Physiology

Question 1

Gestational Age

Answer 1

The time from the Mother’s first day of the last menstrual period, including the two weeks of fertilisation = Embryonic Age +2 weeks
- Full term in this timeline = 40 weeks

Question 2

Embryonic Age

Answer 2

The time from fertilisation/conception = minus 2 weeks from Gestational age

Question 3

Chronological Age

Answer 3

The time from birth (Ex: 2 days old)

Question 4

Post-Menstrual Age (PMA)

Answer 4

Gestational Age + Chronological Age (to account for prematurity or delayed delivery)
- Ex: 35 week pregnancy and the baby is 2 weeks old = 37 week old baby in PMA

Question 5

What gestational age is considered extremely premature?

Answer 5

24-27 weeks

Question 6

What gestational age is considered very premature?

Answer 6

28-30 weeks

Question 7

What gestational age is considered moderately premature?

Answer 7

31-33 weeks

Question 8

What gestational age is considered late premature?

Answer 8

34-36 weeks

Question 9

What gestational age is considered full term?

Answer 9

37-40 weeks

Question 10

Brain development stages from first trimester through to third

Answer 10

First trimester (0-12 weeks):
- Neural tube formation (initial structure that eventually becomes the brain and spinal cord)
- Neuronal proliferation (neural tube begins to produce neurons)
Second trimester (13-26 weeks):
- Neural migration (new neurons migrate to their correct position in the brain)
- Differentiation (neurons take on specialised roles ex: sensory/motor, etc.)
- Cortical development (outer layer of brain develops)
Third trimester (27-40 weeks):
- Synaptogenesis (neurons form synapses so they can communicate w/ each other)
- Myelination initiation (myelin forms allowing more efficient communication)
- Establishment of neural networks (complex networks form that allow movement, breathing, etc.)

Question 11

Foetal circulation from placenta to ascending aorta

Answer 11

Placenta → ductus venosus → IVC → RA → foramen ovale → LA → LV → ascending aorta.
- Oxygenated blood to the upper body (brain, heart, upper limbs)
- Bypassing the lungs via foramen ovale
- Bypassing the liver via ductus venosus
- 50% blood from umbilical vein enters ductus venosus → IVC
- 50% blood from umbilical vein enters liver → IVC via hepatic veins

Question 12

Foetal circulation from placenta to descending aorta

Answer 12

Placenta → ductus venosus → IVC → RA → RV → pulmonary trunk → ductus arteriosus → descending aorta

Question 13

Ductus Venosus

Answer 13

Shunt that allows (50%) blood to bypass the liver and enter straight into the IVC from the umbilical vein.
- Liver is still developing so oxygenation is prioritised toward the brain instead
- Features a sphincter to control umbilical venous pressures before entering the heart (especially during contractions)
- Blood in umbilical vein is highly oxygenated & mixes with deoxygenated blood when it passes the ductus venosus and enters the IVC, still primarily oxygenated from there
- Most blood then enters RA → RV → descending aorta via the ductus arteriosus
- Some blood enters the RA → LA via foramen ovale → LV → ascending aorta so blood can get to the brain

Question 14

O2 levels in ascending v descending aorta

Answer 14

Ascending aorta supplies the brain, heart, upper limbs, so is highly oxygenated.
Descending aorta supplies the lower limbs (35%) and returns to the placenta (65%) via umbilical arteries so has medium O2 content