MICROBIOLOGY – ALCAMOLECTURE:

Immune System, Lymph Node Introduction

The Lymphatic System• The Lymphatic system defends the body from foreign invasion by disease

causing agents such as viruses, bacteria, or fungi

The Lymphatic System• Part of the immune system made of a

network of lymphatic vessels that carry a clear fluid called lymph in one direction - toward the heart

• Also includes structures dedicated to the circulation and production of lymphocytes (spleen, thymus, bone marrow, lymph nodes, tonsils, etc)

The Lymphatic System• Blood does not directly come in

contact with the cells and tissues in the body

• Parts of the blood first exit the blood vessels to become interstitial fluid, which comes into contact with the cells of the body.

• Lymph is formed when interstitial fluid enters the initial lymphatic vessels

The Lymphatic System• Collects and returns interstitial fluid,

including plasma protein to the blood, and thus helps maintain fluid balance 

• Defends the body against disease by producing lymphocytes

• Absorbs lipids from the intestine and transport them to the blood

Lymph Node• Small ball-shaped organs distributed

widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels

• Lymph nodes are found all through the body, and act as filters or traps for foreign particles

• They are important in the proper functioning of the immune system

Lymph Node StructureA. Pericapsular Connective Tissue and Fat

Tissue which clings to outside of node, holds node in place, cushions it, ready supply of blood for energy

B. Capsule• Dense outer covering which surrounds node• Trabeculae – inner branches of capsule

C. The Substance of the lymph node is divided into:• outer cortex

• inner medulla

D. Germinal Centers• Dense, darkly stained round areas just

inside the capsule where certain WBCs are produced

Vessels• Multiple afferent lymph vessels bring

lymph into the lymph node• The lymph gets slowly filtered through

the substance of the lymph node where it encounters lymphocytes

• The efferent lymph vessel carries the lymph out of the lymph node

VesselsA. Artery

– Carries oxygenated blood from heart to node

– Has a thick wall and quite small inside diameter

– May contain visible blood cells

VesselsB. Vein

– Carries used blood from node to heart– Has a thinner wall and larger inside

diameter than the artery– May contain visible blood cells

Vessels

C. Lymph– Has almost no wall

– Has a very large inside diameter

– Never contains visible blood cells

Maintain the pressure and volume of extracellular fluid by returning excess water and dissolved substances from the interstitial fluid to the circulation