Physiology part 3 Flashcards
Define blood pressure?
the outwards (hydrostatic) pressure exerted by the blood on blood vessel walls
Define systemic systolic arterial blood pressure?
pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
Define systemic diastolic arterial blood pressure?
pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
Define hypertension?
Clinic blood pressure of 140/90 mmHg or higher and day time average of 135/85 mmHg or higher
Define pulse pressure?
Is the difference between systolic and diastolic blood pressures
What is the normal range of pulse pressure?
30 and 50 mmHg
What is MAP?
the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
Why is MAP not the average of systolic and diastolic?
Diastolic portion of the cardiac cycle is about twice as long as the Systolic portion of the cardiac cycle
How is MAP calculated?
[(2x Diastolic) + Systolic] divided by 3
What is the normal range of MAP?
70-105mmHg
What MAP is required to perfuse the brain, heart and kidneys?
60mmHg
What is the sensor for negative feedback MAP system?
Baroreceptors
What is the control centre for negative feedback MAP system?
Medulla
What is the effector for negative feedback MAP system?
Heart and blood vessels
What is the response of the heart to change in MAP?
Change in HR, SV
What is the response of the blood vessels to change in MAP?
Varying systemic vascular resistance
Where are the baroreceptors?
Carotid sinus
Aortic
How do the baroreceptor signals reach the medulla?
Carotid- IXth CN
Aortic Xth CN
Define baroreceptors?
Mechanoreceptors sensitive to stretch
What happens to firing rate in baroreceptor afferent neurones in response to increased MAP?
Increases
What happens to firing rate in baroreceptor afferent neurones in response to decreased MAP?
Decreases
What is the nucleus tractus solitairius?
Site of 1st synapse for all CVS afferents in the medulla
What does the medulla do?
- receives CVS afferent information
- Relays information to other regions in the brain e.g. medulla, hypothalamus, cerebellum
- Generates vagal (parasympathetic) outflow to the heart- relay to the nucleus ambiguus in the medulla
- regulates spinal sympathetic neurones
What is systemic vascular resistance?
Sum of resistance of all vasculature in the systemic circulation
How can MAP be regulated?
HR
SV
SVR
Define
autorhythmicity
Hearts ability to beat in the absence of external stimuli
What is the role of the sympathetic division in HR?
Accelerates HR
What is the role of the parasympathetic division in HR?
stimulation of the vagus nerve (10th cranial nerve) slows the heart rate (bradycardia)
What acts on B1 receptors?
Noradrenaline
What acts on muscarinic receptors?
Acetylcholine
When does SV increase?
If the contractile strength of the heart is increased
What regulates the SV?
ANS
What nerves innervate the myocardium?
Sympathetic nerves
What is the intrinsic control of SV?
Frank-Starling Mechanism or the Starling’s Law of the Heart
What are the Major Resistance Vessels?
Arterioles
What regulates SVR?
vascular smooth muscles
What does contraction of vascular smooth muscle cause?
vasoconstriction and increases SVR and MAP (i.e. pressure upstream)
What does relaxation of vascular smooth muscle cause?
vasodilatation and decreases SVR and MAP
What supplies VSM and what is the neurotransmitter?
SYMPATHETIC nerve fibers. The neurotransmitter is NORADRENALINE acting on alpha receptors
Define vasomotor tone?
Vascular smooth muscles are partially constricted at rest.
What causes vasomotor tone?
tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
What increases vasomotor tone?
Increased sympathetic discharge will increase the vasomotor tone
When does baroreceptor firing decrease?
if high arterial blood pressure is sustained
