Vessel III Flashcards
What is extracellular fluid in tissues called?
Interstitial fluid
When does interstitial fluid become lymph?
Once interstitial fluid enters the lymph vascular system, it is called lymph
What is the function and characteristics of the lymph vascular system?
Collects excess interstitial fluid and returns it to blood, en route it carries this fluid to lymph nodes for filtration
Unlike blood, lymph vascular system has no central pump and does not form a complete circulate, flows one way
1 way interaction - collects fluid from tissues and does not return it to tissues
Fluid movement is driven by skeletal muscle contraction - aids slightly by smooth muscle is largest lymphatic vessels
What is the path of lymph?
Tissue
Lymphatic capillary
Lymphatic vessels
Thoracic duct or R lymphatic duct
Venous vessels
What are lymph nodes?
Lymph is filtered in lymph nodes en route to veins
Filter lymph to remove particulates, bacteria, and other foreign material
Lymph arrives at lymph nodes via afferent lymphatic vessels
Lymph leaves lymph nodes via efferent lymphatic vessels
How is lymph returned to blood?
Lymph returned to venous blood via lymphatic ducts that directly empty into internal jugular vein, subclavian vein, or brachiocephalic vein
Where are lymphatic vessels present?
Throughout body
Except orbit, inner ear, epidermis, cartilage, bone, and CNS
What are the main driving forces for movement of fluid out of blood capillaries?
Concentration gradients between plasma in capillary vessels and interstitial fluid (osmotic pressure/oncotic pressure)
Blood pressure (hydrostatic pressure)
What are the opposing forces influencing fluid movement across capillary walls?
Hydrostatic pressure - pressure of blood against inside of capillary walls, forces fluid out of capillary
Oncotic pressure (plasma colloid osmotic pressure) - form of osmotic pressure that results from higher protein within plasma vs. interstitial fluid so osmotic gradient pulls fluid into capillary
Interstitial fluid pressure - pressure of interstitial fluid against the outside of lymph capillary walls, forces fluid into lymph capillaries
Explain how the opposing forces influence fluid movement across capillary walls.
Normally, hydrostatic and oncotic pressure are balanced (little net movement) - most fluid exiting blood capillaries will return to blood capillary
Lymphatic vessels remove most of excess interstitial fluid
As volume of tissue fluid increases, interstitial fluid pressure drives interstitial fluid into lymph capillaries
What are the characteristics of lymphatic capillaries?
Blind ended vessels
One end of the blind ended vessels is a cul-de-sac and fluid will only flow in one direction
All lymphatic capillaries are blind ended vessels - lymph vessels flow but do not circulate
What is the function of lymphatic capillaries?
Remove protein rich interstitial fluid from interstitial spaces and carry it to larger lymphatic vessels
Also take up inflammatory molecules, dietary lipids, and WBCs
Large proteins and WBCs can enter lymphatic capillaries because fluid entry is driven by pressure, not by a concentration (osmotic) gradient
What is the structure of lymphatic capillaries in LM?
No true tunics
very thin endothelium only - no fenestrae, lack junctional complexes, BM absent/discontinuous. Have endothelial folds - flaps that open inwards when pressure outside vessel is higher than fluid pressure inside the vessel that prevent lymph from returning to tissue
Tethered to elastic fibers in ECM by anchoring filaments made of fibrillin - anchor lymph capillaries to ECM and help maintain capillary patency
Lack smooth muscle cells, pericytes, valves
What is the purpose of lymphatic vessels having valves?
Valves are conduits that carry lymph from lymphatic capillaries to lymph nodes and thoracic ducts
Numerous closely spaced valves help prevent backflow within the vessel
What is the structure of lymphatic vessels?
Endothelium lacks folds, but has tight junctions. BM present and continuous to prevent leaks
Thin band of elastic fibers surrounded endothelium
Smooth muscle cells
Layer of collagen and elastic fibers surrounds entire lymphatic vessels
*larger vessels have progressively more smooth muscle and CT
No true tunics
What is the structure of lymphatic ducts?
True tunics and valves!
