Week 4 Conception and Prenatal Development Flashcards
When is the preembryonic peroid?
The first two weeks after conception
The fertilized ovum is considered a ____ after the 4th day and enters the ___
Zygote
uterus
When the zygote divides into 16 cells it is considered a ___
Morula
What stage comes after the morula? how is this formed?
the blastocyst. The outter cells of the morula secrete fluids that divide the morula into and inner and outer cell mass
How does the zygote maintain itself in the uterus
It moves to the uterus during the secretory phase of the mestral cycle
-it then releases hormones that signal pregnancy and the uterus stays in this phases allowing for more nutrients and blood flow
what hormone is released by the conceptus that causes the corpus luteum to persist?
human chorionic gonadotropin
hCG
Why is the site of implantation important?
Because it is where the placenta develops
Where does normal implantation occur?
the upper uterus
Why is the upper uterus the ideal place for implantation?
- Rich supply of blood
- Think lining
- limits blood loss after birth
Explain the mechanism of implantation
the conceptus produces corrosive enzymes that erode the decidua
-chorionic villi project into the surface of the decidua
How many days after fertilization does implantation fully occur?
10days
What is a common reason for women to think they are not pregnant during the time of their next mestral period after conception?
The implantation of the concepus may cause a small amount of spotting that can be confused with a normal menstral period
When does the embryonic period start/end?
Beginning of the third week through the eight wek after conception
What occurs duing the embryonic period?
Basic structures of all major body organs are completed and are in place
When is the fetus most vulnerable for teratogens? Why is this?
-The embryonic period
Because all the major body systems are developing at a rapid rate. If one system is affected by a teratogen than it can cascade and cause a multi system issue
Explain the direction of growth during the embryonic stage
- Cephalocaudal
- Central-to-peripheral
- simple to complex
- General to specific
An infant if considered full term __ weeks after conception and ___ weeks after last menstrual period
36-40
38-42
Most women miss their period after __ weeks
3
Describe the neural tube at 3 weeks?
Open at both ends
When does the primitive/tubular heart begin beating?
22-23 days
When does the neural tube close?
during the 4th week
What happens if the neural tube does not close?
defects such as anencephaly and spinal bifida results
The cranial end of the neural tube forms the ___ and the caudal end forms the ___
Brain
Spinal cord
When does the infant heart develop its 4 chambers and begin beating?
during the 4th week
During what period in fetal development is the fetus at risk for developing a neural type defect?
The embryonic period because the neural tube is still open n the earlier weeks of this stage
When does the pituitary gland a cranial nerves develop?
Week 6
why is the head sharply flexed during week 6?
Rapid brain growth
Describe the spinal cord during week 8
It stops at the end of the vertebral column
When is the heart beat first detectable via ultrasound?
week 8
When does the fetal period start/end?
Weeks 9-birth
When does the fetal digestive tract become patent?
week 10
When should a fetal heart beat be detectable by doppler transducer?
week 12
When does the sucking reflex begin?
week 12
When do the fetal kidneys begin producing urine?
week 12
When does lanugo begin to develop?
week 12
When is the fetal face “human looking”
week 16
When does the fetus begin to excrete urine into the AF
week 16
when does the fetus produce its first meconium. What is the food source?
week 16
swallows AF
When should a woman who has been pregnant before begin to feel fetal movements?
What is this called
week 16
-quickening
When is the fetal heart beat detectable using a regular fetoscope?
week 20
When are fetal movements often felt by all mothers and experienced examiners?
week 20
When is brown fat production complete?
week 20
When does surfactant production begin?
week 20
When do surfactant levels become high enough to support life
26-28 weeks after conception
When does surfactant production reach its peak?
the last 2 weeks of preg
When is the earliest survivable birth?
24 weeks
When is the fetus considered active?
24 weeks
When do fetal movements become progressively more noticeable?
24 weeks
When does the CNS mature?
weeks 25-28
When do the lungs mature?
weeks 25-28
When do the pulmonary capillaries mature?
Week 25-28
When does the fetus assume a head down positon?
Why?
Weeks 25-28
-Because the uterus is shaped like an inverted egg and the fetal head is heavy and gravity pulls it down
When does surfactant reach near mature levels?
week 32
When are the sympathetic and para-sympathetic NS near maturity?
Weeks 29-32
With the maturation of the sym and para-sym nervous systems, what occurs? When does this occur?
Variability on the EFM
-weeks 29-32
when is the pulmonary system matured enough to enable efficient and unlabored breathing?
weeks 33-38
Where does the exchange of substances between mother and baby occur?
the intervillous space
How much of the mothers blood is in the intervillious space?
150ml
What is the circulation rate of the intervillous space?
450-750 ml per minute
The decidua contains ___ to ___ spiral arteries
80-100
What is the key function of the placenta?
Respiration
How does oxygen and carbon dioxide pass through the placenta?
diffusion
What are the three reasons the fetus can survive in such a low O2 environment?
- Fetal Hgb is 20-50% mor efficent
- fetal blood has more hgb
- Hbg is more efficent at lower levels of CO2. Fetal blood entering the placenta is higher in CO2 and diffuses rapidly out of the placent into the mother blood stream. This makes the fetal blood alkaline and more efficent at absorbing O2
What 4 nutrient types can pass directly across the placenta?
Glucose, fatty acids, vitamins, and elecrtolytes
What is the major fuel source for fetal growth and metabolic activities?
Glucose
Why are infant metabolic defects often not detected until after delivery?
Because the placenta removes wasts from the fetal blood stream, causing the waste buildup to only happen after the placenta is no longer a player
What antibodies pass the placenta?
IgG
What are the three main hormones produced by the placenta?
- Estrogen
- Progesterone
- Human Placental Lactogen
What is the function of Human Placental Lactogen?
- Promotes normal nutrition and growth of the fetus
- Causes maternal breast development for lactation
- Decrease maternal insulin sensitivity and glucose use (making more available for baby)
What is the function of estrogen produced by the placenta?
-Enlargement of the mothers uterus, breasts, ductal systems, and external genitalia
What is the function of pregesterone produced by the placenta?
- Maintains uterine conditions for preg.
- Modifies and maintains the endometrium to receive the conceptus and form the decidua
- Reduces muscle contractions of the uterus to prevent spontaneous abortons
What is the function of amniotic fluid?
Protection of the fetus and promotion of normal development
How does AF protect the fetus?
- Cushioning against impacts
- Maintains temp
How does AF promote normal development?
- Allows symmetric development
- Prevents membranes from adhering to developmental fetal parts
- Allows room and buoyancy for fetal movements
What is Oligohydramnios?
An abnormally small quantity of AF (less than 50% expected or under 400mL at term)
What is a normal approx amount of AF at term?
700-800ml
What are some causes of Oligohydramnios?
- Poor placental perfusion
- PPROM
- Poor fetal kidney development
- Blocked urinary excretion
- Poor fetal lung development
- Malformations from fetal compression
What is polyhydraminos?
AF exceeding 200ml
What are some causes of polyhydraminos?
- Imblanaced water exchange of an unknown cause
- Poorly controlled maternal DM resulting on fetal polyuria
- Malformations of the CNS, CV, or Gi tract that interfere with ingestion, metabolism, or excretion
- chromosomal abnormalities
- Multifetal gestation
Why has multifetal pregnancies increased in the US?
Increasing maternal age
What are the two types of twins?
Monozygomatic
Dizygotic
