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CirculationandBlood.ppt* of 33
© Boardworks Ltd 2008
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Boardworks AS Biology
Circulation and Blood
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© Boardworks Ltd 2008
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Boardworks AS Biology
Circulation and Blood
Teacher notes
In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.
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Why need a transport system?
Single-celled organisms, such as bacteria and amoeba (below), can obtain nutrients and excrete waste simply by diffusion.
nutrients
waste products
Multi-cellular organisms, such as insects, fish and mammals, require a more specialized transport system. Why is this?
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Circulation and Blood
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Surface area to volume ratio
In larger organisms, diffusion of substances would occur far too slowly to enable them to survive: the rate of diffusion increases with the square of the distance it has to travel.
Single-celled organisms have a very large surface area to volume ratio, because the diffusion path is so short.
This is not just because of its size, however: more important is an organism’s surface area to volume ratio.
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Circulation and Blood
Photo credit: Jupiterimages Corporation
Teacher notes
Flatworms have no specialized transport system but rely on diffusion to distribute oxygen, nutrients and waste products. Students could be asked to state why they think flatworms are able to survive without a transport system.
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Surface area and volume
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Circulation and Blood
Teacher notes
This activity can be used by students to compare the relationship between surface area and volume between different types of shape, e.g. flat rectangles vs. cubes. Students could plot a graph to follow the trends.
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Components of circulatory systems
Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises:
- a heart
- vessels through which the fluid can flow.
- a fluid in which substances are transported
The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates).
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Circulation and Blood
Photo credit: Jupiterimages Corporation
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Open circulatory systems
An open circulatory system consists of a heart that pumps a fluid called haemolymph through short vessels and into a large cavity called the haemocoel.
When the heart relaxes, the haemolymph blood is sucked back in via pores called ostia.
Haemolymph moves around the haemocoel due to the movement of the organism.
heart
haemocoel
In the haemocoel, the haemolymph directly bathes organs and tissues, enabling the diffusion of substances.
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Circulation and Blood
Teacher notes
Cephalopod molluscs (octopus, squid and nautilus) have a closed circulatory system.
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Closed circulatory systems
In a closed circulatory system, blood is fully enclosed within blood vessels at all times.
From the heart, blood is pumped through a series of progressively smaller vessels. In the smallest vessels, capillaries, substances diffuse in and out of the blood and into cells.
Blood then returns to the heart via a series of progressively larger vessels.
heart
capillaries
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Circulation and Blood
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Closed circulatory systems
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Circulation and Blood
Teacher notes
Students could be asked to list possible advantages a double circulatory system has over single circulatory systems. A major advantage is that the second pass through the heart gives the blood a boost, increasing it’s rate of flow and enabling oxygen and nutrients to be delivered more quickly to cells. This enables birds/mammals to have a higher metabolic rate than fish.
In a double circulatory system, the pulmonary circulation transports blood between the heart and the lungs, whereas the systemic circulation transports blood between the heart and the rest of the body.
Amphibians have a double circulatory system but with a three-chambered heart. Students could be asked to sketch what the structure of an amphibian heart might look like.
See ‘The Heart’ presentation for more information about the structure of the heart.
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The mammalian circulatory system
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Circulation and Blood
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Circulation: true or false?
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Circulation and Blood
Teacher notes
In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.
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Guide to blood vessels
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Circulation and Blood
Teacher notes
As blood at high pressure enters the artery it expands to lower the pressure. As blood at low pressure enters the artery it recoils to maintain the pressure.
The further away from the heart, the less elastic tissue and more smooth muscle an the artery is the less elastic tissue it has and the more smooth muscle. This is because the blood further away from the heart is at a lower pressure.
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Identifying blood vessels
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Circulation and Blood
Photo credit: Karen Hart, Peninsula College
http://www.pc.ctc.edu/hart/index.html
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Blood flow in veins
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Varicose veins
If a vein wall becomes weakened, valves may no longer close properly. This allows backflow of blood, causing the vein to become enlarged and bumpy, and become varicose.
This usually happens in superficial veins, near the skin surface in the lower legs, as opposed to deep veins, which lie underneath muscles.
Varicose veins can be surgically removed without affecting blood flow, as most blood is returned to the heart by deep veins.
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Maintaining high blood pressure
Blood pressure is the main force that drives blood from the heart around the body.
- During systole (heart contraction), blood is pumped through the aorta and other arteries at high pressure. The elastic fibres of arteries enable them to expand and allow blood through.
- During diastole (heart relaxation), the blood pressure in the arteries drops. The elastic recoil of the artery walls help force the blood on.
As blood moves through smaller arterioles into capillaries, and then into venules and veins, its velocity and pressure drop continuously.
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Circulation and Blood
Teacher notes
Students could be asked to draw a line graph of how they think blood pressure varies as it moves through the aorta, arteries, arterioles, capillaries, venules and veins.
See the ‘The Heart’ presentation for more information about systole and diastole.
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Arteries, capillaries and veins
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Circulation and Blood
Teacher notes
In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.
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What is blood?
Blood is a specialized transport medium that is also considered a special type of connective tissue. An average adult has 4–6 litres of blood.
