Immunity 1 – Innate Immunity & Lymphatic System

These flashcards cover the vital concepts from Immunity 1: the innate immune defenses (first and second lines), the lymphatic system’s structure and functions, key leukocytes, the phagocytosis process, and a preview of adaptive immunity.

What are the three main lines of immune defense in the human body?

First line (physical & chemical barriers), second line (innate immune response), and third line (adaptive immunity).

Which two lines of defense are classified as innate immunity?

The first and second lines of defense.

Why is the innate immune response described as "non-specific"?

It targets any invading pathogen the same way, without antigen specificity or memory.

Name three major physical barriers in the first line of defense.

Skin, mucous membranes, and normal microbiota.

Give two chemical barriers that inhibit microbial growth on body surfaces.

Lysozymes and stomach acid (hydrochloric acid); sweat is another example.

Which lymphoid tissues provide early pathogen detection at mucosal sites?

MALT (mucosa-associated), GALT (gut-associated), and BALT (bronchus-associated) lymphoid tissues.

List the four broad mechanisms that make up the second line of defense.

Phagocytosis, inflammation, fever, and antimicrobial substances.

How do lymph nodes assist in the second line of defense?

They trap and filter pathogens from lymph and help activate immune responses.

Which organ removes blood-borne pathogens and old red blood cells?

The spleen (white pulp for immune function, red pulp for RBC breakdown).

What are the primary phagocytic cells in innate immunity?

Neutrophils, monocytes (which mature into macrophages), and dendritic cells.

During phagocytosis, what structure forms when a phagosome fuses with a lysosome?

A phagolysosome.

Which receptors on phagocytes recognize common microbial patterns?

Pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs).

State the five steps of phagocytosis in the correct order.

Recognition & attachment, engulfment, phagolysosome formation, microbial killing, antigen presentation (in APCs).

Which leukocyte is typically the first responder to bacterial infection?

Neutrophils.

What substances do basophils release, and what is their primary effect?

Histamine (promotes inflammation) and heparin (inhibits clotting).

Where are mast cells located and what role do they play?

They reside in tissues and trigger inflammation and allergic responses, similar to basophils.

Which leukocyte specializes in combating parasitic infections and moderating allergies?

Eosinophils.

What does the Mononuclear Phagocyte System (MPS) consist of?

Monocytes in blood and their derivatives, macrophages and dendritic cells, in tissues.

Give one major function of macrophages beyond pathogen destruction.

Presenting antigens to adaptive immune cells (activating T cells).

Explain the primary role of dendritic cells in immunity.

They capture pathogens and present antigens to T cells, bridging innate and adaptive immunity.

What are the two primary lymphatic organs and their main functions?

Bone marrow (produces all blood cells, site of B-cell maturation) and thymus (site of T-cell maturation).

Why does the thymus shrink with age?

It involutes after childhood as naïve T-cell production decreases, leaving residual functional tissue in adults.

What are the main functions of lymph nodes?

Filter lymph, trap pathogens, and house lymphocytes and macrophages for immune activation.

Which lymphoid organ is the largest and where is it located?

The spleen, located in the upper left abdomen.

How do tonsils contribute to innate immunity?

They guard the throat and nasal cavity, capturing inhaled or ingested pathogens.

What is the role of Peyer’s patches in the small intestine?

Monitoring gut bacteria and preventing intestinal infection as part of MALT.

Describe the purpose of lymphatic capillaries.

They absorb excess interstitial fluid, proteins, and large particles (including bacteria) from tissues.

How do lymphatic vessels ensure one-way flow of lymph?

They contain valves that prevent backflow.

What do lymphatic collecting ducts do?

Return filtered lymph to the bloodstream.

Which immune cells dominate the third line of defense, and what key feature do they provide?

Lymphocytes (T cells and B cells) that confer highly specific immunity and long-term memory.