Wandering macrophages accumulate at sites of

wandering macrophages accumulate at
sites of infection
• Diameter is ~ 12 - 20 microns
• Cytoplasm is a foamy blue-gray
• ~ 3 to 8% of circulating WBC’s
• Take longer to arrive at the site of infection, but
arrive in larger numbers
• Become wandering macrophages, once they
leave the capillaries
• Destroy microbes and clean up dead tissue
following an infection

Principles of Human Anatomy and Physiology, 11e 28
WBC examination
• A differential white blood
cell count is a diagnostic
test in which specific white
blood cells are
enumerated. Because each
type of WBC plays a
different role, determining
the percentage of each
type in the blood assists in
diagnosing various
conditions.

29
Complete Blood Count
• Screen for anemia and infection
• Total RBC, WBC and platelet counts;
• Differential WBC;
• Hematocrit and hemoglobin measurements
• Normal hemoglobin range
– infants have ~ 14 to 20 g/100mL of blood
– adult females have ~ 12 to 16 g/100mL of blood
– adult males have ~ 13.5 to 18g/100mL of blood

30
PLATELETS (THROMBOCYTES)
• Thrombopoietin stimulates myeloid stem
cells to produce platelets.
• Myeloid stem cells develop into
megakaryocyte-colony-forming cells that
develop into megakaryoblasts .
• Megakaryoblasts transform into
megakaryocytes which fragment.
• Each fragment, enclosed by a piece of
cell membrane, is a platelet
( thrombocyte ).
• Normal blood contains
~
250,000 to
400,000 platelets/mm
3
. Platelets have a
life span of only
~
5 to 9 days; aged and
dead platelets are removed by fixed
macrophages in the spleen and liver.
• Platelets help stop blood loss from
damaged vessels by forming a platelet
plug. Their granules also contain
chemicals that promote blood clotting.

31

32
Hemostasis
• Stoppage of bleeding in a rapid and localized fashion
when blood vessels are damaged
• Prevents hemorrhage (loss of a large amount of blood)
• Processes
– vascular spasm
– platelet plug formation
– blood clotting (coagulation ⇒ formation of fibrin threads)

33
Vascular Spasm
• Damage to blood vessel produces stimulates pain receptors
• Reflex contraction of smooth muscle of small blood vessels
• Can reduce blood loss for several hours until other
mechanisms can take over
• Only for small blood vessels or arterioles

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Platelet Plug Formation
• Platelets store many chemicals in granules needed for platelet plug
formation
– alpha granules
• clotting factors
• platelet-derived growth factor
– cause proliferation of vascular endothelial cells, smooth
muscle and fibroblasts to repair damaged vessels
– dense granules
• ADP, ATP, Ca +2 , serotonin, fibrin-stabilizing factor, and enzymes
that produce thromboxane A2
• Steps in the process
– (1) platelet adhesion
– (2) platelet release reaction
– (3) platelet aggregation

Principles of Human Anatomy and Physiology, 11e 35
Platelet Adhesion
• Platelets stick to exposed collagen
underlying damaged endothelial cells in
vessel wall
Platelet Release Reaction
•Platelets are activated by adhesion