cardiac muscle and blood vessel phys

action potential in pacemaker cells

• voltage starts at -60mv , where funnny channels open and allow slow influx of Na+ til reaching threshold of -40mv resulting in depolorization known as

• at threshold calcium channels open, Ca+ flow into the cell further depolorizing the membrane, resulting in the rising phase (depolarizing) of the AP

• at the peak of depolorization, K+ channels open and Ca channels inactivate, K+ ions leave the cell and voltage returns to -60mV, this is the falling (repolorization) phase of action potential

action potential in contractile myocytes

• resting at -90mv, depolorize when stimulated by a neighbouring myocyte and bring the membrane voltage up to the threshold of -70mv

• at threshold fast Na+ channels open creating rapid influx in Na+ and a sharp rise in voltage (depolorisation phase)

• L-type, or slowm Ca+ channels also open at -40mv causing slow but steady influx

• when the membrane reaches a peak, K+ channels open allowing K+ to exit, leading to early repolarization, calcium channels remain open and Ca and K end up being balanced keeping the membrane potential steady and making a platuea known as the action potential plateau phase. After the plateau phase, K+ continues to leave the cell, which leads to a full repolarization back to the resting potential of -90mV.

• then calcium induced calcium release sets off muscles contraction via the sliding filament

• Ca+ channels slowing closed and then

the platuea phase leads to longer contraction in the heart and longer refractory period allowing

types of blood vessels (arterial system)

• elastic artery - thick walled near heart

• muscular artery - thick wall, less elastin - deliver blood to tissue

• arterioles - resistance vessels - regulate blood flow to capillaries

• capillaries - thin walled, small lumen diameter

types of blood vessels (venous system)

• venule - connection between capillaries and veins

• veins - lack significant muscle layer - highly compliant - little recoil

endothelium

produces substances that change smooth muscle contraction

• nitic oxide

• endothelin

• prostaglandins

mediates the actions of circulating substance s

• angiotensin

• thrombin

• histamine

• bradykinin

systolic bp

max pressure exerted in arteries when blood is ejected into them during systole (heart contracting phase)

diasstolic bp

MIN PRESSURE WITHIN THE ARTERIES WHEN BLOOD DRAINING off into the remaineder of the vessels during diastole (heart relaxing/ fillinfg phase)

pulse pressure

a measure of strength of pressure wave ( = difference between SBP and DBP)

mean arterial pressure MAP

average pressure responsiple for driving blood forward into tissues throughout cardiac cycle

MAP = diastolic BP + 1/3 pulse pressure

frank-starling mechanism - stroke volume

• increased volume of blood in ventricle leads to increased stretch on muscle wall

• increased muscle stretch leads to increased force contraction

• increased force contraction leads to increases stroke volume

preload

the initial stretching of the cardiac muscle prior to contraction, determined by the volume of blood in the ventricles at the end of diastole.

can also be measured by EDP which is used clinically

afterload

the hydraulic load imposed on the ventricle during ejection

measures include;

• aortic pressure'

• total peripheral resistance

• arterial impedance

• myocardial peak wall stress