Reproductive System and Development
Male Reproductive Structures
Female Reproductive Structures
Meiosis
Spermatogenesis
Oogenesis
Hormones of the Reproductive System
Events of the Menstrual Cycle
Embryonic Development
Fetal Development
Testes lie within the Scrotum
Perineum
Penis
The Duct System
Accessory Glands
Semen
The scrotum is a sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis.
The scrotum helps regulate temperature for optimal sperm production
The scrotum uses dartos and cremaster muscles to change how far it hangs from the body
The testes are two oval gonads that produce testosterone
Seminiferous Tubules inside the testes contain spermatogenic cells
Surrounding each seminiferous tubule are the three to five layers of smooth muscle-like myoid cells. By contracting rhythmically, these myoid cells help to squeeze sperm and testicular fluids through the tubules and out of the testes
The seminiferous tubules of each lobule converge to form a straight tubule that conveys sperm into the rete testis, a tubular network on the posterior side of the testis.
Epididymis
Ductus Deferens
Ejaculatory Duct
Urethra
The Seminal Glands
The Prostate
The Bulbo-Urethral Glands
suspends the scrotum and contains the root of the penis
Designed to deliver sperm to the female
glans penis - enlarge tip at the distal end of the shaft
the skin of the penis is loose, and when it slides distally it forms a cuff called the prepuce
aka the foreskin
erectile tissue is a spongy network of connective tissue and smooth muscle riddled with vascular spaces
the midventral erectile body, the corpus spongiosum surrounds the urethra. It expands distally to form the glans and proximally to form the part of the root called the bulb of the penis
The paired dorsal erectile bodies, called the corpora cavernosa, make up most of the penis and are bound by the fibrous tunica albuginea. Thier proximal ends form the crura of the penis
Ovaries
Germinal Epithelium - simple cuboidal epithelial layer surrounding the ovary
Tunica albugunea
Deep to germinal epithelium
Dense CT capsule
Deep to tunica albuginea
Outer cortex contains highly cellular CT, ovarian follicles
Inner medulla is composed of areolar CT and contains branches of ovarian blood vessels, lymph vessels, nerves
Ovarian follicles
Consist of oocyte surrounded by follicle cells
Uterine Tubes or Fallopian Tubes
extend laterally from both sides of the uterus towards ovaries
transport ovulated oocyte to uterus
Covered and suspended by mesosalpinx
Infundibulum
Free, funnel-shaped, lateral margin of uterine tube
numerous fingerlike folds called fimbriae
enclose ovary only at time of ovulation
Mammary Glands
release breast milk during lactation
sensitive to prolactin and oxytocin
secretes alkaline fluid with fructose and prostaglandins
fructose nourishes the sperm
prostaglandins promotes widening of external os of cervix
compact, walnut -shaped encapsulated organ immediately inferior to bladder
submucosal glands produce mucin
secretes milky fluid rich in citric acid, seminalplasmin, and prostate-specific antigen (PSA)
citric acids aids sperm health
seminalplasmin, antibiotic that combats UTI
PSA, enzyme to liquefy semen following ejaculation
produces a clear, viscous mucin that forms mucous
coats and lubricates urethra during intercourse
formed form seminal fluid and sperm
called ejaculate when released during intercourse
200 - 500 million spermatozoa
Transit time from seminiferous tubules to ejaculate is about 2 weeks
spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis
process begins at puberty, after which time sperm are produced constantly throughout a man’s life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days,
although this timing is not synchronous across the seminiferous tubules
Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other
becomes a primary spermatocyte, the next stage in the process of spermatogenesis
As in mitosis, DNA is replicated
in a primary spermatocyte, before it undergoes a cell division called meiosis I
This results in two cells, called secondary spermatocytes, each with only half the number of
chromosomes. Now a second round of cell division (meiosis II) occurs in both of the secondary spermatocytes.
During
meiosis II each of the 23 replicated chromosomes divides, similar to what happens during mitosis. Thus, meiosis results in
separating the chromosome pairs. This second meiotic division results in a total of four cells with only half of the number
of chromosomes. Each of these new cells is a spermatid
Although haploid, early spermatids look very similar to cells in
the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm
A process called
spermiogenesis transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a
true sperm.
