Transcript Lymphatic System

Lymphatic System
KAMAL SALIH
• The lymphatic system is vital to the
defense against illness.
• If infectious agents manage to breach the
mechanical barriers and gain entry to the
milieu interieur, the cells which deal with
the invasion are those which have arisen,
developed, matured, and/or been stored in
lymphatic organs.
The Lymphatic System
• It is intimately related, both structurally and
functionally, to the blood vascular system.
• Lymph itself is a clear, slightly yellowish
and opalescent fluid derived from blood.
• It contains white blood cells, specifically
lymphocytes.
What is the lymph?
• Lymph is a clear, slightly yellowish and
opalescent fluid derived from blood.
• What is its content?
• It contains white blood cells, specifically
lymphocytes.
Specialized Lymphatic Organs
• Certain specialized organs
devoted to processing and
modifying lymph and
lymphoid cells are present
in all normal mammals.
How it circulate?
• Lymph starts as blood fluid that is "strained" into
the tissue spaces under the hydrostatic pressure
of the pumping blood.
• It's drained from the intercellular spaces by thin
vein-like lymphatic vessels, re-entering the
venous circulation carrying lymphocytes that
enter the stream at certain specific points.
One way to the……
•The lymphatic system
forms a one way flow
system towards the
heart.
Lymphatics……Blind end
• Through this system flows lymph,
which starts from blind ended
capillaries.
Lymphatics……Blind end
• The capillaries are very permeable with the aid of
small anchoring filaments the vessel can take large
particles and stay open where the external pressure is
greater.
This causes problems, as the vessel also carries large
particles, such as:• Viruses
• Pathogens
• Cell debris
Hence can carry infection through
the body.
The Spleen
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The spleen serves two major functions in the body:
1. It is responsible for the destruction of old red blood cells (RBC),
2. It is a major site for mounting the immune response.
The spleen behaves similar to a lymph node but instead of filtering
the lymphatic fluid it filters the blood.
Blood entering the spleen travels through progressively smaller
arterioles until it is deposited in an area known as the red pulp.
This is where the RBCs are processed.
Surrounding each of the arterioles is a sheath of lymphoid cells
which make up the periarteriolar lymphoid sheath (PALS).
The interface between the PALS and the blood is a region of intense
phagocytic activity and sets the stage for an immune response.
The immune reactivity of the spleen is especially effective for
dealing with blood-borne antigens such as bacteria that reach the
blood.
Red &White Pulps
• These are two of those troublesome terms
that really applicable in gross anatomy, but
with which the histologist has to deal as well.
Oh, well...here goes:
• Cut a freshly-removed spleen across and it
looks like a field of dark red material with
white spots in it.
• On the basis of its gross appearance in fresh
sections, the spleen is traditionally said to
have the bulk of its parenchyma as red pulp,
with isolated areas of white pulp
interspersed through it.
Red &White Pulps
• The red pulp gets its appearance from the
formed elements of the blood (mostly
erythrocytes) it contains.
• The white pulp consists almost entirely of
lymphocytes, in a peculiar association with
the arterial blood supply.
• "white pulp" is equivalent to the
lymphocyte population of the spleen, in the
form of the periarteriolar lymphocyte
sheath or PALS .
• "Red pulp" is everything else, which
means the splenic cords and the sinuses
between them.
• "Red pulp" fills the
bulk of the spleen's
volume. White pulp is
the blue stained areas
visible within it.
The "PALS”
• Is the periarteriolar lymphocyte sheath, the
characteristic association of lymphocytes
and blood vessels in the spleen.
• The lymphocytes are arranged along the
arteries forming a sleeve or sheath.
• Collectively, the PALS is the "white pulp."
• The rest of the interior volume of the spleen
is the splenic cords, collectively constituting
the "red pulp," and the blood sinuses
between them.
Splenic Circulation
Splenic Circulation
• Blood enters from the splenic arterial supply,
via the splenic capsule, and the breakup of
arteries into capsular and trabecular
segments begins almost immediately.
• As is true in other organs, the angiogenic
properties of the CT capsule are are needed
to create the routes for the blood supply
entering and leaving the spleen.
Splenic Circulation
• The main input, the splenic artery,
ramifies in the capsule and sends
branches deeper and deeper.
• Blood leaving the organ is drained back
through a series of veins in the septa
and the capsule, eventually exiting via
the splenic vein.
• Both the artery and vein are grossly
located at the hilus.
