Human Reproduction (side view)
The male reproductive
system has two
1. The production of
2. The deposition of the
sperm in the female.
The penis is a structural
adaptation to allow for
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•Testes – Sperm production occurs here.
The testes are located in the scrotum,
where the temperature is 1-2 degrees
cooler than the rest of the body. The
testes also produce the male sex
hormone “testosterone”. Testosterone is
responsible for sperm development and
the development of physical features.
•Urethra – The sperm move from the
testes, through the sperm duct (vas
deferens) and the urethra until they exit
the body (ejaculation). The urethra is a
long tube inside the penis that either
sperm or urine flows through before it is
released. They cannot flow at the same
time. It is either one or the other.
•Semen is the combination of sperm and A Hermaphrodite is an organism
liquid. The liquid is a transport medium that has both testes and ovaries.
for the sperm to travel in.
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Female Reproductive System
Ovaries – Ovaries produce eggs
(ova) in the cavities called
follicles. The process is called
Ovulation is the release of the
egg from the ovary.
After ovulation, the egg cell is
transported through the oviduct
(fallopian tube) to the uterus.
The bottom of the uterus is the cervix. The
cervix is the opening to the muscular tube called
the vagina. The vagina receives sperm from the
male and is also called the birth canal during
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A woman is born with all of her eggs, in the immature form. No more
eggs will develop. Usually, only one egg is released at a time, during
each ovulation period.
In addition to eggs, the ovaries also produce the female sex hormones,
estrogen and progesterone. These hormones regulate the
development of the secondary sex characteristics of a female, as well
as play a role in the menstrual cycle.
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The Menstrual Cycle begins at puberty and ends at menopause.
Menopause is the permanent cessation of the menstrual cycle. The
Menstrual Cycle lasts an average of 28 days, but many women have
shorter or longer cycles. Pregnancy, medications, illness, and other
factors can interrupt the menstrual cycle.
There are 4 stages to the Menstrual Cycle:
1. Follicle Stage – This involves the maturation of an egg in the ovary
and the secretion of estrogen. The estrogen causes the thickening of
the uterine lining (the blood volume builds up).
2. Ovulation – One egg is released from the follicle in the ovary.
3. Corpus Luteum – The follicle breaks down and forms a yellow mass
of cells which secrete progesterone and enhance the thickening of the
4. Menstruation - This is when the uterine lining (blood) is shed and
released through the vagina. This lasts for up to a week and happens
when egg fertilization does not take place.
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The role of hormones in the Menstrual Cycle
During the menstrual cycle, under the influence
of the hypothalamus, the pituitary gland
releases certain hormones.
FSH – Follicle Stimulating Hormone –
Stimulates follicle growth and the ovary to
LH – Luteinizing Hormone – Stimulates the
growth of the corpus luteum (in the ovary) to
secrete progesterone, which stops estrogen
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Human Fertilization and Development
Fertilization usually occurs in the upper part of the oviduct (fallopian
If the egg is not fertilized within approximately 24 hours after ovulation
(when the egg is released), it deteriorates.
If the egg is fertilized it is called a zygote, and Cleavage (the first stage of
development) begins in the oviduct.
Six to ten days later the egg will be implanted into the lining of the
The Gastrulation stage occurs next, after the egg is implanted in the
The Differentiation and Growth stages result in tissues and organs
developing and specializing into an embryo, from the gastrula. At 8
weeks, the embryo becomes a fetus.
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In rare occasions, more than one egg can be released and fertilized.
from the ovary. There are also times when one egg was released, but
split after fertilization.
Identical Twins develop from one egg splits after fertilization in the
Fraternal Twins develop from two eggs that were released at the same
time and each fertilized by a different sperm cell.
There can also be multiple births of 3 (triplets) to 7 (septuplets) babies
Reproductive Technology has increased the amounts of multiple births
across the world. There is in-vitro fertilization, artificial
insemination, and many prescribed medicines that help with the
process of conceiving a baby.
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An average human pregnancy lasts 40 weeks. This is 9
entire months. The pregnancy is broken up into
trimesters, each trimester lasts 3 full months.
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(Refer back to your Fertilization and
Development notes for details on this.)
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Pregnant women must take excellent care of themselves. Most of the
fetus’s organs develop before a women is 10 weeks pregnant.
Unfortunately, this is before some women even know that they are
pregnant. Pregnant women must eat very healthy and avoid the
following risks because everything that the mother ingests or
breathes, goes to the baby.
(Effects of FAS on children)
1. Tobacco (causes low birth weight)
2. Drugs (causes many deformities)
3. Alcohol (causes Fetal Alcohol Syndrome)
4. Regular household chemicals
Many birth defects are caused by a mothers
exposure to harmful environments, but many also
occur for no known reason at all. We will discuss
birth defects in more detail in the Genetics topic.
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As stated earlier, birth occurs about 40 weeks
after conception. Because of modern medicine,
some babies can live with assisted technology,
after 26 weeks. A pregnancy is said to be full
term after 38 weeks. Most babies are very
healthy at that point.
The birth process involves strong contractions in the women’s uterus.
Each contraction pushes the baby down further. This is called labor.
The baby will exit the cervix into the vagina (birth canal) until it is outside
the mother’s body. After the baby is delivered the placenta must exit as
In some cases, a baby cannot be delivered vaginally. This could be
because of a medical emergency on the part of the baby or the mother. If
this is the case, the baby will be born by a cesarean section (c-section).
This is a cut through the uterus of the mother which allows for the baby to
be pulled out.
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Sexually Transmitted Diseases
There are many sexually transmitted diseases that both males and
females can get and also transmit.
•Some of these diseases may cause infertility
•Some can cause death
•Some can be treated with medications and will not return
•Some can never go away and will reoccur many times throughout a
persons life Some examples are:
•Human Papillomavirus (HPV)
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What is a sexually transmitted disease (STD)?
It is an infection or disease passed from person to person
through sexual contact.
How many people have STDs?
The United States has the highest rates of STDs in the
industrialized world. In the United States alone, an estimated
15.3 million new cases of STDs are reported each year.
Women suffer more frequent and more serious complications
from STDs than men.
How do you get an STD?
You can get and pass STDs through vaginal, anal, or oral
sex. Some STDs cause no symptoms. But STDs can still be
passed from person to person even if there are no symptoms.
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