PSC1002/L08 Blood Pressure Flashcards
What is required to drive blood pressure?
A pressure gradient within each circulation
Define mean arterial blood pressure (MABP).
Product of the input to the arterial system and resistance to flow
How is cardiac output calculated?
CO = SV x HR
Define total peripheral resistance (TPR).
Sum of individual vessels resistance to flow
How is mean arterial blood pressure calculated?
MABP = CO x TPR
What is a typical stroke volume and cardiac output?
SV = 70ml
CO = 4.9L/min
Describe how parasympathetic nerves affect the heart. (3)
ACh release
Activated muscarinic ACh receptors
Decreased heart rate
Describe how sympathetic nerves affect the heart. (3)
NA release
Activated B1-adrenergic receptors
Increased heart rate and contractility
Describe why sympathetic stimulation increases HR. (3)
Steeper ‘slope’ of pacemaker potential
RMP is less negative
Threshold is reached quicker
Describe why parasympathetic stimulation decreases HR. (3)
Less steep ‘slope’
More negative RMP
Longer to reach threshold
What occurs as a directly result of muscarinic receptor activation?
Opening out K+ channels (out of cell)
What is a term for changes in heart rate?
Chronotropic effects
What are the 2 basic mechanisms for regulation of stroke volume?
Intrinsic
Extrinsic
What is another name for the intrinsic mechanism of stroke volume regulation?
Frank-Starling Mechanism
Describe Starling’s Law of the heart.
The force of contraction is proportional to the initial (just before contraction) muscle fibre length in diastole
What is a result of increased venous return to the heart? (2)
Stretching of muscle fibres
Directly affects subsequent force of contraction
Describe the basis for Starling’s Law. (2)
Increased stretch increased sensitivity of contractile proteins to Ca2+
Intracellular [Ca2+] required to generate 50% maximal tension is lower than when muscle fibre is not stretched
Give 2 reasons why Starling effects are important.
Helps in matching output of right and left sides of the heart
Enables heart to adapt to changes in pumping capacity when either venous return or arterial blood pressure changes
Describe extrinsic effects on the heart. (6)
Increase in sympathetic activity
Enhances contractility of cardiac muscle
NA/Ad
Binding to B1-adrenergic receptors
Results in enhanced stroke volume
Smaller ESV at end of contraction
Give another term for extrinsic effects on the heart.
Inotropic effects (contractility)
How does NA affect the ventricular function curve?
Causes an upward shift
How do catecholamines increase contractility? (2)
Through cAMP second messenger system
Increased [Ca2+] (trigger calcium)
What is the role of phosphoLAMBA? (2)
Phosphorylated by pKA
Regulates activity of Calcium ATPase in SR (negative regulator)
What is venous return maintained by? (4)
Venous to atrial pressure differences
Venous valves
Venomotor tone
Respiration
What is venomotor tone?
Some veins have smooth muscle and receive sympathetic supply
