Special Circulation Flashcards
Describe the distribution of cardiac output
About 80% at rest goes to the GI tract, kidneys, skeletal muscle, heart, brain. With most going to kidneys and GI tract
There is a range of blood flow for each organ that represents the vasodilator reserve for that organ
What are the phasic changes in coronary blood flow during heart contraction?
Most of the blood flow to the myocardium occurs during diastole due to muscle compression on the coronary vessels during systole
How can increased heart rate reduce coronary perfusion with diseased coronary vessls?
Length of diastole is shortened at higher heart rates, normally coronary arteries dilate to compensate
If they are diseased then their vasodilator reserve is limited, leading to myocardial ischemia and anginal pain with high heart rate
How is coronary blood flow primarily regulated?
Changes in tissue metabolism
Production of adenosine and NO, both vasodilators
Describe the unique sympathetic control of coronary blood flow
Unlike other vasculature, activation of sympathetic nerves causes only transient vasoconstriction followed by vasodilation
Metabolite production overrides sympathetic stimulation within seconds
What is functional sympatholysis?
Term used to describe the functional relationship between sympathetic and metabolic control of coronary blood flow
How can insufficient coronary blood flow be mitigated in coronary artery disease?
Collateral vessels increases myocardial blood supply, helping to supply blood flow to ischemic regions
What are the four major arteries supplying the brain?
Two internal carotid
Two vertebral
Why does increased intracranial pressure cause lower cerebral perfusion?
Collapses veins
Decreases effective CPP and reduces blood flow
How is cerebral blood flow regulated?
Highly related to metabolism of tissue
Increased blood flow in response to excess CO2 or H+
Large decrease in arterial PO2 will increase cerebral blood flow
Describe the autoregulation of cerebral blood flow
Brain has excellent autoregulation between 60 and 130 mmHg
With chronic hypertension, autoregulation curve shifts to protect the brain at higher pressures
What is the role of the sympathetic nervous system in controlling cerebral blood flow?
There is innervation of the larger cerebral vessels
However it has relatively little influence because autoregulation will override its stimulation
Describe the microvascular organization in skeletal muscle
Highly organized
When not contracting, only about 25% of the capillaries are perfused
In contrast, during contraction and active hyperemia, all of the capillaries may be perfused
Describe muscle blood flow during contraction
With rhythmic contraction (e.g. locomotion) the mean blood flow increases, however flow decreases during contraction and increases during relaxation
A sustained contraction decreases mean blood flow, followed by a post-contraction hyperemic response
These effects are due to compression of the vessels
How is skeletal muscle blood flow regulated?
Local regulation during activity (metabolic mechanisms)
Sympathetic generated vascular tone during resting
What is the splanchnic circulation?
Blood flow to the GI tract, spleen, pancreas and liver
How is the splanchnic circulation arranged and what is its significance?
The liver circulation is in series with the GI, splenic, and pancreatic circulation
This means that changes in blood flow in these vascular beds will have a significant effect on hepatic flow
What are the main two sources of hepatic blood flow?
Hepatic artery - 75% of oxygen source
Portal vein - 75% of total blood flow
What is the effect of gut activity and metabolic factors on GI blood flow?
During active absorption of nutrients, blood flow to the GI tract is increased
Metabolic control
What is the effect of sympathetic stimulation on GI blood flow and why is this significant?
Causes intense vasoconstriction and greatly decreased blood flow
Allows blood to be shunted to more vital organs during exercise and shock
The splanchnic circulation functions as a venous reservoir
Describe the shunt system in fetal circulation
Intracardiac: foramen ovale
Extracardiac: Ductus arteriosus and ductus venosus
Designed so that the most highly oxygenated blood is delivered to the myocardium and brain
**Study the slides for specific path of blood shunting
Where does the exchange between the fetal circulation and maternal circulation take place?
The chorionic villi (fetus) and intervillous space (maternal) at the placenta
The maternal and fetal blood does not mix
What is the combined cardiac output or combined ventricular output?
Sum of the outputs of the right and left ventricles
Refers to the cardiac output of the fetus because the right and left hearts pump in series rather than parallel
Right output is slightly larger than left
Why is the fetal pulmonary circuit high resistance?
Collapsed lungs and hypoxic vasoconstriction
Results in low blood flow to the lungs in the fetus (although some is retained for development)
