Reproductive physiology of male and female

REPRODUTIVE
PHYSIOLOGY
Of
MALE and FEMALE

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Introduction
• Sexual reproduction is the process by which organisms
produce offspring by making germ cells called gamete.
• After the male gamete (sperm cell) unites with the female
gamete (secondary oocyte)—an event called fertilization
• The resulting cell contains one set of chromosomes from
each parent.
• Males and females have anatomically distinct reproductive
organs that are adapted for producing gametes, facilitating
fertilization, and, in females, sustaining the growth of the
embryo and fetus.

THE REPRODUCTIVE SYSTEMS
• The male and female reproductive organs work together to
produce offspring.
• The organs of the male reproductive system include
the testes, a system of ducts (including the
epididymis, ductus deferens, ejaculatory ducts, and
urethra), accessory sex glands (seminal vesicles,
prostate, and bulbourethral glands), and several
supporting structures, including the scrotum and the
penis.
• The testes (male gonads) produce sperm and secrete
hormones. The duct system transports and stores
sperm, assists in their maturation, and conveys them
to the exterior.

Spermatogenesis
• Testes are composed of one to three
tightly coiled tubules, the
• seminiferous tubules , where sperm are
produced.
• The process by which the
• seminiferous tubules of the testes produce
sperm is called spermatogenesis.

• The seminiferous tubules contain two
types of cells: spermatogenic cells the
sperm-forming cells,
• and Sertoli cells which have several
functions in supporting
spermatogenesis

• Spermatogenesis
• In humans, spermatogenesis takes 65–75 days. It
begins with the spermatogonia, which contain the
diploid (2n) number of chromosomes.
• Spermatogonia are types of stem cells; when they
undergo mitosis
• spermatogonia remain near the basement membrane
of the seminiferous tubule in an undifferentiated
state to serve as a reservoir of cells for future cell
division and subsequent sperm production

• The rest of the spermatogonia lose contact with the
basement membrane, squeeze through the tight
junctions of the blood–testis barrier, undergo
developmental changes, and differentiate into
primary spermatocytes
• Primary spermatocytes, like spermatogonia, are
diploid (2n); that is, they have 46 chromosomes.
• each primary spermatocyte replicates its DNA and
then meiosis begins
• The two cells formed by meiosis I are called
secondary spermatocytes. Each secondary
spermatocyte has 23 chromosomes, the haploid
number (n).

• Each chromosome within a secondary spermatocyte,
however, is made up of two chromatids (two copies of
the DNA) still attached by a centromere.
• In meiosis II, the chromosomes line up in single file
along the metaphase plate, and the two chromatids of
each chromosome separate. The four haploid cells
resulting from meiosis II are called spermatids.
• single primary spermatocyte therefore produces four
spermatids via two rounds of cell division (meiosis I
and meiosis II).

• The final stage of spermatogenesis, spermiogenesis
is the development of haploid spermatids into sperm.
• No cell division occurs in spermiogenesis; each
spermatid becomes a single sperm cell.
• During this process, spherical spermatids transform
into elongated, slender sperm.
• Finally, sperm are released from their connections to
Sertoli cells, an event known as spermiation.
• Sperm then enter the lumen of the seminiferous
tubule. Fluid secreted by Sertoli cells pushes sperm
along their way, toward the ducts of the testes.

• Sperm
• Each day about 300 million sperm complete the process
of spermatogenesis.
• A sperm is about 60 m long and contains several
• structures that are highly adapted for reaching and
penetrating a secondary oocyte.

• The major parts of a sperm are the head and the tail.
• The flattened, pointed head of the sperm is about 4–5 m long.
• It contains a nucleus with 23 highly condensed
chromosomes.
• Covering the anterior two-thirds of the nucleus is the acrosome ,
• a caplike vesicle filled with enzymes that help a sperm to
penetrate
• a secondary oocyte to bring about fertilization.
• Among the enzymes are hyaluronidase and proteases.
• The tail of a sperm is subdivided into four parts: neck, middle
piece, principal piece, and end piece.

