Lymphatic tissues are a type of connective tissue that contains large numbers of lymphocytes.

1. The lymphatic (lymphoid) system is essentially a drainage system, which is concerned with return of a fluid called "lymph" back to the blood stream. It consists of lymphatic tissues and lymphatic vessels. Its components are not in continuous order, but are scattered throughout the body and it services almost all regions. Lymphatic tissuesare a type of connective tissue that contains large numbers of lymphocytes. Lymphatic tissue is organized into the following organs: the thymus, lymph nodes, spleen, and lymphatic nodules. Lymphatic tissue is essential for the immunologic defenses of the body against bacteria and viruses. • Lymphatic vesselsare tubes that assist the cardiovascular system in the removal of tissue fluid from the tissue spaces of the body; the vessels then return the fluid to the blood. • Lymphatic vessels are found in all tissues and organs of the body except: • Central nervous system. • Eyeball & internal ear. • Epidermis of skin. • Cartilage & bone.

2. LYMPH VESSELS • Lymph vessels are either superficial or deep: • Superficial lymphatics: more numerous than veins in the subcutaneous tissue and anastomosing freely, convergetoward and follow the venous drainage. • These vessels eventually drain into deep lymphatics that accompany the arteries and also receive the drainage of internal organs. • Both superficial and deep lymphatics traverse lymph nodes as they course proximally, becoming larger as they merge with vessels draining adjacent regions. • The lymphatics that carry lymph to a lymph node are referred to asafferentvessels; those that transport it away areefferentvessels. • The larger lymphatics enter large collecting vessels, called lymphatic trunks, which unite to form either the right lymphatic duct or the thoracic duct: • Right lymphatic duct. • Thoracic duct.

3. Functions of the lymphatic system The functions of the lymphatic system are just as varied as its locations. These functions fall into 3 categories: • Fluid balance: • The small lymphatic capillaries pick up excess interstitial fluids and proteins, which accumulate in the tissue spaces. These capillaries then drain into larger vessels, which return these materials to the venous system near the heart. • Absorption and transport of dietary fat: • Many digested fats are too large to enter the blood capillaries and are instead absorbed into lymphatic capillaries. Special lymphatic capillaries, calledlacteals(L. lacteus, milk), receive all lipid and lipid-soluble vitamins absorbed by the intestine. Visceral lymphatics then convey the milky fluid, chyle(G. chylos, juice), to the thoracic duct and into the venous system. • Formation of a defense mechanism for the body: • When foreign protein drains from an infected area, antibodies specific to the protein are produced by immunological cells (lymphocytes) and dispatched to the infected area.

4. Peritoneal covering: • The spleen is surrounded by peritoneum, which passes from it at the hilum to the: • Greater curvature of the stomach as the gastrosplenic ligament (carrying the short gastric and left gastroepiploic vessels). • Left kidney as the splenicorenal ligament (carrying the splenic vessels and the tail of the pancreas). • Blood supply: • Arteries • The large splenic artery is the largest branch of the celiac artery. It has a tortuous course as it runs along the upper border of the pancreas. The splenic artery then divides into about 6 branches, which enter the spleen at the hilum. • Veins • The splenic vein leaves the hilum and runs behind the tail and the body of the pancreas. Behind the neck of the pancreas, the splenic vein joins the superior mesenteric vein to form the portal vein. • Lymph drainage: • The lymph vessels emerge from the hilum and pass through a few lymph nodes along the course of the splenic artery and then drain into the celiac nodes.

5. Clinical Notes • Splenic Enlargement • A pathologically enlarged spleen extends downward and medially. • The left colic flexure and the phrenicocolic ligament prevent a direct downward enlargement of the organ. • As the enlarged spleen projects below the left costal margin, its notched anterior border can be recognized by palpation through the anterior abdominal wall. • Trauma to the Spleen • Although anatomically the spleen gives the appearance of being well protected, automobile accidents of the crushing or run-over type commonly produce laceration of the spleen. • Penetrating wounds of the lower left thorax can also damage the spleen.

6. Lymphatic drainage of the upper limb • Superficial lymph vessels: • The superficial lymph vessels draining the superficial tissues of the upper arm pass upward to the axilla. • Those from the lateral side of the arm follow the cephalic vein to the infraclavicular group of nodes; those from the medial side follow the basilic vein to the lateral group of axillary nodes. • Thedeep lymphatic vessels:draining the muscles and deep structures of the arm drain into the lateral group of axillary nodes.

7. Axillary Lymph Nodes

8. Lymphatic drainage of the lower limb Inguinal lymph nodes: are divided into superficial & deep groups. • Superficial inguinal LNS • They lie in the superficial fascia below the inguinal ligament and can be divided into a horizontal and a vertical group. • Thehorizontal grouplies just below and parallel to the inguinal ligament. • The medial members of the group receive superficial lymph vessels from the anterior abdominal wall below the level of the umbilicus, perineum, urethra, external genitalia of both sexes (but not the testes) and lower 1l2 of anal canal. • The lateral members of the group receive superficial lymph vessels from the back below the level of the iliac crests. • Thevertical grouplies along the terminal part of the great saphenous vein and receives most of the superficial lymph vessels of the lower limb. • The efferent lymph vessels from the superficial inguinal nodes pass through the saphenous opening in the deep fascia and join the deep inguinal nodes.

9. Lymphatic drainage of the thorax • Thoracic Wall:

10. Lymphatic drainage of the abdomen • Abdominal Wall:

11. Abdominal cavity:

12. Regional nodes: are arranged as follows:

13. The efferent lymph vessels from the deep cervical lymph nodes join to form the jugular trunk, which drains into the thoracic duct or Rt. lymphatic duct.

14. Clinical NotesDisease of the Lymphatic System Lymphangitis, Lymphadenitis, and Lymphedema: • Lymphangitisandlymphadenitis:are 2ry inflammation of lymphatic vessels and lymph nodes, respectively. • These conditions may occur when the lymphatic system is involved in chemical or bacterial transport after severe injury or infection. • The lymphatic vessels, not normally evident, may become apparent as red streaks in the skin, and the nodes become painfully enlarged. • Lymphedemaor edema: is a localized accumulation of interstitial fluid, occurs when lymph does not drain from an area of the body, e.g. if cancerous lymph nodes are surgically removed from the axilla, lymphedema of the limb may occur. Spread of cancer: • Cancer invades the body by growing into adjacent tissue or bydissemination of tumor cells to sites distant from the original or primary tumor) metastasis). • Metastasis occurs by one of three ways: • Direct seedingof the serous membranes of body cavities. • Lymphogenous spreadvia lymphatic vessels. • Hematogenous spreadvia blood vessels. • Lymphogenous spread is the most common route for the initial dissemination ofcarcinomas(epithelial tumors), the most common type of cancer. • Hematogenous spread is the most common route for the metastasis of the less common (but more malignant) sarcomas (C.T. cancers. Because veins are more abundant and have thinner walls that offer less resistance, metastasis occurs more often by venous than arterial routes. Since the blood-borne cells follow venous flow, the liver and lungs are the most common sites of secondary sarcomas.