medical Definition of organelle : a specialized cellular part (as a mitochondrion or nucleus) that has a specific function and is considered analogous to an organ Learn More about organelle
RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through the body's capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells.ed blood cells are also known as RBCs, red cells, red blood corpuscles (an archaic term), haematids, erythroid cells or erythrocytes (from Greek erythros for red and kytos for hollow vessel, with-cyte translated as cell in modern usage).
Capillaries are so small that red blood cells can only travel through them in single file. Capillaries measure in size from about 5-10 microns in diameter. Capillary walls are thin and are composed of endothelium (a type of simple squamous epithelial tissue). Gasses, nutrients, and wastes are also exchanged at this point. 2  On the venule end of the capillary bed, blood pressure in the vessel is less than the osmotic pressure of the blood in the vessel. 3  The net result is that fluid, carbon dioxide and wastes are drawn from the body tissue into the capillary vessel.