The Lymphatic System PDF

The Lymphatic System  The Lymphatic System ◼ The cells, tissues and organs responsible for defending the body against both environmental hazards, such as various pathogens, and internal threats, such as cancer cells. ◼ Lymphocytes are the primary cells of this system. ...

The Lymphatic System  The Lymphatic System ◼ The cells, tissues and organs responsible for defending the body against both environmental hazards, such as various pathogens, and internal threats, such as cancer cells. ◼ Lymphocytes are the primary cells of this system.  The Lymphatic System consists of ◼ Lymph ◼ Lymphatic vessels ◼ Lymphoid tissues and organs ◼ Lymphocytes and other cells  Formation of Lymph ◼ Plasma seeps from capillaries, surrounds cells and forms tissue fluid ◼ Most of the tissue fluid returns to general circulation via venules ◼ Excess tissue fluid enters the lymphatic vessels and forms LYMPH  Functions of the Lymphatic System 1. The production, maintenance, and distribution of lymphocytes that provide defense against infections and environmental hazards. Lymph nodes and other lymphatic organs filter lymph to remove microbes and other foreign particles. The Lymphocytes destroy them.  Functions of the Lymphatic System (cont’d) 2. Returns excess interstitial fluid to the blood. Lymph capillaries pick up excess interstitial fluid and proteins and return them to the venous blood. Lymph re-joins blood at the right and left subclavian veins.  Functions of the Lymphatic System (cont’d) 3. Absorption of fats and fat-soluble vitamins from the digestive tract and the subsequent transport of these substances to the venous circulation. In the centre of the villi lining the small intestine are blood capillaries and lacteal vessels. The lacteals absorb the fat and fat-soluble vitamins from the intestinal tract  Vessels that transport lymph ◼ Carry lymph from peripheral tissues to the venous system. ◼ The smallest lymphatic vessels are called Lymphatic Capillaries ◼ Lymph then flows through lymphatic vessels, lymphatic trunks and then lymphatic ducts  Lymphatic Capillaries ◼ Begin in tissue spaces as pockets ◼ Are found throughout the body except the bone marrow, CNS and the epidermis ◼ Composed of an endothelium with limited or absent basal lamina. ◼ The simple squamous cells of the endothelium have overlapping ends that form one-way valves Overlapping Endothelial Cells of Lymphatic Capillaries  Other Features of Lymphatic Capillaries ◼ Larger diameters than blood capillaries ◼ Thinner walls than blood capillaries ◼ Typically flattened or irregular in outline  Lymphatic Vessels ◼ Lymph capillaries merge to form Lymphatic Vessels ◼ Lymphatic vessels lead toward the body’s trunk ◼ The walls of these vessels are similar to those of veins ◼ Lined by valves; seen as bulges on surface Notice bulge at surface of vessel Lymphatic vessel with valve  Two Sets of Lymphatic Vessels ◼ Superficial Lymphatics ◼ Deep lymphatics ◼ Located in the ◼ Located in the ◼ subcutaneous layer deep ◼ Skeletal muscles to the skin ◼ Other organs of the neck, ◼ Areolar tissues of the mucous membranes limbs and trunk lining the digestive, ◼ walls of visceral organs respiratory, urinary and reproductive tracts ◼ serous membranes of the pleural, pericardial and peritoneal cavities  Lymphatic Trunks ◼ Lymphatic vessels join to form larger tributaries called Lymphatic Trunks ◼ Right and Left Lumbar Trunks ◼ Intestinal Trunk ◼ Right and Left Bronchomediastinal Trunks ◼ Right and Left Subclavian Trunks ◼ Right and Left Jugular Trunks  Lymphatic Trunks and the Areas they Drain ◼ Lumbar – lower limbs, walls and viscera of pelvis, kidneys, adrenals and abdominal wall ◼ Intestinal – stomach, intestine, pancreas, spleen and liver ◼ Bronchomediastinal – trachea, bronchi, lungs mamma and heart ◼ Subclavian – subclavian lymph nodes ◼ Jugular – cervical lymph nodes of head and neck  Lymphatic Ducts ◼ Lymphatic trunks merge until the lymph enters two Lymphatic Ducts ◼ Right Lymphatic Duct – drains lymph from the upper right quadrant of the body ◼ Thoracic Duct – drains areas inferior to the diaphragm and from the left side of the body superior to the diaphragm Areas drained by the Lymphatic Ducts Drainage of Right Lymphatic duct Drainage of Thoracic