Lymphatic System

Question 1

Lymphatic system

Answer 1

■ Network of:
■ Ducts
■ Vessels
■ Organs

■ Produces, screens and moves fluid called lymph from tissues to the bloodstream

Question 2

4 parts of lymphatic system

Answer 2

1. Lymph:
   ■ a fluid similar to plasma, identical to interstitial fluid
   ■ does not have plasma proteins
2. Lymphatic vessels (lymphatics):
   ■ network that carries lymph from peripheral tissues to the venous system
3. Lymphoid tissues and lymphoid organs:
   ■ found throughout the body
4. Lymphocytes, phagocytes, and other immune system cells

Question 3

Functions of lymphatic system

Answer 3

■ Is to produce, maintain, and distribute lymphocytes
■ Drain excess interstitial fluid
■ Transports dietary lipids

Question 4

Lymphocyte production

Answer 4

■ Lymphocytes are produced:
■ in lymphoid tissues (e.g., tonsils)
■ lymphoid organs (e.g., spleen, thymus)
■ and in red bone marrow

Question 5

Lymphocyte distribution

Answer 5

■ Lymphocytes:
■ detect and respond to antigens
■ travel into site of injury or infection

Question 6

Lymphocyte circulation

Answer 6

■ From blood to interstitial fluid (lymph) through capillaries
■ Returns to venous blood through lymphatic vessels

Question 7

Circulation of fluids

Answer 7

■ From blood plasma to lymph and back to the venous system
■ Also transports hormones, nutrients, and waste

Question 8

Lymphatic vessels

Answer 8

■ Are vessels that carry lymph
■ Lymphatic system begins with smallest vessels:
■ lymphatic capillaries (terminal lymphatics)

Question 9

Lymphatic capillaries differ from blood capillaries in 4 ways

Answer 9

■ start as pockets rather than tubes
■ have larger diameters
■ have thinner walls (this as one cell)
■ flat or irregular in section

Question 10

Lymphatic capillaries

Answer 10

■ Absent from bones, teeth, bone marrow, and CNS
■ Very permeable (take up proteins, cell debris, pathogens, and cancer cells)
■ Endothelial cells loosely bound together with overlap

■ Overlap acts as one-way valve:
■ allows fluids, solutes, viruses, and bacteria to enter lymphatic system
■ prevents return to intercellular space

Question 11

Lacteals

Answer 11

■ Are special lymphatic capillaries in small intestine
■ Transport lipids from digestive tract

Question 12

Lymphatic vessels and valves: lymph flow

Answer 12

■ From lymphatic capillaries to larger lymphatic vessels containing one-way valves (more numerous than veins)

■ Lymphatic vessels travel with lymph

■ Is due to:
■ ​peristaltic contractions (?) of smooth muscle in lymphatic vessel walls
■ ​Skeletal muscular contractions (like veins)
■ important for lymph flow
■ Immobilizing a limb will slow lymph drainage
■ ​Arterial pulsations
■ ​The respiratory pump

■ There is no lymph heart

■ Rate of lymph return is slow - approximately 120 ml/hr

Question 13

Lymphatic ducts and venous system: lymphatic system

Answer 13

■ Is similar to the circulatory system

■ Is divided into:
■ superficial lymphatics
■ deep lymphatics

Question 14

Superficial lymphatics are located in:

Answer 14

■ skin
■ mucus membranes
■ serous membranes lining body cavities

Question 15

Deep lymphatics

Answer 15

■ Are larger vessels that accompany deep arteries and veins
■ They have smooth muscle in their walls
■ are capable of peristalsis

Question 16

Superficial and deep lymphatics

Answer 16

■ Join to form large lymphatic trunks

■ Trunks empty into 2 major collecting vessels:
■ thoracic duct
■ right lymphatic duct

Question 17

Base of thoracic duct

Answer 17

■ Expands into cisterna chyli

■ Cisterna chyli receives lymph from:
■ right and left lumbar trunks
■ intestinal trunk

Question 18

Thoracic duct

Answer 18

■ Collects lymph from (3/4 of the body):
■ left bronchiomediastinal trunk
■ left subclavian trunk
■ left jugular trunk

■ Empties into left subclavian vein

Question 19

Right lymphatic duct

Answer 19

■ Collects lymph from (1/4 of the body):
■ right jugular trunk
■ right subclavian trunk
■ right bronchiomediastinal trunk

■ Empties into right subclavian vein

Question 20

Lymphedema

Answer 20

Lymphedema is a chronic swelling that occurs when the lymphatic system is blocked, preventing lymph fluid from draining properly.

