Lecture 7.2: Foetal Physiology Flashcards
How does placenta connect to and from the foetus?
Umbilical Chord
What embryonic layer is placenta derived from?
Trophoblast
Roles of the Placenta (4)
- Nutrition
- Gas Exchange
- Waste Removal
- Source of hematopoietic stem cells, endocrine and
immune support
What Hormones does the Placenta produce? (7)
- HCG
- HPL
- Oestrogen
- Progesterone
- Thyrotropin
- Corticotropin
- Relaxin
What is the diameter, thickness and weight of the Placenta?
- 20cm in diameter
- 2.5cm thick
- Average weight of 600g
What are the 2 surfaces of the Placenta?
- Maternal surface, attached to the uterine wall
- Foetal surface, facing towards the amniotic cavity
within which is the foetus
What is the Decidua?
It is the uterine lining during pregnancy. In the non-pregnant uterus the decidua is known as the endometrium
The portion of the decidua associated with the placenta is called the….?
Decidua basalis/placentalis
What is the length and width of the umbilical chord?
- 50 to 60 cm long
- Width of 2 to 3 cm
What does the umbilical cord contain? (4)
- 2 arteries carrying deoxygenated blood
- 1 umbilical vein carrying oxygenated blood back to the
baby - Which are surrounded by Wharton’s jelly
Shape of Umbilical Chord
- These vessels are longer then the cord
- Tend to twist and spiral to add strength and protect
against entanglement, compression and tension
Foetal umbilical pO2 must be …. than maternal pO2
lower
Uterine blood flow can be influenced by? (4)
- Maternal Blood Pressure
- Medication
- Uterine Contractions
- Hormones
Foetal Hb dissociation curve is to the left of adult Hb, what does this mean?
Higher affinity for oxygen
Foetal Hb has lower affinity for …… which results in higher O2 affinity
2,3 DPG
CO2 passively diffuses from foetal to maternal side, this results in ….?
Local acidosis
What is the effect of local acidosis?
- Reduces the oxygen affinity of maternal Hb and
oxygen is released to the diffuse to the foetal side and
to the foetal Hb - This is the Bohr effect
Foetal Umbilical Vein carries oxygenated blood from the
placenta to the foetus at what saturation?
70%
Foetal Blood Flow: Umbilical Vein to Heart (6 Steps)
- The foetal Umbilical Vein carries oxygenated blood.
placenta to the fetus - The Ductus Venosus receives oxygenated blood from
the umbilical vein - Directs it to the inferior vena cava and then to the
RA, open ductus venosus acts to bypass the liver - The oxygenated blood goes from IVC into the R-atrium
- Oxygenated Blood flows from right atrium through the
foramen ovale to the left atrium, thus oxygenated
blood bypasses the lungs - The oxygenated blood goes from LA to LV and then
aorta to the brain and upper limbs at about 60%
saturated
Foetal Blood Flow: Brain back to Heart (6 Steps)
- Blood Returns from head/brain/upper limbs in the SVC
at 30% saturated - From SVC the blood goes to RA and mixes with a little
oxygenated blood (from IVC) in RA and so passes from
RA to RV at 50% saturated - The blood goes from RV to Pulmonary Artery, but 4/5
of this blood goes to the ductus arteriosus (bypasses
lungs) - Then goes to the arch of Aorta distal to the origin of
the left subclavian artery - Then down the descending aorta, supplying bowel,
kidneys and lower limbs and also to the internal iliac
arteries to the two umbilical arteries back to the
placenta - Some mixing occurs at ductus arteriosus and in the
descending Aorta blood is 60% saturated
What structures are visible on the maternal surface of the placenta?
- 15 to 20 polygonal cotyledons, each with 10 to 20
lobules - They are divided by deep septae of the decidua which
also divides up the intervillous space
What form pools of maternal blood in intervillous spaces?
c.200 Branches of the maternal uterine arteries enter each lobule of the space between the chorionic and decidual plates
What is the foetal surface of the placenta covered in?
Covered by the shiny amniotic membrane
The chorionic plate is made up of…?
The amnion and chorion and forms the boundary of the foetal portion of the placenta
What plate forms the boundary of the maternal side of the placenta?
The decidual plate
What lies between the chorionic and decidual plate?
Intervillous spaces
What is in the intervillous space?
Lakes/lacunae of maternal blood
What from the foetus grow into the intervillous lakes of maternal blood?
The arborescent fetal villous trees
Should there be direct contact/connection between the foetal and maternal circulations?
No
What stimulates the the baby to breath in once it’s born?
Physical, thermal and chemical stimuli that occur just prior and during birth
Why does the foramen ovale close after the baby takes its first breath? (5)
- The lungs inflate, fill with air and are quickly emptied of
fluid - This causes a decrease in pulmonary vascular
resistance allowing greater pulmonary blood flow and
oxygenation - Therefore an increase in oxygen tension
- The increased pulmonary blood flow and pulmonary
venous return leads to increase in left atrial pressure - Causing the foramen ovale to close
What causes the ductus arteriosus to close soon after birth?
Response to increased oxygen tension and reduced prostaglandins (metabolised in pulmonary circulation)
What causes the ductus venosus to close soon after birth?
The umbilical cord is cut, the arteries go into spasm and the blood flow in the umbilical vein stops and the ductus venosus closes
What does the Foramen Ovale become?
Fossa ovalis
What does the ductus arteriosus become?
Ligamentum arteriosum
What does the ductus venosus become?
Ligamentum venosum
What does the umbilical vein become?
Ligamentum teres
What do the umbilical arteries become? (2)
- Medial umbilical ligaments
- Superior vesicle arteries to bladder
What cells produce Surfactant?
Alveolar type II cells/Pneumocytes
Surfactant production begins from week….?
24
What does surfactant do in the newborns lungs?
Reduces surface tension at the air-fluid interface on the surface of the alveoli allowing the alveoli to open easily and also stops the alveoli from collapsing. Therefore, the work of breathing is reduced.
Earlier production of surfactant can occur as a result of..?
“Stress” such as an event(s) that may be leading to premature delivery
Administration of …… to a mother with threatened premature delivery is very useful in increasing foetal surfactant production
Steroids
