Physiology 12.12.12 Peripheral Circulation (Hawkins) Flashcards
What is the CO of adults at rest
5.4 L/min
What is avg blood flow for body weight 70kg
7.7 ml/min per 100 g of tissue
However, BF varies greatly between tissues
Which organs receive the most Blood flow(mml/min)
Liver>Muscle>Kidney > Brain
Do brain and kidney receive proprotionate BF as predicted to their weights?
NO!
BF accts for only 0.5% of body weight for 20% CO, brain acts of only 2% of body weight for 14% CO
GI, Spleen, Liver (splanchnic bed) acct fr 2-3% body wieght but receive 25% CO at rest
Which organ receives the most Blood flow (ml/min/100gm)
Kindey
Does brain use the same amt of BF all day long?
Yes!
Does heart use same amt of BF all day long?
NO! Uses more blood during exercise
What is BF at rest? Max CO? Max Dilation?
BF rest = 5 L/min
Max CO = 20L/min
Max dilation = 38 L/min
What is Max dilation?
If all tissues were being perfused at the same time
This is more than the heart can delvier so has to be regulated
Describe the mechanims of BF distribution as the reservoir and faucet
High-presure reservoir function is served by the arterial system
Arterial BP is generated by the heart’s pumping action
Vascular or Arteriole Tone. What causes it?
Arterioles, if not all, vascular beds are partially constricted at any given moment.
This is referred to as vascular tone, and is caused by continuous sympathetic stimulation as well as myogenic contration
How/when does blood flow in beds increase?
by dilating its arterioles in response to metabolic needs
How does the sympathetic NS innervate teh heart? Through what receptors?
What does it do to CO
SNS innervates and stimulates both the chronotropic (rate) and inotropic (contractility) effects on heart medaited by B-1 adreneric receptors, increasing CO under most conditions
How does Symp NS affect Large Arteries? Whch receptors?
Mediated through the alpha-1 receptors
Makes arteries LESS COMPLIANT (stiffer)
Causes an immaterial reduction in diameter (not htat big fo a change in radii)
What does Sympathetic NS do to Veins (large)
Densely innervated by Sympathetic NS
Mediated by alpha-1 R
Makes much less compliant (stiffer)- like vena cava
Increase Central and Peripheral Venous Pressure
Sends Venous Return to heart and Right Atrium!!!!
How much blood do the veins usually contain?
2/3 of the blood supply
How does the Sympathetic NS affect Arterioles? Resistance? BF? Capillary Hydrostatic P? Total Peripheral P? MAP?
Densely innervated by SNS
Mediated through alpha-1 receptors
**PRIMARY MECHANISMS OF SNS On PERIPHERAL CVS
Arterioles contract (reduce diameter)
- Resistance to flow increases (constant P)
- BF decreases (at constant pressure)
-Capillary pressure may drop, which favors REABSORPTION
Total peripheral resistance may increase
MAP Incerease
What is the affect of Sympathetic NS on Adrenal Meduall
Adrenal Medulla releases Epi (80%) and NE (20%)
Essentially a peripheral ganglion on SNS
What does circulating Epi do to cardiac receptors
B-1 receptors
Causes positive inotropic and chronotropic effect
What does high doses of Epi bind to?
alpha-1 R in peripheral vesels and mimics effects of sympathtic stiumaltion (This is PREFERRED) and B-2 is masked
Binds to beta-2 receptors in Skeletal muscle arterioles
What does low doses of epinephrine pereferentially bidn to?
B-2 receptors and produces VASODILATION
What are sympathetic cholinergic fibers? What do they innervate
Limited to Sweat glands and Arterioles of muscles
Release ACh- Muscarinic R
- Dilation of Arterioles
- increase sweating
Little effect on conrol of BP or Flow to other tissues
Role of Parasympathetic NS - how doees it control heart rate
Controls heart rate through INHIBITION (SA node, AV node)
PS on arteries, veins, arterioles
PNS does NOT innervate arteries, veins, or arterioles throughout the body, and therefore, has no material efefct on BP by this mechanism
What does PNS innervate
Genital Organs, Bladder, Colon
What are some molecules (in addtion to Epi and NE) that affect vascular system (3)
Angiotensin II
Vasopressin
Histamine
What is the affect of Histamine. Which side of capillary is most affected
Increases capillary Permeability
Mast cells and basophils; leaks into tissue, Decrease oncotic P – >fluid goes OUT of capillary
Most affected are on Venous side; His causes endothelial cells to separate and thus to create discrete intercellular gaps
Plasma escapes through gaps and into intersitium
Is the effect of Histamine great?