The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which
occurs in the portion of the tubule nearest the lumen. Eventually, the sperm are released into the lumen and are moved along
a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation
Simple Spermatogenesis
Spermatogonium undergoes mitosis to become primary spermatocyte
primary spermatocyte undergoes meiosis I to become secondary spermatocyte
secondary spermatocyte undergoes meiosis II to become spermatid
spermatid undergoes spermatogenesis to become spermatozoa (sperm)
Sperm cells are divided into a head, containing DNA; a mid-piece, containing
mitochondria; and a tail, providing motility. The acrosome is oval and somewhat flattened
a coiled tube attached to the testis where newly formed sperm continue to mature
It takes an average of 12 days for sperm to move through the coils of the epididymis, with
the shortest recorded transit time in humans being one day
Sperm enter the head of the epididymis and are moved along
predominantly by the contraction of smooth muscles lining the epididymal tubes
a thick, muscular tube that is bundled together inside the
scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord
Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt
sperm delivery can be performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is
called a vasectomy
From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the
abdominal wall. From here, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder
where it dilates in a region called the ampulla
The paired seminal vesicles are glands that contribute approximately 60 percent of the semen
volume.
a
short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory
ducts transport the seminal fluid into the next structure, the prostate gland.
Cowper’s glands
Testosterone
androgen
steroid hormone produced by Leydig cells/ interstitial
cells
produce approximately 6 to 7 mg of testosterone per day
normal concentrations of testosterone promotes spermatogenesis, whereas low levels of testosterone can
lead to infertility
plays an important role in muscle development, bone growth, the development of secondary sex characteristics, and maintaining
libido (sex drive) in both males and females
In females, the ovaries secrete small amounts of testosterone, although most is
converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes
The hypothalamus and the pituitary
gland in the brain integrate external and internal signals to control testosterone synthesis and secretion
external female reproductive structures/ vulva
mons pubis is a
pad of fat that is located at the anterior, over the pubic bone. After puberty, it becomes covered in pubic hair
labia
majora are folds of hair-covered skin that begin just posterior to the mons pubis
The
thinner and more pigmented labia minora (labia = “lips”; minora = “smaller”) extend medial to the labia majora. Although
they naturally vary in shape and size from woman to woman, the labia minora serve to protect the female urethra and the
entrance to the female reproductive tract
The superior, anterior portions of the labia minora come together to encircle the clitoris (or glans clitoris), an organ that
originates from the same cells as the glans penis and has abundant nerves that make it important in sexual sensation and
orgasm
The hymen is a thin membrane that sometimes partially covers the entrance to the vagina. An intact hymen cannot
be used as an indication of “virginity”; even at birth, this is only a partial membrane, as menstrual fluid and other secretions
must be able to exit the body, regardless of penile–vaginal intercourse
The vaginal opening is located between the opening
of the urethra and the anus. It is flanked by outlets to the Bartholin’s glands (or greater vestibular glands).
Oogonium undergoes mitosis while female is still in utero to form a primary oocyte
the primary oocyte undergoes meiosis I but stops in prophase until puberty
puberty triggers the end of meiosis I to form a secondary oocyte and a first polar body
the first polar body divides into two second polar bodies
they do NOTHING
the secondary oocyte undergoes meiosis II but stops in metaphase II until fertilized by a sperm
Sperm triggers the secondary oocyte to complete meiosis II and become a mature ovum
The process begins with the ovarian stem cells, or oogonia
Oogonia are formed during fetal development, and divide via mitosis, much like spermatogonia in the testis. Unlike
spermatogonia, however, oogonia form primary oocytes in the fetal ovary prior to birth
even though oogenesis produces up to four cells, only one survives.
three distinct phases
The menses phase of the menstrual cycle is the phase during which the lining is shed; that is, the days that the woman
menstruates
the menses phase occurs during the early days of the follicular phase of the ovarian cycle, when
progesterone, FSH, and LH levels are low
progesterone concentrations decline as a result of the degradation of
the corpus luteum, marking the end of the luteal phase. This decline in progesterone triggers the shedding of the stratum
functionalis of the endometrium.
Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase
granulosa and theca cells of the tertiary follicles begin to
produce increased amounts of estrogen. These rising estrogen concentrations stimulate the endometrial lining to rebuild.
high estrogen concentrations will eventually lead to a decrease in FSH as a result of negative feedback,
resulting in atresia of all but one of the developing tertiary follicles
stimulates the LH surge that will trigger ovulation.
Ovulation marks the end of the proliferative phase as well as
the end of the follicular phase.
