Download Immunology Lecture – 6

Immunology
Lecture – 6
Lymphatic System
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network of tissues, organs and vessels that help to maintain the body’s fluid balance & protect
it from pathogens.
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lymphatic system is an extensive drainage system that returns water and proteins from
various tissues back to the blood stream.
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like the circulatory system
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the lymphatic system consists of a series of vessels, and a fluid called lymph
unlike the circulatory system it is a 1-way system
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lymph doesn’t “circulate” around in a loop like blood
lymph is collected from the tissues and delivered to the blood
lack pump heart - The lymphatic system has no pump, so lymph must be moved through
vessels by the squeezing of skeletal muscles.
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lymphatic system is directly connected to the circulatory system
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it helps the circulatory system to do its job
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without it neither the circulatory system nor the immune system would function.
General Function Lymphatic System
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1. Returns Fluid from Tissues and molecules to Blood
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2. Absorb and Transport Fats
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4. Hemopoiesis
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5. Body Defense immunity/ protection
Lymphatic System
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Lymphatic system components includes :
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1. lymph
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2. Lymphatic vessels- lymphatic capillaries
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3. Lymphatic organs
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4. Lymphatic Tissues
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4. lymphatic cells (Macrophages, Dendritic cell, Lymphocytes)
Organs of Immune System
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Primary ( central) Lymphoid Organs
Bone Marrow
Thymus
Maturation site
Secondary Lymphoid Organs
Spleen
lymph nodes
immune tissues in organs or ( Mucosal associated lymph tissue- MALT): lining of mucosa surfacefound in various sites of body- lymphocytes such as T cells and B cells as well as plasma cells and
macrophages, it is well situated to encounter antigens passing through the mucosal epithelium.
O-MALT (organized mucosa-associated lymphatic tissue); Tonsils
GALT ( gut associated lymph tissue) ( Peyer’s Patchs), ( Appendix)
SALT ( skin associated lymphatic tissue, associated with the dermis of skin)
BALT (bronchus-associated lymphoid tissue)
NALT (nasal-associated lymphoid tissue)
CALT (conjunctival-associated lymphoid tissue)
Trap antigen, APC, Lymphocyte proliferation ( production of Ab and specific T cells)
Bone Marrow
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Located in the middle of bones
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Most specifically vertebrates
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Pelvic
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Leg bones
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Generate T cell, B cell and macrophages- cell that travel throughout the body in the blood and tissue
fluids
Thymus
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A bilobed organ located above heart near throat
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Grows up rapidly for first 2 years
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DiGeorge Syndrome congenital birth defect- lack of thymus- absence of T cell mediated immunity
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Each lobe- many lobules by fibrous septa- outer cortex and inner medulla
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Cortex- tightly packed- contains immature lymphocytes
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Medulla- contain more mature cells
Lymph nodes
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Small, bean- shaped
Laced a on the lymphatic vessels, with clusters in the neck, armpits, abdomen and groin
Each lymph node contains specialized compartments where immune cells congregate and
where they can encounter antigens.
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The lymph node contains numerous specialized structures
Lymphoid cells:
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T cells concentrate in the cortex,
B cells in and plasma cells in the medulla
Macrophages and other phagocytic antigen presenting cells
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Immune cells and foreign particles enter the lymph nodes via incoming lymphatic vessels.
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All lymphocytes exit lymph nodes through outgoing lymphatic vessels.
lymph moves into nodes by way of several afferent lymphatic vessels
cortex: T cell, dendritic cells
medulla: T, B, plasma cells
sinuses: macrophages
Lymph node Function
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include:
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Clean lymph: Removal and destruction of microbes, harmful foreign particles and dead cells
from lymph (through phagocytosis by macrophages)
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filtration of particles and microbes to keep them out of circulation
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Alert immune system to pathogens
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Activation, proliferation of B cells and antibody production
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Activation, proliferation of T cells.
