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Chapter 20
Is There Something in the Water?
Reproductive and Developmental Biology
Copyright © 2010 Pearson Education, Inc.
20.1 Principles of Animal Reproduction
Two main types of reproduction
1. Asexual reproduction
2. Sexual reproduction
Asexual Reproduction
 one parent produces offspring that are
genetically identical to the parent
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20.1 Principles of Animal Reproduction
Two main types of asexual
reproduction
 Binary fission – cells
break away from parent to
form offspring (e.g.,
sponges)
 Budding – daughter cell
remains attached to parent
and breaks away when
mature (e.g., hydra)
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20.1 Principles of Animal Reproduction –
Sexual Reproduction
 Sexual reproduction combines genomes of
two individuals to create variable offspring
 Females = individuals that produce large
gametes (sex cells)
 Males = individuals that produce small
gametes
 Gonads = Organs that produce gametes
 Male gonad = testes
 Female gonad = ovaries
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20.1 Principles of Animal Reproduction
Methods of fertilization
1. Internal fertilization – sperm deposited
by copulation in or near female
reproductive tract.
 Mammals, birds, reptiles, and sharks use
internal fertilization.
2. External fertilization – eggs laid, male
deposits sperm over eggs (usually in
water). Most fish and amphibians use
external fertilization.
 Very susceptible to contaminants
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20.1 Principles of Animal Reproduction
Environmental Contaminants
and Sexual Reproduction
 Developing frogs are
extremely sensitive to
environmental chemicals
 Eggs develop in water
 Embryos absorb toxins
easily
 Frogs are declining globally
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Figure 20.2
20.1 Principles of Animal Reproduction Endocrine Disruptors
 Man-made chemicals alter endocrine
regulation
 interferes with normal gonad development.
 Male amphibians have been feminized.
 These chemicals affect animals living in
water.
 Are humans affected by drinking
contaminated water?
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20.2 Human Reproduction
Male Reproductive Anatomy
 Penis
 Contains spongy erectile
tissue
 Fills with blood to cause
erection
 Testes
 Inside scrotum
 produce sperm and
testosterone
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Figure 20.4
20.2 Human Reproduction
Male Reproductive Anatomy
 Accessory Glands
 Prostate & seminal vesicles
 Secrete fructose, mucous
 Testes
 Inside scrotum
 produce sperm
and testosterone
 Epididymis
 Stores sperm
 Vas deferens
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Figure 20.4
20.2 Human Reproduction
Female Reproductive Anatomy
 External genitalia
 Labia majora & labia minora
 clitoris
 Reproductive tract
 Vagina
 Uterus
 Paired oviducts
 Fertilization
 Separate urethral
opening
Copyright © 2010 Pearson Education, Inc.
Figure 20.5
20.2 Human Reproduction
Female Reproductive Anatomy
 Ovaries
 Endocrine
 Estrogen
 Progesterone
 Produces gametes
 Follicle contains:
 Egg
 Endocrine cells
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Figure 20.5
20.2 Human Reproduction –
Endocrine Disruptors & Humans
 Women
 DES is a chemical known to act as an endocrine
disruptor.
 Given to women to prevent premature delivery
 Daughters of women who took DES have a
higher rate of infertility.
 Men
 Most common cause of male infertility is the
inability to produce healthy sperm.
 Sperm counts are declining globally
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20.2 Human Reproduction
Gametogenesis
= production of gametes (germ cells)
 Involves meiosis
 Reduces number of chromosomes by ½
 Human body cells contain 46
chromosomes, gamete contain 23
 (see chapter 5 for review)
 Male and female gametes undergo further
development to become functional
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20.2 Human Reproduction
Spermatogenesis
• Seminiferous tubules = functional unit of testis
• Developing sperm cells
• Sertoli cells – nurse cells for sperm
• Leydig cells outside seminiferous tubules
• Make and release testosterone
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Figure 20.6
20.2 Human Reproduction
Cell types in Spermatogenesis
• Spermatogonia
• Stem cells
• Divide by mitosis
• Primary spermatocytes
• Enter Meiosis I
• Secondary spermatocytes
• Enter meiosis II
• Spermatids
• Undergo spermiation
• Cytodifferentiation
• Spermatozoa
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Figure 20.6
20.2 Human Reproduction
Spermatozoa Structure
• Head
• Condensed nucleus
• Acrosome
• Contains enzymes for
fertiliztion
• Midpiece
• Lots of mitochondria
• Tail
• Flagellum for swimming
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Figure 20.6
20.2 Human Reproduction - Male Infertility
Human infertility and endocrine disruptors
 90% of male infertility related is to problems
with sperm formation or production
 Low sperm counts
 Improperly shaped sperm
 Low motility
 Chemical exposure (e.g., pesticides) can
decrease sperm viability
 Male infertility also increases with alcohol and
drug use, including cigarettes
 Sperm counts declining globally since WWII
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20.2 Human Reproduction
PLAY
Animation—The Male Reproductive System
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20.2 Human Reproduction
Oogenesis
• Two parts
1. Oocyte development
2. Follicular development
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Figure 20.7
20.2 Human Reproduction
Oocyte Development
•
•
All oogonia (stem cells) become primary oocytes during
her embryonic development
Each month during menstrual cycle
• Primary oocytes enter meiosis I -> secondary oocytes
• Secondary oocytes complete meiosis II at fertilization
• Polar bodies will deteriorate
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Figure 20.7
20.2 Human Reproduction
Follicular Development
•
•
•
•
•
Follicles include oocytes and surrounding endocrine cells
Primary follicle stores primary oocytes until use
FSH causes development to secondary follicle and then
Graffian follicle (both with secondary oocyte)
• Secrete estrogen
LH causes ovulation
Follicle become corpus
luteum
• Secretes estrogen &
progesterone
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Figure 20.7
20.2 Human Reproduction
The Menstrual Cycle
 Changes in the uterine
endometrium
 Prepare endometrium
for pregnancy
 Regulated by:
 Pituitary FSH & LH
 Ovarian estrogen &
progesterone
Copyright © 2010 Pearson Education, Inc.
