Lecture 8: Special Circulations Flashcards
what does the coronary circulation supply
supplies oxygen to the heart
must deliver oxygen at a high rate to meet myocardial demand
what are the major arteries of the coronary circulation
The L and R Coronary arteries
–> each has a circumflex and interventricular branch
where does the L coronary artery open from
the Left aortic sinus
where does the R coronary artery open form
the R aortic sinus
describe the path of the L coronary artery
opens from the left aortic sinus
passes laterally beneath the left auricle
divides into the:
- L (paraconal) interventricular artery (lies in the L IV groove)
- L circumflex artery (lies in the circular coronary groove)
describe the path of the R coronary artery
opens form the right aortic sinus
passes laterally beneath the R auricle
divides into the:
R (subsinuosal) interventricular artery (Lies in the R IV groove)
- R circumflex artery (lies in the circular coronary groove)
in dogs and ruminants, where does the right interventricular artery arise from and why?
arises from the Left coronary artery
b/cause left coronary artery supplies most of the heart
- all of the IV septum
- all L ventricle
- regions of the R ventricle adjoining the L and R IV groove
L coronary artery carries 80% of coronary blood
in horses and pigs where does the right interventricular artery arise from and why?
right interventricular artery arises from right coronary artery
both coronary arteries are similar in size
describe the microcirculation of the heart
most vascular part of the myocardium is the sub endothelial plexus
–> extensive network of arterioles and capillaries
how does venous drainage of the heart occur?
great cardiac vein and coronary sinus
how much blood does the coronary sinus carry?
75% of total coronary flow
how is coronary blood flow controlled?
by metabolic (active hyperaemia) –> coupling of blood flow to demand of oxygen.
describe the process of metabolic hyperaemia
myocardium releases metabolic by-products in proportion to work rate
act as local vasodilators, increasing coronary blood flow
how does sympathetic NS cause coronary vasodilation in-directly
by increasing HR
- increase in HR increases contractility, increase oxygen required, increasing metabolic byproducts thus vasodilation
does most of coronary blood flow occur during systole or diastole and why?
2/3rds of coronary arteries re intramural, intramural vessels are compressed during systole
80% of coronary blood flow occurs during diastole
what blood is received by the pulmonary circulation?
receives the output of the R ventricle, supplies the alveolar capillaries involved in gas exchange
how does blood flow distribute?
blood flow matches local gas supply
blood flow will distribute preferentially to well oxygenated regions of the lungs
what is the major pulmonary artery?
the pulmonary trunk
- arises from the conus arterioles of R ventricle
- bends over the base caudally
- divides caudally to the aortic arch
- gives rise to L and R pulmonary arteries
what is the major pulmonary veins?
only veins to carry oxygenated blood
conduct blood from L aA
no valves
pattern of distribution usually correspond to the number of pulmonary lobes.
how does pulmonary circulation differs from systemic circulation?
pressures are very low due to low pulmonary vascular resistance
–> vessels are more compliant
doesn’t need to go against gravity, low resistance over all
basal tone v low
metabolic vasodilation has no role, alveolar perfusion vastly exceeds metabolic demand
how does alveolar hypoxia affect pulmonary arteries?
alveolar hypoxia is a potent constrictor or small pulmonary arteries
decrease blood flow to poorly ventilated alveoli
increase blood flow to better ventilated areas of lung
nb: in systemic circulation local hypoxia causes vasodilation
what important role does cutaneous blood flow play?
thermoregulation
how is heat lost?
radiation, conduction, convection and evaporation
how vascularised is the dermis and epidermis?
dermis - well vascularised
epidermis - avascular
what is the cutaneous supplied by?
superficial, middle and deep vascular plexus
describe the counter current heat exchange mechanism occurring in superficial and deep vascular beds in WARM conditions
blood perfuses superficial capillary bed –> heat loss is via superficial veins
describe the counter current heat exchange mechanism occurring in superficial and deep vascular beds in COLD conditions
peripheral vasoconstriction –> flow to deep capillaries and deep veins, counter current heat exchange between arteries and veins = conserve heat.
what is the arteriovenous anastomosis?
present in the skin of the extremities
direct connection between dermal/SKIN arterioles and venues
controlled by simp vasoconstrictor fibres
dilate in warm conditions, constrict in cold
in cold conditions what occurs to the arteriovenous anastomosis?
symp vasoconstrictor fibres cause it to constrict = Blood flow is directed through the deeper vascular beds, and heat is transferred by countercurrent exchange from the warm arterial blood to the cooler venous blood. This results in reduced heat loss from the skin and therefore conservation of body heat
in warm conditions what occurs to the arteriovenous anastomosis?
arteriovenous anastomosis open, enhance the total blood flow to the periphery, and the increased heat delivery increases the temperature of the skin, which facilitates heat loss across the skin
what is the primary role of cerebral circulation?
maintain oxygen delivery to the brain at ALL COSTS
brain accounts for nearly 20% of resting oxygen consumption
what are the four major arteries suppling the head?
- L and R common carotid
2. L and R vertebral arteries
where do the common carotids run?
extend up the neck along the trachea
branch at the atlanto-occipital joint into
–> internal carotid –> blood supply intracranial
–> external carotid –> blood supply extracranial
where do the vertebral arteries run?
vertebral artery is first branch off the subclavian artery
extends cranially through traverse foreman at the anterior 6 cervical vertebrae
fuses with occipital artery = cerebrospinal artery
how is the cerebrospinal artery formed?
fusion of the L and R vertebral arteries with the occipital artery artery
how is the basilar artery formed?
fusion of the L and R branches of the cerebrospinal artery
how is the circle of willis formed?
basilar artery anastomoses with the internal carotid artery
what is the functional significance of the circle of willis?
preserves cerebral perfusion
if carotid artery or vertebral artery or their branches are obstructed = safety net for the brain
brain microcirculation consists of functional end arteries = blockage causes local ischaemia –> stroke
what is the function of the blood brain barrier?
- protect cerebral neurons from interference with circulating pathogens and solutes
- maintain tightly controlled pH
- prevent neurotransmitter wash out
what are three key features of the blood brain barrier?
- endothelial cells have closed intercellular junctions
- thick basement membrane
- surrounded by end feet astrocytes - keep it reeal tight
what is the major venous drainage of the head?
external jugular veins
internal jugular veins
vertebral vein
what is the pattern of venous drainage?
all drain into the cranial vena cava –> right atrium
what are the two external jugular veins?
- maxillary vein
2. linguofacial vein
where does the maxillary vein drain?
drains deeper and caudal structures of the head
where does the linguofacial vein drain?
drains superficial and rostral structures
commonly used for venepunctures
