Anatomy & Human Physiology Chapter 10: Blood Anatomy & Human Physiology

Composition and Function of Blood Components Blood is the only fluid tissue Microscopic analysis shows both solid and liquid components It is a complex connective tissue in which living cells are suspended in a nonliving fluid matrix (plasma) If blood is spun in a centrifuge the bottom of the tube will contain erythrocytes, next will be a thin whitish layer (buffy coat) that contains leukocytes and platelets, on top will be the yellow fluid layer (plasma) In total blood volume, erythrocytes account for 45%, leukocytes and platelets less than 1%, and plasma makes up the remaining 55%

Physical Characteristics and Volume Blood is a sticky opaque fluid Depending on the amount of oxygen it is carrying the color varies from scarlet (oxygen-rich) to dull red (oxygen-poor) It is heavier than water and five times thicker due to the formed elements The pH of blood is between 7.35 and 7.45 It accounts for approximately 8 percent of body weight Volume in a healthy male is 5 to 6 liters

Plasma The liquid portion of the blood that is approximately 90% water Over 100 different substances are dissolved in it Nutrients, metal ions (salts), respiratory gases, hormones, plasma proteins, and various wastes and products of cellular metabolism Plasma proteins are the most abundant solutes and they serve a variety of functions Plasma proteins are NOT taken up by cells to be used as food fuels or metabolic nutrients The composition of plasma varies continuously as cells remove or add substances to the blood Assuming a healthy diet the composition is kept fairly constant due to homeostatic mechanisms It also helps to distribute body heat evenly throughout the body

Formed Elements Erythrocytes (red blood cells) vastly outnumber the other types of formed elements (leukocytes – white blood cells and platelets) Formed elements make up 45% of whole blood

Erythrocytes Also called red blood cells (RBCs) Function is to carry oxygen in blood to all cells of the body They differ from other blood cells because they are anucleate They also contain very few organelles Mature RBCs are literally sacs of hemoglobin molecules Hemoglobin (Hb) is an iron-containing protein that transports the bulk of oxygen Hb also binds a small amount of carbon dioxide RBCs lack mitochondria so they make ATP by anaerobic mechanisms Small cells shaped like biconcave disks The small size and shape provide a large surface area relative to their volume Makes them ideally suited for gas exchange

Erythrocytes Continued… RBCs outnumber white blood cells (WBCs) by about 1000 to 1 Major factor contributing to blood viscosity Normally there are about 5 million cells per cubic millimeter of blood in circulation When number of RBC/mm3 increases, blood viscosity increases When number of RBC/mm3 decreases, blood viscosity thins and flows more rapidly The amount of hemoglobin in the bloodstream is what determines how well the erythrocytes are performing The more Hb molecules the RBCs contain, the more oxygen they will be able to carry A single RBC contains 250 million Hb molecules each capable of holding 4 molecules of oxygen Each cell can carry about 1 billion molecules of oxygen A decrease in the oxygen-carrying ability of the blood is called anemia An excessive/abnormal increase in RBCs is called polycythemia

Leukocytes Also referred to as white blood cells (WBCs) Far less numerous than RBCs Crucial to body defense against disease On average, there are 4,000 to 11,000 WBCs per cubic millimeter Account for less than 1% of total blood volume They are the only complete cells in the blood (nuclei and organelles present) Form a protective, movable army that helps defend the body (bacteria, viruses, parasites, and tumor cells) Have the capability to slip into and out of the blood vessels The vessels are simply their means of transportation

Leukocytes Continued… WBCs can locate areas of tissue damage and infection by responding to certain chemicals that diffuse from the damaged cells They move through the tissue spaces by ameboid motion and pinpoint the area of damage following the diffusion gradient When they are mobilized for action, the body speeds up their production A total WBC count above 11,000 cells/mm3 is referred to as leukocytosis Generally indicates that a bacterial or viral infection is stewing Leukopenia (low WBC count) is commonly caused by drugs (corticosteroids and anticancer agents)

Leukocytes Continues… WBCs are classified into two major groups depending on whether or not they contain visible granules in their cytoplasm Granulocytes are granule containing WBCs (granules visible in cytoplasm) They include neutrophils, eosinophils, and basophils

Leukocytes Continued… The second grouping is agranulocytes Lack visible cytoplasmic granules These include lymphocytes and monocytes

Platelets They are not cells in the strict sense They are fragments of bizarre multinucleate cells called megakaryocytes These cells rupture and release thousands of anucleate pieces Normal platelet count is about 300,000/mm3 They are needed for the clotting process when blood vessels are ruptured

Hemostasis If a blood vessel wall breaks, a series of reactions is set into motion to accomplish hemostasis (stoppage of blood flow) The response is fast and localized Involves many substances normally present in plasma, as well as some that are released by platelets and injured tissue cells Involves three phases: vascular spasms, platelet plug formation, and coagulation (blood clotting) Blood loss at the injury site is permanently prevented when fibrous tissue grows into the clot and seals the hole in the vessel

Normally, blood clots within 3 to 6 minutes Once the clotting cascade has started, the triggering factors are rapidly inactivated to prevent widespread clotting

Blood Groups and Transfusions Human Blood Groups The plasma membrane of RBCs bear genetically determined proteins (antigens), which identify each person as unique Each of us tolerates our own antigens, but if another persons blood (with different RBC antigens) is transfused they would be recognized as a foreign invader The recognizers of the foreign invader are the antibodies present in the plasma The antibodies will attach to the foreign blood antigens causing the RBCs to clump

Human Blood Groups Continued… The ABO blood groups are based on which of the two antigens, type A or type B, a person inherits Absence of both antigens results in type O blood Presence of both antigens results in type AB blood

Human Blood Groups Continued… The Rh blood groups are so named because of the Rh antigens Most Americans are Rh+, meaning that their RBCs carry the Rh antigen