Splenic Circulation
• As soon as a branch of the arterial input
reaches the interior space of the spleen, it
acquires the periarteriolar lymphocyte
sheath, or PALS, which it retains almost to
the smallest subdivisions.
• The PALS is a place in which the special
conditions required for proliferation of B
lymphocytes can be met, and at intervals
there will be germinal centers along it.
Splenic Circulation
• Germinal centers are individually
transient and depend on the immune state
of the animal, as they do in other parts of
the immune system; but their presence is
a feature of the spleen in all species to
some extent.
• The arterial vessels that have been
covered with lymphocytes are the central
arteries.
Penicillar Arteries
• Eventually the arteriolar supply subdivides
to the point where the PALS becomes
attenuated to a few cells, or even lost
altogether.
• These small arteries tend to run in bundles
and hence are termed penicillar arteries,
from their resemblance to the hairs of a
paintbrush (the Latin word for a paintbrush
is penicillum).
The role of the penicillar arteries:
"arteries of the red pulp."
• The role of the penicillar arteries is to deliver the
incoming blood to the red pulp (which is not
shown in this sketch) i.e., the splenic cords and
sinuses.
• Some segments of the penicillar arteries acquire
a peculiar "sheath" of phagocytic cells in their
walls, and have been termed sheathed arterioles
in the short regions where this occurs.
• The presence of a sheath is inconstant and
there are species variations; its role is unclear,
as well.
The PALS
• Careful examination
of the right image will
show the dark "cap"
of one of these.
• The PALS is diffuse
lymphatic tissue, but
within it germinal
centers frequently
develop.
• Now, the PALS, being
diffuse, has a loose
stromal framework of
reticular fibers made
by a variant for of
fibroblast.
• The resident lymphocytes of the diffuse
region of the PALS are supported by it,
like birds sitting on telephone wires: this
sort of arrangement is typical of all diffuse
lymphatic tissue.
• Due to the dense
packing of the
lymphocytes in the
PALS you will not be
able to make out the
fibers in an H&E
preparation, even in
the diffuse parts.
• Within the germinal centers, however,
things are different.
• The germinal center is a special place: it's
a clone of B-lymphocytes, and it has to be
isolated so that these cells can develop
properly.
• Consequently the stroma in germinal
centers isn't fibrillar in nature.
• Instead, special cells of a different cell line
than the fibroblasts form a stroma within
the germinal center and support the B
cells in it.
• A similar non-fibrillar stroma is
characteristic of the thymus, and will be
discussed below.
Continuation of the Splenic Blood
Supply Beyond the Central
Arteries
• The central arteries,
like any selfrespecting artery,
break up into smaller
ones eventually. Each
one gives rise to a tuft
of small vessels, the
penicillar arteries.
• The PALS is almost
wholly gone by the
time this level of
branching is reached.
These are very small
vessels, and the
PALS around them is
almost nonexistent.
Splenic Cords and Sinuses
The Thymus
• The thymus is a bilobed, greyish organ located
in the thoracic cavity just below the neck.
• Curiously, when the thymus is removed from
adult mammals, few effects are seen.
• However, when the thymus is removed at birth,
dramatic effects are witnessed as will be
explained later.
• The thymus develops from the endoderm.
• During its development many cells migrate
towards it, most of which are lymphocytes.
The Thymus
• The thymus is divided into two distinct
compartments, the outer cortex and the
inner medulla.
• Both regions are densly populated with
lymphocytes (or thymocytes while in the
thymus).
• Most of the cortical lymphocytes are
immature and unable to carry out immune
functions.
The Thymus
• Mature immunocompetent cells are found in the
medulla in greater numbers.
• The main function of the thymus is to develop
immature T-cells into immunocompetent T-cells.
• This process begins with the production of pre-T
cells in the bone marrow and their subsequent
transport to the thymus via the blood.
• The pre-T cells are then taken into the cortex of
the thymus.
• Here, a series of molecular events take place
allowing the cells to recognize certain antigens.
The Thymus
• Some of the cells recognize selfcomponents, and these are elmiminated
by a process of negative selection.
• Those that fail the selection die and those
that live proceed to the medulla and
eventually into the blood stream where
they act upon foreign agents in the body.
Lymph Nodes
• Lymph nodes can take on
many different sizes and
shapes, but most are beanshaped and are around 1 inch
in length.
