chp 20 Flashcards
lymphatic system function
- Returns fluids leaked from blood vessels back to blood
- Provide structural basis of immune system
- House phagocytic cells and lymphocytes
lymphatic system has three parts
- lymphatic vessels (lymphatics)
- Lymph: fluid in vessels
- Lymph nodes: clean the lymph
lymphoid organs and tissues
spleen, thymus, tonsils, lymph nodes, other lymphoid tissues
Lymphatic organs and tissues Returns \_\_\_\_ per day lymph fluid that has gone into the -Includes
- Returns interstitial fluid and leaked plasma proteins to the blood
- Network of vessels
- Returns ~ 3L interstitial fluid per day
- Lymph
- –Interstitial fluid that has gone into the lymphatics
- Include lymphatic capillaries and larger lymphatic vessels
Distribution and Structure of Lymphatic Vessels
____system
One-way system only toward heart
Lymphatic capillaries Weave between found where Similar to Can act as route for
- Blind-ended vessels
- Weave between tissue cells and blood capillaries
- Where?
- -Almost everywhere NOT: bones, teeth, and bone marrow
- -Even some in the central nervous system!
- —-Once thought to be absent from CNS, but now found to be present but limited to locations in meninges where they help to drain interstitial fluid and CSF.
- Similar to blood capillaries, but more permeable
- Larger molecules and particles can enter
- -Example: proteins, cell debris, pathogens, and cancer cells
- Can act as route for pathogens or cancer cells to travel throughout body
- –This is one way cancers spread…
what makes the capillaries so permeable?
one-way minivalves
- Anchored by collagen filaments to matrix
- Increases in ECF volume opens minivalves
- Decreases in ECF cause minivalves to close
Lacteals
- specialized lymph capillaries in intestinal mucosa
- –What’s mucosa again?
- Absorb digested fat and deliver fatty lymph (chyle) to the blood
Collecting lymphatic vessels
Have structures and tunics similar to
Collecting vessels travel with
- Drain lymph capillaries
- Collecting vessels, trunks, and ducts
- Have structures and tunics similar to veins, except:
- –Have thinner walls, with more internal valves
- –Anastomose more frequently
- Collecting vessels travel with superficial veins, but deep vessels travel with arteries
Lymphatic trunks
- Formed by joining together largest collecting vessels
- Drain large areas of body
- –Named for regions of body they drain:
- Paired lumbar
- Paired bronchomediastinal
- Paired subclavian
- Paired jugular trunks
- Single intestinal trunk
what collects lymph from the trunks
- Right lymphatic duct
- –Drains right upper arm and right side of head and thorax
- Thoracic duct
- –Drains rest of body
- Cisterna chyli
- –Beginning of thoracic duct
- –Only in about 50% of people
-Both empty the junction of internal jugular and subclavian veins on its own side of body
Lymph Transport
physical activity
- Low-pressure system like venous system
- Lymph is moved the way venous blood is moved:
- –Milking action of skeletal muscle
- –Pressure changes in thorax during breathing
- –Valves to prevent backflow
- –Pulsations of nearby arteries
- –Contractions of smooth muscle in walls of lymphatics
- Physical activity increases flow of lymph
- Immobilization
- –Keeps inflammatory material in area for faster healing
Lymphedema
-severe localized edema
- Caused by anything that prevents normal return of lymph to blood
- –Examples: tumors blocking lymphatics or removal of lymphatics during cancer surgery
- –Lymphedema may improve if some lymphatic pathways remain and enlarge
Lymphoid cells consist of
of (1) immune system cells found in lymphoid tissue and (2) supporting cells that form lymphoid tissue structures
Immune system cells
Lymphocytes:
-T cells and B cells both protect against
Lymphocytes: cells of the adaptive immune system; mature into one of two main types
- T cells (T lymphocytes)
- -manage immune response, and some also attack and destroy infected cells
- B cells (B lymphocytes)
- -produce plasma cells, which secrete antibodies
- -Antibodies mark antigens for destruction by phagocytosis or other means
