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What is lymph?

Lymph is fluid in tissue spaces that carries protein molecules, excess fluid, and other substances back to the bloodstream.

How does lymph form?

Blood plasma filters out of capillaries into tissue spaces, forming interstitial fluid, which becomes lymph when it enters lymphatic vessels.

Function of the lymphatic system

Returns excess fluid to the bloodstream, fights infection, and absorbs fats from the digestive system.

What is interstitial fluid?

Fluid found between tissue cells before it enters lymphatic vessels.

Role of lymph nodes in cancer spread

Lymph nodes may trap cancer cells that have spread from the original tumor through the lymphatic system.

Right lymphatic duct

Drains lymph from the right upper extremity and right side of the head, neck, and upper torso.

Thoracic duct

Largest lymphatic vessel that drains lymph from about three-fourths of the body.

Cisterna chyli

Enlarged pouch along the thoracic duct that collects lymph.

Lymphatic capillaries

Tiny blind-ended tubes in tissue spaces that collect lymph.

Lacteals

Lymphatic capillaries in the intestinal wall that absorb fats into the bloodstream.

Why do lymphatic vessels have valves?

To ensure one-way movement of lymph.

Fluid homeostasis role of lymphatic system

Prevents accumulation of excess tissue fluid by returning it to the bloodstream.

Lymphoid tissue

Masses of lymphocytes and related cells that provide immune function and development of immune cells.

Functions of lymph nodes

Filter lymph, support immunity, and aid white blood cell formation.

Lymphedema

Swelling caused by blockage or damage to lymphatic vessels.

Lymphadenitis

Swelling and tenderness of lymph nodes.

Metastasis

Spread of cancer cells through the lymphatic system to other parts of the body.

Afferent lymphatic vessels

Vessels that carry lymph into a lymph node.

Efferent lymphatic vessels

Vessels that carry lymph away from a lymph node.

Thymus

A lymphoid organ in the mediastinum that produces T cells and thymosins.

Thymosins

Hormones secreted by the thymus that stimulate T-cell development.

Involution

Process in which thymus tissue is replaced by fat with age.

Palatine tonsils

The tonsils located on each side of the throat.

Pharyngeal tonsils (adenoids)

Tonsils located near the posterior opening of the nasal cavity.

Lingual tonsils

Tonsils located near the base of the tongue.

Function of tonsils

Act as the first line of defense against pathogens entering through the mouth and nose.

Spleen

Largest lymphoid organ located in the upper left quadrant of the abdomen.

Functions of the spleen

Phagocytosis of bacteria and old RBCs, blood reservoir, and iron storage.

Splenectomy

Surgical removal of the spleen.

Splenomegaly

Enlargement of the spleen.

Nonspecific immunity

General defenses that protect against pathogens regardless of type.

Examples of nonspecific immunity

Skin, tears, mucus, inflammation, and phagocytosis.

Signs of inflammation

Heat, redness, pain, and swelling.

Chemotaxis

Movement of white blood cells toward an injury or infection site.

Specific immunity

Ability of the body to recognize, respond to, and remember specific harmful substances.

Adaptive immunity

Another name for specific immunity.

Inherited immunity

Immunity present from birth due to genetic factors.

Natural active immunity

Immunity acquired after developing and recovering from a disease.

Natural passive immunity

Immunity passed from mother to fetus through the placenta or through breast milk.

Artificial active immunity

Immunity produced after vaccination.

Artificial passive immunity

Immunity obtained by receiving antibodies from another individual.

Which immunity lasts longer?

Active immunity lasts longer than passive immunity.

Antibodies

Proteins that bind specific antigens and help destroy harmful substances.

Antigens

Foreign proteins that trigger an immune response.

Humoral immunity

Immunity produced by antibodies circulating in body fluids.

Functions of antigen-antibody complexes

Neutralize toxins, agglutinate cells, and promote phagocytosis.

Complement proteins

Proteins in blood that assist antibodies in destroying foreign cells.

Complement cascade

A series of reactions that create holes in foreign cell membranes, causing cell lysis.

Cell lysis

Bursting of a cell due to water entering through membrane defects.

Phagocytes

Cells that ingest and destroy harmful substances through phagocytosis.

Neutrophils

Short-lived phagocytic white blood cells.

Monocytes

White blood cells that develop into macrophages.

Macrophages

Large phagocytic cells derived from monocytes.

Dendritic cells (DCs)

Antigen-presenting cells often found near body surfaces.

Antigen-presenting cells (APCs)

Cells that display antigens to activate specific immune responses.

Phagocytosis

Process in which cells engulf and destroy foreign particles.

Lymphocytes

Most numerous immune cells; include B cells and T cells.

B cells

Lymphocytes responsible for antibody production and humoral immunity.

Where do B cells mature?

In the bone marrow.

What activates B cells?

Contact with a specific antigen and signals from T cells.

Plasma cells

Activated B cells that secrete antibodies.

Memory B cells

Long-lived cells that respond rapidly to future exposure to the same antigen.

Function of B cells

Produce humoral immunity through antibody production.

T cells

Lymphocytes responsible for cell-mediated immunity.

Where do T cells mature?

In the thymus gland.

Cytotoxic T cells

T cells that kill infected or tumor cells.

Helper T cells

T cells that activate macrophages and help activate B cells.

Regulatory T cells

T cells that suppress immune responses.

Cell-mediated immunity

Immunity produced by the actions of T cells.

Memory T cells

T cells that remain after infection and allow a faster response upon re-exposure.

Hypersensitivity

An excessive or inappropriate immune response.

Allergy

Hypersensitivity to harmless environmental antigens called allergens.

Immediate allergic response

Usually involves humoral immunity.

Delayed allergic response

Usually involves cell-mediated immunity.