Figure 20.8
20.2 Human Reproduction
The Menstrual Cycle
 Days 1-4
 Menstruation
 Only FSH elevated
 causes new follicle
to grow
 Days 5-14
 FSH causes follicle to
grow & release estrogen
 Causes endometrium
to grow
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Figure 20.8
20.2 Human Reproduction
The Menstrual Cycle
 Day 14
 Surge of LH causes
ovulation & corpus
luteum formation
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Figure 20.8
20.2 Human Reproduction
The Menstrual Cycle
 Day 14-28
 FSH & LH cause ovary to
secrete estrogen &
progesterone
 Prepares for pregnancy
 Corpus luteum dies at
end of cycle
 Results in collapse of
endometrium and
menstruation
Copyright © 2010 Pearson Education, Inc.
Figure 20.8
20.2 Human Reproduction
Regulating The Menstrual Cycle
Regulation involves both positive & negative
feedback loops
 High estrogen causes
positive feedback on
LH
 Leads to LH surge
 High progesterone
causes negative
feedback on LH &
FSH
Copyright © 2010 Pearson Education, Inc.
Figure 20.9
20.2 Human Reproduction
Pregnancy
 If the egg is fertilized, embryo secretes
human chorionic gonadotropin (hCG)
 hCG mimics LH and keeps corpus luteum alive
 Progesterone maintains endometrium during
pregnancy
Birth Control Pills
 Mimic pregnancy by providing estrogen and
progesterone
 prevent ovulation by blocking LH surge
Copyright © 2010 Pearson Education, Inc.
Figure 20.9
20.2 Human Reproduction
Female Infertility
 One cause of female infertility is
endometriosis
 a condition where the endometrial cells can
attach to the ovaries & oviducts
 also grow and shed during menstrual cycle
 Can cause damage and scarring to ovarian
tissue
 Can disrupt ovulation
 Painful
 May be related to exposure to environmental
chemicals like DEHP
Copyright © 2010 Pearson Education, Inc.
20.2 Human Reproduction
PLAY
Animation—The Female Reproductive System
Copyright © 2010 Pearson Education, Inc.
20.3 Human Development
Fertilization
1. Sperm penetrate
follicle cells
2. Sperm head binds
to zona pellucida
3. Acrosome enzymes
released
4. Egg & sperm
membranes fuse
5. Sperm nucleus
enters egg cell
Copyright © 2010 Pearson Education, Inc.
Figure 20.11
20.3 Human Development
Endocrine Disruptors and Fertilization
 Industrial solvents can mimic hormones
and interfere with sperm development and
fertilization.
 Misshapen sperm cannot swim effectively and
are unable to fertilize egg.
 Males exposed to solvents, working as
mechanics or dry cleaners, have a larger
number of abnormal sperm.
 While effect on adults lowers fertility, effects on
developing fetus is more severe
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20.3 Human Development
Human Embryonic Development
 Human zygote undergoes a series of
cleavages to produce an embryo
 Embryo is stage from zygote until body
structures appear
 Blastocyst = hollow ball of cells
 Gastrula = tissue layers start to appear
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Figure 20.12
20.3 Human Development - Human
Embryonic Development
Gastrula has 3 tissue layers
 Endoderm – forms digestive & respiratory
 Mesoderm – forms muscles, skeleton,
excretory, circulatory, & gonads
 Ectoderm – forms skin, nervous &
sensory
 Growth of a particular tissue or organ
relies on chemical stimulus
 Very sensitive to chemical disruption
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20.3 Human Development
Development of Human Reproductive Organs
• Male & female organs
develop from same
embryonic precursors
• Hormonal signals
cause development of
male and female
reproductive organs
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Table 20.3
20.3 Human Development
Endocrine Disruptors & Reproductive Organs
• Chemicals can pass
from mother’s blood to
fetus
• Common herbicides &
fungicides can cause
cryptorchidism
• Undescended testes
• 2 to 4 % of human
males are now born
with undescended
testes
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Table 20.3
20.3 Human Development
Pregnancy or Gestation
 A placenta must develop to
sustain pregnancy
 Embryo blastocyst implants in the
wall of the uterus
 Maternal and fetal blood supplies
are closely intertwined, allowing
exchange of nutrients and wastes
 9 week old fetus has all its limbs
and organs in place
 Environmental chemicals can
seriously effect embryo & fetus
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20.3 Human Development
Childbirth
 Decreasing estrogen in late pregnancy induces
oxytocin receptors to form in uterine muscle
 Hormone oxytocin uses a positive feedback
loop to induce labor.
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Figure 20.15
20.4 Is the Water Safe to Drink?
Human correlations with endocrine disruptors
 abnormal sperm
 lower sperm counts
 decreased fertility
 cryptorchidism
 endometriosis
 uterine abnormalities
EPA requires monitoring of municipal water supplies.
 But it’s unclear what chemicals to monitor and what
is a safe level of chemicals
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