Module 10: Defenses and Immunity

What is nonspecific immunity?

The body’s general defense system that responds quickly to all pathogens, without targeting a specific one. It includes physical barriers, phagocytes, inflammation, fever, and antimicrobial proteins.

What is specific immunity?

the body’s targeted response to particular pathogens. It involves B cells and T cells that recognise specific antigens and form memory cells for faster future responses.

What are examples of nonspecific immune responses?

Skin, mucous membranes, inflammation, phagocytosis, natural killer (NK) cells, fever, and complement proteins.

What are the two main types of specific immunity?

• Humoral immunity – B cells produce antibodies to target pathogens in body fluids.

• Cell-mediated immunity – T cells destroy infected or abnormal cells.

How do nonspecific and specific immunity differ in speed and memory?

Nonspecific immunity acts immediately but has no memory. Specific immunity takes longer to respond initially but has memory, allowing faster responses to future exposures.

What are the three lines of defense in the immune system?

• First line – Physical and chemical barriers

• Second line – Nonspecific internal defenses

• Third line – Specific/adaptive immune response

What is the first line of defense?

Physical and chemical barriers that prevent pathogens from entering the body.

What are examples of first line defenses?

• Skin (physical barrier)

• Mucous membranes

• Tears and saliva (contain lysozyme)

• Stomach acid

• Cilia in respiratory tract

What is the second line of defense?

Internal, nonspecific responses that attack pathogens that get past the first line.

What are key components of the second line of defense?

• Phagocytes (e.g., macrophages, neutrophils)

• Inflammation

• Fever

• Natural killer (NK) cells

• Antimicrobial proteins (e.g., interferons, complement)

How does inflammation help fight infection?

It increases blood flow, attracts immune cells, and makes capillaries more permeable to help deliver immune responses to the infection site.

What is the third line of defense?

Specific, adaptive immune responses that target particular pathogens and create immunological memory.

What are the main cells in the third line of defense?

• B cells – produce antibodies

• T cells – help destroy infected cells and coordinate immune response

• Memory cells – enable faster future responses

How does the third line differ from the first and second?

It is slower to respond at first but targets specific pathogens and provides long-lasting protection through memory cells.

What are the 4 cardinal signs of inflammation?

• Redness (rubor)

• Heat (calor)

• Swelling (tumor)

• Pain (dolor)

What causes redness (rubor) during inflammation?

Increased blood flow due to vasodilation of local blood vessels.

What causes heat (calor) during inflammation?

Increased blood flow brings warm blood from the body core to the inflamed area.

What causes swelling (tumor) during inflammation?

Increased capillary permeability allows fluid and immune cells to leak into tissues.

What causes pain (dolor) during inflammation?

Chemical mediators like bradykinin and prostaglandins stimulate pain receptors; swelling can also press on nerves.

What triggers the inflammatory response?

Tissue injury or infection activates immune cells to release chemical signals like histamine and prostaglandins.

What is an antigen?

An antigen is any molecule (usually a protein) that the immune system recognizes as foreign and triggers an immune response.

Where are antigens found?

On the surface of pathogens (like bacteria and viruses), or abnormal body cells (e.g., cancer cells, infected cells).

What is the function of B cells in specific immunity?

B cells recognize specific antigens and produce antibodies that bind to them, tagging pathogens for destruction.

What happens when a B cell is activated?

It divides into:

• Plasma cells (which produce antibodies)

• Memory B cells (for faster response if re-exposed)

What is the function of T cells in specific immunity?

T cells destroy infected or abnormal cells and help regulate immune responses.

What are the two main types of T cells?

• Helper T cells (CD4⁺): Activate B cells, other T cells, and macrophages

• Cytotoxic T cells (CD8⁺): Directly kill infected or abnormal cells

How do B and T cells contribute to immunological memory?

Some B and T cells become long-lived memory cells, enabling a faster and stronger response to the same antigen in the future.

What is active immunity?

Immunity that develops when the body is exposed to an antigen and produces its own antibodies.

What is passive immunity?

Immunity gained by receiving ready-made antibodies from another source — the body does not produce them itself.

What is naturally acquired active immunity?

Immunity gained after recovering from an infection (e.g. chickenpox), where the body creates memory cells.

What is artificially acquired active immunity?

Immunity gained through vaccination, where an inactive or weakened form of a pathogen triggers antibody production.

What is naturally acquired passive immunity?

Immunity passed from mother to child — e.g., antibodies through the placenta or breast milk.

What is artificially acquired passive immunity?

Immunity from injected antibodies (e.g., antivenom, immunoglobulin therapy), providing immediate but short-term protection.

How long does passive immunity last compared to active immunity?

Passive immunity is immediate but temporary. Active immunity takes longer to develop but provides long-term protection.

What is lymph?

Lymph is a clear fluid that originates from interstitial fluid and contains white blood cells, especially lymphocytes.

Where does lymph formation begin?

In lymphatic capillaries, which collect excess fluid from tissues.

What are lymphatic vessels?

Thin-walled vessels that carry lymph from the capillaries toward larger lymphatic structures. They have valves to prevent backflow.

What happens in lymph nodes along the flow?

Lymph is filtered and monitored for pathogens; lymphocytes can activate an immune response here.

What are the two major lymphatic ducts?

• Right lymphatic duct — drains the upper right quadrant of the body.

• Thoracic duct — drains the rest of the body.

Where does lymph return to the bloodstream?

At the subclavian veins, where the lymphatic ducts empty into the venous circulation.

Outline the flow of lymph from tissues to bloodstream.

• Lymphatic capillaries

• Lymphatic vessels

• Lymph nodes

• Larger lymphatic vessels

• Lymphatic trunks

• Right lymphatic duct or thoracic duct

• Subclavian veins → bloodstream

What are the primary lymphatic organs?

• Red bone marrow

• Thymus

What is the function of red bone marrow in the lymphatic system?

• Produces all blood cells, including lymphocytes

• Site of B cell maturation

What is the function of the thymus?

• Site of T cell maturation

• Most active in childhood, shrinks with age

What are the secondary lymphatic organs?

• Lymph nodes

• Spleen

• MALT (e.g., tonsils, Peyer’s patches)

What is the function of lymph nodes?

• Filter lymph for pathogens

• Site where immune responses can be activated

What is the function of the spleen?

• Filters blood (not lymph!)

• Destroys old red blood cells

• Stores platelets

• Helps mount immune responses to blood-borne pathogens

What is the function of MALT (Mucosa-associated lymphoid tissue)?

• Defends mucosal surfaces (e.g., digestive, respiratory, urinary tracts)

• Includes tonsils, Peyer’s patches (in small intestine), appendix

What is the main difference between primary and secondary lymphatic organs?

• Primary: Where lymphocytes develop and mature

• Secondary: Where immune responses are initiated