Lecture 11- Cardiovascular homeostasis Flashcards
What are the major functions of the cv system?
- Transport of nutrients to the tissue
- Transport waste products away from tissue
- Transport/distribution of hormones
Where does gas and nturient exchange occur?
In the systemic and pulmonary capillary beds
Where is blood velocity slowest?
Capillaries
Where is most blood found?
64% in the veins, reservoir
What is the equation of blood flow?
Q = P/R
What is poseuilles equation?
Q = P x pie x radiuis4 / 8nL
What if pressure?
The force exerted on the vessel wall
Describe where the largest pressure drop occurs
In the arteries/arterioles
What is resistance?
Measure of pressure difference generated for a given flow rate
What is conductance?
Measure of blood flow through a vessel for a given pressure difference
conductance = 1/R or pie r4/ 8nL
Where is majority of resistance found in the vasculature?
In the muscular arteries, arterioles (84%)
What else it is true about the vessels with the largest pressure drop?
They are under the most powerful vasomotor control
Is blood flow controlled locally?
Yes local blood flow is intrinsically controlled;
- Each tissue needs to control its own blood flow proportional to its needs
What are the tissue needs?
- Delivery of O2
- Delivery of nutrients, glucose, AA etc
- Removal of CO2, H and other metabolites
- Transport various hormones and other substrates to different tissues
How is intrinsic control of blood flow achieved?
Autoregulation
What is autoregulation?
The ability of tissue to maintain constant blood flow over a wide range of arterial pressures
What are the theories for autoregulation?
Vasodilator Theory
Oxygen demand theory
Myogenic Theory
What is the vasodilator theory?
1/3
- When there is an increase in tissue metabolism there is an increase in blood flow because local signals i.e CO2, H production cause the release of vasodilators, lowers arterial resistance and increased blood flow
What is the oxygen demand theory?
2/3
Lowered tissue oxygen concentration leads to increased blood flow. This is because;
Low O2 delivery or Increased metabolism results in low tissue O2.
This leads to relaxation of arterioles and precapillary sphincters and increase blood flow to the tissue
What is the myogenic mechanism?
3/3
Proposes that as arterial pressure falls the arterials have an intrinsic ability to dilate in response to decrease in wall tension
Tension = P x r
Which of the three theories are correct?
It is likely that they are all integrated factors and that there are many other factors in reality.
Produces an autoregulation curve.
What does autoregulation play a role in?
Active and reactive hyperemia.
What is active hyperemia?
Increased blood flow in tissue i.e muscles during running to supply demand. This tails off/ back to norm post exercise
What is reactive hyperemia?
Period of vascular occlusion is followed by a period of reactive hyperemia. i.e squatting a static exercise has no increase in blood flow and some occlusion, but there is lactic acid production, reactive hyperemia tries to restore this / the occlusion attempts to dilate to maintain blood flow.
What are external factors regulating blood flow?
1) Humoral control
2) Neural factors
What is humoral control of blood flow?
Adrenalin, adenosine, endothelin, NO
What is neural control of blood flow?
Sympathetic vasomotor activity, tonically active supports blood pressue
Describe some factors of local control of blood flow; *(summery)
- O2 demand
- Metabolic signals
- intrinsic myogenic
- Paracrine signals (ANG 2)
Describe some external factors of blood flow; (summery)
- Endocrine signals
- Neural control
- Systemic blood volume and flow re-distribution
- Arterial pressure and cardiac function
Whats the first step in CV system responding to exercise?
- Blood flow to active muscles can increase by up to 20x during exercise.
- increased systolic BP
- increased CO (HR and inotropy)
What is the second step in cv system responding to exercise?
Redistribution of blood flow
- Skeletal muscle vasodilation autoregulation (O2, CO2, NO, K, adenosine (atp), pH)
- Sympathetic vasoconstriction of other muscles
What is step 3 and 4 of CVS responding to exercise?
Redistribution of blood volume and increase in arterial blood pressure
- constriction of veins (mobilises venous pool into active circulation (inc VR = Inc CO)
- Constriction of almost all arterioles (inc TPR)
- Direct autonomic increase in HR and contractility (inc CO and inc BP)
