section 5, chapter 15: blood pressure
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blood pressureTRANSCRIPT
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Blood Pressure
ivyanatomy.com
section 5, chapter 15
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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
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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
Stroke Volume 70 mL/beat
X Heart Rate70 beats/minute
=Cardiac Output5040mL/minute
Example:
Factors that influence blood pressure
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Cardiac output (and blood pressure) increases with an increase in stroke volume or heart rate.
Factors that influence blood pressure
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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
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Figure 15.24. Some of the factors that influence arterial blood pressure
Factors that influence blood pressure
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Figure 15.36 Controlling cardiac output and peripheral resistance regulates blood pressure
A combination of factors control blood pressure. These include stroke volume, heart rate, and peripheral resistance:
Control of blood pressure
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Control of blood pressureFactors 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
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stroke volumeStroke 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.
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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.
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Figure 15HBlood pressure decreases as blood moves away from the heart.
• 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.
Venous Return
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•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.
Venous Return
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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
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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
Structures at the root of the aorta
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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
arteries of the aortic arch
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Figure 15.42 The major branches of the aortic arch are highlighted in yellow.
end of section 5, chapter 15