Control of arterial blood pressure Flashcards
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
Define postural hypotension
Results from failure of Baroreceptor responses to gravitational shifts in blood, when moving from horizontal to vertical position
What happens to baroreceptor firing if high BP is sustained?
Decreases
Baroreceptors “re-set” - they will fire again only if there is an acute change in MAP above the new higher steady state level
What is the control of MAP in the long term?
Blood volume
total body fluid=
intracellular fluid+extracellular fluid
ECF volume =
plasma volume + interstitial fluid
What are the two main factors affecting ECFV?
Water excess or deficit
Na excess or deficit
How do hormones regulate the ECFV?
regulating the salt and water balance in our bodies
Which three hormones regulate ECFV?
RAAS
NPs
ADH
Where is renin released from?
The kidneys
What does renin stimulate?
Formation of angiotensin I in the blood from angiotensinogen
What is angiotensin I converted to and by what?
angiotensin II
ACE
Where is ACE mainly produced?
Pulmonary vascular endothelium
Angiotensin II stimulates the release of ———– from the ——- ——
aldosterone
adrenal cortex
What does aldosterone cause?
Systemic vasoconstriction… increases SVR also thirst and ASH release
aldosterone acts on the ——- to increase —— and —– retention- increasing —— ——
kidneys
sodium
water
plasma volume
What mechanisms stimulate renin release from the juxtapulmonary apparatus in the kidney?
- renal artery hypotension
- stimulation of renal sympathetic nerves
- decreased NA in renal tubular fluid
Where are peptide hormones NPs synthesised?
Heart, brain and other organs
What are NPs released in response to?
to cardiac distension or neurohormonal stimuli
What do NPs cause?
excretion of salt and water in the kidneys, thereby reducing blood volume and blood pressure
Decreased renin release will do what to blood pressure?
Reduce it
NPs act as what?
Vasodilators- decrease SVR
What do NPs counteract?
RAAS system
What are the two typed of natriuretic peptides released by the heart?
Atrial Natriuretic Peptide and Brain-type natriuretic peptide
ANP is made of how many amino acids? Where is it stored?
28
Atrial myocytes
When is ANP released?
in response to atrial distension (hypervolemic states)
BNP is made of how many amino acids? Where is it synthesised?
32
heart ventricles and brain
What is BNP first synthesised as?
prepro-BNP which is cleaved to pro-BNP and then BNP
When is serif BNP measures?
Suspected Heart Failure
Where is ADH synthesised?
derived from a prehormone precursor synthesised by the hypothalamus and stored in the posterior pituitary
What stimulated ADH secretion?
1) reduced extracellular fluid volume or
2) increased extracellular fluid osmolality (main stimulus)
What does plasma osmolarity indicate?
relative sodium-water balance
What is plasma osmolarity monitored by?
Osmoreceptors mainly in the brain in close proximity to the hypothalamus
What does ADH act upon? To do what?
kidney tubules
Increase reabsorption of water
What does antidiuresis do?
Increase extracellular and plasma volume hence CO and BP
what does ADH do to the blood vessels?
Cause vasoconstriction
Increase SVR and BP
How is Short-term moment-to moment regulation of MAP achieved?
Baroreceptor reflex
