BME 2101 Test 3
equation for flow resistance?
(8*mu*L)/(pi*a^4)
diameter of arterioles
10-15 micrometers
diameter of capillaries
5-9 micrometers
mean circulatory filling pressure (MCFP) and systemic filling pressure (Psf) at rest?
7 mm Hg
The normal operating point for the carotid baroreceptors is
90-100 mm Hg
Cholinergic
Acetylcholine using nerves
In an animal experiment to study control of mean arterial pressure, we ligate the glossopharyngeal nerve. If we infuse i.v. fluid to increase blood volume, what compensatory changes will we observe that attempt to return venous storage volume to normal?
Bainbridge reflex
Within 30 sec after a heart attack, which of the following are primary reflex responses?
Decreased MAP causes arterial baroreceptors to release sympathetic inhibition. Hypoxia causes arterial chemoreceptors to stimulate sympathetic tone. CNS ischemia causes cerebral chemoreceptors to stimulate sympathetic tone.
In response to an acute loss of blood volume, which of the following are primary responses?
Decreased MAP causes arterial baroreceptors to release sympathetic inhibition. Hypoxia causes arterial chemoreceptors to stimulate sympathetic tone. Decreased capillary pressure leads to fluid resorption.
Cardiac output increases with age throughout our lifetimes. T or F?
F
By what mechanism does venous pressure (Pv ) determine cardiac output?
Frank-Starling
Cushing reaction
Increase in intracranial pressure causes compression of blood vessels--> baroreceptors are triggered--> reduce the inhibition of sympathetic stimulation/increase in parasympathetic--> less vasodilation and more vasoconstriction--> increase in MAP
equation for net filtration pressure
NFP = Pc - Pif - (PIc - PIif)
Mean arterial pressure is related to cardiac output using what law?
Ohm's Law
When both the hydraulic pressure difference (ΔP = Pc - Pif) and the osmotic pressure difference (Δπ = πp - πif) are taken into consideration, which way does fluid flow across the capillary wall?
Outward, because ΔP > Δπ
What can cause tissue swelling?
Pc increases πp decreases ΔP increases Δπ decreases
The hydraulic pressures acting on fluid near the capillary wall include capillary fluid pressure acting in the outward direction (Pc) and interstitial fluid pressure acting in the inward direction (Pif). Which one is bigger? Which way would fluid flow across the wall on average if no other forces were purshing fluid?
Pc>Pif so fluid would flow outward
When blood volume decreases, as in acute hemorrhage, what is the primary effect the venous return curve?
Psf decreases
After a heart attack, how does reduced MAP due to compromised cardiac function affect the venous return curve (vascular function curve)?
Psf increases
What happens to the venous return (vascular function) curve after increased sympathetic stimulation of veins?
Psf increases, shifts right
write an equation for venous pressure
Pv = MCFP - (TPR/(1 + Cv/Ca))CO
What is most of the interstitial colloid osmotic pressure due to?
The plasma protein albumin
Aortic pulse pressure in a patient is measured to be 90 mmHg. Which of the following could be an explanation?
The pressure pulse is larger than normal because of arteriosclerosis, a condition that decreases vascular wall compliance.
To test your hypothesis that the myogenic theory is responsible for autoregulation when the endothelium is denuded, what could you do to show that smooth muscle contraction is responsible?
Treat with a vasodilator or remove extracellular Ca2+
What is edema caused by?
accumulation of fluid in the interstitium
What is the neurotransmitter released by all preganglionic nerve fibers?
acetylcholine
In the autonomic nervous system, signals usually travel through 2 nerves before reaching the target organ. What is the one exception in which an organ replaces the postganglionic nerve?
adrenal glands
reactive hyperemia
after brief ischemia, blood flow temporarily increases more than normal temporarily (caused by metabolic theory because blood vessels dilate)
One strategy to manage hypertension is to take an ACE inhibitor, which blocks production of which vasoconstricting hormone?
angiotensin II
vasoconstrictors
angiotensin II, norepinephrine, epinephrine, vasopressin, endothelin
direction of blood flow
arteries, arterioles, capillaries, venules, veins
"resistance vessels"
arterioles
Do central or local mechanisms win in skeletal muscle?
