Flashcards in Specialisations In Individual Circulations Deck (33)
What is the total blood flow/cardiac output ?
5.8L per min
Where do coronary arteries arise from ?
Base of the aorta just below aortic semilunar valve
Why does the heart require its own circulation.?
Because the blood flowing through the heart cannot oxygenate the heart because diffusion distance is too great
What contributes to the good oxygen delivery to myocytes ?
High myocardial capillary density
Small diameter of myocytes for short diffusion distance
What molecule in cardiac myocytes enhances oxygen transport even more ?
What is the percentage of oxygen extracted from arterial blood at cardiac muscle ?
What functional adaptions of cardiac muscle help to contribute to good extraction of oxygen from arterial blood ?
Good blood supply
Fact myocytes are packed with mitochondria
Give 2 examples of metabolic vasodilators
Hypoxia and adenosine
What adaptation occurs by gradual obstruction of coronary vessels ?
Development of collaterals to reduce extent of ischaemia
BUT at increased levels of activity local ischaemia can develop
What is the capillary surface area of the lungs ?
100m squared - enabling lungs to receive large amount of blood
What contributes to the high oxygen diffusion capacity at the lungs ?
High capillary density
Large alveoli surface area
Small diffusion distance between alveolar surface to plasma
What is gas exchange normally limited by ?
Why is the pressure in the pulmonary circulation lower than in the systemic circulation ?
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
Which gender is pulmonary hypertension more common in ?
Where is pulmonary pressure higher in the lungs and what effect does this have ?
Higher at the base due to gravity and this causes the vessels to distend, lowering resistance and increasing flow
What happens to the total blood flow/CO during exercise ?
Increases up to 3 fold
Distribution of blood flow changes
Cerebral perfusion remains the same
Skeletal muscle blood flow increases by about 10 x
What percentage of blood flow can be directed to the skeletal muscle during exercise ?
> 70 %
Which type of skeletal muscle fibres is capillary density greatest ?
Slow twitch - red
- contains lots of myoglobin and mitochondria
- used in endurance exercise
What is hypermedia ?
An excess of blood in vessels supplying an organ or part of the body
What is active hyperaemia ?
Increase in blood flow
What factors contributed to vasodilation of blood vessels ?
High proton concentration
How are the arteries which enter the brain arranged ?
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
How long can you survive with insufficient oxygen supply to brain at normal temperatures and at cold temperatures?
Normal conditions- few minutes
Cold conditions- 10-15 minutes
What percentage of oxygen does the brain extract from arterial blood ?
How does hyperventilation make you feel dizzy ?
It washes out carbon dioxide causing vasoconstriction which reduces cerebral blood flow
What are the factors that contribute to local changes in the amount of blood flow to the brain ?
Caused by increases in interstitial potassium from outward currents at neurons and rise in proton concentration and adenosine
How does gravity directly and indirectly influence cerebral blood flow ?
Decrease in central venous pressure and SV seen in orthostasis
What are the 3 main functions of skin blood flow ?
1- heat exchanger for thermoregulation
2- supply of nutrients to cells
3- blood reservoir- shift blood away from skin
What are the blood flow ranges at the skin ?
50-2500ml/min depending on temperature
What happens to skin blood flow during the heat ?
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
What happens to skin blood flow in the cold ?
Superficial vessels constrict strongly
Blood bypasses capillaries via AV shunts so blod is diverted to vital organs
In the cold skin can appear rosy, why ?
Because blood can become trapped in the superficial capillaries