Part I Vocabulary due Today Discuss RBC Notes Today Part I Text Questions WS due next

time Part I Vocabulary Quiz next time

Chapter #14

Blood

I. Blood & Blood CellsBlood is slightly heavier and 3 to 4 times more viscous than water. Its cells, which are formed mostly in red marrow, include red blood cells (RBCs) and white blood cells (WBCs). Blood also contains some cellular fragments called blood platelets.

A. Volume & Composition of Blood1) The volume of blood varies from

person to person, but an average adult has about 5 liters of blood. Several factors affect blood volume:

a) Body sizeb) Changes in fluid &

electrolyte concentrationsc) Amount of adipose tissue

present

2) If a blood sample is allowed to stand in a tube for a while, the cells will become separated from the liquid and will settle to the bottom. This settling can be sped up by using a centrifuge.

3) A blood sample is usually about 45% cells. This percentage is called the hematocrit or packed cell volume. RBCs comprise over 99% of the hematocrit. The other solids (formed elements) include WBCs and blood platelets.

4) The remaining 55% of a blood sample consists of clear, straw-colored plasma. The plasma is composed of a complex mixture that includes water, amino acids, proteins, carbohydrates, lipids, vitamins, hormones, electrolytes, and cellular wastes.

B. The Origin of Blood Cells1) Blood cells originate in bone marrow

from hemocytoblasts, a type of stem cell.

2) As hemocytoblasts reproduce, the new cells respond to different secreted growth factors, causing the different blood cells to form.

3) See Figure 14.3 on p. 523 for a chart depicting blood cell formation.

C. Characteristics of Red Blood Cells1) RBCs (or erythrocytes) are tiny,

biconcave disks that are thin near their centers and thicker around their rims.

2) This special shape is related to the RBCs function of transporting gases.

a) The shape increases the surface area of the RBC.

b) It also places the cell membrane closer to various interior parts where oxygen-carrying hemoglobin is found.

c) Because of its shape, the RBC can also be deformed readily as it squeezes through the narrow passages of capillaries.

3) Each RBC is about one-third hemoglobin by volume, this substance gives the cells their color.a) When the hemoglobin is combined

with oxygen, the resulting oxyhemoglobin is bright red.

b) When the oxygen is released, the resulting deoxyhemoglobin is darker, with almost a bluish appearance.

c) A person experiencing a prolonged oxygen deficiency (called hypoxia) may develop a symptom called cyanosis. In this condition, the skin and mucous membranes appear bluish due to an abnormally high concentration of deoxyhemoglobin in the blood. See page 522 for more information on this condition.

d) Some individuals produce an abnormal type of hemoglobin molecule, which tends to form long chains when exposed to low oxygen concentrations. This causes RBCs containing such molecules to become distorted, or sickle-shaped, and the person is said to have sickle-cell disease. See page 522 for more information on this condition.

4) RBCs have nuclei during their early stages of development, but the nuclei are lost as the cells mature. This characteristic seems to be related to the function of transporting oxygen, since the space previously occupied by the nucleus is now available to hold hemoglobin.

5) Since their nuclei are missing, RBCs cannot carry on DNA-directed protein synthesis and are unable to reproduce. Old and damaged RBCs are broken down in the spleen and liver and their parts are recycled.

D. Red Blood Cell Counts (RCC): The number of RBCs in a cubic millimeter (mm3) of blood. The following amounts are normal ranges for healthy individuals:1) Adult males: 4.6 - 6.2 million RBCs/mm3

2) Adult females: 4.2 - 5.4 million RBCs/mm3

3) Children: 4.5 - 5.1 million RBCs/mm3

4) The number of RBCs generally increases in the following conditions:

a) After exercise

b) After a large meal

c) After a rise in body temp (fever)

d) In a higher altitude

5) Since the number of circulating RBCs is closely related to the blood’s oxygen-carrying capacity, any changes in this number may be significant. This is why red cell counts are routinely made to help diagnose & evaluate diseases.

E. Destruction of RBCs1) With age, RBCs often become less

flexible and sometimes are damaged while squeezing through capillaries of active tissues.

2) Damaged RBCs are phagocytized by macrophages in the liver and spleen.

3) Hemoglobin from the RBCs is decomposed into heme (an iron-containing pigment) and globin (a protein).

4) Heme is decomposed into iron and biliverdin.

5) Iron is made available for reuse in the synthesis of new hemoglobin or is stored in the liver as ferritin.

6) Some biliverdin is converted into bilirubin.

7) Biliverdin and bilirubin are excreted in bile as bile pigments.

a) About one-third of all newborns develop a mild disorder called physiologic jaundice within a few days following birth. In this condition, as in other forms of jaundice, the skin and eyes become yellowish due to an accumulation of bilirubin in the tissues.

b) Physiologic jaundice is thought to be the result of immature liver cells, which are somewhat ineffective in excreting bilirubin into the bile. The condition is treated by feedings that promote bowel movements and by exposure to fluorescent light, which reduces the concentration of bilirubin in the tissues.

