PHYSIOLOGY OF THE HEART Flashcards
What are the 2 systems that control the functions of the heart?
autonomic nervous system and intrinsic conduction system
decrease or increase the heart rate depending on which division is activated
Autonomic Nervous System
cardiac muscles contracts spontaneously and independently of nerve impulses
Intrinsic Conduction System
Normal Heart Rate
75 bpm
atrial cells beat ___ times per minute
60
ventricular cells beat ___ times per minute
20-40
starts each heartbeat; “Pacemaker of the heart”
Sinoatrial Node (SA)
True or false: The impulse is somewhat delayed to give thenatria ample time to finish contracting
True
rapid heart rate, over 100 beats per minute
Tachycardia
slow heart rate, less than 60 beats per minute
Bradycardia
one complete heartbeat, in which both atria and ventricles contract and then relax
Cardiac cycle
contraction; represents the time during which the left and right ventricles contract and eject blood in the aorta and pulmonary artery respectively
Systole
period of relaxation; where the muscles are relaxed
Diastole
Cardiac cycle length is about
0.8 seconds
First event of the card cycle where the heart is relaxed, pressure is low and the av valves are open, allowing blood to flow into the atria
Atrial diastole
The atria contracts allowing blood to completely fill the ventricles
Atrial systole
Atrial systole ends; ventricular systole begins
And the av valves close
Isovolumetric contraction
Semilunar valves open and blood is ejected from the ventricles
Ventricular systole
Pressure falls below that in the major arteries, semilunar valves close and for another moment, the ventricles are completely closed chambers
Isovolumetric relaxation
longer, louder heart sound caused by the closing of the AV valves
Lub
short, sharp heart sound caused by the closing of the semilunar valves at the end of the ventricular systole
Dup
amount of blood pumped by each side (ventricle) of the heart in 1 minute
Cardiac output
volume of blood pumped by each ventricle in one contraction (each heartbeat)
Stroke volume
How much ml of blood is pumped out of the left ventricle with each heartbeat?
70 ml
Formula for cardiac output
Heart Rate x stroke volume
The more the cardiac muscle is stretched, the stronger the contraction
Starling’s Law of the Heart
is the important factor influencing the stretch of heart muscle
Venous return
Sympathetic nervous system speed heart rate
Neural (ANS) Controls
True or false: hormones like epinephrine and thyroxine influence heart rate
True
True or false: Age, gender, exercise, body temperature do not influence heart rate
False
