Smith 1st Lecture Hemostasis and Blood Clotting

Question 1

Normal Hemostasis

Answer 1

• A well regulated process
• Maintains blood in a fluid, clot free state in normal vessels
• Induces a rapid formation of a localized hemostatic plug at the site of vascular injury
• Promotes healing of wounds

Question 2

Normal Sequence of Hemostasis

Answer 2

• Arteriolar Vasoconstriction (transient….the moment after papercut before the blood is present/temporarily stops blood but doesn’t work well enough to stop blood, just delays it)
  
  • Reflex neurogenic mechanisms
  • Bleeding would resume after vasoconstriction if it weren’t for the activation of platelets and the coagulation systems
• Vasoconstriction (lasts 60 sec/1 minute)
  
  • Reduces blood flow
  • Permits better interaction among:
    
    • Platelets
      * Blood Coagulation
      * Site of Injury

Example: Papercut is a demonstration of local vasoconstriction

Question 3

Systems of Hemostasis

Answer 3

1. The soluble system (procoagulant proteins)
2. The cellular system (platelets)

IMPORTANT: Both of these need to be working well for good hemostasis and eventually good wound healing

Question 4

“Activation of the soluble coagulation system” leads to what end product?

Answer 4

Fibrin clot (red thrombus)

Sidenote: This can also be called “Red Clot”. It floats around in the liquid part of blood (plasma). Know that the word “Plasma”=the liquid part of blood

Question 5

“Platelet Stimulation + Adhesion (sticky) + Aggregation (clump together)” leads to what end product?

Answer 5

Platelet Plug (white thrombus)

Sidenote: Know that the red thrombus is for Soluble system and white thrombus is for cellular system. These clots/thrombus are different and develop in different parts of circulation. Deep vein thrombosis (DBT) is primarily red thrombus
vs. Stuff that causes strokes and heart attacks is primarily white thrombus. You need both systems to work properly to be healthy/safe.

Question 6

The two coagulation systems are Intimately Interwoven (if one isn’t working well, then it will be bad for the other)

Answer 6

*Soluble coagulation proteins (e.g. fibrinogen + Von Willebrand Factor) are essential for normal platelet function

• Platelets
  
  • Suppliers of procoagulation proteins
  • Catalysts of reactions of the soluble coagulation system

Question 7

WHAT TO REMEMBER!!!!

Answer 7

• Both the platelet and soluble proteins contribute equally to normal hemostasis.
• Alterations with the coagulation proteins and/or the platelet number or function may lead to clinical symptoms in your patient.

Question 8

Unstimulated Platelets

Answer 8

• Small 3.6 plus/minus 0.7um in diameter
• Disk shaped
• No nucleus
• Smooth plasma membrane supported by a ring of microtubulin
• Fragments of megakaryocyte cytoplasm (megakaryocytes are in BONE MARROW)
• Normal platelet count is 100,000-450,000/ul of blood
• Platelet life-span is approximately 10 days in the circulation ( prof said 8 to 10 days)…so platelets live longer than granulocytes (which fight infection) but not as long as red cells (which carry oxygen).

Question 9

Functions of Platelets

Answer 9

• Hemostasis
• Inflammatory Response
• Tissue Repair
• (DOWNSIIDE:) ARTHEROGENESIS (so they play a big role in heart attacks, strokes, cardiovascular disease)

Question 10

Cell Biology of Platelets

Answer 10

“Pluripotent Stem Cells (in Bone Marrow)” give rise to the following:

• Red Cells
• White Cells (neutrophils and monocytes)
• Megakaryocytes (which is what the platelets come from)

So Pluripotent stem cell —> Megakaryocytes (and others) —-> Platelets

*So be aware that problems in stem cells of patients could cause problems with all of these, and so it could cause platelet problems!

Question 11

Humoral Regulation of Platelet Production

Answer 11

*Platelet production (from BONE MARROW) can be increased 8x in times of increased demand (example: motorcycle accident patient could have 8x increase in platelet count because the body is trying to respond to prevent tremendous bleeding)

(So, BONE MARROW is VERY IMPORTANT)

*Megakaryocyte numbers in the bone marrow can be increased during times of increased demand for platelets

Question 12

Thrombopoietin

Answer 12

• Identified in 1994
• Lineage specific stimulatory regulator of megakaryocyte development and platelet production (So you could give your patients an analog/synthetic form of this of this to drive their platelet counts up)
• Produced primarily in the LIVER (most things involved in hemostasis are made in liver, except a few things, so if you don’t know guess liver! And so people with liver problems/liver failure will have platelet problems!)
• Trace amounts of mRNA detected in the kidney (but not clinically significant, just small amounts)

Question 13

Platelet Structure

Answer 13

*Contractile microfilaments extend from the submembraneous space throughout the platelet cytoplasm and are responsible for dramatic shape changes which accompany platelet activation

• Four types of granules
• alpha-granules
• Dense granules
• Lysosomes
• Peroxisomes

(Aspirin/NSAIDs impair release reaction/impair platelets)

Question 14

Platelet alpha-Granules

Answer 14

*Most abundant platelet granule

• Contain both platelet specific and platelet non-specific peptides
  
  • contribute to and modulate coagulation, inflammation, immunity, and tissue repair

(alpha-Granules play a lesser role in the hemostatic process)

Question 15

Platelet Dense Granules

Answer 15

• Rich repositories of:
• Serotonin and ADP, lead to aggregation of platelets (So serotonin and ADP recruit platelets to create the white thrombus that we need at the point of injury)

(**Therefore PLATELET DENSE GRANULES are VERY IMPORTANT because they contain the Serotonin and ADP)

• ATP leads to anti-aggregation
• Calcium, an essential coagulation factor (Calcium is needed for clotting, but it will never be low enough to cause bleeding because the patients HEART WOULD STOP before the calcium level was low enough to cause bleeding!)

