Patho

CHAPTER 4: PAIN

1. What is pain?

Pain is an unpleasant sensory and emotional experience. It often warns you that tissue is being injured or threatened.

Its protective purpose is to make you respond: pull away from a hot surface, stop putting weight on an injury, or seek help.

Pain is subjective, meaning the person experiencing it tells you what it feels like and how severe it is.

Two people with similar injuries can experience different amounts of pain. You cannot determine someone’s pain score just by looking at the injury.

2. What causes pain?

Your slides list several triggers:

Ischemia means inadequate blood supply. Necrosis means tissue death. Ischemia can lead to necrosis if it is severe or prolonged.

3. Nociceptors: where the pain signal begins

A nociceptor is a sensory nerve ending that detects potentially harmful stimuli.

Think of it as an injury detector.

Nociceptors respond to harmful:

• Heat or cold.

• Pressure, stretching, or piercing.

• Chemicals released during tissue injury and inflammation.

They convert that stimulus into an electrical nerve signal.

Your slides also use the term free nerve ending. This means the end of the sensory nerve is not enclosed in a specialized capsule. Free nerve endings that detect harmful stimuli function as nociceptors.

4. How pain travels to the brain

Know this sequence:

Tissue injury → nociceptor → sensory nerve fiber → spinal cord → ascending pathway → brain.

Here is what each step means:

1. Tissue injury: You touch a hot pan.

2. Nociceptor activation: Nerve endings detect harmful heat.

3. Afferent fiber: A sensory nerve carries the signal toward the spinal cord.

4. Dorsal horn: The signal enters the back portion of the spinal cord and communicates with another neuron.

5. Crossing: The next neuron crosses to the opposite side of the spinal cord.

6. Spinothalamic tract: The signal travels upward toward the brain.

7. Thalamus and other brain regions: The signal is relayed and processed so you experience and locate the pain.

Afferent = arrives at the central nervous system.
Efferent = exits the central nervous system, such as a motor command going to a muscle.

The spinothalamic tract is an ascending pathway carrying pain and temperature information.

5. A-delta fibers versus C fibers

This is one of the most important comparisons.

Myelin is insulation around a nerve that helps signals travel faster.

Imagine stepping on a tack:

• The immediate sharp “OUCH!” comes mainly through A-delta fibers.

• The lingering ache or burning comes mainly through C fibers.

Both types can respond to the same injury.

Your slides associate:

• Neospinothalamic pathways: fast pain.

• Paleospinothalamic pathways: slower, duller pain.

Remember that slow pain and chronic pain are different concepts. C fibers also carry the lingering pain from a new injury.

6. What the brain does with pain

Several brain regions contribute to the experience.

The somatosensory cortex has an organized map of the body, which helps you recognize whether pain is coming from your hand, foot, or another area.

Pain also has an emotional component. Previous experiences, fear, and attention can influence how distressing pain feels.

7. Reticular activating system, or RAS

The RAS is a network in the brainstem involved in:

• Wakefulness.

• Attention.

• Awareness.

• Filtering sensory information.

A strong pain signal recruits this system, making pain difficult to ignore and sometimes making sleep difficult.

8. Gate control theory

Gate control theory explains how the spinal cord can reduce or increase the transmission of pain signals.

The “gate” is a way of describing nerve activity, rather than a physical door.

Nonpainful sensory input, such as rubbing or electrical stimulation, can activate inhibitory neurons in the dorsal horn. These neurons reduce the pain messages traveling upward.

Example: You bump your elbow and instinctively rub it. Touch signals can help inhibit pain transmission.

Your slides connect this concept to:

• Rubbing.

• TENS.

• Ice and other sensory input.

TENS means transcutaneous electrical nerve stimulation. It delivers electrical stimulation through the skin to help modify pain signaling.

Reducing pain transmission does not necessarily mean the original injury has healed.

9. Substance P and the body’s natural opioids

Substance P promotes pain signaling.

Enkephalins inhibit pain signaling, including reducing Substance P release in the dorsal horn.

