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Year One - Principles of Disease > Circulation > Flashcards

Circulation Flashcards

1
Q

What layers compose an artery?

A

Lumen - innermost layer, allows fluid through the vessel

Endothelial cells - line lumen, form basal lamina (basement membrane)

Smooth muscle cells - around basal lamina, involved in constriction and vasodilation of arteries

Interstitial collagen fibres - outermost layer, woven in a tight and organised structure, protects and strengthens the artery

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2
Q

What cells are contained within the lumen?

A

Platelets

WBCs

RBCs

Plasma

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3
Q

What is plasma made up?

A

Plasma proteins, water, clotting factors and other molecules.

In other words, if you remove RBCs, WBCs and platelets from blood you are left with plasma.

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4
Q

What is plasma referred to if it lacks clotting factors?

A

Serum

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5
Q

What are clotting factors? Where are they produced?

A

Key component of the clotting cascade

Mainly produced in the liver by endothelial cells

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6
Q

What is thrombin?

A

A molecule that is able to convert soluble fibrinogen into insoluble fibrin strands

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7
Q

What can the fibrin strands form?

A

A mesh structure

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8
Q

What does it mean when we say that the clotting cascade is an amplification system?

A

As you go through the cascade, more and more molecules are produced. For example, we start off with a small number of clotting factors but produce a lot of fibrin strands.

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9
Q

What is the clotting cascade initiated by? What are the remaining steps of the clotting cascade?

A
  1. Damage, which results in defects in all layers of the artery. This causes the contents of the lumen to leak out.
  2. The lumen contents therefore come into contact with the interstitial collagen fibres. The clotting factors are activated when they make contact with the collagen fibres.
  3. Tissue factor is usually present on smooth muscle cells. When damage occurs, they can bind to clotting factors and initiate the clotting cascade.
  4. Cascade leads to the conversion of prothrombin to thrombin.
  5. Thrombin converts soluble fibrinogen to insoluble fibrin strands.
  6. Fibrin strands link together to form a mesh structure.
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10
Q

What are serine proteases?

A

Clotting factors which have a serine amino acid in them and able to cleave other clotting factors to form their active forms and a redundant fragment.

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11
Q

How are platelets formed? Where?

A

Bud off as platelets from cytoplasmic extensions of megakaryocytes

Bone marrow.

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12
Q

What megakaryocytes?

A

Large cells with a large cytoplasm and several nuclei.

Undergo nuclear division not cellular division - explains structure

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13
Q

What are the role of platelets during damage to the artery?

A

Bind to interstitial collagen fibres to attempt to form a bridge that closes the gap that the damage formed. Thus stop the bleeding from the site.

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14
Q

What does coagulation mean? What are the two ways in which it can occur?

A

Solidification of blood.

Thrombus formation
Clot formation

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15
Q

When does thrombus formation occur?

A

Flowing blood

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16
Q

What is a thrombus?

A

Consists of platelets and a mesh of fibrin strands

Pale, cream coloured

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17
Q

How do thrombi stick to tissue despite the forces of flowing blood?

A

Platelets have molecules on their surface which allow them to adhere to interstitial collagen even when blood is following at a high pressure past them

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18
Q

When does clot formation occur?

A

When blood becomes stagnant

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19
Q

What is a clot?

A

Consists of RBCs and a mesh of fibrin strands

Red coloured

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20
Q

When does physiological thrombosis occur?

A

In wound healing

To stop bleeding after an injury or menstruation

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21
Q

When does pathological thrombosis occur?

A

In the absence of an injury

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22
Q

What is haemostasis?

A

The process which stops bleeding in normal skin within a wound.

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23
Q

What are the three ways that we can reduce bleeding from a damaged blood vessel?

A

Vasoconstriction

Clot formation, which occurs in the space around the vessel and may fill the void of wounded tissue

Thrombus formation, which occurs in the space around the vessel and may fill the void of wounded tissue

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24
Q

Why do new capillaries (granulation tissue) grow into the wound area?

A

Allow oxygenation of the area, prevents dead tissue formation

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25
Q

What is thrombolysis?

A

The process which breakdown a thrombus.

26
Q

Describe the process of thrombolysis and the process of removing clots.

A

A blood protein called plasminogen converts into plasmin, which is a molecule that breaks fibrin into smaller fragments

27
Q

What is the fibrinolytic system?

A

A system which removes fibrin and stops clots and thrombi from propagating

28
Q

What does the fibrinolytic system depend on?

A

Plasminogen

29
Q

What should the fibrinolytic system be in balance with?

A

The clotting system

30
Q

What is Virchow’s triad?

A

The three situations that may result in thrombus formation…

  1. Changes in the intimal surface of a vessel - eg = rupture of an atheroma
  2. Changes in the pattern of blood flow - eg = atheroma can result in slow and turbulent blood flow, which predisposes to fibrin and platelet clumping
  3. Changes in blood constituents - eg = increase in stickiness of platelets which means that they are more likely to stick together and form a thrombus
31
Q

What happens when a thrombus blocks the lumen of an artery?

