2. Reactivity and resistance

Define reactivity

The ability of an organism to change the functional state of its systems and organs to adapt to new conditions and survive

Reactivity by level: _____ (species, genetically coded), _____ (age, sex groups), _____

biological | group | individual

Biological (species) reactivity

Morphological and physiological responses shared by a whole species

Primary reactivity — genetically coded

Individual reactivity — what shapes it?

Age, sex, heredity, constitution

Functional state of the regulatory (nervous, endocrine) systems

External environmental influences

Specific vs non-specific reactivity

Specific: controlled by the immune system (antigen-directed)

Non-specific: nervous system (CNS, autonomic), endocrine system, barrier systems, cellular and humoral reactions

Specific reactivity: physiological vs pathological

Physiological: specific resistance to bacteria, viruses, fungi, tumour cells

Pathological: allergic reactions, autoimmune disease, immunodeficiency / immunosuppression

Non-specific reactivity: physiological vs pathological

Physiological: the vital reactions of a healthy organism in normal conditions

Pathological: in abnormal conditions, when adaptive capacity falls (e.g. shock, collapse)

By sensitivity to an allergen: _____ (typical), _____ (↓), _____ (↑), _____ (none)

normergic | hypoergic | hyperergic | anergic

Normergic reactivity

Degree of reactivity to an allergen that is typical for the age group and community

Anergy — positive vs negative

Lack of reaction to specific antigens (usually self-antigens)

Positive: an effective defence — prevents autoimmune reactions

Negative: undeveloped or exhausted defence mechanisms (e.g. negative tuberculin test in AIDS or overwhelming TB)

Factors influencing reactivity and resistance

Environmental: chemical, biological, physical, social

Constitutional: sex, age, type of nervous system, heredity

Define resistance

The organism's insusceptibility to pathogenic factors

= ability of a living system to oppose irritants

Natural vs acquired resistance

Natural (species, innate): inborn, genetically determined

Acquired: develops in postnatal life — natural or artificial, active or passive

Acquired resistance: 4 types with examples

Artificial active: vaccination

Artificial passive: serotherapy / immunoglobulin, blood transfusion

Natural active: recovering from an infection

Natural passive: antibodies via placenta or breast milk

Passive vs active (non-specific) resistance

Passive: barrier structures (skin, mucosa, bone, BBB) and inborn insensitivity

Active: protective reactions — phagocytosis, inflammation, fever, antibody production

Immunological resistance

Complex mechanism of defensive and adaptive reactions

Highly specific; aimed at external threats (bacteria, viruses) and internal threats (functionally ineffective or mutated cells)

EXAMINER ASKS: Do reactivity and resistance always change together?

No — resistance depends on reactivity, but they can move apart

Allergy: hyperergic reactivity without better resistance (the reaction itself harms)

Hibernation / deep anaesthesia: ↓ reactivity but ↑ resistance to hypoxia and some toxins

15-MINUTE NOTES / Write your note sheet for essay 02 Reactivity and resistance

1. Reactivity: definition

2. Types: biological / group / individual; specific vs non-specific (each physiological vs pathological)

3. By sensitivity: normergic, hypoergic, hyperergic, anergic (positive vs negative)

4. Factors: environmental vs constitutional

5. Resistance: definition; natural vs acquired; artificial/natural × active/passive

6. Immunological resistance; how reactivity and resistance relate

Draw: a 2 × 2 table of acquired resistance (natural/artificial × active/passive) with one example in each box