Lymphatic System

Question 1

Three parts of the Lymphatic System

Answer 1

1. Network of lymphatic vessels
2. Lymph- fluid in vessels
3. Lymph Nodes- which cleanses lymph

Question 2

Function of Lymphoid Organs and Tissues

Answer 2

Provides structural basis of immune system

Houses phagocytic cells and lymphocytes

Its structure includes:

• spleen
• thymus
• tonsils
• lymph nodes
• other lymphoid tissues

Question 3

Function of Lymphatic Vessels (lymphatics)

Answer 3

It returns interstital fluid and leaked plasma proteins back to blood

Only 3L/day

Once fluid enters lymphatic (they becomes lymph)

Question 4

Distribution and Structure of Lymphatic Vessels

which way does lymph flows

Answer 4

Lymph flows toward the heart (it’s a one way system)

They includes:

• Lymphatic Capilliares
• Collecting Lymphatic Vessels
• Lymphatic trunks and ducts

Question 5

Describe Lymphatic Capilliares(how is it different from blood capilliares)

Answer 5

Similar to blood capilliares

But:
-they are very permeable (takes up proteins, cell debris, pathogen, and cancer cells)

Question 6

Structure of Lymphatic Capilliares

Answer 6

•Endothelial cells overlap loosely to form one-way minivalves
•Anchored by collagen filaments, preventing collapse of capillaries; increased ECF volume opens minivalves
–Pathogens travel throughout body via lymphatics

Question 7

Structure continued

Answer 7

•Absent from bones, teeth, bone marrow, and CNS
•Lacteals: specialized lymph capillaries present in intestinal mucosa
–Absorb digested fat and deliver fatty lymph (chyle) to the blood

Question 8

Describe Lymphatic Collecting Vessels

Answer 8

•Similar to veins, except
–Have thinner walls, with more internal valves
–Anastomose more frequently
•Collecting vessels in skin travel with superficial veins
•Deep vessels travel with arteries
•Nutrients supplied from branching vasa vasorum

Question 9

Lymphatic Trunks

Answer 9

•Formed by union of largest collecting ducts

–Paired lumbar
–Paired bronchomediastinal
–Paired subclavian
–Paired jugular trunks
–Single intestinal trunk

Question 10

Lymphatic Ducts(what two ducts that lymph is delivered into and what do they do)

Answer 10

•Lymph delivered into one of two large ducts
–Right lymphatic duct- drains right upper arm and right side of head and thorax
–Thoracic duct- arises as cisterna chyli; drains rest of body
•Each empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body

Question 11

Lymph is propelled by:

Answer 11

•Lymph propelled by
–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

Question 12

Describe Lymphoid Cells

Answer 12

•Lymphocytes main warriors of immune system
–Arise in red bone marrow
•Mature into one of two main varieties
–T cells (T lymphocytes)
–B cells (B lymphocytes)

Question 13

Lymphacytes(what are the two cells and what do they do)

Answer 13

•T cells and B cells protect against antigens
–Anything body perceives as foreign
•Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells

Question 14

Function of T cells

Answer 14

–Manage immune response

–Attack and destroy infected cells

Question 15

Function of B cells

Answer 15

–Produce plasma cells, which secrete antibodies

•Antibodies mark antigens for destruction by phagocytosis or other means

Question 16

Other Lymphoid Tissues

Answer 16

•Macrophages phagocytize foreign substances; help activate T cells
•Dendritic cells capture antigens and deliver them to lymph nodes; activate
T cells
•Reticular cells produce reticular fiber stroma that supports other cells in lymphoid organs

Question 17

Describe Lymphoid Tissues

Answer 17

•Houses, and provides proliferation site for, lymphocytes
•Surveillance vantage point for lymphocytes and macrophages
•Largely reticular connective tissue – type of loose connective tissue
•Two main types
–Diffuse lymphoid tissue; Lymphoid follicles

Question 18

Lymphoid Tissues continued

Answer 18

•Diffuse lymphoid tissue of lymphoid cells and reticular fibers in ~ every body organ
–Larger collections in lamina propria of mucous membranes

Question 19

Describe Lymphoid Follicles

Answer 19

•Lymphoid follicles (nodules) are solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
–Germinal centers of proliferating B cells
–May form part of larger lymphoid organs
–Isolated aggregations of Peyer’s patches and in appendix

