Chapter 20 - lymphatic system Flashcards
What is the lymphatic system and what does it consist of?
returns fluids leaked from blood vessels back to blood
- network of drainage vessels (lymphatic vessels)
- fluid (lymph)
- structures that cleanse lymph (lymph nodes)
What is the function of lymphoid organs and tissues?
Provide structural basis of immune system
- body’s defense mechanisms
- spleen, thymus, tonsils, lymph nodes, other lymphoid tissues
What are the functions lymphatic vessels?
collect the excess protein-containing interstitial fluid and return it to the blood
- transport pathogens to lymph nodes and absorbed fats from intestine to blood
What are lymphatic capillaries, where are they not found.
blind-ended vessels that weave between tissue cells and blood capillaries
- bones and teeth
How are lymphatic capillaries operate in the brain?
- help drain ECF (inter and cerebro fluids) and their wastes
- malfunction plays a role in degenerative diseases (Alzheimer’s)
Why are lymphatic capillaries more permeable than blood capillaries?
- overlap loosely to form one-way minivalves anchored by collagen filaments, so increase ISF volume
How does the minivalves close and why is it important?
- pressure in lymphatic capillaries increase, the valve closes and prevents leakage
Which tissue is lymphatic capillaries even more permeable?
inflamed tissues, to help take up larger substances
What are lacteals in the small intestine and what is the structure set up?
a specialized set of lymphatic capillaries for absorption and transport of digested fat
- intestinal mucosa
How do large lymphatic vessels drain?
drain into larger and thinker-walled lymphatic vessels than to the subclavian veins
What is the collecting lymphatic vessels composition, location and formation?
- have all three tunica (thinner), valves and anastomoses
- In skin: travel in superficial veins or deep vessels of trunk travel with deep arteries
- larger vessels unite to form lymphatic trunk
How many lymphatic trunks are there and what are the 2 main pairings and one singluar one?
9
- Left: lumbar/ broncho mediastinal and Right: subclavian/ jugular trunks
- intestinal trunk
What are the 2 main ducts the trunks deliver lymph to?
- right lymphatic duct
- thoracic duct (larger)
What parts of the body does the right lymphatic duct serve and where does it drain?
- drains right upper limb and right side of the head and thorax
- venous circulation: right internal jugular and right subclavian
What parts of the body does the thoracic duct serve and where does it drain?
- drains the rest of the body
- venous circulation: left internal jugular and left subclavian veins
How do lymphatic vessels receive their own blood supply and what is it called when it becomes inflamed.
vasa vasorum
- severe inflammation is called lymphangitis (shown as a red streak on arm)
Lymph nodes - what is it composed of and what are the immune system cells?
- made of immune system cells found in lymphoid tissues
- 2 types of lymphocytes (T and B cells) protect the body against antigens
What are antigens and are the functions of the 2 types of lymphocytes?
A: anything that triggers an immune response
T lymphocytes: immune response; some directly attack infected cells
B lymphocytes: bind, produce plasma cells, which secrete antibodies that destroy cells with antigen
What is the difference between macrophages and dendritic cells?
M - engulfs cell and active T cells - granulomas
DC - capture and deliver antigens to lymph nodes to activate T cells
What is a lymphoid tissue?
component of the immune system
- provides activation and proliferation sites for lymphocytes
- ideal surveillance location for lymphocytes and macrophages
What is the lymphoid tissue made of and what resides in it?
reticular connective tissue
- in all lymphoid organs except thymus
- spaces between fibers is where lymphocytes to “live” when they return from patrolling the body
What is diffuse lymphoid tissue?
loose arrangement of lymphoid cells and reticular fibers
- in every body organ
What is lymphoid follicles (lymphoid nodules)?
tightly packed lymphoid cells and reticular fibers
- have germinal centers of proliferating B cells
- helps form larger lymphoid organs
Where are lymphoid follicles found?
- intestinal wall (of ileum) called Peyer’s patches
- the appendix
- MALT
- lymph nodes
- tonsils
Why can lymph nodes become a secondary cancer site?
- cells get trapped causing a bulge that is not painful
What is the primary lymphoid organs?
where T and B cells mature
- B cells mature in RBM
- T cells mature in the thymus
What is the secondary lymphoid organs?
where mature lymphocytes first encounter their antigens and become activated, include:
- lymph nodes and spleen
mucosa-associated lymphoid tissue (MALT) that form:
- tonsils, Peyer’s patches in small intestines and appendix
- diffuse lymphoid tissues
What are the 2 regions of the lymph nodes?
cortex: outer layer with dense follicles and germinal centers filled with dividing B cells
- deep part houses T cell in transit (circulate in blood, lymph and nodes)
Medulla: consists of medullary cords, contains B cells, T cells, and plasma cells
What is the lymph sinuses?
spaces in lymph nodes that separate lymph nodules and are filled with reticular fibers and macrophages
Where does lymph enter the lymph node and what is the first structure in travels through?
