CHAPTER 20

The Lymphatic system

1. Lymphatic system introduction

1. Consists of

1. .
2. .

2. Transports escaped fluid from cardiovascular system back to blood
3. Important in defense

2. Lymphatic vessels

1. Introduction

2. Distribution and structure of lymphatic vessels

1. Distribution

1. Weave between tissues and capillaries in loose connective tissue
2. Widespread in body
3. Absent from __________,__________,__________,_________

2. Capillaries

1. Similar to blood capillaries
2. Much more permeable, due to

1. No tight junctions, endothelial cells overlap to form flap like minivalves
2. Cells anchored to surrounding tissue so cells can be open when pressure outside increase and not collapse

3. One way swinging door (flap like minivalves)

1. Flaps open when __________ pressure higher
2. Flaps close when __________pressure higher

4. Size of particles

1. Large proteins
2. Cell debris
3. Pathogens

3. Lacteals

1. Specialized capillaries
2. Found in __________
3. Chyle (fatty lymph)

4. Lymphatic collecting vessels

1. Collect lymph from capillaries
2. 3 walled, but much thinner
3. Superficially run along with __________
4. Deep run along with__________

5. Lymphatic trunks

1. Collect lymph from lymph vessels

6. Lymphatic ducts

1. Collect lymph from trunks
2. Largest of lymph vessels
3. 2 major ducts

1. .
2. .

1. cisterna chyli

iii. Empty into venous system at junction of internal carotid and subclavian

3. Lymph transport

1. Low pressure, very slow, moves about 3L a day-equal to the amount of excess fluid lost through circulation

1. Muscle activity
2. Pulsing nearby arteries
3. Smooth muscle in walls of lymph vessels
4. Return increased with exercise

3. Lymphoid cells and tissues

1. Lymphoid cells

1. Lymphocytes

1. Main warriors of immune system
2. B cells-antibody production
3. T cells-managers and direct killing

2. Macrophages
3. Dendritic cells
4. Reticular cells

2. Lymphoid tissues

1. Purpose

1. Houses and provide proliferation sites for lymphocytes
2. Furnishes an ideal surveillance point for cells

2. composition

1. Reticular connective tissue
2. Macrophages live on fibers
3. Lymphocytes circulate through

3. Types of tissues

1. Diffuse lymphatic tissue

2. Lymphatic follicles (nodules)

3. Germinal centers
4.  Peyer's patches

3. Lymphoid organs

1. Encapsulated

4. Lymph nodes

1. Introduction

1. Location

1. Embedded in connective tissue
2. Inguinal, axillary, cervical

2. Function

1. Lymph filters
2. Role in activating immune system

1. Monitor for antigens

2. Structure

1. Size and shape

1. Bean shaped
2. 2.5 cm
3. Surrounded by dense capsule
4. Divided into compartments by trabeculae

2. Histology

1. Superficial cortex

1. Contains many __________ with germinal centers (B cells)
2. Dendritic cells

2. Deep cortex

1. Circulating T cells-surveillence

3. Medulla

1. Medullary cords (both T and B cells)

4. Lymph sinuses

1. Where lymph capillaries enter
2. Guarded by macrophages

3. Circulation in the lymph nodes

1. Afferent lymphatic vessels-enter nodes
2. Subcapsular sinus
3. Efferent lymphatic vessels (in hilus)-exit

1. Less vessels exiting than entering to allow for stagnation and improved filtering

5. Other lymphoid organs

1. Spleen

1. Location

1. Left side of abdomen beneath diaphragm
2. Size of fist
3. Largest lymph organ
4. LYMPH does not enter
5. Blood enters through splenic artery

2. Structure

1. Made of __________ tissue
2. Cell types

1. White pulp—around central arteries, responsible for immune functions
2. Red pulp—all other tissue, responsible for destruction of RBC and bloodborne pathogens

3. Functions

1. Lymphocyte proliferation
2. Immune surveillance
3. Blood cleansing
4. Erythrocyte production in fetus
5. Store platelets

2. Thymus

1. Location

1. Inferior neck extends partially over heart
2. Large in childhood
3. Atrophies with age

2. Structure

1. Lobules
2. Cortex contains lymphocytes
3. Medulla contains Hassall’s corpuscles—regulatory T cells-prevent autoimmune response

3. Function

1. T lymphocyte maturation
2. Does not directly fight antigens
3. Blood-thymus barrier keeps antigens out so no premature activation
4. Stroma is thymocytes (epithelial cell) not reticular cells—help T cells become immunocompetent

3. Tonsils

1. Location

1. Palatine—most often infected
2. Lingual
3. Pharyngeal—adenoids
4. Tubal—auditory tubes

2. Structure

1. Follicles
2. Crypts to trap bacteria
3. Not fully encapsulated

3. Function

1. Fight pathogens entering oral route

4. Aggregates of lymphoid follicles

1. MALT (mucosa associated lymphoid tissue)
2. Peyer’s patches

1. Ilium and appendix