Lymphatic System Flashcards
What does the lymphatic system do?
Returns interstitial fluid that has leaked from the vascular system and plasma protein back to the blood.
What are the three parts of the lymphatic system?
- Lymphatics: Network of lymphatic vessels
- Lymph: The fluid in vessels
- Lymph nodes: Cleanse the lymph
Once interstitial fluid enters lymphatics, it is called?
Lymph
What do lymphoid organs and tissues provide?
Structural basis of immune system by housing phagocytic cells and lymphocytes
(e.g. spleen, thymus, tonsils, lymph nodes, other lymphoid tissues)
Why do lymphatic vessels offer a one-way system?
To ensure lymph flows only toward heart
What 2 things do lymphatics (lymph vessels) include?
Lymphatic capillaries
Larger lymphatic vessels
What are lymphatic capillaries?
Blind-ended vessels that weave between tissue cells and blood capillaries.
Lymphatic capillaries are absent from what?
- Bones
- Teeth
- Bone marrow
How do lymphatic capillaries differ from blood capillaries?
- Similar but more permeable
- Can take up larger molecules and particles
(e.g. proteins, cell debris, pathogens and cancer cells) - Can act as a route for pathogens to travel throughout the body
What 2 specialized structures allow increased permeability of lymphatic capillaries?
- Endothelial cells overlap loosely to form one-way minivalves
- Minivalves are anchored by collagen filaments to matrix, hence increases in ECF volume opens minivalves more
What happens to the minivalves when the extracellular fluid decreases?
Close
What are lacteals and their functions?
- Specialized lymph capillaries present in the intestinal mucosa.
- Absorb digested fat and deliver fatty lymph (chyle) to blood
What do larger lymphatic vessels consist of and what’s its structure like?
- Collecting vessels, trunks and ducts.
- Similar to veins, except have thinner walls with more internal valves and anastomose more frequently.
What are the main functions of lymphatic vessels?
- Return excess tissue fluid to the blood
- Return leaked proteins to the blood
- Carry pathogens to lymph nodes
- Carry absorbed fat from the intestine to the blood (via lacteals)
Where do lymph capillaries drain into?
Collecting lymphatic vessels
Collecting vessels in skin travel with ______ veins, but deep vessels travel with _______.
- superficial
- arteries
What are lymphatic trunks formed by?
Union of largest collecting vessels
to drain large areas of the body
Name regions where larger lymphatic trunks drain.
- Paired lumber
- Paired broncho-mediastinal
- Paired subclavian
- Paired jugular trunks
- Single intestinal trunk
Lymph is delivered from trunks into what?
Two large lymphatic ducts
What does the right lymphatic ducts drain?
Right upper arm and right side of head and thorax
What does the thoracic duct drain?
The rest of the body; starts out as an enlarged sac aka cisterna chyli
What do lymphatic vessels do?
- Return excess tissue fluid to the blood
- Return leaked proteins to the blood
- Carry pathogens to lymph nodes
- Carry absorbed fat from the intestine to the blood (via lacteals)
What mechanisms are lymph propelled by?
- Milking action of skeletal muscle
- Pressure changes in the thorax during breathing
- Valves to prevent backflow
- Pulsations of nearby arteries
- Contractions of smooth muscle in walls of lymphatics
What do lymphoid cells consist of?
- Immune system cells found in lymphoid tissue
- Supporting cells that form lymphoid tissue structures
What are the two main types of immune system cells?
- Lymphocytes: cells of the adaptive immune system; mature into a) T cells and b) B cells
What do lymphocytes (T cells and B cells) do?
Protect against antigens
E.g. bacteria, toxins, viruses, mismatched RBCs, cancer cells
What do T cells do?
- Manage immune response
- Attack and destroy infected cells
What do B cells do?
Produce plasma cells that secrete antibodies
Antibodies mark antigens for destruction by ______ or other means
phagocytosis
What do macrophages do?
Phagocytize foreign substances and help activate T cells
What do dendritic cells do?
Capture antigens and deliver them to lymph nodes.
Help activate T cells
What is a supporting lymphoid cell and what does it do?
Reticular cells: Produce reticular fibers (stroma) in lymphoid organs
What is a stroma?
Network like support that acts as scaffolding for immune cells
What are the main functions of lymphoid tissue?
- Houses and provides proliferation sites for lymphocytes
- Offers surveillance vantage points for lymphocytes and macrophages as they filter through lymph
What are lymphoid tissues composed of?
