Transcript Ch. 42 - Development and Aging

Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 42
Animal
Development
and Aging
Lecture Outline
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Outline
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•
•
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42.1 Early Developmental Stages
42.2 Developmental Processes
42.3 Human Embryonic and Fetal Development
42.4 The Aging Process
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42.1 Early Developmental
Stages
• Fertilization requires that sperm and egg unite
to form a zygote
• Details of Fertilization in Humans
 A human sperm cell has three parts:
• The head
– Contains a haploid nucleus covered by acrosome containing enzymes,
allowing the sperm to penetrate the egg.
• A middle piece
– Contains ATP-producing mitochondria
• The tail
– A flagellum that allows the sperm to swim
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Early Developmental Stages
• Details of Fertilization in Humans (cont.)
 An egg
• Actually a secondary oocyte
• Surrounded by layers of adhering follicular cells
termed the corona radiata
– Nourish oocyte and follicle
• Surrounded by the zona pellucida
– Sandwiched between the plasma membrane of the
oocyte and the corona radiata
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Early Developmental Stages
• Details of Fertilization in Humans (cont.)
 Several hundred sperm reach the oocyte
 Sperm secrete enzymes to weaken the
corona radiata and bind to the zona pellucida
 Acrosome releases digestive enzymes to
allow the sperm to pass through the zona
pellucida to the plasma membrane of the
oocyte
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Early Developmental Stages
• Details of Fertilization in Humans (cont.)
 One sperm enters the egg
• Membrane depolarizes to prevent polyspermy




Fertilization membrane forms
The secondary oocyte completes meiosis
The sperm nucleus releases chromatin
A single nuclear envelope surrounds the egg
and sperm pronuclei
 First cell division occurs
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Fertilization
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microvilli of oocyte plasma membrane
2. Acrosomal enzymes
digest a portion of
zona pellucida.
tail
1. Sperm makes its
way through the
corona radiata.
3. Sperm binds to and
fuses with oocyte
plasma membrane.
sperm
4. Sperm nucleus enters
cytoplasm of oocyte.
corona radiata
plasma
membrane
nucleus
middle
piece
5. Cortical granules
release enzymes;
zona pellucida
becomes fertilization
membrane.
head
acrosome
fertilization membrane
cortical granule
sperm pronucleus
6. Sperm and egg
pronuclei are enclosed
in a nuclear envelope.
oocyte plasma membrane
zona pellucida
egg pronucleus
© David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images
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Early Developmental Stages
• Embryonic Development
 Development – all the changes that occur during the
life cycle of an organism
 During first stages of development, an organism is
called an embryo
 Following fertilization, the zygote undergoes
cleavage
• Cleavage is cell division without growth
• Morula forms a blastula with a hollow blastocoel
• Appearance of blastula differs between organisms
– In chickens the blastula resembles a layer of cells spread out
over yolk
– In frogs, the presence of the yolk causes uneven division,
forming both an animal and vegetal pole
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Lancelet Early Development
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a.
Zygote
Late gastrula
mesoderm
Morula
Cleavage is
occurring.
blastocoel
endoderm
ectoderm
Gastrulation
Is occurring.
Early gastrula
Blastula
ectoderm
endoderm
blastopore
b.
archenteron
blastocoel
(a): © William Jorgensen/Visuals Unlimited
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Chick Blastula
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Chick blastula
(cross section)
blastocoel
yolk
(chick): © Photodisc/Getty RF
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Early Developmental Stages
• Tissue Stages of Development
 Gastrulation – formation of a gastrula
• Germ layer formation and differentiation
– Ectoderm – outer layer
– Mesoderm – middle layer of cells
– Endoderm – inner layer
• Blastopore
– Pore created by the inward folding of cells
– Eventually becomes the anus
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Embryonic Germ Layers
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Comparative Development of
Mesoderm
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archenteron
ectoderm
mesoderm
endoderm
cross section
a. Lancelet late gastrula
archenteron
mesoderm
ectoderm yolk plug endoderm
longitudinal section
b. Frog late gastrula
archenteron primitive streak mesoderm
ectoderm
yolk
endoderm
cross section
c. Chick late gastrula
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Early Developmental Stages
• Organ Stages of Development
 Nervous system
• Develops from midline ectoderm located just
above the notochord
– Notochord = dorsal supporting rod
• Thickening of neural plate is seen along dorsal
surface of the embryo
• Neural folds develop on either side of neural
groove
• Neural grove becomes the neural tube
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Development of Neural Tube and Coelom in
a Frog Embryo
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presumptive
notochord
neural plate
neural groove
ectoderm
coelom
mesoderm
gut
gut
endoderm
notochord
archenteron
a.
