Last updated on May 22, 2020 at 17:34
Haemostasis is the process that causes bleeding to stop. It’s basically the opposite of haemorrhage. Coagulation is obviously an important part. Haemostasis has three parts:
- Vasoconstriction of the affected vessel
- Happens within seconds
- Via neural and humoral pathways
- Platelet adhesion and aggregation forms a platelet plug
- Takes 3-7 minutes (the bleeding time)
- Coagulation occurs
- Fibrin is deposited
- Takes 5-10 minutes (the clotting time)
Fibrinolysis then dissolves the clot 48 – 72 hours later.
The normal platelet number is 150 000 – 400 000 platelets per µL, or 150 – 400 billion per litre (150 – 400 G/L).
Vascular disorders of haemostasis
This group of diseases often produce purpuras (small bleedings 0.3 mm – 1 cm in size) due to problems with the small vessels themselves (thereby the name “vascular”). They’re also called vascular purpuras. Common examples are:
- Hereditary haemorrhagic telangiectasia
- Ehlers-Danlos syndrome
- Acquired ones
- Senile purpura occurs in healthy elderly people due to natural weakening of vessels
- Scurvy, because vitamin C is important for collagen synthesis
- Cushing syndrome suppresses collagen synthesis
- Henoch-Schönlein purpura
- Rheumatoid arthritis
The bleeding time will be prolonged (the time it takes for platelets to form a plug), but the clotting time will be normal.
The Rumpel-Leede test is a test to determine how fragile the capillaries are. A tourniquet is applied to the patient with a pressure of around 100 mmHg for 15 minutes. This will cause purpuras to form in the forearm. Healthy people get around 10 purpuras, 10 – 20 purpuras is considered borderline and above 20 purpuras indicate some vascular abnormality.
Thrombotic disorders of haemostasis
This group of diseases also produces purpuras, but because of problems with platelets rather than problems with the vessels. They’re also called thrombocytopenic purpuras, and are either caused by too little platelet production, too high platelet destruction or problems with the platelets. Common causes are:
- Thrombocytopaenias (platelet count below 50 G/L)
- Wiskott-Aldrich syndrome
- Fanconi’s anaemia
- Suppression of bone marrow
- Increased sequestration (destruction) of platelets
- Autoimmune diseases (ITP, TTP)
- Disseminated intravascular coagulopathy
- Haemolytic-uraemic syndrome
- Thrombasthenia (platelet dysfunction)
- von Willebrand disease
- Bernard-Soulier disease
- Glantzman disease
The bleeding time will be prolonged, while the clotting time is normal.
57. Polycythemias, polyglobulias
59. Congenital and acquired coagulopathies