CAM201 Lecture Notes - Lecture 6: Birth Weight, List Of Fables Characters, Diabetic Nephropathy
Learning Objectives
• Revise why blood pressure varies throughout the circulation and the factors that determine
blood pressure
• Describe how blood pressure is regulated acutely by the baroreceptor reflex
• Explain how the kidneys regulate arterial blood pressure with reference to the renin-
aldosterone angiotensin system (RAAS)
• Explain how salt intake influences blood pressure
• Describe the consequences of increased or decreased blood pressure
Pressure Determines and Enables Blood Flow
• Systemic flow is the entire output of the heart (CO)
• Calculated using Ohm's law
• If we assume that right atrial pressure = 0mmHg, rearrange equation:
Blood Pressure Control
• We know that individual tissues/organs generally regulate their own flow according to
demands
• We also know that the heart intrinsically responds to the needs of the tissues via the Frank-
Starling mechanism
• On top of this sits the respiratory system that attempts to keep arterial pressure stable at
nearly all costs
Why?
• First, pressure provide the flow gradient
• If we have good pressure we can maintain organ perfusion (eg brain/heart)
• Second, high blood pressure is damaging to blood vessels and organs
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• If blood pressure increases the oscillations in systole - diastolic pressure is amplified and
passed down the arterial tree to the microvessels (eg capillaries) damaging them and the
tissues they supply
• This is because microvessels aren't suited for a pulsatile flow
How Can We Regulate Systemic Blood Pressure
Physiological Feedback Loops
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Short Term Control of Blood Pressure
1. Two main sensors
• One directly senses blood pressure: stretch in blood vessel walls is sensed by
baroreceptors located in various areas
• The other indirectly sense blood pressure (low perfusion): low oxygen/high carbon
dioxide sensed by chemoreceptors in tissues
2. One control centre
• The vasomotor centre in the brain stem (medulla)
3. Multiple effectors
• Smooth muscle: arteries and arterioles alter total peripheral resistance
• Smooth muscle: veins and venules changes venous return/preload/SV
• SA Node: changes HR
• Ventricular muscle: changes contractility
• Kidneys: SNS activates the Renin angiotensin system
Baroreceptors
• These are stretch receptors located in the aorta and carotid arteries
• They are tonically active and act to regulate blood pressure from moment-moment
• Increased blood pressure ➔ increases baroreceptor stretch
• This inhibits the vasoconstriction centre in medulla
• Results in vasodilation, decreased HR and SV
• Decreased blood pressure ➔ reduced baroreceptor stretch
• Reduced inhibition (ie activation) of vasoconstrictor centre in medulla
• Results in vasoconstriction, increased HR and SV
• Note that there are also different baroreceptors in the atria and pulmonary systems
Reflex
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Document Summary
Systemic flow is the entire output of the heart (co: calculated using ohm"s law. If we assume that right atrial pressure = 0mmhg, rearrange equation: Blood pressure control: we know that individual tissues/organs generally regulate their own flow according to demands, we also know that the heart intrinsically responds to the needs of the tissues via the frank- Starling mechanism: on top of this sits the respiratory system that attempts to keep arterial pressure stable at nearly all costs. If we have good pressure we can maintain organ perfusion (eg brain/heart) Second, high blood pressure is damaging to blood vessels and organs. Smooth muscle: arteries and arterioles alter total peripheral resistance. Smooth muscle: veins and venules changes venous return/preload/sv. Sa node: changes hr: ventricular muscle: changes contractility, kidneys: sns activates the renin angiotensin system. Baroreceptors: these are stretch receptors located in the aorta and carotid arteries, they are tonically active and act to regulate blood pressure from moment-moment.