In the uterus, progesterone
from the corpus luteum begins the secretory phase of the menstrual cycle, in which the endometrial lining prepares for
implantation
High estrogen levels also slightly decrease the acidity of the vagina, making it more
hospitable to sperm
In the ovary, the luteinization of the granulosa cells of the collapsed follicle forms the progesteroneproducing
corpus luteum, marking the beginning of the luteal phase of the ovarian cycle
Over the next 10 to 12 days, the endometrial glands secrete a fluid rich in glycogen. If
fertilization has occurred, this fluid will nourish the ball of cells now developing from the zygote. At the same time, the
spiral arteries develop to provide blood to the thickened stratum functionalis.
If no pregnancy occurs within approximately 10 to 12 days, the corpus luteum will degrade into the corpus albicans. Levels
of both estrogen and progesterone will fall, and the endometrium will grow thinner. Prostaglandins will be secreted that
cause constriction of the spiral arteries, reducing oxygen supply. The endometrial tissue will die, resulting in menses—or
the first day of the next cycle.
series of changes in which the uterine lining is shed, rebuilds, and
prepares for implantation.
the length of the menstrual cycle varies among women, and even in the same woman from one cycle to the next,
typically from 21 to 32 days
The first 2 weeks of prenatal development are
referred to as the pre-embryonic stage
A developing human is referred to as an embryo during weeks 3–8
referred to as a fetus from
the ninth week of gestation until birth
During its journey to the uterus, the zygote undergoes five or
six rapid mitotic cell divisions
each cleavage results in more cells, it does not increase the total volume of the
conceptus
Each daughter cell produced by cleavage is called a blastomere
Approximately 3 days after fertilization, a 16-cell conceptus reaches the uterus. The cells that had been loosely grouped
are now compacted and look more like a solid mass called a morula.
Once inside the uterus, the conceptus floats freely for several more days. It continues to divide, creating a
ball of approximately 100 cells, and consuming nutritive endometrial secretions called uterine milk while the uterine lining
thickens. The ball of now tightly bound cells starts to secrete fluid and organize themselves around a fluid-filled cavity,
the blastocoel
inner cell mass is fated to become the embryo and is made of totipotent cells
The cells that form the outer shell are called
trophoblasts. These cells will develop into the chorionic sac and the fetal portion of the
placenta
As the blastocyst forms, the trophoblast excretes enzymes that begin to degrade the zona pellucida. In a process called
“hatching,” the conceptus breaks free of the zona pellucida in preparation for implantation.
At the end of the first week, the blastocyst comes in contact with the uterine wall and adheres to it, embedding itself in the
uterine lining via the trophoblast cells. Thus begins the process of implantation, which signals the end of the pre-embryonic
stage of development
During the second week of development, with the embryo implanted in the uterus, cells within the blastocyst start to
organize into layers. Some grow to form the extra-embryonic membranes needed to support and protect the growing
embryo: the amnion, the yolk sac, the allantois, and the chorion.
At the beginning of the second week, the cells of the inner cell mass form into a two-layered disc of embryonic cells, and
a space—the amniotic cavity—opens up between it and the trophoblast
Cells from the upper layer of the
disc (the epiblast) extend around the amniotic cavity, creating a membranous sac that forms into the amnion by the end of
the second week. The amnion fills with amniotic fluid and eventually grows to surround the embryo
On the ventral side of the embryonic disc, opposite the amnion, cells in the lower layer of the embryonic disk (the
hypoblast) extend into the blastocyst cavity and form a yolk sac. The yolk sac supplies some nutrients absorbed from
the trophoblast and also provides primitive blood circulation to the developing embryo for the second and third week of
development
a finger-like outpocketing of the yolk sac develops into the allantois, a primitive excretory duct
of the embryo that will become part of the urinary bladder. Together, the stalks of the yolk sac and allantois establish the
outer structure of the umbilical cord.
As the third week of development begins, the two-layered disc of cells becomes a three-layered disc through the process
of gastrulation, during which the cells transition from totipotency to multipotency. The embryo, which takes the shape of
an oval-shaped disc, forms an indentation called the primitive streak along the dorsal surface of the epiblast.
The first layer is the
endoderm, a sheet of cells that displaces the hypoblast and lies adjacent to the yolk sac.
The second layer of cells fills in
as the middle layer, or mesoderm.
