Download MALE REPRODUCTIVE SYSTEM:

Reproductive System
Male Reproductive System:

The primary function of the male reproductive system is to produce sperm cells and
deliver them to the female reproductive system where they will fertilize egg cells.
 In this way:
1. Genetic material is passed from generation to generation
2. New individuals are produced

The major organs of the male reproductive system are the two testes, which are
where sperm cells are produced.
A. Surrounding the testis is a comma-shaped structure called the epididymis.
B. The tightly coiled tubules contained in this organ store sperm cells while they
mature.
C. Arising from the epididymis is a long tube that leads sperm cells out of the body.
This tube is called the vas deferens.
D. The vas deferens soon meets the duct that leads from the seminal vesicle and
forms the ejaculatory duct. The ejaculatory duct joins with the urethra from the
urinary bladder.
E. It is quite a long tube in the male, and runs alongside the prostate gland, and then
enters the penis, which is approximately six to eight inches long.
F. One important feature of the penis is the corona, which is the outer edge of the
glans penis. Covering the glans in the uncircumcised penis is a portion of skin
tissue called the prepuce.
G. The penis is suspended from the muscle above by a suspensory ligament, and is
attached to the sac that contains the testis. This sac hangs from the root of the
penis and is called the scrotum.
 3 Accessory Glands: (glands that add secretions to the sperm cells to produce
semen.)
A. The first accessory gland is the seminal vesicle. This paired gland lies near the
base of the urinary bladder. The seminal vesicle’s alkaline (basic) fluid is added
to the sperm cells as they enter the ejaculatory duct.
B. The second accessory gland is the prostate gland. This large, single gland is
about the size of a walnut and surrounds the urethra. The acidic fluid that it
contributes to sperm from the prostate gland contains several enzymes.
C. The third accessory gland is called the bulbourethral gland, which adds alkaline
secretion to the sperm. This paired gland is also known as the Cowper’s glands.
Female Reproductive System:

The female reproductive system produces sex cells that join with male sperm cells in
the process of fertilization.

In addition, the female system nurtures the developing embryo and fetus for
approximately 9 months. For this reason, the female system is more complex than the
male system.

The ovaries are the female reproductive organs in which egg cells are formed, and
they are also the location of the production of the female sex hormones.
A. The egg cells travel from the ovaries into the Fallopian tubes.
B. The Fallopian tubes lead the egg cell to the uterus, which is a muscular organ that
stretches to hold the fetus until its birth.
 The uterus is found just above the urinary bladder.
 The thick muscle of the uterus is the endometrium, which is rich in blood
vessels.
C. The narrow opening that leads from the uterus is called the cervix, and the next
structure system is the vagina.
D. The vagina is a tubular organ that’s approximately four inches in length.
 It receives the penis during sexual intercourse and acts as the birth canal
through which babies are expelled.
 The walls of the vagina are thinner than are the very muscular walls of the
uterus.
 The vagina passes through the urogenital diaphragm, which is near another
secretory gland called the vestibular gland. Also called Bartholin’s gland,
this paired gland produces lubrication in the form of mucus.
 The vagina opens at the vaginal orifice
 In the region of the vaginal orifice is the vulva or pudendum, which is the
area that encompasses the external genitalia of the female.
 One component of the vulva is the mons pubis. This is an elevation of
adipose tissue that is covered by skin and coarse pubic hair. It cushions the
pubis, which is where the pubic bones come together.
 Another structure of the vulva is the clitoris, a small mass of erectile tissue
that is homologous to the penis of the male.
 The labia are also located in this area;
A. The labium minora is the smaller fold of skin tissue of the vulva, and
B. The labium majora is the larger fold of tissue.
C. The labia are homologous to the scrotum of the male.
GAMETOGENESIS

During the process of reproduction, gametes unite to form the zygote that develops
into the new individual.

Gametes are the sex cells—sperm and egg cells.

They are produced in the testis and ovary, respectively, in the process gametogenesis.
Male:
 Spermatogenesis takes place in the seminiferous tubules, within the testes.
A. The process involves the production of primary spermatocytes from cells called
spermatogonia through mitosis.

The primary spermatocytes (diploid) then undergo the process of meiosis.
A. From meiosis I, secondary spermatocytes are produced.
B. From meiosis II, sperm cells will develop from spermatids (haploid).
Female:
 Oogenesis is similar to spermatogenesis, but there are a few differences. As a result
of meiosis I, two new cells are produced.
1. One cell is the secondary oocyte.
2. Second cell, which is reduced in size, is the polar body. Although the polar
body undergoes meiosis II, it will not divide to produce functional cells.

