Coronary Circulation & Tissue Perfusion

Question 1

When does the heart perfuse itself and why?

Answer 1

During diastole

There is more time for it to perfuse itself during diastole

During systole it is perfusing the rest of the body

Question 2

What is the heart’s main source of energy?

Answer 2

Fat as it carries more ATP per gram

Question 3

What is used if a coronary artery is blocked?

Answer 3

A coronary artery bypass

This involves taking a vessel from the leg to work as a graft to bypass the blockage

Question 4

What are the two types of graft?

Which lasts longer and why?

Answer 4

Arterial and venous

Arterial grafts last longer as arteries have thicker walls

Question 5

How long does an arterial graft work?

Answer 5

12-15 years

Question 6

What is the main function both upstream and downstream of the capillary?

Answer 6

Conduction

Question 7

What is the blood pressure like upstream of the capillary?

Why?

Answer 7

Higher blood pressure is being delivered by the arterial system

The arteries have more muscle in their tunica media

Question 8

What is the purpose of elastic tissue in the arteries?

Answer 8

It stores energy during systole and then recoils to propel the blood along

Question 9

How is the elastic recoil of the arteries damaged in an aneurysm?

Answer 9

There is damage to the elastic tissue

The arterial lumen is dilated

Question 10

How does the composition of the arteries change as you get closer to the capillaries?

Answer 10

The proportion of muscle in the artery increases

They change from being elastic arteries to muscular arteries

Question 11

What is the role of resistance vessels in blood distribution?

Answer 11

They decide how much blood different parts of the body require

They supply the correct amount of blood for maximum efficiency

Question 12

What is blood flow like in a capillary?

Answer 12

There is a single-file line of RBCs

It is a continuous flow of blood that is not pulsatile

Question 13

What is the role of counter-pulsation?

Answer 13

It helps to smooth the flow of blood so that the blood is moving at all times

This gives the maximum amount of time to exchange substances across the capillary

Question 14

Where are capillaries positioned in relation to cardiac myocytes and why?

Answer 14

The capillaries are in close proximity to the cells

Cardiac myocytes need a lot of perfusion as the heart is working all the time

Question 15

What happens to capillaries in the myocardium during systole?

Answer 15

Contraction of the heart compresses the capillaries

It is difficult for blood to flow through them

Question 16

If there are plaques present in the capillaries in the myocardium, how does this affect relative pressures?

Answer 16

The pressure must be higher in the arterioles than in the capillaries

Question 17

How does the heart compensate for plaques in the myocardium capillaries?

Answer 17

It dilates the blood vessels or increases the force of contraction

This increases the pressure of the blood

Question 18

From the aorta to the capillary venules, what is the branching pattern of blood vessels?

Answer 18

1. aorta
2. pre-arterioles (200-500 micrometres)
3. arterioles (40-100 micrometres)
4. smaller arterioles (<40 micrometres)
5. capillary venules

Question 19

In relation to the epicardium and endocardium, where are the capillary venules found?

Answer 19

Closer to the endocardium

The pre-arterioles are closer to the epicardium

Question 20

When does perfusion of the heart occur and why?

Answer 20

During diastole

During systole, blood cannot flow through the smaller vessels due to the increased pressure in the heart

Question 21

How does the amount of blood needed vary in hypertrophy?

Answer 21

More blood is needed to perfuse all of the muscle

There is more muscle in the ventricle walls

Question 22

When is the main flow through the aorta and right coronary artery?

Answer 22

During systole

Question 23

When is the main flow through the left coronary artery?

Answer 23

During diastole

There is little flow in the left coronary artery during systole

Question 24

How does a myocardial infarction affect the amount of perfusion to the ventricle?

Answer 24

Myocytes in a particular region have died and become scar tissue

Scar tissue does not need perfusion as it is not contracting

Question 25

How can compromised blood flow (e.g. blocked coronary artery) be improved?

Answer 25

Through a stent

Question 26

As blood flow increases, what happens to the rate of metabolism in the heart?

Answer 26

The rate of metabolism also increases

Question 27

What happens to metabolism of the heart during exercise?

Answer 27

The heart metabolises more and uses more oxygen and nutrients It also produces more metabolites (waste products)

Question 28

How do metabolites (waste products) alter blood flow to the heart?

Answer 28

Blood vessels can sense waste products such as CO2 and lactic acid They send a message to increase blood flow to the heart

Question 29

What is the process by which producing more metabolites leads to increased blood flow to the heart?

Answer 29

Autoregulation

Question 30

What metabolites will stimulate relaxation? How does this affect blood flow to the heart?

Answer 30

Adenosine, CO2, H+ and K+ These cause blood vessels to dilate and increase blood flow to the heart

Question 31

How is coronary blood flow affected by different blood pressures?

Answer 31

Coronary blood flow decreases when blood pressure is lower It increases when blood pressure is higher

Question 32

What is involved in autoregulation?

Answer 32

Adjusting resistance and dilation of the arteries to smooth out the perfusion to the heart

Question 33

What does autoregulation allow for?

