REVIEW CONCEPTS:
Chapter 20
The Lymphatic System and Immunity
Anatomy of the Lymphatic System
Lymphatic System Overview
Lymphatic system
o Includes cells, tissues, and organs responsible for two functions
1. Immunity
o The ability to defend the body against infection, illness,
and disease
2. Returning interstitial fluid to the bloodstream
Lymphatic system components
o Lymphocytes
Primary cells of the lymphatic system
Respond to:
o Invading pathogens (such as bacteria and viruses)
o Abnormal body cells (such as virus-infected or cancer
cells)
o Foreign proteins (such as bacterial toxins)
Surrounded by lymph
o Interstitial fluid that has entered a lymphatic vessel
o Lymphatic vessels
Often called lymphatics
Begin in peripheral tissues
End at connections to veins
o Lymphoid tissues and lymphoid organs
Scattered throughout the body
Primary lymphoid tissues and organ
o Sites where lymphocytes are formed or mature
o Include red bone marrow and the thymus gland
Secondary lymphoid tissues and organ
o Where lymphocytes are activated and cloned (copied)
o Include lymph nodes, tonsils, MALT, appendix, and
spleen
Lymphocytes
© 2015 Pearson Education, Inc.
, o Account for 20–40 percent of circulating leukocytes
o Most lymphocytes are out in lymphatic tissues
o Three classes circulate in blood
1. T cells (~80 percent of circulating lymphocytes)
o Cell-mediated immunity
2. B cells (10-15 percent of circulating lymphocytes)
o Antibody-mediated immunity
3. NK cells (5-10 percent of circulating lymphocytes)
o Immune surveillance
o All classes of lymphocytes are sensitive to specific chemicals
(antigens)
Most antigens are pathogens, parts or products of pathogens, or
other foreign compounds
Most antigens are proteins
o Could also be lipids, polysaccharides, or nucleic acids
Antigens stimulate an immune response
o Leads to destruction of the target compound or organism
Lymphocyte classes
o T cells (three major categories)
1. Cytotoxic T cells
o Attack foreign cells or body cells infected by viruses
o Attack commonly involves direct contact
o Primary cells involved in production of cell-mediated
immunity (cellular immunity)
2. Helper T cells
o Stimulate activation and function of T cells and B cells
o Also known as regulatory T cells
o Work with suppressor T cells to control sensitivity of
immune response
3. Suppressor T cells
o Inhibit activation and function of T cells and B cells
o B cells
When stimulated, become plasma cells that produce and
secrete antibodies
Responsible for antibody-mediated immunity (humoral
immunity)
o Antibodies circulate in body fluids to attack targets
throughout the body
o NK (natural killer) cells
Attack foreign cells, virus-infected body cells, and cancer cells
Provide continuous monitoring of peripheral tissues
o Involves:
Red bone marrow
Thymus
Peripheral lymphoid tissues
o Red bone marrow plays the primary role in maintaining the normal
© 2015 Pearson Education, Inc.
Chapter 20
The Lymphatic System and Immunity
Anatomy of the Lymphatic System
Lymphatic System Overview
Lymphatic system
o Includes cells, tissues, and organs responsible for two functions
1. Immunity
o The ability to defend the body against infection, illness,
and disease
2. Returning interstitial fluid to the bloodstream
Lymphatic system components
o Lymphocytes
Primary cells of the lymphatic system
Respond to:
o Invading pathogens (such as bacteria and viruses)
o Abnormal body cells (such as virus-infected or cancer
cells)
o Foreign proteins (such as bacterial toxins)
Surrounded by lymph
o Interstitial fluid that has entered a lymphatic vessel
o Lymphatic vessels
Often called lymphatics
Begin in peripheral tissues
End at connections to veins
o Lymphoid tissues and lymphoid organs
Scattered throughout the body
Primary lymphoid tissues and organ
o Sites where lymphocytes are formed or mature
o Include red bone marrow and the thymus gland
Secondary lymphoid tissues and organ
o Where lymphocytes are activated and cloned (copied)
o Include lymph nodes, tonsils, MALT, appendix, and
spleen
Lymphocytes
© 2015 Pearson Education, Inc.
, o Account for 20–40 percent of circulating leukocytes
o Most lymphocytes are out in lymphatic tissues
o Three classes circulate in blood
1. T cells (~80 percent of circulating lymphocytes)
o Cell-mediated immunity
2. B cells (10-15 percent of circulating lymphocytes)
o Antibody-mediated immunity
3. NK cells (5-10 percent of circulating lymphocytes)
o Immune surveillance
o All classes of lymphocytes are sensitive to specific chemicals
(antigens)
Most antigens are pathogens, parts or products of pathogens, or
other foreign compounds
Most antigens are proteins
o Could also be lipids, polysaccharides, or nucleic acids
Antigens stimulate an immune response
o Leads to destruction of the target compound or organism
Lymphocyte classes
o T cells (three major categories)
1. Cytotoxic T cells
o Attack foreign cells or body cells infected by viruses
o Attack commonly involves direct contact
o Primary cells involved in production of cell-mediated
immunity (cellular immunity)
2. Helper T cells
o Stimulate activation and function of T cells and B cells
o Also known as regulatory T cells
o Work with suppressor T cells to control sensitivity of
immune response
3. Suppressor T cells
o Inhibit activation and function of T cells and B cells
o B cells
When stimulated, become plasma cells that produce and
secrete antibodies
Responsible for antibody-mediated immunity (humoral
immunity)
o Antibodies circulate in body fluids to attack targets
throughout the body
o NK (natural killer) cells
Attack foreign cells, virus-infected body cells, and cancer cells
Provide continuous monitoring of peripheral tissues
o Involves:
Red bone marrow
Thymus
Peripheral lymphoid tissues
o Red bone marrow plays the primary role in maintaining the normal
© 2015 Pearson Education, Inc.
