Vessel III

Question 1

What is extracellular fluid in tissues called?

Answer 1

Interstitial fluid

Question 2

When does interstitial fluid become lymph?

Answer 2

Once interstitial fluid enters the lymph vascular system, it is called lymph

Question 3

What is the function and characteristics of the lymph vascular system?

Answer 3

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

Question 4

What is the path of lymph?

Answer 4

Tissue

Lymphatic capillary

Lymphatic vessels

Thoracic duct or R lymphatic duct

Venous vessels

Question 5

What are lymph nodes?

Answer 5

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

Question 6

How is lymph returned to blood?

Answer 6

Lymph returned to venous blood via lymphatic ducts that directly empty into internal jugular vein, subclavian vein, or brachiocephalic vein

Question 7

Where are lymphatic vessels present?

Answer 7

Throughout body

Except orbit, inner ear, epidermis, cartilage, bone, and CNS

Question 8

What are the main driving forces for movement of fluid out of blood capillaries?

Answer 8

Concentration gradients between plasma in capillary vessels and interstitial fluid (osmotic pressure/oncotic pressure)

Blood pressure (hydrostatic pressure)

Question 9

What are the opposing forces influencing fluid movement across capillary walls?

Answer 9

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

Question 10

Explain how the opposing forces influence fluid movement across capillary walls.

Answer 10

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

Question 11

What are the characteristics of lymphatic capillaries?

Answer 11

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

Question 12

What is the function of lymphatic capillaries?

Answer 12

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

Question 13

What is the structure of lymphatic capillaries in LM?

Answer 13

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

Question 14

What is the purpose of lymphatic vessels having valves?

Answer 14

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

Question 15

What is the structure of lymphatic vessels?

Answer 15

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

Question 16

What is the structure of lymphatic ducts?

Answer 16

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

Question 17

Vasculogenesis

Answer 17

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

Question 18

Angiogenesis

Answer 18

New blood vessels branch off and extend from pre-existing vessels

Occurs throughout development, from embryos through fetal life and into adulthood

Question 19

Vascular Remodeling

Answer 19

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

Question 20

How does vasculogenesis occur?

Answer 20

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

Question 21

How does angiogenesis occur?

Answer 21

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

Question 22

What do endothelial cells do to stabilize new tubes during angiogenesis?

Answer 22

1. Synthesize and elaborate a BM
2. Recruit cells that can generate a tunica media and tunica externa (pericytes and smooth muscle cells)

Question 23

How does angiogenesis occur during tissue repair?

Answer 23

Sprouting new vessel extensions that grow toward each other

Newly formed vessel eventually merges with other new vessels to form the new vascular bed

Question 24

How does angiogenesis occur without endothelial cell migration?

Answer 24

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

Question 25

When are EPCs recruited?

Answer 25

Replace endothelial cells when completely lost (damage)

Endothelization of vascular implants (e.g. stents)

Vascularization of ischemic organs, wounds, tumors

Question 26

What are key parts of adaptive vascular remodeling? x3

Answer 26

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

Question 27

What occurs with an increasing BP or the rate of blood flow to vascular walls?

Answer 27

Increase vascular wall stress

Question 27

What occurs with decreasing BP or the rate of blood flow to vascular walls?

Answer 27

Decrease in vascular wall stress

Question 28

What stress does blood flow rate and BP cause to vascular walls?

Answer 28

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

Question 29

Wall thickness stay the same when rate of blood flow _____

Answer 29

Increases

Shear stress irritate the endothelium but does not add pressure to vessel walls

Question 30

What happens to a vessel if flow rate increases?

Answer 30

Adapts by increasing lumen diameter

A larger lumen distributes flow over a larger surface and means less irritation

Question 31

What happens to a vessel if flow rate decreases?

Answer 31

It adapts by decreasing its lumen diameter

Question 32

What is another way the body addresses increased rate of flow?

Answer 32

Angiogenesis

Adding new vessels increases the systemic volume (and thus increases its capacity to deliver blood, oxygen, nutrients, etc)

Question 33

What occurs with increased blood pressure in a large artery?

Answer 33

Outward hypertrophy

Increase in wall thickness

Lumen diameter unchanged

Question 34

What occurs with increased blood pressure in a small artery?

Answer 34

Inward hypertrophy

Outside diameter unchanged

Decrease in lumen diameter

Question 35

What occurs with increased blood pressure in arterioles?

Answer 35

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

Question 36

With increased blood pressure, what changes are occurring?

Answer 36

Changes in amount of smooth muscle in the tunica media

More smooth muscle = stronger walls = increased ability to resist pressure

Question 37

Where are the changes occurring with increased blood pressure (hypertension)?

Answer 37

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

Question 38

What are angioblasts?

Answer 38

Endothelial cell precursors

Question 39

What are hemangioblasts?

Answer 39

Potent stem cells

Can become angioblasts, blood cell precursors, and mesenchymal cells