1. Lymphatic System and Immunity
Chapter 14
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2. Learning Objectives Lesson 14.1: Lymphatic System and Immunity
Describe the generalized functions of the lymphatic system and list the primary lymphatic structures.
Discuss the immune system, and compare nonspecific and specific immunity, natural and artificial immunity, and active and passive immunity.
Discuss the major types of immune system molecules and indicate how antibodies and complement proteins function.
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3. Learning Objectives Lesson 14.1: Lymphatic System and Immunity (Cont.)
Discuss the development and functions of B and T cells, and compare and contrast humoral and cell-mediated immunity.
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Lymphatic System
Organization of the lymphatic system
Lymph
Fluid in the tissue spaces that carries protein molecules and other substances back to the blood
Lymphatic capillaries: Tiny blind-ended tubes distributed in tissue spaces (Figure 14-2)
Lymphatic vessels
Permit only one-way movement of lymph
Microscopic in size
Sheets consisting of single cell layer of simple squamous epithelium
Poor “fit” between adjacent cells results in porous walls
Maintaining consistency of the fluid around each body cell is possible only if numerous homeostatic mechanisms function effectively together in a controlled and integrated response to changing conditions.
The lymphatic system is an important partner of the cardiovascular system—both vital components of the circulatory system.
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5. Lymphatic System (Cont.)
Lymphatic vessels
Right lymphatic duct
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
Lymphatic capillaries in the wall of the small intestine are called lacteals. They transport fat from food nutrients to the bloodstream.
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6. Lymphatic System (Cont.)
Drake RL et al: Gray’s anatomy for students, ed 3, Philadelphia, 2015, Churchill-Livingstone.
The lymphatic system is shown in this illustration.
Figure 14-1, A, shows the principal organs of the lymphatic system. The inset (B) shows the major lymphatic ducts draining into lymphatic fluid into veins. Lymph drainage is shown in C.
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7. Role of Lymphatic System in Fluid Homeostasis
Figure 14-2: Fluid filtered from blood plasma that is not reabsorbed by blood vessels drains into lymphatic vessels.
Lymphatic drainage prevents accumulation of too much tissue fluid.
Lymph nodes and other lymphoid structures filter the lymphatic fluid before it is returned to the bloodstream.
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8. Lymphatic System (Cont.)
Lymph nodes (Figure 14-3)
Lymph travels from its origin toward the thoracic or right lymphatic ducts and then to the venous blood; filtered by passing through lymph nodes
Located in clusters along the pathway of lymphatic vessels
Lymphoid tissue
Mass of lymphocytes and related cells inside a lymphoid organ
Provides immune function and development of immune cells
Lymph nodes and other lymphoid organs have functions that include defense and WBC formation
Once the lymph enters the node, it percolates slowly through spaces called sinuses.
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9. Lymphatic System (Cont.)
Lymph nodes
Biological filtration
Flow of lymph to node via several afferent lymphatic vessels and drained from node by a single efferent lymph vessel
The breast has a uniquely extensive network of lymphatic drainage (Figure 14-4)
Lymph exits from the node through a single efferent lymphatic vessel.
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10. Lymphatic Node Function
Figure 14-3 shows lymph node function by depicting a section of skin in which an infection surrounds a hair follicle.
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11. Lymphatic Drainage of the Breast
Figure 14-4: The lymphatic drainage of the breast involves an extensive network of lymph nodes that receive lymph from the breast.
From Ball JW, Dains JE, Flynn JA, et al: Seidel’s guide to physical examination, ed 8, St Louis, 2015, Mosby.
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12. Lymphatic System (Cont.)
Thymus
Small lymphoid tissue organ located in mediastinum
Total weight of 35 to 40 grams; a little more than an ounce
Plays a vital and central role in immunity
Produces T lymphocytes, or T cells
Secretes hormones called thymosins, which influence T-cell development
Thymus tissue gradually replaced by fat and connective tissue (during childhood) in a process called involution
T lymphocytes (T cells) are critical to function of immune system.
The thymus reaches its maximum size at puberty.
By age 60, the lymphoid tissue is about half its maximum size and is virtually gone by age 80 or so.
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13. Lymphatic System (Cont.)
Tonsils
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
The tonsils serve as the first line of defense from the exterior.
Tonsils may be removed if antibiotic therapy is not successful at treating chronic infection.
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14. Location of the Tonsils
Figure 14-5: Small segments of the roof and floor of the mouth have been removed to show the protective ring of tonsils (lymphoid tissue) around the internal opening of the nose and throat.
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15. Lymphatic System (Cont.)
Spleen
Largest lymphoid organ in the body
Located in upper left quadrant of abdomen lateral to the stomach
Often injured by trauma to abdomen
Surgical removal called splenectomy
Functions include phagocytosis of bacteria and old RBCs; acts as a blood reservoir
The spleen has a very large network of reservoir veins.
The spleen may contain more than 500 mL (about 1 pint) of blood.
Other organs can also perform the spleen’s functions, so we can survive without our spleen if necessary.
