Homeostasis, Haemorrhage and shock Flashcards
What is Shock
Excessive blood loss is a medical emergency
The decreased blood volume results in a fall in blood pressure and impaired delivery of nutrients to cells
This state is called shock
Why should even ‘regular patients’ be asked routinely about changes in their medical condition and medications
“D.B, aged 69, of North London, bled to death from having a tooth removed after failing to tell his dentist about his chemotherapy treatment for leukaemia. An inquest at Hornsey recorded a verdict of death by misadventure.”
What are the physiological responses to blood loss
Immediate:
-Stop the bleeding
Short term:
-Restore blood pressure
Medium term:
-Restore fluid volume
Long term:
-Replace blood constituents
What components are considered when trying to stop blood loss
Vascular response
Platelet response
Plasma response (Coagulation)
What components make up the vascuar response to blood loss
Smooth muscle
-Spasm due to trauma
-Myogenic response
-Humoral factors (vasoconstrictors)
Endothelium
-Platelet adhesion and aggregation
-Anticlotting and fibrinolysis
How do platelets respond to blood loss
Damage to blood vessel - turbulent blood flow - platelets come into contact with vessel wall (collagen)
Platelets adhere; clump together (aggregate)
Release chemicals that cause further aggregation (Positive feedback)
Formation of platelet plug
Effective in sealing small blood vessels
How does the platelet response cause vasoconstriction
The aggregated platelets release thromboxane and ADP which help form platelet plug while thromboxane alsoacts as a vasoconstrictor
How does coagulation occur
Various plasma proteins and tissue components combine to convert fibrinogen fibrin to form the blood clot
Numerous ‘clotting factors’ are involved
Many of these are made in the liver
The synthesis of several clotting factors requires the presence of vitamin K
The clotting factors are activated in an enzyme cascade
One activated factor activates the next one in the sequence
What proteins are needed to form insoluble fibrin
Prothrombin - thrombin
Fibrinogen - soluble fibrin
Factor XIIIa is used to convert soluble fibrin to insoluble fibrin
Why does blood clotting factor VI not exist
Fcator4 and 6 were the same
What blood clotting factors exist
I. Fibrinogen
II. Prothrombin
III. Tissue factor (‘thromboplastin’)
IV. Calcium ions
V. Proaccelerin
VII. Proconvertin
VIII. Antihaemophilic globulin
IX. Christmas factor
X. Stuart-Prower factor
XI. Plasma thromboplastin antecedent
XII. Hageman factor
XIII. Laki-Lorand factor
What occurs within the extrinsic pathway to activate coagulation
Tissue damage,
Tissue factors (‘tissue thromboplastin’)
Factor VII
What are the two pathways of coagulation
Intrinsic and extrinsic
What occurs to activate the intrinsic pathway to coagulation
Vascular damage,
Contact activation involving Factors:
XII, XI, IX, VIII
Phospholipid and calcium ions react with Factor X to create Factor Xa
Why do we have an intrinsic and extrinsic pathway
The extrinsic pathway seems to be more important in initiating clotting after an injury
The intrinsic system serves to maintain the process once it has started
However, the intrinsic system may have a role in events such as thrombosis; here, a blood clot forms inside an intact blood vessel
What is fibrinolysis
When the blood clot has served its purpose it is dissolved
What enzyme is involved in fibrinolysis
Plasmin
How is Plasmin produced
Plasminogen reacts with plasminogen activator to form plasmin
What does plasmin react with to breakdown the blood clot
Breaksdown Fibrin into soluble fibrin fragments
What happens to blood pressure in the short term in response to blood loss
Fall in blood pressure
Compensatory mechanisms triggered by the arterial baroreceptors
These mechanisms aim to restore the blood pressure
What hormones are involved in the mediation of the baroreceptor reflexes
Adrenaline
Angiotensin II
Vasopressin (ADH)
What nerves mediate baroreceptor reflexes
Sympathetic nerves
What effect does a decrease in blood volume have on the CVS centres
They increase the sympathetic NS activity
What does an increase in both ventricular contraction and vein constriction cause
An increase in stroke volume
