Download Lymphatic System

Lymphatic System & Immunity
Lymph is a specialized fluid formed in
tissue spaces. This fluid carries protein
molecules, immune cells, fat and excess
tissue fluid called interstitial fluid (IF)
back to the veins through lymphatic
vessels. IF is formed from blood plasma
coming out of the capillaries under
pumping pressure of the heart.
Lymphatic drainage prevents accumulation
of too much tissue fluid
Lymphatic capillary is 1 cell layer thick.
Lymphatic vessels have 1 way flow (like
veins).
Right lymphatic duct:
- drains right upper quadrant into right
subclavian vein.
Thoracic duct:
- drains rest of body
- largest in body
- in abdomen Cisterna chyli stores
lymph
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Lymph is under low pressure as is the
venous system.
- contracting of skeletal muscle in
appendages
- contracting skeletal muscles used in
breathing (intercostals) and contraction of
smooth muscle of diaphragm.
- contraction of smooth muscle in larger
lymphatic trunks
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Lymphatic tissue:
- lymph nodes
- tonsils
- spleen
- thymus
- bone marrow
Lymph nodes- oval or bean shaped.
- lymph that is drained from the body passes and
is filtered through structures called lymph nodes.
- connective tissue called reticular fibers and are
populated by dense aggregates of lymphocytes
and macrophages.
-Lymph nodes occur along the entire length of the
lymphatic system and tend to increase in size as
they become closer to the thoracic duct.
-arranged in chains or clusters
- scattered in groups; superficial and deep
- cervical
- submandibular
- axillary
- inguinal (groin)
- supratrochlear
- filter lymph
- lymph flows into node from afferent
lymphatic vessel.
- exits from efferent lymphatic
vessel
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Nodes contain large number of
macrophages and lymphocytes
Node has a medulla and a cortex.
Germinal centers are responsible for the
proliferation of B-cells (remember what
they produce?)
-
Distal portion of the small intestine:
- Peyer’s patches
Thymus
- bilobed structure located substernally in
mediastinum
- Immature T-cell lymphocytes (stem
cells)
migrate from bone marrow to thymus
and mature under the direction of
thymosin. Reside in lymph nodes.
- Transforms from large in size (childhood)
and atrophies to fat and connective
tissue in adults- Involution. Still
produces mature T-cells
Spleen:
- largest lymphoid organ
- upper left quadrant between stomach and
diaphragm
-Functions:
- phagocytosis of bacteria
- replace worn out RBC’s (120 days)
- blood reservoir
- erythrocyte production in the fetus
- Stores blood platelets
- Splenomegaly: enlarged spleen (EBV)
- Trauma from rib fx.= splenectomy (removal of
spleen)
Spleen is composed of two tissue types:
White pulp: composed of splenic nodules
that contain many lymphocytes.
Red pulp: rbc’s, lymphocytes and
macrophages. Give the spleen its
reddish/purplish color.
Spleen
Tonsils:
-Pharyngeal tonsil (adenoid) embedded in
posterior wall of nasopharynx.
- Palatine tonsil: tonsillectomy
- Lingual tonsil: base of tongue
Tonsils are first line of defense against
bacteria entering the mouth - tonsillitis
Immunity:
Defending the body against invasion of pathogenic
substances and eliciting an immune response
when the body encounters those substances.

1- Non specific immunity (primary defense)
- skin
- mucous membranes
- tears
- saliva
- micturition (urinating)
- lysozyme in saliva and tears
- HCl in gastric juice in stomach
- Vaginal pH.
Specific Immunity: Immunity against
specific organisms
Specific immunity is more effective than the
nonspecific methods, and has a memory
component that improves response time
when an invader of the same type (or
species) is again encountered.

Inflammatory response
 Damaged cells release chemical signals such as
histamine that increase capillary blood flow
(vasodilation) into the affected area (erythema
and heat). The heat makes the environment
difficult for microbes to function, increases
mobility of white blood cells. Chemotaxis.
 Capillaries pass fluid into tissue spaces
(interstitial) causing the infected/injured area to
swell (edema). Finally, macrophages
(monocytes outside the blood) clean up dead
microbes, cells, and debris.
Fever:
Non specific defense: Pathogen stimulates
lymphocytes to proliferate and secrete a substance
called interleukin-1 (IL-1).
- endogenous pyrogen
IL-1 stimulates the hypothalamus to increase body
temp.
Increased body temp. causes the spleen and liver
to hold Fe (sequester). Fe level drops in blood.
Since pathogens rely on Fe at higher temps to
reproduce, this situation will slow down or stop
their growth and reproductive cycles.
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