Blood-2Lesson # 4 (Chapter 19)

Objectives:

1- To describe the types of white blood cells and their major functions.2- To describe the platelets and their functions.4- To discuss the reaction sequences responsible of blood clotting.

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Splinter

Phagocytosis4

Chemotaxis3

2

Mast cells

Amoeboid movements

Diapedesis1

Neutrophils

Bacteria

Fromdamaged

tissue

Inflammatorychemicals

Frommastcells

Fromblood

Increasedpermeability

Blood capillaryor venule

WBC Circulation and Movement

Circulating WBCs have four characteristics:

1- Diapedesis or migration: They can migrate out the bloodstream.

2- Amoeboid movements: They move through the endothelium and into peripheral tissues

3- Positive chemotaxis: They are attracted by specific chemicals.

4- Phagocytosis: They have the ability to engulf pathogens, cell debris, and other materials.

General Functions of WBCs or Leukocytes

Functions

1- They protect the body against bacteria, virus, parasites, and cancerous cells.

2- They remove foreign substances such as toxins, and waste

3- They destroy dead, abnormal and worn out cells.

4- They participate in the inflammatory and immune response.

They are complete cells with nucleus and organelles.

1- Granulocytes

2- Agranulocytes

They contains granules, which contain lysosomal enzymes and bactericidal compounds.

They have few or any granules.

Neutrophils Eosinophils Basophils

Monocytes Lymphocytes

Types of White Blood Cells

1- Neutrophils

Functions1- They phagocyte bacteria, which have been market by antibodies and complement proteins.

- Their nucleus has 2 to 5 lobes.

- Granules are chemically neutral.

Neutrophils Bacterial infection

- They form 50% to 70% of the circulating white blood cells (WBC). Normal value: 7,000 to 8,000/mm. 3

Granulocytes

(Neutrophilia)

2- Eosinophils

-They form 2% to 4% of circulating WBC.

- They have bilobulated nucleus.

- Granules are chemically acid (red).

Functions

1- They defend the body against parasites worms and flukes.

Eosinophils Infection by parasites and allergy

Granulocytes

2- They phagocyte bacteria, protozoa and cellular debris.

(Eosinophilia)

-They form less than 1% of circulating WBC.

- Granules are chemically basic (purple to blue).

Function

- Granules contain histamine and heparin.

Vasodilator Anticoagulant

They accumulate in damaged tissues and release chemicals that enhance inflammation.

3- Basophils

Granulocytes

- They are the largest leukocytes.

- They are spherical with a nucleus that is oval or kidney bean shaped.

Functions

2- They release chemicals that attract other WBCs to the injury site.

3- They defend the body against bacteria and viruses.

4- They help activate the lymphocytes.

Agranulocytes

4- Monocytes

1- They stay in the blood for only 24 hours and then they move into the peripheral tissues, where they become macrophages, which are very active and aggressive phagocytes.

- They form 20% to 30% of the circulating WBCs.

- They have large nucleus and do not have granules.

FunctionsThey play a crucial role in the specific immunity.

T cells: (cell-mediated immunity): They destroy virus infected cell, and they coordinate the immune response.

B cells: (humoral immunity): They produce the plasma cells, which produce the antibodies.

NK cells: They detect abnormal or cancerous cells and target them for destruction ( Immune surveillance).

5- Lymphocytes

Agranulocytes

WBC Production (leucopoiesis).

Eosinophilicmyelocyte

Basophilicmyelocyte

Neutrophilicmyelocyte

Immature T-lymphocytes migrate to the thymus to complete their development.

PromonocytePro- erythroblast

Day 1

Mature Red Blood Cell

Megakaryocyte

Platelets

Hemocytoblast

LymphoidStem Cell

Lymphoblast

Myeloid Stem Cell

Progenitor cell

Myeloblast

Monoblast

Hemocytoblast

Myeloid Stem Cell

Lymphoid Stem Cell

Progenitor cell

Myeloblast MonoblastMega-karyocyte

Proerythro-blast

Lymphoblast

Lymphocytes

Erythrocytes Platelets Granulocytes

Monocytes

NeutrophilsEosinophilsBasophils

B lymphocytesT lymphocytesNK lymphocytes

Blood Cell Production

6- Platelets

- They are fragments of megakaryocytes.

- There are only 1/3 of them in the blood stream. The rest of them are in the spleen and other vascular organs.

Functions- They transport enzymes and other chemicals that help to initiate and regulate blood clotting.

- They form a temporary plug in the ruptured blood vessel wall.

- They contract to reduce the size of the hole in the vessel wall.

Megakaryocyte

Platelets

Platelet ProductionProduction of platelets is called thrombopoiesis and takes place in the bone marrow.

Megakaryocytes are gigantic cells (150 mm), visible to the naked eye, with a huge multilobular nucleus and multiple sets of chromosomes.

Platelets

Bloodflow

Proplatelets Endothelium

Sinusoid ofbone marrow

Duplication of DNA several times without cytoplasmic division.

Megakaryocyte

Progenitor cell

Hemostasisa) Vascular Phase

b) Platelet Phasec) Coagulation Phase

It is the most immediate protection against blood loss.

It is produced by:

-Pain receptors (some directly innervate blood vessels to constrict).

- Smooth muscle injury.

- Platelets release serotonin (vasoconstrictor).

It is the prompt constriction of a broken vessel.

a) Vascular Phase:

It provides time for other two clotting pathways.

b) Platelet Phase

Platelets do not adhere to the because the endothelium smooth, and coated with prostacyclin, a platelet repellant.

Broken vessel exposes collagen.

Upon contact with collagen, platelet emit pseudopods that stick to damaged vessel and other platelets - pseudopods contract and draw walls of vessel together forming a platelet plug.

Platelets degranulate releasing a variety of substances that attract more platelets, promote platelet aggregation and produce vasoconstriction.

STIMULUS

Clotting occurs as platelets adhere to site

and release chemicals.

Clotting proceeds; newly forming clot grows.

Break or tear in blood vessel wall.

Released chemicalsattract more platelets, which release more chemicals.

Released chemicalsattract more platelets, which release more chemicals.

Feedback cycle initiated

Feedback cycle ends after clot seals break.

Positive feedback

mechanism

It is the last but the most effective defense against bleeding.

The final goal of coagulation is to transform the fibrinogen (a soluble protein) into fibrin, a sticky protein that adheres to the blood vessels and form a net where blood cells are trapped

Fibrinogen FibrinFibrin

polymer

Prothrombin Thrombin

Fibrinpolymer

c) Coagulation Phase:

Prothrombin Thrombin

Damaged tissue

Platelets

Tissue Factor (factor III)

Factor XII

Extrinsic Pathway Intrinsic Pathway

Ca+2 Ca+2

Inactive Factor X

Prothrombinase

Active Factor X

The activation cascade to factor X is longer.

The activation cascade to factor X is shorter.

Fibrinogen Fibrin

Fibrinpolymer

The Two Mechanisms of Coagulation

The Common Pathway

It is initiated by release of tissue factor (factor III) from damaged tissue.

The activation cascade to factor X is shorter.

Extrinsic Pathway

Intrinsic Pathway

It is initiated by platelets releasing factor XII.

The activation cascade to factor X is longer

Calcium is required for either pathway.In most cases of bleeding, both the extrinsic and intrinsic mechanism work simultaneously.