IMED1001 - Lymphatic System (Week 9)

Immune vs Lymphatic System

- Immune System: Collection of all proteins, cells, tissues, organs, widely distributed throughout the body, that function to protect the body

- Lymphatic System: Transport system for cells of the immune system and antigens (foreign substances/cells) to move around the body. Tissues where cells of the immune system hang out

Lymphatic Anatomy

- lymph: fluid

- lymphatic capillaries

- lymphatic vessels

- lymph nodes

- lymphatic nodules

- lymphatic trunks and ducts

- tonsils

- spleen

- thymus

Overview of Lymphatic System

- Primary lymphoid organs function is: lymphocyte generation

- secondary lymphoid organs function is: lymphocytes exposed to antigen and activated for effector function

Lymph Capillaries

- Lymph is water plus solutes from two sources: Plasma (ions, nutrients, gases, some proteins) and Cells (hormones, enzymes, waste products)

- we dont take formed elements into the lymph, these stay in the blood

Lymph Capillaries Path of Fluid

- form lymph fluid can carry away from tissues

- More permeable then blood capillaries (take up cell debris, pathogens and cancer cells)

- Epithelium overlap to function as a series of one-way valves

- Found in all parts of the body except nervous system, bone and avascular tissues (without blood vessels - cornea, epidermis)

- Lacteals: specialised lymph capillaries present in intestinal mucosa -> absorb digested fat (as chylomicrons) and deliver fatty lymph (chyle) to the blood

Lymph Drainage

- One-way system, lymph flows toward the heart

- Lymphatic Capillaries: join to form lymphatic vessels

- Lymphatic Vessels: have valves that ensure one-way flow (beaded appearance)

- Lymph nodes: distributed along vessels and filter lymph

- Lymphatic vessels drain to trunks which drain to ducts: drain tissues of body and move lymph into major veins

Lymph Drainage Ducts Involved

Lymph delivered into one of two large ducts:

- Right lymphatic duct drains right upper arm and right side of head and thorax

- Thoracic Duct arises as cisterna chyli; drains rest of body.

- Ducts empty into junction of internal jugular and subclavians, which drain to brachiocephalic veins and then to superior vena cava

Lymphatic Ducts DIAGRAM

DIAGRAM ON SLIDE 12

Primary: Red Marrow

- Red bone marrow (located in some spongy bones) produces all the formed elements (cellular blood components) via hemopoiesis

- Synthesise mature B-lymphocytes and immature T-lymphocytes (pre T-lymphocytes).

- Both are types of white blood cells

- Immature T-lymphocytes migrate from the bone marrow to the thymus to complete maturation

Primary: Thymus

- located in superior mediastinum

- site of maturation of T cells

- Those that remain can react to foreign substances

- Endocrine functions (thymosin)

Thymus Specific info

- reaches maximum size around puberty, after which shrinks as cells regress and are replaced with adipose tissue

- Older individuals are therefore at higher risk of infection

- thymus is small in older people,

Secondary Lymphatic Organs

- Lymphatic organs contain lymphatic tissue (lymphocytes, macrophages, dendritic cells)

- Lymphocytes: B and T cells - white blood cells derived from bone marrow

- Fine network of reticular fibres. Produced by reticular cells. Act as filter to trap microorganisms and other particles

- May be encapsulated (in a CT capsule): encapsulated - lymph nodes, spleen, thymus

- non-encapsulated: mucosa-associated lymphoid tissue (MALT). Found beneath epithelium as first line of attack against invaders.

Secondary: Lymph Nodes

- only structures to filter lymph

- substances removed by phagocytosis or stimulate lymphocytes to proliferate

- Cancer cells often migrate to lymph nodes, are trapped there, and proliferate. Can move from lymphatic system to circulatory system spreading cancer through body

- Afferent (more) and efferent (less) vessels

- Organised into cortex and medulla (next slide) with dense connective tissue capsule surrounding

- slow flow (its like a lot of people leaving through a small gap)

Lymph Node Size etc.

- Two histologically distinct regions

- Cortex: cortex contains follicles with germinal centers

- Medulla: lymph sinuses contain macrophages

Lymph Node Diagram Cadaveric

DIAGRAM ON SLIDE 19

Secondary: Tonsils

- large groups of lymphoid tissue in nasopharynx and oral cavity

- Provide protection against bacteria and other harmful material

- Palatine (tonsils, usually what people refer to when they say tonsils)

- Pharyngeal (adenoids)

- Lingual

Tonsil Parts Diagram

DIAGRAM ON SLIDE 21

Secondary: Spleen

- located in left hypochondriac region

- Usually not palpable as it lies deep in the rib cage, but may be felt in individuals of slender build

- Distinct areas of white pulp (25%) - lymphatic tissue and red pulp (75%) - fibrous network of macrophages and RBCs.

- Immune response initiated against substance in blood

- monitors blood, detects and responds to foreign antigens, destroys defective red blood cells

- Regulates blood volume

- Limited reserve of RBC

- can be ruptured in traumatic abdominal injuries

- Splenectomy

Secondary: MALT

- Mucosa-associated lymphatic tissue (MALT)

- Bronchial-associated lymphoid tissue (BALT) (found in respiratory system)

- Gastrointestinal-associated lymphoid tissue (GALT). e.g Colon GALT

Secondary: SALT

- Skin associated lymphatic tissues (MALT)

- Stratum spinosum houses epidermal dendritic (langerhans) cells (2-8% epidermal cells)

- dendritic antigen presenting cells (APCs)

- T-lymphocytes can also be found in the stratum spinosum. Dendritic cells + T cells: SALT (Skin Associated Lymphoid Tissue)

How the Lymphatic System is connected to Cardiovascular System

DIAGRAM ON SLIDE 25

Homeostasis

- Ability to maintain a relatively constant internal environment

- The lymphatic system works with the cardiovascular system and the immune system, to achieve homeostasis

- Helps the immune system by housing and transporting immune cells

- Helps the cardiovascular system by returning interstitial/extra-cellular fluid (ECF) from capillary beds (includes excess fluids and excess proteins) to the venous system.

Lymphatic Disorders** (DONT NEED TO KNOW)

- Tonsillitis: Inflammation of the tonsils - bacterial infection

- Lymphoma: cancer (benign or malignant) of the lymphoid tissue or cells, often begins in the lymph nodes, immune system suppressed

- Hodgkin's Disease: malignancy in lymphoid tissue (malignant B cells)

- Non-Hodgkins Lymphoma: any cancer of lymphoid tissue - except Hodgkin's. Can effect cells, nodes or organs

- Lymphedema: swelling due to accumulation of fluid in interstitial fluids, usually related to blocked lymphatic vessels

DIAGRAM ON SLIDE 27

TAKE HOME MESSAGES

DIAGRAM ON SLIDE 28