Lymphatic System & Innate Immune System | UNC | BIOL 252

Lecture 16 | Corey Johnson | Fall 2025

Filtration

Blood plasma leaks out of capillaries due to blood pressure, becoming interstitial fluid surrounding body cells

Absorption

Interstitial fluid enters lymphatic capillaries, becoming lymph

Lymph Transport

Lymph travels through afferent vessels, passes through lymph nodes for filtering

Drainage

Lymphatic ducts return lymph to the bloodstream at the subclavian veins

Thoracic Duct

Drains lymph from most of the body

Right Lymphatic Duct

Drains lymph from the upper right side of the body

Lymph Circulation

Lymph returns to the bloodstream and then to the heart through the subclavian veins → superior vena cava → right atrium

Lacteals

Specialized lymphatic capillaries in intestinal villi that absorb fats

Leaking Plasma Advantage

Helps deliver oxygen and nutrients, speeds exchange, and allows waste removal

Lymphatic Recovery System

Picks up leaked plasma, filters it, and returns it to blood to maintain volume

Edema

Swelling caused by failure of lymph drainage

Lymph Nodes

Filter lymph; contain B-lymphocytes, T-lymphocytes, and macrophages for immune defense

Reticular Connective Tissue

Forms a framework for immune cells in lymph nodes for surveillance of lymph

Spleen

Filters blood, performs immune surveillance; white pulp = immune cells, red pulp = removes dying cells

Tonsils

Immune surveillance of air and food entering the body; contain B-cells, T-cells, and macrophages

MALT (Mucosa-Associated Lymphatic Tissue)

Mucosal immune tissue in digestive, respiratory, and ocular surfaces that detects pathogens

Thymus

Develops and matures T-lymphocytes before and shortly after birth; shrinks into fat with age

Specific (Adaptive) Immunity

Targets specific antigens unique to particular pathogens (T-cells and B-cells)

Non-Specific (Innate) Immunity

General defense mechanisms that respond to any pathogen

First Line of Defense

Surface barriers (skin and mucous membranes)

Second Line of Defense

Innate immune cells and antimicrobial proteins

Third Line of Defense

Adaptive immunity: T-cell mediated and B-cell antibody-mediated responses

Surface Barriers

Physical and chemical defenses preventing pathogen entry at epithelial surfaces

Epithelial Boundary

Main structural barrier pathogens must cross to invade

Goblet Cells

Specialized epithelial cells that secrete mucus in mucosal linings

Mucus

Traps pathogens and particles; protects and lubricates epithelial surfaces

Antimicrobial Peptides (Defensins)

Secreted molecules that kill or inhibit microorganisms

Acidic Secretions

Found in stomach and skin; create low pH that inhibits bacterial growth

Sebaceous (Oil) Glands

Dermal glands that secrete acidic oils to deter bacterial growth

Eosinophil

A cell found in the blood that responds to infection by parasitic worms

Neutrophil

A cell found in the blood that engulfs bacteria

Monocyte

A cell found in the blood that becomes a macrophage after moving into tissues

Basophil

A cell found in the blood that enhances an inflammatory response and signals to other cells

Mast Cell

A cell found in the tissues that enhances an inflammatory response and signals to other cells

Dendritic Cell

A cell found in the tissues (especially the skin and epithelia) that is phagocytic and stationary

Macrophage

A cell found in the tissues (especially connective tissue) that is phagocytic and wandering

Natural Killer (NK) Cell

A lymphocyte found in the blood that destroys virus-infected or cancerous body cells using perforins and granzymes

Resident Phagocytic Cells

Engulf invaders and present antigens (Macrophages, Dendritic Cells)

Blood-Borne Phagocytic Cells

Circulate in blood and move into tissues to attack (Neutrophils, Eosinophils, Monocytes)

Recruiting / Signaling Cells

Release histamine and cytokines to recruit other WBCs (Basophils, Mast Cells)

Cytotoxic Killer Cells

Destroy infected or cancerous body cells (NK Cells)

Signalers to Bone Marrow (↑ WBC Production)

Release cytokines that stimulate leukocyte formation (Neutrophils, Eosinophils, Macrophages)

Complement Proteins

Plasma proteins from the liver that help destroy pathogens

Complement: Cell Lysis

Complement proteins bind to bacterial membranes, form pores, and cause the cell to burst

Complement: Enhanced Inflammation

Amplify inflammatory effects of basophils and mast cells

Complement: Neutralized Viruses

Bind to viruses and make them ineffective

Complement: Opsonization

Tag pathogens to make phagocytosis easier for macrophages

Complement: Clearance of Immune Complexes

Help remove antibody-antigen complexes from the body

Cytokines

Chemical messengers that amplify and coordinate immune responses

Cytokine Function

Tell immune cells where to go, what to do, and when to multiply

Cytokine Effect: Recruitment

Bring in more immune cells to infection site

Cytokine Effect: Activation

Turn immune cells “on” or make them stronger

Cytokine Effect: Builder

Signal bone marrow to produce more WBCs

Cytokine Effect: Inflamer

Cause inflammation and fever

Cytokine Effect: Antiviral

Interfere with viral replication (via interferons)

Cytokine Effect: Bridger

Connect innate and adaptive immune responses

Interferons

Cytokines released by virus-infected cells to alert neighboring cells and prevent viral replication

Interferon Autocrine Effect

The infected cell stops its own replication

Interferon Paracrine Effect

Neighboring cells strengthen barriers to infection

Interferon Systemic Effect

Recruits white blood cells to fight viruses