U2 KA6 - The Structure And Function Of The Heart Flashcards
Describe the Structure of the Heart
The heart consists of four chambers – two atria and two ventricles
Atria
*right atrium receives deoxygenated blood from body via the vena cava
*left atrium receives oxygenated blood from lungs via the pulmonary vein
Ventricles
*right ventricle pumps deoxygenated blood to the lungs
*left ventricle pumps oxygenated blood to the body via the aorta
The chambers are separated by a wall of muscle known as a septum.
Describe the Valves of the heartand their function
The heart also contains valves, all of which are present to prevent backflow.
The valves present between each of the atrium and ventricles are called Atrio-ventricular valves (AV valves). They open to allow blood to flow from atria to ventricle and close to prevent backflow.
The semi-lunar valves (SL valves) are present at the opening of the pulmonary artery and aorta, the vessels responsible for carrying blood away from the heart. These valves ensure that blood flows in one direction through the heart
Define Heart Rate
The number of times the heart beats per minute
Define Stroke volume
The volume of blood pumped out of the heart by each ventricle when they contract
Describe Cardiac output
The volume of blood pumped out of a ventricle per minute
State the Equation for Cardiac Output
CO = HR x SV
Describe Diastole of the Heart
During diastole (relaxation), blood has returned to the heart via the vena cava and pulmonary veins causing the volume of blood to increase in the atrium.
The increased presence of blood opens the the atrio-ventricular valves (AV valves) to allow blood starts to flow into the ventricles (which are relaxed).
Describe Atrial Systole
During atrial systole (contraction), electrical impulses cause the atria to contract together and push the remaining blood into the ventricles through the open AV valves. The ventricles are still relaxed and begin to fill with blood.
Around 0.1 second after atrial systole, ventricular systole (contraction) begins.
Describe Ventricular Systole
Ventricular systole (contraction) begins.
Electrical impulses (via the AV node) are sent down the septum and into the walls of the ventricles…
The AV valves close, the ventricles contract, (from the bottom up) and blood is pumped through the semilunar valves (SL) into the aorta (from the left ventricle) or the pulmonary artery (from the right ventricle).
This occurs because the pressure in the ventricle exceeds the pressure in the major arteries leaving the heart.
What is the Pacemaker and what is its role?
The pacemaker (Sino-atrial node, SAN) is found in the wall of the right atrium. The cells in the SAN initiate electrical impulses that make the cardiac muscle cells contract and are responsible for setting the rate at which the heart beats.
The SAN works automatically
Describe the Cardiac conducting system
The SAN spreads an electrical impulses through the muscle cells of the two atria (right and left) making them contract simultaneously (atrial systole)
This electrical impulse is then picked up by the atrio-ventricular node (AVN) found centrally in the septum of heart between atria and ventricles
The impulse received by the AVN passes through a bundle of conducting fibres which branches into a network of conducting fibres found in the muscular walls of the ventricle
Excitation of these fibres results in a simultaneous contracting of ventricles (ventricular systole)
Label the Parts of An Electrocardiogram
- P wave = atrial systole (atria contract).
*QRS complex = ventricular systole (ventricles contract).
*T wave = recovery of ventricular walls (end of ventricular systole – ventricles relax).
Describe Regulation of the heart beat In Terms Of Nervous control
The medulla of the brain regulates the heart rate (via SAN) through the antagonistic action of the autonomic nervous system (ANS), meaning it can function to increase or decrease the heart rate.
An increase in the number of nerve impulses arriving at the SAN (via the sympathetic nerve) increases heart rate
An increase in the number of nerve impulses arriving at the SAN (via the parasympathetic nerve) increases heart rate
The nerve system that exerts the greatest influence will determine the heart rate
Describe Regulation of the heart beat In Terms Of Hormonal control
When exercising or under stress the sympathetic nervous system releases the hormone adrenaline from the adrenal glands
Adrenaline will travel in the bloodstream to the heart initiating electrical impulses at the SAN
The increase rate of cardiac impulses increases heart rate
Parasympathetic nerves release acetylcholine
What is blood pressure measured by?
It is measured in millimetres of mercury (mmHg) using a sphygmomanometer.
