Copyright © Mosby Inc. All Rights Reserved. Slide 0 The Lymphatic System and Immunity

Copyright © Mosby Inc. All Rights Reserved. Slide 1 The Lymphatic System Lymph — fluid in the tissue spaces that carries protein molecules and other substances back to the blood (Cont’d…)

Copyright © Mosby Inc. All Rights Reserved. Slide 2 The 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

Copyright © Mosby Inc. All Rights Reserved. Slide 3 The 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 4 (…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 System

Copyright © Mosby Inc. All Rights Reserved. Slide 5 The 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

Copyright © Mosby Inc. All Rights Reserved. Slide 6 The 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

Copyright © Mosby Inc. All Rights Reserved. Slide 7 The 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

Copyright © Mosby Inc. All Rights Reserved. Slide 8

Copyright © Mosby Inc. All Rights Reserved. Slide 9 The Immune System Spleen: Protects the body from pathologic bacteria, foreign tissue cells, and cancerous cells Made up of specialized cells and molecules (Cont’d…)

Copyright © Mosby Inc. All Rights Reserved. Slide 10 The 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 11 The 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 12 The 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 13 The 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

Copyright © Mosby Inc. All Rights Reserved. Slide 14 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  Antigen-antibody complexes may:  Neutralize toxins  Clump or agglutinate enemy cells  Promote phagocytosis (Cont’d…)

Copyright © Mosby Inc. All Rights Reserved. Slide 15 Immune 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 16 Immune 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 17 Macrophages Neutrophils Monocytes

Copyright © Mosby Inc. All Rights Reserved. Slide 18 Immune 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

Copyright © Mosby Inc. All Rights Reserved. Slide 19 Immune 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 20 Immune 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

Copyright © Mosby Inc. All Rights Reserved. Slide 21 Immune 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…)

Copyright © Mosby Inc. All Rights Reserved. Slide 22 Immune 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

Copyright © Mosby Inc. All Rights Reserved. Slide 23 A T-cell (orange) killing a cancer cell (mauve).

Copyright © Mosby Inc. All Rights Reserved. Slide 24 Immune 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