Download Introduction - Fullfrontalanatomy.com

Introduction
 The lymphoid system




Lymphatic vessels
Lymph (fluid connective tissue)
Lymphoid tissues
Lymphoid organs
 Plays central role in body’s defenses against viruses, bacteria,
and other microorganisms
 Lymphatic vessels originate in peripheral tissues and deliver
lymph to the venous system.
An Overview of the Lymphoid System
 Lymph consists of:
 Interstitial fluid, which resembles blood plasma, but with a lower
concentration of proteins
 Lymphocytes, cells responsible for the immune response
 Macrophages of various types
 Primary functions of the lymphoid system:
 Produce, maintain, and distribute lymphocytes
 Maintain normal blood volume and eliminate local variations in the
chemical composition of the interstitial fluid
 Provide an alternative route for the transport of hormones, nutrients,
and waste products
Structure of Lymphatic Vessels
 Lymphatic capillaries
 Lymphatic vessels (or lymphatics) carry lymph from peripheral tissues
to the venous system.
 Lymphatic capillaries (or terminal lymphatics) form a complex
network within peripheral tissues.
 Lymphatics contain internal valves that prevent backflow of lymph/
 Two sets of lymphatic vessels:
 Superficial lymphatic vessels travel with superficial veins
 The subcutaneous layer next to the skin
 The loose connective tissues of the mucous membranes
 The loose connective tissues of the serous membranes
 Deep lymphatic vessels are large lymphatic vessels that accompany the deep
arteries and veins.
 Collect lymph from skeletal muscles and other organs of the neck, limbs, and trunk, as well as
visceral organs in the thoracic and abdominopelvic cavities
Lymphocytes
 Lymphocytes are the primary cells of the Lymphoid system, and
they are responsible for specific immunity.
 They respond to the presence of
 Invading organisms, such as bacteria and viruses
 Abnormal body cells, such as virus-infected cells or cancer cells
 Foreign proteins, such as the toxins released by some bacteria
Lymphocytes
 Three different classes of lymphocytes in the blood:
 T cells (thymus dependent)
 Cytotoxic T cells
 Helper T cells
 Suppressor T cells
 Memory T cells
 B cells (bone marrow derived)
 Plasma cells
 Memory B cells
 NK cells (natural killer)
Lymphoid Tissues
 Any tissue containing an abundance of lymphocytes
 Diffuse lymphoid tissues—loosely packed lymphocytes within
connective tissue
 Lymphoid nodules—densely packed lymphocytes within loose
connective tissue
 Tonsils
 Aggregated lymphoid nodules (Peyer’s patches)
Lymphoid Organs
 Lymphoid tissues that are separated from surrounding tissues by
a capsule
 Lymph nodes
 Thymus
 Spleen
Aging and the Lymphoid System
 With advancing age, the lymphoid system becomes less effective
at combating disease.




T cells become less responsive to antigens.
The number of helper T cells is reduced.
B cells are less responsive.
Antibody levels do not rise as quickly after antigen exposure.
 The net result is an increased susceptibility to viral and bacterial
infection, and cancer.