Regulation Of Blood Pressure Flashcards
Why is the volume in arteries called stressed volume?
Because it is under high pressure
What does low compliance mean in aretries?
Ability of blood vessels to expand and hold larger volumes of blood without a significant increase in blood pressure
What in arterioles is tonically active?
The vascular smooth muscles
Key ideas about blood pressure in arterioles
Tonically active vascular smooth muscle
Highest resistance to blood flow, changed in response to catecholamines, vasoactive substances and sympathetic nerves:
Sympathetic nerves:
-Alpha 1 adrenergic receptors contract/ constrict (decrease diameter of arteriole OR increase resistance to blood flow)
-Beta 2 adrenergic receptors dilate/ relax
Balance of alpha 1 and beta 2 receptors regulates blood flow to different organs and tissues in changing conditions
What are alpha 1 adrenergic receptors?
A receptors found on skin, mucous membranes and splanchnic arterioles.
When stimulated, They cause contraction of vascular smooth muscle
What are beta 2 adrenergic receptors?
Receptors found in skeletal muscle and heart arterioles
When stimulated, They cause dilation
Key ides about blood pressure in capillaries
Low pressure and slow flow
Controlled by dilation/ constriction of arterioles
Key ideas about blood pressure in veins and venules
Low pressure
Walls contain less elastic tissue than arteries
Large capacitance
Contain largest % of blood in CV system
Activity can be increased via alpha 1 adrenergic receptors
How can the activity of veins or venules be increased?
Activity can be increased via alpha 1 adrenergic receptors- contraction reduces capacitance so decrease in unstressed volume
Does the flow change across blood vessels?
No because its a closed system
How do we work out velocity in IDENTICAL flow?
Velocity= rate
Velocity= Q / A
Q=flow
A=cross sectional area
What is the relationship between blood flow, resistance and pressure?
Equation
Q= Δ P / R
Q=blood volume per unit of time (mL/s)
P= pressure difference (mmHg)
R= resistance (mmHg/mL per min)
What is vasoconstriction?
Contraction of vascular smooth muscle
What is the significance of the relationship between blood flow, pressure and resistance?
BP regulation:
Vasoconstriction = +resistance = +BP
Vasodilation = - resistance = -BP
Blood flow distribution- adjustment due to need increase or decrease of resistance
What is total peripheral resistance (TPR)?
Resistance of the entire vascular system
Blood vessels and blood offer resistance to flow. What factors determine resistance to blood flow (Poiseuille’s Law)?
Blood viscosity
Blood vessel diameter
Blood vessel length
Series/ parallel arrangement
What is the equation for poiseuille’s law?
R= 8ηℓ / πr4 (power of 4)
What is the equation for poiseuille’s law?
R= 8ηℓ / πr4 (power of 4)
Describe the relationship between values in poiseuille’s law
Resistance to flow- directly proportional to vessel length and blood viscosity
Inversely proportional to fourth power of the radius
Where is the largest decrease in pressure in series resistance? Why?
Arterioles due to large resistance
How does blood pressure vary throughout the circulatory system?
Aorta: High pressure due to large cardiac output and low compliance
Arteries: Remains high due to elastic recoil
Arterioles: Pressure decreases due to high resistance to flow
Capillaries: Low pressure, slow flow due to frictional resistance and filtration
Venules and veins: High capacitance and low pressure
What is hypertension ?
Hypertension is persistent high blood pressure that can lead to:
Heart disease, heart attacks, strokes
Heart failure, aortic aneurysms
Peripheral arterial disease
Kidney disease
Vascular dementia
what drug treatments are available for hypertension?
Diuretics
ACE inhibitors
Angiotensin II receptor blockers (ARBs)
Renin inhibitors
Calcium channel blockers
Beta blockers
How do you calculate pulse pressure ?
Pulse pressure = Systolic pressure - Diastolic pressure
Pulse pressure reflects blood volume ejected from left ventricle (stroke volume)
is systolic or diastolic pressure bigger?
systolic as its contraction
What is venous pressure (Pv) in systemic circulation?
Occurs in venules and veins
Pressure is less than 10mmHg
Results from decreased resistance at each level of vasculature
What is ADH (AVP) and its effects?
Antidiuretic hormone (vasopressin) Secreted from pituitary in response to decreased BP or increased blood osmolarity
Acts on:
V1 receptors in vascular smooth muscle cells
V2 receptors in collecting ducts
Is pulmonary or systemic vasculature pressure lower?
pulmonary as there is lower resistance
how do we work out mean arterial pressure?
Mean arterial pressure = Diastolic pressure + 1/3 pulse pressure
Mean arterial pressure represents average pressure in a complete cardiac cycle
what are baroreceptors?
they are receptors that pick up changes in pressure
how do baroreceptors work and where are they located?
Located in carotid and aortic sinuses:
Increased Pa leads to increased stretch and increased afferent nerve firing
Decreased Pa leads to decreased stretch and decreased afferent nerve firing
Send input to the Solitary Nucleus (SN)
SN directs SNS + PNS changes via medullary CV centres
How does the RAAS system regulate blood pressure?
The Renin-angiotensin-aldosterone system regulates blood volume, electrolyte balance, and systemic vascular resistance
Triggered by decreased renal perfusion pressure
Angiotensin II effects:
angiotensinogen–> angiotensin I–>angiotensin II
angiotensin II–> increased aldosterone –> Na reabsorption–> increase ECF
Hypothalamus stimulates thirst and ADH secretion
what are chemoreceptors?
Receptors that pick up low Oxygen levels
