Chapter 12 - Blood
Blood is considered a type of connective tissue.
Blood transports substances throughout the body, and helps to maintain a stable internal
Blood and Blood Cells
(p. 322; Fig. 12.1; Table 12.1)
The blood includes red blood cells, white blood cells, platelets, and plasma.
Blood Volume and Composition (p. 322)
A blood hematocrit is normally 45% cells and 55% plasma.
Plasma is a mixture of water, amino acids, proteins, carbohydrates, lipids,
vitamins, hormones, electrolytes, and cellular wastes.
Characteristics of Red Blood Cells (p. 322; Fig. 12.2)
Red blood cells (erythrocytes) are biconcave disks that contain one-third
oxygen-carrying hemoglobin by volume.
When oxygen combines with hemoglobin, the resulting oxyhemoglobin is bright
Red blood cells discard their nuclei during development.
Red Blood Cell Counts (p. 323)
The typical red blood cell count is 4,600,000-6,2000,000 cells per mm
males and 4,500,000-5,100,000 cells per mm
The number of red blood cells is a measure of the blood's oxygen-carrying
Destruction of Red Blood Cells (p. 323)
With age, red blood cells become increasingly fragile and are damaged by passing
through narrow capillaries.
Macrophages in the liver and spleen phagocytize damaged red blood cells.
Hemoglobin from the decomposed red blood cells is converted into heme and
Heme is decomposed into iron and biliverdin.
Iron is recycled into new hemoglobin or stored in the liver.
Some biliverdin is converted into bilirubin.
Biliverdin and bilirubin are excreted in bile as bile pigments.
Red Blood Cell Production and Its Control (p. 324; Figs. 12.3-12.4)
In the embryo and fetus, red blood cell production occurs in the yolk sac, liver,
and spleen; in the adult it occurs in the red bone marrow.
The average life span of a red blood cell is 120 days.
The total number of red blood cells remains relatively constant due to a negative
feedback mechanism utilizing the hormone erythropoietin, which is released in
response to low oxygen levels detected in the kidneys and liver.
Dietary Factors Affecting Red Blood Cell Production (p. 324; Fig. 12.5)
and folic acid are needed for DNA synthesis, so they are necessary
for the reproduction of all body cells, especially in hematopoietic tissue.