Special Circulation Flashcards
When do the coronaries fill?
diastole
- during isovolumic contraction, the high pressure compresses the LCA
- when ventricle relaxes the aorta recoils and pushes blood into coronaries
What blood vessels of the heart are most sensitive to ischemia? When does this happen?
vessels on the endocardial surface
aortic valve stenosis, regurgitation, CHF cause diastolic pressure to be high
What neural factors determine coronary blood flow?
VERY WEAK regulation
coronaries have small amount of beta 1 receptors: cause contractility and incr HR
What is the main regulator of coronary blood flow?
metabolism- overrides other regulators
-heat metabolizes fatty acid (req lots of O2)
When oxygen supply and demand don’t match, you get ischemia. Describe factors of both
SUPPLY
-diastolic perfusion pressure: if too low decr in flow so decr in O2
-coronary vascular resistance: disease can increase resistance –> decreases flow
DEMAND
-afterload: increases with a dilated heat cuz incr wall tension (cuz stenosis or valve abnormality or incr pressure)
-HR: demands more O2
-contractility: higher incr O2 demand
What is coronary steal?
When a plaque blocks a coronary or blood vessel that region becomes maximally vasodilated (to allow normal flow of blood through the region)
- when person exercises = BAD
- -other regions vasodilate but this one can’t so blood is ‘stolen’ by the normal region (gets redirected)= pain
Name the mechanisms responsible for regulating skeletal muscle circulation
metabolic, mechanical factors, neurohormonal
What is metabolic control in the skeletal muscles?
active hyperemia- when exercise release metabolites which vasodilate to increase blood flow to the area (deliver more oxygen plus get rid of waste)
What are the mechanistic controls of skeletal muscles?
muscle contraction causes compression
can’t keep an isometric compression more than a few minutes cuz increases pressure and could lead to ischemia
-dynamic exercise: use isotonic contractions which increase blood flow
-skeletal muscle pump: compresses veins in periphery –> incr venous return
-respiration: distents abdominal wall, cause negative pressure so have larger venous return
What is the neurohormonal control of skeletal muscles?
*mainly sympathetics
-alpha adrenergic: constriction (lead to greater tone=more venous return)
-muscarinic cholinergics: vasodilation
-Epi
@ high levels- (alpha receptors): constriction
@ low levels (beta receptors): dilation
@ rest: keep low levels
What factors affect cerebral blood flow?
- autoregulation
- tissue pressure (Monro-Kellie Doctrine)
- Metabolism
- ANS
- Cushing’s response
Explain the role of autoregulation in cerebral blood flow
brain is highly auto regulated!
e. g. when stand up the pressure to brain is decreased to precapillary sphincters vasodilate
e. g. when standing on head the pressure increases so pre capillary sphincters vasoconstricts to decr
Explain the role of tissue pressure
Elevation in intracranial pressure will cause vascular compression = more resistance to flow
What is cerebral perfusion pressure (CPP)? What are factors that can affect it?
CPP= mean arterial pressure - intracranial venous pressure
CPP=MAP-IVP
*can be decreased if decr MAP (e.g. shock) or if incr IVP (tumor, hematoma, hydrocephalus)
What is the impact of increasing CSF in the brain?
it increases vascular resistance and decreases blood flow
- normally CSF pressure is same as cerebral venous pressure
- when it increases, autoregulation kicks in and vasodilates arteries to maintain blood flow
- if pressure gets high enough to surpass arterial pressure, can no longer compensate = ischemia
What is the Monro-Kellie doctrine?
Brain volume + Cerebral vascular volume + CSF volume = constant
*have to always keep constant so if one goes up another needs to decrease to even it out
How is metabolism involved in the regulation of blood flow to the brain?
cerebral blood flow is very sensitive to changes in arterial PCO2 [not blood pH cuz H+ can’t cross BBB]
- blood flow is inversely related to pH:
- -low pH: when too acidic (much CO2)- causes vasodilation and incr blood flow
- -high pH: when too basic (low CO2): causes vasoconstriction to decrease blood flow e.g. hyperventilation
Explain effect of ANS on cerebral blood flow
weak sauce!
- local metabolic activity of brain cells has primary control (overrides ANS)
e. g. adenosine, K+ ions, NO
What is Cushing’s response?
happens under pathological conditions
cerebral pressure exceeds arterial pressure so blood flow is decreased –> ischemia
sympathetics to the rescue!
increase blood pressure = get more flow
elevation of intracranial pressure calls parasympathetics to the rescue!
decreases HR
aka head trauma pt has high arterial blood pressure but low pulse
Describe pulmonary circulation in 3 phrases
pulmonary circulation is a low pressure, low resistance, high flow system
What is special about the capillaries in the pulmonary system?
