Download Unit 2 Notes

Unit 2 – Reproduction
and Development
Unit Outcomes
Examine the principal features of the
human reproductive system
 Identify the male and female reproductive
structures and describe their functions
 Identify the risks that STIs present to
individuals and to human reproduction
 Explain how STIs can interfere with the
passage of eggs and sperm

Unit Outcomes
Research the effects of STIs
 Identify the main reproductive hormones
and describe how they interact
 Explain the role of sex hormones in the
development and regulation of primary
and secondary sex characteristics
 Analyze blood hormone data and
associated physiological events

Unit Outcomes
Research and assess the medical use of
reproductive hormones in humans
 Trace the processes and events that occur
during embryonic development
 Describe the significance of the primary germ
layers and identify the tissues and organs that
come from them
 Compare embryonic changes and
extraembryonic structures in humans and other
animals

Unit Outcomes
Trace the processes and key events that
occur during fetal development
 Describe and investigate the effect of
teratogens and other environmental
factors on the development of prenatal
body structures and systems
 Trace the processes of parturition and
lactation, and outline their control
mechanisms

Why is Reproduction Important
It produces variation within a species
 It provides a basis for natural selection
within a species

14.1 – The Male and Female
Reproductive Systems
Both male and female reproductive
systems include a pair of gonads (which
produce gametes)
 These gonads also produce sex hormones
 These hormones often control primary sex
characteristics and secondary sex
characteristics

The Male Reproductive System
Male & female reproductive organs do not
differ greatly until the 3rd month of fetal
development
 The purpose of this system is to produce
sperm and allow them to leave the body

The Male Reproductive System
Structures:

Scrotum:

Testis:

Epididymis:

Vas deferens:

Seminal Vesicle:

Prostate Gland:

Cowper’s Gland:

Ejaculatory Duct:
Erectile Tissue
The erectile tissue of the penis (corpus
cavernosum) fills with blood when a man
is sexually excited
 This causes the penis to swell and become
rigid

Erectile Dysfunction (ED)
Increased blood flow to the penis is
actually controlled by the parasympathetic
nerves
 They cause a relaxation of muscle tissue
that allows the arteries running into the
penis to dilate and carry more blood
 Therefore, if the parasympathetic nerve is
damaged, erections become difficult or
impossible to sustain

Other factors may also lead to erectile
dysfunction, including an imbalance in
hormones, particularly testosterone
 Stress can also lead to erectile dysfunction
 Viagra is a drug that relaxes the muscles
constricting the blood vessels running into
the penis (these muscles are similar to the
smooth muscle in the digestive system).
 Therefore, it is much easier for the blood
to enter the erectile tissues and cause an
erection.

Sperm
Sperm are very small
cells built for speed
 There is very little
cytoplasm in a sperm
cell, which increases
the cell’s mobility

http://img.tfd.com
A single sperm cell has a large number of
mitochondria
 It also has an acrosome, which contains
special enzymes that allow it to penetrate
the membrane of an egg cell

Spermatogenesis
Inside the testes are tiny tubes called
seminiferous tubules
 They are lined with spermatogonia
 These spermatogonia divide and form

spermatocytes

In about 9 to 10 weeks, the
spermatocytes develop into sperm cells
Sertoli cells
nourish the
developing
sperm
 When they
are ready,
sperm cells
move to the
epididymis to
complete
their
maturation

Spermatogenesis Animation
http://faculty.sunydutchess.edu
Seminal Fluid
Seminal fluid consists of contributions
from three different glands
 This fluid protects and nourishes the
sperm as it travels out of the man’s body
and into the woman’s reproductive tract

Seminal Vesicles
1.
This gland produces two components of
seminal fluid:
Fructose
2.
Prostaglandins

Prostate Gland

The prostate produces an alkaline buffer
Cowper’s (bulbourethral) Gland

This gland produces mucus-rich fluids
Sperm Survival
Within the epididymis, the sperm can
survive for extended periods (some die
and are removed by the immune system)
 However, at body temperature sperm only
live for 24-72 hours
 Sperm can be stored indefinitely at -100oC
(which is how they are stored at sperm
banks)

