chapter 21 physiology, muscle blood flow and cardiac output during exercise; coronary circulation and ischemic heart disease Flashcards
how fast does blood flow through skeletal muscle during rest?
3-4 ml/min/100g of muscle
besides adenosine acting as a vasodilator during exersize, what else causes vasodilation?
potassium ions, adenosine triphosphate, lactic acid, carbon dioxide
what 3 main affects occur during excersize that are essential for circulatory system to supply alot of blood to the muscles?
- . mass discharge of sympathetic nervous sustem throughout the body
- increase in arterial pressure
- increase in cardiac output
what 3 things cause increase in arterial pressure during excersize?
- vasoconstriction of arterioles and small arteries in most tissue (except active muscles)
- increased pumping by heart
- increase in mean systemic filling pressure caused by venous contraction
what happens with the vessels inside the muscles as they contract?
they vasodilate, everywhere else vasoconstricion occurs
why is the arterial pressure increase during exercise so important?
it allows up to 20 times more blood flow to the muscles
what do almost all elderly people have some sort of?…
coronary artery disease
what vessel supplies the heart with nutrients?
coronary arteries
left coronary artery suppies what part of the heart?
anterior and leftlateral portions of the left ventricle
right coronary artery supplies what?
most of the right ventricle, as well as the posterior part of the left ventricle in 80-90 percent of people
where is the Coronary sinus
where the coronary arteries empty into the right atrium
thebesian veins do what?
a small amount of venous blood also flows back into the heart throuogh these veins
the resting coronary blood flow is what percent of the total cardiac output?
4-5 %
describe the capillary blood flow through the left ventricle during systole
the blood flow falls during systole while the blood flow in the capillaries through out the body rises
how is the coronary system regulated?
by the nutritional need of the cardiac muscle. So when the heart needs to pump harder, the coronary vessels dialte
describe adenosine’s role in vasodilation in regards to ATP
muscles use ATP which turns into Adenosine monophosphate which is degraded into adenosine which causes vasodilation
name some other vasodilators
adenosine phoshpate compounds, potassium ions, hydrogen ions, carbon dioxide, prostaglandins, nitric oxide
what does sympathetic stimulation release?
noreepinephrine and epinephrine
what does the parasympathetic stimulation release?
acetylcholine
what does epinephrine and noreepinephrine do in the coronary vessels?
they actually have dilator and constrictor receptors. The constrictor receptors are called alpha receptors and the dilator receptors are called beta receptors
what happens if the alpha receptors are over stimulated?
Angina can occur and ischemia can occur
while at rest, from which molecule does the heart get its nutrients?
fatty acids
what causes anginic pain in anaerobic conditions?
with lack of O2 the heart tissue performs anaerobic respiration which produces lactic acid. This is whats though to cause angina during ischemia.
what is the most frequent cause of diminished coronary flood flow and where does it most oftenly occur?
atherosclerosis, most frequently in the first few cm of major coronary arteries
name one way to have acute coronary occlusion
thrombus development. ( a flowing thrombus is called an embolus)
name another way to have acute coronary occlusion
mucsular spasm of coronary artery which can develope a secondary thrombus
describe the collateral development of vessels and the coronary artery
Collateral vessels develop if the coronary constriction is slow over a period of years. They grow to compensate for atherosclerosis. Even the collateral vessels can develope atherosclerosis and the heart becomes weak and has a low output. ( this is one of the most common causes of cardiac failure)
what is myocardial infarction?
heart muscle has zero flow
requirements for cardiac muscle to stay alive
1.3 ml of oxygen per 100 g
describe what subendocardial muslce is and why its important in regards to infarction.
subendocardial muslce has difficulty obtaining adequate blood flow because the blood vessels in the subendocardium are intensely compressed by systolic contraction of the heart. Subendocardium is usually the first heart tissue to become damaged during an infaction
common causes of death after acute coronary occlusion
decreaed cardiac output, dammin of blood in pulmonary blood vessels and then death resulting from pulmonary edema, fibrillation of the heart, rupture of heart
what is systolic stretch
when normal portions of ventricular muscle contract, the ischemic portion of the muscle is forced outward which dissipates much of the pumping force
whats happening to the heart during coronary shock/cardiac shock
heat becomes incapable of contracting with sufficient force to pump enough blood into the peripheral arterial tree
what is low cardiac output failure
more than 40% of left ventricle is infacted
name 1 factor that leads the heart to fibrillate in regards to blood supply
loss of blood supply to the cardiac muscle causes rapid depletion of potassium from ischemic musculature. This increases the potassium level of the extracellular fluid which causes fibrillation
name 1 factor that leads the heart to fibrillate in regards to polarization
ischemic musculature often cannot completely replarize its membranes after a heartbeat
name 1 factor that leads the heart to fibrillate in regards to sympathetic stimulation
powerful sympathetic reflexes often develop after massive infarction
name 1 factor that leads the heart to fibrillate in regards to the conduction pathway
cardiac muscled that is infected dilates and causes the condution pathway to increase which predisposes the deveopment of circus movements and fibrillation
cardiac tamponade
compression of the heart from the outside of by blood collecting in the pericardial cavity
replacement of dead muscle by scar tissue
fibrous tissue develops among the dead fibers because ischemia stimulates fibroblasts. Then the normal areas of the heart gradually hypertrophy to try and compensate for the tissue loss
coronary steal syndrome
with an excessively active heart the vessels dilate which allows most of the blood in the coronary vessels to flow through the normal muscle tissue. This leaves little blood in the coronary vessels to flow through the small anastomotic channels into the ischemic area so the ischemic condition worsens
angina pectoris
pain associated with contriction of coronary arteries. Usually below upper sternum over the heart, left arm and left shoulder, neck, side of face
what else is associated with angina?
cold temperatures, full stomach, increase of workload of heart
common drugs for vasodilation
nitroglycerin, nitrate
what do beta blockers do?
block sympathetic beta-adregenic receptors which prevent sympathetic enhancement of heart rate and cardiac metabolism during exercise or emotional episodes
