Control of Venous Pressure Flashcards
What is compliance equal to?
Change in volume/change in pressure
What does pressure depend on?
Compliance and volume
What neurotransmitter triggers venous contraction?
Noradrenaline
What does venous contraction cause?
Decrease compliance
Increase blood pressure
Where is venous pressure high when in the supine position?
Head and feet
What 3 things must be considered when moving to upright position?
Gravity
pressure reduced in vessels above heart level
pressure increased in vessels below heart level
What causes venous pooling below the heart?
Additional blood from thoracic region
What happens when unsupported veins collapse?
Blood flow is inhibited - redirected
Stroke volume falls
What causes varicose veins?
Incompetent valves - blood accumulates
What does an increase in capillary filtration in lower limbs cause?
Decrease in plasma volume
Reduced arterial pressure
How does the body compensate for upright posture?
Increased capillary filtration
Neuro-endocrine responses
Renal excretion of salt and water
Which 2 neuroendocrine responses are involved?
Activation of:
RAAS
Vasopressin secretion
Cause vasoconstriction
How is renal excretion of salt and water reduced?
Increase sympathetic stimulation of RAAS
Reflex vasopressin secretion
What are the 5 venous return drivers?
Skeletal muscle pump
Respiratory pump
Cardiac cycle
Sympathetically-mediated vasoconstriction
Total blood volume
What happens to the skeletal muscle pump during exercise?
Venous pressure is reduced
Blood flows only toward the heart
What happens to the skeletal muscle pump at rest?
Blood reaccumulates in veins
What happens during inspiration?
Inferior vena cava blood flow increases
How does inferior vena cava blood flow increase?
Decreased intrathoracic pressure (veins expand)
Increased abdominal pressure - increased venous pressure gradient (blood return from abdomen to thoracic)
What happens to the stroke volume in the right ventricle during inspiration/expiration?
Inspiration - SV rises
Expiration - SV falls
What happens to the stroke volume in the left ventricle during inspiration/expiration?
Inspiration - SV falls
Expiration - SV rises
How does cardiac contraction stimulate venous return?
Vis-a-tergo (push from behind)
Vis-a-fronte (suction from in front)
How does venoconstriction stimulate venous return?
Increased venous pressure
Reduced venous compliance
