Reproductive System
Human Anatomy
Chapter 24
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The reproductive system becomes active after puberty. During puberty the
reproductive organs mature to create a fertile individual capable of
reproducing. The primary sex organs produce the sex cells (egg/sperm)
and sex hormones. The accessory sex organs are all the components
involved in maintaining the sex cell and assisting in the process of
fertilization.
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I. The male reproductive system:
This system is simpler than the female reproductive system.
A. Scrotum: a sac located outside of the abdominal cavity, made up of a
thin layer of smooth and skeletal muscle and skin. It is divided into left and
right by a septum to form different compartments for the testicles. The
scrotum keeps the testicles outside the body so they can be 3 degrees
cooler than normal core temperature. The muscles of the scrotum contract
to bring the testicles closer to the body in cooler conditions. In warm
conditions they relax to allow the skin to stretch and maximize cooling.
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B. Testes: Oval shape organs made up of thousands of seminiferous tubules where
the sperm is produced. It responds to follicle stimulating hormone that signals sperm
production. When the sperm is in its last stages of maturation it moves to the
epididymus.
1. Gross anatomy: about 1 x 4 inches, complete surrounded by a fibrous capsule and
partially enclosed by a serous membrane that develop when the testes traveled
outside the body into the scrotum. The fibrous capsule divides the testicles into
wedge-like compartments called lobules that are filled with seminiferous tubules.
They are innervated by an abundant about of visceral sensory nerves that make
them very sensitive to pain. The high sensitivity serves for protection and in sexual
arousal.
• 2. Seminiferous
tubules and
spermatogenesis:
The seminiferous
tubules consist of a
thick stratified
epithelium
surrounding a
lumen. The
epithelium has
spermatogenic cells
that mature into
sperm. At puberty
the seminiferous
tubules begin to
produce about 400
million sperm. the
spermatogenic cells
are protect by a
blood-testis barrier
that keep the cells
from activating the
immune system.
• Spermatogenesis: these are the stages involved in sperm formation.
• Stage 1: formation of spermatocytes: spermatogonia divide by
mitosis to produce two daughter cells, one remains in the germ line
(to continue regeneration of more spermatogonia) and the other one
goes on to become sperm.
• Stage 2: Meiosis: this is a reduction division that takes a cell through
two rounds of division. At the end four genetically distinctive cells
(spermatids) are created which will each mature into a sperm.
• Stage 3: Spermiogenesis: spermatids mature into sperm, the cell
develops a long flagella, a mid piece with high mitochondria count,
and a “head” filled with DNA= the nucleus. At the tip of the head lies
a sac filled with digestive enzymes called the acromosome (see
page 676).
• Other cells in the testicles perform jobs like assisting the cells to
mature and exit the scrotum (referred to as nurse cells), produce
male androgen (like testosterone), and muscular cells that cause
tiny contractions to push the sperm out of the testes. When sperm
leaves the seminiferous tubules it travels down the efferent tubules
towards the epididymis.
• C. Reproductive duct system is males: This section discusses the
tubules through which sperm travel to exit the body.
• 1. Epididymis: organ that arches over the posterior lateral side of the
testis. If you uncoil the epididymis is can be as long as 6meters or
20 feet! During the twenty days the sperm spend here they
complete maturation and gain the ability to swim and fertilize. During
ejaculation smooth muscle contracts to send mature sperm to the
ductus deferns.
• 2. Ductus deferens: also known as the vas deference, it runs
superior to the testicles, enters the abdominopelvic cavity, runs
posterior to the bladder, passes by the seminal vesicle, form the
ampulla and ejaculatory duct, and finally leads into the prostatic
urethra.
• 3. Spermatic cords: a tube of fascia holding blood vessels, nerves,
and the ductus deference. See page 672 figure 24.2.
• 4. Urethra: As discussed in the previous chapter the urethra and
men carries both sperm and urine. During ejaculation the sphincter
muscles close off the bladder so urine is not released into the
semen. The urethra is divided into the prostatic urethra (section
passing through prostrate gland), the membranous urethra
(urogenital diaphragm) and the spongy urethra (penile). Urethral
glands along the spongy urethra secrete a lubricating solution before
ejaculation.
