Anatomy- Lymphatic System

lymphatic system is the nexus btwn …

cardiovascular, immune, and digestive systems

primary functions

1) help maintain fluid balance

2) immune function

3) dietary fat absorption and transport

components of the lymphatic system

1) clear fluid

2) lymphatic vessels

3) lymphoid tissue

lymphoid tissue composition

1) cells

• reticular cells

• T and B lymphocytes

• macrophages

2) gels

3) fibers (reticular)

lymphoid tissue serves as:

• stations for lymphocytes

  • can activate and multiply

• surveillance point for lymphocytes and macrophages

primary lymphoid organs

where B and T cells mature

• B cells: red bone marrow

• T cells: thymus

where do lymphocytes travel after maturation

secondary lymphoid organs

• s[leen

• lymph nodes

• tonsils

under normal conditions, which riving force is slightly greater?

filtration

what do lymphatic capillaries do with extra fluid from filtration/reabsorption?

it absorbs, and eventually send it back into systemic circulation to maintain fluid balance

where are lymphatic found in relation to blood vessels

lymphatic capillaries weave btwn tissues and blood capillaries in the LOOSE connective tissues of the body

permeability of capillaries

• flap like mINI VALVES that open when interstitial pressure > lymphatic capillary pressure

  • down pressure gradient

  • anchored to connective tissue by collagen fibers and prevent collapse

  • promote on eway flow; prevents draining into interstitium

why does inflammation make lymphatic capillaries more permeable

in response to inflammatory cytokines lymphatic capillaries develop openings to allow the uptake of cells

• transport pathogens to lymph nodes for removal

• downside?→ cancer takes advantage of process/travels through lymph

larger lymphatic vessels

lymphatic capillaries→ collecting lymphatic vessels→ lymphatic trunks→ lymphatic ducts

composition of lymphatic vessels

• same three layers as veins

  • externa

  • media

  • intima

• thinner and have more valves (due to low pressure)

lymph transport

• lacks a pump

• mvmt is slow, but facilitated by:

  • rhythmic smooth muscle contraction

  • arterial pulsations

  • skeletal muscle contractions

function of lymph nodes

1) filter lymph

• macrophages remove pathogens and debris

2) immune system activation

• antigen presentation

lymph node structure

• >2.5cm in length

• outer dense fibrous capsule

  • trabeculae divide node into compartment

• internal reticular mesh

  • lymphatic capillaries spanned by reticular fibers

    • MACROPHAGES: phagocytosis

    • T and B LYMPHOCYTES: interacting with APCs and will proliferate if stimulated

• lymph enters through AFFERENT vessels, is filtered and leaves vis EFFERENT vessels

cercvical nodes

ear/nose/throat/eyes

• all potential routes of infection

inguinal nodes

genitourinary tract

other clinically important groups of lymph nodes

• axillary nodes

• epitrochanter nodes

• supraclavicular nodes

• popliteal nodes

lymphadenopathy

when “bad sample’ is detected, there is INCREASED blood flow and PROLIFERATION OF LYMPHOCYTES within lymph nodes involved

• can be detected with palpation

what is the most concerning sign of malignancy

supraclavicular lymphadenepathy

lymph nodes of head and neck

where do all lymphatics drain toward?

subclavian veins

lymphatic trunks

the largest lymphatic vessels drain into lymphatic trunks

• R and L JUGULAR trunks (head and neck)

• R and L SUBCLAVIAN trunks (upper extremities)

• R and L bronchomediastinal trunks (thorax)

• INTESTINAL trunk (abdomen)

• R and L LUMBAR trunks (lower extremities)

lymphatic ducts

lymphatic trunks lead to two lymphatic ducts that drain into subclavian veins

• R LYMPHATIC DUCT → R subclavian

• THORACIC DUCT→ L subclavian

• CISTERNA CHYLI: enlarged sac that begins the thoracic duct (meeting point of lumbar and intestinal)

right lymphatic duct

empties at junction of RIGHT INTERNAL JUGULAR and TIGHT SUBCLAVIAN VEINS

thoracic duct

empties into junction of LEFT INTERNAL JUGULAR and LEFT SUBCLAVIAN VEINS

lymphedema

localized damage to or compression of the lymphatic system can IMPAIR the body’s ABILITY TO REABSORB FLUID in the INTERSTITIAL SPACE

common causes of lymphedema

1) surgery (removal)

2) radiation therapy

3) trauma

4) cancer

other lymphoid tissues

• MALT

  • tonsils

  • peyers patches

  • appendix

• spleen

• thymus

mucosa- associated lymphoid tissues (MALT)

• lymph tissues strategically located in the MUCOUS MEMBRANES of the body

  • areas of frequent pathogen entry

how does MALT differ from lymph nodes?

1) location (mucosa)

2) first-lune defense (vs systemic)

3) not fully encapsulated

4) do NOT filter lymph

goal of MALT

first line defense to identify and respond to a patogen before it gets into lymphatic circulation

tonsils

• ring of lymphoid tissue around the entrance of the pharynx

  • look like localized swellings of mucosa

• remove ingested/inhaled pathogens

• PALATINE TONSILS are the largest and most often infected

tonsillar anatomy

• CRYPTS: trap pathogens and facilitate their interaction with macrophages and lymphocytes

• GERMINAL CENTERS: site of proliferation of of T and B lymphocytes in response to pathogen recognition

peyer’s patches

• large clusters of lymphoid tissue located in the wall of the ileum

• facilitate the interaction of T and B cells with antigens

  • PATHOGEN DESTRUCTION

  • IMMUNE TOLERANCE

    • food allergies

    • inflammatory bowel disease

intussusception

• bowel obstruction that can occur when the intestines fold in on themselves in the telescope- like fashion

• most often occurs in the ileum

• associated with viral infections

  • inflammation from infection→ pulling in on other areas of bowels

• most seen in kids

appendix

tubular offshoot of the proximal large intestine with a HIGH CONCENTRATION OF LYMPHOID TISSUE

• immune function like peyer’s patches (crypts and memory lymphocytes)

• may have a role in repopulating normal flora after intestinal infections

the spleen

• “big lymph node”

• left upper quadrant beneath diaphragm and posterior to the stomach

• highly vascular

  • fed by splenic artery

  • drains into portal circulation via splenic vein

splenic histology

vessels branch into:

• red pulp

  • “red blood cell graveyard”

  • sinusoidal capillaries trap old RBCs

  • reticular fibers the macrophages engulf and RECYCLE IRON and BILIRUBIN (from heme)

  • store some platelets

• white pulp:

  • lymphocytes suspended in reticular fibers

    • filters blood

    • house many B cells

sea of red pulp

lots of blood

• spleen= reservoir for about 20% of blood volume under normal conditions

what happens to the spleen in times of stress

• it can contract and release blood into the circulation when acted upon by he sympathetic nervous system

  • muscles in the capsule contract to squeeze blood out

clinical relevance: spleen

• thin capsule + reservoir = potential for injury and HEMORRHAGE

• spleen can become enlarged in states of damaged/abnormal cells, or increased B cell proliferation

  • mono

• splenectomy leaves individuals immunocompromised

  • loss of filtering mechanism adn B lymphocytes

thymus

• located in mediastinum, deep to sternum

• site of T cell development

  • largest as infant and dimities with age

  • maturation site for T lymphocytes

components of thymus

• cortex: site of POSITIVE selection

  • can you identify the MHC 1 complex of self cells?

• medulla: site of NEGATIVE selection

  • will you not act against self-antigens

• corpuscles: site of T cell dstruction