Microcirculation Flashcards
What is blood flow rate?
Volume of blood passing through a vessel per unit time. The overall aim for the CVS is the adequate blood flow through the capillaries to deliver respiratory substrate and remove excretory products
What is the equation for blood flow rate?
πΈ=βπ/πΉ
Equation relates blood flow with pressure gradient /vascular resistance
What is vascular resistance?
Hindrance to blood flow due to friction between moving fluid and stationary vascular walls
What is a pressure gradient?
Pressure between two defined regions (A-B), increasing pressure gradient increases the flow rate
What are the three main factors that influences vascular resistance?
Blood viscosity
Vessel radius
Vessel length
What is the relationship between resistance and vascular radius?
Resistance is directly proportional to π/π^π
Which factor most influences vascular resistance?
Vessel radius
Blood viscosity and vessel length is fairly CONSTANT ο resistance changes are thus attributed to vessel radius alterations.
What two main factors is blood flow determined by?
Pressure difference in the vascular bed
Vascular resistance
An increase in blood pressure ___ pressure difference?
Increases
How does arteriolar vasoconstriction influence vascular resistance?
Increases resistance
How does increased blood pressure influence blood flow?
Increases blood flow
How does arteriolar vasoconstriction influence blood flow?
Decreases blood flow
What is the approximate blood pressure referred to as?
Mean arterial blood pressure
Why can systolic and diastolic pressure be used to calculate mean arterial pressure?
There is minimal deviations through the arteriole supply
How does the vascular system facilitate effective nutrient exchange?
As blood traverses through the capillary bed, low velocity is required system enables blood to decelerate through vasoconstriction
What is the average value for venous blood pressure?
Negligible 0mmHg
What is the only factor that contributes to blood flow?
Resistance since the blood pressure gradient is equal to arteriole pressure
Why do arteriolar Smooth muscles display a state of partial contraction?
Described as vascular tone. Partial contraction enables alterations to blood flow through constriction and dilation (room to accommodate movements)
What are the two main functions of independent radius adjustment of arterioles?
Match blood flow to the metabolic needs of specific tissues
Increase in metabolic activity within the muscle
How is blood flow matched to local tissues?
Match blood flow to the metabolic demands of specific tissues (regulated by intrinsic control - local endothelial-derived mediators), tissue determines blood requirement
What is the active hyperaemia?
Increase in organ blood flow, associated with increased metabolic activity of tissue
How does radius influence hyperaemia?
Increase in radius causes a decrease in vascular resistance, this increases blood flow resulting in active hyperaemia.
How is systemic arterial blood pressure regulated?
Regulated by extrinsic controls (nervous influence and hormonal control)
What is myogenic autoregulation ?
Reduction in blood temperature: Vasoconstriction arises (Relevant for peripheral vessels β the integumentary system). Decrease in radius, increases vascular resistance to subsequently decrease blood flow to superficial surface (Less heat radiation).
Baroreceptors detect stretch and blood pressure.
How does a reduction in blood temperature influence vascular radius?
Vasoconstriction arises (relevant for peripheral vessels - the integumentary system) Decreased radius increases vascular resistance to subsequently decrease blood flow to superficial surface (less heat radiation)
Which receptors detect stretch and blood pressure?
Baroreceptors
Which equation relates cardiac output with mean arterial pressure?
Cardiac output = Blood pressure (MAP) / Total peripheral resistance
What is MAP equation in terms of cardiac output?
MAP = Q X TPR
What is total peripheral resistance?
Sum of resistance of all arterioles present in systemic circulation
What is mean arteriole pressure?
Average pressure within the venue system is negligible thus the pressure difference is equated to MAP
How is arteriole blood pressure affected and altered?
Alterations to arteriole radii, influenced by neural and hormonal pathways
Which centre controls the neural regulation of arterial blood pressure?
Regulated by the cardiac control centre within the medulla oblongata
Which types of receptors facilitate constriction and dilation of arterioles?
Adrenoreceptors
Which adrenoreceptor leads to constriction?
Alpha receptors
Which adrenoreceptor leads to dilation?
Beta receptos
Where is the cardiac control centre located?
Medulla oblongata
What is the effect of vasoconstriction of blood flow?
Vasoconstriction decreased the radius, thus increasing resistance and decreases cardiac flow. Reduction preserves blood pressure to reduce cardiac output.
Blood is preserved for which organ?
Brain
What is the purpose of capillary exchange?
The delivery of metabolic substrates to respiring cells.
What is the primary advantage for a thin endothelial cell?
Reduced diffusion distance assisting with effective diffusion of substances
Describe the distribution of capillaries in terms of respiring cells?
Optimum accessibility to the capillaries, ensures that cells are proximal to vasculature
What is the distribution of capillary density?
Variable within tissues beds
What is Fickβs law?
Minimise diffusion distance, maximise surface area and maximise diffusion time
How does capillary density relate to metabolic activity?
Increases capillary density to supply available respiring cells
Which structures/regions have a high capillary density?
Skeletal muscle
Myocardium
Lungs
Why does a brain require a high capillary density?
The brain is vulnerable to hypoxia
Which tissue is poorly perfused?
Adipose tissue
Which capillary sphincter is closed to regulate and divert blood flow to different tissues?
Precapillary sphincter
What are the three types of capillaries?
Continuous
Fenestrated
Discontinuous
What type of gap junctions are present within continuous capillaries?
Water filled gap junctions
What can diffuse through continuous capillaries?
Electrolytes
What are continuous capillaries?
Majority of capillaries have continuous structure. Water-filled gap junctions between endothelial cells, enabling passage of electrolytes. The endothelial wall is one cell thick; transporter proteins embedded within the capillary to export substrate to tissue.
Carrier proteins facilitate diffusion of metabolic substrates.
What are fenestrated capillaries?
Fenestrations are pores within the capillaries, enables relatively larger molecules to pass through the capillaries into the tissue space (Larger gap junctions).
What are discontinuous capillaries?
Relatively large holes in the capillary, important in bone marrow, leucocytes required to enter into systemic circulation post-haemopoiesis for maturation and activation.
Which gap junctions are present within the brain?
Tight gap junctions
There are no water filled gap junctions
What effect does hydrostatic pressure have on plasma?
Concept that specific amount of protein free plasma filters out of the capillary and mixes with surrounding interstitial fluid, hydrostatic force, forces plasma across the capillaries through the gap junctions or fenestrations; oncotic pressure, due to reduction in water potential and plasma protein.
What is oncotic pressure?
Starlings forces; is the osmotic force due to protein in the capillary drawing water back in. Oncotic pressure is constant/uniform because the protein plasma concentrations do not change.
Which part of the capillary bed has the highest pressure?
Arteriolar end
What is the pressure relationship between hydrostatic and oncotic pressure at the arteriolar end?
Hydrostatic pressure > oncotic pressure = fluid leaves the capillary (ULTRAFILTRATION)
What is the pressure relationship at the venular end?
Venular end: Oncotic pressure > hydrostatic pressure = fluid enters the capillary (REABSOPRTION)
What is the net loss of fluid from capillaries?
1mm drains into lymphatic system
