special circulations

coronary circulation- characteristics and anatomy

• left coronary artery

  • left atria

  • left ventricle

• right coronary artery

  • SA node

  • right atria

  • right ventricle

coronary circulation- special tasks

deliver O2 to match myocardial demand. increases max blood flow

coronary circulation- structural adaptations

• very high myocardial capillary density

• myoglobin brings O2 to the mitochondria

• increase capillary number and width

coronary circulation- functional adaptations

• high basal blood flow driven by NO

• high O2 extraction

• fatty acids are the substrates

• metabolic hyperemia does vascular regulation

• good autoregulation

coronary circulation- blood flow

blood flow increases a lot from rest to max

coronary circulation- special problems

• coronary ostia: systole obstructs blood flow

• coronary arteries are function end arteries

• prone to atheromas

coronary circulation- metabolic hyperemia

vasodilators are released as work increases

coronary circulation- neural control

• alpha 1 maintains vascular tone at rest

• Beta1 is in cardiac myocytes

• beta does vasodilation

skeletal muscle circulation- characteristics and anatomy

resistance vessels have high resting tone

skeletal muscle circulation- special tasks

• delivers O2 and nutrients in proportion to work rate of skeletal muscle

• regulate blood pressure by regulating TPR

skeletal muscle circulation- structural adaptations

• high capillary density

  • can depend on the muscle type

skeletal muscle circulation- functional adaptations

• metabolic hyperemia

  • local increase in blood flow to tissue that occurs when cellular metabolic activity increases from resting to active

skeletal muscle circulation- control of blood flow

large range of blood flow but the jump from resting to exercise is not as great

skeletal muscle circulation- special problems

• decreased blood flow with contraction

  • as muscle fibers contract the pressure inside the muscle increases, compressing the blood vessels

• increased capillary filtration with exercise

  • leads to edema

• atheroma induced ischemia= intermittent claudication

  • with exercise, muscles need lots of O2 and when the muscle can’t keep up with O2 it becomes deprived

skeletal muscle circulation- neural control

• dominates at rest

• alpha 1 does vasoconstriction

• dilation is caused by withdraw of SNS

skeletal muscle circulation- metabolic control

dominates during physical activity

skeletal muscle circulation- exercise induced hyperemia

• varies in proportion to intensity

  • increase in blood flow during physical activity to match heightened demands

• mechanisms that regulate

  • induced sheer stress increases NO

  • increased metabolites

  • functional smpatholysis

skeletal muscle circulation- functional sympatholysis regulates exercise induced hyperemia

• SNS is activated in exercise

• within active contracting muscles, local metabolites blunt constrictor signals

• increased blood velocity and sheer stress stimulate release of vasodilators

skeletal muscle circulation- chronic aerobic exercise training

• induces adaptive changes in skeletal muscle circulation

  • increases blood flow capacity

  • improves O2 diffusion capacity

  • prominent in conduit arteries (large arteries like the aorta)

• regulating mechanisms

  • angiogenesis: creating new capillaries

  • vascular remodeling to increase length and diameter

  • increase CNS expression

    • improves flow mediated dilation

splanchnic circulation- characteristics and anatomy

• arterial blood supply of intestine, pancreas, spleen, liver

  • feeds into hepatic portal vein

• low basal sympathetic tone

splanchnic circulation- special tasks

• blood reservoir- SNS mediated veno/vasoconstriction

• movement of water for secretions

• maintenance of plasma oncotic pressure by albunin

• detoxification

• immune

splanchnic circulation- adaptations

• discontinuous capillaries in the liver called sinusoids

  • maximize metabolic exchange between the blood and liver tissue

• high CO at rest (25%-30%) for metabolic need

splanchnic circulation- control of blood flow

metabolic hyperemia predominates

splanchnic circulation- special problems

• portal hyopertension- increase of BP in hepatic portal vein

  • increases blood volume→ increased resistance

  • cause in US is cirrhosis (caused by alcohol)

  • increase filtration out

  • symptoms: ascites (abdominal swelling), spleenomeagly, protosystemic shunts

splanchnic circulation- neural control

• sympathetics

  • Alpha 1 constricts

  • Beta 2 dilates

cerebral circulation- characteristics and anatomy

• 15% CO and 20% resting O2 consumption

• encased by bones so can only swell downwards

cerebral circulation- special tasks

• maintain O2 delivery to the brain at all costs

  • the brain is very sensitive to hypoxia

• adapt to changes in neuronal activity

cerebral circulation- structural adaptations

• circle of willis

  • protects and allows for alternative path of blood flow if one is blocked

• high capillary density

  • short diffusion distance

• blood brain barrier

  • limits starling forces, decreasing filtration

• segmental vascular resistance

  • large and small arteries contribute to resistance

  • they are protective and help maintain a constant blood flow

cerebral circulation- functional adaptations

• high basal blood flow

• high O2 extraction

• brain safeguards its own blood flow

  • built in system to keep well regulated supply of O2 and nutrients no matter what

• blood flow is mainly regulated intrinsically

  • highest autoregulation

  • functional hyperemia sends blood to active neurons

cerebral circulation- control of blood flow

• most blood flow goes to the gray matter which is cell bodies and neurons

cerebral circulation- special problems

• atheroma

• hemorrhage

• vascular dilation

• breakdown of blood brain barrier= vasogenic edema

  • fatal accumulation of fluid

  • mechanisms

    • physical disruption of barrier (systemic hypertension)

    • high altitude and inflammation

  • swelling can lead to cushings reflex

    • increased intracranial pressure due to trauma

    • mechanical compression of brainstem

    • triad of symptoms: hypertension (SNS constrict to maintain blood flow) bradycardia due to baroreflex and irregular respiration

• cerebral infarct (stroke)

