فسيولوجيا الأوعية الدموية

Blood Vessel Diseases

• Normal blood flow through arteries and veins requires a healthy system of blood vessels and sufficient pressure to push blood through them.
• Various diseases can affect the normal function of arteries or veins.
• Changes due to disease can weaken blood flow through arteries, disrupting oxygen and nutrient delivery to tissues, while diseases affecting veins disrupt waste removal from tissues and blood return to the heart.

Arterial Diseases

Atherosclerosis

• One of the most common diseases affecting arteries is atherosclerosis.

• It results from the deposition of fatty plaques in artery walls.

• Coronary arteries of the heart are most affected.

• Since dietary fats and cholesterol are insoluble in plasma, they are transported as part of a complex called lipoproteins.

• Lipoproteins consist of a fat-loving core of cholesterol esters and a water-loving shell of phospholipids.

• All lipoproteins are spherical and composed of:

  • A surrounding core of protein (apolipoprotein or apoprotein) on the surface surrounding the lipid particles.
  • An outer layer of fat (unesterified cholesterol and phospholipid).
  • A water-repelling core (cholesterol esters and triglycerides).

• Lipoproteins are classified by their density, size, and their protein and lipid content.

  • Chylomicrons (CM):
    • Primarily composed of triglycerides (90%) and 10% cholesterol (diameter 160 nanometers).
    • Lowest density.
    • Produced in the intestinal wall.
    • Primarily transport dietary triglycerides from the intestines into the blood.
  • Very low-density lipoprotein (VLDL):
    • Primarily composed of triglycerides (75%) (diameter 80 nanometers).
    • Produced in the liver.
    • Can be converted into IDL in the blood.
  • Intermediate-density lipoprotein (IDL):
    • 50% triglycerides and 50% cholesterol (diameter 40 nanometers).
    • Precursor to LDLs.
  • Low-density lipoprotein (LDL):
    • Primarily composed of cholesterol (75%) (diameter 20 nanometers).
    • Primarily transports cholesterol from the liver to the tissues.
    • Enters cells by binding to LDL receptors on the cell surface.
    • Called "bad" cholesterol due to its role in atherosclerosis.
  • High-density lipoprotein (HDL):
    • 75% cholesterol, the difference is apoprotein (diameter 10 nanometers).
    • Produced in the liver.
    • Called "good" cholesterol because it removes cholesterol from the bloodstream.

• Both IDL, LDL, and VLDL are considered harmful lipoproteins (bad cholesterol).

• HDL is a beneficial lipoprotein (good cholesterol) transferring cholesterol from arteries to the liver.

• Blood cholesterol measurements include all types (less than 240 mg/dL).

• Triglycerides should be below 150 mg/dL and can be up to 200 mg/dL.

• Cholesterol levels should not be ignored.

• HDL and LDL levels are measured separately.

Venous Thrombosis (Blood Clots)

• Clots can form in arteries but are more common in veins due to lower pressure and blood flow.
• Factors contributing to clot formation include:
  • Blood stasis due to poor blood flow, lack of movement, heart failure, heart attack, and low blood pressure.
  • Vessel damage from injury, surgery, intravenous drugs, catheters, or immune response.
  • Hypercoagulability resulting from pregnancy, cancers, clotting disorders, dehydration, or oral contraceptives.
• Clots can form in superficial vessels or deep veins (DVT).
• Most superficial clots resolve spontaneously.
• Deep vein thrombosis (DVT) can be more critical.
• Symptoms include pain, redness, and swelling.

Treatment and Prevention

• Prevention of blood stasis through walking, compression stockings, exercise, or elevation of the legs.
• Anticoagulant therapy (warfarin, heparin).
• Thrombolytic therapy (streptokinase, TPA) to dissolve clots.
• Surgical removal of clots.

