Immunology

Lecture – 6

Lymphatic System

• network of tissues, organs and vessels that help to maintain the body’s fluid balance & protect it from pathogens.

• lymphatic system is an extensive drainage system that returns water and proteins from various tissues back to the blood stream.

• like the circulatory system • the lymphatic system consists of a series of vessels, and a fluid called lymph

• unlike the circulatory system it is a 1-way system • 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.

• lymphatic system is directly connected to the circulatory system

• it helps the circulatory system to do its job

• without it neither the circulatory system nor the immune system would function.

General Function Lymphatic System

• 1. Returns Fluid from Tissues and molecules to Blood

• 2. Absorb and Transport Fats

• 4. Hemopoiesis

• 5. Body Defense immunity/ protection

Lymphatic System

• Lymphatic system components includes :

• 1. lymph

• 2. Lymphatic vessels- lymphatic capillaries

• 3. Lymphatic organs

• 4. Lymphatic Tissues

• 4. lymphatic cells (Macrophages, Dendritic cell, Lymphocytes)

Organs of Immune System • 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 surface-

found 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

• Located in the middle of bones

• Most specifically vertebrates

• Pelvic

• Leg bones

• Generate T cell, B cell and macrophages- cell that travel throughout the body in the blood and tissue

fluids

Thymus • A bilobed organ located above heart near throat

• Grows up rapidly for first 2 years

• DiGeorge Syndrome congenital birth defect- lack of thymus- absence of T cell mediated immunity

• Each lobe- many lobules by fibrous septa- outer cortex and inner medulla

• Cortex- tightly packed- contains immature lymphocytes

• Medulla- contain more mature cells

Lymph nodes

• 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.

• The lymph node contains numerous specialized structures

• Lymphoid cells:

• T cells concentrate in the cortex,

• B cells in and plasma cells in the medulla

• Macrophages and other phagocytic antigen presenting cells

• Immune cells and foreign particles enter the lymph nodes via incoming lymphatic vessels.

• 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

• include:

• Clean lymph: Removal and destruction of microbes, harmful foreign particles and dead cells

from lymph (through phagocytosis by macrophages)

• filtration of particles and microbes to keep them out of circulation

• Alert immune system to pathogens

• Activation, proliferation of B cells and antibody production

• Activation, proliferation of T cells.

Lymph Nodes

• lymph nodes are widespread in body :

• * eg. submental & submaxillary lymph nodes

• floor of mouth;

• drain nose, lips teeth

• * eg. cervical lymph nodes

• neck

• head

• * eg. axillary lymph nodes

• Axilla and upper chest

• drains arm and upper thorax including breasts

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 *

Lymph Nodes

*

*

Swollen Lymph Glands

Spleen • Largest lymphoid tissue - The spleen is an organ at the upper left of the abdomen

• Like lymph nodes, the spleen contains specialized compartments where immune

cells gather and work.

• The spleen plays a major role in mounting immune response to antigens in the blood stream.

• Largest accumulation of lymphoid tissue.

• Abundant phagocytic cells

• Site of destruction of aged erythrocytes

• site of activated lymphocytes which are delivered to the blood.

• 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

• A Swiss anatomist, Johann Peyer, noticed that embedded in the wall of small intestine.

• There are no incoming lymphatics that bring lymph into Peyer’s patches

• Smooth cell that crowns the Peyer’s patchs the one doesn’t have “hairs” on it is called an “ M” cell.

• 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

O-MALT (organized mucosa-associated lymphatic tissue) Tonsils

• 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 Filters bacteria that enters through the nose and mouth • First line of defense against infection

• three main sets of tonsils: • pharyngeal tonsils = ( adenoids) • on wall of pharynx behind nasal cavity • palatine tonsils • at post margin of oral cavity • largest and most often infected = tonsilitis • usually Streptococcus (treated with antibiotics) • lingual tonsils • on each side of root of tongue

Lymph • Lymph is the fluid that circulates throughout the lymphatic

system.

• Lymph: excess tissue fluid carried by lymphatic vessels

• Lymph move toward the heart

• 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.

• Lymph is a clear watery fluid that resembles blood

plasma but: fewer proteins

• composition varies depending on organs that it drains

do not have red blood cells

• the lymphatic system handles 125 ml/hr (2.5-2.8 liters /day)

• ~1/2 of this from the liver and small intestine alone

• 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

• Numerous, small, originate in tissues as tiny blind ended sacs- by side with blood capillaries

• form networks throughout the tissue spaces in the body.

• Carry lymph from tissue spaces to larger lymphatic vessels

• single layer of endothelial cells like blood capillaries

• but much more permeable to solvents, and large solutes and whole cells

• 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 • 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?

Circulation system ( blood) Lymphatic system ( lymph)

Blood is responsible for collecting & distributing oxygen, nutrients & hormones to the tissues of entire body

Lymph is responsible for collecting and removing waste products left behind in the tissues. Part of the circulatory system.

Blood flows in a closed continuous loop throughout the body via the heart, arteries, capillaries, and veins.

Lymph flows in an open system from the tissues into lymphatic vessels. lymph flows in only one direction

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

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

Red in color ( presence hemoglobin in erythrocytes) Colorless ( hemoglobin absent)

Blood consists of the liquid plasma that transports the red and white blood cells and platelets.

Lymph that has been filtered and is ready to return to the cardiovascular system is a clear or milky white fluid.

Blood is visible and damage to blood vessels causes obvious signs such as bleeding or bruising.

Lymph is invisible and damage to the lymphatic system is difficult to detect until swelling occurs.

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.

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

Cont. What is the difference between Circulatory and Lymphatic Systems?

Circulation system ( blood) Lymphatic system ( lymph)

consist of plasma, erythrocytes, leukocytes and platelets.

consists of (leukocytes (lymphocytes most abundant) Lacks: blood- veins – arteries

The conductive mediums of the circulatory system are responsible for the transport of respiratory gasses throughout the body.

the respiratory pigments (hemoglobin) are missing form lymph.

The circulatory system carries digested food material and wastes from cells to and from organs

the lymphatic system only carry digested fats.

The leukocytes in blood pose a defense against the invading foreign bodies and toxins

the lymphocytes of the lymphatic system, which help, build immunity

Blood is responsible for collecting and distributing oxygen, nutrients and hormones to the tissues of entire body

Lymph is responsible for collecting and removing waste products left behind in the tissues.

Blood plasma has more protein, calcium and phosphorous

Fewer protein and less calcium and phosphorous

Glucose concentration is lower in blood Glucose concentration is less in lymph

• Age related changes:

• ↓ thymus

• ↓ T cells

• ↓ antibodies

• ↑ infection & cancer