1. 14.1: Introduction Blood: Is connective tissue
Transports vital substances
Maintains stability of interstitial fluid
Distributes heat
Blood cells:
Form mostly in red bone marrow and are:
Red blood cells (RBCs)
White blood cells (WBCs)
Platelets (cell fragments)
The amount of blood varies with body size, changes in fluid concentration, changes in electrolyte concentration, and amount of adipose tissue
Blood is about 8% of body weight
Adult blood volume is about 5 liters

2. 14.2: Blood Cells
Blood cells originate in red marrow from hemocytoblasts or hematopoietic stem cells
Stem cells can then:
Give rise to more stem cells
Specialize or differentiate

3. Characteristics of Red Blood Cells
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Red blood cells are:
Erythrocytes
Biconcave discs
One-third hemoglobin
Able to readily squeeze through capillaries
Lack nuclei and mitochondria
Top view
7.5 micrometers
2.0 micrometers
Sectional view
(a)
(b)
b: © Bill Longcore/Photo Researchers, Inc.

4. Red Blood Cell Counts
RBC counts is the number of RBCs in a cubic millimeter or microliter of blood
It may vary depending on age and health
Typical ranges include:
4,600,000 – 6,200,000 in males
4,200,000 – 5,400,000 in adult females
4,500,000 – 5,100,000 in children
RBC counts reflects blood’s oxygen carrying capacity

5. Red Blood Cell Production and Its Control
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Low blood oxygen causes the kidneys and the liver to release erythropoietin (EPO) which stimulates RBC production
This is a negative feedback mechanism
Within a few days many new blood cells appear in the circulating blood
Low blood oxygen
Release into
bloodstream
Liver
Kidney
Stimulation
Inhibition –
Erythropoietin
Increased
oxygen-
carrying
capacity
Bloodstream
Increased
number of
red blood
cells +
Red bone marrow

6. Dietary Factors Affecting Red Blood Cell Production
Vitamin B12 and folic acid are necessary
They are required for DNA synthesis making them necessary for the growth and division of all cells
Iron is also necessary
It is required for hemoglobin synthesis