Chapter 20: The Lymphatic System Flashcards
A hematopoietic stem cell will give rise to
erythrocytes
leukocytes
platelets
-all three types of formed elements found in the blood
Predict the outcome of an overdose of the hormone erythropoietin
The blood viscosity increases to levels that may induce heart attacks or strokes. making too many red blood cells
if a patient has pernicious anemia, the inability of the body to absorb vitamin B12, the patient
would have a decreased number of red blood cells
Lymphatic system
- > A network of vessels that absorbs fluid that leaks from the blood into surrounding tissues
- > about 3 liters of fluid leak out each day
- > if leakage continued unchecked the body would swell with fluid
- > one-way system: starts at the capillaries and dumps it back into the circulatory system via the subclavian
Lymphatic system: consists of 3 parts
- A network of lymphatic vessels (lymphatics)
- Lymph-fluid
- Lymph nodes, tissues and organs
- > a functional system.
Lymphatic system functions
- > returns interstitial fluid and leaked plasma proteins back into the blood
- once interstitial fluid enters lymphatics, it is called lymph (clear water)
->together with lymphoid organs and tissues, provide the structural basis of the immune system
area drained by right lymphatic duct
only does right side of the face and the right arm
area drained by thoracic duct
drains the left side of the face, left arm, the abdomen, both legs
Lymphatic vessels
-> one-way system, lymph flows toward the heart
- > lymph vessels (lymphatics) include:
- lymphatic capillaries
- lymphatic collecting vessels
- lymphatic trunks and ducts
*lymphatic capillaries
Similar to blood capillaries, except:
- > very permeable (take up cell debris, pathogens, and cancer cells)
- > endothelial cells overlap to form one-way minivalves
Lacteals: specialized lymph capillaries present in small intestines.
*absorb digested fat and deliver fatty lymph (chyle) to the blood
Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other, forming flaplike minivalves.
*lymphatic collecting vessels
Similar to veins, except:
- > have thinner walls, with more internal valves
- > anastomose (multiple pathways to get from one point to another) more frequently
Collecting vessels in the skin travel with superficial veins
-Deep collecting vessels travel with arteries
Regional lymph nodes
- cervical nodes
- axillary nodes
- inguinal nodes
Lymphatic trunks
Formed by the union of the largest collecting ducts
- > Paired lumbar
- > Paired bronchomediastinal
- > Paired subclavian
- > Paired jugular trunks
- > A single intestinal trunk
Lymphatic capillaries -> collecting vessels -> trunks
-> ducts
true
Lymphatic ducts
Lymph is delivered into one of two large ducts
* right lymphatic duct drains the right upper arm and the right side of the head and thorax
- Thoracic duct arises from the cisterna chyli(large sac) and drains the rest of the body
- > each empties lymph into venous circulation at the junction of the internal jugular and subclavian veins on its own side of the body
Lymph transport
Lymph is propelled by:
- pulsations of nearby arteries
- contractions of smooth muscle in the walls of the lymphatics
- milking action of active skeletal MM
- pressure changes in the thorax during breathing
Lacks an organ to act as pump, low pressure vessels
Lymphoid cells
Lymphocytes the main warriors of the immune system
->2 main varieties: T cells (T lymphocytes): mature in thymus
B cells (B lymphocytes): mature in bone marrow
Lymphocytes
T cells and B cells protect against antigens.
*Anything the body perceives as foreign-> bacteria and their toxins; viruses; mismatched RBCs or cancer cells
T cells:
*attack and destroy foreign cells
B cells:
*produce plasma cells, which secrete antibodies.