Through gametogenesis, sperm and egg cells are produced with the haploid (n
or 23 chromosomes) condition, and when the union takes place to form a
zygote, the diploid (2n or 23 pairs of chromosomes) condition is reestablished.
 Ooctye—birth: 2 million, puberty: 400,000-300,000, after puberty: 400
Oocyte Formation:
 The secondary oocyte develops, deriving nutrients and growing within the follicle,
and then moves toward the surface of the ovary.

At ovulation, the follicle erupts, and the secondary oocyte is released into the
Fallopian tube.

If sperm cells are present, a sperm nucleus will enter the oocyte, and meiosis II will
take place.

Polar body Formation:
The other cell that results from meiosis II is a polar body. Two other polar bodies also
form from the first polar body, and these three polar bodies disintegrate.
FEMALE HORMONE CYCLE

The female hormone cycle is a complex process that involves a number of hormones
as well as various structures of the reproductive system.

It initially involves the building up of the lining of the uterus; the lining is retained if
a fertilized egg cell is present, and the lining is released if there is no fertilized egg.

The menstrual cycle occurs over a period of approximately 28 days.

During the female hormonal cycle, an egg cell develops within the follicle in the
ovary and is released.

Several events accompany this development. There are 3 different series of events
that make up the female hormone cycle. The cycles are:
1. Gonadotropic hormone cycle
2. Ovarian cycle
3. Endometrical cycle
Gonadotropic hormone cycle:
A. The cycle begins with the production of FSH (follicle stimulating hormone) and
LH (Luteinizing hormone) by a hypothalamic releasing hormone (GnRN) in the
anterior pituitary gland.
B. FSH and LH stimulates maturation of the egg cell from the second oocyte,
triggers the production of estrogen in the ovary, and build up of the uterine lining.
C. Just before midcycle, increased estrogen causes surge in LH secretion.
D. Surge of LH stimulates ovulation and formation of corpus luteum
E. Progesterone and estrogen from corpus luteum maintain uterine lining unless no
pregnancy.
F. Increased progesterone and estrogen inhibit secretion of LH and FSH during last
phase of cycle.
Ovarian cycle:
A. In the ovarian cycle or the follicular phase of the cycle, the follicle with the egg
cell is seen inside. At the start of the follicular stage, the level of estrogen is low,
but it rises as this phase continues.
B. A second hormone, progesterone is also in low supply at the start of this phase.
Endometrical cycle:
A. One menstrual phase is coming to an end, and the endometrial lining has been
almost fully release (menstruation).
B. At about day 3 of the endometrial cycle, the endometrium begins its rebuilding
process.
C. At day 7 in the hormonal cycle, we see that the level of gonadotropic hormones
is still relatively low.
D. In the endometrial cycle, the endometrium continues to build up and the
proliferative phase has begun.
E. Day 14 is arbitrarily set at the midpoint of the cycle, but this point may vary two
to 3 days in either direction.
F. A surge of LH (Luteinizing hormone) occurs, and the mature follicle bursts to
release the egg cell.
G. A surge of FSH brings about final maturation of the egg cell.
H. Ovulation occurs when the egg is released, and this happens around day 14.
I. Now the follicular phase comes to an end, and the luteal phase begins.
J. The estrogen level has begun to decline, and now the progesterone level rises
significantly.
K. Once the egg cell has been released from the follicle, the remaining cells revert to
a body called the corpus luteum, and it is these cells that secrete progesterone.
L. Progesterone and estrogen inhibits FSH and LH, which prevents additional
ovulation and stimulates buildup of the endometrial lining.
M. As the amount of tissue increases in the endometrium, we enter the secretory
phase of the cycle.
N. If fertilization takes place, the zygote develops into an embryo.
O. At day 21, levels of LH and FSH are extremely low.
P. The corpus luteum has continued to produce some estrogen and progesterone,
which is at its highest level.
Q. The endometrial lining is thick with blood and tissue in anticipation of a fertilized
egg cell.
R. As we come to day 28 of the hormone cycle, fertilization has not taken place, and
the corpus luteum begins to break down.
S. The level of progesterone drops dramatically, and the endometrial lining begins to
disintegrate; menstruation takes place.
T. Neither estrogen nor progesterone are being secreted, and the pituitary once again
begins its production of FSH, which initiates another cycle.
HUMAN EMBRYONIC DEVELOPMENT:

The development of the human embryo involves numerous cell movements and
changes that begin with the single, fertilized egg.

From the zygote will arise the hundred trillion cells that comprise the adult.

The zygote is created when a sperm cell joins with the egg cell within a Fallopian
tube of the female.

After about 30 hours, the zygote undergoes mitosis and two cells are formed. The first
view we see is the two cell stage and about 30 hours later, each cell undergoes mitosis
again, and the embryo enters the four cell stage.

