Chapter 21 - Guyton Flashcards
What happens in terms of blood flow to a muscle during a tetanic contraction?
During strong tetanic contraction, the blood flow can be almost stopped by sustained compression of the blood vessels, but this also causes rapid weakening of the contraction.
During exercise, what occurs to increase oxygen and nutrient diffusion from blood to muscle (during rest some muscle capillaries have little to no blood flow)?
all the capillaries open
As a means of local regulation, how does decreased oxygen concentration at the tissue level effectively increase blood flow?
muscle tissue oxygen concentration decreases and arteriolar walls cannot maintain contraction in the absence of oxygen and oxygen deficiency causes release of vasodilator substances (namely adenosine, also potassium ions, ATP, lactic acid, and carbon dioxide)
The sympathetic vasoconstrictor nerve fibers secrete ______________ at their nerve endings.
norepinephrine
Three major effects occur during exercise that are
essential for the circulatory system to supply the
blood flow to the muscles.
mass discharge of the sympathetic nervous system throughout the body; increase in
arterial pressure; increase in cardiac output
What occurs as a result of the mass sympathetic discharge that occurs in response to the onset of exercise?
heart is stimulated to greatly increased HR and increased pumping strength from the sympathetic drive plus release from normal parasympathetic inhibition; most of the arterioles of the peripheral circulation are strongly contracted, except for the
arterioles in the active muscles, which are strongly vasodilated by the local vasodilator effects; muscle walls of the veins are contracted powerfully, which greatly increases the mean systemic filling pressure (increased venous return)
Can you think of a couple peripheral circulatory systems that might be spared of the vasoconstrictor effects seen as a result of the mass sympathetic discharge during exercise?
coronary and cerebral systems (you kinda need the heart and brain as much as you need the muscles to run fast)
How is the arterial pressure increased as a result of increased sympathetic stimulation in exercise?
vasoconstriction of the arterioles and small arteries in most tissues of the body except the active muscles, increased pumping activity by the heart, great increase in mean systemic filling pressure caused mainly by venous contraction
Why might a person doing bicep curls experience a greater increase in arterial pressure than a person running (whole body exercise)?
In the few active muscles, vasodilation occurs, but everywhere else in the body the effect is mainly vasoconstriction vs. the whole-body exercise in which a lack of a large increase in pressure results from the extreme vasodilation that occurs simultaneously in large masses of active muscle.
What two changes occur to raise venous return (so that it does not limit cardiac output)?
combination of increased mean systemic filling pressure and decreased resistance to venous return
The _____ coronary artery supplies mainly the anterior and left lateral portions of the left ventricle.
left
The ______ coronary artery supplies most of the right ventricle as well as the posterior part of the left ventricle in 80 to 90 per cent of people.
right
Most of the coronary venous blood flow from the left ventricular muscle returns to the right atrium of the heart by way of the _______ _____—which is about 75 per cent of the total coronary blood flow.
coronary sinus
Most of the coronary venous blood from the right ventricular muscle returns through small anterior _______ ______ that flow directly into the right atrium, not by way of the coronary sinus.
cardiac veins
The coronary capillary blood flow in the left ventricle muscle falls to a low value during ______, which is opposite to flow in vascular beds elsewhere in the body.
systole; The reason for this is strong compression of the left ventricular muscle around the intramuscular vessels during systolic contraction.
What are the direct and indirect effects of nervous control of coronary blood flow?
direct effects - action of the nervous transmitter substances acetylcholine from the vagus nerves and norepinephrine and epinephrine from the sympathetic nerves on the coronary vessels; indirect effects - secondary changes in coronary blood flow caused by increased or decreased heart activity (local blood flow regulatory mechanisms)
The acetylcholine released by parasympathetic stimulation has a direct effect to ______ the coronary arteries.
dilate
There is much more extensive ____________ innervation of the coronary vessels.
sympathetic
The most common cause of death in Western culture is _______ ______ disease, which results from insufficient coronary blood flow.
ischemic heart
The most frequent cause of diminished coronary blood flow is ______________.
atherosclerosis
The atherosclerotic plaque can cause a local blood clot called a ________, which in turn occludes the artery.
thrombus
The area of muscle that has either zero flow or so little flow that it cannot sustain cardiac muscle function is said to be _________.
infarcted (myocardial infarction)
Which area of the heart will experience damage first during infarction?
any condition that compromises blood flow to any area of the heart usually causes damage first in the subendocardial regions, and the damage then spreads outward toward the epicardium
The most common causes of death after acute myocardial infarction are:
1) decreased cardiac output; 2) damming of blood in the pulmonary blood vessels and then death resulting from pulmonary edema; 3) fibrillation of the heart; 4) rupture of the heart
What is systolic stretch?
When the normal portions of the ventricular muscle contract, the ischemic portion of the muscle, instead of contracting is forced outward by the pressure that develops inside the ventricle.
Four factors that may cause fibrillation in the ventricles after myocardial infarction.
acute loss of blood supply to the cardiac muscle causes rapid depletion of potassium from the ischemic musculature (increased extracellular potassium); "injury current" (electric current flows from this ischemic area of the heart to the normal area and can cause fibrillation); powerful sympathetic reflexes; cardiac muscle weakness often causes the ventricle to dilate excessively (circus movement)
Why is angina pain often felt on the neck, side of the face, and left arm and shoulder?
heart originates during embryonic life in the neck, as do the arms and both the heart and these surface areas of the body receive pain nerve fibers from the same spinal cord segments
Why would a beta blocker be prescribed for angina pain?
These drugs block sympathetic beta adrenergic receptors, which prevents sympathetic enhancement of heart rate and cardiac metabolism during exercise or emotional episodes.
What are two common procedures for the treatment of coronary artery disease?
aortic-coronary bypass surgery (CABG) and coronary angioplasty
