8.3.2
The Cardiac Cycle
The Cardiac Cycle
The Cardiac Cycle
The flow of blood from the lungs to the heart and around the body is called the cardiac cycle. The cardiac cycle is the continuous relaxing and contracting of the heart. The steps involved are:
 (1)-min,h_400,q_80,w_640.jpg)
 (1)-min,h_400,q_80,w_640.jpg)
1) Atrial contraction
1) Atrial contraction
- Blood from the lungs flows into the left atrium and blood from the body flows into the right atrium simultaneously.
- The atria contract, increasing the pressure in the atria.
- The blood in the atria is forced into the ventricles.
- The ventricles are relaxed and fill with blood.
 (1)-min,h_400,q_80,w_640.jpg)
 (1)-min,h_400,q_80,w_640.jpg)
2) Ventricular contraction
2) Ventricular contraction
- The atria relax and the ventricles start to contract.
- Contraction of the ventricles causes the pressure inside the ventricles to increase.
- The pressure shuts the atrioventricular valves so that blood does not flow back into the atria.
- The blood in the ventricles is forced out of the ventricles and out of the heart through the pulmonary artery or the aorta.
 (1)-min,h_400,q_80,w_640.jpg)
 (1)-min,h_400,q_80,w_640.jpg)
3) Relaxation
3) Relaxation
- The blood in the pulmonary artery and the aorta is at high pressure. -The pressure shuts the semi-lunar valves so that blood does not flow back into the ventricles.
- Both the ventricles and the atria relax and the atrioventricular valves reopen.
- Blood flows into the ventricles and the atria from the pulmonary vein and vena cava.
 (1)-min,h_400,q_80,w_640.jpg)
 (1)-min,h_400,q_80,w_640.jpg)
4) Repeat
4) Repeat
- The cycle continues.
Interpreting Data
Interpreting Data
At each stage in the cardiac cycle, the pressure and volume of the atria and ventricles changes considerably. These changes can be presented as a change over time.


Pressure in the atria
Pressure in the atria
- When the atria contract, the pressure in the atria increases.
- When the atria relax and the ventricles contract, the pressure in the atria decreases.
- When both the atria and the ventricles relax, there is a slight increase as the atria fill with blood again.


Pressure in the ventricles
Pressure in the ventricles
- When the atria contract, the pressure in the ventricles is relatively low. There is a slight increase in pressure as the ventricles fill with blood.
- When the ventricles contract, the pressure increases dramatically. The pressure increases considerably more than when the atria contract.
- When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.


Volume in the atria
Volume in the atria
- When the atria contract, the volume in the atria decreases.
- When the atria relax and the ventricles contract, the volume in the atria increases again.
- When both the atria and the ventricles relax, there is a slight decrease when blood flows into the ventricles from the atria.


Volume in the ventricles
Volume in the ventricles
- When the atria contract, the volume in the ventricles increases slightly as they fill with blood.
- When the ventricles contract, the volume decreases dramatically. The volume decreases considerably more than when the atria contract.
- When both the atria and the ventricles relax, the volume increases as the ventricles expand again.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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