The lymphatic system

Lymphatic System functions are:
-Supplementary transport system to channel tissue fluid back to blood circulatory system.
-Major part of immune system-maturation of lymphocytes and in destroying pathogens.

3 main components:
-Lymphatic fluid(lymph)
-Lymphatic vessels
-Lymphatic tissues.

Lymphatic Fluid (Lymph)
-formed by diffusion of tissue fluid into lymphatic capillary.
-components alsmost similar as tissue fluid, but contains fewer plasma proteins and does not contain erythrocytes and platelets.
-Formation of lymphatic fluid:
.Ultrafiltration-fine molecules in blood diffuse out through partially permeable membrane (endothelium) of blood capillaries into extracellular space of body cells.
.Ultrafiltration is aided by difference in hydrostatic pressure and water potentials between blood in capillary and tissue fluid in extracellular space.
.Major portion of tissue fluid is reabsorbed into blood capillaries nearer to venule because water potential and hydrostatic pressure is lower in these areas compared to tissue fluid.
.A small portion of tissue fluid enters lymphatic capillaries through special pores with valves to form lymphatic fluid.
.Lymphatic fluid in lymphatic capillaries flows into lymphatic vessels.
.Fat soluble substances produced by digestion diffuses into lacteal in villi of small intestines before flowing into lymphatic vessels.

Lymphatic Vessels
-Consists of capillaries and ducts.

-Lymphatic Capillaries are:
.Smallest lymphatic vessels found in all tissue except spleen.
.Have closed ends that have pores with valves.
.Capillaries join to form venules which then join to form bigger lymphatic ducts.

-Lymphatic Ducts:
.Same structure as blood veins with valves for unidirectional flow of lymph.
.Flow is aided by contraction of skeletal muscle, peristalsis and pulse.
.Biggest lymphatic ducts are thoracic duct and right lymphatic duct which empties its content into subclavian veins.

Lymphatic Tissue
1.Spleen
-Largest lymphoid organ.
-Functions:
.Produces Red Blood Cells-foetal stage and few years after birth.
.Removes worn out white blood cells and platelets.
.Contain lymphocytes-filters blood to remove bacteria and antigens.
.Stores blood when required.

2.Thymus Gland
-Enlarages during childhood, shrinks after puberty.
-Functions:
.Activates T lymphocytes-lymphocytes originating from stem cells-matures, differentiates and functions after passing through thymus gland.
.Produces Hormones-causes T cells to mature by forming specific receptors. (TCR)
.T cells secretes lumphokine-helps in cell mediated response.

3.Lymph Nodes
-Bean Shaped and located at specific parts of body such as groins, armpits, beneath lower jaws.
-Functions:
.Location where antigens are presented to immune system.
.Location for activated B lymphocytes division to form plasma and memory cells.
.Lymphocytes and macropahges-filter pathogens and antigens.