11. Human Physiology
11.7. Gas Exchange and Circulation
11.7.4. The Human Circulatory System. Heart, Blood Vessels and Blood Pressure
A double circulatory system
The human circulatory system is double:
- A pulmonary circulation (to the lungs, blood is oxygenated)
- A systemic circulation (to the rest of the body, where oxygen is consumed)
- Oxygen-poor blood in the vena cava blood enters the right atrium, and then the right ventricle.
- Pumped to the lungs via the pulmonary artery.
- Oxygen-rich blood via the pulmonary vein to the left atrium.
- From the left atrium via the aorta to the system ("the body").
- Oxygen & nutrients consumed, carbon dioxide & waste products taken up
- Back to the heart via the vena cava
Several valves prevent the blood from flowing backward, back into the heart.
Coronary arteries provide blood to the heart.
The entire heart is enclosed by the pericardium:
- Protects the heart from dilating too much.
- Protects the heart from infections from surrounding organs.
A few key terms
- Volume blood/heartbeat
- Approx. 70 ml
- Volume blood/time
- Approx. 5 L/min
- Resting = about 60 beats/min
How the heart beats
Sinoatrial node (SA node)
- At the right atrium.
- Nerve impulses that coordinate the beats.
- Affected by hormones and the nervous system.
Systole (main contraction)
- Ventricles contract.
- Tricuspid & mitral valves close.
- Blood pumped out to the body.
- Venctricles relax
- Pulmonary and aortic valves close.
- The atria contract.
- Ventricles fill with blood.
The blood vessels
The blood exerts a pressure against the arterial walls.
- Systolic pressure = maximum during a heartbeat.
- Diastolic pressure = minimum between heartbeats.
- Normal is approx. 115/70.
Arteries lead blood from the heart.
- Aorta = the main and largest artery.
- Relatively thick to be able to withstand the pressure.
Arteries branch into capillaries.
- Enough for a red blood cell to squeeze through.
Only a thin layer of epithelial cells.
Gases and nutrients may diffuse.
The capillaries form a tight web:
- No cell is more than 130 μm from a capillary.
Large surface area ⇒ lower blood pressure.
Capillaries join, form veins.
- Veins lead blood to the heart.
- Low blood pressure.
- Not as thick as the arteries.
Blood flow in the veins
- Low blood pressure.
- Valves prevent the blood from flowing backwards.
- Muscle contractions push the blood forward.
You may also be interested in:
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- 2. Cellular Structure and Function
- 3. Cellular Genetics
- 4. Mendelian Genetics
- 5. Evolution and Systematics
- 5.1. Roadmap to a Theory of Evolution
- 5.2. The Pillars of Evolution
- 5.3. Evidence for Evolution
- 5.4. Convergent and Divergent Evolution
- 5.5. Coevolution
- 5.6. Stabilizing and Disruptive Selection
- 5.7. Speciation
- 5.8. How to Build a Family Tree
- 5.9. The History of Life
- 5.10. The Formation of Life
- 5.11. The Divisions of Life
- 5.12. Plant Systematics
- 5.13. Animal Systematics
- 5.14. Chordate Systematics
- 5.15. Human Evolution
- 6. Ethology and Behavioural Ecology
- 7. Ecology: Systems of Organisms
- 7.1. Ecosystems
- 7.2. Nutritional Chains and Food Webs
- 7.3. Flow of Energy in an Ecosystem
- 7.4. The Water Cycle
- 7.5. The Carbon Cycle
- 7.6. The Nitrogen Cycle
- 7.7. The Phosphorous Cycle
- 7.8. Populations: Size and Growth
- 7.9. Communities. Living Together
- 7.10. Ecological Succession
- 7.11. From Bedrock to Litter
- 7.12. The Lakes
- 7.13. The Oceans and Seas
- 7.14. Climate and Biomes
- 8. Environmental Science
- 9. Viruses and Biotechnology
- 10. Plant & Fungal Physiology
- 10.1. The Organs of the Plants
- 10.2. Plants With and Without Seeds
- 10.3. The Root. How the Plant Absorbs Water and Nutrients
- 10.4. The Trunk and Water Transport
- 10.5. Structure and Function of the Leaf
- 10.6. Photosynthesis
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- 10.8. How Plants Reproduce
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- 11. Human Physiology
- 11.1. Physiology Basics
- 11.2. The Nervous System
- 11.3. The Senses
- 11.4. The Endocrine System
- 11.5. Food and Digestion
- 11.6. The Locomotor System
- 11.7. Gas Exchange and Circulation
- 11.7.1. Respirational Systems
- 11.7.2. Human Respiration
- 11.7.3. Circulation in Different Animals
- 11.7.4. The Human Circulatory System. Heart, Blood Vessels and Blood Pressure
- 11.7.5. Activity in the Capillaries
- 11.7.6. Blood Constituents
- 11.7.7. Blood Groups
- 11.7.8. Coagulation
- 11.7.9. Some Blood Diseases
- 11.7.10. Water Balance. Kidneys
- 11.8. The Immune System
- 11.9. Sex, Love, and STDs