neural tube
notochord0 coelom
b.
yolk
c.
d.
b: Courtesy Kathryn Tosney
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Vertebrate Embryo, Cross
Section
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neural tube
somite
notochord
gut
coelom
ectoderm
mesoderm
endoderm
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42.2 Developmental Processes
• Development requires:
 Growth
 Cellular Differentiation
• Cells become specialized in structure and function
 Morphogenesis
• Produces the shape and form of the body
• Includes pattern formation
– Arrangement of tissues and organs within the body
– Involves apoptosis
» Programmed cell death
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Developmental Processes
• Cellular Differentiation
 The zygote is totipotent
• Has the ability to generate the entire organism
 Adult body cells lose their totipotency, but do
not lose genetic information
 Each contains all the instructions needed by
any other specialized cell in the body
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Developmental Processes
• Cellular Differentiation (continued)
 Cytoplasmic Segregation
• Maternal determinants are parceled out during
mitosis
• Cytoplasm of a frog’s egg is not uniform
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Developmental Processes
• Cellular Differentiation (continued)
 Induction and Frog Experiments
• Induction
– The ability of one embryonic tissue to influence the
development of another tissue
• Molecular concentration gradients may act as
chemical signals to induce germ layer
differentiation
• Developmental path of cells is influenced by
neighboring cells
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Development of C. elegans, a
Nematode
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egg
gonad
(8–16
divisions)
cuticle
(8–11
divisions)
gonad
vulva
(10–13
divisions)
cuticle
egg
intestine
(3–6
divisions)
nervous
system
(6–8
divisions)
vulva
sperm
intestine
nervous system
pharynx
(9–11
divisions)
pharynx
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Developmental Processes
• Morphogenesis
 Process by which an animal achieves its
ordered and complex body form
• Requires that cells associate to form tissues, which
give rise to organs
• Pattern formation
– Cells of the embryo divide and differentiate,
taking up orderly positions in tissues and
organs
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Developmental Processes
• Morphogenesis in Drosophila melanogaster
 Fruit Fly
 Pattern formation
• Embryonic cells express genes differently in graded,
periodic, and striped arrangements
• Anteroposterior polarity is established in the egg
before fertilization
• Gap genes divide the anteroposterior axis into broad
regions
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Developmental Processes
• Homeotic Genes control pattern formation
 Organization of differentiated cells into specific
three-dimensional structures
 In Drosophila, certain genes control whether a
particular segment will bear antennae, legs, or
wings
• Homeotic genes all contain the same
particular sequence of nucleotides, the
homeobox, that encodes a 60-amino-acid
sequence called a homeodomain
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Pattern Formation in Drosophila
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a.
