CVS Flashcards
(36 cards)
Why does increase in sympathetic activity decrease filtration?
Increases pre cap & post cap resistance ratio–> decreases mean capillary pressure–> decreases filtration
Why does exercise increase filtration?
- Increases sympathetic tone
- Increases local metabolites-
a. Relaxes pre cap sphincters
b. Decreases basal myogenic tone
c. Increases osmolality of interesting fluid
Mechanism of increased filtration in LVF vs. hypoproteinemia
LVF- increased pulmonary hydrostatic pressure
Hypoproteinemia- decreased osmotic pressure
What is the mechanism of filtration and absorption at the capillaries?
Filtration: Capillary pressure at arteriolar end(37)> osmotic pressure
Absorption: osmotic pressure>capillary pressure(15)
Osmotic pressure = mean capillary pressure= 25mmHg
How does lipid solubility affect diffusion across capillaries?
Lipid soluble substances can diffuse through whole capillary-greater surface area
Lipid insoluble substances-intercellular pores
How does molecular weight affect diffusion & what is the range of weights
Increase in MW decreases diffusion- 10000–>60,000
Why is micropinocytosis an impt component of teams capillary exchange?
Allows passages of macromolecules like alpha globulin
What is the mechanism of edema?
- Increase in capillary pressure,
- decrease in osmotic pressure, 3.deposition of osmotically active substances in interstium,
- Lymphatic obstruction
How does velocity affect diffusion across a capillary?
Increased v- decreases time for exchange
Decreased- decreases flow for exchange
Why is velocity low in capillaries and high in aorta?
Velocity=flow/cross sec area
Cross sec area increases from aorta to capillaries, therefore velocity decreases
Why does increased cross sectional area of capillaries optimise exchange?
Increased CSA-decreased velocity-more effective exchange
Why can turbulent flow occur in aorta?
CSA of aorta less than capillaries-increased velocity
Why is a cardiac flow murmur heard in anaemia at the aorta?
Murmurs are caused by turbulent flow. Turbulent flow occurs Reynolds number>2000
Reynolds number= diametervelocitydensity/viscosity
Aorta-high velocity & anaemia causes decreased viscosity
Why are murmurs heard in severe stenosis?
Turbulent flow in vessels due to high velocity of blood
Why is laminar flow in systemic circulation more advantageous than turbulent flow?
More resistance in turbulent flow
Turbulent flow more likely to develop thrombi
How does atherosclerosis affect type of flow of blood?
Reduces Reynolds number- laminar flow
Why are the organs supplied with parallel branches off of the aorta?
Resistors in parallel decrease total resistance, therefore total systemic resistance is less
How do tissues ensure nutrient delivery via blood?
Regulate tone of arterioles-intrinsic regulation
Why does arteriolar vasodilation cause mean arterial pressure (MAP) to plummet?
Arterioles- primary resistors
Vasodilation- decreased resistance-decreases upstream pressure (MAP) and increases downstream pressure
Why do factors which cause vasoconstriction result in an increased MAP?
Vasoconstrictors-decrease radius-increase resistance of arterioles-increase upstream pressure (MAP) and decrease downstream pressure
What factors contribute to vasoconstriction?
NE from sympathetic post ganglionic neurons
Epinephrine from adrenal medulla
Angiotensin 2 via AT1 receptor
ADH via V1 receptor
What factors cause vasodilation of arterioles?
Decreased sympathetic activity
Epi via B2 receptors
NO from endothelium
Metabolites-carbon dioxide, protons, potassium, adenosine
Why does NE from post ganglionic sympathetic neurons cause vasoconstriction of arterioles?
NE-alpha-1 receptors-Gq-increased cytosolic calcium in sm cells-tonic effect on skeletal muscles & cutaneous muscles at rest, splanchnic & renal at stress
As an aneurysm enlarges why is it more likely to burst?
Pressure remains the same then by Laplace law wall tension=P*radius. As radius increases, wall tension increases to maintain pressure-aorta bursts-eg. Subarachnoid haemorrhage, aortic aneurysm
