Anatomy and Physiology of Blood Cells and Platelets

Name and describe four tests for abnormal haemostasis.

1. Bleeding time- an small incision is made, and the time to clot is measured. 2. Whole blood clotting time- time for 1mL of blood to clot. 3. One state prothrombin test- clotting initiated artificially by adding calcium. 4. Kaolin cephalin clotting test- plasma activated in presence of phospholipid/Ca

Describe the three types of anaemia.

1. Haemorrhagic: due to copious blood loss. 2. Hypoproliferate: due to decreased production of RBCs. 3. Haemolytic: due to destruction of existing RBCs.

Where is bone marrow produced?

1. In the foetal bone marrow (all bones), liver, and spleen 2. In a young animal's bone marrow (all bones) 3. In an old animal's bone marrow (long bones only)

How are erythrocytes removed from circulation?

1. Intravascular haemolysis: Old cells lyse when passing through capillaries, are engulfed by macrophages, and recycled into new RBCs. 2. Extravascular haemolysis: Old RBCs are engulfed by macrophages in the vessels and recycled.

What are the three main components of blood?

1. Plasma: 91% water with proteins (mainly albumin, globulin, and fibrinogen), yellow to colourless 2. Erythrocytes 3. Leukocytes

Name and describe three common bleeding disorders.

1. Von Willebrands disease- most common in dogs, primary coagulation pathway is dysfunctional. 2. Haemophilia- Factor VIII in coagulation pathway is dysfunctional. 3. Factor IX deficiency (haemophilia B)- Factor IX is dysfunctional.

What is a pluripotent stem cell?

All blood cells arise from pluripotent stem cells in the marrow (or liver/spleen of foetus), as they have the ability to differentiate into any of the cell types depending on their environment.

Describe how erythropoiesis is regulated.

An enzyme called erythropoietin (EPO) is produced when there is decreased delivery of oxygen to the kidneys. EPO stimulates RBC production in the red marrow.

What are some common anticlotting drugs?

Aspirin, coumarin derivatives (ex. warfarin from rat poison), heparin, and calcium-chelating agents (ex. citrate, EDTA).

How is a blood clot removed from the body?

Clots are removed through fibrinolysis, in which the enzyme t-PA catalyzes the conversion of plasminogen to plasmin, which converts the fibrin clots back into soluble fibrin fragments.

What is the haemostatic vascular response?

Damage to the endothelium causes constriction of smooth muscles in the blood vessels to slow the flow of blood. It is maintained by substances released from the damaged endothelium and platelets.

Describe the cooperative binding of haemoglobin for oxygen.

Each haemoglobin has four subunits, and can therefore carry four oxygen molecules. When an oxygen binds to one subunit, it increases the affinity of the others, and so on until it is full.

Why do we need foetal hemoglobin?

Foetal haemoglobin has a higher binding affinity for oxygen than adult Hb, which is necessary for the foetus to obtain enough oxygen through the mother's blood.

What is haemostatis, and what are the three main physiological processes responsible for it?

Haemostatis, or the arrest of bleeding, occurs through vascular constriction, platelet plug formation, and coagulation to form clot.

Describe the process of platelet plug formation.

Platelets come into contact with collagen of outside tissues through the damaged vessel. This activates them, and they aggregate together. Once aggregated, they bind to the von Willibrand factors on the inside of the vessel epithelium, forming a platelet plug around the wound.

What determines blood groups?

Proteins on the surface of RBCs that can become antigenic to the hose, either through natural or acquired antibodies.

Tell me about erythrocytes.

RBCs' main jobs are to supply oxygen and remove carbon dioxide from tissues. They are biconcave, anucleated (except in birds) disks, which increases their surface area for gas transfer.

Describe (generally) the process of coagulation.

Vessel damage and subsequent exposure of collagen (or tissue factor in extrinsic pathway) triggers a series of coagulation factors to be come activated, eventually resulting in the conversion of fibrinogen to loose, and then stabilized, fibrin.