This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Which of the following would be expected to contain relatively high numbers of functional hematopoietic cells? 
Select and explain. 
A. Adult liver, B. Umbilical cord blood, C. Adult circulating blood, D. Adult spleen
B: Umbilical cord blood
Answer: B: Umbilical cord blood 
Explanation: Ans. B. Umbilical cord blooda. Umbilical cord blood, derived from the circulating blood of newborn infants, possesses high levels of hematopoietic progenitors.b. Levels of circulating progenitors rapidly decrease after birth, depleting the progenitor content within the circulating blood of adults.c. The spleen of adult human's functions as a hematopoietic organ in certain disease states, such as leukemia.d. However, in other animals and in developing human fetuses, the spleen plays an important role in the hematopoietic response.e. While the liver and the thymus are important in hematopoiesis and immune reconstitution prior to birth, these organs are not involved in hematopoiesis in adult humans.