Chapter 20- The lymphatic system Flashcards
Lymphatic system general function
Picks up fluid lost by blood capillaries
The lymphatic system consists of (4)
lymph vessels, lymph, lymphoid organs, and lymph nodes
Lymphoid organs function (3)
- Provide structural basis for immune system
- Monitors body for infection
- Houses phagocytic cells and lymphocytes
Lymphatic vessels function
Picks up protein-containing interstitial fluid that is not reabsorbed by blood capillaries. They only move fluid toward the heart.
Lymph
Interstitial fluid not reabsorbed by the capillaries (called lymph once it enters the lymph vessel).
Lymph capillaries function
Blind ended vessels that weave through capillary beds, they allow intake of large proteins.
Which structures make the lymph capillaries more permeable? (2)
- Loosely aggregated endothelial cells in walls of capillaries- form flaps that open.
- Anchoring filaments- increase in interstitial fluid pulls on anchoring filaments
Anchoring filaments function
Increase in interstitial fluid pulls on anchoring filaments. Flaps of endothelial wall open easily. As you drain more fluid into the lymphatic capillary, the pressure goes down and the trap door closes.
When do capillaries become even more permeable?
During illness/infection capillaries become even more permeable. Pathogens transported to lymph nodes, where the immune system destroys them
Lacteals
Specialized lymph capillaries for movement of fats from small intestine to bloodstream. Fats are very large, so specialized lymph vessels are necessary. Lacteals are very permeable
Lymph capillaries drain into
Collecting lymphatic vessels. These vessels drain into lymphatic trunks, which drain into lymphatic ducts.
Collecting lymphatic vessels
Where lymph capillaries drain into first. They have large lumen to create low pressure, so lymph flows through easily. In skin- vessels travel with superficial veins, in the trunk- vessels travel with deep arteries
Lymphatic trunks (5)
- Lumbar trunk (2)- drains lower extremities (legs)
- Bronchomediastinal trunk (2)- drains thorax
- Subclavian trunk (2)- drains upper extremities (arms) and superficial thoracic wall
- Jugular trunks (2)- drains head and neck
- Intestinal trunk (1)- drains digestive organs
Lymphatic ducts definition
Structures that lymphatic trunks drain into. Both ducts empty into junction at internal jugular vein and subclavian vein
Lymphatic ducts (2)
- Right lymphatic duct
2. Thoracic duct
Right lymphatic duct
Drains lymph from right upper limb, right side of head, and right thorax
Thoracic duct
Drains any part of the body that is not drained by the right lymphatic duct- left upper limb, left side of brain, left side of thorax, entire abdomen and pelvis, both lumbar trunks (right and left limbs), intestinal trunk. Usually begins at the cisterna chyli. Gets lymph from 2 lumbar trunks and intestinal trunk
Adaptations that allow lymph vessels to push lymph through vessels and back into circulation (4)
- Smooth muscle in larger vessel walls helps push lymph through
- Similar to circulation in veins- valves prevent backflow, respiratory pump
- Circulation also improved by pulsatile nature of nearby arteries
- Physical movement (skeletal muscle) is important for increasing lymph flow
How does physical movement increase lymph flow?
For infected regions- body part should be mobilized to increase rate of removal of inflammatory material- lymph is circulated through the body part faster. If you can’t move the limb, eventually the vessels will be blocked off and not be able to carry any more
What happens if lymph vessels are blocked off?
Blocking or removing lymph vessels/nodes causes severe, localized edema- nowhere for interstitial fluid to drain
Immune system cells and supporting cells that form lymphoid tissue (4)
- Lymphocytes
- Macrophages
- Dendritic cells
- Reticular cells
Lymphocytes
Immune cell- B cells and T cells. Lymphocytes regularly circulate through blood vessels, lymphoid tissue, and loose connective tissues of the body- ensures good patrol of the body for foreign bodies
B cells function
Produce plasma cells, which secrete antibodies into the blood, don’t play direct role in body defense. Antibodies put a “red flag” on foreign antigen cells- marked for destruction
Types of T cells (2)
- Helper T cell
2. Killer T cell
Helper T cell (3)
Manages/mediates immune response- helper T cell function is necessary for killer T cell function.
