Chapter 20 - Guyton Flashcards
Define cardiac output.
Cardiac output is the quantity of blood pumped into the aorta each minute by the heart. This is also the quantity of blood that flows through the circulation. (usually about 5 L/min)
Define venous return.
Venous return is the quantity of blood flowing from the veins into the right atrium each minute.
Factors that directly affect cardiac output:
basic level of body metabolism, exercise status, age, size of the body
What is the Frank-Starling law of the heart?
when increased quantities of blood flow into the heart, the heart chambers stretch and the cardiac muscle contracts with more force
Why will the stretching of the heart that occurs with increased blood flow into the heart also result in an increased heart rate?
stretching of the sinus node, also initiates a nervous reflex called the Bainbridge reflex, passing first to the vasomotor center of the brain and then back to the heart by way of the sympathetic nerves and vagi, also to increase the heart rate
What primarily controls cardiac output?
peripheral factors that determine venous return, heart will only become limiting factor when the returning blood is more than the heart can pump
As total peripheral resistance decreases, cardiac output will ________.
increase, and vice versa
About how much can cardiac output increase?
2.5x normal
Factors that can cause hypereffective heart.
nervous stimulation, hypertrophy of the heart muscle
What two nervous system events occur to increase heart pumping?
sympathetic stimulation and parasympathetic inhibition (increase heart rate and contractility)
Factors that cause a hypoeffective heart.
coronary artery blockage, inhibition of nervous excitation of the heart, pathological factors that cause abnormal heart rhythm or rate of heartbeat, valvular heart disease, increased arterial pressure against which the heart must pump, such as in hypertension, congenital heart disease, myocarditis, cardiac hypoxia
During exercise, why does the nervous system function to increase arterial pressure?
The same brain activity that sends motor signals to the muscles sends simultaneous signals into the autonomic nervous centers of the brain to excite circulatory activity, causing large vein constriction, increased heart rate, and increased contractility of the heart.
Name some conditions that can increase cardiac output (decrease peripheral resistance rather than excessive excitation of the heart).
Beriberi disease, arteriorvenous fistula (shunt), hyperthyroidism, anemia
What conditions might decrease cardiac output (caused by cardiac factors)?
severe coronary blood vessel blockage and consequent myocardial infarction, severe valvular heart disease, myocarditis, cardiac tamponade, cardiac metabolic derangements
When the cardiac output falls so low that the tissues throughout the body begin to suffer nutritional deficiency, the condition is called?
cardiac shock (circulatory shock)