1. Chapter 29 Development and Inheritance
2/28/2018
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2. Development and Inheritance
Fertilization – conception- formation of zygote embryo
Takes approximately 72 hours for the egg to reach the UTERUS; fertilization must occur in the fallopian tube otherwise the ovum would die prior to reaching the sperm.
Male pronucleus (nuclear material) and female pronucleus FUSE (fertilization)  Diploid zygote (44XX or 44 XY) 44XY)
Implantation – attachment of embryo to the wall of the uterus
Gestation - fertilization  birth; 38 weeks of pregnancy
Differentiation
Creation of different types of cells required in development
Occurs through selective changes in genetic activity
Development
Gradual modification of anatomical structures and physiological characteristics from fertilization to maturity
Inheritance
Transfer of genetic material from generation to generation

4. Prenatal Development - time before birth. Embryological Development
Occurs during first two months after fertilization
Study of these events is called embryology
Fetal Development
Begins at start of ninth week till birth
Postnatal Development
Commences at birth
Continues to maturity, the state of full development or completed growth
Neonatal period – first 42 days after birth
Labor - events that lead to birthing
Parturition - birthing process
Ectopic pregnancy - development of an embryo or fetus outside the uterine cavity---mostly occur in the uterine tube. Occurs in 1 out of 300 pregnancies
Obstetrics: branch of medicine that deals with pregnancy, labor and delivery
Alternative: Midwife/doula
Certified Professional Midwife (CPM),
Certified Midwife (CM)
16 weeks

5. Stages of Prenatal Development
Pregnancy is divided into month intervals = trimesters
first trimester – from fertilization through 12 weeks
Most dangerous period in pre-natal life - vulnerable to stress, drugs, nutritional deficiencies
Only 40% of conceptions produce embryos that survive past first trimester
second trimester – weeks 13 through 24
organs complete most of their development
chance of survival if born near end of this trimester
third trimester – week 25 to birth
fetus grows rapidly and organs achieve enough cellular differentiation to support life outside of the womb
at 35 weeks and 5.5 lb fetus is considered mature

6. Twins Fraternal twins (dizygotic – from two zygotes)
Release of 2 oocytes  fertilized by 2 sperms  two zygotes are formed  two embryos
genetically as different as any 2 siblings
Identical twins (monozygotic – from one zygote)
Release of 1 oocyte  fertilized by 1 sperm  one zygote is formed  zygote divides to form 2 blastomeres  blastomeres separate to independently develop into 2 embryos
genetically identical & always the same sex
Conjoined twins
If the blastomeres do not completely separate  newborns remain attached to different extents  share some body structures
Twins

8. Biological Stages of Development
Pre-embryonic and Embryonic stage
first 16 days development culminating in the existence of an embryo
cleavage
implantation
embryogenesis
placentation
Fetal stage 1 2
morula
“Hatching” 8

9. Pre-embryonic CLEAVAGE Divisions
Zygote (surrounded by zona pellucida) divides by mitosis
1st cleavage occurs in the fallopian tube 30 hours after fertilization
2 identical BLASTOMERES are formed; then 4, etc.
72 hours (3 days) blastomeres form a pre-embryo = MORULA arrives AT the uterus; lies free for 4-5 days- continues dividing
Morula not much larger than zygote but very compact - each cell provides area for nutrient intake and waste removal.
Continued cell division produces the BLASTOCYST. First sign of cell differentiation (cells becoming different)!
Blastocyst reaches the uterus by day 5 or 6. Inner layer contains Inner cell mass or EMBRYOBLAST that forms the embryo.
Outer layer of cells collectively called the TROPHOBLASTS This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoel. The trophoblast provides nutrients and will form the future embyronic membranes and gives rise to the placenta
To implant into uterus lining, blastocyst must rid itself of the zona pellucida. The trophoblast releases hormones that erodes and sheds the zona pellucida (hatching). Blastocyst now exposed to fluid in uterine cavity.

10. Blastocyst adheres to uterine lining
EMBRYOBLAST
forms the embryo
Blastocyst adheres to uterine lining
Trophoblast cells divide rapidly, creating several layers
(Syncytial trophoblast)
Syncytial trophoblast secretes hyaluronidase to digest endometrial cells that grow over blastocyst; covers the entire surface of the placenta.
direct contact with the maternal blood
Secretes human chorionic gonadotropin (hCG)

12. Embryonic Membranes
AMNION - transparent sac filled with amniotic fluid that completely enclose the embryo and is penetrated only by the umbilical cord
protects embryo from trauma, infections
allows freedom of movement
develop symmetrically- prevents body parts from adhering to each other
stimulates lung development as the fetus ‘breathes’ fluid
fetus urinates into the amniotic cavity
ALLANTOIS forms the foundation for the UMBILICAL CORD and becomes part of the urinary BLADDER
YOLK SAC first element seen in the gestational sac during pregnancy, usually at 3 days gestation. Acts as developmental circulatory system before fetal circulatory system is formed; important site of blood cell formation
CHORION - outermost membrane - First step in creation of functional placenta
Blood source - Chorionic villi sprout from the chorion to give maximum area of contact with the maternal blood.

15. PLACENTA
Formed by chorion and portion of mother’s uteral endometrium during 3rd month. The syncytiotrophoblast covers the surface of the placenta.
Maternal & fetal blood vessels do not join  blood does not mix
Allows diffusion of O2, nutrients, wastes; BLOCKS most microbes
IS NOT A BARRIER TO DRUGS, ALCOHOL, TOXINS IN CIGARETTES
Secretes several hormones to support pregnancy
Detaches from the uterus at birth time (afterbirth)
Acts as respiratory and urinary system for fetus

16. Umbilical cord
Composed of Wharton's jelly, a gelatinous substance
2 ARTERIES that carry deoxygenated blood TO the placenta AWAY from fetus
1 UMBILICAL VEIN that carries oxygenated blood TO the fetus
Vein
Arteries
Not directly connected to the mother's circulatory system, but joins the placenta, transfers materials to and from the mother's blood without allowing direct mixing.
Cut at the time of delivery
Stub drops off in 2 weeks  leaving a scar (umbilicus)

17. Adjustments to Pregnancy

18. Stages of Labor
1. Dilation – longest hours regular contractions of the uterus
- rupture of amniotic sac- amniotic fluid discharged (water breaking)
- dilation of cervix (10 cm)
Effacement: thinning of the cervix
2. Expulsion minutes to several hours
- baby moves through birth canal
- episiotomy; mucus suction; cord cut
3. Placental - 30 minutes
placenta (afterbirth) expelled by uterine contractions
constriction of blood vessels that were torn during placenta detachment reduce the possibility of hemorrhage
Cesarean section (C-section): incision through lower abdominal wall and uterus to remove baby

20. “Lifespan”
Make the most of yours!