How do arterioles modify resistance?
They have lots of smooth muscle which
What is mean arterial blood pressure?
mean pressure over the entire cardiac cycle (average is about 95 mmHg not mean between SBP and DSP due to being in Systole for longer)
What is systolic BP?
Maximum arterial BP during heart contraction
What is diastolic BP?
Min arterial BP during heart relaxation
What is the formula for mean arterial pressure?
CO x TPR
P = QR
What controls cardiac output?
sypathetic and parasympathetic nerves that affect heart rate and stroke volume
What does SVR get affected by?
constriction or dilation of the arterioles and venules (due to preload effect)
What things manipulate Mean Arterial Pressure?
CO
SVR
Blood Volume (more volume = more pressure)
What is chronotropy?
Heart rate effects
What are the excitatory affects on heart rate caused by?
Sympathetic innervation
What are the slowing effects on heart rate caused by?
Parasympathetic innervation
What is the intracellular response of muscarinic ACh binding?
opens potassium channels causing potassium to leak out of the cell to make the cell more negative making gaps between heartbeats longer
No effect on contractility
What does beta adrenergic innervation result in?
More calcium flows into the cell making the heart cells more contractile and contract more often
What is beating harder described as?
Inotropy
What factors affect MAP?
Female M>F
Age Elderly > Children
Emotions Increases due to increases due to secretion of adrenaline and noradrenaline
Exercise increases due to increased venous return
Hormones increases MAP
Gravity increases MAP due to pooling of blood in lower limbs
Sleep decreases MAP due to decrease in venous return
Pregnancy increases MAP due to increased metabolism
What factors affect systemic vascular resistance?
Blood viscosity (ratio of RBCs to plasma and protein concentration)
Total blood vessel length (resistance directly proportional to length of vessel)
Size of lumen (vasoconstriction makes lumen smaller meaning greater resistance)
What happens in blood vessels when responding to noradrenaline binding to alpha receptors?
They narrow with the exception of arteries going to muscles and coronary arteries
How is BP measured?
Short term: Baroreceptors
Long term in kidneys via the tubuloglomerular feedback
How is BP controlled?
Short term controlled by baroreceptor reflex.
Long term controlled by RAAS, ADH, and ANP
What 3 centers are present within the CV center in the medulla?
Cardiostimulatory center (Increase heart rate and heart contractility)
Cardioinhibitory center (Decrease HR)
Vasomotor center (Vasoconstriction)
What part of the brain is the CV center a part of?
The solitary tract
Where are baroreceptors located?
Carotid sinus
Aortic reflex
What fires the baroreceptors?
stretch of the mechanoreceptors
Which receptors cause arteriolar smooth muscle to contrict?
Alpha receptors
Which receptors cause the ventricles to contract harder?
Beta - 1
Which receptors cause the SA node to depolarize more frequently?
Beta - 2
Are there other important receptors that the heart reacts to?
Yes, for example lung stretch receptors will elevate HR
What does the Frank-Starling curve show?
The effect of the venous system on preload. Increasing venous pressure elevates CO.
What happens to venous pressure when cardiac output is elevated?
It drops because blood is being removed from venous circulation
What happens when Venous pressure drops as a result of elevated CO?
the CO drops
This goes back and forth until equilibrium is reached at what is known as a goldilocks zone
There is an optimal cardiac output for an optimal preload
What happens to goldilocks zone with the effect of sympathetic stimulation?
Venous Pressure drops due to increase in tone and an elevation of CO. Increase in preload results in a higher point
What does nitroprisside do?
Elevates heart rate without influencing preload
What does increasing blood volume do to the venous preload?
Elevates both CO and venous pressure. More fluid means venous pressure is higher due to presence of more fluid and CO increases due to higher preload
If CO & CVP are low how can this problem be fixed?
Increasing the amount of fluid in the system.
If CO is low but CVP is raised what can be done?
Use a cardiac stimulant