The cells of the epiblast that remain (not having migrated through the primitive streak)
become the ectoderm
less organized and exist as a loosely connected cell community
ectoderm gives rise to cell lineages that differentiate to become the central and peripheral nervous systems, sensory
organs, epidermis, hair, and nails
Mesodermal cells ultimately become the skeleton, muscles, connective tissue, heart, blood
vessels, and kidneys
endoderm goes on to form the epithelial lining of the gastrointestinal tract, liver, and pancreas, as
well as the lungs
The placenta develops throughout the embryonic period and during the first several weeks of the fetal period; placentation
is complete by weeks 14–16. As a fully developed organ, the placenta provides nutrition and excretion, respiration, and
endocrine function
receives blood from the fetus through the umbilical arteries
Capillaries
in the chorionic villi filter fetal wastes out of the blood and return clean, oxygenated blood to the fetus through the umbilical
vein
Maternal and fetal blood does not commingle because blood cells cannot move across the placenta. This separation prevents
the mother’s cytotoxic T cells from reaching and subsequently destroying the fetus, which bears “non-self” antigens
Organogenesis
Following gastrulation, rudiments of the central nervous system develop from the ectoderm in the process of neurulation
Specialized neuroectodermal tissues along the length of the embryo thicken into the neural plate. During
the fourth week, tissues on either side of the plate fold upward into a neural fold
The two folds converge to form the neural
tube. The tube lies atop a rod-shaped, mesoderm-derived notochord, which eventually becomes the nucleus pulposus of
intervertebral discs
The embryo, which begins as a flat sheet of cells, begins to acquire a cylindrical shape through the process of embryonic
folding
Within the first 8 weeks of gestation, a developing embryo establishes the rudimentary structures of all of its organs and
tissues from the ectoderm, mesoderm, and endoderm.
weeks 4–5, the eye pits form,
limb buds become apparent, and the rudiments of the pulmonary system are formed.
During the sixth week, uncontrolled fetal limb movements begin to occur. The gastrointestinal system develops too rapidly
for the embryonic abdomen to accommodate it, and the intestines temporarily loop into the umbilical cord. Paddle-shaped
hands and feet develop fingers and toes by the process of apoptosis (programmed cell death), which causes the tissues
between the fingers to disintegrate
By week 7, the facial structure is more complex and includes nostrils, outer ears, and
lenses
By the eighth week, the head is nearly as large as the rest of the embryo’s body, and all major brain
structures are in place. The external genitalia are apparent, but at this point, male and female embryos are indistinguishable.
Bone begins to replace cartilage in the embryonic skeleton through the process of ossification.
This 30-week period of
development is marked by continued cell growth and differentiation, which fully develop the structures and functions of the
immature organ systems formed during the embryonic period
Sexual differentiation does not begin until the fetal period, during weeks 9–12
Bipotential gonads, or gonads that can develop
into male or female sexual organs, are connected to a central cavity called the cloaca via Müllerian ducts and Wolffian ducts.
During male fetal development, the bipotential gonads become the testes and associated epididymis. The Müllerian ducts
degenerate. The Wolffian ducts become the vas deferens, and the cloaca becomes the urethra and rectum
During female fetal development, the bipotential gonads develop into ovaries. The Wolffian ducts degenerate. The
Müllerian ducts become the uterine tubes and uterus, and the cloaca divides and develops into a vagina, a urethra, and a
rectum.
The fetal circulatory system includes three shunts to divert blood from
undeveloped and partially functioning organs, as well as blood supply to and from the placenta
Weeks 9–12
Weeks 13–16
Weeks 16–20
Weeks 17–20
Weeks 21–30
The fetus continues to lay down subcutaneous fat from week 31 until birth.
brain continues to expand, the body elongates, and ossification continues.
Fetal movements are frequent during this period, but are jerky and not well-controlled. The bone marrow begins to take
over the process of erythrocyte production—a task that the liver performed during the embryonic period. The liver now
secretes bile. The fetus circulates amniotic fluid by swallowing it and producing urine. The eyes are well-developed by this
stage, but the eyelids are fused shut. The fingers and toes begin to develop nails. By the end of week 12, the fetus measures
approximately 9 cm (3.5 in) from crown to rump
The bone marrow begins to take
over the process of erythrocyte production—a task that the liver performed during the embryonic period. The liver now
secretes bile.
The fetus circulates amniotic fluid by swallowing it and producing urine.
The eyes are well-developed by this
stage, but the eyelids are fused shut.
The fingers and toes begin to develop nails.
By the end of week 12, the fetus measures
approximately 9 cm (3.5 in) from crown to rump
sensory organ development. eyes move closer together; blinking motions begin, although
the eyes remain sealed shut.