Answer 33

Providing maintained coronary blood flow to the heart

Question 34

How does normal cardiac output vary from during rest and during exercise?

Answer 34

Normal cardiac output is 5L per minute This can increase to 20L during exercise

Question 35

What 2 factors work to increase the cardiac output during exercise?

Answer 35

1. increasing the heart rate | 2. increasing the volume of blood pumped out of the heart with each beat (stroke volume)

Question 36

What is required in order for the heart to maintain a high cardiac output?

Answer 36

A lot of adaptation

Question 37

Where is nitric oxide produced?

Answer 37

Endothelium

Question 38

How does blood flow affect nitric oxide production by the endothelium?

Answer 38

Increased blood flow means that more nitric oxide is produced

Question 39

What is the effect of nitric oxide on blood vessels?

Answer 39

It causes the blood vessels to dilate more

Question 40

How is the endothelium stimulated to produce nitric oxide?

Answer 40

The endothelium senses the blood flow and experiences sheer stress due to the blood flowing past it Blood flow stimulates it to produce nitric oxide

Question 41

What is produced by the parasympathetic nervous system that affects blood vessels? What is its effect?

Answer 41

Acetylcholine It causes the blood vessels to relax (dilate)

Question 42

What is produced by the sympathetic nervous system that affects blood vessels? What is its effect?

Answer 42

Noradrenaline It causes blood vessels to contract through action on alpha receptors

Question 43

How does adrenaline affect blood vessels?

Answer 43

It causes blood vessels to dilate

Question 44

What are 'endo-en paracrine' influences on blood vessels?

Answer 44

They are locally produced hormones 1. angiotensin II 2. bradykinin 3. histamine

Question 45

How does histamine affect blood vessels?

Answer 45

It is a vasodilator which is released in response to inflammation

Question 46

How does bradykinin affect blood vessels?

Answer 46

It is produced by the endothelium during exercise It causes dilation of blood vessels

Question 47

What are the metabolic influences on blood vessels?

Answer 47

1. pCO2, H+, K+ 2. adenosine 3. pO2

Question 48

What are extravascular influences on blood vessels?

Answer 48

compression

Question 49

What is the effect of adenosine on blood vessels?

Answer 49

It causes blood vessels to dilate (coronary and all over the body) This increases blood supply to the heart

Question 50

What is the diameter and length of a capillary?

Answer 50

diameter: 5 - 10 micrometres length: 0.5 - 1 mm

Question 51

What are capillaries made from?

Answer 51

A single layer of endothelial cells This is surrounded by a basal lamina

Question 52

what is the blood cell viscosity of capillaries?

Answer 52

They have a slow blood cell velocity of approximately 0.3 - 1.0 mm/sec

Question 53

What is the diffusion distance like between each capillary and the cell it serves?

Answer 53

There is a short distance between each capillary and the cell it serves

Question 54

What are intercellular junctions like between cells?

Answer 54

Junctions between capillary cells are "tight"

Question 55

What are the 2 exceptions to capillary cell junctions being "tight"?

Answer 55

In the liver and bone marrow there are large clefts between cells

Question 56

Why are there large clefts between capillary cells in the liver and bone marrow?

Answer 56

Cells are leaving and entering the circulation at this point The holes allow larger blood cells to enter or exit the circulation

Question 57

What would happen if there were large clefts between capillary cells all over the body?

Answer 57

There would be swellings as too much fluid would leak out of the capillary

Question 58

What are the capillaries like in the central nervous system?

Answer 58

The "blood-brain barrier" in the CNS has capillaries which are very tightly bound together

Question 59

Why are the capillaries tightly bound together in the brain?

Answer 59

To prevent swelling in the brain This causes headache due to a pressure on the nervous system

Question 60

What are the types of blood vessels which lead to the capillary beds?

Answer 60

1. collateral arteries 2. arterioles 3. metarterioles 4. capillary

Question 61

What is a metarteriole?

Answer 61

a short microvessel in the microcirculation that links arterioles and capillaries

Question 62

What is a precapillary sphincter?

Answer 62

a band of smooth muscle that adjusts blood flow into the capillaries

Question 63

Where is a precapillary sphincter found?

Answer 63

at a point where the capillary originates from the metarteriole

Question 64

What is an arteriovenous anastomosis?

Answer 64

a connection between an artery and a vein blood flows from an artery to a vein without passing through a capillary network

Question 65

What are the 2 different types of capillary?

Answer 65

1. continuous capillary | 2. fenestrated capillary

Question 66

What is a continuous capillary and what is its composition like?

Answer 66

the endothelial cells provide an uninterrupted lining only small molecules, such as water and ions, can pass through intercellular clefts

Question 67

where are continuous capillaries found?

Answer 67

blood-brain barrier

Question 68

What is a fenestrated capillary and what is its composition like?

Answer 68

they contain fenestrations or pores which allow larger cells to pass through

Question 69

How is blood flow to the capillaries controlled?

Answer 69

By resistance vessels These are arterioles that determine how much blood enters the capillaries and perfuses an organ/tissue