Special Circulations
Mark T Ziolo, PhD, FAHA
Associate Professor, Physiology & Cell Biology
019 Hamilton Hall
614-688-7905
ziolo.1@osu.edu
Learning Objectives
• Describe the regulation of coronary, cerebral,
and skeletal muscle blood flow
• Differentiate flow regulation in cutaneous,
splanchnic, renal and pulmonary circuits
Detailed Objectives
 Understand how coronary blood flow is regulated
 Know why coronary blood flow must be increased and the primary
factor responsible for coronary blood flow
 Understand extravascular compression in the heart
 Understand how cerebral blood flow is regulated
 Know why cerebral blood flow is always maintained
 Know what is the purpose of Cushing’s Phenomenon
 Know how skeletal muscle blood flow is regulated
 Understand why skeletal muscle blood flow switches from neuronal
to local (metabolic) regulation
 Know the role of the “muscle-pump mechanism”
 Know the purpose of blood flow to the following organs: cutaneous,
splanchnic, renal, and pulmonary
 Understand the major mechanisms of blood flow regulation in the
following organs: cutaneous, splanchnic, renal, and pulmonary
References
• Mohrman DE, Heller LJ. Cardiovascular
Physiology 8th Edition. Lange Medical
Books/McGraw-Hill Publishers, 2014.
• Berne RM, Levy MN. Cardiovascular
Physiology Sixth Edition. Mosby-Year
Book, Inc., 2010.
• MediaPhys 3.0. An Introduction to Human
Physiology. The McGraw-Hill Publishers,
2010.
Coronary Blood Flow
 Myocardium extracts ~75% of the oxygen
 Increase in myocardial O2 consumption must be
accompanied by an increase in blood flow
 1° factor responsible for perfusion is the aortic pressure
 Local control (metabolic)
Flow directly related to O2 consumption
Extravascular Compression
Coronary Blood Flow, cont
Myocardial
Metabolic rate
Arterial O2
content
Myocardial
O2 supply
:
Myocardial
O2 demand
Coronary
blood flow
Vasodilator
metabolites
Local Control
 Vasodilator metabolites

Adenosine


Activates adenosine receptor
O2, CO2, H+, K+
 Neuronal Control

Sympathetic activation

Vasodilation (increase myocardial contractility)
Lack of Blood Flow
 Myocardial Ischemia

Arrhythmias
 Endocardial layer of left ventricle
Cerebral Blood Flow
 In ALL situations, blood flow to the brain is
preserved (55 ml/min/100g)
 Whole brain has a nearly constant metabolic
rate
 Blood flow to discrete regions is not constant

Regulated almost entirely by local mechanisms

O2, H+ (PCO2), K+, adenosine
 Excellent autoregulation
 Some sympathetic vasoconstriction
Cerebral Blood Flow, cont
Hand
Reasoning
Problem Solving
Cerebral Blood Flow, cont
 No reserves- very intolerant to ischemia


5 sec: fainting
Minutes: death
Cushing’s Phenomenon
Ischemic stimulation of vasomotor
regions in medulla
Tumor
Intracranial pressure
systemic blood pressure
CBF
Metabolic
vasodilation
Maintain CBF
Skeletal Muscle
 Rate of blood flow directly related to contractile state of
muscle
 At rest, large percentage of capillary bed is not perfused
 Regulation of flow


Neuronal and local influences
Physical factor- squeezing effect of contracting muscle
Skeletal Muscle, cont
 Neuronal Influence


High basal tone
Sympathetic fibers elicits vasoconstriction

Predominates in resting muscle
Skeletal Muscle, cont
 Local Influence

Very strong in working muscle

Muscle O2 consumption, adenosine, H+, K+, lactic acid
 Neuronal and local influences oppose each other, in
working muscle the local (metabolic) influence
predominates
Skeletal Muscle, cont
 “muscle-pump mechanism”

Contracting muscles push blood in veins towards thorax
Cutaneous




Very low O2 and nutrient requirements
Maintain constant body temperature
Arterioles and arteriovenous anastomoses
AV anastomoses shunt blood from arterioles to
venules

Governed by nervous system in response to
temperature receptors
 NE and E elicit vasoconstriction
 Chiefly influenced by environmental temperature
Splanchnic
 GI tract, spleen, pancreas, and liver
 ~25% of resting cardiac output
 Neuronal and local influences

Sympathetic causes vasoconstriction



Shifts blood to central venous pool (liver important blood reserve)
Gastrointestinal hormones- functional hyperemia
Autoregulation not well developed
Renal Blood Flow
 0.5% TBW but 20% of cardiac output
 Strong autoregulation



Regulate GFR
Myogenic mechanism (stretch)
Tubuloglomerular feedback



Tubular flow sensed by macula densa sends signal via
juxtaglomerular apparatus to afferent arterioles
JGA also releases renin (angiotensin II)
Neuronal Influence

Sympathetic decreases RBF, but GFR only slightly
Pulmonary Blood Flow
 Vascular system is low-resistance and highly distensible
 Capillaries aligned in thin sheets between adjacent
alveoli
 Gravitational effects (regional distribution)
 Hypoxia most important influence on tone
 Low alveolar PO2 leads to shunting of blood from poorly
ventilated regions to better ventilated regions
Summary
 Coronary blood flow is regulated by metabolic influences and the primary
factor responsible is arterial pressure
 With increased oxygen demand, coronary blood flow must be increased
because of the bulk flow principle
 Extravascular compression occurs in the heart due to high systolic forces
 Cerebral blood flow in mostly under metabolic influence
 Cerebral blood flow is always maintained since it is the least tolerant organ
to ischemia and there are no reserves
 Cushing’s Phenomenon is elevation of intracranial pressure results in an
increase in systemic blood pressure to maintain cerebral blood flow
 Skeletal muscle blood flow is regulated by the neuronal influence at rest, and
by the metabolic influence in working muscle
 The muscle pump mechanism pushes blood back towards the heart
Summary, cont
 Purpose of cutaneous blood flow is temperature regulation and is
under neuronal control
 Purpose of splanchnic blood flow is nutrient reabsorption and is
under neuronal control and functional hyperemia
 Purpose of renal blood flow is filtration and has strong autoregulation
and is under neuronal control
 Purpose of pulmonary blood flow is gas exchange and has hypoxic
vasoconstriction
Thank you for completing this module
Questions- mark.ziolo@osumc.edu
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