Chapter 20 - Lymphatic System

Lymphatic system 

Picks up fluid lost by blood capillaries 

The lymphatic system consists of

lymph vessels, lymph, and lymph nodes 

Fluid is picked up by lymph capillaries is 

eventually returned to circulation 

Lymphoid organs 

provide structural basis for immune system

Lymphoid organs monitors 

body for infection

Lymphoid organs house 

phagocytic cells and lymphocytes 

Lymphatic vessels function

Picks up protein-containing interstital fluid that is not reabsorbed by blood capillaries 

Once interstital fluid enters the lymph vessel, 

"fluid is called ""lymph"" "

Lymph vessels only move fluid 

toward the heart

Lymph capillaries 

blind-ended vessels that weave through capillary beds 

Lymph capillaries are highly permeable due to the presence of (1)

Loosely-aggregated cells in walls of lymph capillaries 

Lymph capillaries are highly permeable due to the presence of (2)

Anchoring filaments --> increase in interstital fluid pulls on anchoring filaments 

The walls of lymph capillaries

open easily 

Because lymph capillaries are permable, they allow

large intakes of proteins 

During illness/infection, capillaries become even more 

permable than blood capillaries 

Pathogens are transported to

lymph nodes, where immune system destroys them 

Lacteals 

specialized lymph capillaries for movement of fats from small intestine (digestive system) to bloodstream 

What is absorbed because of lacteals? 

Triglycerides (speeds up) 

Lymph capillaries drain into larger vessels. What is the first they drain into? 

Collecting lymphatic vessels 

Collecting lymphatic vessels 

• In the skin - vessels travel with superficial veins
• In trunk - vessels travel with deep arteries 

Lymphatic trunks 

drainage areas resulting from collecting vessels uniting 

Lumbar trunk (2)

drains lower extremities (legs) 

Bronchomediastinal trunk (2)

drains throax

Subclavian trunk (2)

Drains upper extremities (arms) and superficial thoracic wall 

Jugular trunks (2)

drains head and neck

Intestinal trunk (1)

drains digestive organs 

Lymphatic ducts 

structures that lymphatic trunks drain into 

Both lympathic ducts (left and right) empty into junction at 

internal jugular vein and subclavian vein 

Right lymphatic duct empties into 

veins on right side 

Thoracic duct empties into 

veins on left side 

Right lymphatic duct 

drains lymph from right upper limb, right side of head, and right throax 

Where does the lymph from the right lymphatic duct dump into? 

Subclavian vein 

Thoracic duct 

Drains any part of body that isn't drained by right lymphatic duct 

Where does the thoracic duct begin? 

Cisterna chyli 

The thoracic duct consists of 

• Left upper limb
• Left side of brain
• Left side of throax
• Both lumbar trunks (left and right limbs)
• Intestinal trunk 

Is the lymphatic or thoracic duct larger? 

Thoracic duct 

How are lymph vessels and veins similar? 

"Have no ""pump"" to propel lymph fluid and walls are thin with large lumen "

What are some solutions to pushing lymph through vessels and back into circulation? 

1. Smooth muscle in larger vessel walls help push lymph through 
2. Similar to circulation in veins: valves to prevent backflow, respiratory pump 
3. Circulation also improved by pulsatile nature of nearby arteries 
4. Physical movement (skeletal muscle) is important for increasing lymph flow 

Blocking or removing lymph vessels/nodes causes 

severe, localized edema 

T lymphocytes 

T cell

B lymphocytes 

B cell 

Lymphocytes, T lymphocytes, and B lymphocytes produce 

"antibodies that protects body from ""non-self"" antigens "

Helper T cell 

• Manages and Helps initiate an immune system response 
• Activate or help activate several different immune system cells -> proper immune system response during infection
• WO, would lose more than ~75% of immune system (seen in HIV/AIDS)

Killer T cells 

• Cytotoxic 
• Killing off pathogen, focus on virus and cancerous cells 

Regulatory T cells 

• Mediate immune response 
• Keep rest of immune system in check, allow for enough reponse to fight off pathogen without damaging other parts of the body as well 

