15-­‐11-­‐23  

1  

Lymphatic System

Review

Objectives

1.  Constituents of the Lymph System & Basics –  Interstitial Fluid

•  Difference between plasma and interstitial fluid

2.  Function of the Lymph System

3.  Comparison with veins of cardiovascular system –  Capillaries, wall differences,

movement of fluid 4.  Clinical Aspects 5.  Organization –  Important structures and

ducts

6.  Structure of a Lymph node 7.  Major Lymph Nodes 8.  Spleen 9.  Formed Elements in Buffy

Coat –  Lymphocyte formation and

immunity 10.  Adaptive immunity –  NK cells –  B cells –  T cells

15-­‐11-­‐23  

2  

1. Constituents and Basics

•  Lymphatic System Constituents: – Lymphatic vessels •  Deliver lymph from peripheral tissues to the venous

system

– Lymph (fluid) •  Interstitial fluid + lymphocytes + macrophages

– Lymphoid tissues – Lymphoid organs

1. Constituents and Basics

•  Differences between plasma and interstitial fluid 1.  Dissolved O2 in plasma higher •  O2 diffuses into tissues

2.  [CO2] in plasma lower •  CO2 diffuses out of the tissues

3.  Plasma consists of dissolved proteins

•  How do you get oxygen out of the capillaries into the tissues? –  Concentration gradient

15-­‐11-­‐23  

3  

1. Constituents and Basics

•  Lymph (fluid) –  Interstitial fluid + lymphocytes + macrophages

•  Lymphocytes – Adaptive immunity non-myeloid (bone marrow) derived

cells •  Macrophages –  Innate immunity (phagocytes), derived from monocytes

and myeloid cells – Anything that is not a lymphocyte e.g. basophil,

eosinophil, neutrophil

2. Function of the Lymphatic System

1.  Produces, maintain, and distribute lymphocytes (pathogen defense)

2.  Return interstitial fluid to circulatory system (homeostasis, blood volume) –  Healthy blood pressure, maintenance of volume

3.  Alternative route for transport of various substances (e.g. fatty acids) –  Harmful waste from tissues enter lymph nodes

15-­‐11-­‐23  

4  

2. Function of the Lymphatic System •  Collecting lymphatic vessels deliver lymph from peripheral

tissues to the venous system –  fluid will move directly into the interstitial space, and vice versa –  For fluid to return to the blood

•  Must travel into the heart to get pumped into the blood •  Therefore interstitial fluid must be a higher concentration for it to move

into the lymph vessels

3. Comparison of Vessels and Veins

•  Lymph vessels have a very thin and delicate structure compared to veins

•  Interstitial fluid is taken up by lymphatic capillaries

•  The pressure in these vessels is lower than the surrounding structures –  The lower concentration is

needed for the interstitial fluid to be able to move in

1.  Larger lumens 2.  Thinner walls 3.  Occult tunics

15-­‐11-­‐23  

5  

3. Lymphatic Capillaries •  Know what would happen with changes in

pressure in different areas

3. Lymphatic Capillaries

•  Lymph vessels have some smooth muscle –  Most fluid

movement due to permeability

–  Thin smooth muscle because not a lot of control

•  Diagram of diffusion of interstitial fluid

15-­‐11-­‐23  

6  

4. Clinical Aspects

•  Lymphedema – Accumulation of fluid

(lymph and blood) due to lack of removal

– Blocked passage of lymph due to many reasons

•  Causes of lymphedema Infection Cancer Scar tissue Genetics Overweight Drugs Blood clots in leg Aging

Because of inefficiency of body working properly

Veins that don’t pump properly Immobile body Standing for too long Parasites Irritant soils

4. Clinical Aspects

•  Lymphadenopathy – Pathology od disease of the lymph nodes – Bacterial infection – Autoimmune disorder – Cancer/tumors

