Blood Functionally Connects the Body Organ
Systems 288
• Blood is a liquid connective tissue that consists of a liquid
component called blood plasma and a cellular component
called the formed elements. Blood plasma consists mostly
of water, proteins, and other substances. As shown, the
formed elements include red blood cells, white blood cells,
and platelets.
Appearance of blood cells in a blood smear
• Figure 10.3
blood cell
blood cell
• Blood transports oxygen and carbon dioxide as well as
nutrients, heat, and waste products. It regulates the pH of
body fluids and helps manage body temperature. Blood also
protects the body from infection, disease, and excessive
blood loss during injury.
• Red blood cells transport oxygen and carbon dioxide; plate-
lets are involved in blood clotting; and white blood cells (five
different types) are involved in fighting infections, producing
chemicals involved in the immune reaction, and removing
microbes and cell debris.
Blood Cells Are Created in the Red Bone
Marrow 291
• Within red bone marrow, pluripotent stem cells differentiate
into myeloid and lymphoid stem cells, which in turn differ-
entiate into all of the formed elements. Myeloid stem cells
form the RBCs, platelets, and granulocytes. Lymphoid stem
cells form the agranulocytes.
• Once produced, red blood cells live about 120 days. Old,
worn-out red cells are destroyed in the spleen, liver, and red
bone marrow. The hemoglobin is broken down into various
parts. The amino acids and iron are recycled, and the non-
iron heme pigments are broken down and excreted.
• As shown here, erythropoiesis is regulated by a negative
feedback system involving the kidney, and red bone mar-
row via the hormone erythropoietin. The trigger for this
system is a decrease in oxygen delivery to the kidney and
other tissues.
regulation of red blood cell formation • Figure 10.5
302 CHAPTER 10
The Cardiovascular System: Blood
previous page 337 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 339 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off