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Chapter 15

The Lymphatic System

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Introduction

• Transports lymph through lymphatics

• Lymphatics: lymph capillaries and vessels

• Controls body fluid

• Destroys harmful microorganisms

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Introduction

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The Functions of the System and the Structure and

Functions of the Lymphatic Vessels

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Introduction

• Drain interstitial fluid from tissue spaces– Prevent edema

• Transport digested fat to blood– Lacteals: special lymphatics in small intestine– Chyle: milky lymph in lacteals

• Develop immunities

• Produce lymphocytes

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Lymphatic Vessels

• Lymph capillaries: blind-end tubes

• Lymph capillaries are located between cells

• Lymph capillaries unite to form lymphatics

• Lymphatics converge into two main channels– Thoracic duct and right lymphatic duct

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Lymphatic Vessels (cont’d.)

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Lymph Nodes

• Found along lengths of lymphatics

• Efferent: exit lymph node at the hilum

• Afferent: enter lymph node at various locations

• Trabeculae: divide the node into compartments

• Germinal centers of compartments produce lymphocytes

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Lymph Nodes

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Lymph Nodes

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Lymph Circulation

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Lymph Circulation (cont’d.)

• Interstitial fluid: plasma in interstitial spaces

• Lymph: interstitial fluid in lymph capillaries– Passes into lymphatics

• Lymphatics join to form lymph trunks

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Lymph Circulation (cont’d.)

• Lymph circulation maintained by– Normal skeletal muscle contractions

• Compresses lymph vessels and forces lymph in one direction

– Respiratory or breathing movements– Smooth muscle in lymphatic vessels

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Lymph Circulation (cont’d.)

• Lymph trunks – Lumbar: drains lower extremities and pelvis– Intestinal: drains abdominal region– Bronchomediastinal and intercostal: drain

thorax– Subclavian: drains upper extremities– Jugular: drains head and neck

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Lymph Circulation (cont’d.)

• Individual trunks drain into two main trunks– Thoracic duct: drains into the left subclavian

vein– Right lymphatic duct: drains into the right

subclavian vein

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Lymph Circulation (cont’d.)

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The Organs of the Lymphatic System

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The Organs of the Lymphatic System (cont’d.)

• Tonsils– Palatine, pharyngeal, and lingual– Protect the nose and oral cavity

• Thymus: lymphocyte production and maturation

• Peyer’s patches: found in walls of small intestine

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The Organs of the Lymphatic System (cont’d.)

• Spleen– Largest mass of lymphatic tissue– Phagocytizes worn-out RBCs and platelets

• Recycles hemoglobin

– Produces lymphocytes and plasma cells– Stores blood for release during hemorrhage

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• External view of the Spleen

The Organs of the Lymphatic System (cont’d.)

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Immunity

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Immunity (cont’d.)

• Ability of body to resist– Infection from pathogens– Damage from foreign substances and harmful

chemicals

• Humoral immunity– B lymphocytes: produce antibodies

• Fight circulating bacteria and viral infections• Become plasma cells when they enter tissues

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Immunity (cont’d.)

• Cellular immunity– T lymphocytes

• Come from thymus glands• Fight intracellular viruses, fungi, parasites, cancer

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Antigens and Antibodies

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Antigens and Antibodies (cont’d.)

• Antigen: foreign protein in our body

• B lymphocytes – Produce antibodies in response to antigens– Antibodies bind to specific antigen– Antigens precipitate– Phagocytic WBCs eat the antigens

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Antigens and Antibodies (cont’d.)

• Antibody morphology– Four amino acid chains linked by disulfide

bonds• Heavy and light chains

– Y-shaped molecule– Binding sites at tips of Y– Stem of the Y is always constant

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Antigens and Antibodies (cont’d.)

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Antigens and Antibodies (cont’d.)

• Antibody types– IgG: attacks viruses, bacteria, and toxins;

activates complement– IgA: found in exocrine gland secretions– IgM: response to bacteria or food antigens– IgD: found on surface of B lymphocytes– IgE: associated with allergic reactions

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Antigens and Antibodies (cont’d.)

• Active immunity: B cells contact antigen and produce antibodies– Natural active: exposure to infection– Artificial active: vaccine

• Passive immunity– Natural passive: maternal antibodies to fetus– Artificial passive: gamma globulin

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Cells of the Immune Response and Other

Defenses

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Cells of the Immune Response and Other Defenses (cont’d.)

• B cells: antigen – Antibody binding

• Plasma cells: replicated B cells

• Helper T cells: stimulate production of– Killer T cells– More B cells

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Cells of the Immune Response and Other Defenses (cont’d.)

• Killer T cells: – Attack virus-invaded body cells– Attack cancer cells– Reject body grafts

• Memory cells: descendents of activated T and B cells

• Suppressor T cells: slow down activities of B and T cells

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Cells of the Immune Response and Other Defenses (cont’d.)

• Macrophages – Engulf and digest antigen– Present them to T cell for recognition

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Cells of the Immune Response and Other Defenses (cont’d.)

• Lymphokines: chemicals released by sensitized T cells

• Monokines: chemicals released by activated macrophages

• Skin: mechanical barrier– Acid mantle, sebum

• Lysozyme: (tears and saliva) attacks bacteria

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Cells of the Immune Response and Other Defenses (cont’d.)

• Mucous membranes: trap microorganisms and debris

• Hydrochloric acid: (stomach) destroys microorganisms

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Summary

• Discussed the functions of the immune system

• Described lymph and its flow through the body

• Discussed the functions of the spleen and tonsils

• Described the different types of immunity

• Discussed the immune response