microcirculation Flashcards
What equation connects blood flow, pressure difference and resistance?
Flow = pressure difference/resistance
What factors affect vascular resistance?
Vessel radius, vessel length, blood viscosity
What is the relationship between resistance and radius?
Poiseuille’s law: resistance is inversely proportional to r^4
What are the major resistance vessels?
Arterioles
Why can change in blood pressure be substituted by MAP?
The arterial blood pressure is usually MAP and the blood pressure in the veins is usually around 0 mm Hg so the change in blood pressure through a capillary bed is usually around MAP.
What is the normal state of vascular smooth muscle?
They are normally in a state of partial vascular constriction - vascular tone
What are the two controls of vessel radius?
Intrinsic controls with the aim of changing perfusion to match metabolic needs
Extrinsic controls with the aim of regulating arterial blood pressure
Describe how vessel radius responds to the chemical environment
When tissues are highly metabolically active they will produce a lot of ATP and use up a lot of oxygen. The increase uptake of oxygen is detected by the tissues, which sends a message to the arteriolar smooth muscle to dilate. This is active hyperemia.
Describe how vessel radius responds to the physical environment.
When there is a decrease in blood temperature, the vascular smooth muscle will constrict so that less blood reaches the surface and so less heat is radiated away.
How can the flow rate, pressure difference and resistance equation be applied to the entire circulation?
Flow rate is cardiac output, pressure difference is mean arterial blood pressure and resistance is total peripheral resistance. CO = MABP/TPR
What are the two pathways controlling arterial blood pressure?
Neural and Hormonal Pathways
Where is the centre that regulates arterial blood pressure found?
In the medulla - cardiovascular control centre
Describe the neuronal control of arterial blood pressure.
The brain controls arterial blood pressure via ADRENORECEPTORS:
Alpha - CONSTRICTION
Beta - Dilation
The sympathetic nervous system can also increase production of catecholamines (noradrenaline and adrenaline) from the adrenal medulla, which binds to increase heart rate and blood pressure
Describe the hormonal control of arterial blood pressure.
Main hormones involved in blood pressure:
Angiotensin II
Vasopressin
These are both potent vasoconstrictors
What is capillary exchange?
Delivery of metabolic substrates to the cells of an organism