- Assists in maturation of B cells, macrophages, and other immunity related cells
- Stimulate an immune response to occur at an appropriate rate
- Also prevent an excessive immune response- don’t want to damage the body’s own cells
Killer T cell
Cell destroyer, kills off virus infected and cancerous cells
Macrophages
Immune cell. Phagocytize large, foreign substances and help activate T cells
Dendritic cells
Immune cells- cells that escort “red flagged” cells back to lymph nodes. Dendritic cells put flagged cells on display- other immune cells know to destroy
Reticular cells
Supporting cell. Produce stroma- supports cell types in lymphoid tissue/organs.
Functions of lymphoid tissues (2)
- Houses lymphocyte cells, allows them to proliferate
2. Provides surveillance point for lymphoid cells
What are lymphoid tissues made of?
Mostly made of reticular connective tissue. Exception- not in thymus
Types of lymphoid tissue (2)
- Diffuse lymphoid tissue
2. Lymphoid nodules
Diffuse lymphoid tissue
This tissue is present in most organs of the body. It is a loose aggregation of lymphoid cells and reticular fibers, which gives more room for white blood cells to move around. Larger collections of diffuse lymphoid tissue are found in mucous membranes (any opening in the body leading to the outside has a mucous membrane- inner lining of the mouth and nose).
Lymphoid nodules
Tightly packed lymphoid cells and reticular fibers. Usually form parts of larger lymphoid organs (especially lymph nodes)- lymph nodes are collections of lymphoid nodules pushed together. Contains germinal centers.
Germinal centers
Found in lymphoid nodules. Areas of proliferating B cells- the cells are maturing and are exposed to foreign substance
Primary lymphoid organs
Location where B and T cells mature- B cells mature in the red bone marrow, T cells mature in the thymus
Secondary lymphoid organs
Lymph nodes, spleen, mucosa-associated lymphoid tissue (malt). Location where mature lymphocytes first encounter antigens and become activated
Lymph nodes locations
Form clusters in axillary, cervical, and inguinal regions. Areas where large number of collecting lymph vessels converge and form lymphatic trunks
Importance of lymph nodes (2)
- Activating immune system- dendritic cells bring antigens to lymph nodes to “display” them to lymphocytes- activate T cells
- Cleanses lymph via filtration
How do lymph nodes cleanse lymph?
Lymph passes through nodes before it enters back into circulation- macrophages clean lymph of microorganisms and other particles. Clean lymph can go back to circulation without risking spreading infection to other areas of the body
What is the importance of clusters of lymph nodes?
Clusters means that lymph has to pass through multiple nodes to go to circulation- it will be cleaned more efficiently
Compartments of lymph nodes (2)
- Cortex
2. Medulla
Lymph node cortex
Outer portion of the lymph node. The outer portion of the cortex has dense follicles- follicles contain dividing B cells. The inner portion contains constantly moving T cells.
Medulla of the lymph node
Inner portion of node- both B and T cells found here
Lymph sinus
Sites where macrophages reside
Afferent lymph vessels
There are several of these (more afferent than efferent). They bring lymph into the node, and lymph circulates through the sinuses.
Efferent lymph vessels
There are 2 of these vessels. Allows lymph to leave the node. Lymph enters a node faster than it can leave, so it remains in the node slightly longer and is drained more slowly than it enters. Benefit- ensures lymph is cleaned out before it exits.
Lymphadenopathy
Swollen lymph nodes. Nodes overwhelmed and blocked off due to high infection rate. They become inflamed, swollen, tender, and filled with pus. Usually necessitates use of antibiotic to assist in treatment of infection
Why do secondary cancer sites cause swollen lymph nodes?
