- All organisms need to exchange materials between themselves and the environment:
- Respiratory gases
- Excretory products.
- Exchange surfaces require:
- Large SA
- Moist surfaces
- Small distances
- Concentration gradients
- This is simple in unicellular organisms:
- Unicellular algae
- Increasing size increases problems:
- Diffusion is no longer sufficient.
- Complex multicellular organisms evolved more sophisticated systems.
- Digestive systems
- Flowers etc
- Larger organisms have higher metabolic rate.
- Specialist exchange surfaces evolved to make exchange more efficient
- Mass transport circulatory systems evolved to connect tissues with exchange surfaces.
- Needed when:
- Surface area to volume ration is low
- Metabolic activity is high
General characteristics of a circulatory system
- When it comes to IBDP Biology, a circulatory system provides rapid mass flow of materials in bulk.
- From exchange surfaces to respiring tissues.
- From respiring tissues to exchange surfaces.
- Concentration gradients must be maintained.
- Surfaces must be adapted to allow efficient exchange.
- Various distinct characteristics:
- A circulatory fluid, eg blood or fluid in the phloem
- A closed system of branching vessels through which the fluid can circulate, eg blood vessels, and xylem vessels.
- A mechanism for transporting the fluid, that relies on pressure gradients being maintained. eg a muscular pump such as the heart, or a passive mechanism such as transpiration.
- A mechanism to ensure flow is in one direction eg valves.
- A mechanism to control flow rate depending on metabolic requirements, eg nervous control, or stomatal control.
Arrangement of the Circulatory System in mammals
Double circulation in mammals
- Systemic circulation:
- Left side of heart to
- Tissues and organs of the body
- Back to right side of heart
- Pulmonary circulation
- Right side of heart to
- Back to left side of heart
- When it comes to IBDP Biology, it enables lower pressure to lungs.
- Ensures pressure is high enough for efficient exchange at tissues.
- Mostly parallel circuits – enables even distribution
Circulatory system layout
- When it comes to IBDP Biology, Coronary arteries – branch from aortic arch, delivering oxygenated blood to the cardiac muscle.
- Aorta – takes oxygenated blood from heart to the respiring tissues.
- Vena Cava – takes deoxygenated blood from the respiring tissues to the heart.
- Pulmonary artery – takes deoxygenated blood from the heart to the lungs.
- Pulmonary vein – takes oxygenated blood from the lungs to the heart.
- Hepatic artery – takes oxygenated blood from aorta to the liver.
- Hepatic portal vein – takes deoxygenated, nutrient rich blood from the intestines to the liver.
- Hepatic vein – takes deoxygenated blood from the liver to the vena cava
- Left and right renal arteries – take oxygenated blood to the kidneys.
- Left and right renal veins – take deoxygenated blood to the vena cava.
That's the end of part 1.
You can now proceed to part 2!