Atherosclerosis and Vascular Biology

Introduction:

Cardiovascular diseases represent the leading cause of death worldwide, accounting for eighteen million deaths annually. Cardiac diseases can arise from atherosclerotic vascular disease, obstructive coronary artery disease in myocardial infarction, valvular dysfunction, cardiac inflammation, and genetic disorders. Arteriosclerosis is a disease in which the blood vessels carry oxygen and nutrients from the heart to the peripheral tissues and body parts. Healthy arteries are flexible and elastic. But over time, the walls of the arteries can harden, a condition called hardening of the arteries. Atherosclerosis can begin when a person is very young and can worsen later on.

What Is Atherosclerosis?

Atherosclerosis is a disease where plaque builds up on the inside walls of the arteries (blood vessels). Blood vessels deliver blood and oxygen from the heart to the rest of the body. Hemodynamic stresses cause chronic injury to the endothelium.

• Hypertension causes stress on the vascular epithelium, a major risk factor for atherosclerosis. The posterior wall of the abdominal aorta is the common site for developing atheroma. The posterior wall of the abdominal aorta is under sheer stress because of the systolic pulse from the luminal side of the blood vessel. Hypercholesteremic states initiate the development of atherosclerosis.

• Atherosclerosis is a plaque of cholesterol and other substances in the artery walls. The plaque can cause arteries to narrow, blocking blood flow and leading to a blood clot. Plaque is a fibrofatty tissue of cholesterol, calcium, and other substances. As plaque builds up, the arteries become hard and narrow.

• Hardening the blood vessels can cause several problems, such as blocked arteries that cannot deliver sufficient blood or oxygen to the peripheral tissues. Blockages can lead to tissue death or infection in the arms, legs, or other body parts.

• A plaque can break free and get stuck somewhere in the body, causing damage. A blood clot forms in a narrow blood vessel. It will eventually loosen and pass through the blood vessel.

• Atherosclerosclerosis is the plaque of fats, cholesterol, and other substances in the artery walls. The plaque can cause arteries to narrow, blocking blood flow that leads to blood clots. Healthy lifestyle habits can help prevent atherosclerosis.

It can cause serious health problems and medical emergencies, including:

• Carotid artery disease.

• Chronic kidney disease.

• Coronary artery disease.

• Heart Attack.

• Peripheral artery disease.

• Stroke.

• Blood clot.

What Are the Risk Factors for Atherosclerosis?

The following are the risk factors that contribute to atherosclerosis:

• High blood pressure (hypertension).

• High cholesterol level (hypercholesterolemia).

• High triglycerides (a type of fat in the blood).

• Smoking.

• Diabetes.

• Insulin resistance.

• Obesity.

• An unhealthy diet.

• A family history of early heart disease.

What Are the Symptoms of Atherosclerosis?

Mild atherosclerosis does not have symptoms. Atherosclerosis symptoms happen until a blood vessel is narrowed or clogged so it cannot supply sufficient blood to other body parts. A blood clot can completely block the blood flow. The clot can break apart and can cause a heart attack. Moderate to severe atherosclerosis symptoms depend on which blood vessels are affected. For example:

• If atherosclerosis is in the heart's blood vessels, they may have chest pain or pressure (angina).

• In that case, they may have sudden numbness or weakness in arms or legs, difficulty in speech or slurred speech, temporary loss of vision in one eye, and drooping facial muscles. This signals to transient ischaemic attack (TIA) that leads to stroke.

• Suppose the person has atherosclerosis in the arteries in the arms and legs. The person may have symptoms of peripheral artery disease (pain in the legs while walking) and decreased blood pressure in an affected limb.

• A person with atherosclerosis in the arteries leading to the kidneys may develop high blood pressure or kidney failure.

What Is the Pathophysiology of Atherosclerosis?

The following stages are involved in the pathophysiology of atherosclerosis:

Stage 1:Endothelial Damage and Immune Response-

Atherosclerosclerosis begins when damage occurs to the inner layer of the artery wall. The surface of the intima is lined with a thin lining of blood vessels called the endothelium that acts as the barrier between the blood and the artery wall. Many things can harm the endothelium. The most common risk factors include:

• High LDL (low-density cholesterol) circulating in the blood.

• Smoking releases toxins.

• Hypertension (high blood pressure).

Once the endothelium is damaged, cholesterol from the blood starts forming at the place of the injury. These cholesterols are oxidized at the site of injury, and they cause inflammation and release free radicals. Due to the immune response, the body's white blood cells (defense cells) travel to the site of injury and cause inflammation.

Stage 2: Atheroma

An atheroma (fibrofatty tissue) is the visible sign of atherosclerosis. It is a patch formed from dead cells at the site of endothelial damage. Here’s how it forms:

1. The monocytes that move to the site of inflammation turn into another cell called macrophages. The macrophages surround and consume invaders to get rid of them. In this case, the macrophages consume the atheroma (fibrofatty cholesterol).

2. The macrophages fill up with cholesterol, and they appear foamy. They are called foam cells.

3. The foam cells consume the cholesterol, and they die.

4. The body sends more white blood cells to the area as the foam cells die. These cells continue taking the cholesterol, get foamy, and die. As this process continues, it damages the blood vessels (endothelium).

Stage 3: Plaque Formation

The dead foam cells continue to build up in place of the cholesterol. The cholesterol slowly gets bigger and forms a very big piece of plaque. The artery’s smooth muscle cells form a layer called a fibrous cap covering the plaque. It prevents the plaque from breaking off into the bloodstream. The plaque keeps on increasing the size. The blood still has enough room to pass through. That’s because the artery wall expands outward to make space for the plaque. But it can only expand outward so far. This expansion is called an aneurysm. As the plaque gets too big, the opening of the blood vessel becomes very narrow. There will be less place for the blood to flow. The plaque can remain stable for a long time. But eventually, it will rupture.

Stage 4: Plaque Maturation

The plaque matures and grows larger. It grows in size and takes up more space in the blood vessel. When the fibrous cap breaks, the plaque inside comes into contact with the blood. This can induce a blood clot to form. This blood clot, known as the thrombus, blocks the blood flow and leads to a heart attack or stroke.

How Does Cholesterol Play a Major Role in the Development of Atherosclerosis?

Low-density cholesterol (LDL) is considered a bad lipid. High-density cholesterol (HDL) is considered a good lipid. Because low-density cholesterol is responsible for taking the cholesterol to the peripheral tissues, but HDL helps remove the cholesterol from the peripheral tissues and takes it back to the liver for processing. LDL deposits the cholesterol in the atheromatous plaque. The hepatocyte present in the liver has a receptor for LDL. This receptor can capture the LDL and take it in the hepatocytes. A person with high LDL levels will have more supply of cholesterol to the injured endothelium. The atheromatous lesion will develop more rapidly.

Conclusion:

Atherosclerosis is due to plaque build-up on the inside walls of blood vessels. Getting a yearly checkup to catch and manage any related conditions is important. Healthy lifestyle choices, medications, and surgical procedures can prevent complications of atherosclerosis. A healthcare provider is ready to help manage the condition for a long and healthy life.