BIOL 2304 Fall 2006 Chapter 17 1

Chapter 17 - Blood

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I. hematocrit

= % of blood volume occupied by erythrocytes

 

 

average = 45% (average plasma volume = 55%)

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to determine the hematocrit, a small tube of blood is collected:

BLOOD

then spun in a centrifuge for 5 minutes:

PLASMA BLOOD

• erythrocytes are heavier than plasma and are packed in the bottom of the tube

• plasma is separated from formed elements

a special scale is used to determine the relative volume occupied by the erythrocytes compared to total blood volume (see previous slide)

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II. erythrocytes

A. physical characteristics– 6 - 8 mm diameter – biconcave discs

• more surface area than spherical cells • more flexible and less fragile

– no nuclei or organelles – filled with hemoglobin

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B. hemoglobin– each molecule of Hb is made of 4 subunits – each subunit contains 1 peptide and 1 heme – normal adult Hb has 2 alpha and 2 beta

peptides – each heme contains one

iron atom – the peptide

carries CO2

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C. average lifespan of a RBC = 100 to 120 days– old RBCs are removed from circulation by

phagocytes (spleen, liver, bone marrow)– some components are recycled

• amino acids• Fe (stored in liver)

– the remainder of the heme group is converted to bilirubin and excreted in bile

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D. disorders

1. anemia = reduced ability of blood to carry oxygen– NOT always characterized by low red blood

cell count or low hematocrit

a. iron deficiency

b. vitamin B12 deficiency / pernicious anemia caused by lack of intrinsic factor production in stomach

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c. aplastic anemia due to destruction of stem cells in bone marrow (radiation, cancer drugs, environmental toxins)

d. hemolytic anemia is caused by destruction of red blood cells

e. hemorrhagic anemia is caused by blood loss

f. genetic disorder causing abnormal hemoglobin

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2. polycythemia = high RBC count

a. primary - bone marrow cancer

b. secondary – caused by:

• adaptation to increased activity or altitude • dehydration • excess secretion of erythropoietin

– effect = increased blood viscosity

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A. classification

1. granulocytes (neutrophils, eosinophils, basophils)

cytoplasmic granules

distorted, inactive nuclei

phagocytic

2. agranulocytes (lymphocytes, monocytes)• lack obvious granules in cytoplasm

III. leukocytes

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B. characteristics

1. neutrophils (40 - 70%)– nucleus has 2-6 lobes – cytoplasm stains light purple – phagocytize bacteria

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2. eosinophils (1 - 4%)– nucleus has 2 lobes – cytoplasm stains red, orange or dark pink – phagocytize antigen-antibody complexes and

fight parasitic worms

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3. basophils (0 - 1%)– nucleus has 2 lobes (not visible) – cytoplasm stains dark blue/black – release histamine

and other

chemicals

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4. lymphocytes (20 - 45%)– nucleus round, dark, takes up most of cell – cytoplasm seen as thin rim of light blue – about same size as RBCs – functionally divided into 2 categories: – B cells make antibodies – T cells attack foreign, cancer and virus-

infected cells

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5. monocytes (4 - 8%)– nucleus horseshoe or kidney shaped – cytoplasm pale blue – largest WBC – become macrophages after migrating to c.t.

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IV. thrombocytes

• fragments of cytoplasm enclosed by plasma membrane

• cytoplasm contains secretory granules • involved in hemostasis

– form platelet plugs– secrete chemicals that enhance blood

coagulation

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V. hematopoiesis

occurs in the bone marrow (myeloid tissue)

• bone marrow is located inside bones• there are two categories:

– red - active – yellow - inactive

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A. adult red marrow location:– proximal epiphyses of femur and humerus – axial skeleton – limb girdle bones

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B. bone marrow histology– sinusoids (capillaries) – reticular cells, reticular fibers (stroma) – adipose tissue – multipotent blood stem cells (hemocytoblast) – immature blood cells

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C. stem cell divides by mitosis to form two daughter cells– one daughter cell becomes the new stem cell– one daughter cell differentiates

this daughter cell

becomes the new stem cell

this daughter cell

differentiates into a formed element

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D. lineages

1. lymphoid stem cell • lymphocytes

2. myeloid stem cell• erythrocytes• granulocytes• monocytes• megakaryocytes => platelets

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