Chapter 17
Blood
Blood Composition
•
Blood
–
Fluid connective tissue
–
Plasma
– non-living fluid matrix
–
Formed elements
– living blood "cells" suspended in plasma
•
Erythrocytes
(red blood cells, or RBCs)
•
Leukocytes
(white blood cells, or WBCs)
•
Platelets
•
Spun tube of blood yields three layers
–
Plasma on top (~55%)
–
Erythrocytes on bottom (~45%)
–
WBCs and platelets in
Buffy coat
(< 1%)
•
Hematocrit
–
Percent of blood volume that is RBCs
–
47% ± 5% for males; 42% ± 5% for females
Physical Characteristics and Volume
•
Sticky, opaque fluid with metallic taste
•
Color varies with O
2
content
–
High O
2
- scarlet; Low O
2
- dark red
•
pH 7.35–7.45
•
~8% of body weight
•
Average volume
–
5–6 L for males; 4–5 L for females
Functions of Blood
•
Functions include
–
Distributing substances
–
Regulating blood levels of substances
–
Protection
Distribution Functions
•
Delivering O
2
and nutrients to body cells
•
Transporting metabolic wastes to lungs and kidneys for elimination
•
Transporting hormones from endocrine organs to target organs
Regulation Functions
•
Maintaining body temperature by absorbing and distributing heat
•
Maintaining normal pH using buffers; alkaline reserve of bicarbonate ions
•
Maintaining adequate fluid volume in circulatory system
Protection Functions
•
Preventing blood loss
–
Plasma proteins and platelets initiate clot formation
•
Preventing infection
–
Antibodies
–
Complement proteins
–
WBCs
Blood Plasma
•
90% water
•
Over 100 dissolved solutes
–
Nutrients, gases, hormones, wastes, proteins, inorganic ions
–
Plasma proteins most abundant solutes
• Remain in blood; not taken up by cells
• Proteins produced mostly by liver
• 60% albumin; 36% globulins; 4% fibrinogen
Albumin
•
60% of plasma protein
•
Functions
–
Substance carrier
–
Blood buffer
–
Major contributor of plasma osmotic pressure
Formed Elements
•
Only WBCs are complete cells
•
RBCs have no nuclei or other organelles
•
Platelets are cell fragments
•
Most formed elements survive in bloodstream only few days
•
Most blood cells originate in bone marrow and do not divide
Erythrocytes
•
Biconcave discs, anucleate, essentially no organelles
•
Diameters larger than some capillaries
•
Filled with hemoglobin (Hb) for gas transport
•
Contain plasma membrane protein
spectrin
and other proteins
–
Spectrin provides flexibility to change shape
•
Major factor contributing to blood viscosity
•
Structural characteristics contribute to gas transport
–
Biconcave shape—huge surface area relative to volume
–
>97% hemoglobin (not counting water)
–
No mitochondria; ATP production anaerobic; do not consume O
2
they
transport
•
Superb example of complementarity of structure and function
Erythrocyte Function
•
RBCs dedicated to respiratory gas transport
•
Hemoglobin binds reversibly with oxygen
•
Normal values
–
Males - 13–18g/100ml; Females - 12–16 g/100ml
Hemoglobin Structure
•
Globin
composed of 4 polypeptide chains
