Lymphatic system

• Functions of Lymphatic System

  • Immunity : lymphocytes and plasma cells which can recognize and neutralize antigens (microbes, tumor cells and toxins)
• Functions of Lymphatic System

  • Lipid absorption - Lacteals in small intestine absorb dietary lipids.
  • Fluid recovery (Maintain fluid balance) absorbs plasma proteins and fluid from tissues and returns it to the bloodstream.
• Lymph is a clear, colorless fluid, similar to plasma but much less protein
• Lymphatic capillaries

  • closed at one end
  • allow bacteria and cells entrance to lymphatic capillar
• Fill in the blank

  A) colorless

  B) wider

  C) Narrower

  D) thin

  E) low

  F) absorb

  
• Collecting vessels: course through many lymph nodes
• Lymphatic trunks: drain major portions of body
• Collecting ducts :

  1. right lymphatic duct – receives lymph from right arm, right side of head and thorax; empties into right subclavian vein
  2. thoracic duct - larger and longer, receives lymph from below diaphragm, left arm, left side of head, neck and thorax; empties into left subclavian vein
• Lymphoid tissue is a type of connective tissue characterized by a rich supply of lymphocytes.
• Lymphoid tissue/organs are:

  1. Lymph node 2. Tonsils 3. Thymus 4. Spleen
• A lymph node is an ovoid or bean shaped body, ranging from 1 to 25 mm in diameter.
• A lymph node has a convex surface that is the entrance site of lymphatic vessels and a concave depression, the hilum through which arteries and nerves enter and veins and lymphatic vessels leave the organ .
• Lymph nodes are distributed throughout the body along the course of the lymphatic vessels

  • Size from a pin head to a pea.
  • Color - variable
• Lymph Node Structure:

  • Capsule:
  • Enclosed by a connective tissue capsule.
  • Trabeculae:
  • Trabeculae (septa) extend inward from the capsule.
  • Project vertically, dividing the node into compartments.
  • Function:
  • Supports the lymph node's structure.
  • Trabeculae carry and house blood vessels within the node.
  • Location:
  • Found throughout the lymphatic system.
• Lymph node

  A) Capsule

  B) trabeculum

  C) hilum

  
• Lymph node:

  • Afferent lymph vessels pierce the capsule at various sites on the convex surface and empty into the subcapsular sinuses.
  • Efferent lymph vessels drain the sinuses at the hilum. The lymph vessels have a beaded appearance due to the many valves it contain.
• Parenchyma is divided into 2 regions: cortex & medulla.
• The cortex is the region beneath the capsule. The cortex is absent at the hilum.
• The cortex is characterized by the presence of lymph nodules.
• • The lymphatic nodules with germinal centers are called “ secondary nodules” and those without are called “ primary nodules”.
  • The germinal centers are rich in immature light staining large lymphoblasts.
  • The mature B lymphocytes are smaller & darker and lies at the periphery of the nodule.
• • The cortex and medulla are not sharply demarcated.
  • At the junction of the cortex and medulla is a functionally distinct zone called “the parafollicular zone” which contains T lymphocytes.
• • The interior region of the gland is the medulla.
  • It has medullary cords which branch & anastomose.
  • The medullary cords are separated by spaces, called the medullary sinuses.
• Medullary sinuses run between the cords. They join at the hilum delivering the lymph into the efferent lymph vessels.
• There are 3 parts in the sinus system.

  1.The marginal sinus (or subcapsular sinus) underlies the capsule

  2. The cortical or trabecular sinus lies between the cortical trabeculae and lymph nodules.

  3. The medullar sinuses – between the medullary cords
• Fill in the blank

  A) subcapsular

  B) Trabecular

  C) Medullary

  
• Lymph node

  A) Cortex

  B) Lymphatic nodules

  C) Medulla

  
• Lymphadenopathy is collective term for all lymph node diseases
• Lymphadenitis:

  • Swollen, painful lymph node.
  • Typically responds to a foreign antigen.
• Metastatic Cancer:

  • Lymph nodes are common sites for metastatic cancer.
  • Lymph nodes may become swollen, firm, and usually painless.
• The palatine tonsils are two rounded masses of lymphoid tissue lying between the two arching folds in the oropharynx.
• The tonsils produce lymphocytes.

  The surface of each tonsil is convex and has pits.

  These pits are called tonsillar crypts.
• About 40 tonsillar crypts invaginate into the interior of the tonsil and contains desquamated epithelial cells, lymphocytes and bacteria.
• The luminal surface is covered with stratified squamous non-keratinized epithelium which also lines the tonsillar crypts.
• The deep surface of the tonsil is covered by fibrous tissue which forms a thin capsule ; from which septas extend into the interior of the tonsil, dividing it into some 10 to 20 incomplete lobules
• Lymphoid tissue borders the surface epithelium & also follows the crypts in a layer 1 – 2 mm thick.

  • Both primary & secondary lymphoid nodules are seen abundantly
  • usually in a single layer parallel to the epithelium.
  • The germinal centers are usually large.
• The lymphocytes leave the tonsil via the epithelium into the buccal cavity. Thus, emigrating lymphocytes are seen within the epithelium, especially in the crypts.
• Mucous glands and skeletal muscle lie beneath the tonsil and its capsule.
• Fill in the blank

  A) Tonsillar crypt

  B) Lymphatic nodule

  
• The tonsils differ from the lymph node in:

  1. having an epithelium ( St. sq. non ker.) on its free surface
  2. Presence of tonsillar crypts
  3. No afferent & efferent vessels
  4. No sinus system
  5. Non-differentiation into cortex and medulla
  6. Contains minor salivary gland ( Mucous type).
  7. Below the connective tissue - skeletal muscle fibers are seen
• Tonsils offers first line of defense to the body against antigens (bacteria, viruses etc) as soon as they are swallowed in food or drink.