Microcirculation 5 Flashcards
What is blood flow rate?
Volume of blood passing through a vessel per unit time
What is the equation for flow rate?
Flow = Delta pressure/ Vascular resistance F = DP/R
What is resistance?
Hindrance to the blood flow due to friction between moving fluid and stationary vessel walls
What factors affect resistance?
- blood viscosity
- vessel length
- vessel radius
What are the major resistance vessels?
Arterioles
What is the major determinant of blood flow?
Resistance of the arterioles in the organs
`What is vascular tone?
State of partial constriction when at rest displayed by arteriolar smooth muscle
What two functions are the radii of the arteries adjusted for?
1) Match blood flow to the metabolic needs of specific tissues
2) Help regulate arterial blood pressure (for extrinsic reasons)
What is active hyperemia?
An increase n blood flow to an organ that is due to an increased metabolic activity of said organ or tissue.
Chemical environment stimuli
Example of arterioles responding to physical environment stimuli?
Vasoconstriction when ice applied to swollen ankle to reduce swelling.
What is myogenic vasoconstriction
Blood vessels constrict to prevent increase of blood flow into tissue. this is arterioles responding to stretch, often when increased bp/HR
What regulates constriction and dilation of the vessels?
Adrenoreceptors
Alpha = constriction of arterioles Beta = in heart, increase rate
What hormones cause vasoconstriction and subsequent increase in arterial blood pressure?
Angiotensin 2 and Vasopressin and noradrenaline/adrenaline as well as increased sympathetic activity
What is the BP entering the arterioles?
93mmHg
What is the BP exiting the arterioles?
37mmHg
How are capillaries designed for transport of substrate?
1) Thin wall ( 1 mm thick)
2) thin vessels (7mm diameter)
3) Extensive branching
What do capillaries aim to do?
- minimise diffisuion distance
- maximise diffusion time
- maximise surface area
What does capillary density show?
How metabolically active a tissue is (more density=more metabolically active
What are the 3 types of capillaries?
- continuous
- discontinuous
- fenestrated
What is Bulk flow?
a volume of protein-free plasma
filters out of the capillary, mixes with the
surrounding interstitial fluid (IF) and is
reabsorbed
What are the two main pressures that affect fluid movement into and out of capillaries?
- Hydrostatic Pressure
- Oncotic Pressure
Where does lymph drain to?
- Thoracic Duct
- Right lymphatic duct
- Right subclavian vein
- Left subclavian vein
How much fluid is removed by the lymphatic system daily?
3L
How is oedema caused?
Rate of production of fluid > rate of removal of fluid
