Final answer:
The second major site for bone marrow study in adults is the region near the iliac crest of the pelvic bones due to its accessibility for red bone marrow sampling, despite the procedure being painful. Alternatives to direct bone marrow extraction include isolating stem cells from the patient's blood.
Step-by-step explanation:
The second major site for studying bone marrow in adults. The second major site to study bone marrow in adults is the region near the iliac crest of the pelvic bones (os coxae). In addition to being a site where red bone marrow is present, the iliac crest is chosen because it is more accessible, close to the body surface, and relatively isolated from vital organs. However, the process of obtaining bone marrow from the iliac crest can be quite painful, which is why newer techniques involving the extraction of stem cells from blood are becoming more common. Red bone marrow is essential for the production and differentiation of the formed elements of blood, such as erythrocytes, leukocytes, and platelets.
While the femur is a known site for studying red bone marrow, the iliac crest serves as an alternative location, specifically because red bone marrow can be found in the flat bones of the body like the ilium and the scapula. The sampling of bone marrow has traditionally been done from the iliac crest, but current practices often allow for the avoidance of direct sampling through the isolation of stem cells from patient blood samples. The second major site to study bone marrow in adults is the spleen. In the embryo, blood cells are made in the yolk sac, and as development proceeds, this function is taken over by the spleen, lymph nodes, and liver. Later in adulthood, the liver and spleen maintain their ability to generate the elements.