Lymph Nodes
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lymph nodes are widespread in body :
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* eg. submental & submaxillary lymph nodes
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floor of mouth;
drain nose, lips teeth
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* eg. cervical lymph nodes
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neck
head
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* eg. axillary lymph nodes
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Axilla and upper chest
drains arm and upper thorax including breasts
Lymph Nodes
Superficial groups
-Cervical
-Axillary
-Inguinal
Deep groups
-Tracheobronchial
-Aortic
-Iliac
Drainage
-Superior R 1/4 of body:
R lymphatic duct (green) *
-The rest: thoracic duct *
Swollen Lymph Glands
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Spleen
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Largest lymphoid tissue - The spleen is an organ at the upper left of the abdomen
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Like lymph nodes, the spleen contains specialized compartments where immune
cells gather and work.
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The spleen plays a major role in mounting immune response to antigens in the blood stream.
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Largest accumulation of lymphoid tissue.
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Abundant phagocytic cells
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Site of destruction of aged erythrocytes
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site of activated lymphocytes which are delivered to the blood.
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cell removal
store iron
store platelets
Thus, an important blood filter and antibody forming organ.
Immune Tissues in Organ- GALT ( gut associated lymph tissue)
Peyer’s Patchs
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A Swiss anatomist, Johann Peyer, noticed that embedded in the wall of small intestine.
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There are no incoming lymphatics that bring lymph into Peyer’s patches
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Smooth cell that crowns the Peyer’s patchs the one doesn’t have “hairs” on it is called an “ M” cell.
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M cell is a specialized cell that transport antigen from the interior ( lumen) of the intestine into the
Peyer’s patches.
Resemble tonsil in structure .
Capture and destroy bacteria in intestines
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O-MALT (organized mucosa-associated lymphatic tissue)
Tonsils
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Simplest circle lymphoid tissue embedded in
mucous membranes of pharynx covered by epithelium,
with deep pits(=crypts)
crypts often contain food debris, bacteria, dead wbc’s etc
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Filters bacteria that enters through the nose and mouth
First line of defense against infection
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three main sets of tonsils:
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pharyngeal tonsils = ( adenoids)
on wall of pharynx behind nasal cavity
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palatine tonsils
at post margin of oral cavity
largest and most often infected = tonsilitis
usually Streptococcus (treated with antibiotics)
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lingual tonsils
on each side of root of tongue
Lymph
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Lymph is the fluid that circulates throughout the lymphatic
system.
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Lymph: excess tissue fluid carried by lymphatic vessels
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Lymph move toward the heart
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Lymph is formed when the interstitial fluid (the fluid which lies
in the interstices of all body tissues) is collected through lymph
capillaries . It is then transported through lymph vessels to
lymph nodes before emptying ultimately into the right or the
left subclavian vein, where it mixes back with blood.
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Lymph is a clear watery fluid that resembles blood
plasma but: fewer proteins
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composition varies depending on organs that it drains
do not have red blood cells
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the lymphatic system handles 125 ml/hr (2.5-2.8 liters /day)
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~1/2 of this from the liver and small intestine alone
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lymph contains white blood cells ( lymphocytes and
macrophages ( monocytes)
Lymph
“Lymph” fluid
One way system: to the heart
Return of collected excess tissue fluid
Return of leaked protein
Edema results if system blocked or
surgically removed
Lymph vascular system - Lymphatic Capillaries
Lymphatic Capillaries- properties
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Numerous, small, originate in tissues as tiny blind ended sacs- by side with blood capillaries
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form networks throughout the tissue spaces in the body.
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Carry lymph from tissue spaces to larger lymphatic vessels
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single layer of endothelial cells like blood capillaries
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but much more permeable to solvents, and large solutes and whole cells
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Absent from bone, bone marrow, teeth
The lymph vascular system starts
at capillary. Interstitial fluid
enters the lymph capillaries.
