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Lymphatic system (1)

The lymphatic system includes tissues and organs that produce, store, and carry white blood cells to fight infections. It develops beginning in the fifth week of embryonic life from lymph sacs that become lymph vessels and organs. The main components are lymph, lymph organs like lymph nodes and the spleen and thymus, lymph vessels, and lymphoid tissues. The lymphatic system works to drain fluid into the bloodstream, filter lymph and blood, and help the body fight infections by producing lymphocytes and macrophages.

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Definition The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the Bone Marrow Spleen Thymus
Development Development starts by the end of the fifth week of embryonic life. The lymphatic system begins as a series of sacs 108 at the points of junction of certain of the embryonic veins. The lining walls of its vessels are always endothelial. These lymph-sacs are developed by the confluence of numerous venous capillaries, which at first lose their connections with the venous system, but subsequently, on the formation of the sacs, regain them.
Development in Human Embryo In human embryo the lymph sacs from which the lymphatic vessels are derived are six in number. Two paired Jugular Lymph sac At the junction of the internal jugular and subclavian veins. Retroperitoneal Lymph sac At the root of the mesentery of the intestine. develops from the primitive vena cava and mesonephric veins  Posterior Lymph sacs Develop from the iliac veins
Lymphatic System Components Lymphatic system components includes : Lymph Lymph Organs Lymph Vessels Lymph Tissues
Lymph Lymph means clear water and it is basically the colorless fluid and protein that has been squeezed out of the blood. Lymph is a fluid similar in composition to blood plasma. Changes in plasma composition will change lymph composition.  Protein concentration of lymph is lower than in plasma and varies inversely proportional to rate of formation that varies from tissue to tissue.
Lymph flow rate  Lymph flow rate is usually low. It is influenced primarily by the rate of lymph formation. The flow rate is affected by compression of lymphatics by negative intrathoracic pressure (breathing). Valves in the lymph vessels prevent retrograde flow similar to those in veins.
Formation of lymph  ISF forms at the arterial (coming from the heart) end of the capillaries because of higher pressure of blood, Most of it returns to its venous ends and venules; the rest (10—20%) enters the lymph capillaries as lymph. Thus lymph formed is a watery clear liquid with the same composition as the ISF.  As it flows through the lymph nodes, however, it comes in contact with blood and tends to accumulate more cells (particularly lymphocytes) and proteins.
Lymphatic Organs An organ that is characterized by clusters of lymphocytes and other cells, such as macrophages, enmeshed in a framework of short, branching connective tissue fibers. Formation: The lymphocytes originate in the red bone marrow with other types of blood cells and are carried in the blood from the bone marrow to the lymphatic organs.
Types of Lymphatic organs Primary lymphatic organs Thymus gland  Bone marrow Secondary lymphatic organs  Encapsulated diffuse lymphoid tissue includes the spleen and lymph nodes.  Unencapsulated diffuse lymphoid tissue includes gut-associated lymphoid tissues and the tonsils. 
Lymph nodes One of a number of small swellings found at intervals along the lymphatic system. They are widely distributed throughout the body along the lymphatic pathways.  Lymph nodes are not present in the central nervous system. Composed of lymphoid tissue.
Structure of lymph nodes Small bean-shaped structures Usually less than 2.5 cm (1 inch) in length. Three superficial regions where lymph nodes tend to cluster 1. 2. 3. Inguinal nodes in the groin Axillary nodes in the armpit Cervical nodes in the neck
Function of Lymph nodes Filter the lymph before it is returned to the blood Preventing foreign particles from entering the bloodstream They also produce lymphocytes
Waxing, Waning of Lymph Nodes Waxing and waning terms used to describe transient or short-term fluctuations in the size of lymph nodes that could be accounted Response to treatment Immune activation against lymphoma Collapsing of necrotic areas in lymph nodes may explain a sudden decrease in a large lymph node. Lymph nodes may enlarge when immune cells react to pathogen such as virus or bacteria.
Swollen Lymph Glands
Tonsils Cluster of lymphatic tissue just under the mucous membranes that line the nose, mouth, and pharynx (throat) called tonsils. There are three groups of tonsils. 1. Pharyngeal tonsils 2. Palatine tonsils 3. Lingual tonsils Provide protection against harmful substances and pathogens that may enter the body through the nose or mouth.
Enlarge Tonsil
Spleen
Function of Spleen Filters blood Stores blood
Thymus Primary lymphatic organ in the body; it is located over the heart and/or in the neck area, anterior to the ascending aorta and posterior to the sternum. The thymus consists of two lobes enclosed in a capsule and is further divided internally Function of the thymus is the processing and maturation of special lymphocytes (white blood cells) called T-lymphocytes or T-cells, which are associated with antibody production.
Lymphatics Tubular vessels transport back lymph to the blood ultimately replacing the volume lost from the blood during the formation of the interstitial fluid. Lymph capillaries Lymph vessels Lymphatic trunks Lymphatic ducts
The two main lymph ducts are:  Right lymphatic duct  Thoracic duct Structure of lymphatics is based on that of blood vessels.  Inner lining of single flattened endothelial cells  Smooth muscles arranged in a circular fashion around endothelial cells  Outermost layer consists of fibrous tissue
Lymphoid Tissues Specialized form of reticular connective tissue that contains various types of white blood cells enmeshed In it, most numerous being the lymphocytes. Lymphoid tissue can be of three types depending upon the stage of lymphocyte development and maturation.  Primary(central) lymphoid tissue  Secondary(peripheral) lymphoid tissue  Tertiary lymphoid tissue
Function of Lymphoid Tissues Makes up the spleen, the thymus, and the tonsils, as well as visceral nodes, and lacteals which are all associated with mucous membranes of the gastrointestinal tract. Concerned with immune functions in defending the body against the infections and spread of tumors.
Functions of Lymphatic System Draining fluid into the bloodstream Filtering lymph Filtering the blood helps fight infection in many ways such as Helping to make special white blood cells (lymphocytes) that produce antibodies  Having other blood cells called macrophages inside the lymph nodes which swallow up and kill any foreign particles, 
Draining Fluid into Bloodstream