Lymphatic System Anatomy and Physiology PDF

Lymphatic system Anatomy and Physiology Y. Peter  Components of the lymphatic system ▪ Lymph – the fluid ▪ Lymphatic vessels – transport the lymph ▪ Lymphatic organs and tissues Lymph fluid is a clear–pale yellow fluid In the intestines, lymph fluid is milky (du...

Lymphatic system Anatomy and Physiology Y. Peter  Components of the lymphatic system ▪ Lymph – the fluid ▪ Lymphatic vessels – transport the lymph ▪ Lymphatic organs and tissues Lymph fluid is a clear–pale yellow fluid In the intestines, lymph fluid is milky (due to the presence of dietary lipids) and is termed CHYLE.  Functions of the lymphatic system Lymphatic vessels: ▪ Drain excess interstitial fluid from tissue spaces to the blood (assists in maintaining circulating blood volume) ▪ Transports dietary lipids and lipid-soluble vitamins A, D, E & K from the GIT to the blood. Lymphatic tissues carry out immune responses (mostly responsible for adaptive immunity) Lymph circulation Facilitated by respiratory pump and skeletal muscle pump (same as in venous blood flow). Inhalation - lymph flows from the abdomen (higher pressure) to the chest. Exhalation - valves prevent lymph backflow Blood capillaries (blood) → interstitial spaces (interstitial fluid) → lymphatic capillaries (lymph) → lymphatic vessels (lymph) → lymphatic trunks or ducts (lymph) → subclavian veins (blood)→SVC → heart. Relationship between cardiovascular and lymphatic systems (Tortora & Derrickson, 2017:813) Lymphatic vessels Lymphatic capillaries Lymphatic vessels Lymph trunks and ducts  Lymphatic capillaries and vessels Lymphatic capillaries: located in spaces between cells Throughout the body except for avascular tissues, central nervous system, and red bone marrow. Small intestines: special lymphatic capillaries called lacteals – carry dietary lipids into lymphatic vessels. Lymphatic capillaries unite to form lymphatic vessels Lymphatic vessels: resemble veins but have thinner walls and more valves have lymph nodes follow the same route as veins  Lymph trunks Lymphatic vessels unite to form lymph trunks Major trunks: the lumbar, intestinal, broncho-mediastinal, subclavian, and jugular trunks Lumbar trunks drain the lower limbs, pelvic wall & viscera, kidneys, adrenal glands, and the abdominal wall. Intestinal trunk - stomach, intestines, pancreas, spleen and part of the liver The broncho-mediastinal trunks - thoracic wall, lung, and heart. The subclavian trunks - upper limbs. The jugular trunks - head and neck.  Left side - lymph trunks join to form the left lymphatic/ thoracic duct ▪ Thoracic duct drains into the left subclavian vein. Lymph ducts ▪ Thoracic duct begins as a dilation called cisterna chyli anterior to L2. Right side - lymph trunks drain directly into RT subclavian vein. ▪ The right lymphatic duct is a rare anomaly. Lymphatic drainage Lymph from the right upper body returns to the SVC via the Rt subclavian/ brachiocephalic vein Lymph from the left upper body and the entire lower body returns via the left subclavian/ brachiocephalic vein Lymphatic organs and tissues Functionally classified into 2: 1) Primary lymphatic organs ▪ Sites where stem cells divide and become capable of mounting immune response, i.e., red bone marrow and thymus gland. *Red marrow produces mature B cells & pre-T cells; Immature T cells (pre-T cells) migrate to the thymus, where they mature. 2) Secondary lymphatic organs and tissues ▪ Sites where most immune responses occur, i.e., lymph nodes, the spleen, and lymphatic nodules (follicles) Lymphatic organs/ tissues  Thymus Bi-lobed organ in the mediastinum Each lobe is divided into lobules consisting of the outer cortex and central medulla The cortex has plenty of T cells; dendritic cells, epithelial cells, and macrophages Functions of the different cells: ▪ Dendritic cells assist in the maturation of the T cells ▪ Each epithelial cell surrounds about 50 T cells ▪ Epithelial cells produce thymic hormone, which aids in the maturation of T cells. ▪ Majority of T cells die via apoptosis; macrophages remove the debris of dead cells.  Thymus cont… Surviving T cells enter the thymic medulla. The functional portion of the thymus decreases with age. Before the thymus atrophies, it populates the secondary lymphatic organs and tissues (lymph nodes, the spleen, etc.) with T cells. Some T cells continue to multiply in the thymus throughout an individual’s lifetime, but the number decreases with age.  The spleen Largest lymphatic tissue; surrounded by a capsule of dense connective tissue The parenchyma consists of white pulp and red pulp White pulp is lymphatic tissue consisting of lymphocytes and macrophages. ▪ B cells and T cells carry out immune functions; macrophages destroy blood-borne pathogens The red pulp consists of venous sinuses and splenic cords or Billroth’s cords (cords of splenic tissue). Splenic cords consist of red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes Functions of the red pulp: (1) removal of ruptured, worn out, or defective blood cells and platelets (by macrophages); (2) storage of platelets (up to one-third of the body’s supply) (3) production of blood cells during fetal life. Lymph nodes Bean-shaped organs which consist of many B cells and T cells About 600 lymph nodes throughout the body, along lymphatic vessels Occur in groups - large groups found near mammary glands, axillae, and groin Lymph enters the node through afferent lymphatic vessels and leaves through efferent lymphatic vessels. Lymph nodes filter foreign substances from the lymph before it enters the bloodstream Lymph nodes cont… The parenchyma (functioning part) of a lymph node is divided into the cortex and medulla. The cortex consists of an outer cortex and an inner cortex The outer cortex contains groups of B cells called lymphatic nodules or lymph follicles. The inner cortex consists mainly of T cells and dendritic cells from other lymphatic tissues. The medulla contains B cells, antibody-producing plasma cells from the cortex, and macrophages The antibodies secreted by plasma cells and activated T cells are carried out of the lymph node by efferent lymphatic vessels. Diagram of a lymph node Lymphatic nodules Egg-shaped masses of lymphatic tissue (B cells); not surrounded by a capsule Can be primary or secondary Primary lymphatic nodule – natural Secondary – forms from the primary lymphatic nodule in response to an antigen (a foreign substance). Found in the mucous membranes lining the GIT, urinary and reproductive tracts, and respiratory airways. Also referred to as mucosa-associated lymphatic tissue (MALT) ▪ Examples: tonsils and Peyer’s patches (aggregated lymphatic follicles in the ileum and small intestine) 5 tonsils – at the junction of the oral cavity and oropharynx and the junction of the nasal cavity and nasopharynx ▪ 1 pharyngeal, 2 palatine, 2 lingual tonsils ▪ Fight against inhaled or ingested foreign bodies  References Primal Pictures – accessible from CPUT library page. Tortora, G. & Derrickson, B. 2017. Principles of anatomy and physiology. 15th ed. Wiley: USA.