LYMPHOID SYSTEM General aspects Consists of organs that are made of lymphoid tissue; Immune defense Breakdown of red blood cells. 1 Sinusoids In place of capillaries Endothelium; often fenestrated More permeable to cells and molecules Irregular pathways from arterioles Sinusoids and venous sinuses flows directly into the sinusoids then into venules or small veins. 2
diameter > capillaries several RBCs diameter Slow blood flows more time for exchange Endothelium often fenestrated or discontinuous contact of the blood with the cells of the tissues sinusoids and venous sinuses 3 Sinusoids and venous sinuses In marrow spaces, adrenal cortex, anterior pituitary gland, spleen continuous wall Liver sinusoids ; discontinuous wall, fenestrations Spleen, moderately discontinuous 4
Venous sinuses and sinusoids sinusoids and venous sinuses Venous side of the circuit in place of venules sequence of flow is arterioles -> capillaries -> venous sinusoids/sinuses-> small or large veins Continuous endothelium Spleen and erectile tissue of external genitalia. Later. Venus sinuses drain into large veins. Examples: Coronary sinus: drains the heart into the right atrium Superior sagittal sinus; drains brain into general circulation 5 LYMPHATIC VESSEL SYSTEM Lymphatic vessels. Contain lymph (lymph fluid) similar to GS of CT ~blood plasma ; lower [protein solutes] 6
LYMPHATIC VESSEL SYSTEM Function Primary Return water and other small molecules to blood; lost at the capillaries. Loss would lead to drop in BV and BP ; shock and finally death. Secondary carry B-lymphocytes and immunoglobulins from lymphoid organs to the blood. 7 LYMPHATIC VESSEL SYSTEM Lymph capillaries Smallest Lacteals (singular: lacteal) W/i small intestine villi Lymph fluid is milky due to globules of triglycerides Lymph capillaries are blindended Hard to recognize due lack of erythrocytes Resemble large-diameter capillaries w/o RBCs 8
LYMPHATIC VESSEL SYSTEM Wall is endothelium; more permeable to molecules and cells than capillaries. 9 LYMPHATIC VESSEL SYSTEM Lymph capillaries merge into larger vessels leave the organ merge into larger lymphatic vessels. Pressure and flow rate of lymph fluid < veins lymphatic vessels thinner walls, t. media (essentially SMT), t. adventitia (dense interwoven CT) 10
LYMPHATIC VESSEL SYSTEM Thoracic duct largest lymphatic vessel;, Drains all of body below diaphragm. Left side above diaphragm. Right lymphatic vessel Drains the right arm and right side of head and neck the right subclavian vein Lymphatics have one-way valves Muscle contraction of an adjacent skeletal will push the lymph fluid towards brachiocephalic vein. 11 LYMPHATIC VESSEL SYSTEM Appearance of small lymphatic vessels Unusually thin-walled vein contain lymphocytes; no erythrocytes. Sometimes protein solutes aggregate into granules: artifact of slide prep. 12
LYMPHOID SYSTEM: Nodes Lymph node Small organs, kidney shaped (mm to 2 cm) Especially abundant in 4 body areas. 1- Inguinal 2- Mesentery 3- Axillary 4- Cervical 13 LYMPHOID SYSTEM: Nodes Outer dense CT capsule Septa of dense CT extends into center; Called trabeculae (singular: trabecula). Blood vessels are within trabeculae. Rest is lymphoid tissue. Trabeculae divide the interior into sections; not completely separated. Node has a cortex and a medulla. 14
LYMPHOID SYSTEM: Nodes Cortex is dense lymphoid tissue Each section has a germinal center (less dense lymphoid tissue); cells around the germinal center are large; variant of dense lymphoid tissue; called the cortical stroma. 15 LYMPHOID SYSTEM: Nodes Medulla ; interior; contains extensions of cortical trabeculae. on either side of each trabecula is a layer of loose lymphoid tissue called a medullary sinus; medulla contains extensions of the cortical stroma layers of dense lymphoid tissue are called medullary cords. Loose lymphoid tissue has more matrix volume than has dense lymphoid tissue; more typical of CT 16
