7.2 Foetal Physiology Flashcards
What acts as the organ of respiration for the developing foetus?
The placenta
How does the placenta establish connection between mother and foetus?
It attaches to the uterine wall and establishes connection between mother and foetus via the umbilical cord
What are the core functions of the placenta?
Provides nutrition, gas exchange, waste removal, a source of hematopoietic stem cells, endocrine and immune support
What are the two different surfaces of the placenta?
1) the maternal surface ➞ facing the towards the outside
2) the foetal surface ➞ facing towards the inside (or the foetus)
What is found on the foetal surface of the placenta?
1) the umbilical cord (link between the placenta and fetus) near the center of the organ. Contains the umbilical veins and arteries
2) amniotic membrane
What gives the foetal side of the placenta the shiny appearance?
It is covered by the amniotic membrane
What is the function of the amniotic membrane?
Secretes amniotic fluid which contains cells from foetus and amnion which high in protein ➞ this is swallowed by the foetus
It functions to:
- protect/cushion against the walls of the uterus
- maintain pressures and temperatures
- allows space for foetal growth
- protects against infection
What is found underlying the amnion?
What is this + describe its stucture
The chorion ➞ a thicker membrane that is a structure of the placenta, continuous with the lining of the uterine wall.
Emerging from the chorion are the villi containing a system of foetal capillaries to allow maximum contact area with the maternal blood (also known as the intervillous space) for gas, nutrient and waste exchange.
What is the intervillous space?
Villi emerging from the chorion (located below the amnion) that contain a system of foetal capillaries that allow maximum contact with maternal blood for gas, nutrient and waste exchange
What comprises the maternal surface of the placenta during pregnancy?
Previous to pregnancy what is this structure more commonly known as?
What appearance does this give the placenta
It Is composed of the decidua (what is known as the uterine lining during pregnancy)
Previous to pregnancy the decidua is more commonly known as the endometrial lining of the uterus.
It is this portion that gives this structure a dark red, blood like appearance.
What gives the maternal side of the placenta the dark red, blood like appearance?
The Decidua
Describe the specific structure of the Decidua (include all 5 layers)
Different portions to the decidua have specific names according to their location and function:
- decidua capsularis
- decidua basalis
- decidua placentalis
- decidua vera
- decidua parietalis
What other features are visible on the maternal side of the placenta?
15-20 lobules called cotyledons which are divided by deep channels known as sulci
Each individual lobule is divided into smaller sections containing one villi ➞ These villi are the same ones emerging from the chorion
These villi contain foetal capillaries, which bathe in the intervillous space
Explain how foetal and maternal blood mix?
TRICK QUESTION!!! foetal and maternal blood NEVER mix
How does O2 diffusion take place across the placenta from maternal blood?
The Barrier is small due to the foetal villi in contact with maternal blood
A gradient of partial pressures must be formed (Bohr effect):
• Maternal pO2 increases
• Umbilical venous pO2 is much lower
As the maternal blood has higher O2 and lower CO2 ➞ this creates pressure gradient which favours oxygen transfer to foetal circulation
What determines the O2 transport RATE across the placenta?
determined by umbilical arterial pO2
List 4 factors that can influence the maternal and foetal circulations
1) blood pressure
2) medication
3) uterine contractions
4) hormones
1) Describe the levels of CO2 in the foetus and the mother
2) What acid/base changes are created through the diffusion of CO2 across placenta and how is this corrected
3) How do these changes facilitate uptake of O2 by foetus?
1) Foetus cannot tolerate higher pCO2 than mother. Hence, the mother has lower pCO2 which facilitates placental transfer of CO2 from foetus into maternal blood
2) The raised CO2 in the mother causes local acidosis, hence hyperventilation is stimulated by progesterone to maintain acid/base balance
3) The decreasing pH causes maternal Hb to have a lesser affinity for O2, enhancing placental transfer of maternal O2 offloading to foetus (increase in foetal pH due to removal of CO2 also facilitates uptake of O2)
What is the structure of HbF + 3 comparisons of this to adult Hb
What is the overall effect of this?
HbF: 2α2γ
- low affinity for organic phosphates (2,3 DPG and ATP)
- higher affinity for O2 than adult Hb
- higher concentration
Favour rapid uptake of oxygen by foetus across the placenta at low PO2 levels
What stimulates hyperventilation during pregnancy?
Progesterone
ETA 1 recap
1) What is the Bohr effect?
2) describe the effect of increased temp, 2,3 BPG, pCO2 and H+ on the curve
3) What are the X and Y axis?
1) The extent to which haemoglobin can be saturated with oxygen and how it is affected by [H+], temperature and CO2
2) O2 dissociation curve is shifted to right by increased [H+], PCO2 and temperature
3) X axis = pO2, Y axis = %Hb saturation
Explain the Bohr effect in terms of foetal and maternal O2 (include the shift)
Increased deoxygenated blood arriving in placenta (from foetus) favours release of maternal oxygen into fetoplacental bed because of higher concentration of HbF + other adaptations)
O2 dissociation curve of foetal RBC’s is shifted to the left compared to adult Hb
Where does the umbilical cord emerge and end up?
What is contained within the cord?
Emerges from the foetal side of the placenta to the belly button region of the fetus (0 to 60cm length and 2 to 3cm width)
Contains 2 arteries and 1 vein that are in continuation with the foetal circulation
Describe the pathway of BF through the adult heart (include arteries, veins and valves)
SVC ➞ RA ➞ tricuspid valve ➞ RV ➞pulmonary valve ➞ pulmonary artery ➞ lungs ➞ pulmonary vein ➞LA ➞ mitral valve ➞ LV ➞ aortic valve ➞ aorta ➞ rest of body
