen (e.g., testosterone) production in

the interstitial cells

LH in males is also called interstitial cell-stimulating

hormone (ICSH)

Regula

tion

of

repro

ductio

n

in th

em

ale

Regulation, hormonal products, and interactions

between Leydig and Sertoli cells. ABP, androgen-

binding protein; E, estradiol; T, testosterone; R, receptor.

Negative Feedback Mechanisms

The hypothalamus, anterior pituitary, and testes are

involved in a negative feedback system.

The system maintains testosterone production at a fairly

constant level.

When the amount of testosterone in the blood rises to a

certain level, it causes the hypothalamus and anterior

pituitary to decrease the secretion of GnRH and LH.

As the level of testosterone begins to fall, the

hypothalamus increases its secretion of GnRH, and the

anterior pituitary increases its secretion of LH; thus,

stimulation of the interstitial cells occurs.

Only minor fluctuations of the testosterone level occur in

the male, and the feedback mechanism in this case acts

to maintain testosterone at a normal level.

A similar feedback mechanism maintains the continuous

production of sperm.

The sustentacular cells in the wall of the seminiferous

tubules produce a hormone called inhibin that blocks

GnRH and FSH secretion when appropriate.

Negative Feedback Mechanisms

Negative feedback

Regulation of testosterone

secretion involves negative

feedback by testosterone

on GnRH and LH.

Regulation of sperm

production involves

negative feedback by

inhibin on GnRH and FSH.

Hormonal Feedback and the Regulation of

the Male Reproductive Function

Testosterone

The male sex hormone, has many functions.

It is essential for normal development and function of the

sex organs in males (e.g., greatly increased testosterone

secretion at the time of puberty stimulates maturation of

the penis and the testes).

Secondary Sex Characteristics

Testosterone also brings about and maintains the male

secondary sex characteristics, which develop at the

time of puberty and visibly distinguish males from

females.

These characteristics include

– a pattern of male hair growth,

– activity of cutaneous glands,

– pitch of the voice,

– muscle strength.

At puberty, males experience growth of a beard, axillary

hair, and pubic hair (that tapers toward the navel).

A side effect of testosterone activity is baldness. Genes for

baldness are probably inherited by both sexes, but baldness

is seen more often in males because of the presence of

testosterone. This makes baldness a sex-influenced trait.

Testosterone also causes oil and sweat glands in the skin to

secrete, thereby contributing to acne and body odor.

Testosterone

The larynx and vocal cords enlarge, causing the voice to

change.

The “Adam’s apple” is a part of the larynx, and it is

usually more prominent in males than in females.

Testosterone is responsible for the greater muscular

strength of males.

Testosterone

It prompts the larynx and the vocal cords to enlarge, causing

the voice to change.

It is partially responsible for the muscular strength of males.

Testosterone also stimulates oil and sweat glands in the

skin; therefore, it is largely responsible for acne and body

odor. Another side effect of testosterone is baldness.

Genes for baldness are probably inherited by both sexes,

but baldness is seen more often in males because of the

presence of testosterone.

Testosterone

Quiz

The production of estradiol by the testes requires:

(A) Sertoli cell follistatin

(B) LH and Leydig cells

(C) Activin but not LH

(D) Leydig cell, Sertoli cells, LH, and FSH

(E) Leydig cells and FSH

Quiz

The production of estradiol by the testes requires:

(A) Sertoli cell follistatin

(B) LH and Leydig cells

(C) Activin but not LH

(D) Leydig cell, Sertoli cells, LH, and FSH

(E) Leydig cells and FSH

Quiz - Explanation

The production of estradiol by the testes requires Leydig cell,

Sertoli cells, LH, and FSH.

The production of estradiol requires Leydig cells, under the influence

of LH, which stimulates androgen production. The androgen diffuses

to Sertoli cells, which contain aromatase, the enzyme that converts

androgens to estrogens under the influence of FSH.

Follistatin binds activin and would reduce FSH secretion, an essential

component for estradiol production.

Estradiol is not produced by Leydig cells.

