PSIO202 Exam 1 Lecture 6-7 Flashcards
What is the basic reason that blood flows instead of sitting still?
pressure differences
What is the term for the pressure difference that causes bloodflow?
driving pressure
Where is BP pulsatile?
Elastic arteries near the heart
When does BP rise and fall? What happens to the arteries at these times?
rises during systole so the arteries expand, and falls during diastole so the arteries recoil to push blood through
Where is BP lower, arteries, capillaries, or veins? Why is this important?
Lowest in veins, which favors blood return to the heart
What is the equation for mean arterial pressure?
MAP = DBP + 1/3 (SBP-DBP)
What two factors does arterial blood pressure reflect?
amount of blood and arterial compliance
What is compliance? What is the equation? What does this equation mean?
Ability of arteries to stretch and recoil (opposite of stiffness)
C = dV/dP
C = change in volume / change in pressure
If it takes a lot of pressure to change the volume of an artery, compliance is low. If it doesn’t take much pressure to change the volume, compliance is high.
Are elastic arteries generally compliant or not?
Compliant
What are the two factors that ensure blood is propelled through the cardiac cycle?
expansion and recoil (arterial compliance and elasticity)
Waves of expansion and recoil result in a pressure wave called…
pulse pressure
How do you calculate pulse pressure?
SBP-DBP
How are pulse pressure and stroke volume related?
PP reflects SV if compliance is constant
When arteries are stiff or non-compliant, what must happen for them to eject blood?
The pressure has to increase
Are pressures in the pulmonary circuit low or high? How does this relate to compliance?
low, because it is highly compliant
What is the MAP for the pulmonary artery? What is the mean left atrial pressure? What does this cause?
pulmonary artery: 14 mmHg
left atrium: 5 mmHg
Pressure gradient for atrial filling from the pulmonary artery is 9 mmHg
What is the relationship between CSA (cross sectional area) and flow velocity?
more CSA = slower flow velocity
What structures allow blood to NOT be sent to certain areas?
precapillary sphincters
Do the capillaries have smooth muscle?
No, only arteries and veins
What term is the same as “blood flow”?
cardiac output
What is the relationship between blood flow, resistance, and driving pressure? Explanation and equation.
Blood flow is proportional to driving pressure and inversely proportional to resistance.
CO=MAP/resistance
What is resistance? What is a common cause?
Anything that slows flow, such as friction between the molecules and with the walls of the tube.
What is the equation for resistance?
**not based on Ohm’s Law
R = (viscosity x vessel length) / r^4
resistance radius
What happens when you halve or double radius?
2 r = 1/16 R
1/2 r = 16 R
What impacts viscosity in the resistance equation?
hydration, temperature (think honey)
What is Ohm’s Law? What is the “blood pressure” translation?
V= I x R
voltage = current x resistance
blood pressure = flow x resistance
BP = CO x resistance
BP = (SV x HR) x resistane
What is the simplified equation for systemic resistance?
resistance = BP/Flow
OR
resistance = (DBP + 1/3 (SBP-DBP)) / CO
What are the three regulations of blood flow?
neural, humoral, and local/metabolic
What is neural regulation of blood flow?
nervoussystemrespondstobloodflow
What is humoral regulation of blood flow?
change in blood flow due to circulating hormones
What is local regulation of blood flow?
change in blood flow due to other substances released by the cells related to their metabolic activity
Is sympathetic, parasympathetic, or both involved in neural regulation of blood flow?
Only sympathetic for correcting low BP, but parasympathetic can be involved too
Where do cardiovascular neurons receive input from for blood flow regulation?
higher brain structures: cortex, limbic system, hypothalamus
peripheral afferent input: baroreceptors, chemoreceptors, proprioceptors
Baroreceptors and chemoreceptors are most important in cardiovascular regulation
Where are baroreceptors located? What takes the signals back to the cardiovascular center?
High pressure:
carotid sinus: cranial nerve IX (glossopharyngeal)
aortic arch: cranial nerve X (vagus)
Low pressure:
walls of right atrium and vena cava: cranial nerve X (vagus)
Explain the baroreceptor reflex response for blood pressure homeostasis. Assume BP is dropping.
BP dops
less stretch is sensed by baroreceptors
signal sent to medulla CV center via CN IX and X (glossopharyngeal and vagus)
triggers sympathetic vasomotor response, sympathetic cardioaccelatory response, and inhibits parasympathetic response
sympathetic vasomotor —> vasoconstriction, more vascular resistance, increase BP
sympathetic cardioaccelatory —> NE released and HR and contractility increase, increase cardiac output, increase BP
Where are chemoreceptors located? How do the signals reach the CV center?
carotid sinus: glossopharyngeal IX
aortic arch: vagus X
What do chemoreceptors respond to (specifically)?
reduced O2 (hypoxia) and increase CO2 or hydrogen ion content
What happens if chemoreceptors sense increase CO2 or decrease O2?
signals sent via cranial nerves, sympathetic vasomotor and sympathetic cardioaccelatory are activated while parasympathetic is inhibited.
Vasomotor—-> vasoconstriction, increases resistance, therefore increase BP
Cardioaccelatory—>increase HR and contractility, increase cardiac output, increase BP
How does increase of catecholamines impact blood pressure? What are the two catecholamines in humoral regulation?
increase HR, SV, and vasoconstriction which increases BP
NE and Epi
Where do the arteries NOT vasoconstrict? Do they have SNS or humoral regulation? How do they manage blood pressure?
brain and heart (little smooth muscle), no SNS or humoral regulation, instead they autoregulate
What are the five other hormones in humoral regulation that we know?
antidiuretic hormone, angiotensin II, aldosterone, histamine, and ANP (atrial natriuretic peptide)
What does antidiuretic hormone do? Where is it released from?
vasoconstriction for extremely low BP, water retention by the kidneys
produced in the hypothalamus
What does angiotensin II do?
Causes intense vasoconstriction when renal perfusion is inadequate
What does aldosterone do?
water retention (so increase blood volume)
Explain the renin-angiotensin-aldosterone system through the point that AT II is produced.
low BP sensed by juxtaglomerular cells in kidney causes release of renin by the kidney
angiotensinogen converts renin to Angiotensin 1
Angiotensin converting enzyme (ACE) in the endothelium of the lung converts angiotensin 1 to angiotensin II
What does angiotensin II cause once it is produced in the renin-angiotensin-aldosterone system?
—>increase sympathetic activity
—> increase water retention, Na+ reabsorption, and K+ excretion
—> vasoconstriction, increase vascular resistance and therefore BP
—> triggers aldosterone secretion by the adrenal cortex which promotes salt and water re-absorption (increase blood volume and raise blood pressure)
—> cause pituitary gland to release ADH which prompts water absorption
What substances from humoral regulation lower blood pressure? How?
atrial natriuretic peptide (ANP) release from the atria when BP is high
inhibits the release of renin (effectively stop the entire renin-angiotensin-aldosterone process)
vasodilation, excretion of salt by kidneys, vascular permeability
reduce blood volume and lower blood pressure
histamine: released by mast cells, causes vasodilation by relaxing smooth muscle
When is histamine especially improtant?
Increasing blood flow to inflamed or damaged tissue
What cells in the kidney detect blood pressure and can kickstart the renin-angiotensin-aldosterone system?
juxtaglomerular cells
What other hormones does angiotensin cause to increase?
aldosterone and antidiuretic hormone (ADH)