Blood has a range of functions such as:
- transport
- defence
- thermoregulation
- maintaining pH of body fluids.
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Circulation and Blood
Photo credit: National Cancer Institute / Science Photo Library
Coloured scanning electron micrograph (SEM) of human blood showing red and white cells and platelets. Red blood cells (erythrocytes) have a characteristic biconcave- disc shape and are numerous. These large cells contain haemoglobin, a red pigment by which oxygen is transported around the body. They are more numerous than white blood cells (yellow). White blood cells (leucocytes) are rounded cells with microvilli projections from the cell surface. Leucocytes play an important role in the immune response of the body. Platelets are smaller cells (pink) that play a major role in blood clotting.
Teacher notes
Blood, along with bone and cartilage, is considered a type of connective tissue, even though it is quite different to other connective tissues, such as collagen. Embryologically, it has the same origin as other connective tissues, and could be said to connect other body tissues together through the transport of substances.
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The composition of blood
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The amount of blood occupied by erythrocytes is called the haematocrit. An athlete’s haematocrit is used in drug testing - an elevated level may indicate the athlete has artificially boosted the number of erythrocytes by using the drug erythropoietin, or by ‘blood doping’ - transfusing erythrocytes, either their own (which have been previously harvested and stored) or from a compatible donor.
Only about 2% of all the oxygen in blood is transported in the plasma. The vast majority is bound to haemoglobin in erythrocytes. In contrast, most carbon dioxide is transported in the plasma.
See the ‘Gas Exchange’ presentation for more information about haemoglobin and the transport of oxygen.
See the ‘Immunology’ presentation for more information about leukocytes.
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Features of erythrocytes
What are the specialized features of an erythrocyte?
flattened, biconcave disc shape: ensures large surface area to volume ratio for efficient gas exchange
diameter (6–8 µm) larger than capillary diameter: slows blood flow to enable diffusion of oxygen
no nucleus or organelles: maximises space for haemoglobin, so more oxygen can be transported
large amount of haemoglobin: for transporting oxygen
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Circulation and Blood
Teacher notes
Only the erythrocytes of mammals and a few other vertebrates have no nucleus. They are present in the erythrocytes of most other vertebrates. The lack of nucleus means erythrocytes cannot divide so most be continuously replaced by new cells produced in the bone marrow. Human erythrocytes live for about 120 days.
Haemoglobin makes up about 97% of the dry mass of an erythrocyte.
See the ‘Gas Exchange’ presentation for more information about haemoglobin.
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Blood clotting
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Teacher notes
Serum is plasma from which fibrinogen has been removed, therefore preventing it from clotting. Serum is used to treat plasma loss in people with severe burns (loss of outer layer of skin means tissue fluid, but not blood cells, are rapidly lost).
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Substances in blood clotting
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Plasma proteins and blood pressure
About 8% of blood plasma consists of plasma proteins, of which about half may be albumins.
The balance between the hydrostatic pressure of blood (‘blood pressure’) and the osmotic pressure of blood is important in the formation of tissue fluid.
These are a group of small proteins involved in the transport of other substances (e.g. fatty acids, hormones) and which help regulate the osmotic pressure of blood.
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Circulation and Blood
Photo credit: Borislav Mitev
Human serum albumin, to which six molecules of palmitic acid (grey) are bound.
Teacher notes
See the ‘Transport Across Membranes’ presentation for more information about osmosis.
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Formation of tissue fluid
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Circulation and Blood
Teacher notes
One sign of high blood pressure is oedema – swelling caused by the accumulation of tissue fluid. Students could be asked to explain how this occurs in terms of blood pressure and osmotic pressure.
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Lymph
Not all tissue fluid returns to the capillaries. The excess drains into the lymphatic system, where it forms lymph.
Lymph is a colourless/pale yellow fluid similar to tissue fluid but containing more lipids.
The lymphatic system drains into the circulatory system near the vena cavae via the thoracic duct.
lymphatic capillaries
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Circulation and Blood
Teacher notes
Lymph contains fatty substances because digested lipids are transported from the digestive system via the lymphatic system before being returned to the circulatory system.
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The lymphatic system
The lymphatic system is a secondary circulatory system and a major part of the immune system. It consists of:
- lymphatic capillaries and vein-like lymph vessels, containing valves
- lymph nodes – sac-like organs that trap pathogens and foreign substances, and which contain large numbers of white blood cells
- lymphatic tissue in the spleen, thymus and tonsils – these also contain large amounts of white blood cells and are involved in their development.
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Circulation and Blood
Teacher notes
Lymph moves through the lymphatic system via the action of skeletal muscles and the use of valves to prevent backflow.
Lymphatic tissues and lymph nodes are the site of development and maturation of lymphocytes.
Lymphatic filariasis is a parasitic disease caused when thread-like nematode worms (transmitted by mosquitoes) become lodged in the lymphatic system. In extreme cases, this causes elephantiasis – a swelling and thickening of skin and underlying tissue, usually in the legs or genitals.
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Composition of body fluids
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Circulation and Blood
Teacher notes
In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.
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Glossary
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Circulation and Blood
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What’s the keyword?
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Circulation and Blood
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Multiple-choice quiz
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Circulation and Blood
