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

2. 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%

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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)

11. 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

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

14. 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

15. 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

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

17. 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

18. 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

19. 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