1. Chapter 24 Development & Inheritance
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Fertilization
Genetic material from haploid sperm & ovum merge into single diploid nucleus
Occurs in Uterine tube= 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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Fertilization
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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Fertilization
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Fertilization
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Early Development
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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Early Development
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Early Development
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2nd 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)
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2nd Week of Development
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
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2nd Week of Development
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2nd Week of Development
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3rd 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
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3rd Week
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3rd Week
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16. Allantois, Chorionic Villi & Placenta
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
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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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4th- 8th 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
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Fetal Birth
Continual growth & differentiation
Few new structures added
Last 2 1/2 months – half of weight added
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Fetal Birth
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Hormones
hCG- maintains corpus lutem progesterone & estrogen
Peaks at week 9
Chorion secretes several hormones: estrogens after 3-4 wks & progesterone by wk 6
Rise through pregnancy
Progesterone helps keep myometrium relaxes & cervix closed
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Hormones (cont.)
Relaxin- increases flexibility of pubic symphysis & ligaments & relaxes cervix for birth
Human placental lactogen (hPL)
Rises with fetal mass
Prepare mammary glands
Support metabolic capacity
Corticotrophin-Releasing Hormone (CRH)
Helps support birth timing & cortisol production for lung maturation
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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
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33. Changes During Pregnancy
Uterus fills up pelvic cavity-3rd month
Further growth into abdominal cavity
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
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34. Exercise During Pregnancy
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
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Labor & Delivery
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
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Stages of Labor
Dilation: onset to complete dilation of cervix
Expulsion- dilation to complete delivery
Placental- powerful uterine contractions expel placenta
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Positive Feedback
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
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Negative Feedback Systems Interactions Animation
Positive Feedback Control of Labor
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Lactation
Prolactin(PRL)  milk production
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
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Colostrum
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
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Inheritance
Passage of hereditary traits- genetics
23 pairs of chromosomes-
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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Inheritance
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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Inheritance
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44. Autosomes & Sex Chromosomes
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
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45. Autosomes & Sex Chromosomes
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46. Autosomes & Sex Chromosomes
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End of Chapter 24
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