2.6 - The structure and function of the heart Flashcards
What is the heart
It is a major organ of the circulatory system and is found in the chest and is protected by the rib cage.
It’s function is to pump blood around the body.
The walls of the heart a tree made out of cardiac muscle
Where does the left side of the heart pump blood too
The left side of the heart pumps blood with oxygen to the body cells
Where does the right side of the heart pump blood to
The right side of the heart pumps blood without oxygen to the lungs
Describe the human circulatory system
It is a double system
- pulmonary circuit
- systemic system
Describe the pulmonary circuit
The pulmonary circuit carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the heart
Describe the systemic circuit
The systemic circuit carries oxygenated blood from the left ventricle to the aorta and then the rest of the body and returns deoxygenated blood from the body to the heart
What is heart rate
Number of times to the heart beats in one minute
Normal range 60-90 bpm
What is stroke volume
The volume of blood ejected by each ventricle during contraction (ml)
Normal range 60-100ml
How much blood does each side of the heart pump
The left and right ventricles pump the same volume of blood through the aorta and pulmonary artery
What is cardiac output
Cardiac output is the volume of blood pumped by each ventricle per minute and is the function of two factors: heart rate and stroke volume
CO = HR x SV
L. bpm. ml
What is the contraction and relaxation of the heart known as
Contraction of the heart is known as systole and relaxation of the heart is known as diastole
3 stages of cardiac cycle
Atrial and ventricular diastole
Atrial systole
Ventricular systole
Atrial and ventricular diastole
During this stage all chambers of the heart are relax and filling with blood.
The AV valves are open.
Blood returning to the atria flows into the ventricles. Pressure in the arteries closes the semi lunar valves.
Atrial systole
During this stage, both atria contract.
The remaining blood in the atria is forced into relax ventricles through the open AV valves.
Ventricular systole
AV valves close preventing back flow of blood into atria. The ventricles contract.
Blood is pumped out of the heart through semi lunar valves into the aorta and pulmonary artery.
The SL valves close when pressure in arteries exceeds pressure in ventricles. This prevents back flow of blood into the ventricles.
When is pressure highest in the heart
During ventricular systole
How are heart sounds produced
The opening and closing of the AV (atrio-ventricular) and SL (semi-lunar) valves are responsible for the heart sounds heard with a stethoscope.
What does the conducting system of the heart ensure
Insures that the heart contracts in a coordinated manner
Where does the heartbeat originate
The heart.
It involves the action of 2 nodes within the heart. (SAN, AVN)
What are the nodes in the heart
Sino-atrial node (SAN)
Atrial ventricular node (AVN)
Where is the SAN located
Top wall of the right atrium of the heart
What sets the rate at which the heart contracts
The auto-rhythmic cells of the SAN set the rate at which the heart contracts.
What impulses does the SAN send out and what does it cause
The SAN sends out electrical impulses which are carried through the muscular walls of both atria. These impulses cause atrial systole.
What controls the timing of cardiac muscle cell contraction and what does this cause?
The timing of cardiac muscle cell contraction is controlled by impulses from the SAN spreading through the walls of both atria causing atrial systole.
What does the SAN ensure
The SAN ensures that both atria contract simultaneously
Where do impulses from the SAN travel to and what does this cause
Impulses from the SAN travel to the AVN.
Impulses from the AVN travel down fibres in the central wall of the heart and then up through the walls of the left and right ventricles causing them to contract simultaneously (ventricular systole).
What do electrocardiograms detect
Impulses in the heart generate currents that can be detected by an electrocardiogram (ECG)
How can heart rate be altered
Heart rate is not fixed.
It can be altered by the activity of hormones and the nervous system.
The control centre for regulation of heart rate is located in the medulla of the brain.
How does the medulla regulate heart rate
The medulla regulates the rate of the SAN through the antagonist action of the autonomic nervous system.
What does the autonomic nervous system vary
The autonomic nervous system varies the rate at which the heart contracts
What does the autonomic nervous system consist of
The autonomic nervous system consist of two antagonistic (opposing) branches
- sympathetic pathway (fight or flight)
- parasympathetic pathway (rest and digest)
What does sympathetic nerves release and what does it cause
Sympathetic nerves release nor adrenaline which increases heart rate
What do parasympathetic nerves to release and what does it cause
Parasympathetic nerves release acetylcholine which decrease heart rate
What is blood pressure
Blood pressure is a measure of the force that to your heart uses to pump blood around your body.
When does blood pressure increase or decrease
Blood pressure changes through the aorta during the cardiac cycle. Blood pressure increases during ventricular systole and decreases during diastole
What valves is blood pressure measured in
Systolic BP
Diastolic BP
What is a typical blood pressure reading for a young adult
120/80 mmHg
Measuring blood pressure process
An inflatable cuff stops blood flow in the artery and deflates gradually.
The blood starts to flow (detected by a pulse) at systolic pressure. The blood flows freely through the artery (and a pulse is not detected) at diastolic pressure.
What is hypertension
Hypertension is high blood pressure and is a major risk factor for many diseases including coronary heart disease.