The Female Reproductive System
The female reproductive system involves
more complicated cycles than the male
reproductive system
 Female hormone levels fluctuate
throughout their menstrual cycle (whereas
males maintain a relatively constant level
of testosterone)

The Female Reproductive System
http://www.uh.edu
Structures

Ovary

Oviduct

Uterus

Cervix

Vagina
Oogenesis and Ovulation
The ovary contains many small groups of
cells known as follicles
 Within the follicle, an oocyte undergoes
meiosis and becomes an ovum
 The ovum created contains 23
chromosomes and most of the cellular
material from the oocyte
 The remaining cellular material forms
polar bodies, which die later

When it is ready, the follicle ruptures the
outer ovary wall and releases the ovum
 The remaining cells from the ovary
become the corpus luteum

Oogenesis & Ovulation
http://faculty.sunydutchess.edu
Development of the Female
Reproductive System
During fetal development, ovaries form
near the kidneys, but do not descend
 In an average adult female, the Fallopian
tubes (or oviducts) are approximately 10
cm long

The Uterus
The uterus is lined with a glandular lining
known as the endometrium
 The endometrium is shed each month
during menstruation if a fertilized egg has
not implanted within it

Differences Between Sperm & Eggs
Sperm
Egg
Size
50 μm long (5 μm head, 5 μm
middle piece, 40 μm tail)
100 μm diameter
Energy
Reserves
Mitochondria
Fat before ejaculation, fructose in Fertilized eggs rely on the
seminal fluid after ejaculation
endometrium as an energy
source
Middle piece of sperm has 50 to
100 mitochondria
Cytoplasm contains about
140 000 mitochondria
Number
Produced
300 – 500 million per day
300 – 400 thousand follicles
are present at the start of
puberty – 1 egg is released
per month
Motility
High motility due to flagellum
No structures for propulsion
Other
Structures
Sperm has an acrosome which
contains enzymes that help the
sperm to enter the egg
Egg is covered by an outer
membrane which can only
be penetrated by a sperm of
the same species
14.2 – The Effect of Sexually
Transmitted Infections on the
Reproductive System
During sexual intercourse, body fluids are
exchanged
 The fluids can contain STIs (Sexually
Transmitted Infections) in the form of
bacteria or viruses

Viral vs. Bacterial STIs
Bacterial STIs
Viral STIs
Chlamydia
Gonorrhea
Syphilis
HIV
HPV
Hepatitis
Genital Herpes
HIV / AIDS
AIDS is caused by the
human
immunodeficiency virus
(HIV)
 This virus attacks and
destroys helper T cells

http://biology.kenyon.edu
HIV Replication Animation
Hepatitis B
Hepatitis viral infections
come in 3 subtypes: A, B
and C
 Hepatitis B is transmitted
in the same fashion as
HIV
 The hepatitis B virus
attacks the liver

http://www.torontoliver.ca
Hepatitis B
Symptoms of hepatitis B include flu-like
symptoms, jaundice, and liver failure
 Hepatitis viruses can cross the placenta and
infect the unborn child
 Occasionally, a person who is infected with the
hepatitis B virus may be asymptomatic, and can
therefore pass on the virus to others without
knowing it
 There are effective vaccines for both hepatitis A
and B

Genital Herpes
It is estimated
that 1 in 3
sexually active
Canadians has
genital herpes
 Herpes is caused
by either HSV 1 or
HSV 2 viruses
 The majority of
genital herpes
cases are caused
by HSV 2

Genital Herpes





Symptoms can vary from case to case
Symptoms may include tingling, itching, and
appearance of blisters
Blisters can then rupture and become painful
sores (these open sores increase the chance of
HIV infection)
Outbreaks may be accompanied with swollen
glands, aching joints, and fatigue
The herpes virus may infect babies during the
birthing process, possibly leading to blindness,
neurological disorders, or death
Genital Herpes
There is no cure for herpes
 Even if an infected person is not
symptomatic, they can still pass on the
virus during intercourse
 No vaccine is yet available for herpes