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Immune System
Functions of the immune system
Protects body from pathological bacteria, foreign tissue cells, and cancerous cells
Made up of defensive cells and molecules
Nonspecific immunity (Tables 14-1 and 14-2)
Often called innate immunity because it does not require prior exposure to an antigen
Inflammatory response: 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 14-6)
The immune system is an interactive network of many organs and billions of freely moving cells and trillions of free-floating molecules in many different areas of body.
The skin and mucous membranes are nonspecific mechanical barriers that prevent entry into the body by bacteria and many other substances.
Tears wash harmful substances from the eyes, and mucus traps foreign material that may enter through the respiratory tract.
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Immune System (Cont.)
Specific immunity (Tables 14-1 and 14-3)
Often called adaptive immunity because of the ability to recognize, respond to, and remember harmful substances or bacteria
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
Specific immunity includes protective mechanisms that confer very specific protection against certain types of threatening microorganisms or other toxic materials.
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Immune System (Cont.)
Specific immunity
Artificial immunity: Exposure to causative agent is deliberate
Active: Vaccination results in activation of immune system
Passive: Protective material developed in another individual’s immune system and given to previously nonimmune individual
With specific immunity, when the body is first attached by a virus or bacteria, disease symptoms may occur as the body fights to destroy the threat.
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19. Immune System Molecules
Cytokines
Chemicals released from cells to act as direct agents of innate, nonspecific immunity
Antibodies
Protein compounds with specific combining sites
Combining sites attach antibodies to specific antigens (foreign proteins), forming an antigen-antibody complex; called humoral immunity, or antibody-mediated immunity (Figure 14-7)
Antigen-antibody complexes may:
Neutralize toxins
Clump or agglutinate enemy cells
Promote phagocytosis
The immune system functions because of adequate amounts of defensive protein molecules and protective cells.
Molecules critical to immune system functioning include cytokines, antibodies, and complement proteins.
A defining characteristic of an antibody molecule is the uniquely shaped concave regions, called combining sites, on its surface.
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Immune System Cells
Phagocytes
Ingest and destroy foreign cells or other harmful substances via phagocytosis (Figure 14-9)
Neutrophils: Short-lived phagocytic cells
Monocytes: Develop into phagocytic macrophages and migrate to tissues
Dendritic cells (DCs): Often found at or near external surfaces
Macrophages and DCs act as antigen-presenting cells (APCs) by displaying ingested antigens on their outer surface to trigger specific immune cells
Antibody molecules that bind to and coat certain foreign particles help macrophages function effectively.
Macrophages and DCs destroy threatening cells and particles, as well as act as APCs.
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21. Phagocytosis of Bacteria
Figure 14-9 shows sequence of steps in the phagocytosis of bacteria.
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22. Immune System Cells (Cont.)
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 (Figure 14-12)
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
B cells are small lymphocytes with antibody molecules (which they have synthesized) in their plasma membranes
After they mature, inactive B cells migrate chiefly to lymph nodes
Lymphocytes are responsible for antibody production and other adaptive immune mechanisms.
The two major types of lymphocytes are B cells and T cells.
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23. Immune System Cells (Cont.)
Lymphocytes
Development of B cells
Second stage: Inactive B cell develops into activated B cell
Initiated by inactive B cell’s contact with antigens, which bind to its surface antibodies, plus cytokines (signal chemicals) from T cells
Activated B cell, by dividing repeatedly, forms two clones of cells – plasma (effector) cells and memory cells
Plasma cells secrete antibodies into blood; memory cells are stored in lymph nodes
If subsequent exposure to antigen that activated B cell occurs, memory cells become plasma cells and secrete antibodies
Each clone of B cells is made up of two kinds of cells: plasma cells and memory cells.
Memory cells can secrete antibodies but do not immediately do so.
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24. Immune System Cells (Cont.)
Lymphocytes
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 14-12)
Development of T cells: Stem cells from bone marrow migrate to thymus gland (Figure 14-13)
First stage: Stem cells develop into T cells
Occurs in thymus during few months before and after birth
T cells migrate chiefly to lymph nodes
Second stage: T cells develop into activated T cells
Occurs when, and if, antigen binds to T cell’s surface proteins and a chemical signal is received from another T cell
T cells are lymphocytes that have undergone their first stage of development in the thymus gland.
T cells form a group of effector cells along with memory cells (effector T cells actively engage in immune responses; memory T cells do not).
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25. Immune System Cells (Cont.)
Lymphocytes
Function of T cells: Produce cell-mediated immunity (Figures and 14-14)
Cytotoxic T cells
Kill infected or tumor cells by releasing a substance that poisons infected or tumor cells
Helper T cells
Release chemicals that attract and activate macrophages to kill cells by phagocytosis
Produce chemicals that help activate B cells
Regulatory T cells
Release chemicals to suppress immune responses
Cell-mediated immunity is resistance to disease organisms that results from the actions of cells, chiefly sensitized cells.
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Questions?
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