Activin would increase the secretion of FSH, which is a necessary

component for estradiol, but other cells and hormones are required.

Similarly, Leydig cells would need LH to stimulate the production of

the androgen precursor of estrogen.

Sertoli cells, under the influence of FSH, are needed to aromatize

androgen from Leydig cells.

In the testes, luteinizing hormone (LH) controls the synthesis

of testosterone by Leydig cells, and follicle-stimulating

hormone (FSH) increases the production of androgen-binding

protein, inhibin, and estrogen by Sertoli cells.

Spermatozoa are produced within the seminiferous tubules of

both testes. Sperm develop from spermatogonia through a

series of developmental stages that include spermatocytes

and spermatids.

The sperm mature and are stored in the epididymis. At the

time of ejaculation, sperm are moved by muscular contrations

of the epididymis and vas deferens through the ejaculatory

ducts into the prostatic urethra. The sperm are finally moved

out of the body through the urethra in the penis.

Key concepts

Key concepts (cont.)

LH and FSH secretion by the anterior pituitary are

controlled by gonadotropin-releasing hormone (GnRH).

Testosterone mainly reduces LH secretion, whereas

inhibin reduces the secretion of FSH. The testicular

hormones complete a negative-feedback loop with the

hypothalamic-pituitary axis.

Androgens have several target organs and have roles in

regulating the development of secondary sex

characteristics, the libido, and sexual behavior.

The most potent natural androgen is

dihydrotestosterone, which is produced from the

precursor, testosterone, by the action of the enzyme

5alpha-reductase.

Male reproductive dysfunction is often due to a lack of

LH and FSH secretion or abnormal testicular

morphology.


The Female

Reproductive System

♀

• The female reproductive system is composed of

internal and external organs of reproduction.

• Internal organs of reproduction:

• OVARIES

• FALLOPIAN TUBES

• UTERUS

• VAGINA

• External organs of reproduction

• GENITALIA

Female Organs of Reproduction

Ovaries

The ovaries are located in the pelvic cavity.

The ovaries produce estrogens and progesterone, the

female sex hormones.

The hypothalamus and the pituitary gland control the

hormonal secretions of the ovaries.

Internal Organs of Reproduction

Ovaries are paired glands that produce eggs and hormones

(estrogen and progesterone) for ovulation and pregnancy.

Ovaries store egg cells (oocytes), and mature the stored

eggs until ovulation.

Fallopian tubes (OVIDUCTS = the connection between the

ovary and the uterus) transport the mature ovum from the

ovary to the uterus. Oviducts have FIMBRAE to coax the

ovulated egg into the tube. Once inside the tube, the egg

travels toward the uterus. When sperm is available,

fertilization usually occurs in the oviduct.

Uterus = a muscular pear-shaped, hollow organ located

between the bladder and the rectum. Structure in which

the zygote is implanted following conception. Function is

to nourish and protect the growing fetus until birth.

Cervix = is a term denoting the neck of the uterus and

the extension of it into the top portion of the vagina (for

delivery of a fetus).

Vagina= a muscular tube that extends from the cervix

(neck of the uterus) to the exterior of the body.

Functions: sexual intercourse, receptor of semen,

discharge of menses, and passage for delivery of fetus.

The vagina is lined by mucus. This mucus is a lubricant.

Internal Organs of Reproduction

Female External Organs

The external organs are collectively known as

GENITALIA:

LABIA MAJORA = the larger outer lips of the vagina.

LABIA MINORA = smaller inner lips of the vagina.

CLITORIS = small projection of tissue located between

the labia minora; contains many nerve endings. Similar

to the penis in males.

BARTHOLIN’S GLANDS = for lubrication.

Mammary glands = ducts that secrete milk (lactation)

following pregnancy

Muscular organ

– Mechanical protection

– Nutritional support

– Waste removal for the developing embryo and

fetus

Supported by the broad ligament and 3 pairs

of suspensory ligaments

The uterus

Myometrium – outer muscular layer

Endometrium – a thin, inner, glandular

mucosa

Perimetrium – an incomplete serosa

continuous with the peritoneum

Uterine wall consists of three

layers:

The Uterus

The Uterine Wall

The Uterine Wall

Estrogen and Progesterone

The female sex hormones, estrogens and progesterone,

have many effects on the body. In particular, estrogens

secreted during puberty stimulate the growth of the

uterus and the vagina.

