Define Arteries.
Blood vessels which carry pulses of high-pressure blood away from the heart to organs.
Describe The Artery Wall.
- Tunica Externa: Tough outer layer of connective tissues with collagen fibers.
- Tunica Media: Thick layer containing smooth muscle and elastic fibres made of elastin (a protein).
- Tunica Intima: Smooth endothelium forming the lining of the artery.
- Lumen: Space inside an artery through which blood flows.
Elastic fibres: Proteins that can stretch and recoil.
Collagen fibres: Tough, rope-like proteins with high tensile strength.
List The Adaptions of Arteries.
Artery Wall:
* Relatively Thick.
* Elastic And Collagen Fibres.
Structure:
* Relatively Narrower Lumen.
When the ventricles of the heart pump, a burst of blood under high pressure enters the arteries and flows along them. The pressure then declines, until the next heartbeat (in which, the cycle repeats).
Artery Wall:
* Arteries have relatively narrow lumens, which helps them to maintain high blood pressures and high velocities of blood flows.
* Artery walls are relatively thick and contain elastic fibres and collagen fibres. Therefore, arteries are strong enough to withstand high and variable blood pressures without bulging outwards (aka, aneurysm) or busting.
What is The Function of Smooth Muscle Cells in Arteries?
- When the smooth muscle cells contract, the diameter of the lumen is narrowed (called vasoconstriction), reducing blood flow along an artery or arteriole.
- When they relax, the lumen widens and blood flow is increased (called vasodilation).
Smooth muscle cells also respond to hormone and neural signaling, and enable the body to adjust blood flow to tissues in organs based on need and availability.
Artery walls in the branches of arteries (aka, arterioles) contain smooth muscle cells with a particularly high density. Smooth muscle cells are circular, so when they contract, the diameter of the lumen is narrowed.
What is The Function of Elastic Fibres in Arteries?
- At peak (systolic) pressure: Artery wall stretches and lumen widens. The elastic fibres store the potential energy.
- At the end of heartbeat: Pressure falls in artery, the elastic fibres return the energy by recoiling and squeezing the blood in the lumen.
- As this is done, the semilunar valves at the exit of the ventricles are closed. Meaning, blood cannot flow back towards the heart, it is forced outwards towards the organs.
In this way, elastic fibres help to reduce the amount of energy expended in transporting blood to the organs of the body.
Therefore, elastic fibres help to pump blood along the arteries and prevent the diastolic (or ‘minimum’) pressure from becoming too low. They help to even blood flow in arteries.
Define Veins.
Blood vessels which carry a stream of low-pressure blood from the organs to the heart.
List Adaptions of Veins.
In Vein Wall:
* Fewer Elastic Fibres.
* Fewer Smooth Muscle Cells.
Structure:
* Pocket Valves.
Wall of Veins:
* Fewer Elastic Fibres (in relation to the wall of arteries): There is no pulse, so it does not need to stretch or recoil.
* Fewer Smooth Muscle Cells (in relation ot the wall of arteries): Veins are not used to adjust blood flow to different parts of the body, so it is not needed.
Structure:
* Pocket Valves: Prevents backflow, ensuring sufficient return of blood to the heart.
Describe The Structure of Pocket Valves.
Three cup-shaped flaps of tissue projecting into the vein in the direction of blood flow.
What Do Pocket Valves Do?
If blood flows backward:
* Blood fills the flaps of the pocket valve, causing it to close (blocking the lumen of the vein).
If blood flows forward:
* Pushes the flaps to the sides of the vein, causing it to open (allowing blood to flow freely).
Provide a Brief Arteries VS Veins Comparison.
Arteries:
* Thicker Wall.
* Narrower Lumen.
* Circular in Section.
* Inner Surface Corrugated.
* Fibres Visible in Wall.
Veins:
* Thinner Wall.
* Wider Lumen.
* Circular or Flattened in Section.
* No Inner Surface Corrugation.
* Few or No Fibres Visible in Wall.
Describe The Aorta.
The aorta carries blood pumped by the left side of the heart to all organs (apart from the lungs). Two arteries branch off from the aorta close to its origin at the semilunar valve.
Describe The Right Coronary Artery.
The right coronary artery supports the right side of the heart.
Two arteries branch off from the aorta close to its origin at the semilunar valve.
Describe The Left Coronary Artery.
The left coronary artery branches into two arteries that supply the left anterior and left posterior regions of the heart wall.
Two arteries branch off from the aorta close to its origin at the semilunar valve.
Therefore, there are three main coronary arteries, each of which branches repeatedly to provide oxygenated blood to all parts of the muscular wall of the heart.
How Does An Occlusion Occur?
- The coronary arteries can become narrowed or fully blocked by fatty deposits (atheroma, or plaque), which contain a variety of lipids (including cholestrol). This blockage is an occlusion.
- The deposits build up in the wall of the artery, restricting blood flow to the downstream region of the heart.
- This often causes pain in the chest (angina) or shortness of breath (especially during exercise).
How Does Thrombosis Occur?
- Fatty deposits in the artery wall become impregnated with calcium salts, which hardens the artery and makes the inner surface rough.
- This tends to trigger the formation of a blood clot (aka, thrombosis).
- Blood clots block the flow of blood to part of the muscular wall of the heart, depriving it of oxygen and preventing normal contractions. This is known as a heart attack.
Hypertension (high blood pressure) increases the rise of thrombosis.
How Does a Myocardial Infarction Occur?
If a blockage persists, there will be tissue death, therefore permanently damaging the heart.
A myocardial infarction is tissue death in the heart muscle due to inadequate blood supply.
List Risk Factors of Coronary Heart Disease.
- Hypertension
- Smoking
- Eating Too Much Saturated Fat And Cholestrol
- Obesity
- High Salt Intake
- Drinking Excessive Amounts of Alcohol
- Genetic Predisposition
- Old Age
- Hypertension: Elevated blood pressure increases chance of thrombosis.
- Smoking: Raises blood pressure, as nicotine causes vasoconstriction.
- Eating too much saturated fat and cholesterol: Promotes plaque formation.
- Obesity: Associated with high blood pressure and high blood cholesterol concentrations.
- High salt intake: Large amount of sodium chloride in diet raises blood pressure.
- Drinking excessive amounts of alcohol: Associated with high blood pressure and obesity.
- Genetic predisposition: Some genes increase risk of hypertension or thrombosis.
- Old age: Blood vessels become less flexible.
