Igazi elithathwa ngunobuyisa womthambo i-vena cava ilisa entliziyweni ligcwele i-kharbhondioxide. I-oksijin yayo inganeno kunaleyo ikunothumela (oyi-systemic arterial blood). Icala langasekunene lentliziyo lityhala igazi elikunobuyisa kwi-pulmonary artery. Ize ke yona i-pulmonary artery ithathe igazi ilise emiphungeni. Lisakufika emiphungeni, igazi lihamba nge-pulmonary capillary bed. (Imithanjana yee-cappilaries esemiphungeni). Apha kulapho lifumana i-oksijini ethe eninzi. Kukwalapha apho ishiya khona i-kharbhondioxide eninzi. (Le nto yenzeka apha ichasene nale yenzeka kwimithanjana yee-capillary beds emzimbeni wonke. Kwi-systemic circulation igazi lishiya i-oksijini lize lithathe ikharbhondioxide).