CMU HSC 214 - Chapter 10 The Lymphatic System

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Exam 2 NotesChapter 10 The Lymphatic SystemGeneral Functions of the Lymphatic System1) Surveillance and Defense-Lymphocytes essential to bodies normal defense mechanism produced and stored in lymphatic organs-Lymphoid tissues and organs either primary or secondary-Primary lymphoid structures -contain stem cells that divide to produce daughter cells that differentiate into B,T, or NK cells-Bone marrow and thymus of the adult are primary structures-Secondary Lymphoid Structures-Most immune response begins here-where immature or activated lymphocytes divide to produce additional lymphocytes of the same type-T-Lymphocytes-B-lymphocytes-Marcrophages2) Draining Tissue Spaces of Interstitial Fluid and General Body Fluid Balance-BP at proximal end of a capillary is aprox. 35 mm Hg-BP tends to force water and solutes out of plasma into interstitial fluid along every systemic capillary-Total vol. 3.6 L or 72% of total blood volume enters interstitial fluid each day-Under normal circumstances goes unnoticed-Continual movement of fluid that helps eliminate regional differences in composition of fluid-A break would lead to a fatal decline in blood volume3) Transportation of Hormones, Nutrients, and Waste-Lipids absorbed by digestive tract are carried to the blood stream by lymph vessels rather than by absorption across capillary wallsComponents of the Lymphatic SystemLymphatic Capillaries-Lymphatic network begins with-aka terminal lymphatics-form a complex network within peripheral tissues-Larger in diameter and sectional view then vascular tissues-thinner walls because endothelial cells lack continuous basal lamina-flat or irregular outline-have collagenous anchoring filaments that extend from incomplete basal lamina to surrounding CT-keep passageways open when interstitial pressures increase-endothelial cells overlap instead of being tightly bound together-region of overlap act as one way valve -permits passage of fluid into lymphatic capillary but prevents escape-endothelial cells have pores allowing lymphatic capillaries to fill with fluid-gaps allow for viruses to be absorbed-numerous in CT deep to skin and mucous membranes and in mucousa and submucosa of digestive systemLymphatic Vessels-Often called Lymphatics-Carry lymph from peripheral tissues to the venous system-Range in size from small-diameter lymphatic capillaries to large diameter lymphatic ductsValves-Larger lymphatics have valves like veins -Valves are quite close together and at each valve lymphatic vessel bulges-gives a beaded appearance-prevent backflow of lymph within lymphatic vessels, especially the limbs-Lymphatic vessel blocked or its valves damage lymphatic drainage slows or ceases-fluid continues to leave vascular capillaries lymphoid system unable to remove-interstitial fluid volume and pressure increase causing lymphedemaLymph-fluid similar to plasma but with lower concentration of proteinsLymph nodes-small oval lymphoid organs -covered by dense fibrous CT-fibrous extensions from capsule extend partway into inferior of node (trabecule)Spleen-largest lymphoid organ in the body-lies along the curving lateral border of the stomach between 9th and 11th ribs on left side-attached to lateral border of the stomach by gastrosplenic ligament-spleen red from blood-Performs functions for blood comparable to those performed by lymph nodes for lymph1) removal of abnormal blood cells and other components through phagocytosis2) storage of iron recycled from broke down rbcs3) initiation of immune response by B cells and T cells in response to antigens in blood-lies wedged between stomach, the left kidney, and muscular diaphragm-Splenic blood vessels and lymphatics communicate with spleen on visceral surface at the hilium-splenic artery and vein, and lymphatics draining spleen attached at the hilium-red pulp form splenic cords which contain large quantities of rbcs-while pulp form lymphoid nodulesThymus gland-lies posterior to the manubrium of the sternum in the superior portion of mediastinum -has a nodular consistency and pinkish coloration-reaches greatest size in 1st year or two after birth (relative to body)-maximum absolute size during puberty-after decreases in size and functional cells are replace by CT (involution)-capsule that covers divides it into two lobes-fibrous partitions (septa) divide lobes into lobules-each lobule consists dense outer cortex-cortex contains lymphoid cells that divide rapidly-producing daughter cells that mature into T cells and migrate to medulla-during maturation process any T cells that are sensitive to antigens are destroyed- -surviving T cells eventually enter one of specialized blood vessels in the region-while in the thymus T cells don’t participate in immune response-Capillaries resemble capillaries of CNS-don’t permit free exchange between interstitial fluid and the circulation-blood-thymus barrier prevent premature stimulation of developing T cells by circulating antigens-reticular cells among lymphocytesLymphatic Flow PattersMicroscopic Connection to the Circulatory System-dumps into right and light subclavian veins Macroscopic Connection to the Circulatory System (Collecting Vessels)Lymphatic Trunks-Within the trunk, superficial and deep lymphatics converge to form these large vessels-Include: Lumbar Trunks, Intestinal Trunks, Bronchomediastinal Trunks, Subclavian Trunks, Jugular Trunks-Empty into two large collecting vessels, the lymphatic ducts that deliver lymph to venous circ.Thoracic Duct-Collects lymph from both sides of the body inferior to the diaphragm and from left side superiorto the diaphragm-Begins inferior to the diaphragm at level of L2-Inferior segment lies anterior to vertebral column-Penetrates aorta and ascends along left side of vertebral column to level of clavicle-after collecting lymph from left bronchiomediastinal, subclavian and jugular trunks-empties into left subclavian vein near base of left internal jugular vein-lymph collected from left side of head, neck, and thorax as well as entire body Inferior to the diaphragm reenters the venous system this wayCisterna Chyli-Expanded saclike chamber at base of thoracic duct-receives lymph from the inferior region of the abdomen, pelvis, and lower limbs through right and left lumbar trunks and intestinal trunksRight Lymphatic duct-Relatively small duct that collect lymph from right side of body superior to diaphragm-receives lymph from smaller lymphatic vessels that converge in region of the right

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