Blood Physiology Lecture 5

Question 1

Hemostasis is the _____

Answer 1

prevention of blood loss

Question 2

_____ are important in hemostasis

Answer 2

platelets

Question 3

platelets are found in the middle _______

Answer 3

“buffy coat” mixed with the white blood cells

Question 4

Why is hemostasis necessary? (3)

Answer 4

• Pro-hemostatic factors prevent blood loss

-Anti-hemostatic factors are factors which keep the blood fluid

-Our body tries to maintain a state where blood can circulate smoothly, without
formation of unnecessary clots

Question 5

Steps of homeostasis (3):

Answer 5

1. Vasoconstriction , Vascular Spasm
2. Primary Hemostasis or platelet plug formation
3. Secondary Hemostasis or blood clotting/coagulation

Question 6

Steps of homeostasis:1. Vasoconstriction Vascular Spasm

Answer 6

A ruptured blood vessel contracts to minimize blood loss at the site of the cut

(Factors which trigger vasoconstriction:)

• An injury stimulates pain receptors that activate nerve endings that are directly affected by the cuts, causing vasoconstriction

-Injury to blood vessel smooth muscle, causing vasoconstriction

-Local injury to the platelets causes the release of serotonin, which acts
as a vasoconstrictor

Question 7

Steps of homeostasis: 2. Primary Hemostasis or platelet plug formation

Answer 7

-Platelets aggregate to form a platelet plug or a white thrombus (It is known as white thrombus because platelets are colorless cells)

Question 8

Steps of homeostasis: 3. Secondary Hemostasis or blood clotting/coagulation

Answer 8

-If the bleeding does not stop after the formation of the white thrombus, blood clotting enzymes are activated to form a stronger gel-like clot at the cut site. This is known as red thrombus as it is reddish in color.

Question 9

The word thrombus refers to _______

Answer 9

a blood clot

Question 10

3 steps of the formation of platelets

Answer 10

1. Platelets originate from the pluripotent stem cells of the bone marrow
2. Pluripotent stem cells are converted to cells called megakaryocytes
3. Platelets are pinched off from the cytoplasmic part of megakaryocytes

Question 11

Platelets contain organelles such as _______

Answer 11

Vesicles called alpha granules and dense granules

Question 12

Platelets do not contain a ________

Answer 12

nucleus

Question 13

Things platelets contain (5)

Answer 13

1. Vesicles called alpha granules, and dense granules
2. Glycogen for energy
3. Contractile proteins actin and myosin
4. Surface glycoproteins which act as receptors
5. Canaliculi

Question 14

Contents of Alpha Granules (4)

Answer 14

-Adhesive protein von Wilebrand factor

-growth factors

-some blood clotting factors

-cytokines

Question 15

Contents of Dense Granules (3)

Answer 15

-ADP and ATP

-5-hydroxytryptamine (serotonin)

-calcium

Question 16

Alpha granules contain _______

Answer 16

large molecules

Question 17

Denses granules contain ______

Answer 17

small molecules

Question 18

Platelet Plug Formation (Primary Hemostasis) steps (3):

Answer 18

1. Adhesion
2. Activation of Platelets
3. Aggregation of Platelets

Question 19

Platelet Plug Formation (Primary Hemostasis) steps: Adhesion

Answer 19

-Platelets must adhere to a surface in the process of hemostasis

-Normally do not stick to the smooth surface of blood vessels but an injury to blood vessels disrupts the endothelial layer and exposes the underlying collagen

-Platelets adhere to the collagen tissue using von Willebrand factor

• von Willebrand factor is a protein secreted by platelets and
  endothelial cells

-Once secreted, von Willebrand factor can change conformation
and bind to platelets

• von Willebrand factor forms a bridge between the damaged
  vessel wall and the platelets

Question 20

Platelet Plug Formation (Primary Hemostasis) steps: Activation of Platelets:

Answer 20

• Binding of platelets to collagen triggers the release of chemicals from their storage granules (ADP and serotonin)
• ADP and serotonin act locally on the platelets to change metabolism, shape, and expression of receptors on the surface of the platelet

Question 21

Platelet Plug Formation (Primary Hemostasis) steps: Aggregation of Platelets:

Answer 21

New platelets to adhere to old ones by a positive feedback effect which rapidly
forms a platelet plug inside the vessel

Question 22

Platelet Plug steps (5)

Answer 22

-von Willebrand factor is secreted by platelets and endothelial cells and binds to exposed
collagen molecules in the damaged blood vessel wall, changes its own conformation and
becomes bound to platelets

-von Willebrand factor forms a bridge between the damaged vessel wall and the
platelets

-The activated platelets express a fibrinogen receptor on their surface, which can bind to
fibrinogen, a plasma protein, and other platelets to form a network, or lattice-like
structure, which ultimately forms the plug

-During this process the activated platelets also secrete thromboxane A2 and ADP, which
attract more platelets to the cut site, and the aggregation continues

-After the plug is formed, the plug can contract using its contractile proteins actin and
myosin to tighten the plug and seal the cut site

Question 23

Adhesion of platelets triggers ________

Answer 23

activation of platelets

Question 24

Once platelets are activation they secrete the compounds: (2)

Answer 24

1. Serotonin (5HT) and ADP
2. Thromboxane A2

Question 25

What does serotonin do when it is secreted from activate platelets

Answer 25

It acts as a vasoconstrictor

Question 26

What does ADP do when it is secreted from activated platelets

Answer 26

it plays a role in further platelet aggregation

Question 27

What does Thromboxane A2 do when it is secreted from activated platelets?

