tailieunhanh - Chapter 012. Pain: Pathophysiology and Management (Part 2)

Sensitization When intense, repeated, or prolonged stimuli are applied to damaged or inflamed tissues, the threshold for activating primary afferent nociceptors is lowered and the frequency of firing is higher for all stimulus intensities. Inflammatory mediators such as bradykinin, nerve growth factor, some prostaglandins, and leukotrienes contribute to this process, which is called sensitization. In sensitized tissues, normally innocuous stimuli can produce pain. Sensitization is a clinically important process that contributes to tenderness, soreness, and hyperalgesia. A striking example of sensitization is sunburned skin, in which severe pain can be produced by a gentle slap on the back or. | Chapter 012. Pain Pathophysiology and Management Part 2 Sensitization When intense repeated or prolonged stimuli are applied to damaged or inflamed tissues the threshold for activating primary afferent nociceptors is lowered and the frequency of firing is higher for all stimulus intensities. Inflammatory mediators such as bradykinin nerve growth factor some prostaglandins and leukotrienes contribute to this process which is called sensitization. In sensitized tissues normally innocuous stimuli can produce pain. Sensitization is a clinically important process that contributes to tenderness soreness and hyperalgesia. A striking example of sensitization is sunburned skin in which severe pain can be produced by a gentle slap on the back or a warm shower. Sensitization is of particular importance for pain and tenderness in deep tissues. Viscera are normally relatively insensitive to noxious mechanical and thermal stimuli although hollow viscera do generate significant discomfort when distended. In contrast when affected by a disease process with an inflammatory component deep structures such as joints or hollow viscera characteristically become exquisitely sensitive to mechanical large proportion of AS and C afferents innervating viscera are completely insensitive in normal noninjured noninflamed tissue. That is they cannot be activated by known mechanical or thermal stimuli and are not spontaneously active. However in the presence of inflammatory mediators these afferents become sensitive to mechanical stimuli. Such afferents have been termed silent nociceptors and their characteristic properties may explain how under pathologic conditions the relatively insensitive deep structures can become the source of severe and debilitating pain and tenderness. Low pH prostaglandins leukotrienes and other inflammatory mediators such as bradykinin play a significant role in sensitization. Nociceptor-Induced Inflammation Primary afferent nociceptors also have a .