Properties of Special Circulation Flashcards
What are the 5 special circulations?
→ Cerebral → Pulmonary → Skeletal Muscle → Renal → GI
What are the 3 characteristics to consider with special circulations?
→ Special requirements are met by circulation
→ Special structural or functional features of the circulation
→ Specific problems relating to that circulation
Where do the two coronary arteries originate from?
→ The left side of the heart at the beginning (root) of the aorta just after it exits the left ventricle
Where do cardiac veins carry deoxygenated blood?
→ From the myocardium to the right atrium
Where does most of the blood of the coronary veins return to?
→ Returns through the coronary sinus
What are the special requirements of the coronary circulation?
→ Needs a high basal supply of O2
→ 20 x that of skeletal muscle
Why does the coronary circulation have a high capillary density?
→ Large surface area for O2 transfer
→ Reduces the diffusion distance to the myocytes
What is diffusion time proportional to?
→ Distance squared
What is the blood flow of the coronary circulation during normal activity?
→ High blood flow
→ x10 of the flow per weight of the rest of the body
What is the sympathetic innervation like in the coronary circulation?
→relatively sparse
What is O2 extraction like during normal activity?
→ High O2 extraction 75%
→ average in the body 25%
How does the production of vasodilators change during increased demand?
→ Production of vasodilators out-compete relatively low sympathetic vasoconstriction
Why does adrenaline dilate coronary vessels?
→ Abundance of Beta 2 adrenoreceptors
How is 75% of the oxygen able to be unloaded to the myocardium during normal activity?
→ Coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content
→The high CO2 and low pH has shifted the curve to the right
→Hb has less affinity for O2 and more O2 is given up to myocardial tissues.
How does increased O2 requirement produce increased blood flow?
→Extraction is near maximum during normal activity
→ To provide more O2 during demand blood flow must increase
→ Myocardium metabolism generates metabolites to produce vasodilation which increases blood flow.
Describe ischaemic heart disease
→Coronary arteries are functional end-arteries and therefore decreased perfusion produces major problems
→The heart is very susceptible to sudden and slow obstruction
What does suddden ischaemic heart disease produce?
→ acute thrombosis
→ Myocardial infarction
What can lead to slow ischaemic heart disease?
→ Atheroma
→ Chronic narrowing of lumen - produces angina
→ Systole obstructs coronary flow
What does occlusion of the Left Anterior Descending Coronary Artery in thrombosis lead to?
→ obstruction of blood flow to anterior left ventricle
What does myocardial infarction lead to?
→Ischemic tissue →Acidosis →Pain (stimulation of C-fibres) →Impaired Contractility →Sympathetic activation →Arrhythmias →Cell death (necrosis)
In a normal heart what is the resistance like?
Resistances are in series - they add together
During exercise what happens to the resistances in a normal heart?
→Metabolic vasodilation of arterioles
→reduces total R
→Increased blood flow to meet increased O2 demands
→Total R reduced
What is the resistance like in the heart of someone with angina (Resting) ?
→Stenosis in large coronary artery
→Increases resistance
→Metabolic hyperaemia occurs at rest, so blood flow meets needs
What is the resistance like in the heart of someone with angina (exercise) ?
→During exercise, arterioles further dilate to reduce resistance
→total resistance is still too high due to dominance of stenosis
→O2 demand cannot be met, so angina develops