Question 20

Describe Lymph Nodes

Answer 20

• Principal lymphoid organs of body
• Embedded in connective tissue, in clusters along lymphatic vessels
• Near body surface in inguinal, axillary, and cervical regions of body

Question 21

Function of Lymph Nodes

Answer 21

•Functions

1. Filter lymph—macrophages destroy microorganisms and debris
2. Immune system activation—lymphocytes activated and mount attack against antigens

Question 22

Structure of Lymph Nodes

Answer 22

•External fibrous capsule
•Trabeculae extend inward and divide node into compartments
•Two histologically distinct regions
–Cortex
–Medulla

Question 23

Countined…

Answer 23

• Cortex contains follicles with germinal centers, heavy with dividing B cells
• Dendritic cells nearly encapsulate follicles
• Deep cortex houses T cells in transit
• T cells circulate continuously among blood, lymph nodes, and lymph

Question 24

Countined…

Answer 24

• Medullary cords extend inward from cortex and contain B cells, T cells, and plasma cells
• Lymph sinuses contain macrophages

Question 25

Circulation of Lymph Nodes

Answer 25

•Lymph
–Enters convex side via afferent lymphatic vessels; travels through large subcapsular sinus and smaller sinuses to medullary sinuses; exits concave side at hilum via efferent vessels

Question 26

Spleen

Answer 26

• Largest lymphoid organ

* Served by splenic artery and vein, which enter and exit at the hilum

Question 27

Function of the Spleen

Answer 27

–Site of lymphocyte proliferation and immune surveillance and response
–Cleanses blood of aged cells and platelets, macrophages remove debris

Question 28

Continued…

Answer 28

• Stores breakdown products of RBCs (e.g., iron) for later reuse
• Stores blood platelets and monocytes
• May be site of fetal erythrocyte production (normally ceases before birth)
• Encased by fibrous capsule; has trabeculae
• Contains lymphocytes, macrophages, and huge numbers of erythrocytes

Question 29

Structure of Spleen

Answer 29

•Two distinct areas
–White pulp around central arteries
•Mostly lymphocytes on reticular fibers; involved in immune functions
–Red pulp in venous sinuses and splenic cords
•Rich in RBCs and macrophages for disposal of worn-out RBCs and bloodborne pathogens
•Composed of splenic cords and sinusoids

Question 30

Structure of the Thymus

Answer 30

•Thymic lobules contain outer cortex and inner medulla
•Most thymic cells are lymphocytes
–Cortex contains rapidly dividing lymphocytes and scattered macrophages
•Medulla contains fewer lymphocytes and thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)

Question 31

Describe the Thymus

Answer 31

•Differs from other lymphoid organs in important ways
–Has no follicles because it lacks B cells
–Does not directly fight antigens
•Functions strictly in T lymphocyte maturation
–Keeps isolated via blood thymus barrier

Question 32

Continued…

Answer 32

•Stroma of epithelial cells (not reticular fibers)

–Provide environment in which T lymphocytes become immunocompetent

Question 33

Mucosa associated Lymphoid Tissues (MALT)

Answer 33

• Lymphoid tissues in mucous membranes throughout body
• Protects from pathogens trying to enter body
• Largest collections of MALT in tonsils, Peyer’s patches, appendix
• Also in mucosa of respiratory and genitourinary organs; rest of digestive tract

Question 34

Describe Tonsils

Answer 34

•Simplest lymphoid organs
•Form ring of lymphatic tissue around pharynx
–Palatine tonsils—at posterior end of oral cavity
–Lingual tonsil—grouped at base of tongue
–Pharyngeal tonsil—in posterior wall of nasopharynx
–Tubal tonsils—surrounding openings of auditory tubes into pharynx
•Gather and remove pathogens in food or air

Question 35

Continued..

Answer 35

•Contain follicles with germinal centers
•Are not fully encapsulated
•Overlying epithelium invaginates forming tonsillar crypts
–Trap and destroy bacteria and particulate matter
–Allow immune cells to build memory for pathogens

Question 36

Affregates of Lymphoid Follicles

Answer 36

•Peyer’s patches
–Clusters of lymphoid follicles
–In wall of distal portion of small intestine
–Similar structures are also found in the appendix

Question 37

Continued…

Answer 37

•Peyer’s patches and appendix
–Destroy bacteria, preventing them from breaching intestinal wall
–Generate “memory” lymphocytes

Question 38

Function of the Lymphatic System

Answer 38

Returns fluid that have leaked form blood vessels back into the heart