They have a MAJOR influence on vascular resistance (40%)
[got nothing in systemic circulation]
Describe the 2 types of vessels of the pulmonary system
alveolar: inside the walls!
extraalveolar: in between alveolar walls
* inverse relationship: when one constricts the other dilates
How does inspiration affect pulmonary circ?
when breathe in create negative pressure -> suck air in and incr lung volume!
this distends the extra alveolar vessels (less resistance)
–> blood pools
inflate alveoli so the walls compress the alveolar microvessels (incr resistance)
overall: slight incr in pulmonary peripheral resistance
How does expiration affect pulmonary circulation?
when breath out the opposite happens
you constrict the extra alveolar so that pushes blood along to micros! (now open)
you relax the alveoli so alveolar micro vessels open up (less R)
Describe the distribution of hydrostatic pressure in the lungs
greater in lower lung due to gravity
less in upper cuz less gravity ^o^
e.g. that’s why first hear rales @ base
What is the vascular waterfall effect?
Pressure gradient not as easy as in systemic circulation cuz through alveoli into the mix (affect resistance)
*resistance to blood flow is influenced by alveolar P as you move to the top
Describe zone 3 of the lung
alveolar pressure is smallest here! no much effect
arterial>venous>alveolar
flow dep on arterial-venous pressure gradient ^o^ (easiest)
good flow (cuz no extra resistance)
Describe zone 2 of the lung
now the alveolar pressure exceeds the venous pressure (venous no longer has effect)
arterial>alveolar>venous
capillaries are partially collapsed
flow depends on arterial-alveolar pressure gradient…
less blood flow
Describe zone 1 of the lung
now the alveolar pressure exceeds both! alveolar>arterial>venous capillaries are completely collapsed :( NO BLOOD FLOW! *only exists under abnormal conditions
Under what conditions would you have zone 1?
hypotension (arterial pressure decreases)
or
positive mechanical ventilation (alveolar pressure increases)
What is the main regulator of cutaneous circulation?
neural control!
What is the main function of cutaneous circulation?
to maintain a constant body temperature
How does skin color reveal blood flow?
pale: low blood flow
cyanotic: desaturated Hb
reddish: fully saturated Hb
bright pink: CO poisoning
Why do you get red in cold weather?
low temperatures decreases dissociation of oxygen from Hb so you have more oxyhemoglobin
What are the two types of resistance vessels on the skin?
arterioles: controlled by sympathetic and local reg factors
arteriovenous anastamoses: shunts blood from arterioles to venules/venous plexuses –> bypasses capillary beds!
-exclusively regulated by sympathetic innervation
What are the two types of skin?
- Apical: nose/lips/ears/fingertips/hands/feet- favors heat loss. has special AV anastomoses called “glomus bodies”
* lotz of flow, allow lost of heat! - Nonapical: rest of body. very few AV anastomoses
- innervated by sympathetic fibers that release Ach = vasodilation
* sweat
Describe the neural control of skin
apical: innervation by sympathetic adrenergic
@ rest: vasoconstriction (if take away sympathetics then vasodilation
nonapical: sympathetic vasoconstriction (NE) + sympathetic cholinergic (active vasodilation)
*release Ach->sweat glands release bradykinin-> vasodilation
Explain temperature regulation.
Increase in internal temperature: withdraw sympathetics
=vasodilation (incr blood flow)
decr int T: activate sympathetics
=vasoconstriction (dear blood flow)
What happens during heat stress?
- skin is vasodilated to help maintain T (lose heat)
- problemo? baroreceptors are trying to constrict to maintain blood pressure
- > wasting blood going to the skin X3
Explain the countercurrent flow system
- arterioles and venues run parallel
- solutes (Na+) absorbed in capillaries pass into venules and can diffuse into interstitium and then into arterioles
- since have extra salt absorb more water -> incr blood flow
- this helps reabsorb more water!
What causes of portal hypertension/ascites?
anything that backs up pressure into the IVC e.g. right heart failure
-leads to incr pressure back into the splanchics
or any liver damage! will incr portal pressure that will back up and cause ascites
What regulates intestinal blood flow? (5)
- metabolism: increases when break down food so vasodilators to bring more blood flow
- mechanical: peristalsis- dont really incr blood flow
- hormonal: e.g. neurotensin vasodilate
- neural: postganglionic sympathetic vasoconstriction though NE on alpha receptors (to send blood to vital organs)
- b receptors: vasodilation
* no parasympathetics innervate directly: but stimulate peristalsis and gland secretions -> incr metal -> incr blood flow - postprandial hyperemia: eating increases intestinal blood flow so take away from other areas -> feel tired!
What are the origins of the placenta?
mom: endometrium
baby: chorionic sac
What’s the function of the foramen ovale?
shunt blood b/w atria!
Describe fetal blood flow
fetal branch villi->umbilical vein->ductus venosus(bypass liver)->IVC->RA->foramen ovale->LA->LV->aorta
What happens if some blood enters RV?
goes into pulmonary artery but the lung pressure si super high so forces the blood into the ductus arteriosis -> systemic circulation
What happens when you clamp the cord at birth!?
- decr P of umbilical vein and therefore RA
- clamp umbilical arteries: incr systemic vascular resistance -> incr P on left heart -> incr P of LA
- combination: decr flow cross foramen ovale and shuts it ^^
What happens when a baby takes the first breath?
alveoli open! capillaries open! pulmonary vascular resistance drops
-easier for blood to flow into LV and lungs
Why is it important for the newborn to cry and move?
it increases systemic pressure so decreases flow across ductus arteriosus
*lungs produce bradykinin to close ductus arteriosus