-T cells and B cells both protect against
Antigen: anything the body perceives as foreign
Examples: bacteria, toxins, viruses, mismatched RBCs, cancer cells
Other lymphoid immune cells
- Macrophages
- -phagocytize foreign substances
- -help activate T cells
- Dendritic cells
- -capture antigens and deliver them to lymph nodes
- -help activate T cells
Supporting lymphoid cell
Reticular cells
- produce reticular fibers to form the stroma
- Stroma
- -scaffolding for immune cells to hole on to
Lymphoid Tissue
Structural composition
offers ______points for ________ as they filter lymph
Macrophages live on
Lymphocytes live in
- House and provide proliferation sites for lymphocytes
- -Offers surveillance vantage points for lymphocytes and macrophages as they filter lymph
reticular connective tissue
- -Loose connective tissue
- -Macrophages live on reticular fibers
- -Lymphocytes live in the spaces between the fibers when they are not out hunting
Two main types of lymphoid tissues
Diffuse lymphoid tissue
- -loose arrangement of lymphoid cells and some reticular fibers
- -Found in virtually every body organ
- -Larger collections in lamina propria of mucous membranes
Lymphoid follicles (nodules)
- Solid
- spherical bodies with packed lymphoid cells and reticular fibers
- Germinal centers
- -proliferating B cells
- May form part of lymph nodes
- Found Peyer’s patches and in appendix
Lymphoid organs are grouped into two functional categories
-Both T and B cells originate in
- Primary lymphoid organs
- Where T and B cells mature—
- -B in the red bone marrow
- -T in the thymus
- -Both T and B cells originate in bone marrow
- Secondary lymphoid organs
- -Areas where mature lymphocytes first encounter their antigen and become activated
- -I.e: Nodes, spleen, MALT (mucosa-associated lymphoid tissue) and diffuse lymphoid tissues
Lymph nodes
-secondary lymphoid organs of body
-Where ______ come together and form
-Main secondary lymphoid organs of body
- Hundreds found throughout body
- -Embedded deep in connective tissue in clusters along lymphatic vessels (most)
- -Some are nearer to body surface
- –inguinal, axillary, and cervical regions
- –Where collecting vessels come together and form trunks
lymph nodes two major functions
- Filter the lymph
- -Macrophages remove and destroy microorganisms and debris that enter lymph
- -Prevent unwanted substances from being delivered to blood - Immune system activation
- -Place for lymphocyte activation
- -Place for lymphocytes to attack antigens
Structure of a Lymph Node
- Vary in shape and size
- Most are bean shaped
- Small
- -less than 2.5 cm (~1 inch)
- External fibrous capsule
- Trabeculae
- -Capsule fibers that extend inward
- -Divide node into compartments
- Two regions of node:
1. Cortex
2. Medulla
Cortex
- Superficial (outer part)
- Follicles with germinal centers
- -Dividing B cells
- Deeper in the cortex
- -T cells in transit
- -T cells circulate continuously among blood, lymph nodes, and lymph
- Lots of dendritic cells
- -Play a role in activating T cells and B cells
- -Reminder-T cells and B cells are types of lymphocytes!
Medulla
- Medullary cords
- -Extend inward from cortex
- -Contain B cells, T cells, and plasma cells
- Lymph sinuses
- -Found throughout node
- -Large lymphatic capillaries
- -Mesh of reticular fibers
- –Macrophages attach to the fibers
- –Check for and phagocytize foreign matter
Lymph enters via
- afferent lymphatic vessels
- Travels through large subcapsular sinus and then into smaller sinuses found throughout cortex and medulla
- Lymph then enters medullary sinuses
- Finally exits at hilum via efferent lymphatic vessels
- –Presence of fewer efferent vessels causes flow to somewhat stagnate
- –Allows lymphocytes and macrophages time to function
- –Lymph travels through several nodes
Buboes
- Inflamed, swollen, tender lymph nodes
- When nodes are overwhelmed by what they are trying to destroy
- Often called swollen “glands”
- Buboes are sometimes pus-filled
- Bubonic plague was named after the buboes it causes!