F. RBC Production and Its Control

1) RBC formation is called hematopoiesis.

2) It first takes place in the yolk sac, liver, and spleen.

3) After an infant is born, these cells are produced almost exclusively by the tissue that lines the spaces within the red bone marrow.

4) The Process of RBC Productiona) Within the red marrow, cells called

hemocytoblasts give rise to erythroblasts that can synthesize hemoglobin.

b) The erythroblasts also reproduce and give rise to new cells. The nuclei of these newly formed cells soon shrink and are extruded (eliminated) from the cell by being pinched off in thin coverings of cytoplasm and cell membrane. The resulting cells are RBCs or erythrocytes.

c) Some of these young red cells may contain a netlike structure (reticulum) for a day or two. This network represents the endoplasmic reticulum, and such cells are called reticulocytes.

5) The average life span of a RBC is about 120 days (4 months), and a large number of these cells are removed from circulation by the liver and spleen each day. Yet the total number of cells circulating in the blood remains fairly stable. This means that a homeostatic mechanism regulates the rate of RBC production.

a) The rate of RBC formation is controlled by a negative feedback mechanism involving a hormone called erythropoietin. In response to prolonged oxygen deficiency, erythropoietin in released, primarily from the kidneys and to a lesser extent from the liver.

b) The erythropoietin travels in the blood to the red bone marrow, where it stimulates an increased level of erythrocyte production.

c) When the oxygen level returns to normal, the amount of erythropoietin released decreases and the level of erythrocyte production returns to normal.

G. Dietary Factors Affecting RBC Production1) An absence of vitamin B12 results in the

formation of RBCs that are abnormally large, irregularly shaped, and have particularly thin membranes. These cells tend to be damaged more easily than normal RBCs and consequently have shorter lives. The result is a condition called pernicious anemia. It can be treated with injections of vitamin B12.

2) Iron is necessary for the synthesis of hemoglobin.

3) Folic acid and vitamin B12 are both necessary for the synthesis of DNA.

H. Red Blood Cell Disorders

Anemia is a general term for a deficiency of RBCs or a reduction in the quantity of the hemoglobin in the blood. As a result, the oxygen-carrying capacity of the blood is reduced. A person suffering from anemia may appear pale and lack energy. There are several common types of anemia:

1) Hemorrhagic Anemia: Caused by an abnormal loss of blood and may be mild or severe, depending on the amount of bleeding that occurs.

2) Hypochromic Anemia: Also known as iron-deficiency anemia. Characterized by the presence of small, pale RBCs with relatively low hemoglobin content.

3) Aplastic Anemia: Due to a malfunction of the red bone marrow and is characterized by decreased production of RBCs. It is sometimes caused by over-exposure to radiation, X-rays, or certain chemicals.

4) Hemolytic Anemia: Characterized by an abnormally high rate of RBC rupture (hemolysis), caused by a variety of factors.

5) Pernicious Anemia: Caused by a lack of vitamin B12.

Part I Text Questions due today Discuss WBC & Plasma Notes Quiz Today: Part I Vocabulary Part II Text Questions & Part II

Vocabulary due next time Quiz next time: RBC, WBC, &

Plasma notes

I. White Blood Cells (WBCs) or leukocytes, function primarily to control various disease conditions. Although these cells do most of their work outside the circulatory system, they do use the blood for transportation to sites of infection. Normally, five types of WBCs can be found in circulating blood. They are distinguished by their size, the nature of their cytoplasm, the shape of their nucleus, and their staining characteristics.

1) Some types of leukocytes have granular cytoplasm and are therefore called granulocytes. A typical granulocyte is about twice the size of a RBC. Granulocytes develop in red bone marrow and are produced from hemocytoblasts in much the same manner as RBCs. However, they only live for about 12 hours. There are three types of granulocytes:

a) Neutrophils: Characterized by the presence of fine cytoplasmic granules that stain pinkish. The nucleus is lobed and consists of 2 to 5 parts connected by thin strands of chromatin. Neutrophils account for 54% to 62% of the WBCs in a normal blood sample.

b) Eosinophils: These WBCs contain coarse, uniformly sized cytoplasmic granules that stain deep red. The nucleus is usually bilobed. These cells make up 1% to 3% of the total number of circulating WBCs.

c) Basophils: Similar to eosinophils in size and the shape of their nuclei. However, they have fewer, more irregularly shaped cytoplasmic granules that stain deep blue. Basophils usually account for less than 1% of the leukocytes.

