Visceral Pain

As a rule, pain receptors are the only receptors in viscera whose stimulation produces sensations. Pain receptors in these organs respond differently to stimulation than those associated with surface tissues. For example, localized damage to intestinal tissue during surgical procedures may not elicit any pain sensations, even in a conscious person. However, when visceral tissues are subjected to more widespread stimulation, as when intestinal tissues are stretched or when the smooth muscles in the intestinal walls undergo spasms, a strong pain sensation may follow. Once again, the resulting pain results from stimulation of mechanical-sensitive receptors and to decreased blood flow accompanied by a lower tissue oxygen concentration and accumulation of pain-stimulating chemicals.

Visceral pain may feel as if it is coming from some part of the body other than the part being stimulated—a phenomenon called referred pain (re-furd' pan). For example, pain originating in the heart may be referred to the left shoulder or the medial surface of the left upper limb. Pain from the lower esophagus, stomach, or small

Figure

(a) Light micrograph of a Meissner's corpuscle from the skin of the palm (250x). (b) Light micrograph of a Pacinian corpuscle (25x enlarged to 100x).

Liver and gallbladder

Small intestine

Appendix

Liver and gallbladder

Small intestine

Appendix

Ureter Referred Pain

Heart

Ureter

Figure 12.3

Surface regions to which visceral pain may be referred.

Lung and diaphragm

Heart

Stomach

Pancreas

Ovary (female)

Colon

Kidney

Urinary bladder

Ureter

Figure 12.3

Surface regions to which visceral pain may be referred.

Lung and diaphragm

Urinary bladder

Liver and gallbladder

Visceral Pain Pathway

—Sensory pathway to brain

Paravertebral

Figure 12.4

Pain originating in the heart may feel as if it is coming from the skin because sensory impulses from those two regions follow common nerve pathways to the brain.

Liver and gallbladder

—Sensory pathway to brain

Spinal cord

Paravertebral

Figure 12.4

Pain originating in the heart may feel as if it is coming from the skin because sensory impulses from those two regions follow common nerve pathways to the brain.

intestine may seem to be coming from the upper central (epigastric) region of the abdomen. Pain from the urogenital tract may be referred to the lower central (hypogas-tric) region of the abdomen or to the sides between the ribs and the hip (fig. 12.3).

Referred pain may derive from common nerve pathways that sensory impulses coming both from skin areas and from internal organs use. Pain impulses from the heart seem to be conducted over the same nerve pathways as those from the skin of the left shoulder and the inside of the left arm, as shown in figure 12.4. Consequently, the cerebral cortex may incorrectly interpret the source of the impulses as the shoulder and the medial surface of the left upper limb, rather than the heart.

Pain originating in the parietal layers of thoracic and abdominal membranes—parietal pleura, parietal pericardium, or parietal peritoneum—is usually not referred; instead, such pain is felt directly over the area being stimulated.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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