Lymphatic System and Immunity

Vocabulary flashcards covering the anatomy and physiology of the lymphatic system, types of immunity, innate and adaptive defenses, and related clinical disorders based on the Chapter 16 lecture outline.

Lymphatic system

A collection of cells and biochemicals that travel in lymphatic vessels, containing a network of vessels that assist in circulating fluids and defending the body against diseases.

Lacteals

Specialized lymphatic capillaries in the digestive system that absorb lipids and transport them to the bloodstream.

Lymphatic pathway

The sequence of lymph flow: Lymphatic capillaries $\rightarrow$ lymphatic vessels $\rightarrow$ lymph nodes $\rightarrow$ larger lymphatic vessels $\rightarrow$ lymphatic trunks $\rightarrow$ lymphatic collecting ducts $\rightarrow$ subclavian veins in thorax.

Lymphatic capillaries

Microscopic, closed-ended, thin-walled tubes formed from simple squamous epithelium that parallel blood capillaries and allow tissue (interstitial) fluid to enter.

Lymph

The fluid that results after tissue (interstitial) fluid enters a lymphatic capillary.

Lymphatic vessels

Vessels composed of three layers (inner endothelial lining, middle smooth muscle/elastic fibers, and outer connective tissue) containing semilunar valves to allow one-way flow.

Lymphatic trunks

Structures that drain lymph from lymphatic vessels, named for the regions they serve: Lumbar, intestinal, intercostal, bronchomediastinal, subclavian, and jugular.

Thoracic duct

The longer and wider collecting duct that drains the majority of the body; it begins as a sac called the cisterna chyli and empties into the L. Subclavian Vein.

Right lymphatic duct

A collecting duct that empties into the R. Subclavian Vein and drains the upper left portion of the body (per transcript Page 8).

Tissue fluid equation

$$\text{Tissue fluid} = \text{blood plasma} - \text{plasma proteins}$$

Edema

The accumulation of excess tissue fluid occurs when lymphatic drainage is obstructed, such as after the removal of axillary lymph nodes during breast cancer surgery.

MALT (Mucosa-associated lymphoid tissue)

Unencapsulated lymphatic tissue found in the digestive, respiratory, urinary, and reproductive tracts, including the tonsils and appendix.

Peyer’s patches

Aggregates of lymphatic nodules found in the ileum (distal part of small intestine).

Lymphatic organs

Encapsulated lymphatic tissues comprising lymph nodes, the thymus, and the spleen.

Lymph nodes

Bean-shaped structures $< 2.5 cm$ long that filter pathogens from lymph and serve as centers for lymphocyte production.

Thymus

A soft, bilobed gland in the mediastinum where thymocytes mature into functional T lymphocytes; it is large in childhood and shrinks at puberty.

Thymosins

Hormones produced in the thymus that stimulate T cell maturation.

Spleen

The largest lymphatic organ, located in the upper left abdominal cavity; it contains white pulp (lymphocytes) and red pulp (RBCs, lymphocytes, macrophages) and filters blood.

Pathogens

Disease-causing agents including bacteria, viruses, protozoa, and fungi.

Innate (nonspecific) defenses

General defenses that protect against many types of pathogens, including species resistance and mechanical barriers.

Mechanical barriers

The first line of defense consisting of skin and mucous membranes that prevent the entrance of pathogens.

Inflammation

A tissue response to injury producing redness, swelling, heat, and pain; it walls off the infection site and inhibits the spread of pathogens.

Interferons

Chemical barriers that block viral replication, acting against tumor growth and stimulating phagocytosis.

Defensins

Peptides produced by neutrophils that cripple microbes by making openings in cell membranes or walls.

Collectins

Proteins that provide protection against several types of bacteria, yeast, and some viruses.

Complement

A group of proteins in plasma that stimulates inflammation, attracts phagocytes, and enhances phagocytosis.