• The neck is the constricted region just behind the head that
contains centrioles. The centrioles form the microtubules that
comprise the remainder of the tail. The middle piece contains
mitochondria arranged in a spiral, which provide the energy
(ATP) for locomotion of sperm to the site of fertilization and for
sperm metabolism.
• The principal piece is the longest portion of the tail, and the
end piece is the terminal, tapering portion of the tail.

Hormonal Control of the Testes
• hypothalamic neurosecretory cells increase their secretion
of gonadotropin-releasing hormone
• This hormone in turn stimulates gonadotrophs in the
anterior pituitary to increase their secretion of the two
gonadotropins, luteinizing hormone (LH) and
folliclestimulating hormone (FSH).

• At puberty certain hypothalamic neurosecretory cells
increase their secretion of gonadotropin-releasing
hormone (GnRH)
• This hormone in turn stimulates gonadotrophs in the
anterior pituitary to increase their secretion of the two
gonadotropins:
I. luteinizing hormone (LH)
II. follicle stimulating hormone (FSH)

• LH stimulates Leydig cells, which are located between
seminiferous tubules, to secrete the hormone
testosterone.
• This steroid hormone is synthesized from cholesterol
in the testes and is the principal androgen. It is lipid-
soluble and readily diffuses out of Leydig cells into the
interstitial fluid and then into blood.
• Via negative feedback, testosterone suppresses
secretion of LH by anterior pituitary gonadotrophs and
suppresses secretion of GnRH by hypothalamic
neurosecretory cells.

• FSH acts indirectly to stimulate spermatogenesis
• FSH and testosterone act synergistically on the Sertoli cells
to stimulate secretion of androgen-binding protein (ABP)
into the lumen of the seminiferous tubules and into the
interstitial fluid around the spermatogenic cells.
• Sertoli cells release inhibin, a protein hormone named for
its role in inhibiting FSH secretion by the anterior pituitary
• Testosterone and dihydrotestosterone both bind to the same
androgen receptors, which are found within the nuclei of
target cells.

• Prenatal development. Before birth, testosterone
stimulates the male pattern of development of
reproductive system ducts and the descent of the
testes. Dihydrotestosterone stimulates development of
the external genitals
• Development of male sexual characteristics. At
puberty,
• testosterone and dihydrotestosterone bring about
development and enlargement of the male sex organs
and the development of masculine secondary sexual
characteristics.

• Secondary sex characteristics are traits that
distinguish males and females but do not have a direct
role in reproduction.
• Development of sexual function. Androgens
contribute to male sexual behavior and
spermatogenesis and to sex drive (libido) in both males
and females. Recall that the adrenal cortex is the main
source of androgens in females.
• Stimulation of anabolism. Androgens are anabolic
hormones; that is, they stimulate protein synthesis.

A negative feedback system regulates
testosterone production
• When testosterone concentration in the blood increases
to a certain level, it inhibits the release of GnRH by cells
in the hypothalamus.
• As a result, there is less GnRH in the portal blood that
flows from the hypothalamus to the anterior pituitary.
• Gonadotrophs in the anterior pituitary then release less
LH, so the concentration of LH in systemic blood falls.
• With less stimulation by LH, the Leydig cells in the testes
secrete less testosterone, and there is a return to
homeostasis.

• The organs of the female reproductive system
include the ovaries (female gonads); the uterine
(fallopian) tubes, or oviducts; the uterus; the
vagina.
Female reproductive system

THE FEMALE REPRODUCTIVE
CYCLE
• During their reproductive years, non pregnant
females normally exhibit cyclical changes in the
ovaries and uterus.
• Each cycle takes about a month and involves both
oogenesis and preparation of the uterus to receive
a fertilized ovum.
• Hormones secreted by the hypothalamus, anterior
pituitary, and ovaries control the main events.

The general term female reproductive cycle encompasses the
ovarian and uterine cycles, the hormonal changes that regulate
them, and the related cyclical changes in the breasts and cervix.
• The ovarian cycle
is a series of
events in the
ovaries that occur
during and after the
maturation of an
oocyte.
• The uterine (menstrual) cycle is
a concurrent series of changes
in the endometrium of the uterus
to prepare it for the arrival of a
fertilized ovum that will develop
there until birth.
• If fertilization does not
occur, ovarian hormones wane,
which causes the stratum
functionalis of the endometrium to
slough off.

