Final answer:
The immature erythrocytes in circulation are known as reticulocytes. They are an intermediate stage that eventually matures into fully functional erythrocytes. Macrophages are responsible for removing aging and damaged erythrocytes from the circulation.
Step-by-step explanation:
The immature erythrocytes present in the circulation are known as reticulocytes. Reticulocytes are the developmental stage of red blood cells (RBCs) that comes after the proerythroblast stage and before becoming fully mature erythrocytes. As they mature in the red bone marrow, they eject their nucleus and most other organelles. When reticulocytes are released into the bloodstream, they still contain remnants of organelles, such as reticulum of ribosomes, but these are quickly shed. These cells circulate for about 1-2 days before maturing into erythrocytes which do not have a nucleus and rely on anaerobic respiration due to the absence of mitochondria. Aging and damaged erythrocytes are removed from the circulation by macrophages, not myeloblasts, monocytes, or mast cells. This process helps to maintain the health of the circulatory system by ensuring that only functional erythrocytes are present to transport oxygen.