Ch. 16 Lymphatic System Flashcards Preview

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Flashcards in Ch. 16 Lymphatic System Deck (20):

Function of Lymphatic System

1. drains excess interstitial fluid: return fluid to the blood
2. transports dietary lipids: lipids and lipid soluble vitamins absorbed by the gastrointestinal tract and return to the blood
3. carries out immune responses: with help of macrophages, T & B cells, recognize foreign cells, toxins, cancer cells; B cells produce antibodies and T cells recognize viruses and virally-infected cells, and cancer cells


Lymphatic Capillaries

- lymphatic capillaries are slightly larger in diameter than blood capillaries
- permits interstitial fluid to flow blood capillaries to lymphatic capillaries
- ends of endothelial cells that make up the wall of a lymphatic capillary overlap
- pressure difference between blood interstitial fluid & lymph permit lymph to flow in lymphatic capillaries
- anchoring filaments with elastic fibers attach lymphatic endothelial cells to surrounding tissue


Lacteals and Chyle

- specialized lymphatic capillaries in small intestine called Lacteals, carry dietary lipids into lymphatic vessels & then into the blood
- lymph draining from the small intestine appear creamy white and referred to as chyle
- elsewhere, lymph is a clear pale-yellow fluid


Lymphatic Vessels and Lymph Circulation

- lymphatic vessels begin as lymphatic capillaries
- vessels are closed at one end and located in the spaces between cells
- lymphatic capillaries unite to form larger lymphatic vessels, which resemble veins in structure but have thinner walls and more valves
- at intervals along lymphatic vessels, lymph flows through lymph nodes
- tissue lack lymphatic capillaries include avascular tissues, central nervous system, portions of the spleen and red bone marrow


Sequence of Fluid Flow

blood capillaries- lymphatic capillaries- afferent lymphatic vessel- lymph node (immune response)- efferent lymphatic vessel- venous system
**lymph is repeatedly examined for the presence of foreign or pathogenic materials in lymph nodes


Lymph Trunks

- lymph passes from lymphatic capillaries into lymphatic vessels & then through lymph nodes
- vessels unite to form lymph trunks
1. Lumbar trunks: drain lymph from the free lower limbs, wall & viscera of pelvis, kidneys, adrenal glands & abdominal wall
2. Intestinal trunks: drains lymph from stomach, intestines, pancreas, spleen, and part of liver
3. Bronchomediastinal trunk: drain lymph from the thoracic wall, lung, and heart
4. Subclavian trunks: free upper limbs
5. Jugular trunks: drain head and neck


Lymphatic Trunks & Ducts Flow

lymphatic trunks- lymphatic ducts
- right lymphatic duct: return from rt. subclavian, rt. jugular & lymph from rt. Bronchomediastinal and intestinal trunk
- left lymphatic/thoracic trunk: duct begins as a dilation called cisterna chyli, receive the right and left lumbar trunk and jugular, subclavian & bronchomediatinal trunks, head neck, chest, free left limbs and entire body inferior to the ribs


Formation & Flow of Lymph

- excess filtered fluid (3 liters per day) drains into lymphatic vessels
- plasma proteins are too large to leave blood vessels, interstital fluid contains only a small amount of protein
- proteins that do not leave blood plasma cannot return to the blood directly by diffusion because the concentration gradient opposes such movement
- proteins can move readily through the more permeable lymphatic capillaries into lymph
- important function of lymphatic vessels is to return lost plasma proteins to the blood stream


Regulation of Lymph Flow

skeletal muscle pump: "milking action" of skeletal muscle contractions compresses lymphatic vessels and forces lymph toward junction of the internal jugular and subclavian veins
respiratory pump: act of inhalation and exhalation create pressure difference between abdominal and thoracic regions that allows lymph to flow towards venous system


Lymphatic Organs and Tissues

- lymphatic organ and tissues, widely distributed throughout the body, classified into two groups on their functions
primary lymphatic organs: sites where stem cells divide and become immunocompetent ex. red bone marrow and thymus
- red bone marrow give rise to mature, immunocompetent B cells and to pre-T cells, which become T cells in thymus
secondary lymphatic organs and tissues: sites where most immune responses occur ex. lymph nodes, spleen, lymphatic nodules



- bilobed organ located in mediastinum
- hight content of lymphoid tissue and rich blood supply, thymus has reddish appearance
- enveloping layer of connective tissue holds the two lobes together, connective tissue capsule encloses each lobe
- extensions of the capsule, trabeculae, penetrate inward and divide each lobe into lobules