- convex side of lymph node via afferent lymphatic vessels
- large subcapsular sinus
Where does lymph travel after the subcapsular sinus?
smaller sinuses of the cortex and medulla, then passes through the medullary sinuses before exiting the node at hilum via efferent lymphatic vessels
Why is the flow of lymph slow through the lymph node?
fewer efferent vessels draining the node compared to the afferent vessels
What is the largest lymphoid organs and where is it located?
spleen
- on the left side of the abdominal cavity, under the diaphragm
What arteries and veins serve the spleen?
splenic artery and vein, which enters and exits at the hilum
What role does the spleen play in immune function?
provides a site for lymphocyte proliferation, immune surveillance, and immune response
How does the spleen cleanse the blood?
cleanses the blood of aged and defective blood cells and platelets through macrophages
What is the function of the spleen when it comes to storage and being a site?
- stores iron and recycles breakdown products of RBC
- stores platelets and monocytes from release into blood
- site of fetal erythrocyte production
What is the structure order starting from diaphragm to pancreas?
- diaphragm
- spleen
- adrenal gland
- left kidney
- splenic artery
- pancreas
What are the 2 components that make up the spleen?
White pulp and red pulp
What is the function of white pulp?
where immune function occurs
- mostly in lymphocytes on reticular fibers
- islands of white in sea of red
What is the function of red pulp?
where old blood cells and bloodborne pathogens are destroyed
- lots of RBC and macrophages that engulf
- made of splenic cords (reticular tissue)
What is a potential consequence of a direct blow or severe infection to the spleen?
spleen ruptures, spilling blood into the peritoneal cavity
What have surgeons discovered about the spleen after splenectomy?
can repair itself if left alone.
What happens when the spleen is removed?
The liver and bone marrow take over most of the spleen’s functions
Can the spleen regenerate after removal?
Children (>12), it will regenerate
What is mucosa-associated lymphoid tissue (MALT), where does it and what is its function?
lymphoid tissues in mucous membrane
- lines respiratory, genitourinary and digestive tract
- protects from pathogens trying to enter the body
Where is the largest collection of MALT?
- tonsils
- peryer’s patches
- appendix
What is the main function of tonsils?
lymphoid tissue at entrance of pharynx gathers and remove pathogens in food and inhaled air
How can tonsils be identified and what is the main types?
seen swelling in the mucosa
1. paired palatine tonsils
2. lingual tonsil
3. pharyngeal tonsil (adenoid if enlarged)
4. pair of tubal tonsil
Where are the paired palatine tonsils located?
sides posterior to oral cavity
Which tonsils are the largest and most often infected?
the paired palatine tonsils
Where is the pharyngeal tonsil (adenoid if enlarged) found?
posterior wall of the nasopharynx.
What is the location and function of the pair of tubal tonsils?
openings of the auditory tubes into the pharynx.
What are the components of the tonsils’ lymphoid follicles?
- follicles with germinal centers
- diffusely scattered lymphocytes.
How are tonsils different from other lymphoid tissue?
- partially encapsulated
- epithelium invaginates, forming deep tonsillar crypts
What role do tonsillar crypts play?
trap debris and bacteria, which cross the epithelium to enter the lymphoid tissue
How do tonsils contribute to immune response?
Immune cells in the tonsils are activated and build “memory” against pathogens
What are Peyer’s patches (aggregated lymphoid nodules) and what are the structurally similar to?
large cluster of lymphoid follicles in small intestine
- tonsils
Why is the location of the Peyer’s patches ideal?
prevent bacteria from breaching intestinal wall
- generate “ memory” lymphocytes from long-term immunity
What is the appendix and why is it placed where it is?
first part of large intestine containing lymphoid follicles
- generate “ memory” lymphocytes from long-term immunity
Where is the thymus located and what is its function?
inferior neck, extending into the mediastinum and partially overlying the heart
- site of T lymphocyte development
When is the thymus most active and what happens to it after puberty?
- childhood
- atrophies (gets smaller)
Does the thymus continue to produce immune cells after atrophying?
Yes, but slowly
What happens to the thymus in older adults?
replaced by fibrous and fatty tissue
- difficult to distinguish from surrounding connective tissue
What is found in the cortex of the thymus?
- rapidly dividing lymphocytes
- scattered macrophages
what is found in the medulla of the thymus?
- fewer lymphocytes
- thymic corpuscles (keratinized epithelial cells)
What role does the thymus play in immune regulation?
development of regulatory T cells
- prevents autoimmune responses
How does the thymus differ from secondary lymphoid organs?
- no follicles (no B cells)
- only for T lymphocyte maturation
- has blood-thymus barrier (separates immature T lymphocytes from antigens)
What type of cells make up the stroma of the thymus?
epithelial cells (not reticular fibers)
