Formed Elements in Blood

Hemopoiesis Production of most formed elements found

in the blood

First occurs in the yolk sac of an embryo and later in the liver, spleen, thymus, and lymph nodes of a fetus.

Last three months before birth, red bone marrow becomes primary site of hemopoiesis and continues as the source of blood cells after birth and throughout life.

Erythrocytes

A.k.a. red blood cells (RBCs)

Amount in blood: 4-6 million

Life Span: 120 Days

Biconcave disc without nucleus

Function: transport oxygen in hemoglobin

Leukocytes

A.k.a. white blood cells (WBCs)

Amount in blood: 4,000 to 10,000

Life Span: 13-20 Days

Nucleated? Yes

Function: fight viruses and bacteria-immunity-move out of capillaries to site of infection

Classified as granular or agranular

Granulated - Neutrophil Respond 1st to

bacterial invasion

Function: Phagocytosis (engulf bacteria) and releasing enzymes (i.e. lysozyme)

Multi-lobed nucleus

54 - 62% of white cells present

Granulated - Eosinophil orange histamine granules

– released during allergic reactions

Effective against certain parasitic worms

Helps to detoxify foreign substances

Secretes enzymes that break down clots

1 - 3% of white cells present

Granulated - Basophil Blue granules

Releases anticoagulant heparin

< 1% white cells

Agranulated cells - lymphocytes

Large nucleus

Makes antibodies

Fights viruses

B cells, T cells, and natural killer (NK) cells

20 - 40% of white cells

Agranulated cells - monocytes

Pac Man Cells

Phagocytic cells

Garbage man cell of the blood

3 - 9%

Platelets - thrombocytes Amount in

blood: 150 to 400,000

Life Span: 5-9 Days

Nucleated? In bone marrow – not peripheral blood

Function: enable clotting

Blood Clotting A.k.a. coagulation

Clotting factors: Ca2+, enzymes made by liver cells, and various molecules associated with platelets or released by damaged tissues

Three stages:1. Prothrombinase is formed.2. Prothrombinase converts prothrombin into

the enzyme thrombin.3. Thrombin converts soluble fibrinogen into

insoluble fibrin. Fibrin forms the threads of the clot.

Blood Vessel Repair Once a clot is formed, it plugs the ruptured

area of the blood vessel and thus stops blood loss.

Clot retraction- consolidation or tightening of the fibrin clot. Fibrin threats attached to the damaged

surfaces of the blood vessel gradually contract as platelets pull on them.

As the clot retracts, it pulls the edges of the damaged vessel closer together.

Fibroblasts form connective tissue. Endothelial cells repair vessel lining.