• D. Accessory glands: These glands produce substances that
increases the chances of sperm survival once it is outside the body.
These secretions in addition to sperm form semen.
• 1. Seminal vesicles: paired glands located posterior to the bladder.
During ejaculation smooth muscle contract to help secrete a fluid
that contains fructose (sugar), nutrients, prostagladins to stimulate
the urethra to contract, substances that suppress the immune
system against sperm in females, enzymes the enhance sperm
mobility, and enzymes that thicken the ejaculate.
• 2. Prostate gland: the size of a chestnut, also has smooth muscle
that contracts to assist in the release of prostatic secretion. This is a
milky white fluid that has substances to enhance sperm mobility and
thicken ejaculate. It is susceptible to tumors and sexually transmitted
diseases (STDs).
• 3. Bulbourethral glands: secrete a mucus substances that lubricates
and neutralizes the acid from urine in the male urethra.
E. Penis: Designed to deliver
semen into the female
reproductive tract. It originates
at the root, expends through the
body, and ends at the glans
penis. Skin around the glans
penis is called prepuce
(circumcision has contradicting
arguments that seem to weigh
equally). The penis contains
erectile bodies: corpora
spongiosum, corpora
cavernosa, and others
consisting of smooth muscle
and connective tissue. It is a
spongy network surrounded by
a high amount of blood vessels
that dilate during arousal and
engorge the spongy tissues with
blood. The veins that normally
drain the penis are pressured
shut by the expanding spongy
tissue. The parasymphatetic
branch causes the penis to
become erect by stimulating
vasodilation. The symphatetic
branch cause ejaculation by
stimulating contraction of
smooth muscle along the
reproductive tract.
•
II. The female reproductive system: These organs produce the ova
(eggs), sex hormones, and provide an environment for internal fertilization
and development of the fetus. They undergo changes according to the
menstrual cycle. Mammary glands are considered part of this system
because they nourish the infant.
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A. The ovaries: the size of an almond, this paired organ is suspended by
mesenteries and ligaments. It is surrounded by a fibrous capsule and can
be divided into a cortex and medulla. The cortex houses the developing ova
and the medulla holds vascular tissue. The ovary is the site of oogenesis
and female sex hormone production. It responds to follicle-stimulating
hormone that signals the maturation of an ovum. Typically only one egg is
released from an ovary every month, the ovaries alternate in releasing the
egg. Every time an egg is released the ovaries become scarred. Hormones
that affect the menstrual cycle and female sex organs are also released by
the ovaries; estrogen and progesterone.
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1. Ovarian cycle: this
concerns the changes in the
ovary during the menstrual
cycle. Females are born with
all the potential ova they can
produce in a life time. These
are called the primordial
follicles which consist of a
single immature oocyte and a
single layer of follicular cells.
These cells respond to FSH
and being the maturation of
an oocyte.
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Follicular phase: during the
first two weeks of the
menstrual cycle one follicle
matures up until the stage
when it is able to release an
oocyte. Other primordial
follicles may get activated but
die out along the way. The
primordial follicle becomes
the primary follicle and
continues to develop until it
becomes the vesicular follicle.
At this point the oocyte is
surrounded by follicle cells
that the form a fluid filled
cavity.
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Ovulation (midpoint)
phase: at about the mid
cycle LH is release to
signal the follicle to
rupture and release the
oocyte from the ovary.
The ovum is surrounded
by a group of cells that
continue to nourish it, they
are called the corona
radiata. When the egg
cell is released it enters
the peritoneal cavity but is
swept into the
fallopian/uterine tubes by
fimbriae.
Luteal phase: after
ovulation and during the
last two weeks of the
cycle the follicle that held
the oocyte becomes the
corpus luteum, it is now
considered an endocrine
gland that releases
progesterone. If no
implantation occurs it
becomes the corpus
albicans (now scar
tissue).
