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, pO2=95 mmHg. (Ref. to Fig. 14.2) 
Caution Pulmonary artery takes deoxygenated blood carries oxygenated blood from lungs to from heart to lungs, while pulmonary vein heart. Related Theory (Ref. to Fig. 14.3)