No! only minor
Affect of Angiotensin II
Strong Vasoconstrictor
peptide hormone that cuases BV to cconstrict and increase BP
What is precursor of Angiotensin
Globulin that is produced constitutively and released to circulation mainly by the liver
What converts Angitensinogen to Angiotensin I
Renin form kidneys
What converts Angiotensin I to Angiotensin II?
ACE- angeiotensin-converting enzyme pirmarly through ACE activity within teh kidney
What is the affect of Vasopressin
AKA Antidiuretic hormone, ADH is a homrone repsonsible for increasing water reabsorption by kidney
COnserves Vascular volume
What are ways of Local Regulation of BF
- Autoregulation
- Active Hyperemia (metabolic regulation)
- Reactive Hyperemia (Metabolic Regulation)
What is Autoregulation?
intrinsic action of SM
How is BF regulated by metabolites
Involve changes in tissue BF that can be demonstarted in teh absence of Sympathetic input or humeral agents
This leads to conclusion that local factors can control tissue BF directly
What is active hyperemia?
Blod flow is comensurate with tissue need for energy) Sk muscles BF increases with exercise! The magnitiude of increase in tissue BF is commensurate with the O2 consumption of the tissue.
Increased metabolism creates byproducts that are vasodilators
What are vasodilators that are created as byproducts to increased metabolism
CO2, H, K, lactate, adenosine
Local arterioles respond by dilating
What is Reactive Hyperemia
Blood flow is restricted temporarily and tehnt ehre is an increase when vessels are open afterwords’’
The magnitude of hypermia occurring parallels the extend of BF deprivation during the occlusion
What is the mechanism behind active and reactive hypermia?
Related to metabolic changes in the tissue.
Tissue metabolism consumes O2 and feuls (glucose, FA, etc), produces CO2, and releases K and H, Lactic Acid, Adenosine,etc
In teh absence of adequate BF, ions and metabolites accumulate.
What does low O2 content do?
hypoxia can produce vasodilation
In absence of adqueate BF (due to elevated metabolism or occlued BF) , these metaboltes accumulate resulting in vasodilation
When BF restored, vessels dilate ad flow is elvated until metabolites have been washed out.
What are various metabolites resp for metabolic regulation
Lactic acid H Adenosine NO (endothelial-derived releasing factor) K+
What does it mean to have myogenic autoregulation of blood flow
In many tissue beds (kidney), blood flow does NOT change much despite the large changes in Arterial Pressure
Kidney retains a nearly constant BF over a broad range of arterial pressures (90-180 mmHg)
What does the alteration in arterial pressure have a direct effect on?
on teh resistance of renal arterioles
Reducing arterial Pressure also Reduces vascular resistance –> maintaining BF near constatn
Increase in Pressure in renal artery increases Renal Vascular Resistance
Describe how Myogenic autoregulation works in kidney
Kindey’s BF greatly exceeds its metabolic need.
An increase in stretch of arterial SM, (by Inc Arterial P) has the effect of causing Contraction of the SM –> producing an increase in vascular resistance, thereby minimizing an increase in BF
Describe local regualation of kindey
Almost exclusively MYOGENIC REGULATION
BF is near constant between Pa of 90-180 mmHg
Local regulation of Brain and Heart
Almost exclusively METABOLIC REGULATION
Local regulation of Skeletal Muscle
Combines both mechanism
Under Strong Sympathetic Control, but as energy demand increases,metabolic regulation predominates
Describe the control of arterial pressure
Arterial system is a hihg-pressure reservoir of Blood from which the tissues can draw on demand
There is a limit to the quanitty of flow that can be supplied from this sytem, yet heart and arterial sys can supply sufficient BF to tissues over a wide range of dmeands
What is the Arterial Baroreceptor Reflex
Single most important mechanism for short-term control of ARTERIAL Pressure
Where are pressure receptors for Baroreceptors located. Where does afferent run? Where does integration occyr. Efferent?
