Lymphatic SystemHandout

An Introduction to Cytology of the

Lymphatic System

By Noel Ways

HemopoieticStem Cells

MyloidStem Cells

LymphoidStem Cells

Erythrocytes Thrombocytes Basophils Eosinophils Neutrophils Monocytes

Macrophages

B Lymphocytes(Humeral Immunity)

T Lymphocytes(Cellular Immunity)

Gas Transport & Hemostasis Nonspecific Host Immunity

Conferance ofImmunocompotence

in Bone Marrow

Conferance ofImmunocompotence

in Thymus Gland

SpecifcHost

Immunity

Plasma B CellsAntibodies

Memory B Cells

Helper T Cells

Cytotoxic T Cells

Regulator T Cells

Memory T Cells

HematopoiesisFlow Chart

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A

V

Inflammation and Fluid Exchange

At the arterial end of a capil-lary (A) hydrostatic pressure (blood pressure) exceeds osmotic pressure and �uid leaves that capillary and baths interstitial cells. This brings nutrients and oxygen to the interstitium.

At the venous end of the capillary (V) osmotic pressure exceeds hydrostatic pressure and the interstitial �uid returns to the blood bringing waste and CO2.

As not all �uid returns to the venous end, the lymphatic system functions as a “drainage system” receiving the balance of interstitial �uid. When the �uid enters lymphatic vessels it is called lymph and it will be returned to general circulation. Note that a lymph node �lters the lymph before it enters general circulation.

If trauma or infection occurs, mast cells secrete histamine inducing an in�ammatory response, the purpose of which is to control bacterial growth and enhance immune responses. Hista-mine causes vasodilatation of capillaries, which become increasingly porous resulting in increases in both pressure and �uid movement. This brings resources and creates an environ-ment to promote resolution of the infection and healing. Due to the increase in intersti-tial �uid pressures, there is increased �uid drainage into the lymphatic system. This results in the infectious agent being brought to the lymph nodes, where the immune system in large part resides.

As the agents of infection collect in the lymph nodes, this “informs” the immune system that there is an infec-tion, and a speci�c immune response ensues. Note that in this scenario, the bacteria are not entering general circula-tion.

HemopoieticStem Cells

MyloidStem Cells

LymphoidStem Cells

Thrombocytes Basophils Eosinophils Neutrophils

Monocytes

Nonspecific Host Immunity

Specific HostImmunity

B T“Incompetent”Lymphocytes

“Competent”Lymphocytes

ThymusGlandBone

Marrow

Conferance ofImmunocompetence

in Bone Marrowand

Thymus Gland

B T T TBB

ETC ETC

LymphaticOrgans

Lymphatic CellDevelopment

HumeralImmunity

CellularImmunity

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B T

TT

T

Tc

Tc

TcTc

B B

B

Bp

Tc TcTc Tc

Tc

Tc

Tc

Infection

Subclavian Vein to Right Heart to General Circulation Site of Infection

Introduction to Humoral and Cellular Immunity

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