HPV (Human Papilloma Virus)
HPV is the name of a
group of viruses
 It is transmitted during
skin-to-skin contact
 Some people infected
with HPV develop
genital warts, while
other people can show
no symptoms at all

http://upload.wikimedia.org
Cervical Cancer




Cervical cancer is one of the primary
forms of cancer in women
Pap tests done by physicians collect cells
from the surface of the cervix
These cells are then checked for any
abnormal tissue growth
New evidence indicates that cervical
cancer may be caused by the Human
Papillomavirus (HPV)
Chlamydia
Chlamydia is the most
common bacterial STI
in Canada
 Infection rates are
twice as high in young
women than in young
men

Chlamydia
Symptoms are immediate and often
include discharge from the penis or
vagina, burning pain during urination, or
fever
 75% of infected people show no
symptoms
 In women, the infection may lead to pelvic
inflammatory disease (PID), which causes
scar tissue in the oviducts
 Chlamydia can be treated with antibiotics

Gonorrhea
Often found together with
chlamydia bacterial
infections
 The rate of infections is
higher in men than in
women
 Symptoms are similar to
those of chlamydia
 This can also cause PID and
serious eye infections for
babies born to mothers with
gonorrhea

http://www.faqs.org/health
Syphilis

Although much less
common than other
bacterial STIs, the
rate of syphilis
infection has
increased sharply
since 1997
http://www.wales.nhs.uk
Syphilis





Initially, infectious ulcerated sores appear
(known as chancres)
This is followed by a rash (often on palms of
hands, soles of feet), and then the bacteria
affects the cardiovascular and nervous system
Infected persons may become mentally ill, blind,
lame, or develop heart disease
If bacteria infect a developing embryo, birth
defects or stillbirth can result
Syphilis can be treated effectively with
antibiotics
Preventing STI Transmission

1.
2.
3.
4.
There are a number of ways to reduce
the chance of passing on STIs:
Abstinence
Long-term monogamous relationships
Condom use
Personal responsibility
14.3 – Hormonal Regulation of the
Reproductive System
Hormones play an important role in the
operation of the reproductive system
 The hormones involved in reproduction
are produced in the hypothalamus, the
pituitary, and the gonads

Hormones and The Male
Reproductive System
It has been known that the castration of
males changes their disposition and the
physical makeup of the bodies
 Castrated males also lack a sex drive and
are sterile
 It has been determined that the male sex
hormones, androsterone and testosterone
are responsible for these changes

Testosterone Production
Testosterone is produced in the interstitial
cells of the testes
 Testosterone effects both the primary and
secondary sex characteristics of males

Primary Sex Characteristics
Secondary Sex Characteristics
Testosterone and Sex Drive
Since ancient times, it has been
recognized that the testes produce a
factor that increases sex drive
 In ancient times, eunuchs (males with
their testes removed) were used to guard
the harems of ancient kings

Testosterone and Puberty
When puberty begins, the hypothalamus
releases GnRH (gonadotropin-releasing
hormone)
 This increases LH and FSH from the
pituitary
 LH promotes the production of
testosterone in the interstitial cells

FSH (Follicle Stimulating Hormone)
FSH stimulates the production of sperm in
the seminiferous tubules
 The production of FSH and LH are both
regulated by a negative feedback system

Feedback of Gonadotropins
Chemical Castration
Chemical castration has been used in some
countries (including Canada) as a method of
punishment and/or preventative therapy for sex
offenders
 These offenders are given a form of
progesterone (a female hormone), or an antiandrogen (which blocks receptor sites for male
sex hormones)
 Both types of drugs reduce the effects of
testosterone and therefore reduce sex drive

Chemical Castration
Another use of chemical castration is in
the treatment of prostate cancers
 These cancers often grow in the presence
of testosterone
 Therefore, if testosterone production is
reduced, the tumors often reduce in size
or stop growing

Castration – Middle Ages
In the middle ages, females were
prohibited from singing in choirs in the
Roman Catholic Church
 In some cases, boys were castrated before
their voices changed so that their voices
did not deepen (these boys were known
as castrati)
 This practice was put to an end in the late
1800s

Aging and the Male Reproductive
System
Most men experience a gradual decrease
in testosterone levels starting at about 40
years of age
 This is known as andropause
 As well, hormonal changes in males over
age 40 can also result in gradual growth
of the prostate gland
 Older males also have a higher chance of
prostate cancer as well

