Embryonic Development

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Embryonic Development

• Development series of orderly, precise steps
  that transform a zygote into a multicellular
  embryo early stage of development of
  multicellular organism
• Includes
• 1. cell division
• 2. cell growth
• 3. cell differentiation
• changing of unspecialized embryonic cells into
  specialized cells, tissues, organs

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Early Embryonic Development

• Cleavage is the first major phase of embryonic
  development
• It is the rapid succession of cell divisions
  (Mitotic)
• It creates a multicellular embryo from the zygote
• NO growth
• Stages
• 1. Morulasolid ball of cells
• 2.Blastula single layer of cells surrounding a
  fluid-filled cavity called the blastocoel

ZYGOTE
2 cells
4 cells
8 cells
Blastocoel
Many cells(solid ball)
Cross sectionof blastula
BLASTULA(hollow ball)
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Embryonic Development

• Gastrulation is the second major phase of
  embryonic development
• The cells at one end of the blastula move inward,
  
• It adds more cells to the embryo
• It sorts all cells into three distinct cell
  layers
• The embryo is transformed from the blastula into
  the gastrula

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Embryonic Development

• The three layers produced in gastrulation
• Ectoderm, the outer layer
• Endoderm, an embryonic digestive tract
• Mesoderm, which partly fills the space between
  the ectoderm and endoderm

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Embryonic Development

• The tissues and organs of a tadpole emerge from
  cells of the ectoderm, mesoderm, and endoderm

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Embryonic Development

• ectoderm cells eventually they develop into the
  skin and nervous tissue of the animal
• endoderm cells develop into the lining of the
  animals digestive tract and into organs
  associated with digestion.
• mesoderm cells develop into the muscles,
  circulatory system, excretory system, and, in
  some animals, the respiratory system.

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Embryonic Development

• Organs start to form after gastrulation
• Embryonic tissue layers begin to differentiate
  into specific tissues and organ systems

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Changes in cell shape, cell migration, and
programmed cell death give form to the developing
animal

• Tissues and organs take shape in a developing
  embryo as a result of
• cell shape changes
• cell migration

Ectoderm
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Development

• programmed cell death (apoptosis)

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Embryonic induction initiates organ formation

• Induction is the mechanism by which one group of
  cells influences the development of tissues and
  organs from ectoderm, endoderm, and mesoderm
• Adjacent cells and cell layers use chemical
  signals to influence differentiation
• Chemical signals turn on a set of genes whose
  expression makes the receiving cells
  differentiate into a specific tissue

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Pattern formation organizes the animal body

• Pattern formation is the emergence of a body form
  with structures in their correct relative
  positions
• It involves the response of genes to spatial
  variations of chemicals in the embryo

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HUMAN DEVELOPMENT

• The embryo and placenta take shape during the
  first month of pregnancy
• Gestation is pregnancy
• It begins at conception and continues until birth
• Human gestation is 266 days (38 weeks or 9
  months)
• Mouse gestation is 1 month
• Elephant gestation is 22 months

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HUMAN DEVELOPMENT

• Human development begins with fertilization in
  the oviduct

Cleavage starts
Fertilizationof ovum
Ovary
Blastocyst(implanted
Oviduct
Ovulation
Endometrium
Uterus
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HUMAN DEVELOPMENT

• Cleavage produces a blastocyst
• A blastocyst is a fluid-filled cavity
• The inner cells of the blastocyst form the baby
• The outer cells form the embryo trophoblast

ENDOMETRIUM
ENDOMETRIUM
Inner cell mass
Cavity
Trophoblast
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HUMAN DEVELOPMENT

• The trophoblast secretes enzymes to enable the
  blastocyst to implant in the uterine wall

ENDOMETRIUM
Blood vessel(maternal
Future embryo
Multiplying cellsof trophoblast
Futureyolk sac
Trophoblast
UTERINE CAVITY
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HUMAN DEVELOPMENT

• Gastrulation occurs and organs develop from the
  ectoderm, endoderm, and mesoderm

Amnion
Mesodermcells
Chorion
Yolk sac
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HUMAN DEVELOPMENT

• Meanwhile, the four embryonic membranes develop
• Amnionfluid filled sac for protection
• Chorion will form the embryos part of the
  placenta
• Yolk sac produces first blood cells germ cells
• Allantois will form the umbilical cord
  (ropelike structure that attaches embryo to
  uterus)

Chorion
Amnion
Allantois
Yolk sac
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HUMAN DEVELOPMENT

• The embryo floats in the fluid-filled amniotic
  cavity,
• The placentas chorionic villi absorb food and
  oxygen from the mothers blood

Mothers bloodvessels
Placenta
Yolk sac
Amnioticcavity
Amnion
Embryo
Chorion
Chorionicvilli
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HUMAN DEVELOPMENT

• Embryonic development of essential organs occur
  in early pregnancy
• The embryo many encounter risks form faults in
  its genes from mothers exposure to
  environmental factors
• The placenta allows for a variety of substances
  to pass from mother to fetus
• Protective antibodies
• German measles virus
• HIV
• Drugs (prescription and nonprescription)
• Alcohol
• Chemicals in tobacco smoke

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Human development from conception to birth is
divided into three trimesters

• First trimester
• First three months
• The most rapid changes occur during the first
  trimester

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Human development from conception to birth is
divided into three trimesters

• Second trimester
• Increase in size of fetus
• General refinement of human features

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Human development from conception to birth is
divided into three trimesters

• Third trimester
• Growth and preparation for birth

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Childbirth is hormonally induced and occurs in
three stages

• Hormonal changes induce birth
• Labor is controlled by a positive feedback
  mechanism
• Estrogen released from the ovaries increases the
  sensitivity of the uterus to oxytocin

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Positive feedback Mechanism

• Oxytocin is a powerful stimulant for the smooth
  muscles of the uterus
• Oxytocin also stimulates the placenta to make
  prostoglandins that stimulate the uterine muscles
  to contract even more
• Uterine contractions stimulate the release of
  more and more oxytocin and prostoglandins

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Three stages of labor

• 1.Dilation of the cervix is the first stage
• -Cervix reaches full dilation at 10cm
• Longest stage of labor (6-12 hours or longer)

Dilation of the cervix
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Three stages of labor

• Expulsion is the second stage
• Period from full dilation of the cervix to
  delivery of the infant
• Uterine contractions occur every 2-3 minutes
• Mother feels urge to push down with her abdominal
  muscles
• Infant is forced down and out of uterus and
  vagina within a period of 20 minutes

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Three stages of labor

• The delivery of the placenta is the final stage
  of labor
• Usually occurs within 15 minutes after the birth
  of the baby

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Childbirth is hormonally induced and occurs in
three stages

• Hormones continue to be important after the baby
  and placenta are delivered
• Decreasing progesterone and estrogen levels allow
  the uterus to return to its pre-pregnancy state
• Oxytocin and prolactin stimulate milk secretion

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Reproductive technology increases our
reproductive options

• Reproductive technology
• Hormone therapy can increase sperm or egg
  production
• Surgery can correct blocked oviducts
• Assisted reproductive technology
• In vitro fertilization (IVF)
• Surrogate motherhood