at rest, central vasodilation wins during exercise, local vasodilation wins
Suppose that mean carotid artery pressure increases to 140 mmHg while you are doing a handstand. What mechanism returns mean pressure to normal?
baroreceptor reflex
sympathetic receptor
beta 1 adrenergic
atropine
blocks muscarinic receptor, can be used to treat heart heart failure
curare
blocks nicotinic receptors, signal can't be transmitted to the ganglion
If blood volume decreases, then what happens to venous pressure and cardiac output?
both decrease
If blood volume decreases, then what happens to venous pressure and cardiac output? Draw function curves to help you arrive at an answer.
both decrease
when diameter increases, what happens to resistance? to pressure?
both decrease
What factors are negative inotropic, i.e., shift the cardiac function curve downward?
calcium channel blockers (verapmil, diltiazem, nifedipine), low extracellular calcium, high extracellular sodium, hypertension, arrhythmia, coronary artery blockage, valve disease, hypoxia
A soldier wounded in battle is losing blood volume, and mean carotid artery pressure has dropped to 60 mmHg. What reflex feedback mechanism will be activated to try to return mean pressure to normal?
carotid chemoreceptor reflex
In response to hypoxia, carotid chemoreceptors
cause vasoconstriction.
beta 1 adrenergic receptors
causes increased heart rate and increased contractility
Do central or local mechanisms win in skin?
central vasodilation
+NFP
change in fluid pressure is greater than change in osmotic pressure, fluid pressure inside the capillaries is greater than outside, fluid flows from high pressure to low pressure, so fluid will flow out of capillaries
-NFP
change in osmotic pressure is greater than change in fluid pressure, osmotic pressure inside the capillaries is greater than outside the capillaries, water moves from low pressure to high pressure, fluid will flow into the capillaries
A mountain biker involved in a wipeout hit his head on the ground during the fall. At the ER, the biker is diagnosed with swelling in the brain near the point of impact. Explain two mechanisms that might be at work to maintain blood flow to area of the brain experiencing edema.
chemoreceptor reflex and Cushing reaction
compliance of veins versus arteries
compliance is change in volume over change in pressure Cv=19Ca
alpha 1 adrenergic receptors
constricting arteries and arterioles
If myocardial contractility increases, we expect cardiac output to increase. What happens to venous filling pressure? Draw function curves for yourself to help you arrive at an answer.
decreases
If total peripheral resistance increases, then what happens to cardiac output? Draw function curves to help you arrive at an answer.
decreases
what happens to blood vessel diameter when you increase tone?
diameter increases
Possible pathways for solute transport across capillary walls?
diffusion through intercellular clefts, transcytosis using caveolae, diffusion through fenestrae, diffusion through cell membranes and cells
beta 2 adrenergic receptors
dilates airways and arterioles
how are pressure and resistance related?
directly proportional
The active contraction curve (which is the upper bound of the left ventricle P-V loop) relates the maximum pressure (or force of contraction) that can be generated at a given LV volume. This curve is a representation of
frank-starling
In general, physiological hydrostatic pressure gradients tend to push fluid...?
from the capillaries into the interstitial fluid
Increased venous return stimulates atrial stretch receptors, causing
heart rate to increase (the Bainbridge reflex).
Pressures from highest to lowest? (capillary, arteriole, venular)
highest=ateriolar middle=capillary lowest=venular
metabolic vasodilator theory
if metabolism in the tissue increases or if flow rate through the blood vessel slows down, the cells release a neurotransmitter that will dilate the arterioles, which will increase flow/oxygen delivery
Sympathetic ganglia are mostly located
in a "chain" of cells next to the spinal cord.
increase in blood volume causes what change in venous return graph?
increase in Psf/MCFP, graph shifts right
Bainbridge reflex
increased blood volume in atria--> increase HR
minimizing blood volume affect on MAP
increased blood volume--> vasodilation, decrease in heart rate, decrease in contractility, decrease in MAP
Decreasing arterial wall compliance without changing venous wall compliance would cause
increased cardiac output at a given preload.
