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Chapter 10: Blood

Lecture Notes taken predominantly from:

Marieb,E.N. 2009. Essentials of Human Anatomy and Physiology. PBC

Blood is a fluid connective tissue composed of plasma and blood cells that carry substances to and from cells to help maintain homeostasis. Among other functions, blood delivers nutrients and removes waste from body tissues, helps moderate body temperature, and mobilizes and maintains body defenses.

Composition: 2 major components are plasma and formed elements (cellular)

Plasma – 50-60% of blood volume; fluid portion of blood that is more than 90% water; 7-8% proteins to maintain proper volume via osmotic balance (mainly by albumin), defense (antibodies), clotting, and lipid transport; 1-2% ions, sugars, amino acids, hormones, and vitamins to signal and maintain cells and tissues. To compensate for the constant movement of substances into and out of the blood (to and from cells), organs throughout the body monitor plasma and make constant adjustments to maintain the proper balance of solutes.

For example: Blood pH is slightly alkaline (pH=7.35 – 7.45) and is critical to proper transfer of waste and nutrients between blood and tissues. Acidosis = acidic blood; Alkalosis = basic (alkaline) blood. The kidney and respiratory system coordinate actions to keep blood pH stable (secrete more H+ in urine or change breath rate, for example).

Formed Elements – 40-50% of blood is made of cellular components. Derived from stem cells in bone marrow.

Erythrocytes (a.k.a. Red Blood Cells (RBCs)) – transport O2 to cells and remove CO2; flexible, anucleate (lack a nucleus and organelles), biconcave sacks of hemoglobin. Hemoglobin (Hb) is an iron-containing compound responsible for delivering O2 to body tissues. Too little hemoglobin or erythrocyte disorders that hinder O2 delivery are known as anemias. Sickle Cell Anemia = abnormal Hb causes deformed (sickled) RBCs that rupture or are destroyed prematurely; can be very painful but offers resistance to malaria.

Leukocytes (a.k.a. White Blood Cells (WBCs)) – travel through blood stream and can move into and out of tissues via diapedesis in response to tissue damage. 2 major types include granulocytes (contain granules (really vesicles) of toxins or signal molecules) and agranulocytes (WBCs without visible granules). The granulocytes include: neutrophils – eat microbial pathogens, eosinophils – kill parasitic worms, and basophils – release histamine in response to tissue damage. Granulocytes include: lymphocytes – identify and help kill pathogens and monocytes – eat invaders and fight chronic infections. Leukocytosis = high WBC count indicating an infection; Leukopena = low WBC count from drugs, possibly stress; Leukemia = cancer of bone marrow leading to high numbers of immature WBCs.

Platelets – fragments of specialized cells enclosed in a membrane that begin the clotting process

Blood cells are produced by stem cells in red bone marrow. Hematopoiesis = blood cell formation. RBCs last 100 - 120 days before dead or worn out cells are cleaned up and recycled by the spleen and liver. Kidneys monitor O2 levels in the blood and signal bone marrow to make more RBCs when O2 levels drop by releasing the hormone, erythropoietin. WBCs are made from the same stem cells of bone marrow and are stimulated into production by cell damage and, or certain bacteria.

Hemostasis and blood clotting:

Hemostasis – process that stops bleeding in small blood vessels (luckily, most injuries involve only small vessels).

3 major steps in hemostasis:

• Vascular Spasms: Muscles in vessel wall contract in a spasm to slow blood flow

• Platelets plug hole by sticking to exposed collagen fibers of the broken vessel and send message to activate clotting factors

• Clotting factors activated and form netlike web of protein called fibrin; clot – fibrin net with trapped blood cells contracts, drawing vessel walls back together until wound is healed.

Clotting Disorders: Clots forming inside unbroken blood vessels can clog vessels and prevent blood flow = thrombus – clot that stays where it formed (clinically called thrombosis) and embolus- clot breaks free and circulates in the blood stream (embolism). An embolism can cause sudden death or stroke (partial destruction of brain tissue) if lodged in heart, lungs, or brain.

Thrombocytopenia = platelet deficiency from drugs, radiation, or cancer that produces tiny bruises as a result of normal activity.

Hemophilia – disorder of the blood; insufficient clotting factors can lead to significant blood loss from minor injuries.

All cells have genetic markers on their surfaces that allow the body to recognize itself. Blood types like ABO, +/- are determined by markers found on red blood cells. Over 200 markers have been identified on human blood; 30 are recognized as ‘common’ but only ABO and Rh+/- types usually provoke potentially dangerous immune responses.

The ABO group: determined by the presence or absence of particular antigens (particles or substances that provoke immune systems to mount a response). Type A blood has antigen/marker A. Type B has antigen/marker B. Type AB has both antigens/markers. Type O has neither antigen/marker. Defensive proteins (antibodies) identify and attack foreign antigens. Type A blood carries anti-B antibodies. Type B carries anti-A antibodies. Type O carries both anti-A and anti-B antibodies. Type AB carries neither antibody.

Fill in the following table:

|Blood Type |Antigens on RBC membrane |Antibodies in blood |Transfuses to |Transfuses from |

| | | |(can give to) |(can receive from) |

|A | | | | |

|B | | | | |

|AB | | | | |

|O | | | | |

If incompatible blood types mix, antibodies attach to the antigens on the foreign blood cells and cause them to clump together (a.k.a. agglutination). This either can clog capillaries or lyse the foreign blood cells causing pain and potential tissue death from low O2.

The Rh groups: The Rh (+/-) typing indicates the presence or absence of an Rh marker. Unlike the ABO system, Rh – types do not carry anti-Rh + antibodies unless they have previously been exposed to the Rh antigen.

Hemolytic disease of the newborn occurs when the fetus has an Rh+ blood type and the mother is Rh-. Rh+ antibodies in the mother’s blood enter the fetal blood stream and cause severe agglutination. Because the mother must have previous exposure to the Rh+ antigen before her body makes the antibodies that target Rh+, the first Rh+ child is usually unaffected. The second Rh+ child, however, may die unless the mother is given a special drug (RhoGAM) that prevents her from making Rh+ antibodies after the birth of the first child.

Blood types are determined by adding purified antibodies to blood samples. If the blood clumps together, i.e. agglutinates, the blood cells must contain the specific antigen. So, if blood cells agglutinate in the presence of antibody A, then the blood cells must carry the A antigen (cell marker), etc.

Other common or well-known blood disorders:

Anemias- literally means ‘no blood’; symptoms = tired, listless

Iron-deficiency anemia – anemia due to deficient iron, required for heme groups

Pernicious anemia – RBCs don’t form due to B12 or folic acid deficiencies

Hemolytic anemia – RBCs die or burst before normal life span (malaria is one example)

Thalassemia – anemia due to abnormal hemoglobin (sickle-cell anemia is 1 example)

CO poisoning – CO bonds 200X more tightly than O2, headache, dizziness, potentially fatal; doesn’t take much CO

Mononucleosis – ‘mono’, highly contagious virus causes over-production of white blood cells

Leukemia – ‘white blood’; cancer in bone marrow

Septicemia – bacteria toxins in blood destroy RBCs or prevent clotting (Staphylococcus aureus)

Toxemia – build up of toxic waste in bloodstream; can prevent normal replacement of RBC, platelets

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