Control of arterial blood pressure Flashcards
What is blood pressure?
The outwards pressure exerted by the blood on blood vessel walls
What is systemic systolic arterial blood pressure?
is the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts”
What is systemic diastolic arterial blood pressure?
is the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes”
what is hypertension?
Clinic blood pressure of 140/90 mmHg or higher and day time average of 135/85 mmHg or higher
What is pulse pressure?
The difference between the systolic and diastolic blood pressures
What is the normal range for pulse pressures?
between 30 and 50
What does laminar mean in terms of blood pressure?
There is fluent flow, no obstruction. You will not hear anything.
Is turbulent flow heard through a stethoscope?
Yes
How is turbulent flow created?
If the external pressure is kept between systolic and diastolic
When artery is fully occluded by sphyg what can you hear?
Nothing.
What is the first Korotkoff sound?
The first sound heard at peak systolic pressure
What are the second and third Korotkoff sounds?
Intermittent sounds are heard as blood pressure due to turbulent spurts of flow cycle cyclically exceeds cuff pressure
What is the 4th Korotkoff sound?
The last sound heard at minimum/diastolic pressure. Muffled/muted sound
What is the 5th Korotkoff sound?
No sound is heard thereafter because of uninterrupted smooth laminar flow.
What are the two important sounds for measuring BP?
1st and 5th (systolic and diastolic values)
What is a pressure gradient?
What drives the blood around the systemic circulation
What is the equation for pressure gradient?
mean arterial Pressure - central venous pressure
What is mean arterial blood pressure?
the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
What is the equation for mean arterial blood pressure?
-((2xdiastolic) + systolic)/3
or
-diastolic blood pressure +1/3xpulse pressure
Why dies the mean arterial blood pressure need to be regulated within narrow range limits?
- pressure needs to be high enough to perfuse internal organs including the brain, heart, and kidneys
- But not so high as to damage the blood vessels or place an extra strain on the heart
How can you calculate MAP using cardiac output?
MAP=CO x systemic vascular resistance
What is Cardiac output?
is the volume of blood pumped by each ventricle of the heart per minute
How do you calculate CO?
SV x HR
What is stroke volume?
the volume of blood pumped by each ventricle of the heart per heart beat
What is systemic vascular resistance?
The sum of resistance of all vasculature in the systemic circulation
In what vessel is the most systemic vascular resistance?
Arterioles
What are the effects of vasoconstriction on MAP?
- vasoconstriction will increase venous return to the heart.
- this increases end diastolic volume
- this increases stroke volume
- this increases cardiac output -this increases MAP
What are baroreceptors?
Pressure sensors that detect changes in blood pressure and send signals to the medulla where they get sent to effector muscles
Where are baroreceptors?
Aortic baroreceptors are in the aorta and send signals through Vagus nerve to the medulla.
Carotid baroreceptors are in the carotid sinuses and send signals through the IX Cn to the medulla
When is baroreceptor reflex important?
in moment-to-moment regulation of arterial blood pressure including prevention of postural changes
What happens to baroreceptors when MAP decreases?
A reduces rate of firing of baroreceptors. This causes vagal and sympathetic tones to set in to increase HR, SV and SVR
Baroreceptors can supply information about prevailing steady state blood pressure True or False
False, cannot. Longer term control is in hands of blood volume
whats the proportion of intracellular fluid compared to extracellular fluid in the total body fluid?
2/3 intracellular and 1/3 extracellular
What compensatory mechanism is in place should plasma volume drop?
Fluid is shifted fro the interstitial compartment to the plasma compartment
What is extracellular fluid comprised of?
interstitial fluid and plasma volume
What are the two main factors that affect extracellular fluid volume?
water excess or deficit
sodium excess or deficit
What do hormones do?
act as effectors to regulate the extracellular fluid volume (including Plasma Volume) by regulating the Water and Salt Balance in our bodies
What are the three hormones which regulate extracellular fluid volume?
1- renin-angiotensin-Aldosterone system
2-natriuretic peptides
3-antidiuretic hormone
What does renin-angiotensin-Aldosterone system do?
regulates plama volume and SVR and hence regulation of MAP
How does renin-angiotensin-Aldosterone system work?
- Renin converts protein angiotensinogen to angiotensin I
- Angiotensin 1 is converted to angiotensin II by Angiotensin Converting enzyme
- Angiotensin II will stimulate the release of Aldosterone from adrenal glands. Angiotensin II is also a vasoconstrictor and causes the release of antidiuretic hormone.
Where is renin released from?
juxtaglomerular apparatus in kidneys
When will renin be released?
- If BP drops
- Decrease in sodium in renal tubular fluid
- By stimulation of renal sympathetic nerved
What are natriuretic peptides?
peptide hormones synthesised by the heart (also brain and other organs)
When are natriuretic peptides released?
In response to cardiac distension or neurohormonal stimuli
What do natriuretic peptides do?
-They cause excretion of salt and water in the kidneys, thereby reducing blood volume and blood pressure
Decrease renin release - decrease blood pressure
Act as a vasodilators - decrease SVR and blood pressure
NPs provide a counter-regulatory system for the Renin-Angiotensin-Aldosterone System (RAAS)
What are the two types of Natriuretic Peptides released by the heart?
Atrial Natriuretic Peptide (ANP) and Brain-type Natriuretic Peptide (BNP)
What is the Atrial Natriuretic Peptide (ANP)?
ANP is a 28 amino acid peptide synthesised and stored by atrial muscle cells (atrial myocytes)
ANP is released in response to atrial distension (hypervolemic states)
What is Brain-type Natriuretic Peptide (BNP)?
BNP is a 32 amino acid peptide synthesised by: heart ventricules, brain (where it was originally identified) and other organs
What is the antidiuretic hormone?
Peptide hormone derived from a prehormone precursor synthesised by the hypothalamus and stored in the posterior pituitary
What stimulates secretion of ADH?
Secretion stimulated by (1) reduced extracellular fluid volume or (2) increased extracellular fluid osmolality (main stimulus)
What is the main function of ADH?
ADH acts in the kidney tubules to increase the reabsorption of water (conserve water) - i.e. concentrate urine (antidiuresis)
This would increase extracellular and plasma volume and hence cardiac output and blood pressure
Also causes vasoconstriction
