Blood

Question 1

Steps of haemostasis

Answer 1

1. Vasoconstriction
2. Platelet plug formation
3. Clotting cascade

Question 2

Coagulants and Anticoagulants

Answer 2

Anticoagulants - prevent positive feedback of continuous growth of platelet plug - prevent permanent plug.
Coagulants/clotting: circulatory soluble plasma proteins called fibrinogen are converted to insoluble polymers strands to fibrin which forms a mesh, trapping blood cells ans preventing blood loss.

Question 3

Explain Coagulation and clotting

Answer 3

Most clotting achieved in extrinsic pathway - activated by tissue factor 3 which then activates the production of thrombin, thrombin feedbacks and activates the intrinsic pathway then stimulates more thrombin to be produced. Most thrombin is produced in intrinsic pathway, factor 3 links together glutamen ans liazen. No platelet plug = no clotting

Question 4

Explain clot stabilisation and retraction

Answer 4

Stable fibrin mesh surrounds platelet plug. Clot retraction - actin and myosin filaments in platelet contract, drawing edges of wound together (thrombin stimulates release of intracellular Ca)

Question 5

Fibrolytic System

Answer 5

• clotting is dissolved, catalysed by enzyme plasma. Digest fibrin present in clots
• Plasmin converted from plasminogen which circulates in inactive form (like fibrinogen)
• Tissue plasminogen activator (t-PA), relased by endothelial cells, promotes conversion of plasminogen to plasmin leading to breakdown of fibrin, fibrinogen and Factor V and VIII
• t-PA incorperated into clot during formation
• Binding to fibrin increases the enzymatic activity of t-PA
• inhibition by Plasmin Activator Inhibitor (PAI-1) - platelet rich source

Question 6

What are Cytokines

Answer 6

• Soluble mediators
• Produced by many different cell types in response to microbes, tissue damage or other antigens.
• Communication system - act locally or at a distance
• Regulate and co-ordinate the cells of innate and adaptive immunity

Question 7

Explain Phagocytosis, Degranulation, and NETosis

Answer 7

Phagocytosis - process of engulfing and killing pathogens
Degranulation - release of content of the granules to the environment to kill microbes
NETosis - the process of generation of Neutrophil Extracellular Traps (NETs) formed by DNA and histones, granular proteins, and cytoplasmic proteins

Question 8

Macrophages

Answer 8

Precursors formed in bone marrow
Circulates as monocytes and migrate towards tissues where they become macrophages
Macrophages are found in tissues
Function: clearance of microbes but also apoptotic cells and foreign particles

Question 9

Explain complement system

Answer 9

Three pathways - activated by microbes (lectin and alternative) or antibodes (classical)
Activation of the complement happens on the surface of target cells.
Activation leads to cleavage of complement components into large and small active fragments - they have different functions within the immune response.
C3a and C5a (small fragments) activaate immune cells and serve as chemoattractant - activate further the immune response. Moleclues such as C3b can act as tags which enhance phagocytosis (=opsonins).
C5b can combine with other complement proteins (C6, C7, C8, C9) to make the membrane attacj complex (MAC) - forms pores on the membrane of pathogens (fast).