copyright 2010, john wiley & sons, inc. chapter 24 development & inheritance
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Copyright 2010, John Wiley & Sons, Inc.
Chapter 24Development & Inheritance
Copyright 2010, John Wiley & Sons, Inc.
Fertilization
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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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
Copyright 2010, John Wiley & Sons, Inc.
Fertilization
Copyright 2010, John Wiley & Sons, Inc.
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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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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Allantois, Chorionic Villi & Placenta
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Allantois, Chorionic Villi & Placenta
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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
Copyright 2010, John Wiley & Sons, Inc.
Fetal Birth
Copyright 2010, John Wiley & Sons, Inc.
Fetal Birth
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Fetal Birth
Copyright 2010, John Wiley & Sons, Inc.
Fetal Birth
Copyright 2010, John Wiley & Sons, Inc.
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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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
Endocrine Support
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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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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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Positive Feedback Control of Labor
Negative Feedback Systems Interactions Animation
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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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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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Autosomes & Sex Chromosomes
Copyright 2010, John Wiley & Sons, Inc.
Autosomes & Sex Chromosomes
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End of Chapter 24
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