Lymph Nodes
• The node is covered thickly with the fibrous capsule and
is subdivided into different compartments by inward
pointing trabeculae.
• As with many organs, the lymph node has two basic
parts, the cortex and the medulla.
• The cortex is populated mainly with lymphocytes
(follicles).
• The germinal centers are the primary resting place for
B Cell Lymphocytes (the cells responsible for production
of circulating antibodies).
Lymph Nodes
• In the event of an infecting antigen,
these B Lymphocytes will rapidly
undergo mitosis and divide.
• Each unique kind of B cell produces
only one type of antibody.
• Thus, by dividing, they can produce
large quantities of a specific antibody
to seek out and help destroy the
antigen.
Lymph Nodes
• The rest of the cortex contains T
lymphocytes- cells that circulate through
the lymph nodes, blood stream, and
lymphatic ducts to seek out any infection.
• The medulla of the lymph nodes is
primarily made up of macrophages
attached to reticular fibers.
The lymphatics
• They tend to run within the deep or
superficial fascia.
• The fascia tends to contain disease
processes until it is eroded.
The lymphatics of the neck
• are arranged into deep and superficial
chains.
• The deep jugular chain extends from the
base of the skull to the clavicle and is
formed into
• Superior group of lymph nodes
• Middle group of lymph nodes
• Inferior group of lymph nodes.
The superior deep jugular nodes
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Receive primary drainage from the
Soft palate,
Tonsils,
Palatoglossal and palatopharyngeal arches,
Posterior tongue,
Base of the tongue,
Pyriform sinus and the larynx above the vocal
folds.
The superior deep jugular nodes
• Receive primary drainage from the soft palate,
tonsils, palatoglossal and palatopharyngeal
arches, posterior tongue, base of the tongue,
pyriform sinus and the larynx above the vocal
folds.
• This group of lymph nodes also receives
lymphatic drainage from more superficial nodes
in the upper head and neck (retropharyngeal,
spinal accessory, parotid, superficial cervical
and submandibular nodes).
• The middle deep jugular nodes receive
primary drainage from the larynx above
the vocal folds, lower pyriform sinus and
posterior cricoid.
• They receive secondary drainage from the
deep jugular nodes above them and the
lower retropharyngeal nodes.
The inferior deep jugular nodes
• receive primary drainage from the thyroid,
trachea and cervical esophagus.
• They receive secondary drainage from the
deep jugular nodes above them and the
paratracheal nodes.
The Retropharyngeal &
Paratracheal nodes
• lie posteriorly around the midline viscera.
• They receive drainage from these viscera
and from the deep structures in the midline
of the head, i.e. the nasopharynx,
posterior nasal cavity, paranasal sinuses,
posterior oropharynx.
• They drain towards the deep jugular chain.
The superficial nodes
• The superficial nodes tend to drain
secondarily as mentioned to the deep
nodes.
• The superficial nodes are the submental,
superficial cervical, submandibular, spinal
accessory and anterior scalene.
The Submental &Submandibular
Lymph Nodes
• The submental nodes drain the chin, the middle
of the lower lip, tip of the tongue and anterior
mouth.
• These nodes in turn drain to the submandibular
nodes.
• The submandibular nodes drain the upper lip,
lateral lower lip, lower nasal cavity, anterior
mouth and the skin of the cheek.
• The submandibular nodes in turn drain to the
superior deep jugular nodes.
The superficial cervical nodes
• The superficial cervical nodes located
along the external jugular vein receive
drainage from the cutaneous lymphatics of
the face, especially from around the
parotid gland, behind the ear, parotid and
occipital nodes.
• The superficial cervical then drain into the
superior deep jugular nodes.
The nodes in the posterior triangle
• lie along the spinal accessory nerve.
• They drain the parietal and occipital
regions of the scalp.
• The upper nodes drain to the superior
deep jugular nodes while the lower nodes
drain down to the supraclavicular nodes.
The anterior scalene (Virchow's)
nodes
• The anterior scalene (Virchow's) nodes
receive drainage from the thoracic duct
and are located at the junction of the
thoracic duct and left subclavian vein.
• They are usually the site of metastases
from lower down in the body (e.g.
stomach).
The supraclavicular nodes
• The supraclavicular nodes receive
drainage from the spinal accessory nodes
and from infraclavicular sources.
• All of these lymphatics eventually drain
into the venous system either through or
together with the thoracic duct on the left,
or the right lymphatic duct