The figure shows blood circulation in humans with labels a to b....

a- Artery- Carry blood from heart to body parts. It is thick walled and elastic, under high blood pressure. b- Capillary- thin walled, with only one layer, facilitates the diffusion of nutrients, gases, etc., into tissues c- Vein - thin walled, brings blood from body parts to heart, act as low resistance conduct for blood flow. d- Pulmonary vein-take oxygenated blood to heart, $p \mathrm{O}_2=95 \mathrm{ mm} \mathrm{Hg} . (Ref. to Fig. 14.2) Caution Pulmonary artery takes deoxygenated blood$\quad$carries oxygenated blood from lungs to from heart to lungs, while pulmonary vein heart. \text{ Related Theory } (Ref. to Fig. 14.3)$