Lymphatic System Capillary Dynamics, Overview of the Lymphatic System, Lymphoid Cells, and Lymphoid Organs

Outline The Big Picture Capillary Dynamics Overview of the Lymphatic System Lymphoid Cells Lymphoid Organs

The Big Picture Main functions Contribution to homeostasis Immunity – protecting body from foreign substances Maintenance of blood – returns leaked plasma proteins to blood Contribution to homeostasis Attacks foreign (and potentially deadly) substances Maintains blood volume and molecular concentrations

The Big Picture Mechanism of action Interlaced with capillaries and have similar structure, allowing for absorption Contains specialized cells that provide immunological properties

Capillary Dynamics Capillaries made of endothelium, a thin layer of epithelial cells  epithelial cells use simple diffusion as a means of moving substances in and out of the epithelial cells  capillaries use simple diffusion Intercellular clefts: pores through which material can move in and out of capillaries Plasmalemmal vesicles: vesicles found in endothelium; can be used for transport

Capillary Dynamics Movement of extracellular fluids Cardiovascular loop: blood flow in cardiovascular system Transcapillary loop: filtration and reabsorption of blood Lymphatic loop: compensates for difference between filtration and reabsorption Lymphatic flow restores lost fluid and proteins to blood

Capillary Dynamics Diffusion: movement of solute across a permeable membrane in which solute travels from area of highest concentration to area of lowest concentration; affected by five factors Concentration of solute on both sides of membrane Thickness of capillary wall Surface area of capillary wall Permeability of solute Molecular weight of solute

Capillary Dynamics Diffusion Fick’s law of diffusion: relates five factors of diffusion Direct relationship between rate of diffusion and: Difference in concentrations of solute across membrane Surface area of permeable membrane Permeability of solute Inverse relationship between rate of diffusion and: Thickness of capillary wall Molecular weight of solute

Capillary Dynamics Physics involved in capillary flow Capillary pressure: pressure in capillary from fluids; drives filtration; AKA hydrostatic pressure Plasma colloid osmotic pressure: pressure in capillary from presence of proteins; drives reabsorption; AKA COP Intersitial fluid colloid osmotic pressure: pressure from presence of proteins in interstitial fluid; drives filtration Interstitial fluid pressure: pressure from interstitial fluid pushing on capillary; drives reabsorption

Capillary Dynamics Physics involved in capillary flow Capillary pressure decreases as blood flows across capillary from arterial to venous end Plasma colloid osmotic pressure stays relatively equal across membrane Arterial end – capillary pressure > plasma colloid osmotic pressure  filtration Venous end – plasma colloid osmotic pressure > capillary pressure  reabsorption

Capillary Dynamics Physics involved in capillary flow Overall, filtration > absorption Filtered substances move into lymphatic system Lymphatic system returns substances to cardiovascular system

Capillary Dynamics Important notes More particles of albumin in blood per gram molecular weight  presence of albumin in blood makes up for 80% of plasma colloid osmotic pressure … Okay, I guess there’s only one important note.

Overview of the Lymphatic System Function: return blood from interstitial space; blood returned via venous return Right lymphatic duct: drains right side of head, neck, and right arm; enters right subclavian vein Thoracic duct: drains most peripheral ducts, left side of head, and neck; enters left subclavian vein

Overview of the Lymphatic System Lymph flow At low pressures, interstitial fluid is non-compliant (has high resistance; compliance has inverse relationship with resistance) Small increases in pressure decrease resistance, thereby increasing lymph flow At high interstitial fluid volumes, changes in volume (which lead to changes in pressure) do not cause increased lymph flow

Overview of the Lymphatic System Lymph flow No organ to pump lymph Lymph flow is peristaltic (contraction of circular smooth muscles to move objects) Relies on external compression (pressure from outside capillaries) to move lymph

Lymphoid Cells Lymphocytes: main cells involved in cellular response T cells: manage immune response; attack and destroy foreign particles B cells: produce plasma cells, which secrete antibodies (bind to antigens [substance that stimulates immune response]) to immobilize antigens

Lymphoid Cells Other cells Macrophages Dendritic cells: similar function to macrophages Reticular cells: produce network that supports other cell types in lymphoid organs

Lymphoid Organs Lymph nodes Embedded in connective tissue and clustered along lymphatic vessels Clusters appear in cervical, axillary, and inguinal regions Two functions Filtration Immune system activation Contain germinal centers for T cell and B cell proliferation (synthesis, via mitosis)

Lymphoid Organs Spleen Functions Anatomy Site of lymphocyte proliferation Immune surveillance and response Cleanses blood Salvages and stores iron for later use Stores blood platelets Anatomy White pulp: contains lymphocytes Red pulp: disposes of old RBCs and blood-borne pathogens

Lymphoid Organs Thymus Functions Anatomy Secretes hormones (thymosin, thymopoietin) that cause T cells to become more immunocompetent Does not directly fight antigens Anatomy Has cortex and medulla Cortex – contains lymphocytes and macrophages Medulla – contains lymphocytes and thymic corpuscles