15-­‐11-­‐23  

7  

5. Organization •  Named vessels only in thoracic duct and right

lymphatic duct –  Drain into right or left subclavian vein near internal jugular

vein •  Lymph is not returned directly to the arterial circulation •  All drain into subclavian veins which then go back into the right

atrium of the heart

5. Important Ducts

15-­‐11-­‐23  

8  

5. Important Ducts •  Superficial lymphatics –  Follow superficial veins

•  Subcutaneous, mucous membranes

•  Deep lymphatics –  Follow deep vessels

•  Collect lymph from organs and skeletal muscles

•  Superficial and deep lymphatics come together to form lymphatic trunks –  Lymph goes through these into

the venous circulation •  To reclaim fluid from connective

tissues and be put back into the blood volume

Thoracic duct collects lymph from tissues interior to diaphragm and from the left side of the upper body

Right lymphatic duct drains to the right half of the body superior to the diaphragm

5. Important Lymphoid Structures

•  Thymus •  Tonsils (1st line of defense) –  Pharyngeal tonsils –  Palatine tonsils – Lingual tonsils

•  Lymph Nodes •  Spleen –  Filters and recycles blood –  Stores blood – Triggers white blood cells

15-­‐11-­‐23  

9  

5. Important Lymphatic Structures

•  Primary lymphoid structure –  Thymus gland: causes differentiation of lymphocytes to

Tcells, Bcells, and Nkcells •  Contains stem cells that can make lymphocytes, B, T, cells, and natural

killer cells from sratch

•  Secondary lymphoid structures –  Lymph nodes and tonsils: consist of lymphocytes and

more Bcells for infectious agents •  First immune response: macrophages •  “Training opportunities”: adaptive immunity •  Thymus, spleen, and lymph nodes are encapsulated in connective

tissue –  Tonsils are not (just aggregates of lymphoid tissue)

5. Lymphatic Structures

•  Tonsils: lymphocytes help clear pathogens that enter from food and air (first line of defense)

•  Nodes: filter lymph, cleaning off antigens before return to venous circulation – Antigens consumed by macrophages, transported to

Tcells for further processing – Deeper line of defense because interstitial fluid

15-­‐11-­‐23  

10  

6. Structure Lymph Node •  Don’t need to know the structure •  Can swell up because of fluid build-up •  Filters out bacteria, viruses, etc. •  Attacks pathogens with B/Tcells •  Enter via afferent vessels •  Exit via efferent vessels •  Only one efferent vessel near the hilum •  Several afferent vessels throughout the node •  Lymph Nodes can become infected/inflamed/etc. –  Lymphadenopathy “Black Death”

7. Major Lymph Nodes

•  Clusters in: – Head and neck – Axillary: breast cancer –  Inguinal: superficial inguinal, deep inguinal – Large intestine/mesenteric

•  Important because: – Palpable: doctor feeling for lymph nodes – Common location for cancer spread – Become swollen and tender in infection

15-­‐11-­‐23  

11  

8. Spleen •  Fn: –  Filter and recycle

blood (regulate blood pressure)

– Triggers white blood cells: initiate immune response

–  Stores B/Tcells: makes antibodies

– As a fetus: makes RBC

9. Buffy Coat

•  Pluripotential stem cells – From red bone

marrow – Form into: •  Myeloid stem cells

–  Anything that is not a lymphocyte

•  Lymphoid stem cells – Gives rise to

adaptive immunity cells

15-­‐11-­‐23  

12  

9. Lymphocyte Formation and Immunity

10. Adaptive Immunity

15-­‐11-­‐23  

13  

10. Adaptive Immunity: NK Cells

•  Lymphocytes – NK (Natural Killer) Cells: don’t

need prior exposure to pathogen •  Travel around in the body until

reaches something to kill •  Attacks:

–  foreign cells (no MHC antigens outside cell)

– Normal cells with viral infection –  Cancer cells

10. Adaptive Immunity: B Cells

•  Bone-marrow derived •  Extracellular activities •  Originate and become immunocompetent in bone

marrow •  Differentiate into: –  Plasmocytes: activated by Helper T cells

•  Make antibodies (immunoglobulins) that react with antigens – Memory B cells

•  Can activate if antigen re-appears •  Long-lived cells, not immortal

•  B and T cells work together

15-­‐11-­‐23  

14  

10. Adaptive Immunity: T cells

•  Thymus-dependent cells –  Intercellular attackers

•  Many types – Cytotoxic T cells: foreign cells, viruses – Helper T cells: coordinates immune response – Suppressor T cells: coordinate and down-regulate

immune response – Memory T cells: activated if antigen re-appears