Answer 27

It promotes further platelet aggregation and vasoconstriction of the vascular smooth muscle which will reduce blood flow to the cut site

Question 28

Upon platelet activation, __________ exposed on the surface of the platelet aid in the conversion of ________ to thrombin, which acts to promote further platelet _________

Answer 28

1. Phospholipids 2. Prothrombin 3. Aggregation

Question 29

Why does the plug not expand along the undamaged endothelium of the blood vessel?

Answer 29

Adjacent undamaged endothelial cells synthesize and release prostacyclin, and nitric oxide which inhibit the spread of the platelet plug along undamaged endothelium

Question 30

Prostacyclin function:

Answer 30

Inhibits platelet aggregation

Question 31

Nitric Oxide Function

Answer 31

inhibits platelet adhesion, activation and aggregation

Question 32

The innate response of inflammation occurs within seconds of the initiation of ______. Following some time lag, chemicals are released from the blood vessel wall which start the process of healing by initiating the formation of the ________ at the site of the cut.

Answer 32

1. Injury 2. Platelet Plug

Question 33

Membrane damage, or a disturbance in the cell membrane, initiates the production of _____ acid from membrane _______.

Answer 33

1. Arachidonic 2. Phospholipids

Question 34

What happens in the lipoxygenase pathway?

Answer 34

Arachidonic acid is converted to leukotrienes by the enzyme lipoxygenase, and these chemicals then initiate inflammatory responses of swelling

Question 35

What happens in the cyclooxyrgenase pathway (2):

Answer 35

1. Arachidonic acid is converted to a prostaglandin by an enzyme known as cyclooxygenase or COX 2.Platelets and endothelial cells both have the cyclooxygenase enzyme, but they have different isoforms, or variants, of the enzyme. As a result, the hemostatic responses will vary. The prostaglandins play a role in hemostatic effects that help to prevent blood loss.

Question 36

Generally, the acute inflammatory response precedes _______ effects

Answer 36

hemostatic

Question 37

Aspirin is prescribed to prevent ________________

Answer 37

clot formation in patients that have a potential risk for heart attacks

Question 38

In the cyclooxyenase pathway, ________ is produced from membrane _______ as a results of membrane rupture and ________

Answer 38

1. arachidonic acid 2. phospholipids 3. injury

Question 39

What are the two isoforms of the cyclooxyrgenase enzyme?

Answer 39

COX 1 COX 2

Question 40

Healthy endothelial cells are subject to ________

Answer 40

the action of the COX 2 enzyme

Question 41

What does the COX 2 activity in healthy endothelial cells result in?

Answer 41

the synthesis of prostacyclin and this has an anti-hemostatic effect. The prostacyclin synthesized from arachidonic acid keeps the plug from expanding to adjacent undamaged endothelial cells.

Question 42

Platelets are subject to ________

Answer 42

the action of the COX 1 enzyme

Question 43

COX 1 in platelets produces ________

Answer 43

thromboxane A2 and has a pro-hemostatic effect, or favors the formation of a platelet plug

Question 44

__________ can inhibit the actions of both COX-1 and COX-2

Answer 44

Aspirin

Question 45

What happens when COX-1 is inhibited in the platelets?

Answer 45

the chances of producing thromboxane A2 are completely blocked. Platelets are non-nucleated cells and once their enzyme is inhibited, the actions of the COX 1 enzyme are completely blocked, as they cannot synthesize new COX 1 enzyme.

Question 46

What happens when COX-2 in healthy endothelial cells?

Answer 46

healthy endothelial cells will eventually start synthesizing new COX-2 enzymes as they are nucleated. COX-2 enzymes then convert arachidonic acid to prostacyclin.

Question 47

When may low dose aspirin may be used in patients?

Answer 47

When they have an increased risk of a heart attack, to prevent clot formation

Question 48

Aspirin can block the _________ only and block all the __________ pathways;

Answer 48

1. COX 1 2. pro-hemostatic

Question 49

_______ pathways can overcome the inhibition of aspirin to make ______ and keep the vessels _______ and decrease _______ aggregation

Answer 49

1. COX 2 2. Prostylactin 3. Vasodilator 4. Platelet