If total peripheral resistance decreases, then what happens to cardiac output?
increases
how does arterial vasoconstriction affect VR curve?
increases resistance, flatter VR curve slope
In response to increased mean arterial pressure, baroreceptors
inhibit sympathetic stimulation
what is autoregulation
keeping flow rate constant over a range of pressures
why is the rate of diffusion of solutes faster in the kidneys than in the brain?
leaky junctions vs tight junctions
Do central or local mechanisms win in brain and heart?
local vasodilation
is oxygen a vasoconstrictor or vasodilator?
locally, for example during exercise, oxygen is a vasodilator, but if oxygen concentration gets low enough, the central control system takes over and oxygen becomes a vasoconstrictor
chemoreceptor signaling
low pressure--> hypoxia--> chemoreceptors in aortic arch or carotid sinus detect the change in pressure due to stretch--> afferent nerves (Hering's nerve, glassopharyngeal nerve) --> vasomotor center (medulla)--> efferent nerves --> peripheral vasoconstriction (to preserve oxygen content in brain and heart)
why do feet swell on plane?
lymph pump isn't working to drain interstitial fluid
how to measure rate of solute diffusion across capillaries
mass flux Fick's 1st Law J=-P*delta c (mass flux = permeability * concentration gradient)
Baroreceptor Signaling
mean arterial pressure increases--> baroreceptors in aortic arch or carotid sinus detect the change in pressure due to stretch--> afferent nerves (Hering's nerve, glassopharyngeal nerve) --> vasomotor center (medulla)--> efferent nerves --> vasodilation, HR decreases, contractility decreases
The pressure that would exist everywhere in the peripheral circulation due to filling it with a normal volume of blood is called the
mean systemic filling pressure
adrenergic neurons
most sympathetic post-ganglionic neurons
parasympathetic receptor
muscarinic
What increases lymph flow?
muscle pump activity, increased interstitial fluid pressure, coordinated contraction waves of smooth muscle in the wall of lymphatic vessels
While watching TV, your dog is resting his head on your arm. After a while, you feel like your arm fell asleep and the dog needs to move. When the dog moves his head, you notice that the spot on your arm where he was resting turns red for a few minutes. What is happening? (check all that apply)
myogenic response vasodilation reactive hyperemia
In a rat experiment to study blood flow regulation in skeletal muscle, you accidentally scrape the endothelium on the inside of the artery with your catheter. However, you notice that when you increase the pressure inside the artery, it maintains its diameter anyway. What mechanism maintains the diameter?
myogenic theory
general nerve signaling pathway
nerve cell body in central nervous system--> pre-ganglionic nerve--> peripheral ganglion--> post-ganglionic nerve--> target organ
acetylcholine
neurotransmitter for all pre-ganglionic nerves, sympathetic and parasympathetic also the post-ganglionic nerve for all parasympathetic nerves
preganglionic receptor
nicotinic
how do endothelial cells act on smooth muscle cells to cause vasodilation?
nitric oxide (second messenger)
vasodialator that acts directly on smooth muscle, doesn't require endothelial cells
nitropresside, it mimics NO
Sodium nitroprusside is a vasodilator that acts directly on vascular smooth muscle cells to cause them to relax. In the presence of nitroprusside, what effect would endothelial cell release of nitric oxide have?
no effect
sympathetic post-ganglionic neurotransmitter
norepinephrine
overall, does water move into or out of capillaries? Is this filtration or absorption?
out of capillaries because fluid pressure is greater than osmotic pressure, so NFP will be positive. this is called filtration
parasympathetic nerve signaling pathway
post-ganglionic nerve= in or near the target organ, vagus nerve is the pre-ganglionic nerve
sympathetic nerve signaling pathway
post-ganglionic nerve= sympathetic chain/paravertebral, exception: adrenal gland, no post-ganglionic nerve, directly to blood stream
Atropine blocks muscarinic cholinergic receptors, which leads to increased heart rate and contractility. Which nerve signals are blocked by atropine?
