Control of arterial blood pressure Flashcards
(60 cards)
Define blood pressure
the outwards (hydrostatic) pressure exerted by the blood on blood vessel walls
What is the systolic arterial blood pressure?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts”: should not normally reach or exceed 140 mm Hg under resting conditions
What is the diastolic arterial blood pressure?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes”: should not normally reach or exceed 90 mm Hg under resting conditions
What is hypertension defined as?
Clinic blood pressure of 140/90 mmHg or higher and day time average of 135/85 mmHg or higher
What is pulse pressure?
Is the difference between systolic and diastolic blood pressures
What is pulse pressure normally?
between 30 and 50 mmHg
In which fashion does blood flow through arteries?
Laminar fashion (inaudible)
When does flow become turbulent?
if the external pressure is kept between systolic and diastolic pressure the flow become turbulent whenever blood pressure exceeds cuff pressure
When is the 1st Korotkoff sound heard?
Peak systolic pressure
When are the 2-3rd Korotkoff sounds heard?
Intermittent sounds are heard as blood pressure due to turbulent spurts of flow cyclically exceeds cuff pressure
When is the 4th Korotkoff sound heard?
The last sound is heart at minimum diastolic pressure
When is the 5th Korotkoff sound heard?
No sound is heart thereafter because of uninterrupted, smooth, laminar flow
When is diastolic pressure recorded
5th Korotkoff sound
What delivers the blood around the systemic circulation?
A Pressure Gradient
between the Aorta (AO)
and the Right Atrium (RA)
What is the main driving force for blood flow?
MAP
Pressure gradient=
Mean Arterial Pressure (MAP) – Central Venous (right atrial) Pressure (CVP)
What is MAP?
the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
How can we calculate MAP?
MAP = [(2x diastolic pressure) + systolic pressure]/ 3 or MAP = DBP + 1/3 Pulse Pressure
MAP of at least –mm Hg is needed to perfuse the coronary arteries, brain, and kidneys.
60
Where are the pressure sensors in the baroreceptor reflex?
Baroreceptors
Where is the control centre in the baroreceptor reflex?
Medulla
Where are the effectors in the baroreceptor reflex?
Heart (HR,SV) and blood vessels (SVR)
How do the baroreceptor reflexes reach the medulla?
Through Xth cranial nerve and IXth cranial nerve
Explain the baroreceptor reflexes in the prevention of postural hypotension?
When a normal person suddenly stand-up from lying position:
The venous return to the heart decreases - effect of gravity
mean arterial pressure (MAP) very transiently decreases
This reduces the rate of firing of baroreceptors
The vagal tone to the heart decreases and the sympathetic tone to the heart increases. This increases the heart rate (HR) and stroke volume (SV)
The sympathetic constrictor tone increases. This increases the systemic vascular resistance (SVR) - arterioles are the main site for SVR
The sympathetic constrictor tone to the veins increases the venous return (VR) to the heart and stroke volume
The result is: rapid correction of the transient fall in MAP: HR INCREASES; SV INCREASES; SVR INCREASES
