Basics of the Immune System - Lymphoid Organs and Lines of Defense

This flashcard set covers the basics of the immune system, identifying primary and secondary lymphoid organs, the various anatomical and physiological barriers of the first line of defense, and mechanisms of the second line of defense such as phagocytosis.

Primary Lymphoid Organs

The central organs where development of the immune system occurs, specifically encompassing the Bone Marrow and the Thymus.

Secondary Lymphoid Organs

Peripheral organs where immune responses are elicited, including the Tonsils, Adenoids, Lymph Nodes, Appendix, Spleen, Peyer's patches, and Lymphatic vessels.

Innate Immunity

The first line of defense present from birth that provides protection against microbial invasion through anatomical and physiological barriers.

Epidermis

The outermost layer of the skin composed of dead cells and keratin protein, which lacks blood vessels and undergoes rapid turnover.

Keratin

A protein produced by keratinocytes in the epidermis that prevents water loss and the entry of foreign bodies.

Sebum

An oily secretion produced by sebaceous glands that contains unsaturated fatty acids with antibacterial and antifungal properties; it inhibits microbial growth via low $pH$.

Hypodermis

The layer below the dermis consisting largely of fat that provides structural support, insulation from cold, and shock absorption.

Mucus

A moist, sticky substance or thick glycoprotein containing antimicrobial peptides that serves as a mechanical barrier to trap microbes.

Goblet Cells

Cells found in the respiratory system's ciliated epithelium that produce and secrete mucus to trap pathogens and debris.

Basal Cells

Cells that differentiate into types of the respiratory epithelium to help restore the cell layer.

Competitive Exclusion

The mechanism by which normal microbiota prevent the colonization of pathogens by competing for nutrients and altering the environment like $pH$ and oxygen availability.

Bacteriocins

Harmful substances secreted by colonic $Escherichia \text{ } coli$ that prevent the development of $Shigella$ and $Salmonella$.

Lysozyme

An antibacterial enzyme found in sweat, tears, and saliva that degrades the peptidoglycan layer of the bacterial cell wall.

Gastric Juice

A secretion composed of digestive enzymes, hydrochloric acid, and mucus that creates a highly acidic environment unsuitable for most microbial growth.

Bile Salts

Substances produced in the liver from cholesterol that help prevent microbial colonization.

Spermine

A polyamine biomolecule that accumulates at the site of infection or injury to participate in immune function.

Lactoferrin

An iron-binding protein found in secretions of the eye, nose, respiratory tract, and intestine with immunomodulatory characteristics.

Colostrum

A nutrient-rich fluid secreted by female mammals after birth containing high concentrations of $IgA$ and $IgG$ antibodies.

Phagocytosis

Derived from the Greek words 'phagein' and 'kytos' (cell eating), it is the second line of defense where specialized cells engulf and ingest microorganisms.

Natural Killer (NK) Cells

Large granular lymphocytes that circulate to bring about the lysis of tumor cells and virus-infected cells without requiring prior sensitization.

Perforins

Substances released from the granules of $NK$ cells that create holes in the target cell's membrane, leading to lysis.