Coronary Blood Flow Flashcards
What are the 3 layers of the artery walls?
1. Tunica interna (Intima): endothelial layer that lines the lumen of all vessels. In vessels larger than 1 mm, a sub-endothelial connective tissue basement membrane is present
2. Tunica media (Media): smooth muscleand elastic fiber layer, regulated by sympathetic nervous system; controls vasoconstriction/vasodilation of vessels
3. Tunica externa (Adventitia): collagen fibers that protect and reinforce vessels; larger vessels contain vasa vasorum (micro vessels)
What are the properties of elastic arteries? Where are elastic arteries found?
Largest arteries; function as pressure reservoir; help propel blood forward while ventricles relaxing
Also known as conducting arteries - conduct blood to medium sized arteries
Ex: the aorta
What are the properties of muscular arteries, and where are they found?
Tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries.
Capable of great vasoconstriction and vasodilation in order to adjust blood flow.
Ex: coronary arteries
What are vasodilation and vasoconstriction?
What characteristics of the heart can they alter?
VC: contraction of arterial smooth muscle by the autonomic nervous system
VD: relaxation of arterial smooth muscle
Either VC or VD may alter afterload, peripheral BP, capillary blood flow, or preload.
What are the 4 mechanisms of microcirculation transport?
- Diffusion - most important; H2O, O2, CO2, dissolved particles and electrolytes. Directly related to its diffusion constant across the barrier, SA available, and concentration gradient
- Vesicular transport - translocation of macromolecules across capillary endothelium
- Active transport - minimal role; some molecules like ions, glucose, and a acids can be taken up by vascular endothelial cells, but it is not generally a “transport mechanism”
- Bulk flow filtration - flow of fluid and electrolyte via “pores” and intercellular clefts
What is hydrostatic pressure?
It is the pressure that drives fluid OUT of the capillary. It is highest at the arteriolar end, and lowest at the venular end.
Determined by arterial and venous pressures, and the ratio of post-capillary to pre-capillary resistance
What is oncotic pressure?
Oncotic pressure attracts fluid into the capillaries. It is determined by the impermeable proteins/colloids. Albumin makes up ~ 70% of the contribution to oncotic pressure.
What is Cardiac Output?
CO is total blood flow; the volume of blood that circulates through systemic or pulmonary blood vessels each minute.
CO = HR x SV
Distribution of CO depends on pressure differences, flowing from higher to lower pressure.
How is the blood distributed throughout the bodies vessels?
Heart, arteries, and capillaries: 30-35% of blood volume
Venous system: 60-65% of blood volume
What is MVO2? What limits its ability to increase?
MVO2 or myocardial oxygen consumption is extraction of O2 from the blood by the heart, and is near maximal at rest (~75% of arterial O2 content)
Ability to increase MVO2 is limited by:
- Increases in coronary blood flow
- Oxygen content: Hb and O2 saturation
What are the 4 determinants of coronary blood flow?
- Perfusion pressure (correlates with HR x SBP)
- Myocardial compression
- Myocardial metabolism
- Neuro-humoral control
What results from the transmural blood flow to the ventricular wall?
Blood flows from the outer portion of the wall, to the inner portions.
When coronary perfusion pressure is inadequate, the inner third of the left ventricular wall (sub-endocardium) is the first region to become ischemic or necrotic.
During systole, intra-myocardial pressure is highest in the inner layers of the ventricle, and this restricts perfusion to that area.
How does acetylcholine affect normal arteries? How does it affect arteries that have no “functional” endothelium (aka atherosclerotic)?
ACh normally dilates arteries via an endothelium dependent relaxing factor, NO.
In absence of “functional” endothelium, ACh instead causes vasoconstriction.
