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Chapter 27
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27-1
Sexuality from Different Points
of View
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Sexuality
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Different approaches to sexuality
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All of the factors that contribute to one’s female or
male nature
Structure and function of sex organs
Sexual behavior
Cultural influences
Behavioral
Cultural
Biological
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A Spectrum of Human Sexuality
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27-3
Ranges from heterosexual to homosexual
A complex trait; no one gene dictates where
one falls on spectrum
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Sexual Attraction, Sex and
Sexual Response
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Sexual attraction involves many factors, including
sight and smell.
After initial attraction, the couple may engage in
foreplay and sexual intercourse.
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27-4
In heterosexual sex, the male achieves an erection of the
penis, which allows it to be easily inserted into the female
vagina.
Pelvic movements can result in ejaculation, which allows for
release of sperm and other fluids (semen) from the penis,
and is accompanied by a pleasurable sensation called
orgasm.
Females often also experience orgasm.
Maintaining an active sex-life in a long-term
relationship requires effort.
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Moving Across the Spectrum
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Pseudo-hermaphrodites
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27-5
Humans born with partial development of both
male and female genitalia
Due to a hormonal imbalance during embryonic
development
Gender must be “chosen” and genitalia surgically
altered to become completely female or
completely male
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Moving Across the Spectrum
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Gender dysphoria
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27-6
When one’s physical and psychological gender do
not match
A male who “feels” like a woman, or vice versa
Frequently these individuals dress and act as
members of the opposite sex (cross-dressers or
transvestites).
Often leads to gender-reassignment surgery (sexchange)
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Nature or Nurture?

Studies show that
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A small region of the hypothalamus is of similar size in
trans-gendered males as it is in women, and in transgendered females as it is in men.
Similar studies show differences in brain structure between
homosexuals and heterosexuals.
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27-7
Not confirmed
Complicated because homosexual brain donors were HIV+
and had been on antiviral drugs
Genes on chromosomes 7, 8 and 10 have been suggested
to influence homosexuality.
Homosexuality is a complex behavioral pattern.
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Chromosomal Determination
of Sex and Early Development

2 of the 46 human chromosomes are involved in
gender determination
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Called sex chromosomes
X and Y
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Are not truly homologous because they contain different
sets of information
X carries more information than just that needed for gender
determination.
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Y carries only information regarding maleness.
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27-8
Blood-clotting, color vision, etc.
Contains SRY (Sex-determining Y) gene
SRY encodes for testes determining factor (TDF)
The presence of this gene leads to the development of a male;
the absence leads to the development of a female.
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Chromosomal Determination
of Sex
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Eggs carry 22 autosomes and an X.
Sperm carry 22 autosomes and either a Y or an X.
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Embryos become truly male or female during
differentiation.
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If an X sperm fertilizes an egg, a female is formed (XX).
If a Y sperm fertilizes an egg, a male is formed (XY).
When embryonic gonads develop into ovaries or testes
The presence of SRY will lead to the development of testes.
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Human Male and Female
Chromosomes
27-10
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Chromosomal Abnormalities
and Sex
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Turner’s syndrome (XO)
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Results from a nondisjunction in one parent
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Symptoms
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27-11
Make egg or sperm that lack a sex chromosome.
When this gamete is used during fertilization, the individual
ends up with only one sex chromosome, in this case, an X.
Abnormally short
Failure to complete sexual maturity
Thickened neck
Hearing impairment
Cardiovascular problems
Sterility
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Turner’s Syndrome
27-12
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Chromosomal Gender Disorders
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Klinefelter’s syndrome (XXY)
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Also results from a nondisjunction in one parent
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Symptoms
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27-13
Leads to the development of gametes with two sex
chromosomes
After fertilization, the individual has three sex
chromosomes.
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Sterility
Breast enlargement
Incomplete masculine development
Lack of facial hair
Minor learning problems
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Klinefelter’s Syndrome
27-14
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Fetal Development and Sex
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Development of gonads begins about week 5.
Males
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Between weeks 5-7 testes determining factor made from the
SRY gene begins the differentiation of male gonads.
Week 8, testes begin making testosterone.
Testosterone leads to the differentiation of male sexual
anatomy (penis, etc.).
In the 7th month, testes move through the inguinal canal to
the external sac.
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If this canal opens again later in life, an inguinal hernia can
result.
Cryptorchidism
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27-15
Failure of testes to descend
Can lead to sterility unless corrected
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Fetal Development and Sex
27-16
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Fetal Development and Sex

