Ch. 16 Lymphatic System

Question 1

Function of Lymphatic System

Answer 1

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

Question 2

Lymphatic Capillaries

Answer 2

• 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

Question 3

Lacteals and Chyle

Answer 3

• 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

Question 4

Lymphatic Vessels and Lymph Circulation

Answer 4

• 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

Question 5

Sequence of Fluid Flow

Answer 5

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

Question 6

Lymph Trunks

Answer 6

• 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

Question 7

Lymphatic Trunks & Ducts Flow

Answer 7

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

Question 8

Formation & Flow of Lymph

Answer 8

• 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

Question 9

Regulation of Lymph Flow

Answer 9

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

Question 10

Lymphatic Organs and Tissues

Answer 10

• 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

Question 11

Thymus

Answer 11

• 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

Question 12

Cortex and Medulla

Answer 12

• 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

Question 13

Thymic Lobule

Answer 13

• 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

Question 14

Lymph Nodes

Answer 14

• 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

Question 15

Lympthatic System

Answer 15

• 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

Question 16

Lymph nodes- B cells

Answer 16

• 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

Question 17

Flow of Lymph Node

Answer 17

• 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

Question 18

Spleen

Answer 18

• 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

Question 19

White Pulp vs Red Pulp

Answer 19

• 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

Question 20

Lymphatic Nodules

Answer 20

• 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