2.6 the structure and function of the heart Flashcards
State the definition of cardiac output of the heart.
The cardiac output is a measure of the volume of blood pumped through each ventricle per minute.
Calculate the cardiac output of the heart.
Cardiac output is determined by multiplying together heart rate and stroke volume
(CO = HR x SV).
Identify differences between the right and left ventricles of the heart
Left ventricle wall is thicker than the right ventricle wall.
Left ventricle pumps oxygenated blood and right ventricle pumps deoxygenated blood
Identify the similarities between the right and left ventricles of the heart
The left and right ventricles pump the same volume of blood through the aorta (left) and pulmonary artery (right).
Identify the three stages of the cardiac cycle.
diastole
· atrial systole
· ventricular systole
Describe diastole
In diastole (relaxation), the higher pressure in the arteries closes the SL valves and blood returning to the atria flows into the ventricles.
describe atrial systole
Atrial systole (atrial contraction) transfers the remainder of the blood through the atrio-ventricular (AV) valves to the ventricles.
Describe ventricular systole
Ventricular systole (ventricular contraction) closes the AV valves and pumps the blood out through the semi lunar (SL) valves to the aorta and pulmonary artery.
Explain the ‘lub’, ‘dub’ sounds of the heart that can be heard using a stethoscope.
The heart sounds are caused by the opening and closing of the AV and SL valves. The valves open and close as a result of the pressure changes in the heart during atrial and ventricular contractions.
What does the cardiac conducting system co oridante
The cardiac conducting system co-ordinates the cardiac cycle.
What are the two main structures involved in the sioatral node
The two main structures involved are the sinoatrial node (SAN) and the atrioventricular node (AVN).
Where is the sinoatrial node located
The sinoatrial node (SAN) is located in the right atrium of the heart and is a region of cells that are auto-rhythmic.
where is the electrical impulse spread
These cells generate an electrical impulse called the cardiac impulse which spreads through the atria to the AV node and then through the ventricles. This sets the pace of the heart by determining the rate at which the cardiac muscles contract.
Where is the atrioventricular node located
The atrioventricular node (AVN) is also located in the right atrium of the heart close to the central wall.
State the name of the technique used to record the electrical impulses generated in the heart.
An electrocardiogram – the electrical impulse is recorded as a wave on a piece of graph paper.
Calculate the heart rate from an ECG trace.
An ECG trace is a repeating pattern that corresponds to the heart beating. The heart rate is calculated by measuring the time taken between two repeating points on the graph paper. This tells you the time taken for one heartbeat.
Describe the nervous and hormonal regulation of heart rate.
The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS). Sympathetic nerves of the ANS increase the heart rate and a parasympathetic nerve (the vagus nerve) slows down the heart rate. Sympathetic accelerator nerves release nor-adrenaline and slowing parasympathetic nerves release acetylcholine.
Describe the changes in blood pressure that occur during the cardiac cycle.
Blood will always flow from high to low pressure unless a valve prevents this.
Describe how a sphygmomanometer is used to measure blood pressure.
An inflatable cuff is placed around the upper arm and then inflated to temporarily stop blood flow through the artery due to the pressure applied. The cuff is then deflated gradually and when the blood starts to flow again this is detected by a pulse at the systolic pressure (higher number on the top of the reading). The blood flows freely through the artery and a pulse is no longer detected when the cuff reaches the diastolic pressure (lower number on the bottom of the reading).
A typical reading for a young adult is 120/70 mmHg.
How is blood pressure created
Blood pressure is created by the contraction of the heart. Blood leaving the heart in an artery is under its highest pressure. During systole the walls of the arteries bulge. During diastole the elastic walls recoil, pushing the blood forward through the blood vessel. As the arteries divide into arterioles and then into capillaries, the vessels become narrower
What happens when the vessels become narrow
The narrower the vessels become the greater the resistance created by the vessel walls
Explain why blood pressure measurement is an important diagnostic tool for medical practitioners.
Hypertension is a chronic long-term condition where the blood pressure in the arteries is higher than normal. Hypertension does not normally cause symptoms (it is an asymptomatic condition), but it is a major risk factor for many diseases including coronary heart disease, so monitoring is a crucial diagnostic tool for other conditions.
