now the medullary cavity is also called the marrow cavity however on a lab exam you should make sure that you label it medullary cavity okay now this is going to be a hollow cylindrical space that's found in the diaphysis of long bones it's going to contain fat or bone marrow and then blood vessels now when this marrow is red marrow its function is hematopoiesis or blood cell production all right you mainly will see that in infants or the fetus okay um when this marrow is yellow which is after birth and adults it's going to store triglycerides or fats all right but it can be converted to red marrow if a person needs more blood cells alright so once the crisis is over the red marrow converts back to Yellow marrow the function of this medullary cavity is really to minimize the weight of the bone by reducing the dense bony material where it's not needed so this design in in the engineering of the long bone will provide maximum strength but with minimum weight now the other thing to remember is is this is kind of a clinical something clinical that you'll want to remember remember how I said it has fatty marrow all right what can happen let's say that somebody breaks this bone and fractures it okay if you fracture this bone sometimes those little Globs of fat can break off and they can enter the blood vessels and travel through the blood vessels toward the lungs okay and if they do this they can actually get lodged in the lungs and this would be called a fatty emboli so if you've ever heard of um like a pulmonary embolism all right pulmonary embolisms can be more than just blood clots they can be air they can be a catheter that gets lodged maybe like an IV catheter that breaks off and travels and gets lodged in the lung and it can also be a fatty emboli as a result of a long bone fracture okay so that's just a clinical Pearl that you should know