1. Chapter 20: Lymphatic System

2. OVERVIEW
Two most important functions: maintain fluid balance in the internal environment and immunity
Third function is to collect absorbed fat from the intestines and transport it to the systemic veins
Lymphatic system: component of the circulatory system; composed of lymph, lymphatic vessels, and isolated structures containing lymphoid tissue: lymph nodes, aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow

3. LYMPH AND INTERSTITIAL FLUID
Lymph (lymphatic fluid)
Clear, watery fluid found in the lymphatic vessels
Closely resembles blood plasma in composition but has a lower percentage of protein
Interstitial fluid
Complex, organized fluid that fills the spaces between the cells and is part of the extracellular matrix
Resembles blood plasma in composition with a lower percentage of protein

4. LYMPHATIC VESSELS (cont.)
Structure of lymphatic vessels
Similar to veins except lymphatic vessels have thinner walls, have more valves, and contain lymph nodes
Functions of the lymphatic vessels
Remove high-molecular-weight substances and particulate matter from interstitial spaces

5. CIRCULATION OF LYMPH
From lymphatic capillaries, lymph flows through progressively larger lymphatic vessels to reenter blood at the junction of the internal jugular and subclavian veins

6. LYMPH NODES Structure of lymph nodes
Lymph nodes are oval-shaped structures enclosed by a fibrous capsule (Figure 20-9)
Nodes are a type of biological filter
Once lymph enters a node, it moves slowly through sinuses to drain into the efferent exit vessel

7. LYMPH NODES (cont.) Locations of lymph nodes
Most lymph nodes occur in groups
Groups with greatest clinical importance are preauricular lymph nodes;
submental and submaxillary groups;
and superficial cervical, superficial cubital, axillary, iliac, and inguinal lymph nodes

8. LYMPH NODES (cont.) Lymph nodes perform two distinct functions Defense
Filtration
Mechanical filtration: physically stopping particles from progressing further in the body
Biological filtration: biologic activity of cells destroys and removes particles
Hematopoiesis: lymphoid tissue is the site for the final stages of maturation of some lymphocytes and monocytes

9. LYMPHATIC DRAINAGE OF THE BREAST
Clinically important because cancer cells and infections can spread along lymphatic pathways to lymph nodes and other organs of the body
Distribution of lymphatics in the breast
Drained by two sets of lymphatic vessels
Lymphatics that drain the skin over the breast with the exception of the areola and nipple
Lymphatics that drain the underlying substance of the breast, as well as the skin of the areola and nipple

10. LYMPHATIC DRAINAGE OF THE BREAST (cont.)
Lymph nodes associated with the breast
More than 85% of the lymph from the breast enters the lymph nodes of the axillary region
Remainder of lymph enters lymph nodes along the lateral edges of the sternum

11. TONSILS
Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring
Palatine tonsils: located on each side of the throat
Pharyngeal tonsils: located near the posterior opening of the nasal cavity
Lingual tonsils: located near the base of the tongue
Tubal tonsils: located near the openings of the auditory (eustachian) tubes
Protect against bacteria that may invade tissues around the openings between the nasal and oral cavities;
bacteria are trapped in tonsillar crypts and put in close contact with immune system cells

13. THYMUS Function of the thymus Location and appearance of the thymus
Primary central organ of lymphatic system
Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is replaced by fat
Structure of the thymus
Pyramid-shaped lobes are subdivided into small lobules
Each lobule is composed of a dense cellular cortex and an inner, less-dense medulla
Function of the thymus
Plays vital role in immunity mechanism
Source of lymphocytes before birth
Shortly after birth, secretes thymosin and other regulators, which enables lymphocytes to develop into T cells

15. SPLEEN
Location: in the left hypochondrium, directly below the diaphragm, above the left kidney and descending colon and behind the fundus of the stomach
Structure of the spleen
Ovoid in shape
White pulp: dense masses of developing lymphocytes
Red pulp: near outer regions, composed of cords of white blood cells and related cells surrounded by sinusoids

16. SPLEEN (cont.) Functions of the spleen
Defense: remove microorganisms from the blood and phagocytose them
Hematopoiesis: monocytes and lymphocytes complete their development in the spleen
Red blood cell and platelet destruction: macrophages remove worn-out red blood cells and imperfect platelets and destroy them by phagocytosis; also salvage iron and globin from destroyed red blood cells
Blood reservoir: pulp of spleen and its sinuses store blood

17. CYCLE OF LIFE: LYMPHATIC SYSTEM
Dramatic changes throughout life
Organs with lymphocytes appear before birth and grow until puberty
Postpuberty
Organs atrophy through late adulthood
Shrink in size
Become fatty or fibrous
Spleen: develops early, remains intact
Overall function maintained until late adulthood
Later adulthood
Deficiency permits risk of infection and cancer
Hypersensitivity: likelihood of autoimmune conditions

18. THE BIG PICTURE: THE LYMPHATIC SYSTEM AND THE WHOLE BODY
Lymphatic system drains away excess water from large areas
Lymph is conducted through lymphatic vessels to nodes, where contaminants are removed
Lymphatic system benefits the whole body by maintaining fluid balance and freedom from disease