the body responds to blood loss by hematopoiesis. This occurs by upregulating transferrin (an iron transporter in the blood), erythropoietin production (a hormone made exclusively in the renal peritubular interstitial cells), and heme synthesis. First step of heme synthesis was actually alluded to in another question on this test: condensation of glycine and succinyl CoA into delta-aminolevulinate. This is rate-limiting step of heme synthesis.

not EPO bc it's asking what's made from the bone marrow. EPO is from kidney

If anyone was wondering about Ferritin as I was.

Iron level functions as a regulator of ferritin transcription. "when iron levels are low, ferritin synthesis is decreased; conversely, when iron levels are high, ferritin synthesis increases."

If iron is low as it would be in significant blood loss, the body would want to mobilize iron to produce heme and not sequester it. This results in decreased ferritin production and increased transferrin.

https://ashpublications.org/blood/article/99/10/3505/106937/Regulation-of-ferritin-genes-and-protein

EPO made in kidney, EPO tells the bone marrow to ramp up erythropoiesis.