Download Chapter 13 The Lymphatic System and Immunity

Chapter 13
The Lymphatic System and
Immunity
THE LYMPHATIC SYSTEM (FIGURE 13-1)
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Lymph—fluid in the tissue spaces that carries protein molecules
and other substances back to the blood
Lymphatic vessels—permit only one-way movement of lymph
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Lymphatic capillaries—tiny blind-ended tubes distributed in tissue
spaces (Figure 13-2)
• Microscopic in size
• Sheets consisting of one cell layer of simple squamous epithelium
• Poor “fit” between adjacent cells results in porous walls
• Called lacteals in the intestinal wall (fat transportation from food to
bloodstream)
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Right lymphatic duct (Figure 13-3)
• Drains lymph from the right upper extremity and right side of head, neck,
and upper torso
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Thoracic duct
• Largest lymphatic vessel
• Has an enlarged pouch along its course, called cisterna chyli
• Drains lymph from about three-fourths of the body (Figure 13-3)
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THE LYMPHATIC SYSTEM
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Lymph nodes
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Filter lymph (Figure 13-4)
 Located in clusters along the pathway of
lymphatic vessels (Figures 13-1, 13-5, and 136)
 Functions include defense and WBC formation
 Flow of lymph: to node via several afferent
lymph vessels and drained from node by a
single efferent lymph vessel
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THE LYMPHATIC SYSTEM
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Thymus
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Lymphoid tissue organ located in mediastinum
Total weight of 35 to 40 g—a little more than an
ounce
Plays a vital and central role in immunity
Produces T-lymphocytes, or T cells
Secretes hormones called thymosins
Lymphoid tissue is largely replaced by fat in
the process called involution
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THE LYMPHATIC SYSTEM
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Tonsils (Figure 13-7)
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Composed of three masses of lymphoid tissue
around the openings of the mouth and throat
• Palatine tonsils (“the tonsils”)
• Pharyngeal tonsils (also known as adenoids)
• Lingual tonsils
Subject to chronic infection
Enlargement of pharyngeal tonsils may impair
breathing
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THE LYMPHATIC SYSTEM
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Spleen
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Largest lymphoid organ in body
 Located in upper left quadrant of abdomen
 Often injured by trauma to abdomen
 Surgical removal called splenectomy
 Functions include phagocytosis of bacteria and
old RBCs; acts as a blood reservoir
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THE IMMUNE SYSTEM
(TABLE 13-1)
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Protects body from pathological bacteria, foreign
tissue cells, and cancerous cells
Made up of specialized cells and molecules
Nonspecific immunity
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Also called innate immunity because it does not require
prior exposure to an antigen
Skin—mechanical barrier to bacteria and other harmful
agents
Tears and mucus—wash eyes and trap and kill bacteria
Inflammation—attracts immune cells to site of injury,
increases local blood flow, increases vascular
permeability; promotes movement of WBCs to site of
injury or infection (Figure 13-8)
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THE IMMUNE SYSTEM
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Specific immunity
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Also called adaptive immunity because of the ability of
the body to recognize, respond to, and remember
harmful substances or bacteria
Types of specific immunity
• Natural immunity—exposure to causative agent is not
deliberate
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Active—active disease produces immunity
Passive—immunity passes from mother to fetus through
placenta or from mother to child through mother’s milk
• Artificial immunity—exposure to causative agent is
deliberate
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Active—vaccination results in immunity
Passive—protective material developed in another
individual’s immune system and given to previously
nonimmune individual
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IMMUNE SYSTEM MOLECULES
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Antibodies
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Protein compounds with specific combining sites
Combining sites attach antibodies to specific antigens
(foreign proteins), forming an antigen-antibody
complex—called humoral, or antibody-mediated,
immunity (Figure 13-9)
Antigen-antibody complexes may:
• Neutralize toxins
• Clump or agglutinate enemy cells
• Promote phagocytosis
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IMMUNE SYSTEM MOLECULES
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Complement proteins
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Group of proteins normally present in blood in inactive
state
Complement cascade
• Important mechanism of action for antibodies
• Causes cell lysis by permitting entry of water through a
defect created in the plasma membrane (Figure 13-10)
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Also perform other functions (examples: attracting
immune cells to a site of infection, activating immune
cells, marking foreign cells for destruction, increasing
permeability of blood vessels)
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IMMUNE SYSTEM CELLS
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Phagocytes—ingest and destroy foreign
cells or other harmful substances via
phagocytosis (Figure 13-11)
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Types
• Neutrophils
• Monocytes
• Macrophages
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Kupffer cells (liver)
Dust cells (lung)
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IMMUNE SYSTEM CELLS
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Lymphocytes
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Most numerous of immune system cells
Development of B cells—primitive stem cells migrate from
bone marrow and go through two stages of development
(Figure 13-12)
• First stage—stem cells develop into immature B cells; takes place
in the liver and bone marrow before birth and in the bone marrow
only in adults; immature B cells are small lymphocytes with
antibody molecules (which they have synthesized) in their plasma
membranes; migrate chiefly to lymph nodes
• Second stage—immature B cell develops into activated B cell;
initiated by immature B cell’s contact with antigens, which bind to
its surface antibodies; activated B cell, by dividing repeatedly,
forms two clones of cells—plasma cells and memory cells—
plasma cells secrete antibodies into blood; memory cells stored in
lymph nodes; if subsequent exposure to antigen that activated B
cell occurs, memory cells become plasma cells and secrete
antibodies
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IMMUNE SYSTEM CELLS
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Lymphocytes (cont.)
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Function of B cells—indirectly, B cells produce humoral
immunity; activated B cells develop into plasma cells; plasma
cells secrete antibodies into the blood; circulating antibodies
produce humoral immunity (Figure 13-12)
Development of T cells—stem cells from bone marrow migrate
to thymus gland (Figure 13-13)
• Stage 1—stem cells develop into T cells; occurs in thymus during
few months before and after birth; T cells migrate chiefly to lymph
nodes
• Stage 2—T cells develop into sensitized T cells; occurs when, and
if, antigen binds to T cell’s surface proteins
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Functions of T cells—produce cell-mediated immunity; kill
invading cells by releasing a substance that poisons cells and
also by releasing chemicals that attract and activate
macrophages to kill cells by phagocytosis (Figures 13-14 and
13-15)
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