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AP 2 Unit 2 - Bio186 A&P2 Unit 2 The Lymphatic and Immune...

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Bio186 A&P2 – Unit 2: The Lymphatic and Immune Systems The Lymphatic System A. Functions 1. Return of excess tissue fluid to bloodstream 2. Body defense 3. Distribution of substances throughout the body e.g. lipids are absorbed from intestine into lymph NOT blood B. Components 1. Lymph fluid, resembles plasma, less protein Pressure in capillaries causes fluid to leak out, not all is re-absorbed by osmosis see page 420-421 of text Two competing forces: 1. Pressure of fluid – “pushes” water out of capillary 2. Osmosis – fluid is “pulled back in” because of higher solute in plasma (remember – high amount of albumin, globulins) ~3.6 L per day 2. Lymphatic vessels — “lymphatics” a. Lymphatic capillaries begin in peripheral tissues end in venous system close-ended (unlike capillaries) No basement membrane fluid, solutes, debris, pathogens enter easily pick up excess tissue fluid Overlapping endothelial cells (like shingles) – act as one-way valves low pressure! (valves are essential) b. Large lymphatic vessels – similar to veins in structure including valves c. Lymphatic ducts – large collecting structures i. thoracic duct - largest lymph vessels; empties lymph into left subclavian vein entire left side of body & right side below diaphragm ii. right lymphatic duct – empties into right subclavian vein right side of body above diaphragm 3. Lymphoid tissues = loose connective tissue & lymphocytes Lymphocytes — three types: B-cells, T-cells and NK cells a. Lymphoid organs = encapsulated with fibrous connective tissue i. Lymph Nodes = “lymph filters” oval, up to 1” throughout body, especially at lymphatic junction points filter lymph – remove debris, antigens, foreign material
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Bio186 A&P2 – Unit 2: The Lymphatic and Immune Systems lymphocytes (B and T) and macrophages congregate here to monitor lymph as it moves through if infection present, parts of invaders or dying cells will ultimately filter through nodes immune cells can multiply if sensitized by a specific antigen nodes swell in size ii. Spleen = “blood filter” fist-sized, ~ 5” long; left upper quadrant (between stomach, l. kidney) brittle – when damaged, very hard to surgically repair filters blood (not lymph) – breaks down and removes old RBCs red pulp = RBCs, neutrophils, macrophages contains lymphocytes and macrophages – which can mount immune response white pulp = T cells and B-cells iii. Thymus = “T cell college” (site of T cell development/maturation) lies in mediastinum, above heart T cells are born in bone marrow, but go to thymus to develop into mature T lymphocytes Thymus has VITAL role in teaching your T cells what is you (self) and what is foreign (nonself) b. Lymphoid Nodules = less organized without fibrous capsule found beneath epithelia lining respiratory, digestive, urinary systems (open to external env. – common routes of pathogen entry) i. Tonsils – 5 present (pharyngeal tonsil = ‘adenoids”) ii. Peyer’s patches
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