Mitosis continually takes place, but the overall size of the embryo does not increase,
even though the cells continue to divide.
1. Morula stage
2. Blastocyst stage (called the blastula in other animals).
 The blastocyst is a ball of cells that results from mitosis of the cells of the
morula.
 It contains between five hundred and two thousand cells.
 At its outer edge is the trophoblast, a layer of cells that develops into the
membranes that surround the embryo.
 The blastocyst has a fluid-filled cavity known as the blastocoel.
 At one end of the blastocoel is the inner cell mass. These cells will become the
developing embryo.

By the third day after fertilization, the embryo is a morula.

By the fifty day, the morula has become the blastocyst, and the outer cells of the
trophoblast have begun the implantation process.

The embryo is now about the size of the period at the end of this sentence and is
called the embryonic disc.
A. In the fifth diagram, we see the embryonic disc in place in the uterine wall.
The embryonic disk has two layers, the ectoderm and endoderm.
B. Soon, the third germ layer, the middle mesoderm, will develop and the
nervous and circulatory systems will appear.

In the sixth diagram, we again see the uterine wall. The embryo is slightly larger, and
a connection stalk attaches it to the uterine wall.

The embryo is now in its fourth week, and the umbilical cord has begun to form.
The embryo is surrounded by a sac called the amnion. In the four week embryo, the
nerve cord can be seen and the connecting stalk is also visible. The embryo measures
approximately 5 mm in length.

In the five week embryo, limb buds have appeared, and these later become arms and
legs. The head has enlarged, and the nerve cord is fully formed. Sense organs have
become prominent, and the eyes can be seen. The embryo is now about 8 mm in
length.

In the six week embryo, the head continues to enlarge, and the limbs become more
prominent. The digestive system in this embryo is fully formed, and is about 12 mm
in length.

The seven week embryo is about 17 mm is length. Its back has straightened and its
muscles have differentiated. Eyelids are present, and the external genital organs have
begun to form.

Embryonic development ends at about eight weeks, and the eight week embryo is
about 23 mm in length. It is recognizable as a human being, and hereafter it is called a
fetus. Further development involves growth and maturation of the fetus’ organs.
During the next seven months, it will continue to grow as its body is defined and its
organs mature.
PRIMORDIAL GERM LAYERS:

During embryonic development, the fertilized egg forms a morula, and then a
blastocyst.

At the outer wall of the blastocyst, the trophoblast develops, and at one side of the
blastocyst there is an inner cell mass, which becomes most of the embryonic tissues.

In the next stage, there is a special rearrangement of cells, and this phase is called
gastrulation.

At the completion of gastrulation, the embryo is called a gastrula. The
rearrangements of cells during gastrulation results in three primordial germ layers
called:
1. Ectoderm
2. Mesoderm
3. Endoderm
Process of Gastrulation:
 The process of gastrulation involves pattern of cell movement, and begins with the
blastocyst, the hollow ball of cells.
 First, there is an infolding of the surface called an invagination, then an inward
turning of cells called involution, and finally a flattening and spreading of the cell
layer, after which cells migrate to their functional position.
 According to the picture diagram, we see a cross-section of the embryo in its third
week of development, after gastrulation has taken place. The lining of the uterus is
made up of a layer of cells, the endometrium.
 A membrane called the chorion has developed from the trophoblast and is
surrounding the embryo.
 A collection of cells, the body stalk, is growing, and it will become the umbilical
cord. The large yolk sac is also present. This small cavity below the embryo will
eventually become the umbilical cord.
 Another membrane, the amnion, lies between the trophoblast and the inner cell mass.
The amnionic cavity is developing at this stage.
Germ Layers:
 In the gastrula stage, the embryonic disk has three layers of cells.
1. Ectoderm--which forms the outer wall of the gastrula.
 This tissue includes the entire nervous system; including the brain and spinal
cord.
 The outer layer of the skin (epidermis/dermis) also derives from the ectoderm and
some endocrine glands such as the pituitary glands come from this layer.
 The inner lining of certain structures such as the nose, mouth, and anus are also
derived from ectoderm layers.
2. Mesoderm
 The mesoderm derivatives include the bones and cartilage of the skeleton, and the
muscles and organs of the circulatory and excretory systems.
 Most of the reproductive organs and the inner layer of skin tissue also come from
mesoderm tissue, as do certain structures of the respiratory system.
3. Endoderm
 The endoderm tissue includes the lining of the digestive tract and respiratory
passages.
 The liver, pancreas, urinary bladder, and most glands are also derived from the
endoderm.
 The germ layers are so-called because they are the beginnings of tissues, organs,
and organ systems (germ means beginning).
 In simple animals such as sponges and cnidarians, only endoderm and ectoderm
layers exist.