microcirculation

Question 1

• Define blood flow rate (Q)

- what is the equation for blood flow rate?

Answer 1

Volume of blood passing through a vessel per unit time.

Equation: Q = ΔP (pressure gradient) divided by R (resistance)

Question 2

• What law is linked with the fluid circuit and state the equation of this law?

Answer 2

Darcy’s Law

pressure gradient = Q (flow rate) x R

Question 3

• What happens to blood flow rate if the pressure gradient is increased?
• Define resistance (R) in terms of blood flow.

Answer 3

Blood flow rate (Q) is also increased

Hindrance to blood flow due to friction between moving fluid and stationary walls.

Question 4

• What factors affect resistance (also give the equation)?

Answer 4

Blood viscosity (η)

Vessel radius (r) 

Vessel length (L)

Resistance= ( 8 x L x viscosity) / (pi x radius ^4)

Question 5

when given an arterial pressure and a venous one, how do you calculate the pressure gradient?

Answer 5

pressure arteriole- pressure venule

Question 6

What is vascular tone?

Why is vascular tone important?

Answer 6

when the blood vessel is in a state of partial constriction

So it can constrict/ dilate as needed

Question 7

• What 2 functions are radii of arterioles adjusted independently to accomplish and what regulates each function?

Answer 7

1. Match blood flow to metabolic needs of specific tissues
   Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
   2. Regulation of systemic Arterial Blood Pressure
      Regulated by extrinsic controls (nervous influence and hormonal control).

Question 8

• How is matching blood flow to metabolic needs chemically and physically driven?

Answer 8

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

Question 9

• What arterial responses are most relevant to skeletal muscle and small intestine arterioles respectively?

Answer 9

Skeletal muscle arterioles - Active hyperaemia

Small intestine arterioles - Myogenic vasoconstriction

Question 10

• What is total peripheral resistance?

Answer 10

Sum of resistance of all arterioles present in systemic circulation.

Question 11

• 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)?

Answer 11

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

Question 12

• What is the purpose of capillary exchange?

- Why is capillary density important?

Answer 12

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.

Question 13

• Give examples of tissues that have denser capillary networks

Answer 13

Skeletal muscle

Myocardium 

Brain  

Lung - most dense to aid gas exchange

Question 14

• List the 3 types of capillary structure and briefly describe each one.

Answer 14

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

Question 15

• What type of capillary structure does the blood brain barrier have?
• What type of structure do the sinusoides in the liver have?

Answer 15

Continuous - to protect central nervous system

Discontinuous

Question 16

• Explain what is meant by ‘Bulk Flow’
• what forces are involved
• what results from the parasitic blockage of lymph nodes

Answer 16

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

Question 17

• What is oncotic pressure?
• Why is oncotic pressure uniform?
• What process occurs when the pressure inside the capillary is greater than the interstitial fluid?

Answer 17

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)

Question 18

• 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?

Answer 18

3L

Empties into the junction of the left subclavian and internal jugular veins

Oedema