Place in the system of circulatory disorders and mechanisms
Regional (also known as peripheral or local-tissue) circulatory disorders are divided into two major groups: those occurring in medium-sized vessels and those developing directly in the microvasculature. Arterial hyperemia affects both levels, as both small/medium-sized arteries and arterioles dilate.
There are three main mechanisms for the implementation of this process:
- Neurogenic;
- Humoral;
- Neuromioparalytic.
In practice, these mechanisms often combine, mutually reinforcing each other.
Humoral mechanism of dilatation
This mechanism is always strictly local in nature. Its essence comes down to two factors:
- Excessive accumulation of vasodilators — biologically active substances that relax the smooth muscle of blood vessels. Key mediators include adenosine, nitric oxide (NO), kinins, and specific classes of prostaglandins (PG E and PG I₂).
- Excessive hypersensitization of the arteriole walls themselves to the action of the listed vasodilators. Even at normal concentrations of these substances, the vessels begin to dilate inadequately.
Classification: how to distinguish normal from pathological
According to their biological significance, arterial hyperemias are divided into two varieties: physiological and pathological.
Two strict criteria are used to differentiate them:
- Adequacy: whether the degree of hyperemia corresponds to the actual change in function and metabolic level in the tissues.
- Adaptive significance: whether this vascular reaction has an adaptive, beneficial meaning for the body.
Physiological arterial hyperemia
This form is absolutely adequate to the tissue's demands. It ensures an increased specific function of the organ and stimulates nonspecific processes: hypertrophy, hyperplasia, plastic, and reparative reactions. Due to the enhanced influx of arterial blood rich in immunoglobulins (Ig), lymphocytes, and phagocytes, local immunity mechanisms are sharply activated. Lymph formation and lymph outflow are also enhanced.
External and functional signs:
- Redness and temperature increase of the affected area;
- Increase in tissue volume or turgor.
Changes in microcirculation:
- The number and diameter of arterial vessels, arterioles, and capillaries increase;
- The number of functioning capillaries increases;
- Blood flow accelerates: the axial "cylinder" of blood flow narrows, while the plasma-flow zone broadens.
Physicians often use therapeutic hyperemia. It is induced artificially using compresses, mustard plasters, physiotherapeutic procedures, injections of vasodilator drugs, or even surgically (transection of sympathetic nerve trunks, ganglion excision for angina pectoris). This is necessary for ischemia, organ damage, trophic disorders, and reduced local immunity activity.
Pathological arterial hyperemia
A key sign of the pathological form is its inadequacy to the current level of function and plastic processes. Significantly more blood flows in than the tissue requires.
In pathogenesis, tissue damage comes to the forefront: vessel walls are overstretched, leading to microtears in the microvasculature.
Consequences:
- Micro- and macrohemorrhages into tissues;
- External and/or internal bleeding.
The main goal of therapy in this condition is to eliminate or prevent these life-threatening consequences.
Briefly: answers to topical questions
What are the causes and variants of the neurogenic mechanism of arterial hyperemia?
Neurogenic mechanisms of arterial hyperemia include three types:
- Neurotonic mechanism — predominance of parasympathetic nerve influences on the walls of arterial vessels compared to sympathetic ones.
- Neuroparalytic mechanism — reduction or absence of sympathetic nerve influences on the walls of arteries and arterioles; may be associated with transection or blockade of sympathetic nerves, or the action of ganglion blockers and sympatholytics.
- Neuromyoparalytic mechanism — depletion of catecholamines in the synaptic vesicles of sympathetic nerve fibers in the walls of arterioles, leading to a decrease in the basal tone of vascular smooth muscle cells (VSMCs).
Causal factors of arterial hyperemia cited in sources include psychogenic and emotional influences implemented via neurogenic and humoral mechanisms.
What is the essence of the neuromyoparalytic mechanism?
The essence of the neuromyoparalytic mechanism is the reduction or complete abolition of arterial vessel wall tone:
- myogenic tone;
- regulated tone, predominantly adrenergic.
This mechanism is associated with the depletion of catecholamines in the synaptic vesicles of sympathetic nerve fibers in the walls of arterioles. As a result, the basal tone of VSMCs decreases, vessels dilate, and the volume of flowing arterial blood increases.
How does arterial hyperemia visually differ from venous hyperemia?
| Sign | Arterial Hyperemia | Venous Hyperemia |
|---|---|---|
| Skin/tissue color | Redness, bright red (scarlet) coloration | Bluishness, cyanosis |
| Temperature | Increased local temperature | Decreased local temperature |
| Volume | Increased volume or turgor of the area | Increased volume, pronounced congestive edema |
The criteria for distinguishing physiological hyperemia from pathological can be easily remembered by the "Two As" rule: Adequacy (matching metabolism) and Adaptability (having adaptive significance for the organism).
Class and exam questions
In which vessels does arterial hyperemia primarily develop?
The process begins with the dilation of small and medium-sized arteries, as well as arterioles of the microvasculature.
What is the key sign of the pathological form specifically?
Its absolute inadequacy. The increase in blood inflow completely fails to meet the current needs of the tissue for plastic processes and functioning.
What hemodynamic shifts occur in the microvasculature?
Blood flow significantly accelerates, the axial "cylinder" of blood flow narrows, and the plasma zone widens.
Why do physicians induce hyperemia artificially?
Therapeutic hyperemia is necessary to improve trophic supply, stimulate local immunity, and accelerate repair in ischemia or tissue damage.
What else to study on this topic
- Neurogenic mechanism of arterial hyperemia development
- Neuromyoparalytic mechanism of vasodilation
- Surgical methods for inducing therapeutic hyperemia (sympathectomy)
- Pathogenesis of microvascular ruptures in pathological hyperemia
- Effect of hyperemia on lymph formation and lymphatic drainage
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