What theory encompasses the idea that living organisms today are made of cells and arise from preexisting cells?

Cellular Theory Defined Living cells can come only from other pre-existing cells.Modern cell theory adds two additional points.Cells contain and pass on hereditary information during cell division.All cells are relatively the same in relation to chemical composition and metabolic activity.

explanation:

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.