Question 16

Platelet Function

Answer 16

• Promotion of immediate homostasis by platelet adhesion and platelet aggregation leading to the formation of platelet plug (so adhesion is when platelet sticks to something, usually collagen Vs. aggregation is when platelet and platelet stick together/clump)
• Local release of vasoconstrictors to decrease blood flow to the injured area (this can be good if needed in certain parts for surgery but can be BAD if it occurs in microcirculation in BRAIN or HEART)

Question 17

Platelet Function

Answer 17

• Catalysis of reaction of the soluble coagulation cascade leading to fibrin clot formation
• Initiation of tissue repair process

(so if you have low platelet numbers, the patient won’t heal as well)

*Regulation of local inflammation and immunity (Note: INFLAMMATION = symptoms of Pain, Redness, Swelling in patients and this may be due to/caused by a clot that sets off inflammatory reaction)

Question 18

Platelet Adhesion (This slide has pathway)

Answer 18

“Damaged vascular endothelium” (maybe due to surgery)

Leads to

“Exposure of subendothelial extracellular matrix”
- COLLAGEN binds to platelet membrane GPIa receptor

ENDOTHELIAL CELLS - make LARGE MULTIMERS of von Willebrand Factor (Exam question: know that endothelia cells make von Willebrand Factor! The von Willebrand Factor is the only clotting factor that is NOT made by the liver but by endothelial cells, so it is the exception to the rule!)

The von Willbrand Factor (it really likes Factor VIII (8) and is the best friend of platelets) —–>

Binds to:
1) platelet membrane glyco - protein Ib (GPIb) receptor 2) platelet membrane GPIIb/IIIa receptor (Note: this GPIIb/IIIa (2b/3a) receptor is very specific to the bundle/multimer of van Willbrandand it is IMPAIRED by a lot of DRUGS! Cardiologists depend on that impairment in cathlab and putting stents into patients, etc)

Question 19

EXAM: What you need to know about Platelet Adhesion!

Answer 19

PLATELET ADHESION is the First Step. Here, platelets stick to the collagen and they NEED van Willibrand factor for that to be optimized!

(Prof said this is all you need to know)

Question 20

Platelet Adhesion (Summary)

Answer 20

(So, If you only had adhesion, this would get you started and control bleeding for a little while, but this would not be good enough!)

Platelet adhesion —->

1) Marginal degree of hemostasis
2) Activation of platelets (this is the more important part we need, activation = turning platelets on)…. this leads to ——->

1) Shape change of platelets
2) Irreversible Secretion of dense granule and alpha-granule contents
(The Dense Granules and alpha granules are most important for next step/goal!)

which leads to —-> Platelet Aggregation (so you are building a bigger thrombus)

***Note: The Irreversible Secretion (also called “Release Reaction”) has become a TARGET for a lot of therapy. This is where aspirin/non-steroidals work! So if you were to get operation after taking these, your platelets wouldn’t work as well and you would be oozy, so your surgeon would want to know if you took this beforehand.

Question 21

Laboratory Evaluation of Platelets

Answer 21

1) Platelet count
- uses a particle counting instrument
- “EDTA induced pseudothrombocytopenia” is a rare familial disorder that needs to be recognized so that you don’t diagnose patients as having low platelet count when they really don’t but actually have this rare disorder that reacts with EDTA used during test to lower calcium and temporarily have low platelet count as a result of the EDTA reaction due to this disorder!
- manual counting

2) Platelet volume measurement
- platelet volume increases when production accelerates (because when new platelets are made they are very big, but over time they shrink…so that’s why after surgery you have new platelets made which are big and can result in clots/so that can cause problems, so we need to try and protect these people from clotting post-surgery)

(Platelet volume can be measured and is units MPV=Mean Platelet Volume, and so I think when this is a high value be careful of patients having clots in near future…..older physicians may not know how to use the MPV value, but you will know and they will retire eventually!)

3) -Platelet function
- Qualitative platelet dysfunction (whole blood platelet function or bleeding time)

(Nowadays we don’t do painful “bleeding time” but use the instruments to do “whole blood platelet function” screening in order to pick up these two main things: “Aspirin Effect” or “von Willibrands disease” (the inherited inability to make this sticky protein and lack of it so that we can know about this issue before going to operating room)

4) Platelet aggregometry

(This is extra/last step if there is any doubt, such as if patient needs a neurosurgical procedure where neurosurgeon wants to know if he can operate on patient’s brain. This is done if there is high suspicion of platelet dysfunction and whole blood screening suggests there is something there or if it is normal but patient history is very compelling. This aggregation is much more detailed study of how the platelets respond to various agonists that they see normally (which include collagen and ATP).

Question 22

WHAT TO REMEMBER (about Platelets)!

Answer 22

• Platelets, although small, are VERY important to normal hemostasis.
• Changes in platelet number and/or function can cause significant effects in your patients.

Question 23

Normal Hemostasis slide 38.22 minutes

Answer 23

vascular break or injury —->