■ Interferes with immune system function

Question 21

Lymphocytes

Answer 21

■ Make up 20–30% of circulating leukocytes
■ Most are stored, not circulating

Question 22

2 main classes of circulating lymphocytes

Answer 22

1. T cells:
   ■ thymus-dependent
2. B cells:
   ■ bone–marrow WBCs

Question 23

Other supporting cells

Answer 23

■ 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 24

T Cells

Answer 24

■ Make up 80% of circulating lymphocytes

Question 25

3 main types of T cells

Answer 25

• Cytotoxic T cells • Helper T cells • Suppressor T cells

Question 26

Cytotoxic T cells

Answer 26

■ Attack cells infected by viruses ■ Produce cell-mediated immunity

Question 27

Helper T cells

Answer 27

■ Stimulate function of T cells and B cells

Question 28

Regulatory/Suppressor T cells

Answer 28

■ Inhibit function of T cells and B cells ■ Control sensitivity of immune response

Question 29

B cells

Answer 29

■ Make up 10–15% of circulating lymphocytes ■ Differentiate into plasma cells

Question 30

Plasma cells

Answer 30

■ Produce and secrete antibodies (immunoglobin proteins)

Question 31

Antigens

Answer 31

■ Antibody generators ■ Act as targets which identify any pathogen or foreign compound

Question 32

Antibody-mediated immunity

Answer 32

■ A chain of events which destroys the target compound or organism

Question 33

Lymphocyte distribution

Answer 33

■ Tissues maintain different T cell and B cell populations ■ Lymphocytes wander through tissues: ■ enter blood vessels or lymphatics for transport ■ can survive wk- few months

Question 34

Lymphocyte production involves:

Answer 34

■ bone marrow ■ thymus ■ peripheral lymphoid tissues

Question 35

Hemocytoblasts

Answer 35

In bone marrow, divide into 2 types of lymphoid progenitor cells 1. Myeloid stem cells 2. Lymphoid stem cells

Question 36

Lymphoid stem cells

Answer 36

■ Group 1: ■ remain in bone marrow ■ produce B cells and natural killer cells ■ Group 2: ■ migrate from bone marrow to peripheral tissue ■ produce T cells in environment isolated by blood-thymus barrier

Question 37

T cells and B cells

Answer 37

■ Migrate throughout the body: ■ to defend peripheral tissues ■ Retain their ability to divide: ■ is essential to immune system function

Question 38

Interleukin-7

Answer 38

A cytokine produced by stromal cells in bone marrow

Question 39

Lymphoid tissues

Answer 39

■ Surveillance vantage point for lymphocytes and macrophages ■ Largely reticular connective tissue – type of loose connective tissue

Question 40

2main types of lymphoid tissues

Answer 40

■ Diffuse lymphoid tissue of lymphoid cells and reticular fibers in ~ every body organ ■ 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

Question 41

Distribution of lymphoid nodules

Answer 41

■ Lymph nodes ■ Spleen ■ Respiratory tract (tonsils) ■ Along digestive and urinary tracts

Question 42

Mucosa-associated lymphoid tissue (MALT)

Answer 42

■ Lymph Nodules - Large aggregations of naked (no capsule, trabeculae, or hilum) lymphoid tissue ■ found embedded in mucous membranes of systems that communicate with external environment ■ Protect against outside harmful substances in food or air ■ These include: ■ the Gastrointestinal Tract ■ the Genitourinary Tract ■ the Upper Respiratory Tract ■ Commonly referred to as the Mucosal Associated Lymphoid Tissues or the MALT

Question 43

Gut-associated lymphoid tissues (GALT)

Answer 43

■ Are a type of MALT located specifically in the GI tract ■ Peyer’s patches – aggregated lymphoid nodules located throughout the small intestines ■ Appendix ■ Peyer's patches and appendix: ■ Destroy bacteria, preventing them from breaching intestinal wall ■ Generate "memory" lymphocytes

Question 44

The 5 tonsils (GALT)

Answer 44

■ In wall of pharynx: ■ left and right palatine tonsils ■ pharyngeal tonsil (adenoid) ■ 2 lingual tonsils

Question 45

Lymphoid organs

Answer 45

■ Are separated from surrounding tissues ■ By a fibrous connective-tissue capsule

Question 46

Lymph nodes

Answer 46

■ Range from 1–25 mm diameter ■ Act as filters for lymph fluid ■ Embedded in connective tissue, in clusters along lymphatic vessels ■ Near body surface in inguinal, axillary, and cervical regions of body

Question 47

The stroma (structural portion)

Answer 47

■ structural latticework consisting primarily of reticular connective tissue. Containing: ■ Trabeculae are Bundles of connective tissue fibers ■ Extend from capsule into interior of lymph node ■ Hilus - shallow indentation where blood vessels and nerves reach the lymph node