Estrogen is necessary for egg maturation and is largely

responsible for the secondary sex characteristics in

females, including female body hair and fat distribution.

In general, females have a more rounded appearance

than males because of a greater accumulation of fat

beneath the skin.

Also, the pelvic girdle is wider in females than in males,

resulting in a larger pelvic cavity.

Both estrogen and progesterone are required for breast

development and for regulation of the uterine cycle,

which includes monthly menstruation (discharge of blood

and mucosal tissues from the uterus).


Regulation of Female Hormone

Levels

At the time of puberty in females, the hypothalamus

increases its secretion of GnRH, and the anterior

pituitary releases larger amounts of the gonadotropins,

FSH and LH.

These hormones stimulate the ovaries to produce eggs

and elevated estrogen and progesterone levels.

The Hormonal Regulation of Ovarian Activity

Regula

tion

of

the

rep

rod

uctiv

etra

ctin

the

fem

ale


In particular, estrogen stimulates the growth of the uterus

and the vagina.

Estrogen is also necessary for egg maturation and the

onset of the menstrual cycle, as well as for the

development of the secondary sex characteristics in

females.

Secondary Sex Characteristics

These characteristics include the female pattern of body

hair and fat distribution.

In general, females have a more rounded appearance

than males because of a greater accumulation of fat

beneath the skin.

Also, the pelvic girdle enlarges in females so that the

pelvic cavity has a larger relative size compared to that

of males females have wider hips.

Both estrogen and progesterone are required for breast

development.

Control the reproductive cycle

Coordinate the ovarian and uterine cycles

Key hormones include:

– FSH

Stimulates follicular development

– LH

Maintains structure and secretory function of corpus

luteum

– Estrogens

Have multiple functions

– Progesterones

Stimulate endometrial growth and secretion

Hormones of the female reproductive cycle

Menstrual Cycle

Lasts approximately 28 days.

A complex process of hormone secretion and tissue

changes in the uterus.

A mature ovum is released from an ovary on about the

14th day of each cycle.

If the released ovum is not fertilized, the endometrium is

released from the body along with the ovum.

The sloughing of this bloody tissue, or menses, lasts from

3 to 7 days.

The menstrual cycle continues until app. 50 years of age.

Repeating series of changes in the

endometrium

Continues from menarche to menopause

– Menses

Degeneration of the endometrium

Menstruation

– Proliferative phase

Restoration of the endometrium

– Secretory phase

Endometrial glands enlarge and accelerate their rates

of secretion

Uterine cycle

The Uterine Cycle

Menstrual Cycle

a monthly series of events that involve the ovaries and

uterus plus the female sex hormones

is about 28 days long, but it can be as short as 18 days

or as long as 40 days

• Pre-Ovulation Events

• Ovulation

• Post-Ovulation Events

Pre-Ovulation Events

Under the influence of FSH from the anterior pituitary,

several follicles begin developing in the ovary.

Therefore, this period of time (days 1–14) is called the

follicular phase of the ovary.

Although several follicles begin growing, only one follicle

continues developing, and it secretes increasing amounts

of estrogen. This particular follicle becomes more and

more sensitive to FSH and then LH.

Eventually, the very high level of estrogen exerts positive

feedback control over the hypothalamus so that it secretes

ever greater amounts of GnRH.

GnRH induces a surge in FSH and LH secretion by the

pituitary.

The LH level rises to a greater extent than does the FSH

level. Under the influence of so much stimulation,

ovulation occurs.

Pre-Ovulation Events and

Ovulation

While the ovary is experiencing its follicular phase, first

menstruation and then the proliferative phase occur in the

uterus.

During menstruation (days 1–5), a low level of female sex

hormones in the body causes the endometrial tissue to

disintegrate and its blood vessels to rupture.