  • causes are

    • thrombo-embolic stroke

    • hemmoragic (subarachnoid, intracerebral and subdural)

cerebral circulation- neural control

ANS has very weak involvement

pulmonary circulation- characteristics and anatomy

• high flow, low pressure circuit

• 2 circulations

  • pulmonary

    • right ventricle to lungs, 200% of blood flow

  • bronchial

    • arises from the aorta empty into pulmonary vein

    • part of systemic

    • carry oxygenated blood

    • supplies supporting tissues

pulmonary circulation- special tasks

• efficient gas exchange of CO2 out of capillary and O2 into

  • large capillary gas exchange

  • normal pulmonary blood flow

  • normal pulmonary alveoli

• accommodate changes in cardiac output

• convert Ang 1 to Ang II

pulmonary circulation- structural adaptations

• large capillary SA

• thinner vessels at some levels

  • large compliance because of right ventricle SV

  • pulmonary arteries less smooth muscle

• vessels are short in length

• arteries have larger diameter than systemic

• lower pressure

  • pulmonary vascular resistance is 1/10 of systemic

pulmonary circulation- functional adaptations

• lack of autoregulation because an increase in pressure would decrease blood flow in the lungs

• hypoxic pulmonary vasoconstriction

  • alveolar hypoxia causes vasoconstriction at precapillary arteriole via sympathetics

  • reduces mismatching ventilation and perfusion

  • basal NO is reduced in the presence of PaO2

• keeping lungs dry

• fluid exchange is similar to systemic

  • capillary hydrostatic pressure is much lower (less filtration out)

  • rich lymphatic system that takes away any fluid that gets out

pulmonary circulation- control of blood flow

• systemic pressure has to work against gravity but pulmonary doesn’t

• systemic pressure has to redirect blood flow based on needs but pulmonary doesn’t

• systemic pressure is greater than pulmonary pressure because it needs to drive flow across a longer distance

• pulmonary vascular resistance

  • resistance to blood flow from pulmonary artery to left atria

  • extravascular causes

    • lung volume, gravity, hypoxia, body position

• effect of lung volume

  • inspiration: increase resistance in capillaries

  • expiration: decrease resistance in capillaries

pulmonary circulation- special problems

• gravity and body position

  • lead to higher flow on the base vs the apex of lung

  • can cause perfusion mismatch in apex because less amount of blood flow

• exercise (high level athletes with high CO)

  • decreases transit time- shortens the available window of diffusion of oxygen and carbon leading to insufficient gas exchange and hypoxemia

  • exercise increases blood flow to the lungs, increasing pulmonary pressure and more blood pushed out

  • mechanisms

    • capillary recruitment

    • distending capillaries

    • decreased resistance in capillary bed

pulmonary circulation- special problems: pulmonary edema

• pulmonary interstitial pressure increases leading to filling of pulmonary interstitial space with fluid

• life threatening

• common causes

  • mitral valve disease

  • left heart failure

pulmonary circulation- special problems: pulmonary embolism

• travels

• common source of DVT

• large

  • complete block of pulmonary artery, obstructing blood flow to the lungs

  • hypoxemia

  • decrease return to left ventricle

• small

  • passes through main pulmonary arteries but becomes stuck in peripheral arteries supplying lower lobes

  • raises pulmonary pressure

  • affected lung segment undergoes necrosis; pulmonary infarct

pulmonary circulation- special problems: pulmonary hypertension

• increased pulmonary resistance

• leads to right side hypertrophy and heart failure

• common causes

  • genetic

  • COPD

  • left heart conditions

• treatment is to remove if possible

pulmonary circulation- special problems: pulmonary hypertension in newborn

• failure of normal cardiopulmonary transition

  • pulmonary artery remains constricted after birth

  • maintain use of foramen ovale and ductus arteriosus

pulmonary circulation- special problems: acute respiratory distress syndrome

• damage to pulmonary endothelium

• causes

  • aspiration

  • sepsis

  • burns

• characterized by widespread inflammation in the lungs

cutaneous circulation- characteristics and anatomy

• acral skin

  • found in no hair locations

  • has atrio-venous anastomoses

    • shunts that are controlled by SNS

• non acral skin

  • lacks anastomoses

  • still contribute to thermoregulation

cutaneous circulation- special tasks

• regulate core body temperature

• respond to trauma- immune

cutaneous circulation- structural adaptations

• 2 types of SNS

  • adrenergic

    • only found in non hair bearing skin

  • cholinergic

    • only activated during inflammation

• arteriovenosus anastomoses

  • direct connections between arteriole and venule, bypassing nutritional capillaries

  • fully dilated in heat

  • constricted in cold

cutaneous circulation- functional adaptations

• hypothalamic control: temperature control center

  • mediate increase and decrease in SNS to cutaneous vessels depending on body heat

  • at thermal equilibrium= sympathetic vasoconstrictor mild basal tone

    • keep AV anastomoses closed

cutaneous circulation- control of blood flow

• blood flow decreases from resting to cold

• blood flow increases from cold to heat

cutaneous circulation- special problems

• heat stroke/ heat exhaustion

  • common causes

    • high core body temperature

    • decrease in MAP

    • sweat does not cool body down

• cold

  • damage due to sustained vasoconstriction

  • paradoxical cold vasodilation

    • paralysis of adrenoreceptors by cold

cutaneous circulation- exposure to heat

• decreases SNS, reducing vasomotor tone

• AV anastomoses dilate

• progressive cutaneous dilation

• activate sympathetic cholinergic dilation

  • activate sweat glands

• = heat dissipation

cutaneous circulation- exposure to cold

• increase in SNS discharge

  • sympathetic adrenergic constrictors

• vasoconstriction

• leads to heat conservation