duct Intestinal trunk Left & Right Lumbar trunks  Lymphatic Ducts ◼ The Right Lymphatic Duct receives lymph from ◼ Right jugular trunk ◼ Right subclavian trunk ◼ Right bronchomediastinal trunk ◼ The Thoracic Duct receives lymph from ◼ Right and left lumbar trunks ◼ Intestinal trunk ◼ Left bronchomediastinal, subclavian and jugular trunks  Lymphatic Ducts ◼ The Thoracic Duct empties into the left subclavian vein near the left internal jugular vein ◼ The Right Lymphatic Duct empties into the right subclavian vein Lymphatic Ducts  Lymphoid Tissues ◼ Connective tissues dominated by lymphocytes ◼ Lymphoid Nodules have densely packed lymphocytes in an area of areolar tissue ◼ Lymphoid nodules may occur in clusters in many areas in the body  Lymphoid Tissue ◼ Lymphoid Nodules occur in connective tissue deep to the epithelia lining the ◼ Respiratory tract ◼ Digestive tract ◼ Urinary tract ◼ Reproductive tract ◼ They also occur within complex lymphoid organs ◼ Lymph nodes ◼ Spleen Lymph Nodules within the Wall of the Digestive Tract  MALT ◼ Mucosa-Associated lymphoid tissue ◼ A collection of lymphoid tissues that protect the epithelia of the digestive, respiratory, urinary, and reproductive systems ◼ Examples: ◼ Aggregated lymphoid nodules or Peyer’s Patches ◼ Appendix ◼ Tonsils  Tonsils ◼ Clusters of lymphatic tissue under the mucous membranes that line the nose, mouth and pharynx. ◼ There are three groups of tonsils: 1. Pharyngeal – near the opening of the nasal cavity into the pharynx 2. Palatine – near the opening of the oral cavity into the pharynx 3. Lingual – on the posterior surface of the tongue Tonsils  Tonsils ◼ Lymphocytes and macrophages in the tonsils provide protection against harmful substances and pathogens that enter the body through the nose or mouth.  Lymphatic Organs ◼ Characterized by clusters of lymphocytes and other cells such as macrophages, enmeshed in a framework of short, branching connective tissue fibres. ◼ Lymphocytes proliferate in lymph organs when the body is exposed to microbes and other foreign agents. They are sent to the site of invasion via the blood.  Lymph Nodes ◼ Small, bean-shaped ◼ Usually less than 2.5 cm in length ◼ Distributed throughout the body along the lymphatic pathways ◼ Three superficial regions on each side of the body where lymph nodes cluster: ◼ Inguinal ◼ Axillary ◼ Cervical Superficial Lymph Nodes  Lymph Nodes ◼ Surrounded by a connective tissue sheath ◼ Divided into compartments called Lymph Nodules ◼ Lymph nodules are dense masses of lymphocytes and macrophages separated by lymph sinuses  Lymph Nodes ◼ Afferent lymphatic vessels enter lymph nodes on their convex side and carry lymph into the node ◼ An efferent lymphatic vessel leads lymph away from the node at the Hilum  The Thymus ◼ A soft, bi-lobed organ located anterior to the ascending aorta and posterior to the sternum ◼ Decreases in size after puberty  The Thymus ◼ Functions: ◼ Processing and maturation of T-lymphocytes ◼ While in the thymus the T-cells do not respond to pathogens and foreign agents ◼ After maturation the T-cells enter the blood and go to other lymphatic organs where they help in defense ◼ Production of Thymosins which stimulate the maturation of lymphocytes in other lymphatic organs  The Spleen ◼ Located in the upper left abdominal cavity, just beneath the diaphragm, and posterior to the stomach.  The Spleen ◼ Similar in structure to lymph nodes but is much larger ◼ The largest lymphatic organ ◼ Surrounded by a connective tissue capsule which extends inward to divide the organ into lobules.  The Spleen ◼ Consists of two types of tissue: ◼ White pulp – lymphatic tissue consisting mainly of lymphocytes around arteries ◼ Red Pulp – consists of venous sinuses filled with blood and cords of lymphatic cells  Functions of the Spleen ◼ Filters blood as it passes through the sinuses ◼ Lymphocytes in the spleen react to pathogens in the blood and attempt to destroy them. Macrophages engulf debris, damaged cells and large particles. ◼ Removes old and damaged RBCs from the blood ◼ Produces lymphocytes especially in response to invading pathogens ◼ The sinuses in the spleen are a reservoir for blood. ◼ Blood is squeezed out of the sinuses into general circulation in cases of emergency