Hox-2
Hox-1
mouse
chromosomes
Hox-3
Hox-4
fly chromosome
mouse
embryo
b.
fruit fly embryo
mouse
fruit fly
Courtesy E.B. Lewis
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42.3 Human Embryonic and
Fetal Development
• Human gestation time - time from conception
to birth - is approximately nine months
 Embryonic Development - Months 1-2
• Formation of major organs
 Fetal Development - Months 3-9
• Major organs become larger and refined
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Human Embryonic and Fetal
Development
• Embryonic Development
 First Week
• Morula transformed into blastocyst
• Blastocyst consists of
– A fluid-filled cavity
– A single layer of outer cells called the trophoblast
» gives rise to chorion
– Inner cell mass - develops into a fetus
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Human Embryonic and Fetal
Development
• Embryonic Development (continued)
 Second Week
• Implantation begins
– Trophoblast secretes human chorionic gonadotropin
(HCG)
» Maintains corpus luteum, therefore maintaining the
endometrium and preventing menstruation
» Hormone that is the basis of the pregnancy test
• Gastrulation occurs
– Inner cell mass flattened into embryonic disk
– Ectoderm, mesoderm, and endoderm differentiate
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Human Embryonic Development
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amniotic cavity
embryonic disk
yolk sac
blastocyst cavity
trophoblast
a. 14 days
amniotic cavity
embryo
yolk sac
chorionic villi
chorion
b. 18 days
body stalk
amniotic cavity
embryo
allantois
yolk sac
chorionic villi
c. 21 days
chorion
amniotic cavity
allantois
yolk sac
amnion
chorionic villi
d. 25 days
amniotic cavity
chorion
digestive tract
chorionic villi
amnion
umbilical cord
e. 35+ days
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Human Embryonic and Fetal
Development
• Embryonic Development (continued)
 Third Week
• Nervous system and circulatory system appear
 Fourth and Fifth Weeks
•
•
•
•
Umbilical cord is fully formed
Limb buds appear
Head enlarges
Sense organs more apparent
– Discernable eyes, ears, and nose
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Human Embryo at Beginning of
Fifth Week
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tail
brain
brain
optic
vesicle
optic
vesicle
tail
pharyngeal
pouch
pharyngeal
pouch
heart
region of
heart, liver
liver
limb bud
limb bud
umbilical
vessel
umbilical
vessel
a.
somite
b.
gastrointestinal tract
limb bud
a: © Lennart Nilsson, A Child is Born, Dell Publishing
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Human Embryonic and Fetal
Development
• Embryonic Development (continued)
 Sixth Through Eighth Weeks
• Head achieves normal relationship with the body
as a neck region develops
• Nervous system is developed enough to permit
reflex actions
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Human Embryonic and Fetal
Development
• The Structure and Function of the Placenta
 Placenta
• a mammalian structure that functions in gas,
nutrient, and waste exchange between embryonic
and maternal cardiovascular systems.
• Begins formation once the embryo is fully planted
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Human Embryonic and Fetal
Development
• The Structure and Function of the Placenta (cont.)
 Chorionic villi
• Project into the maternal tissues
• Surrounded by maternal blood sinuses
• The maternal and fetal blood do not mix
• Exchange between the fetal and maternal blood takes
place across the walls of the chorionic villi
– CO2 and wastes move across from the fetus
– O2 and nutrients flow from the maternal side
 By the tenth week, the placenta is fully formed
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Anatomy of the Placenta in a Fetus
at Six to Seven Months
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amniotic fluid
placenta
umbilical cord
endometrium
vagina
umbilical cord
umbilical blood vessel
chorionic villi
maternal
blood
vessels
Placenta
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Human Embryonic and Fetal
Development
• Fetal Development and Birth
 Fetal development (months 3–9) involves:
• Extreme increase in size
 The genitalia appear in the third month
 A fetus soon acquires hair, eyebrows, eyelashes, and
nails
 A fetus at first only flexes its limbs and nods its head
• Later it moves its limbs vigorously
• A mother feels movements from the fourth month on
 After 16 weeks, a fetal heartbeat is heard through a
stethoscope.
 A fetus born at 24 weeks may survive
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Preventing and Testing for Birth
Defects
• It is believed that at least 1 in 16 newborns
has a birth defect
• Hereditary defects can sometimes be
detected before birth
 Amniocentesis allows the fetus to be tested
for abnormalities of development;
 Chorionic villi sampling allows the embryo to
be tested;
 During preimplantation genetic diagnosis,
eggs are screened prior to in vitro fertilization
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