Fetal Development & Fetal Membranes Flashcards
What is the amnion?
A thin but tough membrane that is filled amniotic fluid around the embryo/fetus.
What is the role of amniotic fluid?
Plays a major role in fetal development and growth
Where is amniotic fluid derived from?
Fetal urine, amniotic cells, secretion of fluid from respiratory tract.
How is the amniotic fluid removed to control volume?
Through maternal circulation
What is the function of the amniotic fluid?
Protection: fluid cushion: barrier to infection
Growth and Development: contains growth factors and swallowing amniotic fluid is necessary for normal growth, practice breathing ensures normal development of lungs
What is oligohydramnios?
Too little amniotic fluid within the amnion.
What causes oligohydramnios?
No kidney formation, no kidneys = no urine, which becomes amniotic fluid. (Renal agenesis)
Premature rupture of the membranes.
What is polyhydramnios?
Excessive amniotic fluid surrounding the fetus.
What causes polyhydramnios?
Foregut obstruction: amniotic fluid is not absorbed by the embryo.
Anencephaly: brain controls swallowing, if the brain is not developed properly then embryo cannot swallow the volume of amniotic fluid required.
What is the yolk sac?
Small membranous structure outside the embryo with various functions during embryonic development.
What is the yolk sac lined by?
Exocoelomic membrane and hypoblasts.
What do the yolk sac endoderm cells form?
Extraembryonic mesoderm.
What happens as the primary yolk sac decreases in size?
The secondary yolk sac forms.
What are the functions of the yolk sac?
Nutrient transfer,
Primordial germ cells appear in the wall of the yolk sac
What is the allantois?
Appears in the 3rd week as a diverticulum from the caudal wall of the yolk sac.
Why is the allantois important?
Early blood formation,
Blood vessels form umbilical vessels.
What does the allantois develop into?
The urachus.
What separated the cytotrophoblasts from the embryo?
The extra-embryonic mesoderm.
What does the extra-embryonic mesoderm divide into?
Extra-embryonic splanchnic mesoderm and extra-embryonic somatic mesoderm.
What does the extra-embryonic coelom become?
The chorionic cavity.
How many structures make up the chorion? What are they?
3: Extra-embryonic somatic mesoderm, syncytiotrophoblasts, cytotrophoblast core.
Where does the bushy chorion come from?
Branching and growth of the decidua basalis.
Which part forms the fetal side of the placenta?
Villous chorion
What is the placenta?
An organ that facilitates the physiological exchange of substances between mother and fetus.
What is the maternal side of the placenta divided into?
Cotyledons.
Where is the umbilical cord attached?
The chorionic plate of the fetal side.
What is transferred from the mother to the fetus?
Nutrients and oxygen.
What is transferred from the fetus to the mother?
Waste products.
What hormones does the placenta produce?
Human Chorionic Gonadotropin,
Progesterone and Estrogen.
What is the placenta barrier?
A barrier which only allows certain substances to pass to the fetus, in order to protect it.
Why do the substances the placenta barrier is formed of decrease in number?
The embryo grows and requires more nutrients so more substances need to pass through to it.
What are some placenta abnormalities?
Placenta abruption,
Placenta accrete: abnormal adherence of chorionic villi to myometrium,
Placenta percreta: penetration of villi through the full thickness of the myometrium,
Placenta praevia: low-lying placenta partially or fully covering internal os.
What do you measure in order to know the age of the fetus?
Crown rump length,
Circumference of head,
Femur length.
When is genitelia recognised?
12 to 14 weeks.
What is the fetus skin covered with during the 17 to 20 weeks?
Vernix caseosa and lanugo hair.
What is IUGR?
Gases and nutrients cannot pass from mother to fetus so limited growth.
What causes IUGR?
Smoking, Alcohol, Impaired uteroplacental blood flow, genetic factors and poor nutrition.
What are the substances of the placenta barrier at week 4?
Syncitium
Cytotrophoblasts
Connective tissue
Endothelium
What are the substances of the placenta barrier at week 16?
Synciotium
Endothelium
