Control Of Blood Flow Flashcards
What does TPR stand for?
Total peripheral resistance
What does TPR control?
Blood flow and blood pressure- increase in resistance means need to increase pressure to keep the same flow
What is TPR controlled by?
- Darcy’s and poiseuilles laws
- myogenic response
- blood viscosity
What is conductance in relation to resistance?
Conductance is the opposite of resistance
What is hypertension in the arterioles?
Overconstriction of arterioles
What happens when the arterioles dilate?
Decrease in TPR. Means decreased blood pressure upstream but greater flow
What happens when the arterioles constrict?
Increase TPR. Means there’s an increased blood pressure upstream, but less flow
What are the features of blood flow in the common iliac and superior mesenteric arteries when sedentary?
Superior mesenteric is dilated
Increased flow to intestines
Common iliac constricted
Decreased flow to legs
What are the features of common iliac and superior mesenteric arterioles when exercising?
Superior mesenteric is constricted
Decreased flow to intestines
Common iliac dilated
Increased flow to less
What does poiseuilles law describe?
The parameters that govern TPR
What is resistance related to?
Blood viscosity
Radius of vessel
Vessel length
What does increased distension of vessel do?
Makes it constrict
What does the Baylis myogenic response do?
Maintains blood flow at the same level during changing arterial pressures
What does stretching of the vessel cause?
Ion channels to open, which then depolarise, leading to smooth muscle contraction
What is viscosity?
A measure of the internal friction opposing the separation of the lamina
What are four factors in viscosity?
Haematocrit, tube diameter, red cell deformability, velocity of blood
What do veins do when there is very little pressure?
Fold up
What is Bernoulli’s theory?
Mechanical energy of flow is determined by pressure, kinetic and potential energies
What does stimulation of sympathetic nerves cause in the CVS?
Vasoconstriction, which shifts blood centrally. This increases venous return as CVP and EDP is increased. CVP increases preload so increases stroke volume
What effect does cardiac output have on venous return?
The circulation is a closed system so the heart pushes the blood further through the vascular system via the arterial side of the capillary system into the veins in the direction of the right side of the heart
What effect does breathing have on venous return?
The pressure in the chest is negative on inhalation at the same time intra-abdominal pressure rises as the diaphragm moves downwards. This causes the venous valves in the pelvic veins to close, and the blood moves into the thorax. On exhalation, the intra-abdominal pressure decreases and the pelvic veins and inferior vena cava refills
What effect does muscle pump have on venous return?
The deep venous system is embedded in muscles. Due to this, every muscle contraction squeezes the veins to push the column of blood in them in the direction of the heart. When the muscle relaxes, the venous valves prevent the retrograde flow of blood towards the capillaries
What effect does venous tone have on venous return?
The blood in the veins exerts pressure on the veins wall, which generates tension and maintains pressure. Furthermore, sympathetic vasoconstriction can mobilise more blood back to the heart
