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

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

3. 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

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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

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

12. 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.

13. 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

14. 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

15. 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

16. 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

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

18. 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)

19. 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

20. 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