White Blood Cells and Platelets Flashcards
Leukocytes
- WBCs (white blood cells, less than 1% of blood volume)
- The only formed element that are complete cells
- Critical for our defense against disease
Diapedesis
- When WBCs leave the blood to enter the tissues
- Moving through tissue in an ameboid movement in extracellular fluids
Leukocytes functions
- Exhibit positive chemotaxis
- Leukocytosis
Positive chemotaxis
The following of WBCs to chemical trails of molecules from damaged cells as they migrate towards tissue damage and infection
Leukocytosis
An elevated WBC count
Characteristic of infection as different types of WBCs are activated by different types of infection
Granulocytes
- Major group of leukocytes
- Large cells with lobed nuclei and visibly staining granules
- Phagocytic
- Also known as Polymorphonuclear cells (PMNs)
Agranulocytes
- Lymphocytes and monocytes that lack visibly staining granules
- Also known as Peripheral Blood Mononuclear Cells (PBMCs)
Neutrophils
- 55-70% of all leukocytes (active phagocytes)
- Increased count is indicative of a bacterial infection
- pinkest-looking cell with a multi-blob (nucleus)
Eosinophils
- 1-4% of leukocytes
- Attack parasites in loose connective tissue (asthma and allergies)
- Effective against multicellular endoparasites (worms)
- Reddest looking leukocyte, more grainy than neutrophils
Basophils
- Least numerous types of leukocyte (0.5-1%)
- Release histamine to promote inflammation
- Associated with multicellular exoparasites (ticks)
- Almost entirely purple, nucleus not visible under microscope
Lymphocytes
- 20-40% of leukocytes
- T lymphocytes: directly attack infected cells and tumour cells
- B lymphocytes: Bind antigens and produce antibodies as plasma cells
- Natural killer (NK) cells: similar functions as T cells but are part of the innate immune response
Monocytes
- 2-8% of leukocytes
- Enter tissues and activate lymphocytes
- Common in chronic infections and inflammatory autoimmune diseases
- Active phagocytic macrophages to clean up dead cells
Leukopoiesis
Formation of white blood cells
- Regulated by the production of interleukins and colony-stimulating factors (CSF)
Differentiation of hemocytoblasts
2 Pathways of leukopoiesis
- Lymphoid stem cells develop into lymphocytes
- Myeloid stem cells develop into all other WBCs, platelets and RBCs
Band cells
Immature granulocytes like reticulocytes are immature erythrocytes
Leukopenia
- An abnormally low WBC count from drugs like glucocorticoids or anticancer cells
Leukemia
- Cancers in which clones of a single WBC remain unspecialized and divide out of control
Infectious mononucleosis
Disease caused by Epstein-Barr virus that provokes the body to create lots of B cells and they all get infected
Platelets
Not complete cells, but fragments of megakaryocytes (bone marrow cells)
- Lifespan of approximately 10 days
- Critical to the blood clotting process
Thrombopoietin
A hormone that regulates the formation of platelets by the repeated mitoses of megakaryocytes without cytokinesis
Hemostasis
- Prevention of blood loss
3 Steps: - Vascular spasms
- Platelet plug formation
- Coagulation (blood clotting)
Vascular spasms
Immediate vasoconstriction by the smooth muscle in response to blood vessel injury, causing less blood to flow so other mechanisms can begin
Platelet plug formation
When the endothelium is damaged, platelets stick to exposed collagen fibres forming the platelet plug
- When activated, the platelets swell, become spiked and stick to each other and the damaged blood vessel wall
- This activates a positive feedback loop
Coagulation
A multi-step process where the blood goes from liquid to gel
- Reinforces platelet plugs with fibrin threads
- Pro/anticoagulant; factors that promote or inhibit clot formation
3 stages of the clotting process
- Formation of prothrombin activator through intrinsic/extrinsic pathways
- Prothrombin activator catalyzes the transformation of prothrombin to thrombin
- Thrombin converts soluble fibrinogen to fibrin, fibrin causes the plasma to turn into gel, thrombin also activates the fibrin stabilizing factor to cross-link fibrin into a strong mesh to stabilize the clot
Intrinsic pathway
- This is called this because all factors necessary are present in the blood
- This is a slower clotting pathway but can clot blood
- Does not play a major role in injuries
Extrinsic pathway
- triggered through an endothelium-derived glycoprotein tissue factor (TF)
- Can occur rapidly by bypassing some steps of the intrinsic pathway
- Much more important for clotting blood
Clot retraction
The contractile proteins (myosin and actin) within platelets contract and pull on neighbouring fibrin strands, squeezing the plasma to clot and pulling damaged tissue edges together
Platelet-derived growth factor
This stimulates repair by endothelial cell division
Fibrinolysis
This removes unneeded clots through the action of the fibrin-digesting enzyme, plasmin
Factors limiting clot formation
- Rapidly moving blood spread apart clotting factors before they can start clotting
- Activated clotting factors are inhibited by other compounds in the blood, they need to have a minimum concentration for clotting to occur
- Vascular endothelium being smooth and intact prevents platelets from clotting
