A and P lymphatic system

Diffuse lymphoid tissue

A loose arrangement of lymphoid cells and some reticular fibers - is found in virtually every body organ. Larger collections appear in the lamina propr. of mucous membranes such as those lining the digestive tract.

Lymphatic system consists of three parts

A meandering network of lymphatic vessels Lymph, the fluid contained in those vessels. Lymph nodes that cleanse the lymph as it passes through them.

Appendix

A tubular offshoot of the first part of the large intestine and contains a high concentration of lymphoid follicles. Ideal position to - prevent bacteria from breaching the intestinal wall - generate many memory lymphocytes for long-term immunity.

Lymph node structure

Beans shaped and less than 2.5 cm (inch) in length. Surrounded by a dense fibrous capsule from which connective tissue strands called trabecular extend inward to divide the node into a number of compartments

Primary lymphoid organs

Both B and T cells originate int he red bone marrow. - B cells mature in the red bone marrow - T cells mature in the thymus.

lymph nodes have two basic protective functions

Cleansing the lymph - As lymph is transported back to the bloodstream, the lymph nodes act as lymph filters. Macrophages in the nodes remove and destroy microorganisms and other debris that enter the lymph from the use connective tissues, preventing them form being delivered to the blood and spreading to other parts of the body. Immune system activation - Lymph nodes and other lymphoid organs are strategically located sites where lymphocytes encounter antigens and are activated to mount an attack against them.

Lymphoid Cells

Consist of immune system cells found in lymphoid tissues together with the supporting cells that form the scaffolding of those tissues.

What happens to the lymphatic capillaries when tissues become inflamed.

Develops openings that permit uptake of even larger particles such as cell debris, pathogens, and cancer cells. Then the pathogens use the lymphatics to travel throughout the body.

Cisterna chyli

In about half of individuals, the thoracic duct begins as an enlarged sac, the sisterna chyli. Located in the region between the last thoracic and second lumbar vertebrae.

lymph

Interstitial fluid that enters the lymphatic vessels

The spleen's uses

It's macrophages remove debris and foreign matter. Recycles the breakdown products of red blood cells for later reuse. It releases the breakdown products to the blood for processing by the liver and stores some of the iron salvaged from hemoglobin. Stores blood platelets and monocytes for release into the blood when needed. May be a site of erythrocyte production in the fetus.

Reticular connective tissue

Loose connective tissue that composes lymphoid tissue

Order of lymph flow

Lymph flows through successively larger and thicker-walled channels. Collecting vessels, then trunks, and finally the largest of all, the ducts.

Lacteals

Lymphatic capillaries that transports absorbed fat from the small intestine to the bloodstream.

Lymph Transport

Lymphatic vessels are low-pressure conduits, and the same mechanisms that promote venous return in blood vessels act here as well - milking action of active skeletal muscles - pressure changes in the thorax during breathing - valves prevent backflow Lymphatic vessels usually bundle together in connective tissue sheaths along with blood vessels, and pulsation of nearby arteries also promote lymph flow. Smooth muscle in the walls, except the smallest lymphatic vessels, contracts rhythmically, helping to pump the lymph along.

Lymphocytes

Main warriors. - T cells and B cells Protect the body against antigens.

T cells (T lymphocytes)

Manage the immune response, some of them directly attack and destroy infected cells.

Lymphoid organs and tissues

Provide the structural basis of the immune system. These organs and tissues play essential roles in the body's defense mechanisms and its resistance to diesesase. Spleen thymus tonsils other lymphoid tissues scattered throughout the body

Lymphatic system

Returns fluids that have leaked from the vascular system back to the blood.

Interstitial fluid

The hydrostatic and colloid osmotic pressures operating at capillary beds force fluid out of the blood at the arterial ends of the beds (upstream) and cause most of it to be reabsorbed at the venous ends (down stream). The fluid that remains behind in the tissue spaces is the interstitial fluid.

When fluid pressure in the interstitial space is greater than the pressure in the lymphatic capillary

The minivalve flaps gape open, allowing fluid to enter the lymphatic capillary

lymph nodes

The most important of the secondary lymphoid organs. Cluster along the lymphatic vessels of the body. Embedded in connective tissue. Large clusters occur near the body surface in the inguinal, allay, and cervical regions.

