3rd month to birth: fetus and placenta I

Fetal period

9th week to birth

What occurs during the fetal period?

maturation of tissues and organs

CRL and CHL grows ost rapid when?

3rd-5th months with weight most rapid last 2 months

Length of pregnancy

280 days or 40 weeks after last normal menses

Length of pregnancy related to fertilization

266 days or 38 weeks

Head makes up half of CRL when?

begin of 3rd month shrinking till 1/4th of CHL at birth

What happens in face at 3rd month?

Eyes move ventrally, ears move, limbs reach relative length

When do primary ossification centers present?

3rd month in long bones and skull

When do external genitalia develop?

3rd month

When do intestinal loops withdraw into abdominal cavity?

3rd month

When does the fetus lengthen rapidly causing CRL ~15cm

4th and 5th month

Lenugo

fine hair covering baby at 4th and 5th month

When can mom feel baby?

5th month

Skin at 6th month?

skin is red and wrinkled due to lack of underlying CT

Why might baby not survive if born at 6th month?

CNS and respiratory have not yet differentiated enough and no coordination betwen the two

6.5-7 month

90 % chance of survival ~25 cm

Baby is covered with what at last 2 months?

Vernix caseosa

Well rounded contours because of subq fat occurs....

last 2 months

By the end of the 9th month...

skull has largest circumfrence and sexual characteristics are pronounced

When do oocytes usually fertilize?

within 12 hours of ovulation

Major changes in the placenta during 9th week?

Increase in SA and amniotic fluid

Fetal component of placenta forms from what?

trophoblast and chorion (extraembryonic mesoderm)

Maternal component of placenta is from what?

uterine endometrium

Trophoblast at begin of 2nd month?

2ndary and tertiary villi giving a radial appearance

Villi extend from...

mesoderm of chorionic plate to cytotrophoblast shell

How does extraembryonic vascular system form?

capillary systems in core of villous stem come into contact w/capillaries of chorionic plate

How is maternal blood delivered into placenta?

spiral arteries

Cytotrophoblasts invade endovasculature by..

eroding maternal vessels to release blood into intervillous spaces and vessels get biffer

When is there a thin syncytial layer between maternal and fetal blood?

begin of 4th month

Over time villi covering whole surface continue to grow and give rise to what?

chorion frondosum

When villi degenerate on abembryonic pole in 3rd month is is smooth...

chorion laeve

Decidua

funcitonal layer of endometrium shed during birth

Decidua over chorion frodosum

decidual basalis

decidual layer over abembryonic pole that eventually degenerates is called?

decidua capsularis

Chorion fuses with uterine wall...

forming decidua parietalis and obliterating uterine lumen

Chorion frondosum and decidua basalis form what?

placenta

amniochorionic membrane formed by

fucion of amnion and chorion which ruptures during labor

2 components of placenta by begin of 4th month

fetal and maternal

Intervillous spaces are filled with what in placenta?

maternal blood. villous trees grow into blood lakes

When does decidual septa form?

4th and 5th months

placenta divides into what during septal formation?

cotyledons

Characteristics of full term placenta?

Discoid, 15-25 cm, 3cm thick, 500-600 grams

maternal placenta surface

15-20 bulging cotyledons covered by decidual basalis

fetal placental side

covered by chorionic plate w/vessels that converge at umbilical

cotyledns recieve blood through...

spiral arteries filling intervillous spaces with blood

maternal blood intervillous lakes are renewed...

3-4 times per minute

functions of placenta

gas/nutrient exchange, transmission of maternal antibodies, hormone production, detoxification of drugs

Some fetal blood cells may escape across barrier causing...

potential antibody response to mother if Rh incompatible

anemia from Rh rejection may be so severe that is causes

fetal hydrops

Amniotic cavity

Large sac containing amniotic fluid in which fetus is suspended, cuschioned, and allowed to move

Amniotic cavity allows movement of fetus so...

embryo doesn't adhere to amnion

Hydramnios

excess amniotic fluid associated with anencephaly and esophageal atresia

Oligohydramnios

Insufficient fluid related to renal agenesis

Umbilical cord is surrounded by

Amnion

Umbilical cord contains...

2 arteries

1 vein

Wharton jelly

Tortuous umbilical cord

False knot

If umbilical cord is too long...

May wrap around neck but isnt always dangerous

If umbilical cord is too short...

Difficulties in delivery by pulling placenta from uterus

What happens if there is only one artery and one vein in umbilical cord?

20% chance of cardiac or other vascular defects

Tears in amnion result in amniotic bands

May encircle part of fetus and result in amputations, constrictions, and other defects