Females
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27-17
Ovaries develop about week 12 in the absence of
TDF.
The absence of testosterone leads to the
differentiation of female sexual anatomy (vagina,
etc.).
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Sexual Maturation in Young
Adults
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Puberty is the developmental period when:
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27-18
The body changes to the adult form.
The body becomes sexually mature and able to
produce offspring.
Usually occurs between 12-14 years old
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Hormones and Sexual Function
27-19
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The Maturation of Females
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At 9-12 years of age
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Hypothalamus and pituitary gland
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27-20
The hypothalamus, pituitary, ovaries and adrenal glands
begin producing sex hormones.
Hypothalamus releases gonadotropin-releasing hormone
(GnRH)
GnRH stimulates the pituitary to release luteinizing hormone
(LH) and follicle-stimulating hormone (FSH).
FSH stimulates the development of follicles in the ovary.
LH stimulates the ovary to produce more estrogen.
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The Maturation of Females
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Estrogen stimulates secondary sex characteristics.
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Growth of breast tissue
Maturation of the uterus and vagina
Increased blood supply to the clitoris
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Changes in pelvic bone structure
Production of androgens by adrenal gland
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27-21
The clitoris is a small, elongated erectile structure located at
the head of the labia. It is equivalent to the penis.
Leads to the growth of pubic hair
Influence female sex drive
Involved in the production of acne
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The Maturation of Females
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During puberty, females begin to experience
the menstrual cycle.
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LH from the pituitary causes the egg to be
released from the follicle in the ovary (ovulation).
The ruptured follicle becomes the corpus luteum.
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27-22
Begins releasing progesterone
Progesterone maintains the lining of the uterus.
When uterine lining breaks down, menstruation
occurs.
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Ovulation
27-23
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The Maturation of Males
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Between 11-14 years of age in males, the
hypothalamus releases GnRH.
Like in females, GnRH stimulates the
pituitary to release LH and FSH.
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27-24
LH is also called interstial cell-stimulating
hormone (ICSH) in males.
LH stimulates the production of testosterone by
the testes.
FSH stimulates the production of sperm cells.
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The Maturation of Males
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Testosterone stimulates the development of male
secondary sex characteristics.
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27-25
Increased size of the penis
Growth of testes and scrotum
Growth of pubic hair
Facial and body hair
Larynx changes shape, leading to the deepening of the
male voice
Increased height
Body shape changes (broad shoulders, more muscles)
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The Maturation of Males
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Semen production
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Mixture of sperm and secretions released during ejaculation
Involves seminal vesicles, prostate gland, and bulbourethral gland
Seminal vesicles secrete an alkaline fluid that contains
fructose and hormones.
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27-26
Alkaline fluid neutralizes the acidic nature of the female
reproductive tract.
Fructose is fuel for the sperm.
Prostate gland produces a thin milky fluid containing
sperm-activating hormones.
Bulbo-urethral gland produces alkaline secretions.
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Gametogenesis
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The process of producing gametes
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27-27
Spermatogenesis is the process of producing
sperm, the male gamete.
Involves meiosis
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Spermatogenesis
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Takes place in the seminiferous tubules of the
testes
The seminiforous tubules converge and become
the epididymis.
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The epididymis leads into the vas deferens
(sperm duct).
The vas deferens empties into the urethra.
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27-28
Sperm are stored here and mature prior to
ejaculation.
Conducts sperm out of the body through the penis
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Sperm Production
27-29
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The Human Male Reproductive
System
27-30
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Spermatogenesis
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After puberty the cells in the seminiferous
tubules begin to undergo meiosis.
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27-31
Meiosis I produces two haploid cells.
Meiosis II produces four spermatids.
Spermatids lose most of their cytoplasm and
develop long tails and mature into sperm.
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Spermatogenesis
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Sperm
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27-32
Have only a small amount of food
Very active when released
Live about 72 hours
Can be deactivated and frozen for use in artificial
insemination
Are produced throughout the life of a male
Normal males produce about 150 million
sperm/ml.
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Oogenesis
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Oogenesis is the production of egg cells in
females.
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Occurs via meiosis in the ovary
Begins during prenatal development of the ovary
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27-33
Special cells in the ovary stop dividing by mitosis and
enlarge.
These are future eggs, called primary oocytes.
They go through the early stages of meiosis and stop
until after puberty.
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Oogenesis
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At puberty (and every month after)
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FSH stimulates a primary oocyte to complete
meiosis.
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27-34
Meiosis I generates two cells, but one receives most of
the cytoplasm.
The smaller cell is called a polar body.
The larger cell will become the egg.
Prior to ovulation, the larger cell becomes encased in a
follicle.
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Oogenesis
27-35
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Oogenesis