B Cells 

Activation leads to release of antibodies (red flag, proteins that enter blood plasma) into blood -> Antibody sticks itself to pathogen, easier for other immune system cells to find something that doesn't belong (easier to see the pathogen)

Macrophages (Defense cell)

• Phagocytize large, foreign substances and help activate T cells 
• Perform basic housekeeping (Ex: picking off debrie) 

Dendritic cells (Defense cells)

"

• Cells that escort ""red flagged"" cells back to lymph nodes 
• Dendritic cells put flagged cells on display -> other immune cells know to destroy 
• No direct defense

"

Reticular cells (Supporting cells)

• Produce stroma -> supports cell types in lymphoid tissue/organs
• Produces reticular fibers (short branching fibers that form a meshwork/fishnet) which helps support lymphocytes and macrophages in lymphatic system 
• Could help keep them in lymphatic system
• Spread far enough apart to allow WBCs to wander around lymphatic system -> allows WBCs to patrol the lymph (more likely to bump into a pathogen earlier) 

Lymphoid tissues function 

1. Houses lymphocyte cells, allows them to proliferate (immune system cell produces more when exposed to a pathogen)
2. Provides surveillance point for lymphoid cells 

Lymphoid tissue is mostly made of 

reticular connective tissue (form of loose connective tissue)

What is the exception to lymphoid tissue being made up of mostly reticular connective tissue? 

Thymus - made up of epithelial tissue 

Lymphocytes regularly circulate through 

blood vessels, lymphoid tissue, and loose connective tissue of body -> ensures good patrol of body for foregin bodies 

Diffuse lymphoid tissue 

• Loose aggregation of lymphoid cells and reticular fibers 
• Present in most organs of the body (scattered)
• Larger collections found in mucous membranes (leads into and out of the body) 
• Organs have direct immune access, don't have to wait for immune system/cells to help 

Lymphoid nodules 

• Tightly packed lymphoid cells and reticular fibers 
• Usually form parts of larger lymphoid organs (especially lymph nodes) 
• Germinal centers are areas of proliferating B cells (antibody production) 

Primary lymphoid organs 

• Lymphocyte maturation 
• Red bone marrow and thymus 

B cells mature in 

Bone marrow

T cells mature in 

Thymus 

Both B and T cells are from bone marrow but 

T cells leave to finish in thymus 

Secondary lymphoid organs location 

where mature lymphocytes firsy encounter antigens and become activated 

Secondary lymphoid organs

• Lymph nodes 

• Spleen

• Mucosa associated lymphoid tissues (MALT)

Lymph nodes form

clusters in axillary, cervical, and inguinal regions (top of leg meets pelvic region) 

The axillary, cervical, and inguinal regions are areas where 

large number of collecting lymph vessels converge and form lymphatic trunks 

Importance of lymph nodes (1)

"Activating immune system 

• Dendritic cells bring antigens to lymph nodes to ""display"" them to lymphocytes -> activate T cells 

"

Importance of lymph nodes (2)

Cleanses lymph via filtration 

• Lymph passes through nodes before it enters back into crculation -> macrophages clean lymph microorganisms and other particles 
• Dead and dying cells -> don't want in blood supply -> macrophages clean it out 

Anatomy of lymph nodes 

Bean-shaped organ surrounded by dense fibrous capsule (hold in place, protect from surrounding) 

Lymph node - Cortex 

Outer portion of node 

• Follicles contain dividing B cells
• Contains constantly moving T cells 

Lymph node - Medulla 

Inner portion of node 

• Both T and B cells found here 
• No proliferation
• Move freely and form patrol for inner region 

Lymph sinus 

sites where macrophages reside 

• larger open space 
• Macrophages are phagocytic - pick off pathogens as they travel through and debris 

Afferent lymphatic vessels 

• Bring lymph into node from a vessel 
• Lymph circulates through the sinuses 
• Supplying structure 

