Microcirculation Flashcards
Define blood flow rate (Q)
Volume of blood passing through a vessel per unit time.
Equation: Q = ΔP (pressure gradient) divided by R (resistance)
What law is linked with the fluid circuit and state the equation of this law?
Darcy’s Law
Delta P = Q x R
What happens to blood flow rate if the pressure gradient is increased?
Blood flow rate (Q) is also increased
Define resistance (R) in terms of blood flow.
Hindrance to blood flow due to friction between moving fluid and stationary walls.
What factors affect resistance (also give the equation)?
Blood viscosity (η) Vessel radius (r) Vessel length (L)
R = 8Ln/pi.r^4
How does resistance affect blood flow?
Increased vascular resistance would decrease blood flow (e.g. Vasoconstriction → Increased resistance and decreased blood flow)
What effect does vasoconstriction and vasodilation have on radius (r), resistance (R) and blood flow (F) of blood vessels? Why is this important?
Vasoconstriction: Lower r, higher R and lower F
Vasodilation: Higher r, lower R and higher F
Arteriolar smooth muscle displays a state of partial constriction → described as vascular tone. Partial constriction enables alterations to blood flow through constriction and dilation (room to accommodate movements).
What 2 functions are radii of arterioles adjusted independently to accomplish and what regulates each function?
- Match blood flow to metabolic needs of specific tissues - Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation.
- Regulation of systemic ABP: regulated by extrinsic controls (nervous influence and hormonal control).
How is the first function in the answer above chemically and physically driven?
Chemically - Increase metabolites and oxygen usage leading to vasodilation of the arterioles → Active Hyperaemia.
Physically - Decrease blood temperature and increased stretch (distension) due to ^ BP leading to vasoconstriction of arterioles → Known as myogenic auto-regulation.
What arterial responses are most relevant to skeletal muscle and small intestine arterioles respectively?
Skeletal muscle arterioles - Active hyperaemia
Small intestine arterioles - Myogenic vasoconstriction
What is total peripheral resistance?
Sum of resistance of all arterioles present in systemic circulation.
Explain how the brain is involved in helping regulate arterial blood pressure (ABP).
Regulated by cardiovascular control centre in the medulla oblongata. Vasoconstriction proceeds to increase BP, reducing blood flow to organs.
Which 3 hormones can lead to vasoconstriction of arterioles in order to help regulate ABP?
Vasopressin (ADH)
Angiotensin II
Adrenaline/Noradrenaline
What is the purpose of capillary exchange?
Delivery of metabolic substrates to the cells of the organism (this is the ultimate function of the CVS).
Why is capillary density important?
Fick’s Law - Minimise diffusion distance, maximise SA and maximised diffusion time.
Increase in metabolic activity → Increase capillary density to supply available respiring cells.
Give examples of tissues that have denser capillary networks.
Skeletal muscle
Myocardium
Brain
Lung
List the 3 types of capillary structure and briefly describe each one.
Continuous - water-filled gap junctions between endothelial cells, enabling passage of electrocytes. The endothelial cells, enabling passage of electrolytes.
Fenestrated - pores within capillaries, enables relatively larger molecules to pass through capillaries into the tissue space (Larger gap junctions).
Discontinuous - relatively large holes in capillary
What type of capillary structure does the blood brain barrier have?
Continuous
Explain ‘Bulk Flow’
A volume of protein-free plasma filters out of the capillary, mixing with the interstitial fluid and is reabsorbed.
Involves oncotic ‘pulling’ force and hydrostatic ‘pushing’ force.
What is oncotic pressure?
Osmotic force due to protein in capillary drawing water back in. Oncotic pressure is constant/uniform as protein plasma concentrations don’t change.
What process occurs the pressure inside the capillary is greater than the interstitial fluid?
Ultrafiltration - fluid leaves capillary
other way around → Reabsorption
How many litres of fluid are drained by the lymphatic system daily?
3 L
What occurs if the rate of production of fluid (release of fluid into interstitial space) exceeds the rate of drainage?
Oedema
(Elephantiasis - type of oedema caused by parasitic blockage of lymph nodes leading to enlargement of affected lower limb)
Generate an equation for flow across the whole circulation and rearrange to generate a BP equation.
Cardiac output = MAP (blood pressure)/TPR
MAP = Cardiac output x TPR