Question 48

Lymph node vessels

Answer 48

■ Many afferent vessels carry lymph from peripheral tissues to lymph node ■ Fewer vessels leave lymph nodes at hilus ■ Slows lymph flow through the node ■ allows lymphocytes and macrophages time to function

Question 49

Lymph node functions

Answer 49

■ 2 main functions ■ Filtering and Immune System Activation (Antigen presentation) ■ filtering: ■ purifies lymph before return to venous circulation ■ Removes: ■ debris ■ pathogens ■ 99% of antigens ■ Antigen Presentation ■ First step in immune response ■ process where an antigen-presenting cell (APC) takes up a foreign antigen, processes it into smaller peptides, and then displays those peptides on its surface, bound to MHC molecules, for recognition by immune cells like T lymphocytes ■ or attached to dendritic cells to stimulate lymphocytes

Question 50

Lymphoid functions

Answer 50

■ Lymphoid tissues and lymph nodes: ■ distributed to monitor peripheral infections ■ respond before infections reach vital organs of trunk

Question 51

Lymph glands

Answer 51

■ Large lymph nodes at groin and base of neck ■ Swell in response to inflammation

Question 52

Lymphadenopathy (Lymphadenitis)

Answer 52

Chronic or excessive enlargement of lymph nodes may indicate infections, endocrine disorders, or cancer

Question 53

Lymphangitis

Answer 53

■ inflammation of the lymphatic channels ■ Pathogens invade the lymphatic vessels through a wound or as a complication of infection ■ irregular streaks on the skin extending proximally toward regional lymph nodes. ■ Treat with large does of antibiotics ■ Iimobalize the limb (Why?)

Question 54

The thymus

Answer 54

■ Located in mediastinum ■ Deteriorates after puberty: ■ diminishing effectiveness of immune system

Question 55

Division of thymus

Answer 55

■ Thymus is divided into 2 thymic lobes ■ Septa divide thymus parenchyma into smaller lobules

Question 56

Thymic lobule

Answer 56

■ Contains a dense outer cortex ■ And a pale central medulla

Question 57

Lymphocytes

Answer 57

■ Divide in the cortex ■ T cells migrate from cortex into medulla ■ Mature T cells leave thymus by medullary blood vessels

Question 58

Reticular epithelial cells in the cortex

Answer 58

■ Dendritic cells surround lymphocytes in cortex ■ Maintain blood-thymus barrier (only in cortex) ■ Secrete thymic hormones that stimulate: ■ stem cell divisions ■ T cell differentiation

Question 59

The medulla

Answer 59

■ Contains fewer lymphocytes ■ The medulla has no blood–thymus barrier: ■ T cells can enter or exit bloodstream ■ Keratinized Epithelial Cells form concentric layer (Hassall’s or Thymic corpuscles). ■ thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)

Question 60

Thymus hormones

Answer 60

■ Thymosins ■ Promote development of lymphocytes

Question 61

DiGeorge syndrome

Answer 61

■ Congenital absence of thymus ■ Marked by serious combined immuno-deficiencies (SCIDS). ■ Life in a sterile bubble with death often resulting from opportunistic infection.

Question 62

Functions of the spleen

Answer 62

1. Removal of abnormal blood cells and other blood components by phagocytosis 2. Storage of iron recycled from red blood cells 3. Initiation of immune responses by B cells and T cells: ■ in response to antigens in circulating blood 4. The Stores blood platelets and monocytes 5. May be site of fetal erythrocyte production (normally ceases before birth)

Question 63

Structure of spleen

Answer 63

■ Attached to stomach by gastrosplenic ligament ■ Splenic veins, arteries, and lymphatic vessels: ■ communicate with liver at hilus ■ Inside fibrous capsule: ■ red pulp: which contains many red blood cells ■ white pulp: resembles lymphoid nodules

Question 64

Red pulp

Answer 64

■ Contains elements of circulating blood: ■ plus fixed and free macrophages

Question 65

Splenic circulation

Answer 65

■ Blood passes through: ■ network of reticular fibers ■ Then enters large sinusoids (lined by macrophages): ■ which empty into trabecular veins

Question 66

Spleen function

Answer 66

■ Phagocytes and other lymphocytes in spleen: ■ identify and attack damaged and infected cells ■ in circulating blood ■ The spleen filters and cleans the blood

Question 67

Splenectomy

Answer 67

■ Removal of the spleen, usually due to damage ■ The spleen is very difficult to repair surgically ■ Surgeons now know that the spleen will repair its self with time – less splenectomies today ■ People with out a spleen are more susceptible to infections ■ specifically blood infections