AHE II 3.1 - LYMPHATIC SYSTEM

• The lymphatic system aids the cardiovascular system.
• It transports excess interstitial fluid through lymph vessels.
• Fluid homeostasis is maintained by the lymphatic system.
• Lymph is interstitial fluid and solutes within the lymphatic vessels.
• Foreign or pathological materials are filtered in the lymph.
• Immune responses are initiated by specialized structures and organs.

Lymphatic System in Circulation

• Arterial blood pressure forces fluid out of capillary beds and into interstitial fluid.
• At the venous ends of capillary beds, interstitial fluid is reabsorbed.
• Interstitial fluid that is not reabsorbed enters lymphatic vessels and becomes lymph.
• This lymph is eventually returned to venous circulation.
• Lymph flowing through the system is filtered by organs.

Functions

• The lymphatic system helps maintain hydrostatic pressure.
• It prevents rising levels of interstitial fluid.
• It helps maintain blood volume levels.
• Edema occurs when excess fluid is not reabsorbed from cells.
• One mechanism of edema is abnormal vascular hydrostatic pressure.
• Dietary lipids from the GI tract, are too large to be absorbed by blood vessels, and are transported by the lymphatic system.
• Lipids enter via lacteals in intestinal villi.
• Lipids are packaged into protein-coated lipid droplets called chylomicrons.
• Fats form a specific type of lymph called chyle.
• The lymphatic system provides a site for lymphocyte maturation and replication.
• Lymphocytes are common immune cells located in lymphatic organs.
• Lymphocytes attack pathogens or produce antibodies.
• Interstitial fluid is monitored for antigens by lymphatic organs.
• The system reacts by producing antibodies, attacking antigens, and creating memory immune cells.
• Lymphocytes derive from a unique lymphoid line.

Lymphatic Vessels

• The system is comprised of lymphatics, which lead into the venous system and increase in size.
• Types of lymphatic vessels are:
  • Capillaries
  • Vessels
  • Trunks
  • Ducts

Lymphatic Capillaries

• These vessels are close-ended tubes woven into most blood capillary networks.
• They are not found surrounding bone marrow, the meninges in the central nervous system, or avascular tissue.
• Vascular walls are formed from overlapping endothelial cells.
• Endothelial cells form a one-way valve allowing interstitial fluid to enter but not leave.
• Compared to blood vessels, they are larger and lack a basement membrane.
• They are held in place by anchoring filaments.

Lymphatic Vessels

• Lymphatic vessels form when lymphatic capillaries merge together
• They are similar to veins with three tunics: externa, media, and intima.
• They contain one-way valves to prevent backflow and pooling.
• Contraction of nearby skeletal muscle aids lymph movement through lymphatic vessels.
• Vessels connect to lymph node clusters for filtration.
• They arrive via afferent lymphatic vessels and exit via efferent lymphatic vessels.

Lymph Trunks

• Lymph Trunks are larger than lymphatic vessels.
• They drain lymph from regions of the body:
  • Jugular - head and neck
  • Subclavian - upper limbs, breast, superficial thoracic wall
  • Bronchomediastinal trunk - deep thoracic structures
  • Intestinal trunk - abdominal structures
  • Lumbar trunk - lower limb, abdominal pelvic wall, pelvic organs

Lymph Ducts

• Lymph Ducts Drain lymphatic trunks and empties lymph into venous system.
• The Right lymphatic duct:
  • Drains at the junction of right subclavian and internal jugular veins
  • Recieves Lymph from right head, neck, upper limb, and thorax
• The Thoracic duct:
  • Is the largest lymphatic Duct
  • It drains lymph drains from the rest of the body
  • It drains at the junction of left subclavian and internal jugular veins
  • It is connected to the cisterna chyli inferiorly and receives lymph from small intestines, intestinal trunk, and lumbar trunks.

Lungs

• Lymph nodes and vessels are located in/around the pulmonary CT, bronchi, and pleura.
• These collect carbon, dust particles, and pollutants not caught by the ciliated epithelium.
• Subpleural lymphatic plexus contains:
  • Pulmonary lymph nodes
  • Bronchopulmonary lymph nodes
  • Trachiobronchial nodes
  • Bronchomediastinal trunk (right side- lymphatic duct, and left side- thoracic duct)
• Pleural effusion is “water-on-the-lungs".
• It is defined as the build-up of excess fluid between the layers of the pleura outside the lungs.

Lymphatic Structures

• These are structures that Filter and monitor lyphm/blood and mount an immune response if required via cytokines and leukocytes. Key structures and organs include

• Primary lymphoid organs, which produce lymphocytes, such as the thymus and bone marrow

• Secondary lymphoid organs, which facilitate the location of lymphocyte proliferation and activation, e.g., lymph nodes, spleen and mucosa-associated lymphoid tissue

Primary Lymphoid Organs: Bone Marrow

• Spongy bone marrow is located within the medullary cavities of long bones.
• at the cranial vault and the trabeculae
• At birth, all marrow is red
• Overtime red marrow transitions to yellow as age progresses.
• Hemocytoblasts form myeloid or yellow lines and produce leukocytes and red blood cells.
• The cells develop into lymphocytes
• B-lymphocytes develop specific structures related to bone marrow.
• Leukocytes access blood vessels through cell motility.
• They travel to secondary lymphoid organs to activate and differentiate.

