microcirculation Flashcards
- Define blood flow rate (Q)
- what is the equation for blood flow rate?
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
pressure gradient = Q (flow rate) x R
- What happens to blood flow rate if the pressure gradient is increased?
- Define resistance (R) in terms of blood flow.
Blood flow rate (Q) is also increased
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)
Resistance= ( 8 x L x viscosity) / (pi x radius ^4)
when given an arterial pressure and a venous one, how do you calculate the pressure gradient?
pressure arteriole- pressure venule
What is vascular tone?
Why is vascular tone important?
when the blood vessel is in a state of partial constriction
So it can constrict/ dilate as needed
- 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 Arterial Blood Pressure
Regulated by extrinsic controls (nervous influence and hormonal control).
- Regulation of systemic Arterial Blood Pressure
- How is matching blood flow to metabolic needs chemically and physically driven?
Active hyperaemia: chemically, increase in metabolites and increased oxygen usage leading to vasodilation of the arterioles
Myogenic auto-regulation: Physically, de
creased blood temperature and increased stretch (distension) due to ^ BP leading to vasoconstriction of arterioles
- 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.
- What is the neural method of regulating arterial blood pressure?
- Which 3 hormones can lead to vasoconstriction of arterioles in order to help regulate ABP (hormonal method of regulating ABP)?
Regulated by cardiovascular control centre in the medulla oblongata. Vasoconstriction proceeds to increase BP
Reducing blood flow to organs.
Vasopressin (ADH)
Angiotensin II
Adrenaline/Noradrenaline
- What is the purpose of capillary exchange?
- Why is capillary density important?
Delivery of metabolic substrates to the cells of the organism (this is the ultimate function of the CVS).
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 - most dense to aid gas exchange
- List the 3 types of capillary structure and briefly describe each one.
Continuous - water-filled gap junctions between endothelial cells, enabling passage of electrocytes.
Fenestrated - pores within capillaries, enables relatively larger molecules to pass through capillaries into the tissue space (Larger gap junctions) 80nm Discontinuous - relatively large holes in capillary
- What type of capillary structure does the blood brain barrier have?
- What type of structure do the sinusoides in the liver have?
Continuous - to protect central nervous system
Discontinuous
- Explain what is meant by ‘Bulk Flow’
- what forces are involved
- what results from the parasitic blockage of lymph nodes
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.
Elephantitis
- What is oncotic pressure?
- Why is oncotic pressure uniform?
- What process occurs when the pressure inside the capillary is greater than the interstitial fluid?
Osmotic force due to protein in capillary drawing water back in.
Oncotic pressure is constant/uniform as protein plasma concentrations don’t change.
Ultrafiltration - fluid leaves capillary (other way around → Reabsorption)
- How many litres of fluid are drained by the lymphatic system daily?
- Where does the thoracic duct of the lymphatic system drain into?
- What occurs if the rate of production of fluid (release of fluid into interstitial space) exceeds the rate of drainage?
3L
Empties into the junction of the left subclavian and internal jugular veins Oedema