A flow of blood and tissues, known as the menses, passes

out of the vagina during menstruation, also called the

menstrual period.

Under the influence of estrogen released by the new

follicle, the endometrium thickens and becomes vascular

and glandular. This is the proliferative phase of the uterus,

which ends when ovulation occurs.

Post-Ovulation Events

Under the influence of LH, the ovulated follicle becomes

the corpus luteum.

Therefore, this period of time (days 15–28) is known as

the luteal phase of the ovary.

The corpus luteum secretes progesterone and some

estrogen.

As the blood level of progesterone rises, it exerts

negative feedback control over the anterior pituitary’s

secretion of LH so that the corpus luteum in the ovary

begins to degenerate.

If fertilization of the egg does occur, the corpus luteum

persists for reasons that will be discussed shortly.

Under the influence of progesterone secreted by the

corpus luteum, a secretory phase (days 15–28) begins in

the uterus.

During the secretory phase of the uterus, the

endometrium of the uterus doubles or even triples in

thickness (from 1 mm to 2–3 mm), and the uterine glands

mature, producing a thick, mucoid secretion.

The endometrium is now prepared to receive the pre-

embryo. If implantation of a preembryo does not take

place, the corpus luteum disintegrates, and menstruation

occurs.

If fertilization occurs and is followed by implantation, the

developing placenta produces human chorionic

gonadotropin (HCG), which maintains the corpus

luteum in the ovary until the placenta begins to produce

progesterone and estrogen.

The placental hormones shut down the anterior pituitary

so that no new follicle in the ovaries matures, and they

maintain the endometrium so that the corpus luteum in

the ovary is no longer needed.

Usually, no menstruation occurs during pregnancy.

During the menstrual cycle, FSH and LH are released by

the anterior pituitary. FSH promotes the maturation of a

follicle in the ovary. The follicle produces increasing

levels of estrogen, which cause the endometrium to

thicken during the proliferative phase in the uterus. An

LH surge causes ovulation.

After ovulation, LH promotes the development of the

corpus luteum. This structure produces increasing levels

of progesterone, which causes the endometrial lining to

become secretory. Menses due to the breakdown of the

endometrium begins when progesterone production

declines to a low level due to corpus luteum

disintegration.

Menstrual Cycle

Menstrual Cycle

The Hormonal Regulation of the Female Reproductive Cycle

The Hormonal Regulation of the Female Reproductive Cycle

Ovum production

Occurs monthly in ovarian follicles

Part of ovarian cycle

– Follicular phase (preovulatory)

– Luteal phase (postovulatory)

Oogenesis

Oogenesis

Different Stages in the Development

of an Ovum and Follicle

The Ovarian Cycle

The Ovarian Cycle

Key concepts

Pulses of hypothalamic GnRH regulate the secretion of

LH and FSH, which enhance follicular development,

steroidogenesis, ovulation, and formation of the corpus

luteum.

LH and FSH, in coordination with ovarian theca and

granulosa cells, regulate the secretion of follicular

estradiol.

Ovulation occurs as the result of a positive feedback of

follicular estradiol on the hypothalamic-pituitary axis that

induces LH and FSH surges.


Follicular development occurs in distinct steps:

primordial, primary, secondary, tertiary, and graafian

follicle stages.

Follicular rupture (ovulation) requires the coordination of

appropriately timed LH and FSH surges that induce

inflammatory reactions in the graafian follicle, leading to

dissolution at midcycle of the follicular wall by several

ovarian enzymes.

Follicular atresia results from the withdrawal of

gonadotropin support.


The formation of a functional corpus luteum requires the

presence of an LH surge, adequate numbers of LH

receptors, sufficient granulosa cells, and significant

progesterone secretion.

The uterine cycle is regulated by estradiol and

progesterone, such that estradiol induces proliferation of

the uterine endometrium, whereas progesterone induces

differentiation of the uterine endometrium and the

secretion of distinct products.


During puberty, the hypothalamus begins to secrete

increasing quantities of GnRH, which increases LH and

FSH secretion, enhances ovarian function, and leads to

the first ovulation.

