Lecture 4 development & inheritance

1. Chapter 24
Development &
Inheritance
Copyright 2010, John Wiley & Sons, Inc.

2. 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
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3. 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
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4. Fertilization
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5. Fertilization
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6. 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
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7. Early
Development
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8. Early Development
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9. 2nd Week of Development
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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)
Copyright 2010, John Wiley & Sons, Inc.

10. 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
Copyright 2010, John Wiley & Sons, Inc.

11. 2nd Week of Development
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12. 2nd Week of Development
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13. 3rd Week
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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
Copyright 2010, John Wiley & Sons, Inc.

14. 3rd Week
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15. 3rd Week
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16. 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
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Exchange organ.
Some viruses can get through
Copyright 2010, John Wiley & Sons, Inc.

17. Allantois, Chorionic Villi & Placenta
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18. Allantois, Chorionic Villi & Placenta
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19. Allantois, Chorionic Villi & Placenta
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20. 4th- 8th Weeks
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All major organs appear at this time
Converted from disc to cylinder
22 days
Ear- otic placode & eyes- lens placode
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4th week- upper & lower limb buds & heart
prominence on surface
5th week- rapid growth of brain & head
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Neck & trunk straighten, 4 chambered heart,
digits appear
End of 8th week looks human fetus
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21. Fetal Birth
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Continual growth & differentiation
Few new structures added
Last 2 1/2 months – half of weight added
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22. Fetal Birth
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23. Fetal Birth
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24. Fetal Birth
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25. Fetal Birth
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26. Fetal Birth
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27. Fetal Birth
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28. Fetal Birth
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29. Fetal Birth
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30. Hormones
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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
Copyright 2010, John Wiley & Sons, Inc.

31. 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)
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Helps support birth timing & cortisol production
for lung maturation
Copyright 2010, John Wiley & Sons, Inc.

32. 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
Copyright 2010, John Wiley & Sons, Inc.

33. 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
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Stomach acid reflux & nausea
Bladder  frequent urination
Copyright 2010, John Wiley & Sons, Inc.

34. 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
Copyright 2010, John Wiley & Sons, Inc.

35. 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
Copyright 2010, John Wiley & Sons, Inc.

36. Stages of Labor
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Dilation: onset to complete dilation of cervix
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Expulsion- dilation to complete delivery
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Placental- powerful uterine contractions expel
placenta
Copyright 2010, John Wiley & Sons, Inc.

37. Positive Feedback
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Contractions baby’s head against cervix
Neural signals  hypothalamus more
oxytocin  more pushing
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Stops after birth when cervix is not stretched
True labor shows rhythmic pulses of
contraction
Copyright 2010, John Wiley & Sons, Inc.

38. Negative Feedback Systems
Interactions Animation
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Positive Feedback Control of Labor
You must be connected to the internet to run this animation.
Copyright 2010, John Wiley & Sons, Inc.

39. Lactation
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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
Copyright 2010, John Wiley & Sons, Inc.

40. 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
Copyright 2010, John Wiley & Sons, Inc.

41. 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)
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42. 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.
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43. Inheritance
Copyright 2010, John Wiley & Sons, Inc.

44. 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
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Maleness from SRY of Y chromosome
Traits on X but not Y sex linked inheritance
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45. Autosomes & Sex Chromosomes
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46. Autosomes & Sex Chromosomes
Copyright 2010, John Wiley & Sons, Inc.

47. End of Chapter 24
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