Lymphatic Capillaries
Lymph vascular system - Lymphatic Vessels
Lymphatic Vessels- properties
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Small lymphatic capillaries merge with others to form larger lymphatic vessels
One way system toward the heart - No pump
Collecting lymph from lymphatic capillaries
Carry lymph to and away from lymph nodes
transparent, thin walled, very permeable vessels that carry lymph
Distributed throughout most tissues and have characteristic beaded appearance.
Small oppenenig between endothelial cells allow for high permeability to large substances
lymphatic vessels resemble veins in structure: a. three layers – but much thinner wall than veins
b. contain many valves to prevent backflow ( 1-way valves
c. excess fluid to enter but not leave
lymph vascular system
Lymphatic and blood vasculature
The lymphatic vascular network includes blind-ended capillaries and larger collecting lymphatic vessels. The lymphatic
capillaries are composed of a single layer of overlapping ECs and lack a continuous basement membrane. Collecting
lymphatic vessels are covered by smooth muscle cells, and possess a basement membrane and luminal valves that prevent
lymph backflow. The unique structure of capillary lymphatic vessels allows for the uptake of interstitial fluid,
macromolecules, cells, and lipids that filtrate continuously from the blood capillary network .
Draining Fluid into Bloodstream
What is the difference between Circulatory and Lymphatic Systems?
Lymphatic system ( lymph)
Lymph is responsible for collecting and removing
waste products left behind in the tissues.
Circulation system ( blood)
Part of the circulatory system.
Blood is responsible for collecting & distributing
oxygen, nutrients & hormones to the tissues of entire
body
Lymph flows in an open system from the tissues into
lymphatic vessels. lymph flows in only one direction
Blood flows in a closed continuous loop throughout
the body via the heart, arteries, capillaries, and veins.
Lymph is not pumped. It passively flows from the
tissues into the lymph capillaries. Flow within the
lymphatic vessels is aided by other body movements
such as deep breathing and the action of nearby
muscles and blood vessels
Blood is pumped. The heart pumps blood into the
arteries that carry it to all of the body. Veins return
blood from all parts of the body to the heart
Colorless ( hemoglobin absent)
Red in color ( presence hemoglobin in erythrocytes)
Lymph that has been filtered and is ready to return to
the cardiovascular system is a clear or milky white
fluid.
Blood consists of the liquid plasma that transports the
red and white blood cells and platelets.
Lymph is invisible and damage to the lymphatic system
is difficult to detect until swelling occurs.
Blood is visible and damage to blood vessels causes
obvious signs such as bleeding or bruising.
Lymph is filtered by lymph nodes located throughout
the body. These nodes remove some fluid and debris.
They also kill pathogens and some cancer cells
Blood is filtered by the kidneys. All blood flows
through the kidneys where waste products and excess
fluids are removed. Necessary fluids are returned to
the cardiovascular circulation.
Cont. What is the difference between Circulatory and Lymphatic Systems?
Lymphatic system ( lymph)
Circulation system ( blood)
consists of
(leukocytes (lymphocytes most consist of plasma, erythrocytes, leukocytes and
abundant)
platelets.
Lacks: blood- veins – arteries
the respiratory pigments (hemoglobin) are missing The conductive mediums of the circulatory system
are responsible for the transport of respiratory
form lymph.
gasses throughout the body.
the lymphatic system only carry digested fats.
The circulatory system carries digested food
material and wastes from cells to and from organs
the lymphocytes of the lymphatic system, which The leukocytes in blood pose a defense against the
help, build immunity
invading foreign bodies and toxins
Lymph is responsible for collecting and removing Blood is responsible for collecting and distributing
oxygen, nutrients and hormones to the tissues of
waste products left behind in the tissues.
entire body
Fewer protein and less calcium and phosphorous
Blood plasma has more protein, calcium and
phosphorous
Glucose concentration is less in lymph
Glucose concentration is lower in blood
• Age related changes:
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↓ thymus
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↓ T cells
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↓ antibodies
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↑ infection & cancer