pain pathophysiology, Lecture notes of Animal Anatomy and Physiology

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Pain

Definition

The sensation of pain is defined as the

physical adjunct of an imperative protective

reflex.

pain is an, unpleasant sensory and emotional

experience associated with actual or potential

tissue damage - The International Association

for the Study of Pain (IASP)

Fast pain & Slow pain

• Fast pain: is also described as sharp pain, pricking pain, Acute pain, electric pain. it is elicited by mechanical and thermal type of stimuli.
• Slow pain is also called as, slow burning pain, aching pain, throbbing pain, nauseous pain, chronic pain. slow pain can be elicited by mechanical, thermal and chemical stimuli.

Types of Pain

Fast pain Slow pain

Felt within about 0.1 second after a painful stimulus.

Begins after 1 second or more and then increases slowly over many sec. or min.

“Bright," sharp, localized

sensation

Dull, intense, diffuse, and unpleasant feeling

sharp pain, pricking pain, acute

pain, and electric pain

slow burning pain, aching pain, throbbing pain, nauseous pain, and chronic pain

Felt mainly in skin. Not felt in most deeper tissues of the body

It can occur both in the skin and in almost any deep tissue or organ

Stimuli

• Physical
  • pressure etc
• Electrical
• Thermal
  • cold, hot
• Chemical
  • H+, lactic acid, K+, histamine, bradykinin, serotonin, leucotrines, acetylcholine, proteolytic enzymes, capsiacin
  • Prostaglandins (PGE2)
    • Cannot directly stimulate nociceptors
    • Increase the sensitivity of nociceptors for other stimuli (decrease the threshold) 7

Receptors

• Nociceptors are very slowly adapting type
• Different types of nociceptors
  • Some respond to one stimulus
  • Some respond to many stimuli (polymodal)
  • Some may not respond to the standard stimuli (silent nociceptors)
    • they respond only when inflammatory substances are present
• Capsaicin receptor (TRPV1 receptor)
  • Respond to capsaicin, heat, low pH
  • Stimulation leads to painful, burning sensation

TYPES OF PAIN

source of origin -- three types of pain.

• Superficial pain : pain arising from skin and

mucous membrane.

• Deep (somatic) pain : pain originating from

somatic structures deep to the skin are known

as deep pain.

• Visceral pain : pain arising from different

internal organs or viscera

VARIETIES OF PAIN

• ACUTE PAIN

• CHRONIC PAIN

• CUTANEOUS PAIN

• DEEP SOMATIC PAIN

• VISCERAL PAIN

• REFERRED PAIN

• NEUROPATHIC PAIN

• PHANTOM PAIN

CAUSES OF VISCERAL PAIN

• Ischaemia: The substances released during ischaemic reactions like bradykinin and proteolytic enzymes stimulate the pain receptors of viscera.
• Chemical stimuli: The chemical substances like acidic gastric juice leaks from ruptured ulcers into peritoneal cavity and produce pain.
• Spasm of hollow organs: spastic contraction of muscles in gastrointestinal tract and other hollow organs of viscera cause pain by stimulating the free nerve endings.
• Overdistension of hollow organs also cause pain.

PAINS OF SPECIAL INTEREST

• Coronary occlusion: In addition to P factor, there is release of 5HT and plasma pain producing polypeptide.
• Nerve pain : partial compression of nerve or a nerve root leads to irritability of the nerve or the nerves concerned and gives rise to the formation of areas of Hyperalgesia and pareaesthesia
• Ischaemic Muscular pain : Due to release of P factor during active work, on accumulation cause pain. The P factor may be potassium or kinin. Repeated muscular contraction compress blood vessel.

REFERED PAIN

Definition:

The pain sensation produced in some part of the

body is felt in other structures away from the

place of development. This is called refered

pain.

The deep pain and some visceral pain are

referred to other areas. But superficial pain is

not referred.

Referred Pain

Pain in organs is poorly localized

May be displaced if

Multiple 1° sensory neurons converge on single ascending tract

Mechanism of Referred Pain

When the visceral pain fibers are stimulated

pain signals from the viscera are conducted

through some of the neurons that conduct

pain signals from the skin and the person has

the feeling that,

the sensation

originate in the

skin itself.