The Lymphatic System and Immunity

Chapters 20 & 21

Objectives

1. SC.912.L.14.52 - Explain the basic functions of the human immune system, including specific and nonspecific immune response, vaccines, and antibiotics.

2. SC.912.L.14.42 - Describe the anatomy and physiology of the lymph system.

3. HE.912.C.1.3 - Evaluate how environment and personal health are interrelated.

Objectives

4. SC.912.L.14.6 - Explain the significance of genetic factors, environmental factors, and pathogenic agents to health from the perspectives of both individual and public health.

5. SC.912.L.16.10 - Evaluate the impact of biotechnology on the individual, society and the environment, including medical and ethical issues.

Functions

• Protects us against disease

• Respond to: – environmental pathogens

– toxins

– abnormal body cells, such as cancer

Pathogens

• Microscopic organisms that cause disease

• Ex: – viruses

– bacteria

– fungi

– parasites

Major Components

• Lymph – a fluid

• Lymphatic vessels

• Lymphoid tissues

• Lymphoid organs

• Lymphocytes – phagocytes

Major Components

• Spleen

• Thymus

• Lymphatic vessels

• Lymph nodes

• Tonsils

• Bone marrow

Lymphocyte Distribution

• Wander through tissues

• Enter blood vessels or lymphatics for transport

• Can survive many years

Lymphoid Tissues

• Dominated by lymphocytes

Lymph Nodes

• A filter – purifies lymph before

return to circulation

• Removes: – debris

– pathogens

– 99% of antigens

Thymus

• Deteriorates after puberty – diminishing effectiveness

• Site of T cell maturation

Spleen

• Removes abnormal blood cells/blood components

• Stores iron recycled from RBC’s

• Initiates B and T cell immune response

Lymphocytes

• Produced in lymphoid tissue, organs, and red bone marrow

• Function: – detect problems

– travel to an injury/infection site

• Travel in lymph through lymphatic vessels

Lymphocytes

• Make up ~20-30% of circulating leukocytes

• Most are stored, not circulating

• 3 classes: – T cells

– B cells

– NK cells

T cells

• Thymus dependent • ~80% of circulating lymphocytes • 3 main types:

– Cytotoxic T cells • attacks cells infected by viruses

– Suppressor T cells • inhibit function of T and B cells

– Helper T cells • stimulate function of T and B cells

B cells

• Bone marrow derived

• ~10-15% of circulating lymphocytes

• Produce and secrete antibodies – bind to specific antigens

– destroys a target

NK cells

• Natural killer cells

• ~5-10% of circulating lymphocytes

• Attack: – foreign cells

– virus-infected cells

– cancer cells

NK cells Tumor cell

Body Defenses

• Provide resistance to fight infection, illness, and disease

• 2 categories: – nonspecific defenses

– specific defenses

Nonspecific Defenses

• Always work the same way • Against any type of invading agent • 7 types:

– physical barriers – phagocytic cells – immunological surveillance – interferons – complement – inflammation – fever

Physical Barriers

• Keep hazardous materials outside the body

• Examples: – skin – mucous membranes – saliva – mucus – nasal hair – sweat – tears

Phagocytes

• Attack and remove dangerous microorganisms

• Examples: – microphages

– macrophages • engulf & destroy pathogens

• bind to pathogen so others can destroy it

• release toxic chemicals into interstitial fluid

Immunological Surveillance

• Constantly monitors normal tissues – NK cells

• ID and attach to abnormal cells (not selective)

• can attack cancer/viral-infected cells

Interferons

• Trigger production of antiviral proteins in normal cells – do not kill

viruses

– block replication in the cell

Complement (C) Proteins

• Form the complement system

• Complements actions of antibodies

Inflammation

• Triggers a complex inflammatory response

• Fever – accelerates defenses

– inhibits some viruses & bacteria

• Signs & symptoms: – swelling, redness, heat, pain

Specific Defenses

• Protect against specific pathogens

• Depend on activities of lymphocytes

• Specific resistance (immunity) – develops after exposure to environmental

hazards

Forms of Immunity

• Innate – present at birth

• Acquired – after birth

Acquired Immunity

• Active – antibodies develop after exposure to

antigen

• Passive – antibodies are transferred from another

source

Active Immunity

• Naturally acquired – through environmental

exposure to pathogens

• Induced – through vaccines

containing pathogens

Passive Immunity

• Naturally acquired – antibodies acquired

through the mother

• Induced – by an injection of

antibodies

Effects of Aging

• Immune system deteriorates – increased vulnerability to infections &

cancer

• T cells become less responsive to antigens

• Immune surveillance against tumor cells declines