Lymphatic System & Immunity

Lymph is a specialized fluid formed in tissue spaces. This fluid carries protein molecules, immune cells, fat and excess tissue fluid called interstitial fluid (IF) back to the veins through lymphatic vessels. IF is formed from blood plasma coming out of the capillaries under pumping pressure of the heart. Lymphatic drainage prevents accumulation of too much tissue fluid

Lymphatic capillary is 1 cell layer thick. Lymphatic vessels have 1 way flow (like veins). Right lymphatic duct: - drains right upper quadrant into right subclavian vein. Thoracic duct: - drains rest of body - largest in body - in abdomen Cisterna chyli stores lymph

Lymph is under low pressure as is the venous system. Lymph is under low pressure as is the venous system. - contracting of skeletal muscle in appendages - contracting skeletal muscles used in breathing (intercostals) and contraction of smooth muscle of diaphragm. - contraction of smooth muscle in larger lymphatic trunks

Lymphatic tissue: Lymphatic tissue: - lymph nodes - tonsils - spleen - thymus - bone marrow

Lymph nodes- oval or bean shaped. - lymph that is drained from the body passes and is filtered through structures called lymph nodes. - connective tissue called reticular fibers and are populated by dense aggregates of lymphocytes and macrophages. -Lymph nodes occur along the entire length of the lymphatic system and tend to increase in size as they become closer to the thoracic duct. -arranged in chains or clusters

- scattered in groups; superficial and deep - cervical - submandibular - axillary - inguinal (groin) - supratrochlear - filter lymph - lymph flows into node from afferent lymphatic vessel. - exits from efferent lymphatic vessel

Nodes contain large number of macrophages and lymphocytes Nodes contain large number of macrophages and lymphocytes Node has a medulla and a cortex. Germinal centers are responsible for the proliferation of B-cells (remember what they produce?) - Distal portion of the small intestine: - Peyer’s patches

Thymus - bilobed structure located substernally in mediastinum - Immature T-cell lymphocytes (stem cells) migrate from bone marrow to thymus and mature under the direction of thymosin. Reside in lymph nodes. - Transforms from large in size (childhood) and atrophies to fat and connective tissue in adults- Involution. Still produces mature T-cells

Spleen: - largest lymphoid organ - upper left quadrant between stomach and diaphragm -Functions: - phagocytosis of bacteria - replace worn out RBC’s (120 days) - blood reservoir - erythrocyte production in the fetus - Stores blood platelets - Splenomegaly: enlarged spleen (EBV) - Trauma from rib fx.= splenectomy (removal of spleen)

Spleen is composed of two tissue types: White pulp: composed of splenic nodules that contain many lymphocytes. Red pulp: rbc’s, lymphocytes and macrophages. Give the spleen its reddish/purplish color.

Spleen

Tonsils: -Pharyngeal tonsil (adenoid) embedded in posterior wall of nasopharynx. - Palatine tonsil: tonsillectomy - Lingual tonsil: base of tongue Tonsils are first line of defense against bacteria entering the mouth - tonsillitis

Immunity: Immunity: Defending the body against invasion of pathogenic substances and eliciting an immune response when the body encounters those substances. 1- Non specific immunity (primary defense) - skin - mucous membranes - tears - saliva - micturition (urinating) - lysozyme in saliva and tears - HCl in gastric juice in stomach - Vaginal pH.

Specific Immunity: Immunity against specific organisms Specific Immunity: Immunity against specific organisms Specific immunity is more effective than the nonspecific methods, and has a memory component that improves response time when an invader of the same type (or species) is again encountered.

Inflammatory response Damaged cells release chemical signals such as histamine that increase capillary blood flow (vasodilation) into the affected area (erythema and heat). The heat makes the environment difficult for microbes to function, increases mobility of white blood cells. Chemotaxis. Damaged cells release chemical signals such as histamine that increase capillary blood flow (vasodilation) into the affected area (erythema and heat). The heat makes the environment difficult for microbes to function, increases mobility of white blood cells. Chemotaxis. Capillaries pass fluid into tissue spaces (interstitial) causing the infected/injured area to swell (edema). Finally, macrophages (monocytes outside the blood) clean up dead microbes, cells, and debris. Capillaries pass fluid into tissue spaces (interstitial) causing the infected/injured area to swell (edema). Finally, macrophages (monocytes outside the blood) clean up dead microbes, cells, and debris.

Fever: Fever: Non specific defense: Pathogen stimulates lymphocytes to proliferate and secrete a substance called interleukin-1 (IL-1). - endogenous pyrogen IL-1 stimulates the hypothalamus to increase body temp. Increased body temp. causes the spleen and liver to hold Fe (sequester). Fe level drops in blood. Since pathogens rely on Fe at higher temps to reproduce, this situation will slow down or stop their growth and reproductive cycles.