Blood practical

Question 1

Blood’s transport function

Answer 1

1) deliver oxygen and nutrients to cells
2) Transport hormones to target organs
3) Remove metabolic waste products from cells

Question 2

Regulatory function of blood

Answer 2

1) Absorb and distribute body heat
2) Maintain adequate fluid volume

Question 3

Protective function of blood

Answer 3

1) Prevent blood loss via clotting
2) Prevent infection

Question 4

Components of blood

Answer 4

Plasma- cell-free, contains proteins, ions and molecules.

Buffy coat- thin white layer seen between RBCs and plasma after centrifution. Contains platelets and leukocytes.

Erythrocytes- haematocrit or packed cell volume

Question 5

Meaning of a reduced PCV

Answer 5

• Patient has fewer RBCs
• Blood therefore has a reduced carrying capacity than normal and HR and CO may increase to try and compensate.
• Reduced viscosity of blood

Question 6

Structure of a platelet

Answer 6

Anucleate cells

Biconcave discs

Contain granules that contain substances crucial for haemostasis

Contain functional mitochondria

Question 7

Initial function of platelets

Answer 7

Rapid response to vessel injury

Accumulate and bind to exposed collagen in wall and surrounding

Question 8

How are platelets activated?

Answer 8

1) Exposed collagen binds via GP Ia/IIa (receptor for collagen)
2) soluble agonists released by activated cells such as
(1) ADP
(2) thromboxane A2 (TxA2)
(3) thrombin

trigger platelet activation through GPCR

Question 9

How do activated platelets change function?

Answer 9

1) Change shape and spread across damaged tissue
2) Activated platelets aggregate (bind together)
3) Release chemical mediators to support haemostasis, promote further platelet activation and recruit adittional circulating platelets
4) Move phosphatidylserine (PS) lipids from the inner leaflet of their memebrane to the outer leaflet.

Question 10

How do platelets change shape

Answer 10

Become activated then become star shaped and increase their surface area

Question 11

Process of platelet aggregation

Answer 11

mediated by fibrinogen binding to platelet receptors GPIIIb / IIIa

Each fibrinogen molecule has 2 spatially distant binding sites for platelets and can therfore bind 2 at once. This cross linking sustains aggregation.

Question 12

What chemical mediators do platelets produce?

Answer 12

Thromboxane (T_xA2 )

ADP

Arachidonic acid

Question 13

Thrombaxane T_xA₂

Answer 13

Produced by platelets during haemostasis

has prothrombotic properties by activating platelets

circulating fibrinogen binds thromboxane receptors on platelets activating them.

Vasoconstrictor

Question 14

ADP (adenosine diphosphate)

Answer 14

Platelet agonist

causes platelet shape change, aggregation and generte thromboxane

Question 15

Effect of platelets moving PS lipids

Answer 15

By flipping PS lipids from the inner leaflet of their membrane to the outside leaflet (Platelets) they are engaging in procoagulant activity.

Negatively charged PS provides a scaffold on wjich coagulation factors accumulate in a Ca2+ dependant manner.

Therefore, platelets help localise and activate coagulation factors at the site of injury

Question 16

Platelet production

Answer 16

Thrombopoietin stimulates megakaryoblasts –> megakarypcyte –> plasma membrane invades cytoplasm, dividing it into compartments

Cell then ruptures and the compartments become cells

Question 17

What part of the vessel are platelets found

Answer 17

Borders

Question 18

3 steps of haemostasis

Answer 18

1) vascular spasm (vasoconstriction to reduce BF)
2) Platelet plug formation
3) Coagulation

Question 19

Vascular spasm

Answer 19

Local vasoconstriction

Triggered by the damage itself as well as chemicals released by endothelial cells and platelets (e.g. serotonine and thromboxane)

Question 20

3 steps of platelet plug formation

Answer 20

1) adhesion
2) activation
3) aggregation

Question 21

adhesion step of platelet plug formation

Answer 21

platelets are slowed and captured at the site of injury by von Willebrand Factor (vWF simultaneosly bonds to collagen and platelets).

Platelet adhesion to collagen is mediated by the platelet receptor GpVI

Question 22

Activation step of platelet plug formation

Answer 22

When platelets bind to collagen, they become activated (mediated by glycoprotein VI receptor)

Change shape and spread out

PS lipids relocate from the inner aspect of the platelet membrane to the outside, creating a negative framweork for the coagulation factors to stick to

Question 23

Arachidonic acid

Answer 23

Produced by plateletes

converted to thromboxane A2 by COX and thromboxane synthase

Question 24

Aggregation step of platelet plug formation

Answer 24

mediated by the binding of fibrinogen to activated GPIIb/IIIa on the surface of platelets thereby cross-linking them. As more platelets arrive in the circulation, they are activated by released ADP and TxA2, and aggregate to platelets already in the plug. This leads to the formation of a primary haemostatic plug.

Question 25

Arterial thrombosis

Answer 25

platelet rich

responsible for the thrombi in coronary arteries

Question 26

venous thrombosis

Answer 26

rich in fibrin

red thrombi due to the number of RBC trapped in

DVT and PE

Question 27

Order of events from vessel injury to formation of stable blood thrombus

Answer 27

vessel injury

platelets adhere to sub-endothelial collagen

platelet activation

adherent platelets release bioactive mediators (ADP and TxA2)

platelet aggregation with formation of primary haemostatic plug

coagulation factors accumulate on activated platelets

conversion of prothrombin to thrombin

conversion of soluble fibrinogen to insoluble fibrin

Question 28

Name 3 factors or receptors that help platelet adhesion to damaged tissue

Answer 28

Integrin a2B1

Glycoprotein Ib (GpIb)

von Willebrand factor

Question 29

Thrombocytopaenia

Answer 29

high platelet count

Question 30

thrombocytopenia

Answer 30

low platelet count

sign is petechiae

Question 31

Prothrombotic factors

Answer 31

Long periods of immobility

Combined oral contraceptive pill

more…?

Question 32

Anti-thrombotic factors

Answer 32

Vitamin k deficiency- some coagulation factors are dependant (II, VII, IX and X)

Haemophilias

Aspirin