When the follicle is mature, LH stimulates it
to release the egg into the fallopian tube
(oviduct).
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Once ruptured, the follicle becomes the corpus
luteum.
The corpus luteum releases progesterone that
prevents the release of more eggs.
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27-36
The egg travels through the fallopian tube to the uterus.
The egg completes meiosis in the uterus after it is
fertilized.
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Oogenesis
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If it is not fertilized, it is released from the
body through the vagina during
menstruation.
Since eggs begin production during
embryonic development, the older a woman
is, the older her eggs are.
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27-37
Contributes to abnormal births that are more
common in older women.
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The Human Female
Reproductive System
27-38
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Hormonal Control of Female
Sexual Cycles
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Estrogen and progesterone stimulate changes in the
female body that will support a pregnancy.
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If fertilization does not occur, menstruation results.
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Growth of uterine lining
Milk production in breasts
Lining of uterus breaks down and is released (menses)
Once shed, the lining begins to build back up again.
This cycle happens about once a month.
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Menstruation is Coordinated
with Ovulation
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FSH causes the follicle to grow.
At the same time, the follicle releases estrogen.
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After ovulation, LH stimulates the ruptured follicle to
become a corpus luteum.
The corpus luteum releases progesterone.
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27-40
This increases blood flow to the uterine lining.
If the egg is not fertilized, the corpus luteum will
break down.
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This causes the uterine lining to become thicker.
This reduces the amount of progesterone released.
Without progesterone, the uterine lining breaks down
and is shed.
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The Ovarian and Uterine Cycles
in Human Females
27-41
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Hormonal Control of Fertility
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Fertility drugs
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Hormones given to women to stimulate the
release of eggs from the ovary (ovulation)
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Will often result in the release and fertilization of
more than one egg
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27-42
May increase the likelihood of achieving pregnancy
May be retrieved for use in in vitro fertilization
Leads to multiple implantations
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Hormonal Control of Fertility
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Female contraception
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Male contraception
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27-43
Estrogen and progesterone inhibits ovulation.
Can help relieve the symptoms of PMS
Testosterone and progesterone can temporarily
turn off the production of sperm.
Newly developed
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Common Causes of Infertility
27-44
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Fertilization, Pregnancy
and Birth
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In most women, the egg is released on day 14 of
the menstrual cycle.
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Once released, the egg is moved into the
oviduct toward the uterus.
The egg must be fertilized in the oviduct.
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27-45
About 2 weeks before the next menstruation
Sperm swarm around the egg, but only one
penetrates it.
The other sperm contribute an enzyme that
digests away the mucus barrier around the egg.
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Fertilization
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Once fertilized, the egg can complete meiosis.
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The second polar body is pinched off.
The true ovum is formed.
The chromosomes from the ovum and the sperm
pair up, forming a diploid zygote.
The zygote begins to divide by mitosis.
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This process is called cleavage.
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27-46
Produces a ball of cells called a morula
The morula continues to divide to form a blastocyst.
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Pregnancy

