Cardiovascular System: Blood Vessels, Blood Pressure & Cardiovascular Disorders.
Blood Vessels.
Blood vessels are the channels through which blood is distributed to body tissues.
The vessels make up two closed systems of tubes that begin and end at the heart.
Based on their structure and function, blood vessels are classified as,
Arteries,
Veins &
Capillaries.
Arteries:
Carry blood from Heart to Organs.
Contains Oxygenated Blood, exceptions are Pulmonary arteries.
Structure:
The wall of an artery consists of three layers.
a) Tunica intima (also called tunica interna), innermost layer,made up of simple squamous epithelium.
b) The tunica media, Middle layer it is primarily smooth muscle and is usually the thickest layer. Responsible for changing the diameter of arteries to regulate blood flow.
Tunica adventitia (Also called tunica externa): The outermost layer, which attaches the vessel to the surrounding tissue, is the or. This layer is connective tissue with varying amounts of elastic and collagenous fibers.
Veins:
Carry blood from Organs to Heart.
Contains Deoxygenated Blood, exceptions are Pulmonary veins, Umbilical vein.
Structure:
The walls of veins have the same three layers as the arteries.
In Tunica media, there is less smooth muscle and connective tissue.
Walls of veins are thinner as there is less blood pressure than arteries.
Because the walls of the veins are thinner and less rigid than arteries, veins can hold more blood.
Medium and large veins have venous valves that help keep the blood flowing toward the heart.
Venous valves are especially important in the arms and legs, where they help blood to flow against gravity.
Capillaries:
Capillaries, the smallest and most numerous of the blood vessels.
They form the connection between the arteries and the veins.
The primary function of capillaries is the exchange of materials between the blood and tissue cells.
Blood pressure:
Pressure exerted by the blood on the walls of blood vessels is called blood pressure.
It consists of systolic blood pressure and diastolic blood pressure.
Systolic blood pressure is the highest arterial pressure during systole and diastolic blood pressure is the lowest arterial pressure during diastole.
The systolic blood pressure in a normal adult human is 120 mm of Hg and the diastolic blood pressure is 80 mm of Hg.
Pulse pressure is the difference between systolic and diastolic pressure.
This pressure provides the information about the condition of the cardiovascular system and is normally about 40 mm of Hg.
The device used to measure blood pressure is a sphygmomanometer.
Factors modifying blood pressure:
1) Cardiac output
2) Blood volume
3) Peripheral resistance
4) Elasticity of blood vessels
5) Diameter of the lumen of blood vessels
6) Viscosity of blood
1) Cardiac output:
It is the volume of blood pumped by the heart per minute.
It depends on the stroke volume, when stroke volume increases systolic blood pressure increases.
When cardiac output increases both systolic and diastolic pressure increases.
2) Blood volume:
Sufficient blood volume is necessary to maintain normal blood pressure.
Loss of blood (in haemorrhage) decreases blood pressure.
3) Peripheral resistance:
It is the resistance by the walls of blood vessels for the flow of blood due to friction between blood and the walls of blood vessels.
The diameters of arteries and veins are large, so their resistance is very small.
The smallest vessels like arterioles, capillaries and venules contribute more resistance.
When blood vessels get contracted blood pressure increases as there is an increase in peripheral resistance.
When blood vessels get dilated blood pressure decreases as there is a decrease in peripheral resistance.
4) Elasticity of blood vessels:
Decrease in elasticity results in increase in the blood pressure.
5) Diameter of the lumen of blood vessels:
When blood vessels get contracted (smaller the lumen) blood pressure increases as there is an increase in peripheral resistance.
When blood vessels get dilated (Larger the lumen) blood pressure decreases as there is a decrease in peripheral resistance.
6) Viscosity of blood:
Higher the viscosity of blood, higher is the resistance which increases blood pressure.
The viscosity of blood mainly depends on the concentration of red blood cells in the plasma volume.
In a condition Polycythemia the abnormal rise in RBCs increases the viscosity of the blood and apparently the blood pressure.
Cardiovascular Disorders.
These are divided into
A) Disorders of the heart.
B) Disorders of the blood vessels.
C) Disorders of the heart
1) Cardiac failure:
In this the heart is failing to maintain the circulation of sufficient blood to meet the needs of the body.
In cardiac failure left ventricular failure is more common than right, because of the greater workload of the left ventricle.
2) Angina pectoris:
Partial obstruction of blood flow in the coronary arteries leads to reduced blood flow to the heart. It causes severe chest pain, which may also pass to the arms, neck and jaw.
Angina pectoris is a symptom of imbalance in oxygen demand and supply to myocardium.
3) Myocardial infarction:
A complete obstruction of blood flow in the coronary artery results in myocardial infarction commonly known as a heart attack, because of the interrupted blood supply there is the death of the heart tissue.
4) Rheumatic heart disease:
It is an autoimmune disease caused due to streptococcal infection.
The antibodies produced to fight the original infection damage the connective tissues of the heart.
5) Infective endocarditis:
Pathogenic organisms such as bacteria or fungi in the blood may settle at any part of the heart, the most common sites are on or near the heart valves.
6) Cardiac arrhythmias:
The rhythm of heartbeats is produced by the SA node.
The arrhythmia is an abnormal rhythm as a result of a defect in the conduction system of the heart.
Symptoms include chest pain, shortness of breath, dizziness.
7) Congenital heart disease:
Congenital heart disease is abnormalities in the heart and blood vessels at birth.
Most of the defects are in variation in the formation of the septum dividing the heart into right and left side.
B) Disorders of the blood vessels
1) Arteriosclerosis:
Thickening of the walls of the arteries and loss of elasticity is called arteriosclerosis.
It is due to excessive plasma levels of triglycerides and lipids causing deposition of lipid products on the internal wall of arteries.
2) Atherosclerosis:
It is nothing but the formation of atherosclerotic plaques in the walls of large and medium sized arteries due to high blood levels of cholesterol.
3) Aneurysm:
It is an abnormal local dilation of arteries.
4) Embolus:
A blood clot, air bubble or fat is transported by the bloodstream and blocks the small vessels.
5) Thrombus:
Clotting in the blood vessel which obstructs a blood vessel at the point where it is actually formed.
6) Phlebitis:
(Phleb- Vein) It is an inflammation of a vein.
7) Thrombophlebitis:
Inflammation of vein due to clot formation.
8) Varicose veins:
Varicose vein is a condition in which leaky venous valves can cause veins to become dilated and twisted in appearance.
The leaking venous valves allow the backflow of blood which causes pooling of blood.
This in turn, creates pressure that distends the vein.
As a result the affected veins and the tissue around it may become inflamed and painful.
Commonly Asked Questions:
Draw a well labelled diagram of L.S. of the human heart.
What is blood pressure? Explain factors affecting blood pressure.
Mention any seven cardiovascular disorders.
Describe how circulation of blood takes place through heart chambers.
Define blood pressure. Explain all factors that modify blood pressure.
Describe in brief, cardiac cycle.
Describe in brief systemic circulation.
Define: i) Myocardial infarction ii) Cardiac output iii) Pulse iv) Stroke volume
Describe a conducting system of heart.
Explain the anatomy of the heart.