Other lymphoid cells
Macrophages:
*phagocytize/eat foreign substances and help activate T cells
Dendritic cells:
*capture antigens and deliver them to lymph nodes
Reticular cells:
*produce lymphoid tissue stroma (mattress) that supports other cells in lymphoid organs
… can enter lymphatic capillaries
bacteria, large proteins, interstitial fluid
Lymphoid tissue
- > houses and provides a proliferation site for lymphocytes
- > furnishes a surveillance vantage point
- > 2 main types:
a) diffuse lymphatic tissue
b) lymphatic follicles
Diffuse lymphatic tissue
- found in every organ in the body
- made of loose reticular CT
- larger collections appear in mucous membranes (i.e digestive tract) and lymphoid organs
Lymphatic follicles (nodules)
solid, spherical bodies of tightly packed reticular elements and cells
- Germinal center: composed of dendritic and B cells (enlarge when B cells are dividing and producing plasma cells)
- may form part of larger lymphoid organs (lymph nodes)
- NO T CELLS in the nodules
Primary lymph organs
- where B and T cells mature
- B cells mature in red bone marrow (where they originate, they don’t have to go anywhere to mature)
- T cells mature in thymus
Secondary lymph organs
Where lymphocytes encounter their antigens and are activated:
*lymph nodes
*spleen
- MALT (mucosa-associated lymphoid tissue)
- > tonsils
- > appendix
- > peyer’s patch (small intestine)
Lymph nodes
Principal lymphoid organs of the body
- embedded in connective tissue, in clusters along lymphatic vessels
- near the body surface in inguinal, axillary, and cervical regions of the body
Lymph nodes functions
- filter lymph: macrophages destroy microorganisms and debris
- Immune system: lymphocytes are activated and mount an attack against antigens
structure of lymph node
- bean shaped
- external fibrous capsule
- nodes are divided into compartments
- 2 histologically distinct regions:
- > cortex– germinal centers
- > Medulla–macrophages
structure of lymph node
- cortex contains follicles with germinal centers, (heavy with dividing B cells)
- T cells circulate continuously among the blood, lymph nodes, and lymphatic stream
- medullary sinuses contain macrophages
circulation in the lymph nodes
Lymph:
*enters via afferent lymphatic vessels
- travels through large subcapsular sinus and smaller sinuses
- exits the node at the hilum via efferent vessels
- fewer efferent vessels, causing flow of lymph to stagnate, allowing lymphocytes and macrophages time to carry out functions
lymph nodes and cancer
- > Primary site (cancer started in the lymph node):
- Hodgkin’s lymphoma or non-Hodgkin’s lymphoma – swollen lymph nodes (not painful), fatigue and fever
- > Secondary Site:
- cancer spreads via lymph to lymph nodes
*sentinel node: first node from cancer site, tested for metastatic disease
breast cancer and lymphedema
-one of the most common causes of lymphedema is removal of the breast (mastectomy) and underarm lymph tissue
Lymph tends to stall inside lymph nodes. This is due to _______.
fewer efferent lymphatic vessels than afferent lymphatic vessels. less exiting pathways
What cells populate the germinal centers of lymphoid follicles?
B lymphocytes
Spleen
- Largest lymphoid organ
- served by splenic artery and vein, which enter and exit at the hilus
- contains lymphocytes, macrophages, and huge numbers of erythrocytes
- graveyard for red blood cells
Spleen functions
- Stores breakdown products of RBCs (iron) for later reuse
- stores blood platelets
- site of fetal erythrocyte production (normally ceases after birth)
- cleanses the blood of aged cells and debris
- site of lymphocyte proliferation and immune surveillance and response
structure of the spleen
- White pulp: near central arteries- lymphocytes
- red pulp in sinuses which houses macrophages
splenomegaly
enlargement of spleen due to accumulation of infectious microorganisms
*typically from mono, malaria, and leukemia
thymus
- Changes size with age
- increases in size and is most active during childhood
- stops growing during adolescence and then gradually atrophies
Thymus
- Differs from other lymphoid organs in important ways:
- it functions strictly in T lymphocyte maturation (NO B cells)
- it does not directly fight antigens
-These thymocytes provide the environment in which T lymphocytes become immunocompetent (ability to start immune response)
An advantage to having reticular connective tissue present in lymph nodes is that ________.
- the loose organization of reticular connective tissue provides niches for macrophages and lymphocytes
- lymph filters through the nodes and is exposed to lymphocytes and macrophages
- lymphocytes cycle to various areas of the body and back to lymph nodes
Red pulp of the spleen is most concerned with __________, while white pulp is most concerned with __________.
blood filtering; immunity
MALT
- Mucosa-associated lymphatic tissue, including (lymphoid tissue located in mucous membranes)
- Peyer’s patches (small intestine), tonsils, and the appendix (offshoot of large intestine)
- Lymphoid nodules in the walls of the bronchi (respiratory tract)
- > protects the digestive and respiratory systems from foreign matter
aggregates of lymphoid follicles
- Peyer’s Patches:
- clusters of lymphoid follicles
- in the wall of the distal portion of the small intestine
- Appendix:
- tubular offshoot of large intestine
- high concentration of lymphoid follicles
- > both destroy bacteria, preventing them from breaching the intestinal wall
- generate “memory” lymphocytes
appendix
- vermiform appendix= worm-shaped
- houses helpful bacteria for intestine
- lymph tissue accumulates after birth until 2nd/3rd decade
Tonsils
- > simplest lymphoid organs
- > form a ring of lymphatic tissue around the pharynx
- Palatine tonsils: at posterior end of the oral cavity
- Lingual tonsils- grouped at the base of the tongue
- Pharyngeal tonsil (adenoids)-in posterior wall of the nasopharynx
- tubal tonsils: surrounding the openings of the auditory tubes into the pharynx
Tonsils
- contain follicles with germinal centers
- are not fully encapsulated
- epithelial tissue overlying tonsil masses invaginates, forming tonsillar crypts
- crypts trap and destroy bacteria and particulate matter that enter the pharynx in food and inhaled air
