lesson 7

Function of the lymphatic system

1. Drainage of fluid from blood stream into the tissues 2. Filtration of the lymph at the lymph nodes 3. Filtering blood 4. Raise an immune reaction and fight infections

Bone Marrow

Bone marrow is the soft, flexible tissue found inside bone. Bone marrow is responsible for the production of blood cells: red blood cells, white blood cells, and platelets. Bone marrow stem cells play an important role in immunity as they generate lymphocytes. While some white blood cells mature in bone marrow, certain types of lymphocytes migrate to lymphatic organs, such as the spleen and thymus, to mature into fully functioning lymphocytes.

describe the mechanisms of transport of lymph

Lymphatic capillaries which empty into Lymphatic collecting vessels which empty into Lymphatic trunks and ducts • The lymphatic system lacks an organ that acts as a pump. lymphatic vessels are low-pressure conduits, and the same mechanisms that promote venous return in blood vessels act here as well—the milking action of active skeletal muscles, pressure changes in the thorax during breathing, and valves to prevent backflow. • lymph transport is sporadic and slow. About 3 L of lymph enters the bloodstream every 24 hours, a volume almost exactly equal to the amount of fluid lost to the tissue spaces from the bloodstream in the same time period.

distribution of the lymphatic vessels

The lymphatic vessels form a one-way system in which lymph flows only toward the heart. This transport system begins in microscopic blind-ended lymphatic capillaries. These capillaries weave between the tissue cells and blood capillaries in the loose connective tissues of the body. They are absent from bones and teeth, bone marrow, and the entire central nervous system

Tonsils

Tonsils house lymphocytes and other white blood cells called macrophages. These immune cells protect the digestive tract and lungs from disease-causing agents that enter the mouth or nose.

Lymphatic Vessels

absorb fluid that diffuses from blood vessel capillaries into surrounding tissues. This fluid is directed toward lymph nodes to be filtered and ultimately re-enters blood circulation through veins located near the heart. The smallest lymphatic vessels are called lymph capillaries. Lymphatic capillaries come together to form larger lymphatic vessels. Lymphatic vessels from various regions of the body merge to form larger vessels called lymphatic trunks. Lymphatic trunks merge to form two larger lymphatic ducts. Lymphatic ducts return lymph to blood circulation by draining lymph into the subclavian veins in the neck.

LYMPHOCYTES

cell of the lymphoid system that participates in the immune response.

function of the lymphatic vessels

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

reticular cells

fibroblast like cells that produce a stroma or network that supports other cell types in lymphoid organs

Spleen

filter blood of damaged cells, cellular debris, and pathogens. Like the thymus, the spleen houses and aids in the maturation of lymphocytes. Lymphocytes destroy pathogens and dead cells in the blood. The spleen is rich in blood supplied via the splenic artery. The spleen also contains efferent lymphatic vessels, which transport lymph away from the spleen and toward lymph nodes.

Lymph Nodes

filter lymph of pathogens, such as bacteria and viruses . Lymph nodes also filter cellular waste, dead cells, and cancerous cells. Lymph nodes house immune cells called lymphocytes. These cells are necessary for the development of humoral immunity (defense prior to cell infection) and cell-mediated immunity (defense after cell infection). Lymph enters a node through afferent lymphatic vessels, filters as it passes through channels in the node called sinuses, and leaves the node through an efferent lymphatic vessel.

Name 4 lymphatic organs

lymph nodes, tonsils, spleen, thymus gland

T cells

manage the immune system response, attack and destroy foreign cells.

macrophages

phagocytize foriegn substances and help activate T cells

B cells

produce plasma cells, which sectrete antibodies, Antibodies immobilize antigens

Thymus

promote the development of specific cells of the immune system called T-lymphocytes. Once mature, these cells leave the thymus and are transported via blood vessels to the lymph nodes and spleen. T-lymphocytes are responsible for cell-mediated immunity, which is an immune response that involves the activation of certain immune cells to fight infection. In addition to immune function, the thymus also produces hormones that promote growth and maturation.

dendritic cells

spiny-looking cells with function similar to macrophages

lymph nodes

the principal organ of the body, aggregations of these nodes occur near the body surface in inguinal,axillary and cervical regions of the body.Nodes are bean shaped and surrounded by a fibrous capsue. Trabeculae extended inward from the capsule and divide the node into compartment, nodes have two histologically distinct regions a cortex and medulla

Structure of the lymphatic vessels

vessels are thin-walled, valved structures that carry lymph. Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscles and adventitia that bind the lymph vessels to the surrounding tissue.