Lecture 4 development & inheritance

Copyright 2010, John Wiley & Sons, Inc.

Chapter 24Development & Inheritance


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


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


Fertilization


Fertilization


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


Early Development


Early Development


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)


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






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


3rd Week


3rd Week


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


Allantois, Chorionic Villi & Placenta






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


Fetal Birth

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 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


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


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


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


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


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


Stages of Labor

Dilation: onset to complete dilation of cervix

Expulsion- dilation to complete delivery

Placental- powerful uterine contractions expel placenta


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


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


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


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)


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.


Inheritance


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


Autosomes & Sex Chromosomes


Autosomes & Sex Chromosomes


End of Chapter 24

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Lecture 4 development & inheritance