Applied Pathophysiology Chapter 12

Applied Pathophysiology: A Conceptual Approach to the Mechanisms of Disease

• This lecture series covers applied pathophysiology, specifically focusing on the mechanisms of disease.
• The course material is adapted from 2022 Wolters Kluwer Health, Lippincott Williams & Wilkins.
• Dr. Romeo Batacan Jr. is the instructor for the MPAT12001 Medical Pathophysiology Lecture Series.
• Chapter 12 focuses on altered somatic and special sensory function, module 1 emphasizing pain.

Why Do We Have Pain?

• Pain acts as a protective mechanism, warning of actual or impending tissue damage.
• Pain motivates individuals to seek medical attention for problems.
• Pain encourages behaviors aimed at promoting healing.
• Pain is defined as an unpleasant sensory and emotional experience associated with, or described in terms of, actual or potential tissue damage (International Association for the Study of Pain).

Mechanism of Acute Pain

• Tissue injury leads to the release of inflammatory mediators.
• Inflammatory mediators stimulate nociceptors, sensory nerve endings specialized in pain detection.
• Pain impulses travel through first-order neurons to the dorsal horn of the spinal cord.
• These impulses then synapse with second-order neurons that cross to the opposite side of the spinal cord, ascending through the spinothalamic tract.
• The signals from the spinothalamic tract transmit to the reticular activating system (RAS) and thalamus for further processing.
• Pain localization and interpretation occur in the somatosensory cortex.

Conduction of Pain Sensation (Nociception)

• Nociception involves stimulation of free nerve endings, leading to autonomic and motor reflexes interpreted as pain.
• The processes involved are transduction, transmission, modulation, and perception.

Transduction

• Nociceptive stimuli are transformed into nerve impulses (depolarization).
• This process involves the release of chemicals (e.g., substance P, histamine, prostaglandins).
• These chemicals contribute to pain transduction, where electrical signals are converted into a pain sensation.

Transmission of Nerve Impulses

• Nerve impulses travel along type A (delta) and type C fibers.
• Type A fibers transmit sensations such as sharp, stinging, or pinprick, induced by mechanical or thermal stimuli.
• Type C fibers transmit sensations like dull ache or burning, often associated with generalized or prolonged stimuli.

Modulation of Pain

• During pain impulse transmission, pain modulation occurs due to the release of substances from inhibitory processes.
• Serotonin, norepinephrine, and endorphins are examples of such substances, that slow down the release of nociceptive neurotransmitters.

Perception of the Pain Response

• Pain perception combines sensory (somatosensory cortex), emotional (limbic system) and subjective components.
• Factors influencing pain perception include pain threshold, perceptual dominance, and pain tolerance.

Pain Theories

•  Pattern theory: Pain is a collective response from multiple shared pathways involving various senses. Individual experiences vary greatly as the pathways do not explain all pain types.
• Specificity theory: Pain originates from special pain-specific receptors and pathways, where the intensity depends on the degree of tissue damage.
• Gate control theory: A nonpainful stimulus can block the transmission of a noxious stimulus. Large fiber stimulation from stimuli like massage, closes the gate preventing pain impulses from reaching brain.
• Neuromatrix theory: Pain perception is complex, resulting from impulse generation in a widely distributed neuronal network in the brain, influencing all sensory, cognitive, and emotional responses. Pain can be present without stimuli activation.

Pain Classification

• Nociceptive: Pain from outside the nervous system, activating specific receptors.
• Non-nociceptive: Pain originating from the nervous system, not activating specific pain receptors, and lacking typical transmission/response.

Pain Classification: Temporal

• Acute pain: Self-limiting, lasting less than three months, resulting from tissue injury, with rapid onset, responsiveness to treatment, and triggering autonomic responses.
• Chronic pain: Persistent, exceeding three months, resisting treatment, often associated with conditions like anorexia, insomnia, and depression.

Pain Classification: Types

• Somatic pain: Pain in skin, muscles, bones, joints, from activated nociceptors; can range from sharp, localized to diffuse, aching.
• Visceral pain: Pain originating from visceral organs; vague, aching, burning, often accompanied by nausea, vomiting, hypotension.
• Referred pain: Pain perceived in a location distinct from the source of stimulation, where visceral and somatic pain travel through the same nerves.

Nonpharmacologic Pain Control Techniques

• Cognitive behavioral interventions: Relaxation, distraction, cognitive reappraisal, imagery, biofeedback aimed at reducing muscle tension or focusing on positive thoughts.
• Physical agents: Heat boosts blood flow, reducing ischemia and releasing endogenous opioids. Cold constricts blood flow, decreasing swelling and nerve stimulation.
• Other methods: Transcutaneous electrical nerve stimulation (TENS), acupuncture, and neurostimulation. TENS sends electrical impulses to block nerve pathways. Acupuncture, involving needle insertion at specific points, can stimulate endorphin secretion. Neuromodulation delivers electric impulses to either the spinal cord or peripheral nerves to block pain sensation.

Pharmacologic Pain Control

• Non-narcotic analgesics (e.g., aspirin, NSAIDs): Block nerve impulses, inhibiting cyclooxygenase, reducing prostaglandin production, lowering sensitivity to pain mediators.
• Opioid analgesics (e.g., morphine, codeine): Modulate pain via mu, delta, and kappa receptors on the spinal cord stimulating endogenous opioids, enkephalins, and endorphins.
• Adjuvant analgesics: Block neurotransmitter reuptake and improve pain tolerance, particularly useful for chronic conditions.
• Pharmacologic treatment ladder: A tiered approach to pain management, starting with non-opioid analgesics and progressing to more potent opioid analgesics with adjuvants when necessary; should escalate at designated intervals when necessary.
• Surgical intervention: Includes techniques like spinothalamic tract or anterolateral cordotomy, for severe chronic pain that is not controlled by other means.

Pain Measurement

• Various scales are used to quantify pain level and quality (e.g., visual analog scale, Wong-Baker FACES pain rating scale, or a pain drawing scale).

This quiz explores the concepts of altered somatic and special sensory function, with a focus on pain mechanisms as discussed in Chapter 12 of the Applied Pathophysiology course. Understand how pain serves as a protective mechanism and encourages healing behaviors. Test your knowledge on the physiological and emotional aspects of pain.