Specialisations In Individual Circulations

Question 0

Where do coronary arteries arise from ?

Answer 0

Base of the aorta just below aortic semilunar valve

Question 1

What is the total blood flow/cardiac output ?

Answer 1

5.8L per min

Question 2

Why does the heart require its own circulation.?

Answer 2

Because the blood flowing through the heart cannot oxygenate the heart because diffusion distance is too great

Question 3

What contributes to the good oxygen delivery to myocytes ?

Answer 3

High myocardial capillary density

Small diameter of myocytes for short diffusion distance

Question 4

What molecule in cardiac myocytes enhances oxygen transport even more ?

Answer 4

Myoglobin

Question 5

What is the percentage of oxygen extracted from arterial blood at cardiac muscle ?

Answer 5

65-75%

Question 6

What functional adaptions of cardiac muscle help to contribute to good extraction of oxygen from arterial blood ?

Answer 6

Good blood supply
Myoglobin facilitation
Fact myocytes are packed with mitochondria

Question 7

Give 2 examples of metabolic vasodilators

Answer 7

Hypoxia and adenosine

Question 8

What adaptation occurs by gradual obstruction of coronary vessels ?

Answer 8

Development of collaterals to reduce extent of ischaemia

BUT at increased levels of activity local ischaemia can develop

Question 9

What is the capillary surface area of the lungs ?

Answer 9

100m squared - enabling lungs to receive large amount of blood

Question 10

What contributes to the high oxygen diffusion capacity at the lungs ?

Answer 10

High capillary density
Large alveoli surface area
Small diffusion distance between alveolar surface to plasma

Question 11

What is gas exchange normally limited by ?

Answer 11

Flow limited

Question 12

Why is the pressure in the pulmonary circulation lower than in the systemic circulation ?

Answer 12

1- pulmonary circulation only has to supply 1 organ which is effectively at the level of the heart
2- the pulmonary capillaries in the pulmonary circulation are not supported by surrounding tissue so they are more likely to suffer from stress failure

Question 13

Which gender is pulmonary hypertension more common in ?

Answer 13

Women

Question 14

Where is pulmonary pressure higher in the lungs and what effect does this have ?

Answer 14

Higher at the base due to gravity and this causes the vessels to distend, lowering resistance and increasing flow

Question 15

What happens to the total blood flow/CO during exercise ?

Answer 15

Increases up to 3 fold
Distribution of blood flow changes
Cerebral perfusion remains the same
Skeletal muscle blood flow increases by about 10 x

Question 16

What percentage of blood flow can be directed to the skeletal muscle during exercise ?

Answer 16

> 70 %

Question 17

Which type of skeletal muscle fibres is capillary density greatest ?

Answer 17

Slow twitch - red

• contains lots of myoglobin and mitochondria
• used in endurance exercise

Question 18

What is hypermedia ?

Answer 18

An excess of blood in vessels supplying an organ or part of the body

Question 19

What is active hyperaemia ?

Answer 19

Increase in blood flow

Question 20

What factors contributed to vasodilation of blood vessels ?

Answer 20

High proton concentration 
Reduced oxygen 
Adenosine 
NO 
Increased potassium

Question 21

How are the arteries which enter the brain arranged ?

Answer 21

They (carotid arteries and basilar arteries) anastomose forming circle of wills
This helps ensure cerebral perfusion if a blockage of one of the vessels occurs

Question 22

How long can you survive with insufficient oxygen supply to brain at normal temperatures and at cold temperatures?

Answer 22

Normal conditions- few minutes

Cold conditions- 10-15 minutes

Question 23

What percentage of oxygen does the brain extract from arterial blood ?

Answer 23

35%

Question 24

How does hyperventilation make you feel dizzy ?

Answer 24

It washes out carbon dioxide causing vasoconstriction which reduces cerebral blood flow

Question 25

What are the factors that contribute to local changes in the amount of blood flow to the brain ?

Answer 25

Caused by increases in interstitial potassium from outward currents at neurons and rise in proton concentration and adenosine

Question 26

How does gravity directly and indirectly influence cerebral blood flow ?

Answer 26

Decrease in central venous pressure and SV seen in orthostasis

Question 27

What are the 3 main functions of skin blood flow ?

Answer 27

1- heat exchanger for thermoregulation
2- supply of nutrients to cells
3- blood reservoir- shift blood away from skin

Question 28

What are the blood flow ranges at the skin ?

Answer 28

50-2500ml/min depending on temperature

Question 29

What happens to skin blood flow during the heat ?

Answer 29

Hypothalamus reduces vasomotor tone to induce vasodilation to increase blood flow
Substances in sweat lead to production of bradykinin which stimulations endothelial cells to release NO and this further enhances vasodilation

Question 30

What happens to skin blood flow in the cold ?

Answer 30

Superficial vessels constrict strongly

Blood bypasses capillaries via AV shunts so blod is diverted to vital organs

Question 31

In the cold skin can appear rosy, why ?

Answer 31

Because blood can become trapped in the superficial capillaries

Question 32

What effect does alcohol have on skin blood flow ?

Answer 32

Causes dilation of blood vessels in skin causing a flushed appearance, increasing sweating and heat loss