Cardiovascular system: Blood pressure Flashcards
What is the blood pressure equation?
Cardiac output (CO) * Total peripheral resistance (TPR)
What is blood pressure the driving force of?
Nutrient exchange in the capillaries
How do capillaries respond to changes in blood pressure?
Not very well, sensitive to changes in blood pressure due to their weak structure of a single cell thick of endothelial cells
How does the body try to minimise damage from blood pressure to capillaries?
The body has a set point for blood pressure
What does the set point for blood pressure mean?
Throughout the day the body tries to maintain the mean blood pressure (~100mmHg)
How does mean blood pressure change throughout the day?
It is pretty constant
What condition develops when there is sustained higher mean blood pressure? How does this affect the circulatory system?
This leads to hypertension (FYI defined as 140/90 mmHg –> 14% of NZ has this) causing hypertrophy of the heart
How does blood pressure change per heart beat?
There are lots of small changes in blood pressure, the diagram attached shows how there are micro adjustments in blood pressure all the time
What is the blood distribution in the body?
Heart = 7%
Systemic capillaries = 7%
Pulmonary vessels = 9%
Systemic arteries and arterioles = 13%
Systemic veins and venues = 64%
How is it that the blood volume is so low in then capillaries even though this is where nutrient exchange occurs?
There is a high flow rate through them
How does the movement of the blood vary throughout the systemic circuit?
Blood pressure is the highest and also drops rapidly through the arteries (Aorta, arteries and arterioles), pressure is lower in the capillaries and much lower in the veins (venues, veins, vena cavae)
As the blood moves through the circuit there is also less pulsating
Why does the blood pressure decrease as the blood moves through the systemic circuit?
As the blood moves through the circuit, vessels absorb some of the energy due to their resistance therefore reduce the pressure of the blood
How much of the blood is returned to the heart after each beat?
The same amount is returned as there is delivered
How much of the blood that is delivered to the capillary beds is pumped out of the capillary bed normally?
The same amount
What happens when not all the blood from the capillary beds is removed?
Causes oedema (i.e. swelling) as there is excess fluid in the interstitial space
What are the most important type of blood vessels for controlling blood pressure? Why?
Arteries as they can vasoconstrict/dilate
What is the condition of the arteries always?
They always have vascular tone (i.e. always slightly constricted)
How is the vascular tone influenced?
By hormones (i.e. noradrenaline), Nerves (in particular sympathetic nerves) and intrinsic factors
How is blood in the capillary beds reabsorbed?
The blood pressure is lower at the venous end of the capillaries which allows for net re-absorbtion due to osmotic pressure difference and also some of the fluid is re-absorbed via the lymph system
What is the net filtration pressure (NFP) of the capillary at the arterial end? Why?
10mmHg, There is a large blood hydrostatic pressure and the constant blood colloid osmotic pressure is less than this so interstitial fluid is able to drain out of the capillaries
What is colloid pressure?
The pressure exerted by the proteins and other substances in the interstitial fluid
What is the net filtration pressure (NFP) of the capillary at the venous end? Why?
-9mmHg, There is a smaller blood hydrostatic pressure and the constant blood colloid osmotic pressure is more than this so interstitial fluid is able to drain into the capillaries
How are arteries and arterioles controlled?
They are all connected to the brain via the sympathetic nerves
How and why does the brain influence blood pressure?
Using sympathetic nerves able to control the degree of constriction
It is able to re-distribute blood to where it is needed (i.e. kidneys usually use ~20% of CO but when exercising, vasoconstricts renal tract to 2-3% CO so more blood for muscles)
How are arteries and arterioles measured? What does this create?
They all have receptors such as baroreceptors and proprioceptors which monitor the blood and return the information to the brain –> negative feed back loop
What is the arrangement of the blood vessels around the body? Why this?
It is in parallel so that each organ receives the same pressure (i.e. in series the blood pressure of the organ at the end would be so low that it would be insufficient for for exchange)
How are baroreceptors able to measure blood pressure?
They sense the stretch of blood vessels
How do baroreceptors signal to the brain the pressure changes?
When there is more stretch the nerve fires more
How does the negative feedback loop of the baroreceptors work in a situation of decreasing blood pressure?
1 - Baroreceptors will fire less indicating decreasing blood pressure
2 - These signals are communicated back to the brain via afferent nerves
3 - The signal is received by the cardiovascular centre in the medulla
4 - This causes increased sympathetic and decreased parasympathetic stimulation
5 - this increases the secretion of epinephrine and norepinephrine (mainly this one) from adrenal gland increasing stroke volume, heart rate and causes vasoconstriction of the arteries resulting in increased blood pressure –> increases CO and TPR, BP = CO * TPR
6 - once baroreceptors have sensed normal blood pressure again, return back to homeostasis
When there is increased blood volume, what does this cause?
Increased blood pressure
How does the body regulate high blood pressure?
Cardio effects: Stimulate vasodilation (decreased sympathetic and decrease parasympathetic activity) and decrease CO
Renal effects: Increase fluid secretion
What are the relative speeds and effectiveness of action of the cardio and renal effects on high blood pressure?
The cardio effect is fast (i.e. baroreceptors work within a single heart beat) but is only a temporary measure, renal effect is slower to work but it is able to make more significant longer term changes in blood pressure