Metastasizing cancer cells break free from the original tumor, get “stuck” in lymph nodes in different parts of the body and form other tumors. Lymph nodes become swollen/enlarged, but are not painful, just feel like a hard lump underneath the skin. More common in the clusters- cervical, axillary, inguinal. Ex- swelling of axillary nodes indicates breast cancer
Which is the largest lymphoid organ?
The spleen
Functions of the spleen (3)
- Important for cleansing blood (doesn’t do anything with lymph)
- Recycles parts of old RBCs for later reuse. Stores iron, ships other recyclables to liver for processing
- Stores platelets and monocytes
How does the spleen cleanse blood?
The spleen is very well vascularized- pulls old and damaged blood cells (RBCs, platelets) from blood supply. Macrophages in spleen monitor the blood and pull microorganisms straight out of blood
2 components of the spleen
- Red pulp- “recycling center”. Area of erythrocyte and pathogen destruction, packed with red blood cells and macrophages
- White pulp- serves immune function, contains mostly lymphocytes on reticular fibers
Can you bleed to death if the spleen ruptures?
Yes, if the injury if severe. Bone marrow and liver will take over the functions of the spleen if it’s removed- they can clean blood as well since this is an important function. About 20% of people have a “secondary” spleen- they have a second spleen that will develop when the first is removed. Won’t be as good as the original spleen, but it will still work
Mucosa associated lymphoid tissues (MALT) definition
Lymphoid tissues found specifically in mucous membranes. Most mucous membranes lead into/out of the body- easy “in” for pathogens- MALT prevents pathogen entrance at these areas
MALT locations (3)
- Tonsils
- Peyer’s patches
- Appendix
Tonsils function
Found at entrance to pharynx in throat- fight infections/bacteria coming in from the mouth
Types of tonsils (4)
- Palatine tonsils- largest, most likely to become infected
- Lingual tonsils- lymphoid follicles at base of tongue
- Adenoids (pharyngeal tonsils)- in posterior wall of nasopharynx
- Tubal tonsils- surround openings of auditory tubes into pharynx
Peyer’s patches
Aggregated lymphoid nodules that are structurally similar to tonsils. Prevent bacteria from entering, found in the wall of the ileum of the small intestine. Good for the generation of “memory” lymphocytes.
Appendix
High concentration of lymphoid follicles. Similar to Peyer’s patches- prevents bacteria from going from the large to the small intestine. You can live without the appendix. Good for the generation of “memory” lymphocytes.
Thymus location
Located in the chest in front of the aorta
Thymus
Site of T cell maturation. Without the thymus, mature T cells capable of body defense wouldn’t exist
When is the thymus the largest and the most active?
Young children need to develop an appropriate set of T cells to defend against new pathogens, but the thymus begins to atrophy in early adolescence (8-11). Will still put out immune cells, but at a reduced rate- immune system remembers these infections, don’t need a huge amount of T cells. In old age, thymus is mostly fibrous and fatty tissue
Cortex of the thymus
packed tightly with lymphocytes
Medulla of the thymus
Medulla has fewer lymphocytes. It contains Hassell’s (thymic) corpuscles- site of regulatory T cell production. Function- regulatory T cells prevent autoimmune responses
Thymosin
Hormone in thymus, regulates function. Function- stimulates development/maturation of T cells- stimulates immunocompetency. Immunocompetency teaches the T cell what it should be looking for
How is the thymus different from other lymphoid organs?
- No B cells found in thymus
- No direct immune response
- No reticular fibers. Has epithelial cells instead- ideal for T cell maturation.
Why doesn’t the thymus participate directly in immune response?
The thymus is only a site for T cell maturation, not launching an immune response. The blood thymus barrier prevents immature T cells from being exposed to antigens too early. If the thymus had access to the blood supply, immature T cells would encounter pathogens or cancerous cells.
