LHR Revision Notes
[Topic 1] Lifestyle, Health and Risk
, A Level Notes LHR: Circulatory Systems Biology
Open Circulatory Systems:
In insects and other animal groups blood circulates in large open spaces
Simple heart pumps out blood into cavities surrounding organs; substances can diffuse between the blood and cells
Heart muscles relaxes, blood drawn from cavity back into heart through small valved openings along its length
Positives Negatives
Pressure changes don’t create vulnerabilities – makes it Near impossible to increase blood distribution; with each
possible for life to exist in high pressure environments, heartbeat the heart causes blood to fill into body cavities
like the bottom of the ocean. which fills the total capacity of the system.
Oxygen and carbon dioxide processed via separate Creates a low metabolic rate as there are limits to the
systems; reduces amount of urgency within the system diffusion process which cannot be change. This results in
to restore balance. slower movements and adaptability to new
environments.
Can dispel heat more efficiently; makes it possible to live Only benefits small creatures because the size limits the
in a high temperature environment – in colder distance the blood must travel to each body cavity. For
temperatures, heat can be maintained if shelter can be larger creatures, the diffusion process would be slow
found. enough that cell starvation could occur because not
enough oxygen could be processed in time.
Closed Circulatory Systems:
Most animals (including all invertebrates) circulate blood enclosed within blood vessels
This generates higher blood pressures as the blood is forced through narrow channels instead of flowing into
large cavities
This means the blood travels faster and is a more efficient
• Blood leaves heart under pressure → arteries → arterioles → capillaries
• Many capillaries; close contact with cells where transfer of substances occurs
• Blood returns to heart → venules (small veins) → veins
• Valves ensure blood flow in one direction
Animals with this system are generally larger in size and are more active
Animals with a closed circulatory system have either single or double circulation.
Single Circulatory Systems:
Fish have single circulation.
Heart pumps deoxygenated blood to gills
Gaseous exchange takes place; diffusion of CO2 from blood to water surrounding gills and diffusion of oxygen
from this water into blood within gills
Blood leaving gills flows round rest of body before returning to heart
Double Circulatory Systems:
Birds and mammals have double circulation.
Right ventricle of the heart pumps deoxygenated blood to lungs where it receives oxygen
Oxygenated blood returns to heart to be pumped a second time (by left ventricle) out to rest of the body
This means blood flows through heart twice for each complete circuit of the body. The heart gives blood returning from
lungs and extra ‘boost’ that reduces time it takes for blood to circulate whole body. This allows bids/mammals to have
a high metabolic rate as oxygen and food substances required for metabolic processes can be delivered more rapidly to
cells and meet needs of organism.
The alveoli have several adaptations for efficient gas exchange:
• Large surface area • Thin lining; just one cell thick
• Permeable (they let substances pass through their surface)
• Moist surface (the gases must be dissolved so that they can diffuse across the surface)
• Good blood supply (capillary network)
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