Thinner walls than large veins
Tunica intima: endothelium + BM, fibroelastic CT, band of elastic fibers at position of EL
Tunica media: longitudinal layer and circumferential layers of smooth muscle
Tunica externa: Longitudinally- orientated smooth muscle cells, collagen fibers, and has vasa vasorum
Vasculogenesis
Process of making blood vessels when there is no pre-existing model to grow from
Mainly occurs in embryos, sometimes occurs in adults after injury
Angiogenesis
New blood vessels branch off and extend from pre-existing vessels
Occurs throughout development, from embryos through fetal life and into adulthood
Vascular Remodeling
Reshaping of vessel walls in response to environmental changes like BP or rates of blood flow
These environmental changes often results from changes in behavior or activity level
How does vasculogenesis occur?
Embryonic stem cells divide and form primitive vessels called endothelial capillary tubes - these stem cells are usually angioblasts and sometimes are hemangioblasts
Angioblasts differentiate into endothelial cells
Endothelial capillary tubes merge together, forming primitive network and acquire arterial or venous features over time
After network forms, most vessels form via angiogenesis by branching off the network
How does angiogenesis occur?
New vessels branch and extend from pre-existing vessles
Differentiated endothelial cells migrate from existing vessels to site where new vessels are needed
Initial destabilization of parent vessel is induced by angiopoietin
Parent vessel vasodilates and becomes more permeable
Existing endothelial cells detach from adjacent cells and from the BM - disrupting lateral and basal cell junction and degrade/dissolve the underlying BM
Endothelial cells then migrate to the angiogenic stimulus
Aftermigration, endothelial cells form a tube of endothelium
New tubes stabilized by endothelial cells
What do endothelial cells do to stabilize new tubes during angiogenesis?
- Synthesize and elaborate a BM
- Recruit cells that can generate a tunica media and tunica externa (pericytes and smooth muscle cells)
How does angiogenesis occur during tissue repair?
Sprouting new vessel extensions that grow toward each other
Newly formed vessel eventually merges with other new vessels to form the new vascular bed
How does angiogenesis occur without endothelial cell migration?
If no endothelial cells available to migrate, endothelial progenitor cells 9EPCs) are recruited from red marrow
EPCs are adult stem cells
EPCs mobilize in response to dramatic alterations in the tissue environment and then migrate where they are needed
When are EPCs recruited?
Replace endothelial cells when completely lost (damage)
Endothelization of vascular implants (e.g. stents)
Vascularization of ischemic organs, wounds, tumors
What are key parts of adaptive vascular remodeling? x3
Changes in mechanical stress drive morphological changes in blood vessel walls
BP and flow rate are different kinds of stressors and they stress different layers of the vessel wall
Vessel size and the type of stimulus/stressor determine how the wall changes and adapts
What occurs with an increasing BP or the rate of blood flow to vascular walls?
Increase vascular wall stress
What occurs with decreasing BP or the rate of blood flow to vascular walls?
Decrease in vascular wall stress
What stress does blood flow rate and BP cause to vascular walls?
Rate of blood flow drives shear stress because it pries up endothelial cells edges and irritate the endothelium
BP is hydrostatic pressure puts pressure of blood on inside of vessel walls
Wall thickness stay the same when rate of blood flow _____
Increases
Shear stress irritate the endothelium but does not add pressure to vessel walls
What happens to a vessel if flow rate increases?
Adapts by increasing lumen diameter
A larger lumen distributes flow over a larger surface and means less irritation
What happens to a vessel if flow rate decreases?
It adapts by decreasing its lumen diameter
What is another way the body addresses increased rate of flow?
Angiogenesis
Adding new vessels increases the systemic volume (and thus increases its capacity to deliver blood, oxygen, nutrients, etc)
What occurs with increased blood pressure in a large artery?
Outward hypertrophy
Increase in wall thickness
Lumen diameter unchanged
What occurs with increased blood pressure in a small artery?
Inward hypertrophy
Outside diameter unchanged
Decrease in lumen diameter
What occurs with increased blood pressure in arterioles?
Inward hypertrophy - Increased wall thickness of tunica media and decrease in lumen diameter
Inward (eutrophic) remodeling - decrease in wall thickness (losing t. media components) and wall diameter
Rarefaction - vessel loss
With increased blood pressure, what changes are occurring?
Changes in amount of smooth muscle in the tunica media
More smooth muscle = stronger walls = increased ability to resist pressure
Where are the changes occurring with increased blood pressure (hypertension)?
Occur in arterial vessels because BP is already so much higher in arteries and veins
Higher BP stresses arteries (and the heart) more than it stresses veins
What are angioblasts?
Endothelial cell precursors
What are hemangioblasts?
Potent stem cells
Can become angioblasts, blood cell precursors, and mesenchymal cells