Reticular connective tissues.
- Macrophages live on reticular fibers
- Spaces b/w fibers offer a place for lymphocytes to occupy when they return from patrolling body
What are the two main types of lymphoid tissues?
- Diffuse lymphoid tissues
- Lymphoid follicles (nodules)
What are diffuse lymphoid tissues?
Loose arrangement of lymphoid cells and some reticular fibers
- Found in every body organ
- Larger collections in lamina propria of mucosae
What are lymphoid follicles (nodules)?
Solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers
- Contain germinal centers of proliferating B cells
- Found in nodes, spleen, MALT
- Isolated aggregations of Peyer’s patches and in the appendix
What is mucosa?
The combination of an epithelial tissue and a connective tissue, lamina propria
What are primary lymphoid organs?
Areas where T and B cells mature.
- Red bone marrow: B cells
- Thymus: T cells
What are secondary lymphoid organs?
Areas where mature lymphocytes first encounter their antigen and become activated
E.g. Nodes, spleen, MALT, and diffuse lymphoid tissues
What are lymph nodes?
Principal secondary lymphoid organs of body
- Found throughout body
- Most embedded deep in connective tissue in clusters along lymphatic vessels
- Some near to body surface in inguinal, axillary, and cervical regions where collective vessels converge into trunks
What are the two main functions of lymph nodes?
- Cleansing the lymph as filters
- Macrophages remove and destroy microorganisms and debris - Immune system activation
- Offer a place for lymphocytes to become activated and mount an attack against antigens
Structure of a lymph node
- Surrounded by external fibrous capsule
- Capsule fibers extend inward as trabeculae that divide node into compartments
- Two distinct regions: cortex and medulla
What does the medulla of lymph node contain?
B cells, T cells, and plasma cells are found.
What does lymph sinusus found throughout the node consist of?
- Large lymphatic capillaries spanned by crisscrossing reticular fibers.
- Macrophages reside on fibers, checking for and phagocytizing any foreign matter
How do lymph nodes circulate?
- Enters convex side of node via afferent lymphatic vessels
- Travels through medullary sinuses
- Exits concave side at helium via efferent lymphatic vessels
What is a spleen and the two areas within?
- Largest lymphoid organ
- White and red pulps
What are the two main functions of the spleen?
- White pulp: immune; site of lymphocyte proliferation and immune surveillance and response.
- Red pulp: cleaning; cleans old cells and platelets in the blood; macrophages remove debris in the red pulp. The cemetery of RBC
What are the additional functions of the spleen?
- Recycles the breakdown products of red blood cells for later reuse. Releases the breakdown of the iron salvaged from hemoglobin
- Stores blood platelets and monocytes for release into the blood when needed
- Site of erythrocyte production in the fetus
What is MALT? What does it do and where is it found?
- Lymphoid tissues in mucous membranes throughout body
- Protects from pathogens trying to enter body
- Found in the mucosa of the respiratory tract, genitourinary organs, and digestive tract. Large collection found in tonsils, Peyer’s patches and appendix
What is the function and characteristics of tonsils?
- To gather and remove pathogens in food or air
- Contain follicles with germinal centers; scattered lymphocytes
- Not fully encapsulated
- Form tonsillar crypts; crypts trap and destroy bacteria
- Allows immune cells to become activated and build memory cells against pathogens
What are Peyer’s patches? What does it do.
- Clusters of lymphoid follicles in wall of distal portion of small intestine (aka aggregated lymphoid nodules)
- Destroy bacteria, preventing them from breaching intestinal wall.
- Generate memory lymphocytes
What does the appendix consist of?
A large number of lymphoid follicles
- Destroy bacteria, preventing from breaching intestinal wall
- Generate memory lymphocytes
What does thymus do?
Functions as lymphoid organ where T cells mature
- Most active and largest in childhood
- Stops growing during adolescence, then atrophies
- Still produces immunocompetent cells, slowly
- Does not directly fight antigens
- Most thymic cells are lymphocytes
- No follicles due to lack of B cells
- Contains blood thymus barrier which prevents premature activation
- The stroma of the thymus consists of epithelial cells instead of reticular fibers to provide the right conditions for T cells to mature
What are thymic corpuscles?
- Sites of T cell destruction
- Involved in the development of regulatory T cells, important for preventing autoimmune responses
