Week 4 Flashcards
Vascular structure of viens
- Lowest pressures
- thin muscled walls
- highly distensible
Vascular structure of arteries
- Highest pressures
- Strong muscular walls
- low flow resistance
Vascular structure of microcirculation
- Arterioles are main site of vascular resistance
- Capillaries and venules are sites of exchange
calculating vascular compliance
change in volume over change in pressure
Vascular compliance in the veins
- Highly compliant
- Small changes in pressure cause large changes in volume
Vascular compliance in arteries
- less compliant than veins
- still respond to increase in pressure with slight increases in volume
Aortic Complience
- High systolic pressure expands the volume of the aorta
- stretching stores potential energy
- aortic walls recoil during diastole, squeezing the blood and helping maintain aortic pressure and blood flow
Aortic Pulse Pressure
- Systolic pressure usually similar to that in left ventricle
- Pulse pressure= SP - DP
- Pulse pressure magnitude determined by stroke volume and arterial compliance (PP proportional to SV/Compliance)
Why is a dicrotic notch observed in pulse pressure
Closure of the aortic valve prevents any possible back flow
Aortic Valve Stenosis definition and effect
- A condition in which the diameter of the aortic valve opening is reduced, which reduces flow into aorta
- Increased resistance = decreased SV = decreased pressure
- Smaller systolic pulse pressure
Aortic Regurgitation definition and effect on pulse pressure
- the aortic valve does not close completely and blood flows back into the ventricle in late systole and diastole
- decrease pressure in diastole due to faster decrease in blood volume
Transmission of pressure pulse through the arteries
- Pressure (and flow) oscillations are transmitted along the arteries
- The pressure decreases progressively in smaller arteries due to VESSEL COMPLIANCE and VASCULAR RESISTANCE
Arterial wall tension
- Def: Force needed to resist the outward push of hydrostatic pressure
- Calculation: T(tension) = Transmural pressure (r/h(wall thickness))
- Vessels with larger radius and/or higher pressures have stronger walls with more smooth muscle and are reinforced with fibrous bands of collagen
- high transmural pressure and radius leads to significant wall tension
Transmural pressure
Internal (intravascular) pressure - External (tissue) pressure
Effect of chronic increase in blood pressure on wall thickness
Causes remodeling increasing vessel wall thickness and reducing radius
Purpose of high compliance in venous system
- Helps keep the pressure in the venous system low
- can accommodate large changes in blood volume with only small changes in pressure
- Acts as a blood reservoir ( volume can be controlled via changes in vascular tone, shifting blood to/from other parts of the circulation)
Venous blood reservoir
Blood in reservoir can be redistributed to perfuse more/fewer capillary beds as necessary
Central Venous pressure
- Diastolic pressure in the right atrium
- normally very low (0 mmHg) but can vary with changes in EDV
- increases in pressure stimulate heart pumping via intrinsic mechanisms (Frank-starling)
- increases in atrial pressure can reduce atrial filling leading to back up because of a decrease in pressure gradient
Gravity and the venous system
- Hydrostatic pressure is affected by gravity and increases with fluid height
- Gravity tends to increase venous pressure in the lower extremities)
Venous Valves
- assure blood only flows back toward the heart
- helps control pressure increases due to gravity
Venous muscle pump
Muscle contraction squeezes the veins and thus pushes blood out of that section of vein back toward the heart
Functions of microcirulation
Transport nutrients to the tissues and remove cell waste
Muscle of Arterioles
Arterioles are highly macular and control blood flow based on signals from local tissuee
Capillaries
think-walled vessels where most blood-tissue exchange happens
- most cells are generally within 50um of a capillary
Branching in vascular networks
- Arteries branch 6-8 times to arterioles
- arterioles branch 2-5 times to metarterioles (each of which supplies a capillary network)
- branching increases total cross-sectional area, slowing the blood and maximizing time for exchange
Blood Capillary Structure
- Single layer of endothelial cells surrounded by basement membrane
- intercellular clefts between endothelial cells allow water, ions and small solutes to cross
- Caveolae are believed to play a role in endocytosis and transcytosis of large macromolecules across the interior of the endothelial cell
Flow of gases through capillaries
Driven by partial pressure gradient
- can permeate surface
- O2 in and CO2 out
Flow of lipid soluble substances through capillaries
driven by concentration gradient
- can permeate capillary surface
- moves substance inward
Flow of small water-soluble solutes through capillaries
driven by concentration gradient
- must pass through intracellular cleft
Flow of water-soluble proteins through capillaries
Must use membrane transport proteins or transcytosis to move through surface
Water movement across blood capillaries
- Water flow is determined by the combination of hydrostatic pressure and osmotic pressure
Hydrostatic pressure gradient in the capillaries
Capillary pressure (Pc) > Interstitial pressure (Pif)
- Flow out of vessel
Osmotic Pressure gradient in the capillaries
Plasma Colloid osmotic pressure (PIp) > Interstitial fluid colloid osmotic pressure (PIif)
Colloid Osmotic pressure
The osmotic pressure that arises from the effects of the water soluble plasma proteins that cannot easily cross the endothelium
Net filtration pressure (NFP)
NFP= (Pc - Pif) - (Pip - Piif)
- Flow from blood to interstitial fluid called filtration (positive NFP)
- Flow from interstitial fluid to blood is called absorption (negative NFP)
- Filtration is slightly higher than absorption in most capillary beds
Capillary characteristics in the brain
Blood brain barrier
- Intracellular clefts are closed by tight junctions that only allow small uncharged molecules to pass
Capillary characteristics in the glomerular capillaries
Kidneys have channels through cells so small molecules and ions can pass much easier (high rates of filtration)
Capillary Characteristics in the liver
intercellular clefts are wider to allow larger macromolecules to pass
- due to liver’s role in nutrient processing
Lymph Vessels
- Highly permeable
- junctions between adjacent endothelial cells can flap open and closed allowing fluid to flow in
Lymph flow
- interstitial fluid pressure drives fluid into lymph capillaries
- increases in Pif will drive an increase ink lymph flow
Lymphatic Pump
- Valves created by the junction between endothelial cells exist all along lymphatic vessels to direct lymph fluid towards the heart
- lymphatic vessels contract when filled with fluid, pumping lymph fluid along the vessel
- after contraction, anchoring filaments cause vessels to recoil, reducing inside pressure and drawing fluid in
- skeletal muscle contraction pumps lymph fluid
What are some potential causes of edema
- Hypertension
- leaking of endothelium
- not moving for extended periods of time (on flights)
- Infections and congenital issues (elephantiasis)
