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 Rate 70 beats/minute = Cardiac Output 5040mL/minute Example: 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
Blood Volume Average blood volume in adults = 5 Liters (1.3 gallons) As blood volume increases, blood pressure initially increases Peripheral Resistance Peripheral resistance = friction between blood and blood vessels Vasoconstriction increases resistance and increases blood pressure Vasodilation decreases blood pressure 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 Factors that influence blood pressure
Figure 15.36 Controlling cardiac output and peripheral resistance regulates blood pressure Control of Blood Pressure A combination of factors control blood pressure. These include stroke volume, heart rate, and peripheral resistance:
Control of Blood Pressure
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.
Figure 15H Blood 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
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
ARTERIAL SYSTEM
STRUCTURES AT Aortic Root Aortic Valve
Aortic Sinus Swelling at aortic root
Right and left coronary arteries Supply blood to myocardium of the heart Myocardial infarction = blocked coronary artery
Aortic Bodies Chemoreceptors - monitor CO2 & O2 levels in blood
Branches of Aortic Arch 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 Left common carotid artery – supplies blood to left side of face and head 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
