All the circulating red blood cells in an adult originate in the

This question lacks options, options are:

A) heart.

B) thymus.

C) spleen.

D) red bone marrow.

E) lymph tissue.

The correct answer is D) red bone marrow.

All the circulating red blood cells in an adult originate in the red bone marrow.

Explanation:

Red blood cells fulfill the important function of transporting oxygen, they contain hemoglobin a substance rich in iron whose function is to transport said oxygen. Oxygen from the air is taken up by hemoglobin in the capillaries (blood vessels of a minimum thickness) of the lungs and is carried to all parts of the body inside the red blood cells to carry oxygen to all the cells of our body. The bone marrow is a type of tissue found inside the bones. It can be of two kinds: red and yellow. Blood cells are made in the red bone marrow. This process is called hematopoiesis, which is the production of blood cells from the stem cells. It is reddish in color due to the abundance of hematopoietic stem cells and immature blood cells. The hormone that regulates the formation of red blood cells is called erythropoietin and is produced in cells of the kidneys. The function of erythropoietin is to stimulate the bone marrow to form more red blood cells.