Minor Calyces are wide tube like projections present on apex of every Renal Medullary Pyramid. They are lined by epithelium as well as smooth muscle cells in their walls allowing them to contract.
Major Calyces are still wider tubes formed by two or three minor calyces. Its wall also contains smooth muscle cells.
Calyces contract rhythmically towards Renal Pelvis, by the help of smooth muscles, thus push the urine towards it and out of the Pyramids in Renal Medulla.
Due to constant insult by waste material tumors can arise in Renal Calyces. Hence cancers arise in this part of kidney more frequently.