Download Chapter 20- Lymphatic system

Lymphatic System
Human Anatomy
Chapter 20
•I. The lymphatic system- This
system involves a set of vessels
that transports tissue fluid back
into the blood stream and a set of
organs that are involved in the
immune system. The lymph
vessels are as branched and
abundant as arteries and veins.
They collect lymph- tissue fluid
arising from fluid that has leaked
from the capillaries. Proteins also
leak from capillaries and are
returned to the blood system by
the lymph vessels. The lymphatic
system also collect lipids from the
digestive tract and is involved in
exposing pathogens to the
immune system.
•A. lymph capillaries- one cell layer thick made up of endothelial cells that are
permeable to tissue fluid, proteins, bacteria, and viruses. Lymph capillaries are
not located in bone, bone marrow, teeth, and the central nervous system.
Lacteals are lymph capillaries in the small intestine that are permeable to lipids.
• B. lymphatic collection
vessels- These vessels
connect to the
capillaries and carry
the fluid away. Their
tunic structures are like
those of blood vessels
but overall they are thin
and difficult to identify.
They contain valves as
veins do but unlike
veins they contain
bulges making the
vessel resemble a
beaded string.
• C. lymph nodes- organs along the
lymphatic collecting vessels that
accumulate the pathogens carried by
lymph. This is an area highly
concentrated with lymphocytes ready
to activate an immune response.
• D. lymph trunks- a conversion of
lymphatic collection vessels that
results in a vessel of a larger diameter.
They drain large areas of the body.
Five major locations areL lumbar
trunks, intestinal trunks,
bronchomediastinal trunks, subclavian
trunks, and jugular trunks.
• E. lymph ducts- The larges vessel into
which the lymph trunks empty. The
thoracic duct is found in everyone but
only some people have the right
lymphatic duck that empties into the
neck veins. The thoracic duct empties
into the left internal jugular and left
subclavian veins.
Lymph node
A look inside the human lymphnode: the removal of most
lymphocytes reveals the reticular tissue network.
Detailed Immune Response Description
• II. The Immune system- This is a very complex system with
multiple layers and forms of defense. In this section we focus on the
organs closely associated with cellular response of the immune
system. The immune system identifies and attacks specific
pathogens.
• A. Lymphocytes and other cells of the immune system- Inflammation
may be the first response to infectious organisms entering the body.
Cells involved in an immune response are macrophages and
lymphocytes. These include T and B cells. WBCs can move in and
out of the blood vessels and also travel through lymph tissue in
order to fight disease.
• 1. activation of lymphocytes- lymphoid stem cell in bone marrow
give rise to lymphocytes. As they mature they are “taught” what
tissue or cells are “self”, anything deviating from this, is a pathogen
and will be “attacked”.
• a. Lymphocytes mature in the thymus (T-cell) or in the bone marrow
(B-cell). b. Once they are mature they travel through the body until
they encounter an antigen.
• c. Cells such as macrophages and dendritic cells engulf pathogens
and present antigens to lymphocytes.
• d. A T-helper cell is activated once presented with antigen and it
sends signals to activate other T-cells and the B-cells.
• e. Once activated the cells produce effector cells that fight the
pathogen and memory cells. Memory cells guard against
subsequent infections.
• B. Lymphoid tissue- this is located throughout the body and is often
infected because it is designed to collect pathogens for the purpose
to destroying them. At the site of infection multiple lymphocytes
collect to fight infection and memory cells reside. This tissue is
located in areas frequently exposed to pathogens such as: mucous
membranes of digestive, respiratory, urinary, and reproductive tracts.
Also in the lymphoid organs which easily collect pathogens.
C. Lymphoid organs
• 1. lymph nodes- organs
that filter lymph fluid
before it has an
opportunity to enter back
into the blood vessels. It
also collects antigens
that are funneled to
lymph tissue so they can
engulf by macrophages
and presented to
lymphocytes. They are
a cortex and medulla.
• .
2. spleen- largest lymphoid organ, it is almost the size of the
heart, it is in the superior left abdominal area. It is designed to
remove blood born pathogens and aged/damaged RBCs. It also
stores platelets. It has areas identified at white (lymphoid tissue)
and red pulp (vacular tissue).
• 3. thymus- lies posterior to the sternum in superior
thorax, site to T-cell development. It also releases
hormones. It is gradually replaced by fibrous tissue as
one ages. It also has a cortex and medulla.
• 4. tonsils- simplest lymphoid organs, humans have four
groups: palatine, lingual, pharyngeal, and tubal. They
gather pathogens entering through the nose and mouth
• 5. aggregated
lymphoid follicles
and the
appendixdensely packet
units of lymphoid
tissue forming
lymphoid
nodules, they are
especially around
the appendix and
distal part of the
small intestine,
and in the cecum
of the large
intestine.
• D. HIV virus and AIDS
• 1. HIV is transmitted through bodily secretions such as
blood,semen and viginal secretions. If the fluid is
exposed to air it dries, the virus dies and cannot be
infectious. Any microscopic tear in the body can allow
the virus entry if one is exposed to an infected body fluid.
Entry can also occur via a needle or blood transfusion
(rare).
• 2. The virus targets T-Helper cells and destroys them. It
has the ability to incorporate itself into the cell’s genome
and to mutate rapidly such that the immune system has
a hard time keeping up with it. It also affects microglia
cells (brain tissue) and immune system cells (dendritic
and macrophages).
• 3. The infection stages are
• a. Acute stage (2 weeks): first infected presents flu-like
symptoms, fever, rash, fatigue, headache, muscle/joint pain,
diarrhea, swollen lymphnodes
• b. Asymptomic period (up to 10 years): there are no obvious
symptoms but the immune system is silently fighting the HIV
virus
• c. AIDS (time varies but it results in death): The persons’s
immune system declines and the body is invaded by
opportunistic organisms. AIDS patients have infections not
seen in people with healthy immune systems.
• 4. The virus has the ability to quickly mutate and many of the
treatments developed, like the cocktails, are not efficient. The
number of people newly infected puts AIDS at the fourth
leading cause of death world wide. It most severe spread is
in Asia, Eastern Europe, and Africa. In the US 25% of people
infected do not know they are. There is no absolute
prevention of spreading infection other than abstinence.
(Hint- don’t have sex with a partner until they take an AIDs
test- remember the test can give a false positive for sixmonths after newly infected)