LYMPHOID SYSTEM: Nodes Lymph fluid passes into a lymph node percolates through the tissue bacteria, viruses, cell fragments, and toxins produced by immune cells(macrophages and T-lymphocytes) are removed Maturing lymphocytes and immunoglobulins added to the fluid. Lymph fluid leaves the lymph node via larger lymphatic vessels 17 LYMPHOID SYSTEM: Nodes Several afferent lymphatic vessels carry lymph into nodes, from lymphatic capillaries. Larger, efferent lymphatic vessels carry lymph fluid away at the hilus. Vein carries blood away and an artery may carry blood into the node. 18
LYMPHOID SYSTEM: Nodes "Swollen glands Pathogen (bacterium or virus) may heavily infect node; becomes swollen, and painful. Not a real gland 19 Spleen LYMPHOID SYSTEM: Spleen Unpaired organ in the abdominal mesentery; adjacent to the stomach. Erythrocyte production (erythropoiesis) during embryonic life in humans in adults; organ of destruction of old erythrocytes; also marrow and liver. 20
LYMPHOID SYSTEM: Spleen Spleen Outer capsule of dense CT (in humans) or fibromuscular tissue smooth muscle fibers scattered among the collagen fibers, with scattered fibroblasts; in some other mammals Septa (singular: septum) of dense CT (or fibromuscular tissue) extend into the interior of the organ from the capsule (trabeculae) 21 Within trabeculae LYMPHOID SYSTEM: Spleen Larger blood and lymphatic vessels: trabecular arteries, veins and lymphatic vessels. Trabeculae divide the interior into several incompletely separated regions. 22
LYMPHOID SYSTEM: Spleen Trabecular arteries branch to arteries that leave the trabeculae and enter the lymphoid tissue of the organ Sheathed arteries and arterioles Small muscular arteries and arterioles; covered by dense lymphoid tissue ; several times the diameter of the artery or arteriole Vessels in the center of the sheath; called central arteries and arterioles. 23 LYMPHOID SYSTEM: Spleen White pulp Masses of dense lymphoid tissue in the interior of the organ May contain germinal centers present; called lymphatic nodules. In life, tissue has a whitish color. Red pulp Remaining volume is loose lymphoid tissue: contains abundant non-circulating erythrocytes; Erythrocytes are relatively deoxygenated; dark red. 24
LYMPHOID SYSTEM: Spleen Red pulp has abundant sinusoids and venous sinuses Endothelial cells are not in contact with each other. Gaps allow the non-circulating erythrocytes to enter easily and re-enter circulation. Endothelium only. Blood in the red pulp sinusoids and venous sinuses flows next into venules and veins in the red pulp, lead to the trabecular veins, drain into splenic vein 25 Tonsils General aspect: LYMPHOID SYSTEM: Tonsils Pharyngeal lymphoid organs lie directly against the lumenal epithelium of the pharynx Immune defense against bacteria, viruses, etc., that enter the mouth and nasal cavities from outside; three types pharyngeal, palatine tonsils, lingual tonsils. 26
LYMPHOID SYSTEM: Tonsils Histology of the tonsil Entirely dense lymphoid tissue; several lymphoid follicles and the surrounding dense lymphoid tissue. Lymphoid follicle is composed of a germinal center surrounded by a narrow region of dense lymphoid tissue lymphoid follicles is less-dense dense lymphoid tissue 27 LYMPHOID SYSTEM: Tonsils Lumenal epithelium of the pharynx is stratified squamous epithelium Two special features: Immune-defense cells infiltrate the epithelium difficult to recognize it as stratified squamous epithelium basal surface is difficult to locate. Crypts of the epithelium extend into the interior of the organ Increase higher surface area for uptake of bacteria, etc., The bacteria, etc., are then passed inward to the lymphoid follicles. 28
LYMPHOID SYSTEM: Tonsils 29 LYMPHOID SYSTEM: Tonsils Basal side of the pharynx is a capsule of dense C.T trabeculae of dense C.T. extend into the interior of the organ from the capsule, alternating with the epithelial crypts. 30
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