Hormonal Control of the Female
Reproductive System
The pituitary and hypothalamus control
the production of estrogen and
progesterone
 FSH (Follicle-stimulating hormone) and LH
(lutenizing hormone) regulate the
production of estrogen and progesterone

At the onset of
puberty, GnRH is
released from
the
hypothalamus
 This signals the
pituitary to start
production of
FSH and LH

http://faculty.sunydutchess.edu
FSH stimulates follicular development,
which in turn increases estrogen levels
 Estrogen release increases the thickness
of the endometrium
 It is also responsible for female secondary
sex characteristics:

Increased levels of estrogen halts the
production of FSH, but increases the
release of LH from the pituitary
 An increase in LH levels helps the
remaining follicular cells to mature and
form the corpus luteum
 The corpus luteum produces both
estrogen and progesterone, which help to
maintain and develop the endometrium

High levels of progesterone and estrogen
in the body shuts down the production of
FSH and LH
 Without LH to maintain it, the corpus
luteum deteriorates
 When this happens, there is not enough
estrogen and progesterone to maintain
the endometrium

Feedback – Female Reproductive
Hormones
The Menstrual Cycle
This cycle is divided into 4 phases:
1. Flow Phase

2. Follicular Phase
3. Ovulation
4. Luteal Phase
Birth Control Pills
Along with its effect of maintaining the
uterine lining, progesterone also prevents
further ovulations
 Women can prevent ovulation by ingesting
progesterone in a pill form, or through
implanted capsules containing similar
hormones
 The pill increases a woman’s progesterone
levels, preventing the release of an ovum

Aging and the Menstrual Cycle
Women have a limited number of
menstrual cycles due to their limited
number of follicles
 As the number of follicles decreases, the
amount of estrogen and progesterone in
the woman’s body decreases
 The woman’s menstrual cycles become
irregular and eventually stop completely

Menopause


1.
2.
3.
4.
5.
Menopause (the cessation of menstrual
cycles) often occurs around age 50
During menopause, a number of
different effects are experienced:
‘Hot flashes’
Variable changes in mood
Increasing cholesterol levels
Diminished bone mass
Increased risk of breast and uterine
cancer
Treatment for Menopause
Many women consider hormone
replacement therapy during or following
menopause
 However, there are some risks to the
hormone replacement therapy (increased
risk of blood clots, stroke, breast &
colorectal cancer, and dementia)

Endocrine Disruptors
A number of man-made chemicals can
interrupt the function of hormones
 If these disrupt the function of sex
hormones, then the reproductive cycles of
men and women can be effected as well
 As well, testosterone-blocking chemicals
can lead to feminization in males

15.1 – Fertilization and Embryonic
Development
Fertilization & Pregnancy
150 to 300 million sperm cells travel
through the cervix upon ejaculation during
intercourse
 Ultimately, only a single sperm cell fuses
with the ovum

http://content.answers.com
Embryonic Development
The fertilized egg (the
zygote) undergoes a
number of cellular
divisions on its way to
the uterus
 By the time it reaches
the uterus, the single
fertilized egg has
become a cell mass
known as a blastocyst


The blastocyst then attaches to the
endometrium wall (this is known as
implantation)
Maintenance of the Endometrium
If the corpus luteum deteriorates, then the
endometrium will be shed
 High levels of estrogen and progesterone
must be maintained to prevent this from
happening
 However, the level of the pituitary
gonadotropin, LH, decreases as the
estrogen and progesterone levels increase

The outer layer of cells in the blastocyst
produces a hormone called HCG (Human
Chorionic Gonadotropin)
 HCG maintains the corpus luteum during
the first three months of pregnancy,
preventing the shedding of the
endometrium
 The functioning corpus luteum keeps
producing estrogen and progesterone
 Pregnancy tests identify HCG in the urine
of a woman

Once cells from the endometrium and
embryo form the placenta, HCG is no
longer produced
 Instead, the placenta itself produces
estrogen and progesterone which maintain
the endometrium until birth

Prenatal Development – The
Blastocyst
The outer layer of the blastocyst produces
two membranes - the chorion and the
amnion
 Within the blastocyst’s inner layers,
different germ layers form:

Germ Layers
Ectoderm – forms hair, nails, sweat
glands, nervous system, eyes, ears, teeth,
mouth lining
 Mesoderm – forms muscles, blood vessels
& blood, kidneys & reproductive
structures, connective tissue, cartilage &
bone
 Endoderm – forms liver, pancreas, thyroid,
bladder, lining of digestive system &
respiratory tract

The Germ
Layers
Neurulation and Organ Formation
Between weeks 3 and 8, the organs form
 The germ layers separate and form organs
 During the 3rd week, a band of mesoderm
cells forms along the back of the
embryonic disk
 These cells forms a rod-like notochord,
which will make up the skeleton
 The nervous system develops from the
ectoderm located above the notochord

Neurulation
Organ Formation
After neurulation, the heart begins to form
 This is followed by blood vessels, lungs,
kidneys, arms & legs, and structures of
the head
 The brain continues its development, and
the gonads begin to produce hormones
that develop external genetalia (about the
6th week)

Extra-Embryonic Membranes
The Allantois & Placenta
The placenta forms from cells from the
endometrium and the fetus
 The placenta has numerous blood vessels
 Chorionic villi ensure that the placenta’s
blood vessels come in close contact with
the blood vessels of the mother
 The blood vessels that are found in the
placenta come from the allantois, a third
membrane in the blastocyst

The Amnion and Yolk Sac
The amnion is a transparent sac that
contains the amniotic fluid
 This fluid acts to cushion the fetus and
prevents temperature fluctuations while
allowing freedom of movement
 The yolk sac does not provide nutrients,
but rather will become part of the
digestive system later

Uterine Structures
1.
2.
3.
4.
5.
Cervix
Umbilical Cord
Placenta
Oviduct
Amniotic Fluid
(Amniotic Sac)
15.2 – Fetal Development and Birth

1.
2.
3.

Fetal development is typically broken
into three (roughly equal) trimesters:
1st Trimester (Weeks 1 to 12)
2nd Trimester (Weeks 13 to 24)
3rd Trimester (Weeks 25 to 38)
The number of weeks is counted from
the last day of the mother’s last flow
cycle, not the time from fertilization
Fetal Development – First Trimester
By week 2, germ layers
form
 By the end of this
trimester, the heart,
brain, limb buds (with
fingers & toes) have all
developed
 Arms & legs move and
there is a sucking reflex
 By end of the trimester,
external reproductive
organs distinguish male
from female

http://www.babyart.org
Second Trimester
Fetus moves enough to be noticed
 All organs have formed
 Eyelids and eyelashes form
 Cartilage has been replaced with bone
cells
 Soft hair covers the body

http://static.flickr.com
Third Trimester
Rapid growth of baby (from 680 g to
3400 g), particularly layers of fat
 Organ systems are already established,
but continue to develop

http://health.state.ga.us
Teratogens
Whatever the mother inhales or ingests
can end up in her circulating blood
 Many of these compounds can pass across
the placental system into the fetal blood
 A number of substances and conditions
can affect the normal development of the
embryo and fetus

Various Teratogens
1.
2.
3.
4.
Cigarette Smoke – constricts fetus’s blood
vessels, preventing the fetus from receiving
enough oxygen
Alcohol – affects the fetus’s brain, CNS, and
physical development
Prescription medications – antibiotics, acne
medications, anti-thyroid drugs, and anticancer drugs
Some nutrients – vitamin C in excess during
pregnancy can lead to scurvy after birth (the
drop in vitamin C supply after birth is
responsible for this)
Birth (Parturition)
At the end of the third trimester, the fetus
turns so that the front of the head faces
the backbone
 The fetus also drops into the birth canal

Stages of Labor
Labor – Latent Phase
Labor begins 38-40 weeks after
conception
 Initially, the cervix begins to thin and the
mucus plug that sealed the cervix falls out
(usually one or two days prior to birth)

Stage 1 (Active Phase)
The cervix begins to dilate due to muscle
contractions
 These contractions become more regular and
intense as labor progresses
 Sometimes the amniotic sac will break because
of uterine contractions, but often the attending
physician will break the sac with a long needle
 This stage usually ends when the cervix has
dilated to a diameter of 10 cm

