Download Ch 10 Hematopoeisis and Hemostasis

Pages 349-353

The process of blood cell formation
◦ Includes all blood cells- red and white

Occurs in red bone marrow from stem cells
known as hemocytoblasts
◦ Hemocytoblast differentiation
 Lymphoid stem cell produces lymphocytes
 Myeloid stem cell produces all other formed elements
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Hemocytoblast
stem cells
Lymphoid
stem cells
Myeloid
stem cells
Secondary stem cells
Erythrocytes
Platelets
Lymphocytes
Basophils
Eosinophils
Monocytes Neutrophils

Because RBCs are anucleate they cannot
divide, grow, or synthesize proteins
 Life span of 100 to 120 days
 phagocytes in the spleen/liver eliminate remains
 New RBCs produced by hemocytoblasts in the red
bone marrow (a 3-5 day process)
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
erythropoietin : hormone that controls RBC
production rate
 Produced by kidneys in response to O levels
 Targets bone marrow to mfr RBCs
2

negative feedback maintains blood oxygen levels
(see figure 10.5 on page 346)

works by increasing/decreasing erythropoietin release
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Slide 1
Homeostasis: Normal blood oxygen levels
1 Stimulus
Low blood O2–carrying
ability due to
• Decreased RBC count
• Decreased amount of
hemoglobin
• Decreased availability
of O2
5 O2–carrying
ability of blood
increases.
4 Enhanced
erythropoiesis
increases RBC
count.
2 Kidney (and liver,
to a smaller extent)
releases erythropoietin.
3 Erythropoietin
stimulates red bone
marrow.

A group of Colony stimulating factors (CSFs)
and interleukins prompt bone marrow to
generate leukocytes
 CSFs are specific to the types of WBCs they act on
 used to stimulate cell production in cancer patients
undergoing chemo or radiation therapy

Hormone thrombopoietin stimulates
production of platelets from megakaryocytes
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
involves three phases:
1. Vascular spasms
2. Platelet plug formation
3. Coagulation (blood clotting)
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
Vasoconstriction causes blood vessel to
spasm
 Narrowing of the blood vessel
 Slows blood loss
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Slide 2
Step 1 Vascular spasms occur.
• Smooth muscle contracts,
causing vasoconstriction.



Collagen fibers are exposed by a break in a
blood vessel
Platelets become “sticky” and cling to fibers
Anchored platelets release chemicals to
attract more platelets
 A positive feedback mechanism

Platelets pile up to form a platelet plug (white
thrombus)
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Slide 3
Collagen
fibers
Step 2 Platelet plug forms.
• Injury to lining of vessel exposes collagen
fibers; platelets adhere.
• Platelets release chemicals that make
nearby platelets sticky; platelet plug forms.
Platelets

Clotting factors in blood plasma and injured tissue
cells interact with Ca²⁺ to produce the enzyme
thrombin
◦ Thrombin catalyzes the joining of fibrin molecules to make
a meshwork that traps RBCs and platelets
◦ This forms the clot, which is broken down after repair of
damaged tissue

This mechanism is controlled so that the presence
of the clot inactivates the factors that initiated the
response
◦ To avoid clotting of all blood in the body
◦ http://tube.medchrome.com/2010/10/hemostasis-and-coagulationcascade.html
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Slide 4
Fibrin
Step 3 Coagulation events occur.
• Clotting factors present in plasma and released
by injured tissue cells interact with Ca2+ to form
thrombin, the enzyme that catalyzes joining of
fibrinogen molecules in plasma to fibrin.
• Fibrin forms a mesh that traps red blood cells
and platelets, forming the clot.

Thrombus
 A clot in an unbroken blood vessel
 Can be deadly in areas such as the heart

Embolus
 A thrombus that breaks away and floats freely
within the bloodstream
 Potential to clog vessels in critical areas

Potential causes:




Burns
Physical blows
Fatty material (plaque)
Slow blood flow
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
Thrombocytopenia
 Platelet deficiency
 Results from bone marrow suppression
 Cancer, radiation, drugs, autoimmune condition, bacteria
 Evidenced by petechiae (purplish skin blotches)

Liver problems
 due to cirrhosis, hepatitis, or low Vitamin K stores
 Liver synthesizes the clotting proteins

Hemophilia
 Hereditary bleeding disorder
 Normal clotting factors are missing
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