Mother & Baby

By Amanda Diaz

2002b(16)/1999a(1): Explain the Bohr and Haldane effects in transplacental gas exchange General: Placenta functions as gas exchange unit for the fetus

- Removes CO2 from fetal to maternal circulations - Transfers O2 from maternal to fetal circulations

Obeys Fick’s Law of Diffusion - Less efficient diffusion → ↓surface area placenta, ↑diffusion distance,

↓solubility coefficient Aim of Bohr & Haldane Effects: ↑O2 transfer to fetus and removal of CO2 waste The Bohr Effect: ↑pCO2 will facilitate offloading of O2 and formation of deoxyHb. Also facilitated by ↓pH, ↑T°C, 2,3DPG → Right shift; ↑pH / ↓pCO2 → Left shift Fetal Circulation

- Umbilical artery → high pCO2 (52mmHg)

- Placenta → CO2 diffuses across maternal uterine artery down its conc gradient (PaCO2 32mmHg)

- ↓pCO2 in fetal blood causes a left-shift in fetal OHDC → ↑O2 affinity of Hb → ↑O2 transfer

Maternal Circulation - ↑pCO2 of maternal blood from

diffusion from placenta → right-shift maternal OHDC → ↑offloading of O2 → Bohr Effect

Combined, opposite movements of maternal and fetal OHDC enhancing fetal O2 transfer known as Double Bohr Effect The Haldane Effect: DeoxyHb has a higher affinity for CO2 than oxyHb Maternal Circulation

- As O2 offloaded → the more basic deoxyHb has ↑CO2 carrying capacity as carbaminoHb (70% of Haldane) and H+ buffered by imidazole moieties on histidine residues (30% Haldane) → ↑CO2 content of maternal blood (52ml/100ml blood) with minimal change in tension (45mmHg)

Fetal Circulation - As O2 transferred across → ↑OxyHb, ↓Hb affinity for CO2 → enhanced

offloading from fetal Hb Double Haldane Effect