<prompt> What is a placental cotyledon?All branches from one stem villiArea supplied by one spiral aeryQuaer of placentaArea drained by one terminal villi  <response>: Each of the truncal or main stem villi and their ramifications constitutes a placental lobule or cotyledon. Each lobule is supplied with a single truncal branch of chronic aery. And each lobule has a single vein so that lobules constitute functional units of placental architecture. Ref: Williams 24e pg 94. 