D’YOUVILLE COLLEGE
BIOLOGY 108/508 - HUMAN ANATOMY & PHYSIOLOGY II
LECTURE # 11
BLOOD I
RED CELLS
1.
Properties and Functions of Blood:
a. Volume: approx. 5 liters (5000 ml.); consists of formed elements (approx.
45% by volume) and plasma (approx. 55% by volume) (fig. 17 - 1)
b. Plasma: water & solutes (plasma proteins, salts, nutrients, hormones, etc.)
c. Formed Elements: erythrocytes or red cells (> 99%), leukocytes (white cells)
and thrombocytes (platelets) (fig. 17 - 2)
d. Functions:
• transport of gases, nutrients, wastes, hormones, etc.
• defense against infection and repair of tissue damage
• regulation of body temperature, osmotic balance, pH
• prevention of blood loss from vessels (hemostasis)
2.
Erythrocytes (Red cells):
• biconcave discs, enucleated and metabolically deficient (fig. 17 - 3)
• contain hemoglobin (97% of intracellular solids) (fig. 17 - 4) and carbonic
anhydrase
• lifespan averages 120 days; replaced by marrow; disposal by spleen & liver
a. Disposal: damaged/dying red cells phagocytized by macrophages in
spleen, transferred to liver (fig. 17 - 7)
• hemoglobin ------> globin (to amino acid pool) + heme (to iron &
porphyrin)
• porphyrin -----> bile pigments, e.g. bilirubin (excreted with bile);
excessive bilirubin (hyperbilirubinemia) causes jaundice
• iron - recycled into new Hb (65%), transported in blood (bound to
transferrin), stored in liver, spleen, & bone marrow (bound to protein, ferritin); small
loss each day (0.9 mg, in men; 1.7 mg. in women)
b. Erythropoiesis (red cell formation): bone marrow populated with stem cells
for all types of formed elements (hemocytoblasts) (fig. 17 - 5)
• hemocytoblasts ---> erythroblasts ---> ---> ---> reticulocytes --->
erythrocytes
• developmental sequence requires several nutrients (iron, vitamins B6, B12
and folacin + amino acids); also requires erythropoietin
c. Erythropoietin Mechanism (fig. 17 - 6):
• hypoxia stimulates release of renal product (erythrogenin) that causes
erythropoietin formation from a plasma protein
• erythropoietin promotes erythropoiesis in bone marrow
d. Methods of Assessing Red Cell Status of Blood:
a. Red Cell Count: averages 4 - 5.5 x 106/cu. mm.
Bio 108/508
lec. 11 - p. 2
b. Hematocrit (packed cell volume): 45% average (fig. 17 - 1)
c. Hemoglobin: 12 - 17 gm./dl.
d. Derived Values: aid in diagnosing type of anemia/red cell disorder
Mean Corpuscular Volume (MCV): hematocrit divided by red cell count
Mean Corpuscular Hemoglobin (MCH): Hb divided by RBC count
Mean Corpuscular Hemoglobin Concentration (MCHC): hemoglobin
divided by hematocrit
e. Anemias (red cell deficiencies): arise through depletion (blood loss),
nutrient deficiency (inadequate iron, inadequate vitamin B12), or excessive rate of
breakdown (hemolysis, e.g. sickle cell anemia) (fig. 17 - 8)
f. Polycythemias (elevated RBC levels): arise through overproduction (bone
marrow tumor), or elevated erythropoietin mechanism (high altitude, respiratory
disease, kidney disease or kidney ischemia)