These cells are only included in one model each. models a constant population of bone lining cells. They also include a dynamic parameter that describes bone lining cell differentiation into osteoblasts. This parameter varies with PTH dosage, introducing another mechanistic avenue for PTH to regulate osteoblastogenesis. The mononuclear cells modeled in remove collagen fibrils from the bone surface during resorption. The behavior of these mononuclear cells is in line with current understanding of the role that reversal cells play in bone remodeling, indicating that the so-called mononuclear cells in are reversal cells. While reversal and bone lining cells have historically been excluded, future mathematical models paired with experimental work could help provide mechanistic insights into their functions.