Lymph nodes can become secondary
secondary cancer sites if metastasizing cancer cells become trapped in node
-Cancer-infiltrated lymph nodes are swollen but usually not painful, a fact that helps distinguish cancerous nodes from those infected by microorganisms
Spleen
structure and function
- Spleen blood-rich
- About size of fist
- Located in left side of abdominal cavity, just below stomach
- Largest lymphoid organ
- Served by splenic artery and vein, which enter and exit at the hilum
- Encased by fibrous capsule and has trabeculae
- Functions
- Site of lymphocyte proliferation and immune surveillance and response
- Cleanses blood of aged blood cells and platelets; macrophages remove debris
- Stores breakdown products of RBCs (e.g., iron) for later reuse
- Stores blood platelets and monocytes for release into blood when needed
- May be site of fetal erythrocyte production
spleen Histologically, consists of two components
- White pulp
- -Immune function
- -Mostly lymphocytes on reticular fibers
- -Clusters are found around central arteries
- —islands of white in a sea of red pulp
- Red pulp
- -Where old blood cells and bloodborne pathogens are destroyed
- Rich in RBCs and macrophages that engulf them
- Splenic cords
- –reticular tissue
- -separate blood-filled splenic sinusoids (venous sinuses)
The spleen has a thin capsule, so direct blow or severe infection may cause it to
rupture, spilling blood into peritoneal cavity
This can lead to shock and death!
Splenectomy
- Surgical removal of ruptured spleen
- Used to be the standard to prevent hemorrhage and shock
- BUT we now know the spleen can often repair itself
- -Frequency of emergency splenectomies has decreased dramatically
- If spleen removed
- –liver and bone marrow take over most of its functions
- -In children younger than 12, spleen will regenerate if a small part is left!
Mucosa-associated lymphoid tissue (MALT)
Lymphoid tissues in mucous membranes throughout body
- Protects from pathogens trying to enter body
- Locations:
- –respiratory tract
- -genitourinary organs
- -digestive tract
- -largest collections of MALT found in:
- —Tonsils
- —Peyer’s patches
- —Appendix
Tonsils
Simplest lymphoid organs
Ring of lymphatic tissue around pharynx
Look like swellings of mucosa
Named according to location
palatine tonsils
Posterior end of oral cavity
Largest of tonsils
Most often infected
Lingual tonsil
base of tongue
Pharyngeal tonsil
AKA adenoids
in posterior wall of nasopharynx
Tubal tonsils
surround openings of auditory tubes into pharynx
Tonsils (Function and Structure)
- Function
- —Gather and remove pathogens in food or air
- Contain follicles with germinal centers and scattered lymphocytes
- Are not fully encapsulated
- Overlying epithelium invaginates, forming tonsillar crypts
- –Bacteria or matter get into the crypts and get trapped
- -Immune cells to become activated and build memory cells against these potential pathogens
Peyer’s patches
- Clusters of lymphoid follicles in wall of small intestine
- AKA aggregated lymphoid nodules
- Structurally similar to tonsils
- Location aids in functions
- -Destroy bacteria to prevent them from escaping the intestines
- -Generate “memory” lymphocytes
Appendix
- Offshoot of first part of large intestine
- Has a large number of lymphoid follicles
- Location aids in functions (like Peyer’s patches)
- -Destroy bacteria, preventing them from breaching intestinal wall
- -Generate “memory” lymphocytes
Thymus
bilobed lymphoid organ
Inferior neck into mediastinum and partially overlies heart
Function
- Where T cells mature
- Most active and largest in size during childhood
- Stops growing during adolescence, then gradually atrophies
- Still produces immunocompetent cells, but is slow
Thymus differs from other lymphoid organs in important ways
-stroma has
- No B cells so no follicles
- Does not fight antigens
- Functions strictly in T lymphocyte maturation
- -blood thymus barrier
- —Keeps immature T lymphocytes away from pathogens so they don’t get activated before they are ready!
- Stroma
- –epithelial cells instead of reticular fibers
- –Where T lymphocytes become immunocompetent
