Blood Loss Flashcards
What is Hemostasis?
- A sequence of responses that stop bleeding when blood vessels are injured
- Response must be quick, localized, and carefully controlled
What are the three mechanisms that can reduce loss of blood from cells?
- Vascular spasm
- Platelet plug formation
- Blood clotting (coagulation)
Where can/cannot hemostasis prevent hemorrhage?
- Can: smaller blood vessels
- Cannot: larger vessels
What is vascular spasm?
- When vessel is damaged, the smooth muscle in its wall contracts immediately
How long does vascular spasm last?
- Several minutes to several hours
What is platelet plug formation?
When platelets come into contact with damaged vessels, they change characteristics and form a plug to fill the gap in the injured vessel.
What are the steps to platelet plug formation?
- Platelets contact and stick to injured blood vessel
- Platelets interact with each other and begin to release chemicals
- Chemicals activate near platelets and sustains vascular spasm
- Chemical release causes stickiness which brings multiple platelets together
- Large number of platelets forms plug
What is blood clotting (coagulation)?
Blood thickens and forms a gel that eventually separates from liquid.
- Gel is the clot
- Consists of network of fibrin
What is fibrin?
Insoluble protein fibers
What is the process of coagulation?
- Series of chemical reactions that culminates in formation of fibrin threads
- Too easy to form clot, thrombosis forms
- To long to form, hemorrhage results
What are the clotting factors?
- Calcium ions (CA2+)
- Several enzymes made by liver cells and released into blood
- Various molecules associated with platelets and released by damaged tissue
How are clotting factors identified?
Roman numerals
What are the 3 steps to clotting?
Step 1: Prothrombinase is formed
Step 2: Prothrombinase converts prothrombin into the enzyme thrombin
Step 3: Thrombin converts soluble fibrin into insoluble fibrin
What is Prothrombin and where is it created?
Plasma protein formed in the liver with the help of Vitamin K
What forms the threads of the clot?
Fibrin
What contains substances that interfere with fibrin and clot formation?
Cigarette smoke
What is clot retraction?
Consolidation or tightening of the fibrin clot
What is the purpose of clot retraction?
Pulls the edges of injured vessels walls closer together, decreasing risk of further injury
What do fibroblasts form?
Connective tissue in the ruptured area
- new endothelial cells repair the vessel lining
What occurs simultaneously with coagulation?
Fibrinolysis
What is fibrinolysis?
Enzymatic breakdown of fibrin within clots
How can endothelial surfaces of blood vessels be roughened?
- Atherosclerosis
- Trauma
- Infection
What is clotting in an unbroken blood vessel? The clot itself?
Thrombosis; Thrombi
What are the two ways clots can form in unbroken blood vessels?
- Blood vessel surfaces may be roughened
- When blood flows too slowly
