Lecture 4: Hemostasis Flashcards
Hemostasis
Prevents blood loss from a broken blood vessel
Hemostasis
Prevents blood loss from a broken blood vessel
Hemostasis Involves 3 major steps
- Vascular spasm
- Reduces blood flow through a damaged vessel
- Formation of a platelet plug
- Platelets aggregate on contact with exposed collagen in
damaged wall of the vessel - Platelets release ADP which causes surface of nearby circulating
platelets to become sticky in order to adhere to first layer of
aggregated platelets
- Platelets aggregate on contact with exposed collagen in
- Blood coagulation (clotting)
Transformation of blood from liquid into a solid gel
Platelets
cellular entities important for clotting
Thrombocytes
(AKA platelets)
Cell fragments shed from megakaryocytes
- Lack nuclei
- Have organelles and cytosolic enzymes for generating energy
and synthesizing secretory products
- High concentrations of actin and myosin
- Remain functional for an average of 10 days
- Removed from circulation by tissue macrophages
Do thrombocytes leave blood as WBCs do
NO:
- About ⅓ are stored in blood-filled spaces in spleen
- Released when needed by sympathetically induced splenic
contraction
Thrombopoietin
Hormone produced by liver increases number of megakaryocytes and therefore increases platelet production
What do platelets do?
thrombocytes are actually tiny cell fragments that circulate in blood and are essential for normal blood clotting.
When there is an injury and bleeding begins:
- platelets help stop bleeding by adhering to the injury site and
clumping together to form a temporary plug.
- They also release chemical signals that attract and promote
clumping of additional platelets and eventually become part of a
stable blood clot at the site of the injury that remains in place until
the injury heals.
High/ low platelet count
If you have a disease or condition that causes low platelets (thrombocytopenia) or dysfunction of platelets, you may be at an increased risk of excessive bleeding and bruising.
An excess of platelets (thrombocytosis) can cause excessive clotting.
Label these 4 images
A- RBCs and a platelet
B- RBC
C- RBC membrane
D- Platelet
Clot formation
- In circulation platelets and plasma proteins allow the body to form clots - prevents bleeding out
- Reinforces platelet plug and converts blood in the vicinity of vessel injury into a nonflowing gel
Abnormal blood clotting
Results from:
- Too much inflammation and inflammatory biomarkers in circulation
that act on the plasma proteins and platelets
- the platelets become hyperclottable and they hypercoagulate
= Clots = cause strokes and heart attacks
Abnormal Blood Clotting: hypercoagulation types
- Thrombus: Abnormal intravascular clot attached to a vessel wall
- Emboli: Freely floating clots
Plasma clot in a healthy person
plasma clot when inflammation is present e.g. diabetes
- Sample from a person which had a stroke less than 2 hours
before - The platelets are totally destroyed and are hyper-activated
- Also see strange RBC (in B) = aerothotic red blood cell - cant carry
O2 properly - This person had a thromboembolic stroke;
Where the specific blood areas - the platelets and different plasma proteins (in C) form a clot in one vessel = stroke