The blastocyst travels down the oviduct and enters
the uterus.
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The blastocyst continues to divide and the cells
migrate and differentiate to form an embryo.
The embryo is contained within the amnion.
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In the uterus, the blastocyst implants into the uterine lining.
A fluid-filled sac that keeps the embryo moist
The chorion and allantois fuse with the lining of the
uterus to form the placenta.
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Provides nutrients to the embryo
Stimulates the corpus luteum to continue releasing
progesterone
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27-47
Inhibits ovulation and menstruation during pregnancy
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Placental Structure
27-48
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Embryonic Development
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As the embryonic cells divide, they become
differentiated into specialized cell types.
Molecules from the mother provide
nourishment for this process.
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Harmful substances that the mother may ingest
can disrupt the development of the embryo.
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27-49
Alcohol, drugs, medication, viruses, etc.
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Human Embryonic Development
27-50
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Twins
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Twinning occurs in two ways.
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Identical twins are the result of the splitting of the
embryo during cleavage.
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Fraternal twins are the result of a double
fertilization event.
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27-51
These individuals are genetically identical.
Two separate eggs are fertilized by two separate sperm
at the same time.
Are no more genetically similar than any other set of
siblings.
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Twins
27-52
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Birth
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Also known as parturition or birthing
At the end of about 9 months of pregnancy,
hormonal changes stimulate uterine
contractions.
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Involves oxytocin from the posterior pituitary
The contractions
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Cause the amnion to burst (water breaking)
Move the baby head first, face down through the vagina
(birth canal)
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27-53
If the baby is oriented feet first (breech), oxygen supply
from the placenta could be cut off.
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Childbirth
27-54
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Birth
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Breech and other fetal position problems can
be resolved by performing a C-section birth.
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An incision in the abdomen is made and baby is
removed.
After the baby is born
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The placenta is expelled.
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27-55
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Also called afterbirth
The umbilical cord collapses and the baby begins
to breathe and function on its own.
The mother’s breasts begin to produce milk.
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Contraception
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27-56
Also called conception control
There are many methods to prevent
ovulation and/or fertilization.
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Chemical Methods
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Contraceptive (spermicidal) jellies and foam
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27-57
Placed into the vagina prior to intercourse
Increase the acidity of the vagina
Lowers the sperms’ chances of survival
Do not protect against sexually-transmitted
diseases
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Hormonal Control Methods

The birth control pill, implant or patch
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Prevents ovulation by manipulating estrogen and
progesterone levels
The hormones “fool” the ovary into thinking
that the woman is
already pregnant.
Hormones can be
delivered in a pill,
implant, patch or
vaginal ring.
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Hormonal Control Methods

The “morning after” pill
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High dose of the hormones in birth control pills
Can prevent
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27-59
Ovulation
Transport of egg and sperm
Fertilization
Implantation of fertilized egg
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Timing Method
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Also called the rhythm method
Prevents sperm from coming into contact with an egg
Involves avoiding intercourse during the time of the
menstrual cycle when ovulation is likely happening
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27-60
Usually a few days before and after day 14
Can be estimated by tracking changes in body temperature
and vaginal pH
Not effective for women with irregular menstrual cycles
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Barrier Methods
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Involves preventing the sperm from reaching the egg
Diaphragm
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Contraceptive sponge
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27-61
Specially fitted, membranous shield that is inserted into the
vagina before intercourse
Covers the cervix and serves as a barrier to sperm entering
the uterus
A sponge soaked in a spermicide that is placed within the
vagina
No longer available in the USA
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Barrier Methods

Condom
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Thin sheath of rubber placed over the penis
before intercourse
Provides a physical barrier to sperm
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Protects against sexually-transmitted diseases
Female condom
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27-62
Some are coated with spermicide as well.
A polyurethane sheath that lines the vagina
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Barrier Methods
27-63
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IUD
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An apparatus that is inserted and fitted in the
uterus
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27-64
Must be performed by a physician
Thought to interfere with implantation
Can be used after unprotected sex to prevent
pregnancy
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Surgical Methods
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Tubal ligation
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Vasectomy
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27-65
Involves cutting and tying off the oviducts
(Fallopian tubes)
Ovulation occurs, but sperm and egg cannot
meet.
The vas deferens (sperm duct) is cut and tied.
Prevents sperm from entering semen
Does not interfere with sex drive or ejaculation.
Both procedures are generally irreversible.
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Tubal Ligation and Vasectomy
27-66
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Termination of Pregnancy—
Abortion
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A medical procedure that causes the death and
removal of the developing embryo or fetus
A highly controversial subject
Can be done in a number of ways
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Dilation and curettage (D and C) involves
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The drug RU-486
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27-67
Scraping the inside of the uterus
Injecting a saline solution into the uterus
Using a suction device to remove the embryo
Induces uterine contractions that expel the embryo
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Changes in Sexual Function
with Age
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Menopause in women
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About age 50, hormone production changes in the
ovaries
This change in hormone balance causes
ovulation to stop along with other symptoms.
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27-68
Mood swings
Cramps
Hot flashes
The symptoms can be treated with hormone
replacement therapy.
Sexual enjoyment is not significantly affected.
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Changes in Sexual Function
with Age
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Males
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Production of sperm declines
May experience impotence
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Lack of sexual desire
Erectile dysfunction
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Recurrent inability to get an erection firm enough for
intercourse
– Can be caused by injury, disease, or medication
– Can be treated with medications such as Viagra or Levitra
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Sexual desire decreases with age
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27-69
Problems with ejaculation
May involve changes in hormone levels
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