Special Circulations Flashcards
Where does most venous blood drain
Via coronary sinus into RA
What is coronary heart disease
Area of Cardiac muscle deprived of blood supply if coronary vessel is blocked at a specific area
What are some adaptations of coronary circulation
High capillary density compared to other areas of circulation
High basal blood flow
High oxygen extraction under resting conditions means extra oxygen cannot be supplied by increasing oxygen extraction
Can only be supplied by increasing Coromary blood flow
Coronary blood flow controlled by intrinsic and extrinsic mechanisms
What are the intrinsic mechanisms of coronary blood flow
Decrease Po2 causes vasodilatation of the coronary arterioles increase blood flow
Metabolic hyperaemia matches flow to demand increase blood flow to heart
Adenosine from atp is a potent vasodilator
What are some extrinsic mechanisms of coronary blood flow
Coronary arterioles supplied by symp vasoconstrictor nerve but over ridden by metabolic hyperaemia (intrinsic) as a result of increased heart rate and stroke volume = increase blood flow
So symp stimulation of the heart results in coronary vasodilatation despite direct vasoconstrictor effect
Circulating adrenaline activates beta2 adregenic receptors, which cause vasodilatation
What supplies the blood
Brain is supplied mainly by internal carotids and vertebral arteries - circle of Willis some protectionn to the Brian
What is grey matter very sensitive to
Hypoxia
Where consciousness lost after few seconds of ischaemic, irreversible cell damage within
What are some special adaptations of cerebral circulation
Basilar - formed by two vertebral arteries and carotid arteries anastomoses to form circle of Willis
Major cerebral arteris form circle of Willis
Cerebral perfusion should be maintained even if one carotid artery gets obstructed
Nevertheless, obstruction of a smaller branch of a main artery would deprive a region of the brain of its blood supply
Cause of a stroke
What is stroke caused by
Interruption/cut off blood supply to a region of the brain
What are the types of stroke
Haemorrhagic bleeding stroke which is less common
Ischaemic stroke - block by blood vessel clot or thrombus
What are further special adaptations of cerebral circulation
Autoregulation - cerebral blood flow guards against changes in cerebral blood flow if mean arterial blood pressure changes within a range wide range blood flow is constant
Direct symp Stim has very little effect in overall cerebral blood flow
Participation of the Brian in baroreceptor reflexes is negligible which is just as well
What is the autoregulation of cerebral blood flow
If MABP rises resistance vessels automatically constrict to limit blood flow
If MABP falls resistance vessels automatically dilate to maintain blood flow
Autoregulation fails if MABP fall below 60mmHg or above 160 mmHg
MABP below 50mmHg results in confusion p, fainting and brain damage
What is some other important regulation of cerebral blood flow
Increase Pco2 causes cerebral vasodilatation
Decrease Pco2 causes vasocons why hypervent lead to fainting
Blood flow increases to active parts of the Brain for specific actions - regional hyperaemia
What is the effect of intracranial pressure in cerebral blood flow
Skull rigid closed box filled with approximately
Perfusion pressure = MAP - ICP
normal intracranial pressure in skull 8-13mmHg
Increasing ICP due to head injury decreases CPP and cerebral blood flow
What is the blood brain barrier
Cerebral caps have very tight intercellular junctions - the blood brain barrier
Cerebral caps are highly permeable to oxygen and carbon dioxide
Glucose crosses the bbb by facilitated diffusion using specific carrier molecules
Brain has obligatory requirement for glucose
Bbb is exceptionally impermeable to hydrophillic substances such as ions, catecholamines, proteins
This helps protect brain neurones from fluctuating levels of ions
What are some special adaptations of pulmonary circulations
Pulmonary cap pressure is low compared to systemic cap pressure
Absorptive forces exceed filtration forces - protects against pul oedema
Hypoxia causes vasocons of pulmonary arterioles
Help divert blood from poorly ventilated areas of lungs
How much of body mass is skeletal muscle
40%
Why is resting blood flow low
Coz symp vasocons tone increase enormously in exercise
How does the skeletal muscle blood flow change during exercise
Increases
During exercise what overcomes the symp vasoconstrictor activity
Metabolic hyperaemia which causes vasodi
What does the circulating adrenaline do
Act on beta2 adregenic recipes which causes vasodilatation
The skeletal muscle pump
Large veins between skeletal muscle
Contraction of muscles aids venous return
One way ensured by valves
Skeletal muscle pump reduces chance of postural and hypotension and fainting
If blood pools in lower limbs
Give varicose veins which cause chronic compensatory in as blood vol
Where do the right and left for oral arteries arise form
The base of the aorta