Menopause ensues from the loss of numerous oocytes

in the ovary and the subsequent failure of follicular

development and estradiol secretion. LH and FSH levels

rise from the lack of negative feedback by estradiol.

The illustration

summarizes

the eight steps

of fertilization.

ZP, zona

pellucida.

Reproduction is

accomplished

when the egg cell

(female gamete)

is fertilized by the

sperm cell (male

gamete)

Fertilization

Fertilization

The acrosome reaction causes a fusion of the plasma

membrane and the acrosomal membrane of the sperm,

with subsequent release of proteolytic enzymes that help

the sperm enter the ovum.

The zona reaction and pronuclei formation occur after the

sperm has entered the ovum.

Sperm enter the perivitelline space after penetration.

Cumulus expansion assists in movement of the sperm

through the mass of granulosa cells for the sperm to get to

the surface of the zona pellucida.

Development of the placenta

A. Shortly after the blastocyst has

implanted (6 to 7 days after

fertilization), the

syncytiotrophoblast invades

the stroma of the uterus.

B. The invading

syncytiotrophoblast breaks

through into endometrial veins

first, and then later into the

arteries, creating direct

communication between

lacunae and maternal vessels.

In addition, the proliferation of

cytotrophoblasts creates

primary chorionic villi.

Development of the placenta

C. The primary chorionic villus

continues to grow with the

proliferation of

cytotrophoblastic cells. In

addition, mesenchyme from

the extraembryonic coelom

invades the villus, forming the

secondary chorionic villus.

Eventually, these

mesenchymal cells form fetal

capillaries; at this time, the

villus is known as a tertiary

chorionic villus. The lacunae

also enlarge by merging with

one another.

D. With further development, the outer surface of the mature chorionic

villus is covered with a thin layer of syncytiotrophoblast. Under this

are cytotrophoblasts, mesenchyme, and fetal blood vessels. In the

mature placenta, "spiral" arteries from the mother empty directly into

the intervillous space, which is drained by maternal veins.

Pregnancy

Pregnancy results from the union of the ovum and sperm,

usually in the fallopian tube.

Growth of an offspring in the uterus lasts about 280 days (9

months).

The fertilized egg is known as a zygote from the time of

conception to 2 weeks.

It is then considered to be the morula and enters the uterus.

As a blastocyst, it implants in the uterine wall and is

considered to be an embryo through the eighth week.

From 8 weeks to birth, the unborn baby is called a fetus.

During the first 30 days of life, the baby is considered to be

a neonate.

Labor and Delivery

• Three stages of labor:

– First stage: muscle contractions of the uterus cause

the amniotic sac to rupture and the cervix to open

(dilate) to about 10 cm in diameter allowing passage

of the fetus

– Second stage: delivery of the baby, called parturition

– Third stage: delivery of the afterbirth, or placenta,

which takes place about 15 minutes later

Growth and Development

Growth refers to the changes that can be measured by

changes in height and weight as well as changes in body

proportions

Development describes the stages of change in

psychological and social functioning

The Mammary Glands

A, The breast consists of a series of

secretory lobules, which empty into

ductules. The ductules from 15-20

lobules combine into a duct, which

widens at the ampulla-a small

reservoir. The lactiferous duct

carries the secretions to the outside.

B, The lobule is made up of many

alveoli, the fundamental secretory

units.

C, Each alveolus consists of secretory

epithelial cells (alveolar cells) that

actually secrete the milk, as well as

contractile myoepithelial cells, which

are in turn surrounded by adipose

cells.

D, The alveolar cell secretes the

components of milk via five

pathways.

Cross section of the breasts and milk production

Suckling has four effects:

1.It stimulates sensory

nerves, which carry the

signal from the breast to the

spinal cord where they

synapse with neurons that

carry the signal to the brain.

2.In the arcuate nucleus of

the hypothalamus, the

afferent input from the

nipple inhibits neurons that

release dopamine (DA). DA

normally travels via the

hypothalamic-portal system

to the anterior pituitary

where it inhibits PRL

release by lactotrophs.

