Transport, exchange & defense · Topic 14 of 18

Lymphatic & Immune Systems

Lymphatic Organs & Innate Defense

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Anatomy · lymphatic system & innate defense

Lymphatic Organs & Innate Defense

The lymphatic system returns tissue fluid and filters it through nodes; innate defenses (barriers, phagocytes, inflammation) act fast against any invader.

01 · Three jobsReturns fluid · carries fat · filters germs

02 · Innate defenseInnate = fast, nonspecific, no memory

03 · InflammationHeat · redness · swelling · pain

What it is

Lymphatic system: returns tissue fluid, carries fats, filters pathogens must know

First line of defense: intact skin and mucous membranes must know

Inflammation's four signs: heat, redness, swelling, pain must know

Lymph = tissue fluid inside lymph vessels; it flows one way, toward the heart

No pump: muscles and breathing move lymph; valves prevent backflow

Barrier helpers: lysozyme in saliva, stomach acid, cilia moving mucus

Complement proteins tag microbes, call phagocytes and punch holes

Parts & jobs

Thoracic duct drains most of the body; right duct only the upper right

Lymph nodes filter lymph; they swell when fighting an infection

Spleen filters blood: removes microbes and worn-out red cells

Thymus (behind the sternum): T cells mature here; shrinks after puberty

Tonsils and MALT (Peyer's patches) guard the mouth, throat and gut

NK cells: innate lymphocytes that kill virus-infected and cancer cells

Step by step

Phagocytosis: neutrophils and macrophages engulf and digest invaders

Histamine: vessels widen (heat, redness) and leak (swelling)

Don't confuse

Innate = fast, nonspecific, no memory · adaptive = specific, remembers must know

Primary (mature): marrow, thymus · secondary (respond): nodes, spleen, tonsils

Innate or adaptive defense?

Commonly confused

	Innate	Adaptive
Speed	Rapid	Slower, especially the first time
Targets	Nonspecific: any invader	Specific: one antigen
Memory	None	Yes, so the next response is faster
Main players	Barriers, phagocytes, NK cells, inflammation	B and T lymphocytes

More detail

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Lacteals in the small intestine absorb fats → milky chyle

~20 L filtered daily − ~17 L reabsorbed = ~3 L returned as lymph

Pus = dead neutrophils plus debris at an infection site

Interferons: virus-infected cells warn neighbors to resist the virus

Fixed macrophages: Kupffer cells (liver), alveolar macrophages (lung)

~500–600 lymph nodes; lymph enters by afferent, leaves by efferent vessels

Pearl

Heat, redness, swelling and pain: the four classic signs that inflammation is under way.

Sources · OpenStax Anatomy & Physiology 2e §21.1 Anatomy of the Lymphatic and Immune Systems · OpenStax Anatomy & Physiology 2e §21.2 Barrier Defenses and the Innate Immune Response · Union Test Prep — HESI A2 Anatomy & Physiology study guide, page 1 (lymph drains interstitial fluid) · NurseHub — HESI A2 Anatomy & Physiology review course (lesson list: Lymphatic System, Innate Immunity) · Varsity Tutors — HESI A2 lesson: Immune/lymphatic and integumentary system basics (lines of defense, lymphoid organs, inflammation) · TSTC Library — HESI A2 guide (A&P/Biology topic list: functions of the immune system) · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.

Adaptive Immunity & Immunization

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Anatomy · adaptive immunity

Adaptive Immunity & Immunization

Adaptive immunity is specific and remembers: B cells make antibodies, T cells direct or kill, and immunity is either made (active) or received (passive).

01 · B cellsB cells → plasma cells → antibodies

02 · T cellsHelper T direct · cytotoxic T kill

03 · Immunity typesActive = made by you · passive = given to you

What it is

Adaptive immunity: B and T cells, specific to one antigen, builds memory must know

Antigen = the foreign marker · antibody = the Y-shaped protein that binds it must know

T cells (cell-mediated): helper T direct, cytotoxic T kill infected cells must know

Memory B and T cells last for years and answer a repeat antigen fast

Antibodies clump pathogens, tag them for phagocytes, trigger complement

Vaccine = artificial active immunity: memory without the disease

Passive immunity works at once but fades: no memory cells form

Parts & jobs

Helper T cells (CD4) send cytokines that activate B cells and other cells

Cytotoxic T cells (CD8) destroy virus-infected and diseased body cells

IgG: main antibody of repeat responses; crosses the placenta

Step by step

B cells → plasma cells → antibodies (humoral immunity)

The rules

B cells mature in bone marrow; T cells mature in the thymus

Don't confuse

Active = your body makes antibodies · passive = you receive them ready-made must know

Secondary response is faster and stronger than the primary response

Active: infection (natural), vaccine (artificial) · passive: placenta/milk, antibody shot

Active or passive immunity?

Commonly confused

	Active	Passive
Who makes the antibodies	The person's own immune system	Someone else: they arrive ready-made
Starts working	After a delay of days	Right away
Memory cells	Yes: long-lasting	None: temporary
Natural example	Recovering from an infection	Antibodies across the placenta or in breast milk
Artificial example	A vaccine	An immune globulin injection

More detail

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Five antibody classes: IgG, IgA, IgM, IgE, IgD

IgM: largest antibody; first one made in a primary response

IgA: in mucus, saliva, tears and breast milk

IgE: allergies and anaphylaxis (binds mast cells)

Macrophages, dendritic cells and B cells present antigen to T cells

Regulatory (suppressor) T cells turn immune responses down

Self-tolerance removes self-reactive cells; failure → autoimmunity

Pearl

B for bone marrow, T for thymus: each lymphocyte is named for where it matures.

Sources · OpenStax Anatomy & Physiology 2e §21.1 Anatomy of the Lymphatic and Immune Systems · OpenStax Anatomy & Physiology 2e §21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types · OpenStax Anatomy & Physiology 2e §21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies · OpenStax Anatomy & Physiology 2e §18.4 Leukocytes and Platelets (B, T and memory cells) · OpenStax Anatomy & Physiology 2e §18.6 Blood Typing (Y-shaped antibodies) · NurseHub — HESI A2 Anatomy & Physiology review course (lesson list: Adaptive Immunity) · Varsity Tutors — HESI A2 lesson: Immune/lymphatic and integumentary system basics (B and T cells, memory) · TSTC Library — HESI A2 guide (A&P/Biology topic list: functions of the immune system) · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.

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