Other Diseases

Aneurysm

• Localized balloon-like swelling in an artery wall.
• Aortic aneurysms are common due to continuous high pressure on the vessel walls.
• Cerebral aneurysms can also occur.
• Causes include:
  • Atherosclerosis (plaque formation affecting the vessel walls).
  • High blood pressure, inflammation, and natural aging processes.

Raynaud's Phenomenon

• Common vascular disorder.
• Characterized by severe spasm of small blood vessels in the fingers and toes.
• More common in young women due to stress or cold exposure.
• Secondary causes include malignancy or vessel injury or prolonged cold exposure.

Thromboangiitis Obliterans (Buerger's Disease)

• Inflammatory disorder affecting arteries.
• More common in heavy smokers.
• Microscopic causes are unknown but involves inflammatory lesions in arteries that result in spasm, blockage, and clot formation.

Varicose Veins

• Veins with dilated walls due to chronic blood pooling in the legs.
• Chronic distension reduces the effectiveness of one-way valves preventing backward blood flow—resulting in valve incompetence.
• Varicose veins are swollen veins resulting from blood accumulation in the lower extremities.
• More frequent in individuals spending a long time standing or with reduced blood return from the lower limbs.

Chronic Venous Insufficiency

• Varicose veins and incompetent valves can lead to chronic venous insufficiency.
• Chronic reduced blood flow, edema, and poor tissue nutrition cause eventually tissue changes in the lower extremities.
• Skin atrophy, inflammation, ulcers, and tissue necrosis are possible manifestations.
• Infections or injuries to the lower extremities.

Hypertension

• Defined as elevated blood pressure above the normal range.
• Diagnosed when blood pressure readings consistently reach 140 mmHg systolic or above and 90 mmHg diastolic or above.
• Approximately 90% of all hypertension cases are primary (essential) hypertension, without a known cause.

Essential (Primary) Hypertension

• Genetic, environmental, and dietary factors increase essential hypertension risk.
• Family history of hypertension.
• Increasing Age.
• Ethnicity/Gender (higher incidence in older Black men).
• High sodium intake.
• Hyperinsulinemia.
• Excessive alcohol consumption.
• Obesity.
• Smoking.
• Low dietary intake of potassium, calcium, and magnesium.
• Chronic fluid volume increase, enhanced sympathetic activity, or abnormal renal sodium and water excretion.

Secondary hypertension

• Represents a small proportion of hypertension cases.
• A common cause is renal artery stenosis due to atherosclerosis. Reduced renal blood flow results in activation of the renin-angiotensin system, causing further vasoconstriction and sodium/water retention.
• Other causes include hyperaldosteronism (excessive aldosterone production) and pheochromocytoma (tumor of adrenal medulla).

Malignant Hypertension

• Sudden, significant increases in blood pressure (more than 120-130 mm Hg diastolic).
• Potentially damaging to the retina and kidneys, leading to cerebral edema and stroke.
• Requires immediate medical intervention using potent vasodilators (e.g., diazoxide or sodium nitroprusside).

Hypotension

• Abnormally low blood pressure.
• Orthostatic hypotension (postural hypotension) is a common form occurring upon standing.
• Standing initiates a series of reflex responses to prevent pooling of blood in lower extremities.
• Vasoconstriction and increased heart rate are reflexes.

Treatment

• Lifestyle modifications (for milder hypertension):
  • Weight loss
  • Exercise
  • Low-sodium diet
  • Smoking cessation
  • Reduced alcohol intake
• Medications:
  • Diuretics (thiazides, furosemide) lower blood pressure by reducing blood volume
  • Beta-blockers
  • Diuretics + Beta-blockers
  • ACE inhibitors (enalapril, captopril) Block Angiotensin II formation.
  • Calcium channel blockers (nifedipine, diltiazem) Relaxes vascular smooth muscles.
  • Direct vasodilators (hydralazine, diazoxide) Directly relax smooth muscles.
  • Central-acting agents (methyldopa) Reduce sympathetic output from the brain.