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2. Oogenesis: while in men spermatogenesis happens in about a month, in
females oogenesis takes several years. During fetal development oocytes
undergo meiosis I but do not completel it; at this point they are called
primary oocytes. At ovulation the primary oocyte completes meiosis I and
begins meiosis II which is completed only if fertilization occurs. At the
completion of meiosis II the oocyte is called an ovum.
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B. Uterine tubes: also called fallopian tubes, they take the oocyte and
provide a site for fertilization. The tube is lined with ciliated epithelium that
gently guides the oocyte towards the uterus. There are also peristaltic
waves caused by smooth muscle contraction to aide the movement of the
oocyte. There are also non-ciliated cells the nourish the oocyte or embryo
on its way to the uterus. sometimes a fertilized egg can implant in a uterine
tube and cause a life threatening ectopic pregnancy.
Uterine Tube Histology
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C. The uterus: a thick muscular pouch about the size of a pear that lies in
the pelvic cavity superior to the bladder. The function of the uterus is to
receive an embryo and provide an environment for its development. During
pregnancy it stretches to accommodate the growth of the fetus. When there
is no pregnancy the cavity within the uterus is small. The opening of the
uterus is at the cervix, during child birth it dilates to allow the child to pass
by. The cervix tissue may become infected by a virus called HPV human
papilloma virus. It can cause abnormal tissue growth including cervical
caner. The purpose of pap-smears is to check the cervical tissue for
abnormal growth.
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1. Supports of the uterus: The uterus, cervix, and vagina are supported by
ligaments and mesenteries. Most uterine support is provided by muscles of
the pelvic floor. Sometimes these muscles are torn during child birth and the
unsupported uterus results in a prolapsed uterus. In this condition the tip of
the cervix protrudes through the opening of the external vagina.
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2. Uterine wall: composed of three layers: perimetrium (outer= serous
membrane), myometrium (middle= layers of smooth muscle), and
endometrium (inner= simple columnar epithelium). The thick layer called
stratum functionalis (above myometrium) undergoes most of the changes
during the uterine cycle.
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3. Uterine cycle: also called the menstrual cycle, it relates to changes
occurring in the endometrium of the uterus that are induced by female sex
hormones.
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Menstrual phase: (days 1-5) during this phase the endometrium is shed
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Proliferative phase: (days 6-14) during this phase the endometrium builds a
new stratum functionalis as it responds to rising estrogen levels. As the
layer thickens glands release a clear sticky mucus secretion that assist the
sperm in finding the egg.
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Secretory phase: (days 15-28) during this point the stratum functionalis is
highly vascularized and there is secretion of glycoproteins to support a
developing embryo in case fertilization occur. These changes are a
response to progesterone released by the corpus luteum in the ovary. If
there is no fertilization the progesterone levels drop signaling changes that
cause death of the stratum functionalis. The arteries constrict cutting out
blood supply and suddenly open again but the weak capillaries fragment
and the menstrual phase begins again.
D. The vagina: also
known as the birth canal.
It is the opening that
leads into the cervix and
is located anterior to the
anus but posterior to the
clitoris and urethral
opening. The vagina is
also the site where
sperm is deposited. This
canal is very flexible and
it composed of three
layers: adventitia,
muscularis, and mucosa.
It also has ruggae to
stimulate the penis
during intercourse and
stretch out during
childbirth. The mucosa is
made up of stratified
squamous epithelium. It
secretes glycogen to
maintain healthy
beneficial bacteria that
produce lactic acid. This
creates an acidic
environment that is not
beneficial to other
bacteria or sperm.
• E. External genitalia: also called the vulva and often incorrectly
referred to as the vagina. It includes the mons pubis (fatty rounded
pad over the pubic symphisis), the labia majora (thick skin fold
analogous to the scrotum), the clitoris (erectile tissue analogous to
the penis), and vestibule associated structures( the vaginal and
urethral orifice and vestibule glands). The vestibule are protected by
the mucus membrane sheathes called the labia minora.
•
F. Mammary glands: modified sweat glands that are active in pregnant
females to produce milk for the infant. These first appear as rudimentary
structures in both men and women. When females reach puberty the ducts
grow but the glands do no fully develop; the mas of the breast is mostly
adipose. During pregnancy glandular alveoli form and produce milk shortly
after childbirth. The breast include the nipple and the areola (ring around
nipple). The glands consist of lobes that drain into the nipple by lactiferous
ducts and lactiferous sinuses where milk accumulates during breastfeeling.
