Chapter 19: The Lymphatic System

lymphatic system function

returns fluids back to blood

3 parts of lymphatic system

1. lymphatic vessels (lymphatics)

2. lymph: fluid in vessels

3. lymph nodes: cleanse lymph

lymphoid organs

1. spleen

2. thymus

3. tonsils

4. lymph nodes

5. lymphoid tissues

lymphoid organs and tissues function

house phagocytic cells and lymphocytes

what does the lymphatic system return

1. interstitial fluid that isn’t returned

2. “leaked” plasma proteins

lymphatic vessels

1. network of vessels

2. circulates 3L per day

3. interstitial fluid = lymph

lymph flows towards the..

heart

flow of lymph

1. capillaries

2. vessels

3. trunks

4. ducts

lymphatic capillaries

1. more permeable than blood capillaries

2. takes up proteins, cell debris, pathogens, and cancer cells

3. route for pathogens or cancer cells to travel

specialized structures that increase permeability of lymphatic capillaries

1. endothelial cells overlap loosely to form one-way minivalves

2. minivalves anchored by collagen filaments

   1. increase in ECF open minivalves

   2. decrease in ECF closes minivalves

where do lymph capillaries drain into?

vessels

lymphatic vessels structure

1. thinner walls than veins

2. similar tunics

3. more valves than veins

lymphatic trunks

formed by union of collecting vessels

right lymphatic trunk

1. empties blood into junction of right internal jugular and subclavian veins

2. drains lymph from right upper limb, head, and thorax

thoracic duct

1. empties blood at the junction of left internal jugular and subclavian veins

2. drains lymph from rest of body

lymph transport pressure

low-pressure system

lymph is propelled by…

1. milking action of skeletal muscle

2. pressure changes in thorax during breathing

3. valves to prevent backflow

4. pulsations of nearby arteries

5. contractions of smooth muscle in walls of lymphatics

6. physical activity

lymphedema

severe localized edema

lymphedema causes

1. tumors blocking lymphatics

2. removal of lymphatics during cancer surgery

lymphocytes

1. adaptive immune system

2. protect against antigens

T cells

1. manage immune response

2. destroy infected cells

B cells become…

plasma cells that produce antibodies

macrophages

phagocytize foreign substances and help activate T cells

dendritic cells

1. capture antigens and deliver them to lymph nodes

2. activate T cells

reticular cells

produce reticular fibers called stroma

lymphoid ti

reticular connective tissue

1. macrophages live on reticular tissue

2. lymphocytes occupy space

2 types of lymphoid tissue

1. diffuse lymphoid tissue

2. lymphoid follicles (nodules)

diffuse lymphoid tissue

1. loosely packed lymphoid cells and reticular fibers

2. found in every body organ

lymphoid follicles (nodules)

1. tightly packed lymphoid cells and reticular fibers

2. germinal centers

   1. proliferating B cells

3. form larger lymphoid organs (nodes)

4. Peyer’s patches in small intestine

primary lymphoid organs

areas where T and B cells mature—red bone marrow and thymus

red bone marrow

origin site of T and B cells; where B cells mature

thymus

where T cells mature

secondary lymphoid organs description

where mature lymphocytes first encounter their antigen and become activated

secondary lymphoid organs

1. lymph nodes

2. tonsils

3. spleen

4. Peyer’s patches

5. appendix

lymph nodes

1. hundreds are found throughout body

2. most are clusters along lymphatic vessels

2 functions of lymph nodes

1. cleansing the lymph: act as lymph “filters”

2. immune system activation

lymph nodes function: cleansing the lymph: act as lymph “filters”

1. macrophages remove and destroy microorganisms and debris that enter lymph

2. prevent unwanted substances from being delivered back to blood

lymph node function—immune system activation

lymphocytes become activated to mount an attack against antigens

structure of lymph node

1. surrounded by fibrous capsule

2. two distinct regions of node: cortex and medulla

cortex

1. follicles with germinal centers with dividing B cells

2. deep cortex houses T cells in transit

3. T cells circulate among blood, lymph nodes, and lymph

4. dendritic cells

5. T and B cells—activates both

medulla

B, T, and plasma cells

circulation of lymph nodes

1. lymph enters convex side of node via afferent lymphatic vessels

2. exits concave side via efferent lymphatic vessels

3. fewer efferent vessels = stagnation

4. travels through several nodes

spleen

1. blood rich organ

2. largest lymphoid organ

functions of spleen

1. lymphocyte proliferation

2. immune surveillance and response

3. cleanses blood of aged blood cells and platelets

4. macrophages remove debris

5. stores breakdown products of RBCs

6. stores platelets and monocytes

2 components of spleen

1. white pulp

2. red pulp

white pulp

1. site where immune function occurs

2. lymphocytes on reticular fibers

red pulp

1. site where old blood cells and bloodborne pathogens are destroyed

2. rich in RBCs and macrophages

mucosa-associated lymphoid tissue (MALT)

1. lymphoid tissues in mucous mems throughout body

2. found in mucosa of respiratory tract, genitourinary organs, and digestive tract

MALT function

protects from pathogens trying to enter the body

largest collections of MALT are found in

1. tonsils

2. Peyer’s patches

3. appendix

tonsils

1. simplest lymphoid organs

2. form ring of lymphatic tissue around pharynx

functions of tonsils

1. gather and remove pathogens in food or air

2. follicles with germinal centers and scattered lymphocytes

3. overlying epithelium invaginates, forming tonsillar crypts

4. bac or particulate matter enters crypts, where they are trapped and destroyed

location of peyer’s patches and appendix aid in

1. destroying bac—can’t breach intestine

2. generate “memory” lymphocytes

appendix

1. offshoot of first part of large intestine

2. large number of lymphoid follicles

thymus

1. bilobed lymphoid organ

2. inferior neck

3. active and largest in size during childhood

4. stops growing during adolescence, then atrophies

5. produces immuocompetent cells

Thymus differences

1. no B cells

2. does not directly find antigens

thymus function

T lymphocyte maturation—become immuocompetent