CIRCULATORY SYSTEM
Introduction
Circulatory System - A fluid filled network of tubes or vessels through which material/blood is transported between cells in animals.
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1. Open Circulatory System - No vessels involved (e.g. insects and anthropods)
2. Closed Circulatory System - Have blood vessels
- Single circulatory system - Pass heart once in one round (e.g. fish, frog)
- Double circulatory system - Pass heart twice in one round (e.g. humans, elephants)
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*The circulatory system is required for the transport and removal of materials from cells. These materials are:
- Urea
- Carbon dioxide
- Glucose
- Oxygen
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NETWORK OF TUBES
1. Arteries - Oxygenated blood away from heart (except pulmonary artery)
2. Veins - Deoxygenated blood back to heart (except pulmonary vein)
3, Capillaries - Single cell thick, diffusion, mesh of vessels
Arteries
Arteries receive blood directly from the heart. They need to be able to withstand the immense pressure of the blood as it is forced out of the heart.
- Arteries have walls that are thick, muscular and elastic. The elastic layer is much thicker near the heart (higher blood pressure)
- Elasticity of an artery allows the artery wall to stretch and recoil; this helps push the blood in spurts along the artery (what one feels in a "pulse")
- When an artery constricts, its lumen becomes narrower, and less blood flows per unit time, whereas when an artery dilates, the lumen becomes wider and more blood flows per unit time.
- Most arteries carry oxygenated blood except the pulmonary artery which carries deoxygenated blood from the heart to the lungs.
Figure 1. Diagram of Artery
Veins
The blood pressure in the veins is much lower than that in the arteries. Blood flows smoothly and slowly in the veins, which is why their walls need not be thick and muscular like the walls of arteries.
- Veins contain internal semi-lunar valves along their lengths to prevent the backflow of flood. Valves are folds on the inner walls of arteries.
- Veins are less elastic in nature.
- Movement of blood in veins is assisted by the action of skeletal muscles on the veins.
- Veins carry deoxygenated blood (except for the pulmonary vein which carries oxygenated blood from the lungs to the heart).
Capillaries & Tissue Fluid
The tiny spaces in between tissue cells contain a colorless fluid called tissue fluid. The tissue cells are bathed with this liquid (which carries substances in solution between cells and blood capillaries)
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How are substances transferred between capillaries and tissue fluid?
- Through simple diffusion and the creation of a concentration gradient, required substances enter the tissue fluid from the oxygenated blood (coming from arteries) and waste products from the tissue fluid diffuse into the capillaries which later becomes veins.
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Artery - Arterioles - Capillaries - Veinioles - Veins
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- For RBCs to diffuse through the capillaries into the tissue fluid, they may become bell shaped to squeeze through the small spaces. As the cell becomes bell shaped, its surface areas increases the speed of absorption/release of oxygen.
- Rate of blood flow is reduced in capillaries, giving more time and thus increasing efficiency of, exchange of materials between he blood and tissue cells.
Figure 2. Movement of blood
Figure 3. Diagram of a vein
TYPES OF VEINS AND ARTERIES
1. Pulmonary Artery - Transports deoxygenated blood to lungs
2. Pulmonary Vein - Transports oxygenated blood to heart
3. Aortic arch & trunk - Main arteries from heart
4. Common caratoid artery - Carries oxygenated blood to brain
5. Renal vein & artery - Connects kidneys
6. Hypatic portal vein - Takes blood from GI tract to liver
7. Messentric vein - Connects to intestine
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Remember "PHAMPCR"
The Heart
BASIC INFORMATION OF HEART
- In heart, left is RIGHT and right is LEFT
- 4 chambers in the heart, upper chambers are atrium (left and right), and lower chambers are ventricles (left and right)
Right Side: Pumps deoxygenated blood to the lungs
Left side: Pumps oxygenated blood to the body (thicker walls as needed to regulate pressure)
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Blood Pressure - Measure of force exerted by blood on arteries
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Valves in heart:
- Tricuspid Valve (Between right atrium and ventricle)
- Mitral Valve (Between left atrium and ventricle)
- Aortic Valve (Between left ventricle and aorta)
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VENTRICULAR SYSTOLE - Ventricles contract
VENTRICULAR DYSTOLE - Ventricles relax
Figure 4. Diagram of a heart
PROCESS OF CIRCULATION OF BLOOD
1. Deoxygenated blood from various parts of the body is returned to the right atrium (from superior and inferior vena cava).
2. Right atrium contracts, blood flows through the tricuspid valve into the right ventricle.
3. When the right ventricle contracts, the pressure forces the tricuspid valve to close (no backflow of blood) and the blood leaves through the pulmonic valve into the pulmonary artery (leading to the lungs).
4. The blood in the pulmonary arteries is at a lower pressure than the blood in the aorta. This slows down the rate of blood flow to give more time for gas exchange in the lungs.
5. Oxygenated blood from the lungs is brought back to the left atrium by the pulmonary veins. When the left atrium contracts, blood flows through the bicuspid valve into the left ventricle.
6. When the left ventricle contracts, the bicuspid valve closes, and the oxygenated blood is forced through the aortic valve into the aorta and to the rest of the body (except lungs). The left ventricle has the thickest muscle, because when it contracts it has to create enough pressure to move the blood through the entire body.
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** Two small coronary arteries emerge from the aorta. They bring oxygen and nutrients to the heart muscle so that the heart can keep functioning.
Coronary Heart Disease
CORONARY HEART DISEASE
- Most common heart disease
- Coronary arteries emerge from the aorta (provide oxygen/nutrients to the heart)
- Blood supply to the heart muscles can be greatly reduced if the coronary arteries become blocked. This reduced supply of blood can cause a heart attack.
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HEART ATTACK
- During a heart attack, blood flow to a particular part of the heart may be completely blocked. Due to the blocked blood flow, the heart does not receive sufficient oxygen and nutrients. That region of the heart muscle dies.
- Extensive heart muscle damage is often fatal as the heart is no longer able to pump blood to the various parts of the body.
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Figure 5. Build up of cholestrol in arteries
CAUSES OF CORONARY HEART DISEASE
- Fatty substances such as cholestrol and saturated fats may be deposited on the inner surface of the coronary arteries. This is called atherosclerosis.
- These deposits narrow down the lumen of arteries, and increase blood pressure (more blood through a smaller space).
- Such an affected artery develops a rough inner surface, and increases the risk of a blood clot being trapped in the artery - this is called thrombosis. If thrombosis occurs, the supply of blood and oxygen to the heart is cut off resulting in heart muscle damage. A thrombosis could also enter the heart and block the passage resulting in death.
- A blood clot that forms in the artery is called a thrombosis.
- Atherosclerosis begins early in life. Factors that increase the risk of coronary heart disease and atherosclerosis are:
i. A diet rich in cholestrol and saturated animal fats
ii. Emotional stress
iii. Smoking
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PREVENTATIVE MEASURES
- A proper diet (polyunsaturated fats instead of saturated fats; polyunsaturated fats do not stick to the inner surfaces of arteries).
- Proper stress management
- No smoking
- Regular physical exercise helps maintain elasticity of arterial walls, strengthens heart, and decreases risk of high blood pressure (hypertension).