The lips exhibit sucking motions.
The ears move upward and lie flatter against the head. The
scalp begins to grow hair.
The excretory system is also developing: the kidneys are well-formed, and meconium, or fetal
feces, begins to accumulate in the intestines. Meconium consists of ingested amniotic fluid, cellular debris, mucus, and bile.
limb movements become more powerful, the mother may begin
to feel quickening, or fetal movements. However, space restrictions limit these movements and typically force the growing
fetus into the “fetal position,” with the arms crossed and the legs bent at the knees.
Sebaceous glands coat the skin with a
waxy, protective substance called vernix caseosa that protects and moisturizes the skin and may provide lubrication during
childbirth.
A silky hair called lanugo also covers the skin
rapid weight gain
bone marrow completely takes over erythrocyte synthesis, and the axons of the spinal cord
begin to be myelinated, or coated in the electrically insulating glial cell sheaths that are necessary for efficient nervous
system functioning.
the fetus grows
eyelashes. The eyelids are no longer fused and can be opened and closed.
The lungs begin producing surfactant, a substance
that reduces surface tension in the lungs and assists proper lung expansion after birth.
Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our sex cells – sperm in males, eggs in females.
Meiosis can be divided into nine stages. These are divided between the first time the cell divides (meiosis I) and the second time it divides (meiosis II):
Meiosis I
Interphase
The DNA in the cell is copied resulting in two identical full sets of chromosomes
Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division
microtubules extend from these centrosomes.
Prophase I
The copied chromosomes condense into X-shaped structures that can be easily seen under a microscope.
Each chromosome is composed of two sister chromatids containing identical genetic information.
The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on.
The pairs of chromosomes may then exchange bits of DNA in a process called recombination or crossing over.
At the end of Prophase I the membrane around the nucleus in the cell dissolves away, releasing the chromosomes.
The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles.
Metaphase I
The chromosome pairs line up next to each other along the centre (equator) of the cell.
The centrioles are now at opposites poles of the cell with the meiotic spindles extending from them.
The meiotic spindle fibres attach to one chromosome of each pair.
Anaphase I
The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole.
In meiosis I the sister chromatids stay together. This is different to what happens in mitosis and meiosis II.
Telophase I and cytokinesis
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new nuclei.
The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
Meiosis II
Prophase II
Now there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids)
In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be easily seen under a microscope.
The membrane around the nucleus in each daughter cell dissolves away releasing the chromosomes.
The centrioles duplicate.
The meiotic spindle forms again.
Metaphase II
In each of the two daughter cells the chromosomes (pair of sister chromatids) line up end-to-end along the equator of the cell.
The centrioles are now at opposites poles in each of the daughter cells.
Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids.
Anaphase II
The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle.
The separated chromatids are now individual chromosomes.
Telophase II and cytokinesis
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new cell nuclei.
This is the last phase of meiosis, however cell division is not complete without another round of cytokinesis.
Once cytokinesis is complete there are four granddaughter cells, each with half a set of chromosomes (haploid):
in males, these four cells are all sperm cells
in females, one of the cells is an egg cell while the other three are polar bodies (small cells that do not develop into eggs).
Gonadotropic Hormones
Released by the anterior pituitary gland
At puberty gonadotropin-releasing hormone (GnRH)
is produced and released from the
hypothalamus.
Gn-RH release stimulates the secretion of both
follicle-stimulating hormone (FSH) and lutenizing
hormone (LH) from the pituitary gland
(gonadotropic hormones).
In males, FSH causes spermatogenesis in the
testes.
In males, LH stimulates the interstitial cells of the
testes to produce testosterone.
Estrogen
During puberty, estrogen stimulates breast development
and causes the vagina, uterus and fallopian tubes to
mature.
From puberty onwards, LH, FSH, estrogen and
progesterone all play a vital part in regulating a woman's
menstrual cycle, which results in her periods
Progesterone
Secreted at ovulation, helps to prepare the
endometrium (womb lining) for the
implantation of an egg
Prepares mammary glands for milk
production
Primarily concerned with procreation and
survival of the fetus.
FSH in Females
Stimulates the follicles to ripen several
eggs.
LH in Females
Further develops the follicles, triggers
ovulation and stimulates production of
other hormones necessary for the post
ovulatory stage of the menstrual cycle.
FSH in males
FSH causes spermatogenesis in the
testes.
LH in males
stimulates the interstitial cells of the
testes to produce testosterone