Hormonal Regulation of the Female
Reproductive Cycle
• GnRH secreted by the hypothalamus controls
the ovarian and uterine cycles.
• GnRH stimulates the release of FSH and LH from
the anterior pituitary.
• Both FSH and LH stimulate the ovarian follicles to
secrete estrogens.
• FSH initiates follicular growth, while LH stimulates
further development of the ovarian follicles.

FSH
• FSH initiates follicular
growth.
• Under the influence of
FSH, the androgens are
taken up by the granulosa
cells of the follicle and
then converted into
estrogens.
LH
• LH stimulates further
development of the
ovarian follicles.
• At midcycle, LH triggers
ovulation and then
promotes formation of the
corpus luteum
• Stimulated by LH, the
corpus luteum produces
and secretes estrogens,
progesterone, relaxin,
and inhibin.

ESTROGENS
• Estrogens promote the development and
maintenance of female reproductive structures,
secondary sex characteristics, and the breasts.
• Estrogens increase protein anabolism, including
the building of strong bones. In this regard,
estrogens are synergistic with hGH.
• Estrogens lower blood cholesterol level.
• Moderate levels of estrogens in the blood inhibit
both the release of GnRH by the hypothalamus and
secretion of LH and FSH by the anterior pituitary.

PROGESTERONE
• secreted mainly by cells of the corpus luteum
• cooperates with estrogens to prepare and maintain
the endometrium for implantation of a fertilized
ovum and to prepare the mammary glands for milk
secretion.
• High levels of progesterone also inhibit secretion of
GnRH and LH.

RELAXIN
• produced by the corpus luteum
• During each monthly cycle relaxes the uterus by
inhibiting contractions of the myometrium.
Presumably, implantation of a fertilized ovum
occurs more readily in a “quiet” uterus.
• During pregnancy, the placenta produces much
more relaxin, and it continues to relax uterine
smooth muscle.
• At the end of pregnancy,relaxin also increases the
flexibility of the pubic symphysis and may
help dilate the uterine cervix, both of
which ease delivery of the baby.

INHIBIN
• secreted by granulosa cells of growing
follicles & by the corpus luteum after
ovulation.
• It inhibits secretion of FSH.

Menstrual Phase: first five days
• Under the influence of
FSH, several primordial
follicles develop into
primary follicles and then
into secondary follicles.
• This developmental
process may take several
months to occur.
Therefore, a follicle that
begins to develop at the
beginning of a particular
menstrual cycle may not
reach maturity
• and ovulate until several
menstrual cycles later.
• Menstrual flow from the uterus
consists of 50–150 mL of blood,
tissue fluid, mucus, and epithelial
cells shed from the endometrium.
• Declining levels of progesterone
and estrogens stimulate release of
prostaglandins that cause the
uterine spiral arterioles to constrict.
• As a result, the cells become
oxygen-deprived and start to die.
Eventually, the entire stratum
functionalis sloughs off.
• At this time the endometrium is
very thin, about 2–5 mm, because
only the stratum basalis remains.
• The menstrual flow passes from
the uterine cavity through the
cervix and vagina to the exterior.

Preovulatory Phase:6 to 14 days
• Some of the secondary follicles in the ovaries begin to
secrete estrogens and inhibin.
• By about day 6, a single secondary follicle in one of the two
ovaries has outgrown all the others to become the
dominant follicle.
• Estrogens and inhibin secreted by the dominant follicle
decrease the secretion of FSH, which causes other, less
well-developed follicles to stop growing and undergo atresia.
• Normally, the one dominant secondary follicle becomes the
mature (graafian) follicle, which continues to enlarge
until it is more than 20 mm in diameter and ready for
ovulation.
• This follicle forms a blisterlike bulge due to the swelling
antrum on the surface of the ovary.
• During the final maturation process, the mature follicle
continues to increase its production of estrogens

• Estrogens liberated into the blood by growing ovarian
follicles stimulate the repair of the endometrium; cells of
the stratum basalis undergo mitosis and produce a new
stratum functionalis.
• As the endometrium thickens, the short, straight
endometrial glands develop, and the arterioles coil and
• lengthen as they penetrate the stratum functionalis.
• The thickness of the endometrium approximately
doubles, to about 4–10 mm.
• With reference to the uterine cycle, the preovulatory
phase is also termed the proliferative phase because
the endometrium is proliferating.