Endorphins, enkephalins, and dynorphins are endogenous opioids:

• Endogenous: made inside the body.

• Exogenous: comes from outside the body.

Opioid medications bind to opioid receptors and reduce pain signaling. At these receptors, activity can reduce neurotransmitter release or make the next neuron less likely to transmit the message.

10. Somatic versus visceral pain

Examples:

• A cut on your finger: somatic pain.

• Pain originating in the stomach or intestines: visceral pain.

Your slides explain that many visceral pain fibers travel alongside sympathetic nerves.

11. Referred pain

Referred pain means you feel pain somewhere other than its actual source.

Example: Heart ischemia may cause pain felt in the shoulder or arm.

Why?

Signals from an organ and signals from a body surface can converge on the same spinal cord neurons. The brain may interpret the incoming information as coming from the surface location.

The source is the heart; the perceived location may be the arm.

One wording clarification: the slides sometimes place “heart attack” beside “ischemia.” Ischemia is inadequate blood flow; infarction is tissue death caused by inadequate blood flow.

12. Phantom pain

Phantom pain is pain perceived in a body part that has been amputated.

The person may feel burning, aching, or other painful sensations where the limb used to be. Nonpainful phantom sensations, such as tingling or itching, can also occur.

The experience is real because pain depends on nervous system processing. The brain and nerve pathways can continue producing sensations associated with the missing limb.

Your slides note that it can be difficult to treat. Its duration varies.

13. Acute versus chronic pain

Acute pain can activate the sympathetic fight-or-flight response, producing:

• Increased heart rate and blood pressure.

• Faster breathing.

• Sweating and pallor.

• Muscle tension.

• Anxiety.

• Sometimes nausea or vomiting.

A person can still have significant pain without these visible signs.

Chronic pain may require pacing activities, meaning balancing activity with rest to preserve function.

14. Pain threshold versus pain tolerance

• Pain threshold: The point at which a stimulus begins to feel painful.

• Pain tolerance: How much pain a person can cope with or endure.

Example:

• When pressure first becomes painful: threshold.

• How much longer the person can tolerate it: tolerance.

Fatigue, stress, anxiety, and previous experiences can affect coping.

Your slide says thresholds usually do not vary among individuals. Treat that as a simplified course statement; the essential distinction to learn is when pain begins versus how much someone can tolerate.

15. Other pain categories

Neuropathic pain may feel burning, shooting, or electrical.

Your slides separate central and peripheral neuropathic pain for teaching. More broadly, neuropathic pain can arise from injury or disease affecting the somatosensory nervous system centrally or peripherally.

16. Headaches

A headache is a symptom with different possible mechanisms.

Your slides include:

• Sinus congestion.

• Eye strain.

• Muscle tension or spasm.

• Emotional stress.

• Temporomandibular joint problems.

• Migraine.

• Increased pressure inside the skull.

Brain tissue itself lacks nociceptors. Pain-sensitive surrounding structures, including the meninges and blood vessels, can produce headache pain.

For migraine, the slides mention altered blood flow and metabolism. Understand this as a simplified description of a more complex neurologic process.

17. Assessing pain

Ask about more than the number.

Observe guarding, sweating, pallor, and vital signs, but combine those observations with the patient’s report.

Important correction to the slide’s abdominal pain case: You cannot assign a pain score of 7–8 based only on appearance or vital signs. Ask the patient for their rating.

18. Pain management

The chapter’s approach is to identify and address the cause while also reducing pain and improving function.

Methods include:

• Analgesic medications.

• Nonmedication approaches such as relaxation, positioning, distraction, and appropriate sensory stimulation.

• Other interventions when pain remains severe or difficult to control.

Medications may be given orally, by injection, or through the skin, depending on the medication and situation.

Sedatives and antianxiety medications may be adjuncts, but sedation itself does not establish that pain has been relieved.

PCA: patient-controlled analgesia

A programmed pump lets the patient receive a prescribed dose when they press a button. Settings limit dosing, including a lockout interval.

The patient controls the button, and clinicians monitor pain relief and adverse effects.

