chapter 13 the lymphatic system and immunity. copyright © 2005 mosby, inc. all rights reserved. 2...

Chapter 13The Lymphatic System and

Immunity

Copyright © 2005 Mosby, Inc. All rights reserved. 2Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc.

THE LYMPHATIC SYSTEM (FIGURE 13-1)Lymph—fluid in the tissue spaces that carries protein molecules and other substances back to the bloodLymphatic vessels—permit only one-way movement of lymph

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) Right lymphatic duct (Figure 13-3)

Drains lymph from the right upper extremity and right side of 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-fourths of the body (Figure 13-3)

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THE LYMPHATIC SYSTEMLymph nodes Filter lymph (Figure 13-4) Located in clusters along the pathway of

lymphatic vessels (Figures 13-1, 13-5, and 13-6)

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 SYSTEMThymus 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 SYSTEMTonsils (Figure 13-7) 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

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 of

bacteria and old RBCs; acts as a blood reservoir

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THE IMMUNE SYSTEM (TABLE 13-1)

Protects body from pathological bacteria, foreign tissue cells, and cancerous cellsMade up of specialized cells and moleculesNonspecific immunity 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 SYSTEMSpecific immunity 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 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 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

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 (Figure 13-9)

Antigen-antibody complexes may: Neutralize toxins Clump or agglutinate enemy cells Promote phagocytosis

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IMMUNE SYSTEM MOLECULES

Complement proteins 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) 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

Phagocytes—ingest and destroy foreign cells or other harmful substances via phagocytosis (Figure 13-11) Types

Neutrophils Monocytes Macrophages

Kupffer cells (liver) Dust cells (lung)

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IMMUNE SYSTEM CELLSLymphocytes 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 CELLSLymphocytes (cont.) 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

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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chapter 13 the lymphatic system and immunity. copyright © 2005 mosby, inc. all rights reserved. 2...

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