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Transcript
Chapter 24
Development &
Inheritance
Copyright 2010, John Wiley & Sons, Inc.
Fertilization
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Genetic material from haploid sperm &
ovum merge into single diploid nucleus
Occurs in Uterine tube= 12-24 hours after
ovulation
Sperm last ~48 hours
Contraction of uterus & uterine tube walls
help move sperm
Prostaglandins in semen help stimulate
Fertilization
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Sperm Capacitation- ready for penetration
Acrosomal enzymes penetrate outer cell
layers and one sperm fuses with ovum
meiosis II is completed- polar body
discarded
Fusion of DNA’s  diploid = zygote
Rapid cell division = cleavage
Fertilization
Fertilization
Early Development
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Continual division ball of small cells
=Morula- enters uterine cavity ~ day 4-5
Reorganizes around fluid filled cavity
=blastocyst- about same size as zygote
Rearrangement Inner cell mass embryo
+ Trophoblast fetal part of Placenta
Implants after ~2 days
 ~6 days after fertilization
Early
Development
Early Development
nd
2

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Week of Development
Trophoblast synctiotrophoblast +
cytotrophoblast  chorion
 Aids in implantation & secretes hCH
Inner cell mass hypoblast & epiblast
Cavity in epiblast  amniotic cavity
 Thin membrane develops to surround embryo
 = amnion filled with amniotic fluid
Hypoblast ceils –cover inner surface= wall of
yolk sac (from blastocyst cavity)
2nd Week of Development
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Yolk sac –nutrients for weeks 2 & 3
+ source of blood cells (week 3-6)
Day 9 – blastocyst embedded in endometrium
Lacunae develop in trophoblast
 Maternal blood and secretions fill
 Serve as exchange point for embryonic
nutrient and waste removal
Day 12 - cells from yolk sac + two layers of
trophoblast  chorion
 surrounds embryo & becomes fetal part of
placenta
2nd Week of Development
2nd Week of Development
rd
3

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Week
Gastrulation= transformation of disc from 2 -> 3
layers=
Primary ectoderm, mesoderm & endoderm
 Cells of epiblast move inward & detach
 Push out cells of hypoblast endoderm
 Become mesoderm
 Rest of epiblast  ectoderm
Mesoderm notocord vertebrae
Ectoderm neural plate neural tube
 neurulation
rd
3
Week
rd
3
Week
Allantois, Chorionic Villi & Placenta

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Outpouch of yolk sac  allantois
Chorionic villi develop with capillaries
end 3rd week - capillaries connect to
embyronic heart via umbilical arteries &
veins
Placenta: chorionic villi & maternal
endometrium


Exchange organ.
Some viruses can get through
Allantois, Chorionic Villi & Placenta
Allantois, Chorionic Villi & Placenta
Allantois, Chorionic Villi & Placenta
th
4 


th
8
Weeks
All major organs appear at this time
Converted from disc to cylinder
22 days
Ear- otic placode & eyes- lens placode

4th week- upper & lower limb buds & heart
prominence on surface
5th week- rapid growth of brain & head

Neck & trunk straighten, 4 chambered heart,
digits appear
End of 8th week looks human fetus


Fetal Birth
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Continual growth & differentiation
Few new structures added
Last 2 1/2 months – half of weight added
Fetal Birth
Fetal Birth
Fetal Birth
Fetal Birth
Fetal Birth
Fetal Birth
Fetal Birth
Fetal Birth
Hormones

hCG- maintains corpus lutem
progesterone & estrogen

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Chorion secretes several hormones:
estrogens after 3-4 wks & progesterone by
wk 6

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Peaks at week 9
Rise through pregnancy
Progesterone helps keep myometrium
relaxes & cervix closed
Hormones (cont.)

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Relaxin- increases flexibility of pubic
symphysis & ligaments & relaxes cervix for
birth
Human placental lactogen (hPL)

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Rises with fetal mass
Prepare mammary glands
Support metabolic capacity
Corticotrophin-Releasing Hormone (CRH)

Helps support birth timing & cortisol production
for lung maturation
Endocrine Support
Trophoblast cells secrete hCG
hCG maintains corpus luteum
corpus luteum continues to secrete relaxin,
progesterone and estrogen & Chorion adds hPL,
progesterone + estrogen & CRH
Estrogen & progesterone promote growth, development
and maintenance of the uterine wall hPl supports
maternal growth and changes CRH corticoids lung
maturation
Changes During Pregnancy

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Uterus fills up pelvic cavity-3rd month
Further growth into abdominal cavity
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Pushes on intestines, stomach, liver
Skin changes: areola, pigmentation
around eyes, stretch marks
Increased: maternal C.O., blood volume,
nutrient consumption appetite , O2
needs ventilation , renal activity
Pressure: diaphragm  dyspnea


Stomach acid reflux & nausea
Bladder  frequent urination
Exercise During Pregnancy
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Major issues: postural changes with weight
gain
extra Heat production may affect
development early on
Care to avoid dehydration
Moderate exercise doesn’t hurt
May be beneficial
Labor & Delivery
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Labor = expelling fetus from uterus
through vagina= parturition
Progesterone inhibits contractions
Estrogen rises toward end  overcome
inhibition
+  prostaglandin production
+  oxytocin receptors on myometrium
Oxytocin contractions
Stages of Labor

Dilation: onset to complete dilation of cervix

Expulsion- dilation to complete delivery

Placental- powerful uterine contractions expel
placenta
Positive Feedback

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Contractions baby’s head against cervix
Neural signals  hypothalamus more
oxytocin  more pushing


Stops after birth when cervix is not stretched
True labor shows rhythmic pulses of
contraction
Negative Feedback Systems
Interactions Animation

Positive Feedback Control of Labor
You must be connected to the internet to run this animation.
Lactation

Prolactin(PRL)  milk production

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PRL increases as pregnancy proceeds
Progesterone inhibits milk production
Progesterone decreases after delivery
Oxytocin milk letdown
feedback loop for maintenance
Suckling  nerve input to
hypothalamus maintain PRL & release
oxytocin
Colostrum
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Formed during first few days after birth
Less lactose & no fat + antibodies
Protect infant during first few months of life
Good nutrition for infant
Oxytocin also speeds maternal recovery
Inheritance
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Passage of hereditary traits- genetics
23 pairs of chromosomes

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1 maternal and 1 paternal
Each homolog (one of pair) has gene for
same traits
variant genes for a trait = alleles
Genotype= genetic makeup
Homozygous = have 2 of same allele
Heterozygous= 2 different alleles
Phenotype= trait that is visible (brown
eyes)
Inheritance
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Dominant allele  shows product no matter
what the other allele is
Recessive allele  masked by other allele
Can have incomplete dominance
phenotype mixture of allele products
Inheritance can be simple (one gene) or
multiple allele.
Inheritance
Autosomes & Sex Chromosomes
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Autosomes: chromosomes where members
of pair look alike - 22 pairs
Sex chromosomes - look different
Females have 2 X chromosomes
Males have X and Y chromosomes


Maleness from SRY of Y chromosome
Traits on X but not Y sex linked inheritance
Autosomes & Sex Chromosomes
Autosomes & Sex Chromosomes
End of Chapter 24

Copyright 2010 John Wiley & Sons, Inc.
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