Intractable pain

Pain that remains very difficult to control despite treatment.

Your slides list specialized interventions:

• Rhizotomy: interrupting selected nerve roots.

• Cordotomy: interrupting selected pain pathways in the spinal cord.

• Injections or nerve blocks: reducing signaling in a targeted area.

19. Anesthesia

CHAPTER 5: IMMUNITY, INFLAMMATION, AND HEALING

The beginning of this chapter reviews immunity because immune cells carry out much of the inflammatory response.

20. The three lines of defense

The first and second lines belong to innate immunity.

Innate immunity

• Responds rapidly.

• Recognizes common patterns of injury and microbes.

• Includes barriers and internal defenses.

Adaptive immunity

• Targets specific antigens.

• Takes longer to develop during a first encounter.

• Produces memory cells for a faster response later.

An antigen is a structure the adaptive immune system specifically recognizes.

21. First-line defenses

Your body helps prevent infection through:

• Skin: A physical barrier with keratin, shedding cells, oils, and an environment that limits many microbes.

• Normal microbiota: Compete with potentially harmful organisms.

• Mucus: Traps microbes and particles.

• Respiratory cilia: Move mucus out.

• Tears and saliva: Wash surfaces and contain antimicrobial substances such as lysozyme.

• Stomach acid: Destroys many swallowed organisms.

22. Immune cells: who does what?

A useful way to remember:

Neutrophils respond early. Macrophages clean and coordinate. B cells supply antibodies. Helper T cells direct. Cytotoxic T cells kill.

23. Phagocytosis

Phagocytosis means engulfing and digesting material.

The steps are:

1. Recognize and attach to the target.

2. Surround and engulf it.

3. Enclose it in a phagosome.

4. Fuse that compartment with a lysosome containing digestive substances.

5. Break down the material and remove the remnants.

Neutrophils and macrophages are major phagocytes.

24. Complement

Complement is a group of blood proteins that supports immune defense.

Know three functions:

Opsonization = tagging for easier eating.
MAC = membrane attack complex.

25. B cells and antibodies

Activated B cells can produce:

• Plasma cells: Secrete antibodies.

• Memory B cells: Help generate a faster response to the same antigen later.

Antibodies are also called immunoglobulins.

An antibody is a Y-shaped protein with:

• Two heavy chains.

• Two light chains.

• Variable regions: Recognize a particular antigen.

• Constant regions: Determine class and help recruit other immune functions.

• An Fc region: Interacts with certain immune cells and complement.

Think: the tips recognize the target; the stem helps recruit assistance.

26. The five antibody classes

Memory cues:

• M = made first.

• A = guards mucosal areas.

• E = allergy association.

• D = displayed on B cells.

Long-term immune memory depends on memory cells and long-lived antibody production; an antibody molecule itself is not a memory cell.

27. How antibodies help

• Neutralization: Block a toxin or microbe from attaching to its target.

• Opsonization: Coat a target for phagocytes.

• Complement activation: Trigger complement functions.

• Agglutination: Clump targets together for easier clearance.

ADCC: antibody-dependent cell-mediated cytotoxicity

1. Antibodies bind an infected or abnormal cell.

2. An NK cell recognizes the antibodies’ Fc regions.

3. The NK cell releases substances that trigger target-cell death.

Your slides identify the NK cell receptor CD16 in this process.

This connects adaptive antibodies with an innate immune cell.

28. Helper T cells versus cytotoxic T cells

Helper T cells: CD4

They release cytokines that help activate and coordinate B cells, macrophages, and other immune cells.

Cytotoxic T cells: CD8

They recognize specific abnormal peptides displayed on MHC class I molecules.

MHC I molecules are found on nearly all nucleated body cells. Think of them as displaying samples of what is happening inside the cell.

Cytotoxic T cells release:

• Perforin: Helps create access for killing molecules.

• Granzymes: Enter the target cell and activate enzymes called caspases.

• Caspases: Carry out apoptosis, or programmed cell death.

For your slides, remember:

Perforin makes pores; granzymes trigger apoptosis.

