CH 13

CHAPTER 13-THE LYMPHATIC SYSTEM AND DEFENSES AGAINST DISEASE
I. FUNCTIONS OF THE LYMPHATIC SYSTEM
A. Draining Excess Interstitial Fluid
B. Transporting lipids and the lipid-soluble vitamins (A, D, E, and K) through the body.
C. Immune responses
II. THE LYMPHATIC SYSTEM
A. This system is composed of three primary parts:
1. Lymphatic Vessels which transport fluids back to the blood.
2. Lymphatic Organs which are scattered throughout the body.
3. Lymph-the fluid contained in lymphatic vessels.
III. TYPES OF LYMPHOID CELLS
A. Lymphocytes-serve as the primary cells of the immune system. 2 Types of
Lymphocytes:
1. T Cells (T Lymphocytes)-these manage immune responses, and they attack viruses
and
tumor cells.
2. B Cells (B Lymphocytes)-protect the body by producing plasma cells. Plasma cells
secrete
antibodies that attach to and immobilize foreign materials until they can be
destroyed.
B. Lymphatic Macrophages-protect the body by removing foreign substances and by
activating T Cells.
IV. LYMPHATIC VESSELS
A. These vessels remove interstitial fluid and proteins and return them to the bloodstream.
Once the
Interstitial fluid enters lymphatic vessels, it is known as lymph.
B. The Lymphatic Vessels
1. These vessels begin as Lymphatic Capillaries which are small vessels located in the
spaces
between cells. Lymphatic capillaries are typically closed at one end (unlike
capillaries).
a. Lymphatic capillaries are composed of very thin endothelial cells whose ends
overlap.
1) The ends of these cells are easily pushed open when fluid pressure is
great on
their external surfaces; thus, allowing fluid to enter the lymphatic
capillary.
2) When fluid pressure is greatest on the inside of the lymphatic capillary,
the
ends of the endothelial cells are forced shut, preventing fluid from
leaking back
into tissue spaces.
b. Lymph flows from lymphatic capillaries into lymphatic collecting vessels.
2. Lymphatic Collecting Vessels
a. These are larger than lymphatic capillaries. These flow into lymphatic trunks.

3. Lymphatic Trunks –formed by the union of the largest lymphatic collecting vessels.
a. These drain fairly large areas of the body. These are named for the area of
the body that
they drain: lumbar trunk, subclavian trunk, intestinal trunk.
4. Lymphatic Ducts-receive lymph from lymphatic trunks.
a. Two major lymphatic ducts:
1) Right Lymphatic Duct-drains lymph from the right upper arm and the
right side
of the body.
2) Thoracic Duct-large, receives lymph from the rest of the body.
V. LYMPHATIC ORGANS
A. Lymph Nodes-cluster along the major lymphatic vessels of the body.
1. These act to filter lymph as it moves through the lymphatic system.
2. Lymph nodes are located throughout the body, but they cluster in the inguinal,
axillary and
and cervical regions of the body (these are areas where lymphatic collecting vessels
converge
to form lymphatic trunks). There are not lymph nodes in the Central Nervous
System.
3. Lymph Nodes have two primary functions:
a. Filtering lymph
b. Activating the Immune System
4. Structure of a Lymph Node
a. They are typically small and bean shaped.
b. Each node is surrounded by a thick, protective Capsule.
c. Nodes are composed of numerous Lymphoid Nodules that store Lymphocytes
(both
T and B Cells) and macrophages.
5. Lymph enters a lymph node through an Afferent Lymphatic Vessel, and it exits
through
Efferent Lymphatic Vessels.
B. The Spleen-the largest lymphoid structure in the body. Located in the left side of the
abdominal cavity
beneath the diaphragm.
1. Functions of the Spleen include:
a. Stores erythrocytes and removes old erythrocytes from circulation.
b. Storing blood platelets.
2. Structurally, the spleen resembles a large lymph node.
a. It is surrounded by a capsule. Internally, the spleen is divided into
compartments
that are named for their appearance. The compartments are:
1) The White Pulp-that stores lymphocytes.
2) Red Pulp-involved primarily in storing and removing old red blood cells.
C. Tonsils-are considered to be the simplest of all the lymphoid organs.
1. Types of Tonsils:

a. Palatine Tonsils-paired, located on either side at the posterior end of the oral
cavity.
b. Lingual Tonsils-paired, located at the base of the tongue.
c. Pharyngeal Tonsil-located at the posterior wall of the nasopharynx.
2. The tonsils gather and remove pathogens entering the pharynx via food or inhaled
air.
VI. HUMAN IMMUNITY-A variety of cells and structures work together to protect the
human
body from bacterial, fungal and viral infection. This resistance to disease (also known
as
immunity) allows the body to maintain its health.
A. There are two primary defense systems in the body that work both independently
and
cooperatively to provide resistance to disease. Those two systems are:
1. The Innate (Nonspecific) System
2. The Adaptive (Specific) System
VII. INNATE (NONSPECIFIC) DEFENSES-this system responds quickly to protect the
body
from pathogens and infection. Types of Innate Defenses in the Body:
A. Surface Barriers: Skin and Mucosae
1. Mucous Membranes line body cavities that open directly to the outside of
the
body. Functions of mucous membranes in innate body defense include:
a. Serving as sticky surfaces to trap microorganisms before they enter
body systems (such as the digestive and respiratory systems).
b. Secreting chemicals that are toxic to some microbes. This
includes antibiotics and acids.
2. Phagocytes-cells that feed on and destroy invading microorganisms.
a. Macrophages-primary phagocytes in the body. These are derived
from
monocytes.
3. Natural Killer Cells-cells in the blood and lymph that can lyse and kill
cancer
cells and virus-infected cells before the adaptive immune response is
initiated.
B. Inflammation
1. The inflammatory response is initiated when body tissues are injured. The
primary goal of inflammation is to clear the injured area of pathogens,
dead
cells and any other debris so that tissue repair can begin.
2. Benefits of Inflammation:
a. Prevents the spread of damaging agents into the body.
b. Removes cell debris and pathogens
c. Sets the stage for repair.
d. Turns on the adaptive immune system
3. Redness, heat, pain and swelling are the key indicators of inflammation.

C. Antimicrobial Proteins-attack microbes directly or they limit the ability of microbes
to
reproduce. Types of antimicrobial proteins include:
1. Interferons-proteins secreted by some cells that are infected by viruses.
These
chemicals protect healthy cells from being attacked by viruses.
2. Complement System-this refers to a group of plasma proteins that
circulate
through the blood in an inactive state. These proteins destroy cells via cell
lysis.
D. Fever-abnormally high body temperature. This is another defense against
infection.
1. Foreign microbes initiate the hypothalamus to raise body temperature.
2. Mild fever appears to have a positive effect on the body since it:
3. Extreme fever can be dangerous since it denatures enzymes.
VIII. ADAPTIVE (SPECIFIC) DEFENSES
A. This specific system protects the body from a wide range of microorganisms and
abnormal body cells. This system is turned on by exposure to a foreign
substance.
Adaptive responses were first documented in dogs during the 1800’s.
B. Important Characteristics of the Adaptive Defense System
1. It is specific-it recognizes and attacks particular pathogens or foreign
debris
in the body.
2. It is systemic-immunity is not restricted to the site of the initial infection.
3. It has memory-after an initial exposure, it recognizes and strongly attacks
a
previously encountered pathogen.
C. Antigens-substances that can mobilize the immune system and provoke an
immune
response. The immune system identifies foreign proteins on antigens as foreign.
D. B and T Lymphocytes play a key role in Adaptive Immunity.
E. 2 Major Types of Immunity in the Adaptive Defense System
1. Humoral (Antibody-Mediated) Immunity-produced by antibodies present in
the
body’s fluids. Antibodies bind to pathogens, inactivating them and marking
them for destruction by phagocytes or the complement system. B
Lymphocytes
are involved in this process. Types of Humoral Immunity:
a. Active Humoral Immunity-occurs when B Cells encounter antigens
and
produce antibodies against them. Active immunity is naturally
acquired
when you are exposed to pathogens. It can also be artificially
acquired
when you receive vaccines.

1) Vaccines-contain dead or weak pathogens or their
components. Vaccines provide two benefits: they spare
us of
many of the symptoms of an illness and they provide us
with
immunity against an antigen. Booster shots may be
given to
provide extensive immunity to a particular microbe.
b. Passive Humoral Immunity-antibodies in this case are made from
the
serum of an immune human or animal donor. As a result, B cells
are
not challenged by antigens. Memory does not occur but protection
occurs when the borrowed antibodies degrade in the body.
1) This occurs when Immune sera are used to treat
snake
bites.
2. Cell-Mediated Immunity-occurs when T Lymphocytes themselves defend
the
body from microbial invasion. These cells can produce cell lysis or they
can
initiate an inflammation response.
IX. DISORDERS
A. Acquired Immunodeficiency Syndrome (AIDS)-caused by the Human
immunodeficiency
virus (HIV). This virus attacks lymphocytes, thus making the infected person
susceptible
to other microbes.
B. Elephantiasis-occurs when lymphatic vessels are blocked by roundworms. This
leads to
greatly swollen body parts.
C. Allergy-an intense immune response to an antigen that is typically harmless to
most
people.
D. Autoimmune Diseases-occur when the body’s lymphocytes produce an immune
response against our own body tissues. Common Autoimmune Diseases:
1. Rheumatoid arthritis-damages joints.
2. Multiple Sclerosis-destruction of myelin sheaths in the CNS.
3. Grave’s Disease-hyperthyroidism.