AQA A level Biology
AQA A level Biology
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Topic 3: Organisms exchange substances with their environment
Topic 3: Organisms exchange substances with their environment
The heart
The heart
Structure of the heart
Structure of the heart
The heart consists of four chambers:
Atria (upper chambers): Receive blood entering the heart and pump it into the ventricles.
Ventricles (lower chambers): Pump blood out of the heart into the arteries.
Right Side of the Heart:
Pumps deoxygenated blood to the lungs via the pulmonary artery.
Blood picks up oxygen and releases carbon dioxide in the lungs.
Left Side of the Heart:
Pumps oxygenated blood to the body via the aorta.
Blood returns to the right side of the heart through the inferior and superior vena cava, restarting the cycle.
Differences in Heart Wall Thickness
Right ventricle: Thinner walls; pumps blood to the nearby lungs (requires less force).
Left ventricle: Thicker walls; pumps blood to the entire body (requires more force).
Atria: Thinner walls compared to ventricles, as they only pump blood into the ventricles.
Heart Valves
Atrioventricular (AV) valves: Located between the atria and ventricles.
Semi-lunar valves: Located between the ventricles and arteries leaving the heart.
Function of Valves:
Ensure blood flows in the correct direction.
Prevent backflow by opening only when pressure is higher on one side.
Held in place by tendinous cords, attached to papillary muscles in the ventricle walls.
Structure of the human heart.
Cardiac output
Cardiac output
Definition: The volume of blood ejected by the heart per minute (cm3.min-1).
Factors Influencing Cardiac Output:
Stroke volume: Volume of blood pumped by the ventricles per contraction (cm3).
Heart rate: Number of beats (contractions) per minute.
Equation: Cardiac output (CO) = Stroke volume (SV) × Heart rate (HR)
The cardiac cycle
The cardiac cycle
The Myogenic Nature of the Heart
The heart is myogenic, meaning it can contract without electrical impulses from nerves.
Coronary arteries supply oxygen and nutrients to the heart muscle.
The Cardiac Cycle
Diastole (Relaxation Phase):
Atria and ventricles relax.
Blood flows into the atria from veins (low-pressure blood).
Pressure in the atria increases as they fill with blood.
Blood trickles into the relaxed ventricles through open AV valves.
Atrial Systole (Atrial Contraction):
Atria contract, increasing pressure.
Blood is forced through the AV valves into the ventricles.
Valves in the veins close, preventing backflow into veins.
Ventricular Systole (Ventricular Contraction):
After a brief delay, ventricles contract from the apex upwards.
Rising pressure closes the AV valves, preventing backflow into the atria.
Semi-lunar valves open, allowing blood to leave the heart into the arteries.
Definitions
Definitions
Aorta: major artery that conveys oxygenated blood from the left ventricle to the body.
Apex/base: bottom of the heart.
Atrial systole: period in the cardiac cycle when the atria contract simultaneously.
Atrioventricular valves: valves between the atria and ventricles.
Atrium/atria: chambers at the top of the heart that receive blood from the major veins and pump it into the ventricles.
Cardiac cycle: a continuous series of events which make up a single heart beat.
Cardiac output: the total volume of blood that the heart can pump each minute. It is calculated as the volume of blood pumped at each beat (stroke volume) multiplied by the number of heart beats per minute (heart rate).
Cords (tendinous chords): cord-like tendons that connect the interior structure of the heart muscle to the atriventicular valves, thus preventing the valves from inverting.
Coronary arteries: arteries that supply blood to the cardiac muscle of the heart.
Diastole: the stage in the cardiac cycle when the heart muscle relaxes. See also systole.
Myogenic: electrical activity originating in the heart tissue resulting in contraction of the heart muscle without (necessarily) needing input from the nervous system.
Pulmonary artery: major artery that conveys deoxygenated blood from the right ventricle to the lungs.
Pulmonary vein: major vein that conveys oxygenated blood from the lungs to the left atrium.
Semi-lunar valve: valves between the ventricles and the major arteries.
Septum: tissue that separates the left and right sides of the heart.
Stroke volume: the volume of blood pumped at each ventricular contraction of the heart.
Vena cava (inferior and superior): major vein that conveys deoxygenated blood from the body to the right ventricle.
Ventricles: chambers at the bottom of the heart that receive blood from the atria and pump it into the major arteries.
Ventricular systole: period in the cardiac cycle when the ventricles contract simultaneously.
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