2) Agranulocytes lack cytoplasmic granules. There are 2 different types of agranulocytes:a) Monocytes: The largest cells found in

the blood, with a diameter 2 to 3 times greater than RBCs. Their nuclei vary in shape. They are generally made in bone marrow and make up 3% to 9% of the WBCs in a blood sample. Monocytes live for several weeks or even months.

b) Lymphocytes: These cells are formed in the organs of the lymphatic system as well as in bone marrow. They are only slightly larger than RBCs. A typical lymphocyte contains a relatively large, round nucleus surrounded by a thin rim of cytoplasm. These cells make up 23% to 33% of the WBC count and can live for several years.

J. WBC Counts1) Normally there are about 5000 to

10000 WBCs per mm3 of blood.2) Some infectious diseases are

accompanied by a change in the white cell count.

a) If the total number of WBCs exceeds 10000 per mm3 the person is said to have leukocytosis. This condition occurs during certain acute infections, such as appendicitis.

b) If the WBC count drops below 5000 per mm3, the condition is called leukopenia. Such a deficiency may accompany typhoid fever, influenza, measles, mumps, chicken pox, or poliomyelitis.

3) A differential WBC count (DIFF) is sometimes performed to determine levels of particular WBCs.

K. Functions of WBCs1) Leukocytes can squeeze between the cells

that form blood vessel walls. This movement, called diapedesis, allows the WBCs to leave the circulation (see figure 14.14 on page 531). Once outside the blood, they move through interstitial spaces using a form of self-propulsion called ameboid motion.

2) The most mobile and active phagocytic leukocytes are the neutrophils and monocytes. Both of these types of phagocytes contain numerous lysosomes, which are filled with digestive enzymes.

a) When tissues are invaded by microorganisms, certain body cells respond by releasing substances that cause local bv’s to dilate. One such substance, histamine, also causes an increase in the permeability of nearby bv’s.

b) As these changes occur, the tissues become reddened and filled with fluids. The swelling produced by this inflammatory reaction tends to delay the spread of invading microorganisms into other regions.

c) At the same time, WBCs are attracted to the injured area by chemicals released from damaged cells. This process, called positive chemotaxis, results in large numbers of WBCs moving quickly to the inflamed area.

3) Eosinophils kill parasites and help control inflammation and allergic reactions.

4) Basophils release histamine along with an anticoagulant called heparin.

5) Lymphocytes play an important role in the mechanism of immunity. For example, some can form antibodies that act against foreign substances entering the body.

L. Leukemia is a form of cancer characterized by an uncontrolled production of specific types of leukocytes. There are 2 major types of leukemia:1) Myeloid Leukemia results from an

abnormal production of granulocytes in bone marrow.

2) Lymphoid Leukemia is accompanied by increased formation of lymphocytes in lymph nodes.

3) In both types of leukemia, the newly formed cells fail to mature into functional cells, so the patient has a lowered resistance to infections. (See page 533 for more information)

M. Blood platelets, or thrombocytes, are not complete cells. They are cell fragments that arise from megakaryocytes. Platelets are each about half the size of RBCs that live for about 10 days. In normal blood, the platelet count will vary from 130,000 - 360,000 platelets per mm3. Platelets help close breaks in damaged bv’s by sticking to broken surfaces. They also release serotonin, which constricts the walls of the bv, reducing blood flow.

II. Plasma......is the liquid portion of blood. It is 91.5 %

water, 7% protein, and 1.5% other substances such as electrolytes, nutrients, & gases.A. Plasma Proteins

1) Albumins: Account for about 60% of the plasma proteins. They are synthesized in the liver and help maintain the osmotic pressure of the blood. They also help transport certain molecules, such as bilirubin and free fatty acids.

2) Globulins: Make up about 36% of the plasma proteins. There are 3 groups of globulins:a) Alpha Globulins: Made in the liver. They

transport lipids and fat-soluble vitamins.b) Beta Globulins: Also made in the liver.

They also transport lipids and fat-soluble vitamins.

c) Gamma Globulins: Formed in lymphatic tissues. They constitute the antibodies of immunity.

3) Fibrinogen: Constitutes about 4% of the plasma proteins. It is formed in the liver and plays a key role in blood clot formation.

B. Nutrients and Gases1) Amino Acids2) Simple Sugars (glucose)3) Lipids

a) Fats (triglycerides)b) Phospholipidsc) Cholesterol

4) Blood Gasesa) Oxygenb) Carbon Dioxidec) Nitrogen (has no function)

C. Nonprotein Nitrogenous Substances

1) Amino Acids: From protein digestion and amino acid absorption

2) Urea & Uric Acid: Products of protein & nucleic acid catabolism

3) Creatine & Creatinine: Forms creatine phosphate -- stores energy

D. Plasma Electrolytes: They help maintain the osmotic pressure and pH of plasma.

1) Sodium**2) Chloride**3) Potassium4) Bicarbonate5) Calcium6) Phosphate7) Magnesium8) Sulfate** = most abundant