Primary Lymphoid Organs: Thymus

• This structure is formed from interconnected epithelial cells. It is located in the mediastinum and anterior to great vessels of the heart (large in infants and children and diminishing in adults).
• Two lobes are surrounded by a CT capsule.
• These lobes are subdivided by septa.
  • Each lobe contain a cortex and medulla.
• Thymus functions:
  • Primary player in adaptive immunity or gradually acquired immunity.
  • T-lymphocyte precursor cells develop here.
  • Nurse cells secrete thymic hormones to stimulate T-lymphocyte maturation and differentiation.
  • Differentiated T-lymphocytes travel from the cortex, into the medulla, and bloodstream

Secondary Lymphoid organs

• Lymph nodes
• MALT / GALT
• Spleen

Lymph Nodes

• A location where lymph is filtered
• Identified antigens initiate an immune response
• Small ovoid structures surrounded by CT capsules connect to lymph vessels.
• Each node has its own blood supply.
• Typically in clusters that receive lymph (watersheds):
  • Cervical nodes- head and neck
  • Axillary nodes- breast, axilla, and upper limb
  • Inguinal nodes- lower limb and pelvis
• They are also found individually throughout the body.
• Internally consists of various structures and key areas
• Contain Lymphoid modules
• Contain Germinal Centres
• surrounded by a layer of capsules

Lymph Node Anatomy and Lymph Flow

• The capsule represents the thick CT layer surrounding the lymph node
  • Extensions called trabeculae subdivide the node into segments or compartments.
• The Cortex contains Lymphatic nodules and cortical sinuses.
• The Medulla Contains medullary cords as well as medullary sinuses
  • Lymph arrives via afferent lymphatic vessels and merges with other such vessels before entering an internal flow

The Flow of Lymph follows this pattern: 1. Lymph travels through the various openings located on either side of the trabeculae. 2. Lymph enters key structures called Cortical sinuses 3. Lymph arrives in Medullary sinuses which are contained within the Medulla. 4. Lymph finally exits the efferent lymphatic vessels in hilum which helps to transport into nearby veins to return fluid into the venous system

• If Antigens are detected as the fluid filters through the lymph node Lymph nodes
  • undergoes mitosis which increases lymphatic production in Germinal centre specifically to signal the presence as well act accordingly with immune functions
  • Antigens with certain antigens enter Bloods supply so the body can coordinate a full systematic immune response as antigens are identified.

MALT (mucosa-associated lymphoid tissue)

• MALT tissue is responsible for the filtration as well as attack of antigens.

  • Ovoid clusters are used to cluster B related Lymphatic tissue especially that lacks a connective tissue capsule
  • Germinal Center (nodule like centre structure housing B related lymphocytes as well as support cells that help with immune functions or macrophages)
  • T related lymphocytes

• Location: Is widely seen in tonsils- can be of pharyngeal, lingual as well as palatine origins

  • Lamina propria of digestive tract also has high concentrations of lymphoid tissue as it constantly filters pathogens (GALT), as well digestive functions helps aid lymphatic function with specialized small structures such as villi, which are especially prominent in the Peyers patches intestines

Spleen

• This a lymphatic organ and is located within Left quadrant quadrant (Upper location):

• Inferior near diaphragm

• Lateral in relation to kidney.

• Posterolateral in relation to stomach

• Hilum (entry point for vessels as well as other related blood vessels) Lacks a Cortex and therefore lacks a medulla

  • Surrounded by Red Pulp instead

• The Spleen is covered by a thick membrane consisting of irregular CT capsule that has multiple trabeculae.

• This organ:

  • Contains White Pulp that helps surround centre artery and is highly associated with both B related as well support cells
  • Functions with antigen detection as it highly monitors blood. The red pulp transports blood through splenic cords.
    • Blood reenters near sinusoid and is travels through the structure
    • Macrophages within this region remove debris through phagocytosis.

• Splenic cords which help transport blood:

  • Sinusoids (are barrel like capillaries help to facilitate passage via cells

• They contain discontinuous lamina help facilitate easy transport amongst a network comprised by cells Lumen region is filled by macrophages which phagocytize pathogens as well defective erythrocytes or platelets. Function with spleen related tissue will initiate immune function when:

• 1, detect the signal Then serve as as reservoir

• help phagocytosis.

Thymus Histology

• Structure is composed out of Capsule, lobules, which can be divided with septa and
• The key internal organization can be classified with
  • Regions for the Cortex are basophilic region- highly stain
  • Medulla regions stain lighter and help to facilitate different biological function such the and will have darker parts which indicate more staining.

Lymph Nodes

• There is a general region for context
• and some sort of vessel running throughout

1. cortex - highly strained due to location
2. medualla- appears light and less dense
3. capsule a cellular cover consisting of fibres.

Development of the Lymphatic System in Embryonic Origin

• This vessel develops through means of Blood flow
  • The cardinal vessels that facilitate this help vessels develop in a similar manner such formation from the cardinal veins
• At Week (9) or roughly around embryonic phase the primordial origin is 6 (primary site) in general.
• At 6 primary spot they are developing to connect with nearby groups
  • Mesenchyme is migrating in similar fashion as well
  • The primary cell for lymphocytes is lymphoblast.

vessels

• These lymphatic vessels help to connect with 6 to sacs of fluid to improve drainage

• Jugular (related with head, neck, as well upper lim)

• Veins are linked with iliac- (lower trunk, as wells trunk and lower limb) the lymph travels parallel and drains locally

  • Retropetitonea
  • The fluid is released via primordial gut however is controlled by nearby sac 2 vessels- large on left however is small.

-The vessels merge and remain small as fluid moves along The fluid moves down, and portion generates and become the trunk

• Spleen develops during (the primordial mesentery)

Structures of Tonsils

1. As the structure divides and the tissue moves
   • Dorsel (forms omentum, bursa as a region to place these spleen forming cells)

Tonsils

1. A 2nd paired process in pouches

• lymphoid tissue and will help with nasopharynx
• tongue