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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Lymphoidstem cells

Myeloidstem cells

Hemocytoblaststem cells

Secondary stem cells

Erythrocytes

Platelets

Basophils

Eosinophils

NeutrophilsMonocytesLymphocytes

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 O2 levels Targets bone marrow to mfr RBCs

negative feedback maintains blood oxygen levels (see figure 10.5 on page 346)

works by increasing/decreasing erythropoietin release

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Stimulus

Homeostasis: Normal blood oxygen levels

1IMBALANCE

IMBALANCE

Low blood O2–carryingability due to• Decreased RBC count• Decreased amount of

hemoglobin• Decreased availability

of O2

Kidney (and liver,to a smaller extent)releases erythropoietin.

2

Erythropoietinstimulates red bonemarrow.

3

Enhancederythropoiesisincreases RBCcount.

4

O2–carryingability of bloodincreases.

5

Slide 1

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 spasms2. Platelet plug formation3. 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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Vascular spasms occur.1Step• Smooth muscle contracts,

causing vasoconstriction.

Slide 2

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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Collagenfibers

Platelet plug forms.Step• Injury to lining of vessel exposes collagen

fibers; platelets adhere.

• Platelets release chemicals that makenearby platelets sticky; platelet plug forms.

Platelets

Slide 3

2

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-coagulation-cascade.html

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Coagulation events occur.Step• Clotting factors present in plasma and released

by injured tissue cells interact with Ca2+ to formthrombin, the enzyme that catalyzes joining offibrinogen molecules in plasma to fibrin.

• Fibrin forms a mesh that traps red blood cellsand platelets, forming the clot.

Fibrin

Slide 4

3

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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