NK cells can also use perforin and granzymes. The key distinction is that NK cells provide rapid innate defense, while cytotoxic T cells recognize specific antigen–MHC I combinations.

29. Inflammation versus infection

• Inflammation: The body’s protective response to injury or harmful stimuli.

• Infection: Invasion and multiplication of disease-causing microorganisms.

Inflammation can occur without infection.

Examples:

• Sprained ankle: inflammation can occur without microbes.

• Bacterial wound infection: infection triggers inflammation.

Other inflammatory triggers include burns, chemicals, ischemia, foreign material, allergic responses, and autoimmune reactions.

30. The five cardinal signs of inflammation

The two vascular changes to distinguish are:

Vasodilation = wider blood vessels.
Increased permeability = leakier vessel walls.

Wider vessels mainly explain redness and warmth.

Leakier vessels mainly explain edema.

31. The sequence of acute inflammation

1. Tissue becomes injured.

2. Local cells release inflammatory mediators.

3. Blood vessels dilate.

4. Vascular permeability increases.

5. Fluid and proteins move into tissue.

6. White blood cells leave the bloodstream.

7. They move toward the injury and remove microbes and debris.

8. The response settles and repair proceeds, or the stimulus persists and inflammation continues.

Neutrophils commonly predominate early. Monocytes/macrophages become important afterward.

These events overlap rather than occurring in completely separate stages.

32. How white blood cells reach an injury

Your slides associate:

• Selectins: Rolling.

• Integrins and cell adhesion molecules: Firm attachment.

Chemotaxis is directed movement toward chemical signals.

33. Why swelling occurs

Normally, fluid movement depends partly on:

• Hydrostatic pressure: Pushes fluid out of vessels.

• Plasma oncotic pressure: Blood proteins exert an inward pull on water.

• Lymphatic drainage: Returns excess tissue fluid and proteins to circulation.

During inflammation, vessel walls allow more protein and fluid to escape.

Protein in the tissue helps retain fluid there, contributing to edema.

For your exam, understand the push–pull concept shown in the slides and the central point: increased vascular permeability produces protein-rich tissue fluid.

34. Inflammatory chemical messengers

A chemokine is a type of cytokine that guides cell movement.

Important cytokines:

• IL-1: Promotes inflammation and fever.

• TNF-alpha: Promotes inflammation and activates vascular and immune responses.

• IL-6: Especially associated with stimulating the liver’s acute-phase response.

IL-6 → liver → acute-phase proteins is a key connection.

35. Exudates

An exudate is protein-rich fluid that escapes from vessels during inflammation. It may contain inflammatory cells and debris.

An abscess is a collection rather than simply a fluid description.

Appearance provides clues, but it does not establish the exact cause by itself.

36. Local versus systemic effects

Local means at the affected site: redness, warmth, swelling, pain, and reduced function.

Systemic means effects throughout the body:

• Fever.

• Fatigue.

• Malaise, meaning a general feeling of illness.

• Reduced appetite.

• Headache.

• Changes in blood tests.

37. Why fever occurs

Inflammatory signals promote production of prostaglandin E₂, which raises the hypothalamus’s temperature set point.

The body then conserves and generates heat to reach that higher target.

Sequence:

Inflammatory signals → PGE₂ → higher hypothalamic set point → fever.

The hypothalamus acts as the body’s temperature regulator.

38. What happens in the liver and bone marrow

Liver: Cytokines, especially IL-6, increase production of acute-phase proteins, including:

• C-reactive protein, or CRP.

• Fibrinogen.

• Serum amyloid A.

Bone marrow: Inflammatory signaling can increase white blood cell production and release.

An increased white blood cell count is leukocytosis.

An increased neutrophil count is neutrophilia.

These findings may accompany infection, tissue injury, and other inflammatory or stress responses.

39. Inflammatory laboratory tests

Why can ESR rise?

Inflammation increases proteins such as fibrinogen. These promote red blood cell aggregation, so cells settle faster.

An elevated inflammatory marker tells you inflammation may be present; it does not prove a specific infection or cause.

