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Cardiovascular System Summary Notes
The cardiovascular system includes:
The heart, a muscular pump
The blood, a fluid connective tissue
The blood vessels, arteries, veins and capillaries
Blood flows away from the heart in arteries, to the capillaries and back to the heart in the veins
There is a decrease in blood pressure as the blood travels away from the heart
Arterial branches of the aorta supply oxygenated blood to all parts of the body
Deoxygenated blood leaves the organs in veins
Veins unite to form the vena cava which returns the blood to the heart
Pulmonary System
This is the route by which blood is circulated from the heart to the lungs and back to the heart again
The pulmonary system is exceptional in that the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood
Hepatic Portal Vein
There is another exception in the circulatory system – the hepatic portal vein
Smooth muscle can contract or become relaxed
This contraction or relaxation brings about vasodilation or vasoconstriction to control blood flow
During strenuous exercise the arterioles leading to the muscles undergo vasodilation – the circular muscle in the arteriole wall is relaxed and the lumen is wide
This allows an increased blood flow to the skeletal muscles
At the same time, the arterioles leading to the small intestine undergo vasoconstriction
The circular muscles are contracted and the lumen is narrow
As a result, this reduces the blood flow to the gut
Veins carry blood back to the heart
The muscular layer and layers of elastic fibres in the vein wall are thinner than those in an artery because blood flows along a vein at low pressure
The lumen of a vein is wider than that of an artery
Valves are present in veins, to prevent the backflow of blood
Following two slides compare an artery and vein
Capillaries and Exchange of Materials
Blood is transported from arterioles to venules by passing through a dense network of blood vessels called capillaries
All exchanges of substances between blood and living tissue takes place through capillary walls
Capillary walls are composed of endothelium and are only one cell thick
The only difference between plasma and tissue fluid is that plasma has proteins
Tissue fluid contains a high concentration of dissolved food, oxygen, useful ions etc.
These diffuse, down a concentration gradient, into the surrounding cells
Carbon dioxide and other metabolic wastes diffuse out of the cells, down a concentration gradient, into the tissue fluid to be excreted
Tissue fluid and Lymph
Much of the tissue fluid returns to the blood in the capillaries at the venule end of the capillary bed
This is brought about by osmosis
Tissue fluid lacks plasma proteins so it has a higher water concentration than the blood plasma
Some of the tissue fluid does not return to the blood in the capillaries
This excess tissue fluid is absorbed by thin-walled lymphatic vessels
When the tissue fluid is in the lymphatic vessel it is called lymph
Tiny lymph vessels unite to form larger vessels
Flow of lymph is brought about by the vessels being compressed when muscles contract during breathing, movement etc.
Larger lymph vessels have valves to prevent backflow
Lymph vessels return their contents to the blood via two lymphatic ducts
These enter the veins coming from the arms
Structure and Function of the Heart
Continuous circulation of blood is maintained by a muscular pump, the heart
The heart is divided into 4 chambers, two atria and two ventricles
The right atrium receives deoxygenated blood from all parts of the body via the vena cavae
Deoxygenated blood passes into the right ventricle before leaving the heart through the pulmonary artery
The pulmonary artery divides into two branches, each leading to a lung
Oxygenated blood returns to the heart by the pulmonary veins
It flows from the left atrium to the left ventricle before leaving the heart by the aorta
The wall of the left ventricle is more muscular and thicker than that of the right ventricle
The left ventricle is required to pump blood all around the body
The right ventricle only pumps blood to the lungs
Valves between the atria and ventricles are the atrio-ventricular (AV) valves
Valves prevent the backflow of blood
The presence of valves ensures the blood flows in one direction through the heart