Efferent lymph vessels 

• Allows lymph to leave node 
• Lymph enters a node faster than it can leave 
• Lymph remains in node slightly longer -> increasing cleansing function of these nodes 

Lymphadenopathy 

• Nodes overwhelmed and blocked off due to high infection rate 
• Nodes become inflamed, swollen, tender, and filled with pus
• Usually requires use of antibotic to assist in treatment of infection 
• Large amount of bacteria, lymph nodes can't handle the amount -> become infected themselves 

Secondary cancer sites 

"

• Metastasizing cancer cells break free from original tumor, get ""stuck"" in lymph nodes in different part(s) of body
• Lymph nodes become swollen/enlarged, but are not painful 
• Ex: swelling of axillary nodes indicates brest cancer 

"

The Spleen 

• Largest of the lymphoid organs

• Well vascularized because cleanse blood directly (nothing with lymph)

• Upper left abdominal cavity

Primary function of the spleen 

• Important for cleansing blood

• Pulls old and damaged blood cells (RBCs, platelets) from blood supply

• Macrophages in spleen pull microorganisms straight out of blood 

Other functions of the spleen 

1. Recycles parts of old RBCs for later reuse. Stores iron, ships other recyclables to liver for processing

2. Stores platelets and monocytes 

Red pulp

• RBC recycling center
• Area of erythrocyte and pathogen destruction
• Packed with RBCs and macrophages 

White Pulp

• Serves immune function
• Contains mostly lymphocytes on reticular fibers 

Spleen is well vascularized, can you bleed to death if it ruptures? 

"Yes if the rupture is severe

• Bone marrow and liver will take over the functions of the spleen
• ~20% of people have a ""secondary"" spleen 

"

Mucosa Associated Lymphoid Tissues (MALT) 

"Found specifically in mucous membranes 

• Most mucous membranes lead into/out of the body -> easy ""in"" for pathogens
• MALT prevents pathogen entrance at these areas 

"

What are the three main areas of MALT?

• Tonsils
• Peyer's patches
• Appendix 

Tonsils 

Found at entrance to pharynx in throat -> fight infections/bacteria coming in from the mouth 

Palatine tonsils 

• Largest, most likely to become infected (most exposed to pathogens) 

• Either side of throat 

Lingual tonsils 

Lymphoid follicles at base of tongue 

Adenoids (Pharyngeal tonsils)

• Where throat meets nasal cavity

• In posterior wall of nasopharnyx 

• Prevents infection from anything inhaled from nasal passages 

Tubal tonsils 

• Surrounding openings of auditory tubes into pharynx 
• Prevent ear infections 

Peyer's patches 

• Aggregated lymphoid nodules 
• Structurally similar to tonsils
• Found in the wall of the ileum (where small intestine meets the large intestine) of the small intestine 

Appendix 

• High concentartion of lymphoid follicles 
• Appendicitis - Blocked off, cells build up and leads to infection 

Peyer's patches and Appendix are good for 

"preventing invading bacteria/pathogens at the small intestine and for the generation of ""memory"" lymphocytes "

Thymus is the site of 

T cell maturation 

Without the thymus 

mature T cells capable of body defense would not exist 

The thymus is ___ and most ___ in infants 

large and active

The thymus begins to atrophy in early adolescence, will 

still put out immune cells, but at a reduced rate 

In old age, thymus is mostly 

fibrous and fatty tissue (doesn't allow for T cell maturation) 

The cortex in the thymus is packed

tightly with lymphocytes 

The medulla of the thymus has 

fewer lymphocytes 

Hassell's (thymic) corpuscles 

sites of regulatory T cell production 

Hassell's (thymic) corpuscles function

Regulatory T cells prevent autoimmune responses (attack our own healthy body tissues) 

Thymosin

Hormone in thymus 

Thymosin function 

Stimulates development/maturation of T cells -> stimulates immunocompetency (having a competent immune system, need to learn what belongs in the body and what doesn't)