A

A clot can now form in the stagnant blood behind the thrombus, as RBCs become trapped in the fibrin meshwork.

This causes more turbulence and slowing of blood flow which means a third layer of thrombus forms.

Cycle continues.

32
Q

What are multiple layers of thrombus and clot referred to as?

A

Lines of Zahn

33
Q

What are the consequences of a thrombus completely blocking an artery?

A

No flow beyond blockage

Ischaemia, hypoxia and necrosis

34
Q

What are the consequences of a thrombus partially blocking an artery?

A

Decreased flow beyond blockage.

Ischaemia, hypoxia

35
Q

What is ischaemia?

A

When a tissue receives less blood flow.

36
Q

What is hypoxia?

A

When there is a decreased oxygenation of tissues - normally follows from ischaemia

37
Q

What is necrosis?

A

The process of tissues dying in an alive individual

38
Q

What is an infarct?

A

The localised area of dead tissues in an alive individual

Reserved for necrosis as a result of ischaemia

39
Q

Hypoxia in which two organs can be very fatal quickly?

A

Brain

Heart

40
Q

What is an embolism?

A

Result from a mass of material moving in the vascular system and becoming lodged in a vessel and block its lumen

41
Q

What are most emboli derived from?

A

Thrombi or clots which have broken off and travelled elsewhere in the circulation

42
Q

What is thromboembolism?

A

The process in which thrombi or clots embolise

43
Q

Describe the formation of a pulmonary embolism.

A

Usually occurs after surgery which immobilises patients

Sluggish flow in leg veins, leads to thrombosis and clot formation.

Part of the thrombus or clot breaks off and travels up the vein.

Embolus passes into the pulmonary artery where it becomes lodged

Blocks the pulmonary artery and results in pulmonary infarct

44
Q

Describe the formation of a marrow embolism.

A

A fracture in the leg occurs. Marrow enters a ruptured vein and can embolise into the lung vessels

45
Q

Describe the formation of an air embolism.

A

Knife wound to the neck, allows air to enter the vein which can embolism to the heart.

46
Q

What is circulatory shock?

A

Profound circulatory failure, causing poor profusion of vital organs

Physiological consequences of low blood pressure

47
Q

What does the elastic tissue around the basal lamina allow?

A

If the vessel is contracting, the elastic tissue can fold.

When no blood is present, the vessel can collapse

When blood is present, the vessel can open

48
Q

What is the normal blood pressure in arteries and veins?

A

120/80

Lower in veins

49
Q

What three things does normal blood pressure rely on?

A

Enough blood in the system, which is usually 5L. No blood causes the vessels to collapse and blood pressure becomes low and then unrecordable.

Smooth muscle in vessel having a certain tone. If smooth muscle tone is decreased, the vessel will dilate. If enough vessels are affected, the blood pressure may fall.

Heart pumping blood

50
Q

How is the body able to detect changes in the partial pressure of oxygen (which is related to blood pressure and flow)?

A

Carotid bodies

51
Q

Where are carotid bodies found?

A

Bifurcation of arteries

52
Q

How do carotid bodies respond to drops in the partial pressure of oxygen?

A

They send nerve signals to the brain stem. The brain stem then…
Causes the heart to pump faster, increasing heart rate

Increased vascular tone in vessels of the limb and abdomen. This results in any remaining blood being pushed to heart, lungs and brain to keep them alive.

Cause adrenal gland to secrete adrenaline, which causes the heart to pump harder and faster

53
Q

What is the overall physiological response to low blood pressure?

A

Increased heart rate

54
Q

What is the average low blood pressure?

A

60/40 - can vary due to patients having hyper or hypotension

55
Q

What is a fast pulse?

A

Over 100 beats per minute

56
Q

What are three main causes of circulatory shock?

A

Hypovolaemic

Septic

Cardiogenic

57
Q

Describe hypovolaemic shock

A

There is a reduction in the amount of blood in the circulation.

This causes vessels supplying blood to the heart collapsing. This means no blood enters the right side of the heart and is transported to the rest of the body.

Systemic blood pressure drops, which is detected by carotid bodies.

They up regulate the sympathetic NS - causing increased heart rate.

58
Q

Describe septic shock

A

Bacteria from infections spread to blood, known as septicaemia.

Molecules released which cause vasodilation.

Not enough blood gets back to the heart, as venous pressure and filling are low.

Not enough blood gets to the rest of the body.

59
Q

Describe cardiogenic shock

A

Heart starts to fail, no longer pumps enough blood to maintain blood pressure.

60
Q

How do we treat hypervoleamic shock?

A

Transfuse blood ASAP

61
Q

How do we treat cardiogenic shock?

A

Prescribe drugs that increase function of heart.

62
Q

What are the two main complications of shock?

A

Decreased perfusion of the brain, which is initially reversible but then permanent. This is known as ischaemic infarction of brain tissue.

Decreased perfusion of the kidneys, which is initially reversible but can then become more severe. This is known as ischaemic necrosis of renal tubules.

Year One - Principles of Disease (15 decks)

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