Special Circulations Flashcards
Where do the right and left coronary artery arise from?
Base of aorta
How does most coronary venous blood drain?
Via the coronary sinus into the right atrium
Special adaptions of coronary circulation?
-High capillary density
-High basal blood flow (under resting conditions blood flow to heart is significantly higher than other tissues)
-High oxygen extraction under resting conditions
^Means extra O2 (when required) cannot be supplied by increasing O2 extraction
^Can only be supplied by increasing coronary blood flow
What is coronary blood flow controlled by?
Intrinsic and extrinsic mechanisms
What happens to coronary arterioles when there is decreased PO2?
Vasodilation
Coronary blood flow intrinsic mechanisms?
Decreased Po2= vasodilation of coronary arterioles Metabolic hyperaemia (XS of blood in vessels) matches flow to demand Adensine (from ATP) is potential vasodilator
Coronary blood flow extrinsic mechanisms?
- Coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT are over ridden by metabolic hyperaemia (by increased HR and SV)
- Sympathetic stimulation of heart= coronary vasodilation
- Circulating adrenaline activates B2 adrenergic receptors which= vasodilation
What does circulating adrenaline activate as an intrinsic mechanism?
B2 Adrenergic receptors= vasodilation
When does peak left coronary blood flow occur?
Diastole
When does most of the coronary blood flow and myocardial perfusion occur?
Diastole - when subendocardial vessels from the left coronary artery are not compressed**
What is the brain supplied by?
Internal carotid and vertebral arteries
What matter is very sensitive to hypoxia?
Grey matter
Where do major cerebral arteries arise from?
Circle of Willis
What would obstruction of a smaller branch of a main artery cause?
Deprive a region of the brain of its blood supply
What forms the circle of Willis?
Basilar and Carotid arteries
Basilar is formed by two vertebral arteries
What is stroke caused by?
Stroke is caused by interruption/cut-off
blood supply to a region of the brain
What happens if Mean arterial Blood pressure rises?
Resistance vessels automatically constrict to limit blood flow
What happens if MABP falls?
Resistance vessels automatically dilate to maintain blood flow
When does autoregulation fail?
If blood MABP is below 60mmHg or above 160mmHg
What MABP results in confusion, fainting and nbrain damage?
Below 50mmHg
Why can hyperventilation lead to fainting ?
Increased Po2 causes vasodilation
Decreased Po2 causes vasoconstriction
Why can hyperventilation lead to fainting ?
Increased Po2 causes vasodilation
Decreased Po2 causes vasoconstriction
Percentages of brain?
Brain 80%
Blood 12%
Cerebral spinal fluid 8%
Normal intracranial pressure within skull?
8-13mmHg
Cerebral perfusion pressure equation?
CPP=MAP- ICP (intercranial pressure)
What does increasing ICP cause? due to head injury/trauma
Decreased cerebral perfusion pressure and decreased cerebral blood flow
What can some conditions which increase ICP lead to?
Failure of autoregulation of cerebral Blood flow
Describe the blood brain barrier (BBB)?
Cerebral capillaries have very tight intercellular junctions
Cerebral capillaries are not permeable to O2 and CO2. True or false?
False. Highly permeable
How does glucose cross the BBB?
Facilitated diffusion using specific carrier molecules
What is the BBB exceptionally impermeable to? How does this help the brain?
Hydrophillic substance- ions, catecholamines and proteins.
Helps protect brain neurones from fluctuating levels of ions etc in blood
Where does entire cardiac output flow from?
Right ventricle into pulmonary circulation
How are the metabolic needs of airways met?
Systemic bronchial circulation
Special adaptions of pulmonary circulation?
- Pulmonary capillary pressure is low compared to systemic capillary pressure
- Absorptive forces exceed filtration forces
- Hypoxia causes vasoconstriction of pulmonary arterioles
Why is the effect of hypoxia on pulmonary circulation completely different to systemic arteriole?
Helps divert blood from poorly ventilated area of lung
What does resistance of skeletal muscle vascular bed have an effect on?
Large impact on blood pressure
Why is resting blood flow low?
Low sympathetic vasoconstrictor tone
What happens to skeletal muscle blood flow during excercise?
Increases
- Local metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
- Circulating adrenaline causes vasodilation
- Plus increased cardiac output during exercise, these could increase skeletal muscle blood flow many folds
What lies between skeletal muscles?
Large veins in limbs
What aids venous return?
Contraction of muscles (skeletal muscle pump)
What does the skeletal muscle pump aid?
Reduces the chance of postural hypotension and fainting
What do one way venous valves allow?
Allows blood to move forward to heart
What happes if venous valves become incompetent?
Blood pools in lower limb veins= varicose veins
Why do varicose veins not usually lead to reduction of cardiac output?
Because of chronic compensatory increase in blood volume
Main types of stroke?
Haemorrhagic stroke
Ischaemic stroke
What guards against changes in cerebral blood flow if MABP changes within a range? what is that range
Autoregulation of cerebral blood flow(60-160mmHg)
Direct sympathetic stimulation has a large effect on overall cerebral blood flow. True or false?
False- Very LITTLE
Participation of the brain in the baroreceptor reflex is very little. True or False?
TRUE
What is the unknown mechanism for regulation of cerebral blood flow?
Blood flow increases to active parts of the brain (regional hyperaemia)
This may be due to the rise in [K+]0 as a result of K+ efflux from respectively active neurones