Ovulation
• the rupture of the mature (graafian) follicle and the release of the
secondary oocyte into the pelvic cavity, usually occurs on day 14 in a
28-day cycle.
• During ovulation,the secondary oocyte remains surrounded by its
zona pellucida and corona radiata.
• The high levels of estrogens during the last part of the preovulatory
• phase exert a positive feedback effect on the cells that secrete LH
and (GnRH) and cause ovulation, as follows:
1 A high concentration of estrogens stimulates more frequent
release of GnRH from the hypothalamus. It also directly stimulates
gonadotrophs in the anterior pituitary to secrete LH.
2 GnRH promotes the release of FSH and additional LH by the
anterior pituitary.
3 LH causes rupture of the mature (graafian) follicle and expulsion
of a secondary oocyte about 9 hours after the peak of
the LH surge.

• The ovulated oocyte and its corona radiata cells are
usually swept into the uterine tube.
• From time to time, an oocyte is lost into the pelvic cavity,
where it later disintegrates.
• The small amount of blood that sometimes leaks into the
pelvic cavity from the ruptured follicle can cause pain,
known as mittelschmerz, at the time of ovulation.
• An over-the-counter home test that detects a rising level
of LH can be used to predict ovulation a day in advance.

Postovulatory Phase:15 to 28 days
• After ovulation, the mature follicle collapses,
• and the basement membrane between the granulosa
cells and
• theca interna breaks down. Once a blood clot forms from
minor
• bleeding of the ruptured follicle, the follicle becomes the
corpus hemorrhagicum
• (hem-o-RAJ-i-kum; hemo- blood; rrhagic-
• bursting forth) (see Figure 28.13). Theca interna cells
mix with the
• granulosa cells as they all become transformed into
corpus luteum

• cells under the influence of LH. Stimulated by LH, the corpus
luteum
• secretes progesterone, estrogen, relaxin, and inhibin. The
• luteal cells also absorb the blood clot. With reference to the ovarian
• cycle, this phase is also called the luteal phase (LOO-te¯-al).
• Later events in an ovary that has ovulated an oocyte depend on
• whether the oocyte is fertilized. If the oocyte is not fertilized, the
• corpus luteum has a lifespan of only 2 weeks. Then, its secretory
• activity declines, and it degenerates into a corpus albicans (see
• Figure 28.13). As the levels of progesterone, estrogens, and inhibin
• decrease, release of GnRH, FSH, and LH rises due to loss of
• negative feedback suppression by the ovarian hormones. Follicular
• growth resumes and a new ovarian cycle begins.

• If the secondary oocyte is fertilized and begins to divide,
the
• corpus luteum persists past its normal 2-week lifespan. It
is “rescued” from degeneration by human chorionic
gonadotropin. This hormone is produced by the
chorion
• of the embryo beginning about 8 days after fertilization.
Like LH,
• hCG stimulates the secretory activity of the corpus
luteum. The
• presence of hCG in maternal blood or urine is an
indicator of
• pregnancy and is the hormone detected by home
pregnancy tests.

• Progesterone and estrogens produced
• by the corpus luteum promote growth and coiling of the endometrial
• glands, vascularization of the superficial endometrium, and
thickening
• of the endometrium to 12–18 mm (0.48–0.72 in.). Because
• of the secretory activity of the endometrial glands, which begin to
• secrete glycogen, this period is called the secretory phase of the
• uterine cycle. These preparatory changes peak about 1 week after
• ovulation, at the time a fertilized ovum might arrive in the uterus.
• If fertilization does not occur, the levels of progesterone and
estrogens
• decline due to degeneration of the corpus luteum. Withdrawal
• of progesterone and estrogens causes menstruation

Reproductive physiology of male and female

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Reproductive physiology of male and female