Properties of special circulations: heart and skin Flashcards
Where do coronary arteries originate from
two coronary arteries originate from the left side of the heart at the beginning of the aorta, just after it exits the left ventricle
Explain what cardiac veins do
cardiac veins carry blood with a poor level of oxygen, from the myocardium to the right atrium. Most of the blood of the coronary veins returns through the coronary sinus
What are special requirements of coronary circulation
special requirements:
-needs a high basal supply of O2- 20x resting skeletal muscle
-increase O2 supply in proportion to increased demand
What are special structural features of coronary circulation
Special structural features:
-high capillary density
-large surface area for 02 transfer
-together these reduced diffusion distance to myocytes
(Diffusion time is proportional to distance squared so O2 transport is fast)
Explain special functional features during normal activity
during normal activity:
-high blood flow- 10x the flow per weight of rest of the body
-relatively sparse sympathetic innervation
-high nitric oxide released leading to vasodilation
-high O2 extraction (75%)- average in body is 25%
Explain special functional features during increased demand
During increased demand:
-coronary blood flow increases in proportion to demands
-production of vasodilators, out compete relatively low sympathetic vasoconstriction
-circulating adrenaline dilates coronary vessels due to abundance of a2- adrenoceptors
Explain oxygen haemoglobin dissociation curve
-a measure of the uptake and removal of oxygen by haemoglobin by haemoglobin under different partial pressure
-it is dependent on different factors
Explain what a left and right shift in the oxygen haemoglobin dissociation curve means
left shift- increased affinity
Right shift- decreased affinity
Explain the Bohr shift
Bohr shift:
-coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content due to high capillary density, surface area and small diffusion distance.
-the high C02 and low pH has shifted the curve to the right meaning that haemoglobin has less affinity for O2 and more O2 is given up to the myocardial tissues.
Explain how myocardium metabolism increases blood flow
myocardium metabolism generates metabolites to produce vasodilation-increases blood flow
Explain Ischaemic heart disease
-many coronary arteries are functional end-arteries and therefore decreased perfusion in one of them can cause major problems
-heart is susceptible to both sudden and slow obstruction
Explain slow and sudden in ischaemic heart disease
sudden- acute thrombosis, produces myocardial infarction
Slow- atheroma- chronic narrowing of lumen
Explain thrombosis
Occlusion leading to obstruction of blood flow to anterior left ventricle which causes myocardial infarction
What is stenosis
stenosis- partial occultation due to plaque formation
Explain the problem of angina during increased activity
- Normal Heart:
The coronary arteries have low resistance (R), allowing adequate blood flow.
The arterioles (smaller vessels)lhave high resistance, but during exercise, they undergo metabolic vasodilation (widening),
which reduces total resistance and allows more oxygen (O₂) delivery.
Blood flow increases to meet the heart’s oxygen demands during activity.
- Angina ( Diseased Heart with Stenosis):
A stenosis (narrowing) in the large coronary artery increases resistance (R).
At rest, the body compensates using metabolic hyperemia (small vessels dilate to maintain normal blood flow).
During exercise, arterioles try to dilate further to reduce resistance, but the dominant stenosis prevents sufficient blood flow.
This results in O₂ demand NOT being met, leading to angina (chest pain due to ischemia/lack of oxygen to the heart muscle).
What are mechanical factors that reduce coronary flow
Mechanical factors that reduce coronary flow:
1) Shortening diastole
2) Increased ventricular end-diastolic pressure
3) Reduced diastolic arterial pressure
What are special properties of the cutaneous circulation
1) Defence against the environment
2) Temperature regulation:
- Blood flow delivers heat from body core by conduction
- Radiation in the infra red
-Convection from skin as heat carried away by the air
-sweating
3) skin temperature depends on:
-skin blood flow
-ambient temperature
What are special structural features of AVAs
Aterio-venous anastomoses (AVAs)- direct connections of arterioles and venules expose blood to regions of high surface area
Explain what sympathetic vasoconstrictor fibres do
sympathetic vasoconstrictor fibres- release noradrenaline acting on a1- receptors
Explain what sudomotor vasodilator fibres do
Sudomotor vasodilator fibres- acetylcholine acting on endothelium to produce nitric oxide
What are special functional features of the cutaneous circulation
Special functional features:
1) Help heat loss
-increase ambient temperature which causes vasodilation and venodilation
2) Help to conserve heat
-decrease ambient temperature causes vasoconstriction and venoconstriction
Explain cold induced vasoconstriction
Cold induced vasoconstriction:
-conserves heat
-sympathetic nerves react to local cold by releasing noradrenaline which binds to a2 receptors on vascular smooth muscle in skin
-a2 receptors bind NA at lower temperatures than a1 receptors
Explain paradoxical cold vasodilation
Paradoxical cold vasodilation :
Protects against skin damage
-caused by paralysis of sympathetic transmission
-long term exposure leads to oscillations of contract/relax
What happens if there is an increased cutaneous perfusion with increased core temperature
This causes sweating (increased sympathetic activity to sweat glands mediated by acetylcholine)
Also causes vasodilation:
-increases sympathetic sudomotor activity such that acetylcholine can act on endothelium to produce NO which dilates arterioles
