Transcript Overview of the Lymphatic System

Lymphatic System
Capillary Dynamics,
Overview of the Lymphatic System,
Lymphoid Cells,
and Lymphoid Organs
Outline
I.
II.
III.
IV.
V.
The Big Picture
Capillary Dynamics
Overview of the Lymphatic System
Lymphoid Cells
Lymphoid Organs
The Big Picture
Main functions
 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 noncompliant (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





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 bloodborne pathogens
Lymphoid Organs
Thymus
 Functions
 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