▁body ▁in ▁order ▁to ▁facil itate ▁the ▁transfer ▁of ▁g ases ▁between ▁blood ▁and ▁al ve olar ▁air , ▁and ▁the ▁type ▁II ▁cells ▁are ▁typically ▁found ▁at ▁the ▁blood - air ▁bar rier . ▁▁ ▁Type ▁II ▁cells ▁start ▁to ▁develop ▁at ▁about ▁ 2 6 ▁weeks ▁of ▁gest ation , ▁secre ting ▁small ▁amounts ▁of ▁sur fact ant . ▁However , ▁ade qu ate ▁amounts ▁of ▁sur fact ant ▁are ▁not ▁secret ed ▁until ▁about ▁ 3 5 ▁weeks ▁of ▁gest ation ▁– ▁this ▁is ▁the ▁main ▁reason ▁for ▁increased ▁rates ▁of ▁infant ▁resp ir atory ▁dist ress ▁synd rome , ▁which ▁dr ast ically ▁reduces ▁at ▁ages ▁above ▁ 3 5 ▁weeks ▁gest ation . ▁ ▁Type ▁II ▁cells ▁are ▁also ▁capable ▁of ▁cell ular ▁division , ▁giving ▁rise ▁to ▁more ▁type ▁I ▁and ▁II ▁al ve olar ▁cells ▁when ▁the ▁lung ▁t issue ▁is ▁dam aged . ▁▁ ▁M UC 1 , ▁a ▁human ▁gene ▁associated ▁with ▁type ▁II ▁p neum ocy tes , ▁has ▁been ▁identified ▁as ▁a ▁marker ▁in ▁lung ▁cancer . ▁ ▁Al ve olar ▁macro ph ages ▁The ▁al ve olar ▁macro ph ages ▁res ide ▁on ▁the ▁internal ▁l umen al ▁surfaces ▁of ▁the ▁al ve oli , ▁the ▁al ve olar ▁du ct s , ▁and ▁the ▁bron chi oles . ▁They ▁are ▁mobile ▁sc av engers ▁that ▁serve ▁to ▁eng ulf ▁foreign ▁particles ▁in ▁the ▁l ungs , ▁such ▁as ▁dust , ▁b acter ia , ▁carbon ▁particles , ▁and ▁blood ▁cells