Pregnancy & Embryonic Development

Prenatal development

encompasses time period of these events:

fertilization of an egg cell; implantation of zygote in the uterus; multiple cell divisions to initiate growth and directionality of embryo; development of embryo into the fetus; maturation of organ systems in the fetal body; to the point of birth

Gestation

desribes this period of prenatal development

Gestation, in humans, takes place over course of

40 weeks, about 9 months

Prenatal development is divided into:

3 trimesters (each one is 3 months in duration)

In the first trimester:

major germ layers are created and internal “scaffolding” of embryo is created

the germ layers give rise to all major tissues of the body (cardiovascular structures, skin, nervous tissue, etc)

In the second trimester:

there is continued development of major organs and organ systems. The embryo starts to look like a human body

In third trimester:

there is significant growth of body and its systems. these organs start to become functional

The _____ trimester is the period during which the viability of the embryo is most vulnerable.

first; only 40% of conceptions survive during this period.

________ is a key step that occurs during the first trimester

Gastrulation

Gastrulation involves a series of steps to create major germ layers

These germ layers ultimately create the major tissues and organs of the body. Directionality of the embryonic body is also established here.

During gastrulation, 3 germ layers created are:

ectoderm; mesoderm; endoderm

_____ develops during the first trimester

Placenta

Umbilical cord physically connects

embryonic/fetal body with the placenta

Placenta is physically adjacent to the

uterine wall in the mothers body

Umbilical cord contains multiple blood vessels

Inside umbilical cord, there are ____ umbilical vein and ____ umbilical arteries

1 vein; 1 arteries

The umbilical ____ carries O2 and nutrient rich blood away from mother/placenta and carries that blood into the fetal body

vein

the umbilical ____ carry the waste blood and O2 poor blood out of the fetal body and bring this blood back to the placenta so that it can be replenished w O2 and nutrients

arteries

Umbilical blood vessels enter and exit the fetal body at the

umbilicus (belly button)

In the fetal body, there are also bypasses (shortcuts) that exist in the fetal heart and the liver. In the fetal heart, the blood largely bypasses the fetal lungs.

Remember that the fetus is in a liquid environment. There is no mechanical breathing taking place in the fetal lungs. Gas and nutrient exchange is taking place at the interface between the uterine wall and the placenta. It is not necessary in the fetal body to send a significant amount of blood towards the lungs. That is why these bypasses exist. After birth, however, these bypasses should seal off. This then forces blood to enter into the newborn’s lungs.

Amnion

holds in the amniotic fluid surrounding the fetus

for a woman in labor, when her water breaks, it indicates that the amnion has torn allowing the fluid to escape.

Note: the mucus plug that forms at the base of the uterus to serve to prevent entry of bacteria into uterus

organogenesis

process of organ formation during 1st trimester

Organ maturation

takes place during 2nd and 3rd trimester

By birth, most organs have formed but are still maturing

the lungs tend to be the last organs to mature

uterus will increase in length; by time the pregnancy is full term, the uterus and its contents will weigh ~ 22 pounds (avg)

Mothers digestive organs remain active, but they have been displaced upwards because of expansion of uterus

urinary bladder in mother’s body will be pushed down upon by the expanded uterus. that is, the bladder is pushed in the ____ direction. this is why prego women feel urge to urinate so much.

inferior

technical term for labor is

parturition

labor involves a series of strong, rhythmic contractions of the uterine wall. the goal of labor is the expulsion of fetus

labor occurs in 3 stages:

In order:

1. dilation stage

2. expulsion stage

3. placental stage

Dilation stage

The cervix dilates, the fetus is pushed by muscular contractions into the cervical canal, and the amnion ruptures – water breaking

Expulsion stage

• The movement of the fetus through the cervical canal and vagina

• Delivery can be helped by episiotomy or cesarian section

Placental stage

Ejection of the placenta (afterbirth)

Amnion tears during

dilation stage (water breaking)

Fetus emerges during

expulsion stage

Placenta emerges during

placental stage (after birth)

Premature labor refers to

labor that begins prior to full development being reached.

Fetusus born prior to 36/37 weeks are considered to be premature. In this case, these babies will survive provided they receive adequate medical care. Fetuses born before 24 weeks will usually not survive because organ systems have not developed enough to sustain life outside the womb.

The first month after birth is referred to as

neonatal period

During neonatal period, following should occur in the newborn’s body

• lungs will fill w air

• breathing commences

• heart bypasses (shortcuts) should slowly begin to seal shut

• HR should drop to ~80-130 bmp

• digestive organs start working

• kidneys become active and start filtering the blood

• metabolism increases to sustain adequate warmth for the newborn