Thus, inhibition of DA

release leads to an increase

in PRL release.

Effect of suckling on the release

of PRL, oxytocin, and GnRH

3. In the supraoptic and

paraventricular nuclei of the

hypothalamus, the afferent

input from the nipple triggers

the production and release of

oxytocin in the posterior

pituitary.

4. In the preoptic area and

arcuate nucleus, the afferent

input from the nipple inhibits

GnRH release. GnRH

normally travels via the

hypothalamic-portal system

to the anterior pituitary, where

it stimulates the synthesis

and release of FSH and LH.

Thus, inhibiting GnRH

release inhibits FSH and LH

release, and thereby inhibits

the ovarian cycle.

Effect of suckling on the release

of PRL, oxytocin, and GnRH

Prolactin

Prolactin (cont.)

Prolactin (cont.)

Neural Control of the

Hypothalamic-Pituitary Axis

Menopause

Menopause, the period in a woman’s life during which

the menstrual cycle ceases, is likely to occur between

ages 45 and 55.

The ovaries are no longer responsive to the

gonadotropic hormones produced by the anterior

pituitary, and the ovaries no longer secrete estrogen or

progesterone. At the onset of menopause, the uterine

cycle becomes irregular, but as long as menstruation

occurs, it is still possible for a woman to conceive.

Therefore, a woman is usually not considered to have

completed menopause until menstruation has been

absent for a year.

The hormonal changes during menopause often produce

physical symptoms, such as “hot flashes” (caused by

circulatory irregularities), dizziness, headaches, insomnia,

sleepiness, and depression. These symptoms may be mild

or even absent. If they are severe, medical attention should

be sought.

Women sometimes report an increased sex drive following

menopause. It has been suggested that this may be due to

androgen production by the adrenal cortex.

Menopause

Key concepts

Fertilization of the ovum occurs in the oviduct.

Progesterone and estrogen released from the ovary

prepare the oviduct and uterus for receiving the

developing embryo.

The blastocyst enters the uterus, leaves the surrounding

zona pellucida, and implants into the uterine wall on day

7 of gestation.

Human chorionic gonadotropin (hCG), produced by

trophoblast cells of the developing embryo, activates the

corpus luteum to continue producing progesterone and

estradiol beyond its normal life span to maintain

pregnancy.


Shortly after the embryo implants into the uterine wall, a

placenta develops from embryonic and maternal cells and

becomes the major steroid-secreting organ during pregnancy.

Major hormones produced by the fetoplacental unit are

progesterone, estradiol, estriol, hCG, and human placental

lactogen. Elevated estriol levels indicate fetal well-being,

whereas low levels might indicate fetal stress. Human placental

lactogen has a role in preparing the breasts for milk production.

The pregnant woman becomes insulin-resistant during the latter

half of pregnancy in order to conserve maternal glucose

consumption and make glucose available for the developing

fetus.


The termination of pregnancy is initiated by strong uterine

contractions induced by oxytocin. Estrogens, relaxin, and

prostaglandins are involved in softening and dilating the

uterine cervix so that the fetus may exit.

Lactogenesis is milk production, which requires prolactin

(PRL), insulin, and glucocorticoids. Galactopoiesis is the

maintenance of an established lactation and requires PRL

and numerous other hormones. Milk ejection is the

process by which stored milk is released; “milk letdown” is

regulated by oxytocin, which contracts the myoepithelial

cells surrounding the alveoli and ejects milk into the ducts.


Lactation is associated with the suppression of menstrual

cycles and anovulation due to the inhibitory actions of PRL on

GnRH release and the hypothalamic-pituitary-ovarian axis.

The hypothalamic-pituitary axis becomes activated during the

late prepubertal period, resulting in increased frequency and

amplitude of GnRH pulses, increased LH and FSH secretion,

and increased steroid output by the gonads.

Most disorders of sexual development are caused by

chromosomal or hormonal alterations, which may result in

infertility, sexual dysfunction, or various degrees of

intersexuality (hermaphroditism).

Documents

Reproductive Physiology