postganglionic parasympathetic
You set up another artery experiment in which you are sure that the endothelium is intact. You hypothesize that the metabolic theory is responsible for autoregulation in the artery. You temporarily occlude the feed artery and then release the occlusion. The flow rate after you release the occlusion increases temporarily then settles to an intermediate value. What is this phenomenon called?
reactive hyperemia
paracrine
released by a cell and acting on its neighbor
autocrine
released on a cell and acting on itself
when pressure decreases, what happens to resistance to keep flow rate constant?
resistance decreases (F=deltaP/R)
A good measure of venous return is
right atrial pressure or another measure of preload
If we want to relate venous return to preload, then what is a good clinical measure of preload?
right atrial pressure, venous pressure, LVEDV, LVEDP, RVEDV, RVEDP
vasodilators that act on endothelial cells, which then act on smooth muscle cells
sheer stress from pressure in arterioles, acetylcholine, histamine, bradykinin, adenosine, carbon dioxide, potassium ions, hydrogen ions, lactic acid, prostaglandins
net filtration rate equation
starling hypothesis net filtration rate = Kf * NFP
Normal cardiac output and right atrial pressure occur where the cardiac function curve and the venous return curve intersect. This point is known as (two different names)
steady-state operating point or equilibrium point
What is the response to brain ischemia?
strong sympathetic stimulation--> vasoconstriction--> increase in HR and contractility hypoxia--> chemoreceptors--> increase in sympathetic Cushing reaction: increase in intercranial pressure--> baroreceptors--> de-inhibit sympathetic stimulation--> increase pressure in capillaries to prevent them from collapsing
If total peripheral resistance increases and, as a result, venous pressure decreases, what mechanism would enable cardiac output to return to normal?
sympathetic stimulation to increase cardiac contractility
What factors are positive inotropic, i.e., shift the cardiac function curve upward?
sympathetic stimulation, adrenergic agonists (NE, epi), cardiac glycosides (digitalis), high extracellular calcium, low extracellular sodium, hypertrophy
During a heart attack (myocardial infarction), part of the ventricular muscle is damaged and does not contribute to pump function. What is the instantaneous effect on the cardiac function curve?
the curve shifts down
what prevents edema?
the fluid is taken in by the lymph vessels and returned to the circulation
What is Starling's Law of filtration?
the rate of fluid movement across the capillary wall as a function of the balance between hydrostatic and osmotic pressures
If venous return to the heart increases, then
the slope of the cardiac function curve does not change.
function of capillaries
to exchange of materials such as oxygen & carbon dioxide between plasma and interstitial fluid
myogenic theory
transmural pressure (difference in pressure from inside artery walls to outside) increases--> smooth muscle contracts/SM tone (state of contractility) increases--> vasoconstriction
equation used to show osmotic pressure
vant hoff's law pi = phi * i * c * R * T
What are effects of sympathetic stimulation?
vasoconstriction--> more resistance--> venous return curve gets flatter cardiac output curve shifts right--> Psf increases
if blood volume is increased and arterial stretch increases, what are the main results?
vasodilation, decrease in contractility, decrease in MAP, HR stays constant, increase in urine volume
Volume reflex
vasodilaton in kidneys--> increase in capillary pressure downstream--> increase in filtration--> increase in urine volume decrease in anti-diuretic hormone (ADH)--> increase in urine volume increase in atrial natriuretic peptide (ANP)--> increase in urine volume
"blood volume storage vessels"
veins
According to the Frank-Starling mechanism (also known as Frank-Starling law of the heart), cardiac output increases as
venous return increases
flow resistance is most sensitive to which parameter?
vessel radius radius increases, flow decrease radius decreases, flow increases
metabolic oxygen demand theory
when metabolism goes up (oxygen concentration goes down=hypoxia), the vessels dilate
what is the continuous smooth muscle layer?
wraps around arterioles to regulate vessel diameter vasodilation or vasoconstriction
The osmotic pressures acting on fluid near the capillary wall include plasma osmotic pressure inside the capillary (πc) and interstitial fluid osmotic pressure outside the capillary (πif). Which one is bigger? Which way would fluid flow across the wall on average if no other forces were pushing fluid?
πp > πif, so fluid would flow inward
