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Blood Pressure
section 5, chapter 15
CATALYST #3
1) Define systole and diastole
1) Define cardiac cycle
1) What fibers and nodes are a part of the cardiac
conduction system? (starts on pg. 332)
1) What is an ECG?
Blood Pressure
•Blood pressure is the force the blood exerts
against the inner walls of the blood vessels
•Usually refers to pressure in systemic arteries
Arterial blood pressure:
•Rises with ventricular contractions and falls as
ventricles relax
•Systolic pressure is the maximum pressure
during ventricular contraction
•Diastolic pressure is the minimum pressure
when the ventricles relax
Factors that influence blood pressure
1. Cardiac Output- volume of blood ejected from one ventricle per minute
• Product of heart rate and stroke volume
Stroke Volume
• Volume of blood expelled from ventricle with each contraction
• Average = 70 milliliters per beat (mL/beat) for adult male
Heart Rate
• Average = 72 beats per minute
Example:
70 mL/beat
Stroke Volume
70 beats/minute
X
Heart Rate
5040mL/minute
= Cardiac Output
Factors that influence blood pressure
Cardiac output (and blood pressure) increases
with an increase in stroke volume or heart rate.
Factors that influence blood pressure
2. Blood Volume
• Average blood volume in adults = 5 Liters (1.3 gallons)
• As blood volume increases, blood pressure initially increases
3. Peripheral Resistance
• Peripheral resistance = friction between blood and blood vessels
• Vasoconstriction increases resistance and increases blood pressure
• Vasodilation decreases blood pressure
4. Viscosity of blood
• Viscosity = resistance of a fluid to flow (thickness of a fluid).
• Blood cells and some plasma proteins increase the viscosity of blood.
• Anemia (deficiency of red blood cells) reduces viscosity & lowers
blood pressure
Factors that influence blood pressure
Figure 15.24. Some of the factors
that influence arterial blood pressure
Control of blood pressure
A combination of factors control blood pressure. These include stroke
volume, heart rate, and peripheral resistance:
Figure 15.36 Controlling cardiac output and peripheral resistance regulates blood pressure
Control of blood pressure
Factors that affect stroke volume
•End-diastolic volume (EDV)
•Volume of blood in ventricles at the end of ventricular
diastole
•Ventricles are filled with blood
•End-systolic volume (ESV)
•Volume of blood in ventricles at the end of ventricular
systole
•Only 60% of blood is expelled from heart during a normal
contraction
•Increasing the force of ventricular contractions decreases
ESV
•Stroke volume = EDV– ESV
•Increase stroke volume by increasing EDV or decreasing
ESV
stroke volume
Stroke Volume is directly related to the force of ventricular contraction.
Two events that occur in the ventricles coincide with stroke volume:
1. End-diastolic volume (EDV)
Volume of blood in ventricles at the end of ventricular diastole
As ventricles fill with blood, muscle fibers are mechanically
stretched - preload
2. End-systolic volume (ESV)
Volume of blood in ventricles at the end of ventricular systole
A normal health heart expels 60% of blood present in ventricle.
stroke volume
Stroke Volume is the difference between end diastolic
volume (EDV) and end systolic volume (ESV): Stroke Volume = EDV - ESV
Frank-Starling Principle:
• The ability of a heart muscle to generate force depends on the original
stretch of a muscle prior to contraction (similar to stretching a rubber band)
• The degree of stretch (preload) of the myocardial fibers before contraction
determines the stroke volume
• A greater end diastolic volume results in a greater force of contraction,
leading to a greater stroke volume.
Venous Return
•Blood pressure rapidly decreases as the blood moves through the
arterial system and into the capillary network.
•Little pressure remains in the veins, therefore heart actions contribute
very little to venous return.
Figure 15H
Blood pressure decreases as blood
moves away from the heart.
Venous Return
•Venous return depends on:
•Skeletal muscle contractions – massaging actions push blood towards heart
•Respiratory movements – generates pressure in abdominal and thoracic cavities
•Changes in pressure pushes blood along veins
•Vasoconstriction – contraction of smooth muscles in tunica media
•Sympathetic reflexes vasoconstrict the smooth muscles in veins, which can
propel additional blood from venous reservoir towards the heart.
Systemic Arteries
Aorta - Main trunk of the systemic
circulation.
Divisions of the aorta
•Aortic root = attachment to heart
•Ascending Aorta
•Aortic arch
•Thoracic aorta
•Abdominal aorta
Structures at the root of the aorta
1. Aortic Valve
2. Aortic Sinus
• Swelling at aortic root
3. Right and left coronary arteries
• Supply blood to myocardium of the heart
• Myocardial infarction = blocked coronary artery
3. Aortic Bodies
• Chemoreceptors - monitor CO2 & O2 levels in blood
arteries of the aortic arch
1. Brachiocephalic Artery
Brachiocephalic artery divides into:
• Right common carotid artery -Supplies blood to
right side of face and head
• Right subclavian artery - Supplies blood to right
arm
2. Left common carotid artery – supplies blood to left
side of face and head
3. Left subclavian artery – supplies blood to left arm
Figure 15.42 The major branches of the aortic arch are highlighted in yellow.
end of section 5, chapter 15