Haemostasis practical

Question 1

Blood has 3 general functions

Question 2

examples of transport function of blood

Answer 2

deliver oxygen and nutrients to cells

transport hormones to effector organs

remove metabolic waste products from cells

Question 3

regulatory function of blood

Answer 3

absorb and districute body heat

naintain adequate fluid volume

Question 4

protective function of blood

Answer 4

prevent blood loss via clotting

prevent infection

Question 5

what is plasma

Answer 5

it makes up 54% of blood volume

is the cell-free component of blood. It contains proteins, molecules and ions. Its pale-yellow colour comes from bilirubin.

Question 6

Buffy coat

Answer 6

(<1% of volume) is the thin white layer that is observed between plasma and red cells after the centrifugation of blood. It contains leukocytes (white blood cells) and thrombocytes (platelets).

Question 7

erythrocytes

Answer 7

make up 45% of volume in males and ~42% in females. This value is called the haematocrit, or packed cell volume (PCV).

Question 8

a reduced PVC means that

Answer 8

Patient has fewer RBCs. Their blood therefore has a reduced carrying capacity than normal and her heart rate and cardiac output may increase to compensate. The viscosity of the blood will also be reduced. Conversely, an increased PCV increases the viscosity increasing the force (afterload) required to pump blood around the body.

Question 9

what is the structure of a platelet

Answer 9

Platelets are anucleate cells and are the smallest formed element in blood.

They are bi-convex discs (smartie-shaped) with a maximum diameter of approx. 2-3 micrometres. They are approx. 1/10 the size of RBCs by volume. Platelets contain granules that contain a variety of substances important in haemostasis.

They also contain functional mitochondria. Platelet lifespan is approx. 7-10 days.

Question 10

function of platelets

Answer 10

Play an essential role in haemostasis. They respond rapidly when a blood vessel in injured.

Within seconds, platelets accumulate at the site of injury and bind to exposed collagen in the vessel wall and surrounding tissue.

Question 11

collagen binding, activates the platelets via

Answer 11

glycoprotein VI (GpVI)

Question 12

how to activated platelets change?

Answer 12

1. shape
2. bind to each other
3. release chemical mediators to support haemostasis
4. Move PS (phosphatidylserine lipids) from the inner leaflet to the outer leaflet

Question 13

explain how platelets change shape and spread across damaged tissue

Answer 13

they project pseudopodia, giving them a star shaped appearance

they increase their surface area for their interaction with damaged tissues and each other

Question 14

explain activated platelets binding together- aggregation

Answer 14

• process is mediated by fibrinogen binding to the platelet receptor GPIIb/IIIa
• this receptor is usually present in high concentrations but has a low affinity for fibrinogen until it is activated and changes its conformation
• each fibrinogen molecule can bind to and activate 2 platelets simultaneously- cross linking
• the GPIIB/IIIa receptor is an important target for therapeutic anti-platelet drugs

Question 15

Why do platelets release chemical mediators? what do they release?

Answer 15

to support haemostasis

promote further platelet activation

recruit additional circulating platelets

most important mediators are:

ADP (released from dense granules)

T_xA₂ (synthesised de novo by COX and thromboxane synthase enzymes)

they both activate other platelets and cause aggregation at the site of injury- aiding in the production of thr primary haemostatic plug

Question 16

Explain the flipping of phosphatidylserine (PS) lipids

Answer 16

• moving PS lipids from the inner leflet to the outer membrane exposes the PS lipids
• they are negatively charged and provide a scaffold on whjich coagulation factors can accumulate in a Ca2+ manner
• • this supports the localisation and activation of coagulation factors at the site of injury

Question 17

for a venous clot what drugs do you use

Answer 17

anticoagulation

Question 18

for an arterial clot what drugs should you use

Answer 18

antiplatelet

Question 19

what does haemostasis mean

Answer 19

arresting of bleeding

Question 20

what part of the blood vessel is occupied by platelets

Answer 20

closer to the vessel wall, away from the centre

Question 21

whta are the 3 steps of haemostasis:

Answer 21

1. vascular spasm
2. platelet plug formation
3. coagulation

Question 22

explain vascular spasm

Answer 22

local vasoconstriction in response to vessel injury to reduce the speed and volume of blood extravasating

triggered by injury itself as well as chemicals relased from endothelial cells and platelets

Question 23

name two chemical mediators relased by platelets that cause vasospasm

Answer 23

serotonine

thromboxan A2

Question 24

what are the 3 steps involved on platelet plug formation

Answer 24

adhesion

activation

aggregation

Question 25

explain the adhesion step in platelet plug formation

Answer 25

platelets are slowed down and captured at the site of injury via an interaction with von Willebrand factor (bonds to collagen and platelets)

platelets then bind directly to collagen by receptor GPIIIb/IIa

Question 26

explain the activation step of platelet plug formation

Answer 26

when they bind to collagen via the they are activated GPVI, changing shape and spreading out

Question 27

What do alpha granules contain

Answer 27

vWF, firbinogen, factor V and GPIIb/IIIa

Question 28

What is thromboxane originated from

Answer 28

it is synthesised de novo from released arachidonic acid via COX and thromboxane synthase

it is an agonist at TP receptors causing platelet activation and vasoconstriction

Question 29

what is coagulation

Answer 29

the process of changing from a liquid to a solid

means that the primary secondary plug matures into a secondary one

Question 30

An inappropriately formed thrombus is called a

Answer 30

thrombosis

Question 31

2 kinds of thrombosis

Answer 31

arterial- platelet rich (white thrombi) and are responsible for thromboses in coronary arteries resulting in MI and thrombotic stroke

venous- tend to be rich in fibrin (red- due to RBC) and form in deep vein thrombosis, these are the kind that typically cause PE

Question 32

what is a bleeding diathesis and give 2 examples

Answer 32

A bleeding diathesis (predisposition or sensibility) is a tendency to bleed excessively. Inherited bleeding diatheses include:

Von Willebrand Disease and haemophilia A

Question 33

haemostasis pathway from vessel injjury to formation of stable blood thrombus

Answer 33

platelets adgere to sub-endothelial collagen

platelet activation via GPIIb/IIIa receptor

adherent platelets relase mediators ADP and TxA2

platelet aggregation with formatin of primary haemostatic plug

coagulation fac tors accumualte on activated platelets

conversion of prothrombin FII to thrombin IIa

conversion of soluble fibrinogen to insoluble fibrin Ia

Question 34

What is thrombocytopaenia

Answer 34

low platelet count

Question 35

antithrombotic factors

Answer 35

some coagulation factors are K+ dependant (II, VII, IX and X), having a K+ deficiency can lead to excessive bleeding

haemophilias are genetic disorders that impair the blood’s ability to coagulate

aspirin is an irreversible COX inhibitor- preventinf platelets from synthesising TxA2 from arachidonic acid