Lymphatic System
returns fluids that have leaked from the blood vascular system back into the blood
three parts of lymphatic system
- Network of lymphatic vessels
- Lymph = fluid contained in those vessels
- Lymph nodes – cleanse the lymph as it passes through them
Lymphoid Organs & Tissues
- provide the structural basis of the immune system
- House phagocytic cells and lymphocytes which play roles in the body’s defense mechanisms and resistance to disease eg. spleen
- Largest lympathic organ = spleen
lymphatic vessels
- are elaborate networks of drainage vessels that collect the excess interstitial fluid and return it to the bloodstream
- Lymphatic vessels form a one-way system in which lymph flows ONLY TOWARD the heart!!
Lymphatic Capillaries
Weave between the tissue cells and blood capillaries in the loose connective tissues of the body
What 2 unique structural modifications allow lymphatic capilliaries to be EXTREMELY permeable
1) Endothelial cells: not tightly joined, but overlap each other loosely forming easily opened flaplike minivalves
2) Collagen filaments: anchor endothelial cells to surrounding structures
an increase in interstitial fluid volume will open the minivalves
Pressure greater in interstitial space:
• minivalve flaps open
• fluid enters lymphatic capillary
Pressure greater in lymphatic capillary,
• forces endothelial minivalve flaps shut
• preventing lymph from leaking back out as the pressure moves it along the vessel
Structure of Collecting Lymphatic Vessels
have the same three tunics as veins
thinner walls and more internal valves
Lymphatic Trunks
drain fairly large areas of the body
named mostly for the regions from which they drain lymph
Lymphatic Ducts
Right Lymphatic Duct
drains lymph from the right upper limb and the right side of the head and thorax
Thoracic Duct
much larger because receives lymph from the rest of the body
Lymph Flow
Lymphatic Capillaries (smallest) –> Collecting Lymphatic Vessels –> Lymphatic Trunks –> Lymphatic Ducts (largest)
Lymph Transport
• low-pressure conduits
• use the same mechanisms that promote venous return
> milking action of active skeletal muscles
> pressure changes in the thorax during breathing
> valves to prevent backflow
List 3 Lympch Cell Types
- Functions
- Subcells
1) Lymphocytes > T lymphocytes (T cells) > B lymphocytes (B cells) 2) Macrophages: 3) Reticular Cells:
Lymphocytes Function/ Subtype functions
1) Lymphocytes – mediate immune responses, arise in red bone marrow and mature into one of two main types
i) T lymphocytes (T cells): they mature in thymus gland, manage the immune response, directly attack and destroy infected cells,
ii) B lymphocytes (B cells): mature in bone marrow, Protect the body by producing plasma cells that secrete antibodies, Antibodies mark antigens for destruction by phagocytes or other means
B-lymphocytes (B cells) give rise to:
2
a) Plasma Cells – produce antibodies that will attach to foreign cells (antigens) and destroy them
b) Memory B Cells – “remember” pathogens encountered and can have a rapid response if it is detected again
T-lymphocytes (T cells) give rise to:
4
a) Effector T Cells (cytotoxic T cells) – secrete cytotoxic agents that destroy virus-invaded cells and cancer cells
b) Helper T Cells – secrete chemical messengers to activate T and B cells as well as macrophages
c) Regulatory T Cells – act to control immune responses/suppressors
d) Memory T Cells – “remember” antigen so can have rapid immune response to second encounter
Macrophages Function
body protection and the immune response phagocytize foreign substances. Help to activate T cells
Reticular Cells
produce the reticular fiber stroma
Becomes the network that supports the other cell types in lymphoid organs and tissus
Lymphoid Tissues Function
- houses and provides a proliferation site for lymphocytes
* is an ideal surveillance vantage point for lymphocytes and macrophages
Types of Lympohoid Tissues -2
Diffuse Lymphoid Tissue
- found in virtually every body organ
Lymphoid Follicles/Nodules
- follicles form part of larger lymphoid organs such as lymph nodes
Lymph Nodes Function -2
Function #1: FILTRATION
• macrophages in the nodes remove and destroy microorganisms/debris that enter the lymph from the connective tissues
• prevents them from being delivered to the blood and spreading to other parts of the body
Function #2: IMMUNE SYSTEM ACTIVATION
• Sites where lymphocytes will encounter antigens and are activated to mount an attack against them
Thymus
maturation site for T lymphocyte precursors
must be kept isolated from foreign antigens to prevent their premature activation
Spleen Function
- site for lymphocyte proliferation and immune surveillance and response
- blood cleansing
- stores RBC breakdown + blood platelets/monocytes for release into the blood
- products of RBC’s for later reuse
- erythrocyte production in the fetus
Histologically the spleen
A) White Pulp: where immune functions take place
B) Red Pulp: where worn-out RBCs and bloodborne pathogens are destroyed
Mucosa-Associated Lymphoid Tissue (MALT)
set of distributed lymphoid tissues strategically located in mucous membranes throughout the body
Includes:
1) Tonsils
• ring of lymphoid tissue around the entrance to the pharynx
• gather and remove many of the pathogens entering the pharynx in food or in inhaled air
2) Peyer’s Patches
• located in small intestine (ileum)
3) Appendix
• destroys bacteria & generates many “memory” lymphocytes for long-term immunity
