8.1 The circulatory system:
Circulatory system - a system of blood vessels with a pump and valves to ensure one-way flow
of blood
• Systems can be open or closed and single or double:
◦Single circuits share the load
◦Double circuits have blood flow through the heart twice
• The human circulatory system consists of a pump (the heart) and a system of blood vessels
which link together.
◦It is a closed system as the blood always remains within the vessels
Blood vessel structures:
• Arteries, veins and capillaries are the main types of blood vessel in the circulatory system.
◦Arteries e.g. aorta - carry blood away from the heart at high pressure
◦Veins e.g. vena cava - carry blood back to the heart at low pressure
◦Capillaries - connect arteries and veins (thin wall to allow glucose and oxygen to pass)
‣ The small size allows them to bring blood as close as possible between cells and
the blood
• Venules link capillaries to veins + arterioles link capillaries to arteries
◦Sphincter muscle in arterioles contract and release to regulate blood flow through the capillary beds
• Elastic fibres - withstand changes in blood volume and pressure without
bursting - arteries have more due to high pressure.
• Muscle - helps to maintain blood pressure, by contracting and relaxing
• Collagen - a protective outer layer
• Valves - found in the vein and ensure one-way blood flow (due to low pressure,
they would move back otherwise)
Layers:
• Tunica intima - squamous epithelial layer
• Tunica Media - Muscle and elastic fibres
• Tunica externa (adventitia) - collagen layer
The Blood:
-55% plasma - for osmotic balance, buffering and carrying substances (plasma
proteins, glucose, dissolved ions and gases e.g. CO2 and sodium, water, hormones, salts and waste e.g. urea)
-45% cells (erythrocytes, leukocytes, thrombocytes)
• Erythrocytes (RBCs) - contain haemoglobin for the transport of oxygen through the body
◦Biconcave disk shape - increases SA:VOL ratio, so more oxygen is moved in and out
◦very small - 7um - therefore, haemoglobin molecules are near to the cell membrane for oxygen exchange.
◦Flexible - capillaries are v small, so they can deform to fit through them and then reform
◦No nucleus - more room for haemoglobin and oxygen uptake
• Leukocytes (WBCs) - there are a number of different types, but they all fight against infection
◦Granulocytes: (lots of specs in the cell)
‣ Neutrophils (70% of WBC) - multi-lobed nucleus, engulf bacteria by hydrolytic enzymes in lysosomes and can
squeeze between cells (due to stretched nucleus)
‣ Basophils - release histamine which causes swelling or serotonin
which makes capillary walls more leaky so that phagocytes can be
released, with a bean shaped nucleus
‣ Eosinophils - releasing anti-histamine in the immune response of
parasites or allergens, with a 2-lobed nucleus
◦Agranulocytes:
‣ Lymphocytes - T-helper, memory and killer, B-memory and plasma -
releasing antibodies in the immune response - large circular nucleus
‣ Monocytes - becomes a macrophage - engulf and present bacteria
Circulatory system - a system of blood vessels with a pump and valves to ensure one-way flow
of blood
• Systems can be open or closed and single or double:
◦Single circuits share the load
◦Double circuits have blood flow through the heart twice
• The human circulatory system consists of a pump (the heart) and a system of blood vessels
which link together.
◦It is a closed system as the blood always remains within the vessels
Blood vessel structures:
• Arteries, veins and capillaries are the main types of blood vessel in the circulatory system.
◦Arteries e.g. aorta - carry blood away from the heart at high pressure
◦Veins e.g. vena cava - carry blood back to the heart at low pressure
◦Capillaries - connect arteries and veins (thin wall to allow glucose and oxygen to pass)
‣ The small size allows them to bring blood as close as possible between cells and
the blood
• Venules link capillaries to veins + arterioles link capillaries to arteries
◦Sphincter muscle in arterioles contract and release to regulate blood flow through the capillary beds
• Elastic fibres - withstand changes in blood volume and pressure without
bursting - arteries have more due to high pressure.
• Muscle - helps to maintain blood pressure, by contracting and relaxing
• Collagen - a protective outer layer
• Valves - found in the vein and ensure one-way blood flow (due to low pressure,
they would move back otherwise)
Layers:
• Tunica intima - squamous epithelial layer
• Tunica Media - Muscle and elastic fibres
• Tunica externa (adventitia) - collagen layer
The Blood:
-55% plasma - for osmotic balance, buffering and carrying substances (plasma
proteins, glucose, dissolved ions and gases e.g. CO2 and sodium, water, hormones, salts and waste e.g. urea)
-45% cells (erythrocytes, leukocytes, thrombocytes)
• Erythrocytes (RBCs) - contain haemoglobin for the transport of oxygen through the body
◦Biconcave disk shape - increases SA:VOL ratio, so more oxygen is moved in and out
◦very small - 7um - therefore, haemoglobin molecules are near to the cell membrane for oxygen exchange.
◦Flexible - capillaries are v small, so they can deform to fit through them and then reform
◦No nucleus - more room for haemoglobin and oxygen uptake
• Leukocytes (WBCs) - there are a number of different types, but they all fight against infection
◦Granulocytes: (lots of specs in the cell)
‣ Neutrophils (70% of WBC) - multi-lobed nucleus, engulf bacteria by hydrolytic enzymes in lysosomes and can
squeeze between cells (due to stretched nucleus)
‣ Basophils - release histamine which causes swelling or serotonin
which makes capillary walls more leaky so that phagocytes can be
released, with a bean shaped nucleus
‣ Eosinophils - releasing anti-histamine in the immune response of
parasites or allergens, with a 2-lobed nucleus
◦Agranulocytes:
‣ Lymphocytes - T-helper, memory and killer, B-memory and plasma -
releasing antibodies in the immune response - large circular nucleus
‣ Monocytes - becomes a macrophage - engulf and present bacteria