The thymus differs from secondary lymphoid organs in three ways

The thymus has no follicles because it lacks B cells. The thymus does not directly fight antigens. Instead, the thymus functions strictly as a maturation site for T lymphocyte precursors. These precursors must be kept isolated from foreign antigens to prevent their premature activation. In fact, there is a blood thymus barrier that keeps blood borne antigens out of the thymus. The storm of the thymus consists of epithelial cells rather than reticular fibers. These epithelial cells provide the physical and chemical environment in which T lymphocytes mature.

Tonsillar crypts

Trap bateria and particulate matter, and the bacteria work their way through the mucosal epithelium into th lymphoid tissue, where most are destroyed.

Lymphatic trunks

United largest collecting vessels. Drain fairly large areas of the body. Lumbar bronchomediastinal subvlavian jugular trunks intestinal trunk

Secondary lymphoid organs

Where mature lymphocytes first encounter their antigens and are activated. Lymph nodes, spleen, and the collections of mucosa-associated lymphoid tissue (MALT) that form the tonsils, Peyer's patches (aggregated lymphoid nodules) in the small intestine, and the appendix.

Lymphatic capillaries

Where the transport of lymph begins. Widespread but absent from bones, teeth, NS, bonemarrow.

Dendritic Cells

capture antigens and bring them back to the lymph nodes.

stroma

is the network that supports the other cell types in lymphoid organs and tissues.

white pulp

is where immune functions take place, so it is composed mostly of lymphocytes suspended on reticular fibers. The white pulp clusters or forms cuffs around central arteries. These clusters of white pulp look like island sin a sea of red pulp.

Red pulp

is where worn-out red blood cells and blood borne pathogens are destroyed, so it contains huge numbers of erythrocytes and the macrophages that engulf them. It is essentially all splenic tissue that is not white pulp. Consists of splenic cords, region of reticular connective tissue, that separate the blood-filled splenic sinusoids.

When the pressure is greater inside the lymphatic capillary

it forces the endothelial minivalve flaps shut, preventing lymph from leaking back out as the pressure moves it along the vessels.

Peter's Patches / aggregate lymphoid nodules,

large clusters of lymphoid follicles, structurally similar to the tonsils. Located in the wall of the distal portion of the small intestine.

Thoracic duct

receives lymph from the rest of the body. It collects lymph from the two large lumbar trunks that drain the lower limbs and from the intestinal trunk that drains the digestive organs.

Why are lymphatic capillaries so permeable

the endothelial cells forming the walls are adjacent and overlap each other loosely, forming easily opened, flaplike minivalves. P. 758 Collagen filaments anchor the endothelial cells to surrounding structures so that any increase in interstitial fluid volume opens the minivalves, rather than causing the lymphatic capillaries to collapse.

The spleen consists of two components

white pulp and red pup

B cells (B lymphocytes)

Protect the body by producing plasma cells, daughter cells that secrete antibodies into the blood.

Lymphoid tissue comes in various packages

Diffuse lymphoid tissue Lymphoid follicles (lymphoid nodules)

Right lymphatic duct

Drains lymph from the right upper limb and the right side of the head and thorax

Lymphatic vessels/ lymphatics

Elaborate networks of drainage vessels that collect the excess protein-containing interstitial fluid and return it to the bloodstream.

Chyle

Fatty lymph that drains through lacteals

Tonsils

Form a ring of lymphoid tissue around the entrance to the pharynx, where they appear as swellings of the mucosa. Contains follicles with germinal centers surrounded by diffusely scattered lymphocytes.

Thymus

Found in the inferior neck and extends into the superior thorax. In thymus, T lymphocyte precursors mature to become immunocompetent lymphocytes. Promient in newborns.

Collecting lymphatic vessels have

Have the same three tunics as veins, but the collecting vessels have thinner walls and more internal valves, and they anastomose more.

Lymphoid tissue

Houses and provides a proliferation site for lymphocytes. Furnishes an ideal surveillance vantage point for lymphocytes and macrophages.

MALT

Mucosa-associated lymphoid tissues are a set of distributed lymphoid tissues strategically located in mucous membranes throughout the body. Helps protect us from the never ending onslaught of pathogens. Tonsils, peer's patches, and appendix.

Macrophages

Phagocytizes foreign substances and helps activate T cells.

Reticular Cells

Produce reticular fiber stroma,

Lymphoid follicles (lymphoid nodules)

Solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers. Follicles often have lighter-staining germinal centers where proliferating B cells predominate. These centers enlarge dramatically when the B cells are dining rapidly and producing plasma cells.