113. Endothelial dysfunction, arterial and venous hyperemia - etiology, pathogenesis, clinical manifestations.

Endothelial dysfunction, arterial and venous hyperemia – etiology, pathogenesis, and clinical manifestations.

Endothelial dysfunction

Endothelial dysfunction is an early, reversible alteration in endothelial cell function, characterized by reduced vasodilation, pro-inflammatory, and pro-thrombotic properties.

Etiology

Atherosclerosis risk factors:

• Hypertension.
• Hyperlipidemia.
• Diabetes mellitus.
• Smoking.
• Oxidative stress (ROS).
• Infections or chronic inflammation.
• Hyperhomocysteinemia.
• Aging.

Pathogenesis

1. Reduced nitric oxide (NO) bioavailability → impaired vasodilation.
2. Increased expression of adhesion molecules → leukocyte adhesion → chronic inflammation.
3. Pro-thrombotic state → increased endothelin (vasoconstrictor), tissue factor expression → thrombosis risk.
4. Promotion of smooth muscle proliferation and migration → vascular remodeling and plaque formation.

Clinical manifestations

Initially asymptomatic.

Underlies development of:

• Atherosclerosis.
• Hypertension.
• Thrombosis.
• Microvascular complications in diabetes.

Arterial hyperemia

Active (arterial) hyperemia is increased blood flow to tissues due to arteriolar dilation, usually in response to increased metabolic demand or physiological stimuli

Etiology

Physiological:

• Exercise (skeletal muscle).
• Digestive activity (splanchnic circulation after meals).
• Local heating.

Pathological:

• Inflammation (release of histamine, prostaglandins).

🟦 1 Local metabolic and chemical signals cause arteriolar dilation

When tissues are more active (like during exercise or digestion), they produce more metabolic byproducts:

• Lactic acid, CO₂, adenosine → all signal the need for more blood flow.

At the same time, local vasodilator mediators like nitric oxide (NO) and prostaglandins are released.

These signals work together to relax smooth muscle in arteriolar walls, causing them to dilate and reduce resistance to blood flow.

2 Increased blood inflow brings more oxygenated blood

Because of arteriolar dilation, there is a greater inflow of fresh, oxygen-rich blood into the area.

This leads to:

• Redness of the tissue (due to higher concentration of oxygenated hemoglobin ).
• Increased warmth (due to higher blood volume and metabolic heat).
• Improved supply of nutrients and removal of metabolic waste products.

Clinical manifestations

• Redness (rubor) and warmth ( calor ) in inflamed areas.
• Throbbing sensation (due to pulsatile increased flow).
• Enhanced local function (e.g., active muscles).