Download - Copyright © 2004. Mosby Inc. All Rights Reserved. Slide 0 The Lymphatic System and Immunity
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The Lymphatic
System and
Immunity
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The Lymphatic SystemThe Lymphatic System
• Lymph — fluid in the tissue spaces that carries protein molecules and other substances back to the blood
(Cont’d…)
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The Lymphatic SystemThe Lymphatic System
• Lymphatic vessels—permit only one-way movement of lymph
Lymphatic vessel capillaries—tiny blind-ended tubes distributed in tissue spaces Microscopic in size Sheet consisting of one cell layer of simple
squamous epithelium
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The Lymphatic SystemThe Lymphatic System
(…Cont’d)
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 Has an enlarged pouch along its course,
called cisterna chyli Drains lymph from about three quarters of
the body
(Cont’d…)
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(…Cont’d)
• Lymph nodes:
Filter lymph Located in clusters along the
pathways of lymphatic vessels 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
The Lymphatic SystemThe Lymphatic System
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The Lymphatic SystemThe Lymphatic System(…Cont’d)
• Thymus Lymphoid tissue organ located in
mediastinum = chest 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
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The Lymphatic SystemThe Lymphatic System
(…Cont’d)
• Tonsils:
Composed of three masses of lymphoid tissue around the openings of the mouth and throat Palatine tonsils (“the tonsils”) Pharyngeal tonsils (adenoids) Lingual tonsils
Subject to chronic infection Enlargement of pharyngeal tonsils may
impair breathing
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The Lymphatic SystemThe Lymphatic System
(…Cont’d)
• Spleen:
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
(engulfs and destroys) of bacteria and old RBCs; acts as a blood reservoir
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The Immune SystemThe Immune System
• Spleen:
• Protects the body from pathologic bacteria, foreign tissue cells, and cancerous cells
• Made up of specialized cells and molecules
(Cont’d…)
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The Immune SystemThe Immune System
(…Cont’d)
• Non-immunity:
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
(Cont’d…)
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The Immune SystemThe Immune System
(…Cont’d)
• Specific immunity—ability of body to recognize, respond to, and remember harmful substances or bacteria
• Inherited or unborn immunity—inherited immunity to certain diseases from birth
(Cont’d…)
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The Immune SystemThe Immune System
(…Cont’d)
• Acquired immunity:
Natural immunity — exposure to causative agent is not deliberate
Active—active disease produces immunity
Passive—immunity passes from mother to fetus through placenta or from mother to child through mother’s milk
(Cont’d…)
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The Immune SystemThe Immune System
(…Cont’d)
Artificial immunity — exposure to causative agent is deliberate
Active—vaccination results in immunity
Passive—protective material developed in another individual’s immune system and given to previously non-immune individual
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Immune System MoleculesImmune System Molecules
• Antibodies: 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
Antigen-antibody complexes may: Neutralize toxins Clump or agglutinate enemy cells Promote phagocytosis
(Cont’d…)
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Immune System MoleculesImmune System Molecules
(…Cont’d)
• Complement proteins Group of at least 14 proteins normally
present in blood in inactive state Complement fixation
Important mechanism of action for antibodies
Causes cell lysis by permitting entry of water through a defect created in the plasma membrane
(Cont’d…)
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Immune System CellsImmune System Cells
• Phagocytes — ingest and destroy foreign cells or other harmful substances via phagocytosis:
Types of WBC: Neutrophils – fights infection/inflammation
Monocytes – first line defense to inflammation/ eats foreign antigens
Macrophages – a monocyte that has left the blood circulation and has settled in the tissue. Found in large quantities in the spleen, lymph nodes and tonsil
(Cont’d…)
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Macrophages
Neutrophils Monocytes
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Immune System CellsImmune System Cells
• Lymphocytes:
Most numerous of immune system cells
Development of B cells — primitive stem cells migrate from bone marrow and go through two stages of development
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Immune System CellsImmune System Cells
• Lymphocytes:
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
(Cont’d…)
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Immune System CellsImmune System Cells
• Lymphocytes: 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 CellsImmune System Cells
(…Cont’d)
• Lymphocytes:
Function of B cells—indirectly, B cells produce humoral (fluid or semifliud in the body) immunity; activated B cells develop into plasma cells; plasma cells secrete antibodies into the blood; circulating antibodies produce humoral immunity
(Cont’d…)
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Immune System CellsImmune System Cells
• Lymphocytes Development of T cells — stem cells from
bone marrow migrate to thymus gland
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 cells’ surface proteins
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A T-cell (orange) killing a cancer cell (mauve).
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Immune System CellsImmune System Cells
• Lymphocytes:
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