Cortex and Medulla

- T cells, dendritic cells, epithelial cells (maturation of T cells & produce thymic hormones) and macrophages (clear debris of dead and dying cells)
- mature T cells, epithelial cells, dendritic cells, and macrophages
clusters are called thymic corpuscles= where T cell death occurs


Thymic Lobule

- consists of cortex and medulla
- immature T cells migrate from red bone marrow to cortex of thymus, where they proliferate and begin to mature
- dendritic cells, assist the maturation process; dendritic cells in lymph nodes, play a key role in immune responses
- thymic (Hassall's) corpuscles may serve as sites of T cell death in the medulla
- T cells that leave the thymus via the blood are carried to lymph node, spleen, and other lymphatic tissues where they colonize parts of these organs and tissues


Lymph Nodes

- distributed in mammary glands, axillae, and groin area
- covered by a capsule of dense connective tissue
- capsule extend & become trabeculae, divide into node into compartments, give support, and provide a route for blood vessels into interior of a node
- capsule, trabecular, reticular fibers, and fibroblasts constitute the stroma, of a lymph node
- parenchyma of a lymph node is divided into a superficial cortex and a deep medulla
- within outer cortex are aggregates of B cells called lymphatic nodules (follicles), consisting chiefly of B cells


Lympthatic System

- 4 components: lymph, lymphatic vessels, lymphoid organs (spleen, thymus, lymph nodes), and lymphocytes
- circulation of body fluids and defend body against disease-causing agents
- blood plasma is filter through blood capillary walls to form interstitial fluid; after pass through lymphatic vessels its called lymph
- intersitital fluid and lymph are similar
- lymphatic tissue are composed of reticular connective that contains large numbers of lymphocytes


Lymph nodes- B cells

- in outer cortex are secondary lymphatic nodules, which form in response to challenge by an antigen and are sites of plasma cell and memory B cell formation
- After B cells in primary lymphatic nodule recognize an antigen, primary lymphatic nodule develops into a secondary lymphatic nodule
- center of a secondary lymphatic nodule contains a germinal center; which houses B cells, follicular dendritic cells and marcophages
- when fdc "present" an antigen, B cells proliferate and develop into antibody-producing plasma cells or memory B cells
- memory B cells persist after an immune response and remember having encountered a specific antigen


Flow of Lymph Node

- flow in one direction only
- enters through afferent lymphatic vessels, which penetrate convex surface of the node at several points
- within the node, lymph enters sinuses, series of irregular channels that contain branching recticular fibers, lymphocytes and macrophages
- from afferent lymphatic vessels, lymph flows into the subscapular sinus
- through trabecular sinuses, which extend through cortex parallel to the trabeculae, and into medullary sinuses
- medullary sinuses drain into one or two efferent lymphatic vessels; efferent lymphatic vessels emerge from one side of the lymph node at a slight depression called a hilum; blood vessels also enter and leave the node at the hilum



- largest single mass of lymphatic tissue in the body; soft organ
- spleen has a hilum; through it pass the large tortuous splenic artery and splenic vein, along with efferent lymphatic vessels and sympathetic nerves that regulate the blood flow in the vessels
- dense connective tissue surrounds speel and is covered by serous membrane, visceral peritoneum
- trabeculae extend inward from the capsule; capsule plus trabeculae reticular fibers ,and fibroblasts consitute the stroma of a spleen
- parenchyma of the spleen consists of two different kinds of tissue called white pulp and red pulp


White Pulp vs Red Pulp

- lymphatic tissue consisting of lymphocytes and macrophages arranged around central arteries
- blood filled venous sinuses; splenic cords: red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes
- red pulp spleen performs: removal by macrophages of ruptured, worn out or defective blood cells and platelets; storage of platelets, up to one-third of body's supply; production of blood cells during fetal life


Lymphatic Nodules

- masses of lymphatic tissue that are not surrounded by a capsule
- scattered throughout lamina propria of mucous membrane lining the gastrointestinal, urinary, reproductive tracts, and the respiratory airways, lymphatic nodules in these areas are also referred to as mucous-associated lymphatic tissue (MALT)
- small and solitary, some occur in multiple large aggregations
ex. tonsils in the pharyngeal region and the aggregated lymphatic follicles in the ileum; can also occur in appendix