Stage 2 (Birth or Parturition)
As the contractions continue, the fetus is
moved down the birth canal
 A hormone known as relaxin (which is
produced by the placenta prior to labor)
causes a loosening of the ligaments in the
pelvis
 Uterine contractions (along with active
pushing of the mother) push the baby out
of the birth canal

Stage 3 (Afterbirth)
Once the baby is
born, the umbilical
cord is clipped and
cut
 A number of
contractions expel
the placenta and
most of the
umbilical cord

http://en.wikipedia.org
Lactation
During pregnancy, high levels of
estrogen and progesterone
prepare the breasts for milk
production
 Each breast has about 20
glands that produce milk
 Prolactin, whose levels rise
dramatically after birth,
stimulates milk production in
these glands
http://www.breastguide.info

Feeding
Immediately after birth, the breast
produces colostrum
 It takes a few days for true breast milk to
be produced
 When a baby feeds, the suckling action
stimulates the nerve endings in the areola
of the breast

The stimulation of these nerve endings
causes the release of oxytocin, which
causes muscle contractions in both breast
and uterine tissue
 At the height of lactation, some women
can produce as much as 1.5 L of milk per
day (containing 50 g of fat and 100 g of
sugars)

Medical Issues
1.


Teratogens and the Fetus
A teratogen is any agent that can cause
a structural abnormality of the fetus
during pregnancy
Cigarette smoke, drugs, some
prescription medications and alcohol are
all teratogens
2.




Fertility Treatments
A number of treatments may be used to
increase fertility
About 15% of Canadian couples cannot
conceive a child
Drugs may be used to increase the
number of eggs produced by the
woman’s ovaries
In vitro fertilization can be used to
increase the chance of a sperm cell
fertilizing an egg cell
In some cases, a man cannot produce
sperm
 TSE (testicular sperm extraction) may be
used
 In this case, seminiferous tubule tissue is
taken from the testicle and is cultured to
produce sperm, which can then be used in
in vitro fertilization or in ICSI (intracytoplasmic sperm injection)
 Artificial insemination can also be an
option

Etopic Pregnancy
On rare occasions, a fertilized embryo embeds
itself in the wall of the fallopian tube (or other
structure) instead of in the uterine lining
 As the fetus develops, it may rupture some of
the blood vessels in the lining of the fallopian
tubes
 About half of the ectopic pregnancies
spontaneously abort, while the other half
require medical intervention to remove the
fetus
3.

4.



Problems During Labor
If the front of the baby’s head is facing
forward instead of the spine, labor can be very
painful and difficult for the mother
In some cases, a baby might also be
transverse (where the shoulders are turned 90
degrees to their normal position)
In the case of a transverse birth, the attending
physician can try to turn the baby with his or
her hands while the mother rests between
pushes
In rare instances, a breech birth occurs
 During a breech birth, the baby enters the
birth canal feet or buttocks first
 A breech baby who is delivered buttocks
first can be delivered normally, but an
episiotomy may be required
 If the baby arrives feet first, then a
Caesarian section birth must be performed
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After Birth
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Immediately following birth a baby is given an
APGAR score one and five minutes after birth
This indicates the general health of the baby
A score of 7 or more indicates a healthy baby
Scores between 4 and 6 may require additional
care for the baby
Scores of 3 or less indicate that the baby needs
critical care (in the neo-natal intensive care unit)
APGAR Descriptors
1.
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2.
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Skin Color (Appearance)
0 – blue all over
1 – blue at extremities, body is pink
2 – body is all pink
Heart Rate (Pulse)
0 – no pulse
1 – less than 100 beats per minute
2 – above 100 beats per minute
3.
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4.
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Reflex Irritability (Grimace)
0 – no response to stimulation
1 – grimace/feeble cry when stimulated
2 – sneeze/cough/pulls away when
stimulated
Muscle Tone (Activity)
0 – none
1 – some flexion (stretching)
2 – active movement
5.
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Respiration
0 – absent
1 – weak or irregular
2 – strong
If a baby has a low APGAR score initially,
and it does not improve, then there is a
risk of serious neurological damage