CVS 5: Microcirculation Flashcards
What are post-capillary venues also known as?
Pericytic venules
What is Blood flow rate?
Volume of blood passing through a vessel per unit time
What is the equation for flow rate?
Flow= delta P (pressrure gradient) / R (vascular resistance)
What is resistance?
Hindrance to the blood flow due to friction between moving fluid and stationary vascular walls
Give three factors which affect resistance
- Blood Viscosity
- Vessel Radius
- Vessel Length
Give the equation for resistance
R= 1/r^4
How d you determine the pressure gradient?
Difference in pressure between arterial pressure and pressure in the capillary bed
What is the normal blood pressure also called?
Mean Arterial Pressure (MAP)= blood pressure in many artery around the body
What is the significance of the capillary beds?
Blood flows more slowly= Blood pressure decreases
More exchange of nutrients
more diluted= lower blood pressure
How can you find the flow rate in an organ?
MAP/ Resistance of the organ
How is vasodilation and vasoconstriction achieved?
- Arteriolar smooth muscle is in a state of partial constriction= VASCULAR TONE
What are the two functions of changing the radii of arterioles?
- Match blood low to metabolic needs of specific tissue (local intrinsic control)
- Help regulate arterial blood pressure (extrinsic control)
Give an example of arterioles responding to changes to the chemical environment
ACTIVE HYPERAEMIA
- muscle becomes more active
- metabolism increases and O2 consumption increases
- change is detected in the tissues–> signal sent to arterioles–> vasodilation
Define Active hyperaemia
Increase in organ blood flow that is associated with increased metabolic activity of that tissue or organ
Give an example of arterioles responding to the physical environment
Placing an ICEPACK on muscle
- tissue senses fall in temp
- arteriolar smooth muscle contracts so less blood reaches surface and less heat lost through radiation
What is the equation for applying F= dP/R to the whole circulation?
CO= MAP/ TPR
- MAP because delta P= change in arterial and venous pressure and venous pressure is basically 0
- TPR= sum of resistance in all arterioles in the body
MAP= CO x TPR
How is arterial blood pressure regulated?
Changing the ready of the arterial by neural and hormonal pathways
Where in the brain is arterial blood pressure neurally regulated?
- Regulated by Cardiovascular control centre in the medulla
Which receptors in the medulla sense arterial blood pressure and which cells cause dilation and constriction?
ADRENORECEPTORS
Alpha- constriction
Beta- dilation
What are the two methods of hormonally regulating the arterial blood pressure and give examples of hormones for each of the mechanisms
- Vasoconstrictors= increase in TPR
a. Vasopressin
b. Angiotensin II - Increasing Sympathetic activity= increase in CO
a. Adrenaline/ Noradrenaline
What is the function of capillaries?
Deliver metabolic substrate to the cells of the organism
What is the thickness of capillary walls
1 micrometer
What is Fick’s Law?
The factors which enhance diffusion:
- minimise diffusion distance
- maximise surface area
- maximise diffusion time
What is the significance of capillary density?
The more metabolically demanding a tissue is, the greater the tissue density