40. Acute versus chronic inflammation

Fibrosis means excess fibrous connective tissue, or scarring.

Chronic inflammation continues when the trigger remains, repeatedly returns, or the immune response stays active.

It can produce a cycle of injury, inflammation, and attempted repair.

41. Granulomas

A granuloma is an organized collection of macrophages that can form around a persistent inflammatory trigger.

Important cells:

• Epithelioid macrophages: Activated macrophages with an appearance resembling epithelial cells.

• Multinucleated giant cells: Form when multiple macrophages fuse.

Granuloma and granulation tissue are different:

• Granuloma: Organized inflammatory cell collection.

• Granulation tissue: New repair tissue that fills a healing wound.

42. Complications of persistent inflammation

Your slides list:

• Secondary infection.

• Ulceration.

• Tissue destruction.

• Perforation.

• Excessive fibrosis and impaired function.

An ulcer is an area where surface tissue has broken down.

A perforation is a hole through a structure’s wall, such as the wall of an organ.

43. Medications that affect inflammation

Glucocorticoids reduce vascular permeability and inflammatory signaling, but can also cause:

• Increased infection risk.

• Delayed healing.

• Hyperglycemia.

• Fluid retention.

The connection is important: suppressing the inflammatory response can improve symptoms while also interfering with defense and repair.

44. RICE

Your chapter presents supportive injury care as:

• Rest/protect: Limit further injury.

• Ice: Can help short-term pain.

• Compression: Can help limit swelling.

• Elevation: Can reduce dependent edema.

The slides emphasize that the type and severity of injury determine the overall treatment.

45. Three healing outcomes

Regeneration restores tissue. Replacement forms scar.

Scar provides structural support but may not perform the original tissue’s specialized function.

46. What repair tissue does

Important repair concepts in the chapter include:

• Fibroblasts: Produce collagen and extracellular material.

• Granulation tissue: New connective tissue with small blood vessels that fills a defect.

• Epithelialization: Surface epithelial cells cover the wound.

• Wound contraction: The wound becomes smaller.

• Remodeling: The repair tissue changes and strengthens over time.

47. Primary versus secondary intention

Secondary intention usually takes longer because the body must fill a larger gap before covering it.

48. Scar complications

Example: A scar across a joint can tighten and limit the joint’s movement.

BURNS

49. Causes and severity

Burns can result from:

• Heat.

• Chemicals.

• Electricity.

• Radiation or light.

• Friction.

Severity depends on depth, surface area, location, and patient factors.

50. Burn depth

Your slides connect these to first-, second-, and third-degree terminology.

A deeper burn may have less sensation in its center because nerve endings have been destroyed. Reduced pain does not establish that the injury is mild.

51. Why major burns cause swelling and low blood volume

This is the major pathophysiology connection:

1. Burns damage tissue and capillaries.

2. Capillary permeability increases.

3. Fluid and proteins leave the bloodstream.

4. Fluid accumulates in tissues, causing edema.

5. Circulating volume falls.

6. Organ perfusion may decrease.

7. Severe losses can produce hypovolemic shock.

A person can be swollen in the tissues while having too little fluid circulating in the blood vessels.

Possible consequences in the chapter’s case:

• Tachycardia: The body tries to maintain circulation.

• Reduced urine output: The kidneys receive less blood flow.

• Falling blood pressure: Circulating volume becomes inadequate.

Hypovolemia = low circulating blood volume.
Hypoperfusion = inadequate blood flow to tissues.

52. Other systemic effects of burns

• Inhalation injury: Can compromise breathing.

• Loss of the skin barrier: Raises infection risk.

• Hypermetabolism: The body uses more energy during recovery.

• Increased nutritional demands: Repair requires additional resources.

• Scarring and contractures: Can impair long-term movement and function.

53. Adult rule of nines

This estimates the percentage of total body surface area, or TBSA, affected.

These total 100%.

For the burn TBSA calculation in your slides, exclude superficial burns.

Example from the chapter:

Entire anterior trunk + one entire arm:

18% + 9% = 27% TBSA.

54. The clinical checks explained