Lymoph vessels drain into the parasternal and axillary lymphonodes.
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III. Pregnancy and childbirth: This section briefly describes the evens that
occur in the woman’s body during fertilization, pregnancy, and childbirth.
A. Pregnancy: occurs once an egg is successfully fertilized and
successfully implants.
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1. Events leading to
fertilization: Sperm swims
from the vagina through the
cervix, through the uterine
wall until it reaches the
oocyte in the uterine tubes.
When burrows into the zona
pellucida of the oocyte
enzymes digest it way to
allow the sperm to reach the
egg. The plasma membranes
fuse and sperm nucleus
enters the oocyte’s
cytoplasm. This initiates the
cortical reaction in which the
egg destroys other sperm
receptors so no other sperm
binds and fertilizes the egg.
When the male and female
chromosomes come together
fertilization has been
completed and the zygote
will begin to divide. Once it is
large enough and has
formed a blastocyst it enters
the uterus to implant.
•2. Implantation: Six days after fertilization the
blastocyst implants as it burrows into the
endometrium. At this point some cells will become
the developing embryo and some the placenta. As
the trophoblast burrow into the endometrium it
causes bleeding (about 10-12 days after
fertilization).
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3. Formation of the placenta: The embryonic tissues from finger like
projection called chorionic villi that come in contact with the area of the
bleeding endometrium (lacunae) and the embryo connect to the chorionic
villi via the body stalk which will become the future umbilical cord. By the
end of the first month the embryo’s blood is in close contact with the
mother’s blood and exchange of nutrients and waste is happening at the
chorionic villi. At the start of the 4th month the endometrium and the
chorionic villi make a thick disc called the placenta. This is the site where
nutrient and waste exchange occur. After childbirth the placenta detaches
from the uterus.
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4. The placenta: produces hormones such as progesterone and human
chorionic gandotropin HCG that keep the placenta attached. It prevents
bacteria from the mother to transfer to the child, allows nutrients and
antibodies to flow from mother to child, and the transfer of waste from child
to mother. Viruses and drugs do cross the placenta. As soon as one week
after fertilization HCG can be detected in blood test and two to three weeks
in urine.
• B. Childbirth: also known
as parturition, labor is the
events prior to childbirth.
When the fetus grows so
much that the placenta
cannot meet its nutritional
needs stress hormones are
release to signal the
beginning of labor.
Oxytocin and
prostaglandins cause the
uterus to contract. Stages
of labor:
• Dilation stage: begins when
the uterus first contracts
and ends when cervix
dilates (10cms). Cervical
dilation can take 6-12
hours.
• Expulsion stage: from the time the
cervix is fully dilated until the child
leaves the mother’s womb. There
are strong placental contractions,
this process can take up to 2 hours.
• Placental stage: uterine contractions
discharge the placenta. The
umbilical cord is checked for the
presence of two arteries and one
vein (one indicates a heart disorder).
• IV. Disorder of the reproductive
system: Study on your own the
section on reproductive system
cancers in males and females
STD STATS
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Chlamydia- (bacteria) 3 million new cases per year- 75% have no
symptoms. Painful frequent urination, discharge, painful sex, sore throat,
fever, nausea
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Gonorrhea- (bacteria) 700,000 cases/year 50% have no symptoms or the
same simptoms as Chlamydia
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Herpes (virus) 1 million new cases/year, 45 million already have it. 1 in 4
pregnant women have herpes HSV-1 (oral sores) HSV-2 genital
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HIV- 7,000 women give birth per year. 20% of infected babies develop AIDS
and die by age 4
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HPV- 75% of the reproductive population is infected ( 3 in 4 people)
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Syphilis- 32,000 new cases/year. A pailess sore is followed by a rash,
followed by rough “copper penny” spots on the palm and bottom of feet
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Trichomoniasis- a bacteria that affects 5 million women/year. Foul smell,
green discharge, itching,redness