Chapter 12: The Innate Immune System & Second Line of Defense

A comprehensive vocabulary review of the innate immune system, cell classifications, defensive mechanisms, and the first and second lines of defense.

The Lymphatic System

A network of organs, vessels, and lymph nodes that transport lymph fluid, filter out foreign pathogens, and house immune cells.

Granulocytes

White blood cells characterized by prominent cytoplasmic granules filled with chemical mediators and enzymes used to fight infections (Basophils, Eosinophils, Neutrophils, and Mast cells).

Agranulocytes

White blood cells that lack prominent cytoplasmic granules and have clear, non-lobed nuclei (Lymphocytes, Monocytes, and Dendritic cells).

Phagocytosis

The process by which specialized white blood cells (phagocytes like neutrophils and macrophages) engulf, internalize, and destroy foreign particles, cell debris, and microbes.

Cytokines

Small signaling protein molecules secreted by immune cells that regulate, guide, and coordinate immune and inflammatory responses.

Chemotaxis

The directional movement of white blood cells in response to chemical gradients (cytokines/chemokines) released at the site of injury or infection.

Fever (Pyrexia)

An abnormally elevated systemic body temperature regulated by the hypothalamus, triggered by pyrogens (like bacterial toxins or cytokines).

Pyrogens

Substances such as bacterial toxins or cytokines that trigger the hypothalamus to regulate an abnormally elevated systemic body temperature.

Innate Immunity

Natural, native immunity you are born with that is non-adaptive, non-specific, and lacks immunological memory, reacting the exact same way every single time.

Physical Defenses

First line of defense structural blockades preventing microbe entry, such as the skin and mucous membranes.

Mechanical Defenses

First line of defense physical actions that flush or sweep microbes away, including respiratory cilia, tears, blinking, and urine flow.

Chemical Defenses

Antimicrobial chemicals produced by the body that destroy pathogens, including stomach acid, lysozyme in tears and saliva, and sebum/sweat.

Lysozyme

An antimicrobial chemical found in tears and saliva that destroys bacterial cell walls as part of the body's chemical defenses.

Second Line of Defense

A cellular and chemical internal innate defense system that kicks in immediately if a microbe breaches the first line of defense, composed of phagocytosis, inflammation, fever, and antimicrobial proteins.

Neutrophils

Granulocytic white blood cells that act as first-responders and bacterial eaters.

Eosinophils

Granulocytic white blood cells that fight parasitic worms and participate in allergic responses.

Basophils

Granulocytic white blood cells that release histamine for inflammation.

Mast Cells

Closely related tissue-dwelling granulocytes that are similar to basophils.

Monocytes

Agranulocytic white blood cells that mature into powerful macrophages.

Lymphocytes

Agranulocytes

Monocytes

Agranulocytes

Dendritic cells

Agranulocytes

Basophil

Granulocytes

Eosinophil

Granulocytes

Neutrophils

Granulocytes

Mast cells

Granulocytes