Lymphatic System: Overview

® Consists of two semi-independent parts:

®  A network of lymphatic vessels

®  Lymphoid tissues and organs scattered throughout the body

® Returns interstitial fluid and leaked plasma proteins back to the blood

® Lymph – interstitial fluid once it has entered lymphatic vessels

Lymphatic System: Overview

Lymphatic System: Overview

Lymphatic System

®   Lymphatic vessels

®   One-way system, lymph flows toward the heart

®   Lymph vessels include:

®   Microscopic, permeable, blind-ended capillaries

®   Lymphatic collecting vessels

®   Trunks and ducts

®  Thoracic duct

l   Drains the rest of the body

®  Right lymphatic duct

l   Drains the right upper arm and the right side of the head and thorax

Lymphatic Organs

® Primary

®  Red bone marrow

®  Thymus

® Secondary

®  Lymph nodes

®  Filter lymph

®  Spleen

®  Lymphatic nodules

Spleen

®   Largest lymphoid organ, located on the left side of the abdominal cavity beneath the diaphragm

®   Functions:

®   Site of lymphocyte proliferation

®   Immune surveillance and response

®   Cleanses the blood

®   Stores breakdown products of RBCs for later reuse

®  Spleen macrophages salvage and store iron for later use by bone marrow

®   Site of fetal erythrocyte production (normally ceases after birth)

®   Stores blood platelets

Thymus

®   A bilobed organ that secretes hormones (thymosin and thymopoietin) that cause T lymphocytes to become immunocompetent

®   Size of the thymus varies with age:

®   In infants, it is found in the inferior neck and extends into the mediastinum where it partially overlies the heart

®   It increases in size and is most active during childhood

®   It stops growing during adolescence and then gradually atrophies

®   The thymus differs from other lymphoid organs in important ways

®   It functions strictly in T lymphocyte maturation

®   It does not directly fight antigens