Natural Killer (NK) Cells

A small population of lymphocytes that secrete cytolytic substances called perforins to lyse the membranes of virus-infected and cancer cells.

Chemotaxis

The process where chemicals from damaged tissue attract phagocytic cells, such as neutrophils and monocytes, to the injury.

Endogenous pyrogen

Also known as interleukin-1 ($IL-1$), a substance secreted by lymphocytes that raises the thermoregulatory set point to cause fever.

Adaptive (specific) defenses

The third line of defense based on the ability to distinguish ‘self’ from ‘non-self’, targeting specific antigens via lymphocytes and macrophages.

Antigens

Non-self molecules, often large and complex like proteins or glycoproteins, that can evoke an immune response.

Haptens

Small molecules that are not antigenic on their own but can evoke an immune response when combined with a larger molecule in the body.

T cells (T lymphocytes)

Thymus-derived lymphocytes that make up $70 \text{to} 80 \text{\%}$ of circulating lymphocytes and provide cellular immune response.

B cells (B lymphocytes)

Lymphocytes that differentiate in the red bone marrow, make up $20 \text{to} 30 \text{\%}$ of blood lymphocytes, and provide humoral immune response.

Cytokines

Polypeptides secreted by T cells that enhance cellular responses to antigens, such as colony-stimulating factors and interleukins.

Helper T cells

Specialized T cells that activate other cells and stimulate B cells to produce antibodies.

Cytotoxic T cells

T cells that attack virally infected or cancerous cells directly.

Plasma cells

Differentiated B cells that synthesize and secrete large globular proteins called antibodies.

Humoral immune response

An antibody-mediated immune response where antibodies are carried by the blood to the site of infection.

Immunoglobulins

Globular Y-shaped proteins (antibodies) composed of $2$ heavy and $2$ light amino acid chains joined by disulfide bonds.

IgG

The most common antibody ($80 \text{\%}$) found in plasma and tissue fluid; it defends against bacteria, viruses, and toxins and activates complement.

IgA

Antibody ($13 \text{\%}$) found in exocrine gland secretions like breast milk and tears.

IgM

Antibody ($6 \text{\%}$) that reacts with antigens on RBC membranes following mismatched transfusions and activates complement.

Direct attack methods

Antibody actions including agglutination (clumping), precipitation (insolubility), and neutralization (covering toxic portions).

Opsonization

An action of activated complement proteins that coats antigen-antibody complexes to make them more susceptible to phagocytosis.

Monoclonal Antibodies

Single types of antibodies produced by fusing a specific B cell with a cancerous cell; used in research and pregnancy tests.

Primary immune response

Produced by the first encounter with an antigen; antibodies appear in $5 \text{to} 10 \text{days}$.

Secondary immune response

A rapid response to subsequent exposure to the same antigen, producing high antibody concentrations in $1 \text{to} 2 \text{days}$ due to memory cells.

Naturally acquired active immunity

Permanent immunity obtained through exposure to live pathogens and stimulation of an immune response with symptoms.

Artificially acquired passive immunity

Short-term immunity resulting from an injection of antiserum containing specific antibodies, without stimulating an immune response.

Hypersensitivity

An exaggerated and harmful immune response to a non-harmful antigen, such as an allergy.

Anaphylactic shock

A life-threatening, severe form of Type I (immediate-reaction) hypersensitivity.

Type IV hypersensitivity

A delayed-reaction response resulting from repeated skin exposure to an allergen, taking about $48 \text{hours}$ to occur.

Autograft

A transplant where the donor is the self; it does not cause a rejection reaction.

Xenograft

A transplant from a different species, such as heart valves from a pig; tends to cause a rejection reaction.

Autoimmunity

An attack by the immune system against the body's own tissues via autoantibodies and cytotoxic T cells.

HIV (Human Immunodeficiency Virus)

A virus that attacks macrophages and Helper T cells, leading to a decline in B cell antibody production and an eventual loss of immune response (AIDS).