Located in Carotid arteries and Aortic Arch
afferent neurons running to CN medulla
Integration occurs in the medulla.
Efferent pahtway fo refelx involve bot PS and SYmp
Describe how Arteria BaroR Reflex works
Rise in Arterial P == Inc neural input to medulla –> Increase in PS activity (through vagus) and decrese in sympt
REDUCE ARTERIAL PRESSURE
What is the EFFERENT pathway of the Arterial BaroR Reflex
Symp and PS
PS = heart slow
Symp = increase heart rate and contractility and arteriolar constriction
Describe the CNS integration of BaroR Reflex.
Where do axons synapse?
What kind of synapse (excitatory or inh) what NT
Input from Pressure Receptors (AP) ascend to the medulla, via axons of teh glossopharyngeal and vagus nerves, bilaterally
Axons synapse in two bilateral nuclei (NTS) in teh medualla–> excitatory synapse that employs GLUTAMATE (though tehe are both inh and exc from other palce)
Where does NTS neurons send axons to?
bilateral vagal nuclei and the midline cardiovascular center
What do AP coming form NTS stimulate?
Vagal nuclei
esp Dorsal Vagal Nucleus and Nucleus Ambiguus
These inc PS output via vagal nerves
What do Efferent AP from NTS influence?
medullary sympathetic pacemaker region located in teh RVLM via innervation of the CVLM
What does stimulation of NTS inhibit?
activity of SymP NS
ARTERIAL BAROR REFLEX
Which is more sensitsive? Carotid BaroR or Aortic Arch R?
Baroreceptors respond more strongly to changing (pulsatile pressure) than to constant pressure
BaroR response parallels mean pressure within a limited range
Carotid baroR are more sensitive to change than aortic arch R
Does BaroR reflex respond rapidly wihin a single pulse?
Yes
Hypothalamic Regions
Inc in temperatue
Integrat heart rate and BP in response to emotion-evoking situations
Also elevation of Temperature of anterior hypothalamus eleicits signals taht depress CV center –> actviatind vas mechanisms of heat loss (vasodilation and sweating)
How does output of hypothalamus affect baroR reflex?
By acting on the NTS nuclei
What kind of receptors are those that monitor arterial pressure?
Where are they located
Stretch Receeptors
Located in teh wall of Aortic Arch and Carotid sinus that are stimualted by stretch
Where are Carotid Sinuses Located
both sides of neck near bifurcation of the internal and external carotid arteries
When are AP initiatied
when nerve endings are stretched, such as woudl happen as arterial pressure rises
THis stimualtes vagal nuclei and increases PS output
What are Cardiopulmonary BaroReceptors and what are the function?
Stretch receptors respond to absolute pressure in the atria and pulmonary veins.
They discharge at lower pressures than teh arterial baroreceptors, on reaching the brain, the impulses initiate a similar response
Elevated cardiopulmonary pressure inhibits sympathetic output
Wher eare Cardiopulmonary Reflexes located
in the walls of heart (atria, ventricles),
Great Vessels (vena cava)
and lungs
Respond like baroreceptors but at lower pressures;
Capable of adapting to sustained pressures
What are Peripheral ChemoReceptors.
What happens duing asphyxia
Located in Carotid and Aortic Bodies
Main function is with REspiration
Responds to :
Increased PaCO2
Increased H+
Decreased PaO2
By stimulating Sympathetic System (Inc BP and Vasoconstriction)
When baroreceptors and peripheral chemoreceptors are stimualted, whicih predominates?
Baroreceptors
What is the Brainbridge reflex
An increased stretch of Right Atrium can sometimes increase Heart Rate when HR is SLOW
What mediates Bainbridge reflex
Vagal Afferents from heart to CV center
and Sympathetic efferents to teh heart
What is the main mehcanism for maintaining a uniform cardiac output on both sides of heart?
Frank-Sterling Mechanism
What is unusual about transplanted hearts, which do not hav ea Bainbridge reflex
Shows no imbalance
Where is the location of the best possible sites for monitoring and controlling arterial pressure
IN aortic arch
and right and left internal carotid arteries 3
