Download Lymph System - Trinity Christian School

Ch 12 – The Lymphatic
System
Functions of the Lymphatic
System and Body Defenses
—  LS - Returns leaked plasma to the blood vessels after
cleansing it of bacteria & foreign matter
—  LS - Provides sites for surveillance by immune
system
—  Non-specific defenses hinder pathway entry,
prevent the spread of disease-causing
microorganisms & strengthen the immune response
—  Immune system protects by destroying foreign cells,
inactivating toxins & foreign chemicals with
antibodies
Parts of the Lymphatic
System
1.  Lymphatic Vessels
2.  Lymphoid Tissues & Organs
Function of the Lymphatic
Vessels
•  Lymphatic vessels are also called lymphatics
•  Function to pick up the excess tissue, plasma and
fluid “leaked” into the interstitial fluid (the lymph)
and return it to the blood stream
•  Lymph capillaries spider-web through the capillary
beds and loose connective tissues of the body
•  If they fail edema results
•  Lymphatic vessels are one way vessels
Design of Lymphatic
Vessels
—  One way valves of epithelial tissue closed by
osmotic pressure
—  Designed to allow bacteria, virus and cancer cells to
more readily enter lymphatics than to enter
capillaries
—  Designed to route invaders towards lymph nodes
—  Size increases until large lymphatics eventually
drain from large ducts into the venous system
—  Major lymphatic ducts exist in the thorax
Major Lymphatic Ducts
—  Right Lymphatic duct – drains the lymph from the
right arm and right side of the head
—  Thoracic duct – drains lymph from the rest of the
body
—  Both ducts empty lymph into the subclavian vein on
their respective sides of the body
Features of Lymph Vessels
—  Thin walled, composed of epithelial cells
—  Larger ones have valves
—  Low pressure and pumpless
—  Skeletal muscular action and pressure changes in
the thoracic cavity provide the moving (milking)
mechanism
—  Larger lymph vessels also have smooth muscle to
aid in movement of lymph
Lymph Nodes
—  Are associated with the immune system
—  Remove foreign material, bacteria, viruses and
tumor cells by producing phagocytes (lymphocytes)
—  Literally thousands of lymph nodes exist in the
body
—  Large clusters are found in the inguinal, axillary and
cervical regions (see page 14)
—  Lymph nodes filter lymph as it moves towards the
heart
Lymph Nodes – cont.
—  Vary in size and shape, but most average less than
one inch long & are kidney shaped
—  Composed outwardly of a fibrous capsule
connective tissue – trabeculae
—  Inward folds of the trabeculae compartmentalize the
lymph node
—  Inward compartments are filled with soft reticular
connective tissue
Lymph Node
Lymph Node – cont.
—  Outer region referred to as cortex
—  Inner – medulla
—  Outer region contain follicles (Germinal cells) that
nurture the B-cell lymphocytes to produce daughter
cells called plasma cells that produce antibodies
—  Cortical region houses T-Cell Lymphocytes that are
in-transit between the circulatory and lymphatic
systems
Lymphocytes
—  Lymphocytes are a type of white blood cell
—  Collections of lymphocytes are strategically located
in lymph nodes
Lymph Flow through a
Lymphocyte
—  Lymph enters the convex side of the node through
afferent lymphatic vessels
—  Lymph exits at the hilus portion of a lymph node
through the efferent lymphatic vessels
—  The node is designed with fewer efferent vessels
than afferent vessels
—  The design causes lymph flow thru each node to be
very slow and allows time for lymphocytes and
macrophages to perform their function
Lymph Node Problems
—  Concentrate fight against infectious agents, but can
become overwhelmed and swollen
—  Are sensitive to the touch
—  Can become secondary cancer sites
—  Particularly in cancers that spread by moving thru the
lymphatic system
—  Cancer-infiltrated nodes are not sensitive to touch
Other Lymphoid Organs
—  The Spleen
—  Thymus Gland
—  Tonsils
—  Peyer’s Patches of the intestine
The Spleen
—  Is a blood rich organ that filters blood removing:
—  Bacteria
—  Viruses
—  Other debris including
—  Worn out blood cells
—  Iron is returned to the liver (ever hear that it is iron rich)
—  Broken hemoglobin molecules become a constituent of bile
—  Other functions:
—  Acts as a blood reservoir (similar to the liver)
—  Stores platelets
—  In infants contributes to hematopoiesis
The Thymus
—  Functions as an Endocrine Gland, but only during
youth
—  Secretes thymosin and other hormones
—  function to program different types of lymphocytes
—  Linked to aging
—  It is theorized that the lack of further programming
and maturing of lymphocytes leads to a lack of
adaptation against fighting newly encountered
diseases
The Tonsils
—  Are small masses of lymphatic tissue that ring the
pharynx
—  Are found in the mucosa
—  Function to trap and eliminate bacteria and other
foreign particles that enter the throat
—  Are very effective, but can become overwhelmed
and infected (a condition called tonsilittis)
Peyer’s Patches
—  Resemble tonsils and are found on the walls of the
small intestine
—  Contain macrophages that destroy invaders
—  Together with tonsils are classified as mucosaassociated lymphatic tissue (MALT)
—  The common feature of ALL lymphoid organs is a
predominance of reticular connective tissue and
lymphocytes
In Class Assignment
—  Web Exercise #12 – Lymphatic Collecting Vessels
and Regional Lymph Nodes
—  Read Pages 373 – 377 be prepared to discuss
—  Body Defenses (specific and non-specific)
—  Be PREPARED to give examples