Chapter 14: Cardiovascular Physiology
Overview of Cardiovascular System
● Cardiovascular system: comprised of a heart, blood vessels, and blood
○ It is a one-way circuit that ensures systematic distribution of gases, nutrients,
signal molecules, and wastes
● Capillaries: the vessels where blood exchanges material with the interstitial fluid
○ Very thin and small individually, but all together it has the largest surface area
● Arteries: carry blood away from the heart
● Veins: return blood to the heart
● Septum: central wall of the heart that divides left and right side
● Atrium: receives blood returning to the heart from the blood vessels
● Ventricle: pumps blood out into the blood vessels
● The right side of the heart receives blood from the tissues and sends it to the lungs for
oxygenation. The left side of the heart receives newly oxygenated blood from the lungs
and pumps it to tissues throughout the body.
○ The left wall of the heart is thicker since it pumps blood all throughout the body,
whereas the right wall is thinner since it only needs to pump blood to the lungs
● Pulmonary circulation: From the right atrium, blood flows into the right ventricle of the
heart. From there it is pumped through the pulmonary arteries to the lungs, where it is
oxygenated. From the lungs, blood travels to the left side of the heart through
pulmonary veins and enters the left atrium to the left ventricle.
○ I.e. Blood vessels that go from the right ventricle to the lungs and back to the left
atrium
● Systemic circulation: Blood pumped out of the left ventricle enters the aorta. The aorta
branches into a series of smaller arteries that leads into networks of capillaries where
oxygen can be diffused into tissues. After leaving the capillaries, blood flows into the
venous side of the circulation, moving from small veins to larger and larger veins. Veins
in the upper part of the body join to form the superior vena cava, whereas those from
the lower part form the inferior vena cava. Both venae cavae empty into the right
atrium.
○ I.e. Blood vessels that carry blood from the left side of the heart to the tissues
and back to the right side of the heart
● Coronary artery: Some blood from the left ventricle enters the coronary artery which
nourishes the heart muscle itself. It then flows into capillaries in the heart muscles and
into the right atrium.
Pressure, Volume, Flow, and Resistance
● Pressure gradients: the basis of why blood flow; liquids and gases will flow from regions
of higher pressure to regions of lower pressure
○ The heart creates high pressure when it contracts. Blood flows out of the heart
(the region of higher pressure) into the closed loop of blood vessels (the region of
lower pressure). As blood moves through the system, pressure is lost because of
, friction between the fluid and vessels walls. Pressure falls continuously as blood
moves farther from the heart.
○ The highest pressure can be found in the aorta and systemic arteries as they
receive blood from the left ventricle.
○ The lowest pressure can be found in the venae cavae just before they empty into
the right atrium.
● Pressure: in a fluid, it’s the force exerted by the fluid on its container
● Hydrostatic pressure: pressure exerted when fluid is not moving (think of it being
plugged), force is equally exerted in all directions
○ When fluid is moving (unplugged), pressure falls with distance as energy is lost
due to friction
● Driving pressure: the force that drives blood through the blood vessels
○ Contraction of blood-filled ventricle creates high pressure, high-pressure blood
flows out of the ventricle and into the blood vessels--displacing lower-pressure
blood already there
○ Example of pressure changing in liquids (such as blood) without a change in
volume
○ When heart relaxes and expands, pressure in the chambers fall
● Likewise, when blood vessels dilate, blood pressure inside the circulatory system falls. If
the blood vessels constrict, blood pressure in the system increases.
● Flow from a tube is directly proportional to pressure gradient (flow α ΔP)
○ The higher the pressure gradient, the greater the fluid flow
○ Blood flows from higher pressure to lower pressure
● Flow is inversely proportional to resistance (Flow α 1/R)
○ The higher the resistance of a blood vessel, the lower the flow is through that
vessel
○ Resistance is influenced by: radius of tube (r), length of tube (L), viscosity of fluid
(η)
○ Poiseuille’s Law: R = 8Lη/πr^4 ➝ R α Lη/r^4
■ Resistance increases as length of tube increases
■ Resistance increases as viscosity increases
■ BUT resistance decreases as tube’s radius increases
● R α 1/r^4
● Small increase in radius has large effect on the flow
● Vasoconstriction: decrease in blood vessel diameter, decreases blood flow
● Vasodilation: increase in blood vessel diameter, increases blood flow
● Flow rate: “flow,” the volume of blood that passes a given point in the system per unit of
time
○ How much blood flows past a point in a given period of time
, ● Velocity of flow: the distance a fixed volume of blood travels in a given period of time
○ How fast blood flows past a point in a given period of time
● V = Q/A
○ If flow rate constant, velocity is faster in narrow sections and slower in wider
sections
○ If diameter constant, velocity is directly proportional to flow rate
● Mean arterial pressure (MAP): primary driving force for blood flow
○ Influenced by cardiac output (the volume of blood the heart pumps per minute)
and total peripheral resistance (the resistance of the blood vessels to blood flow
through them) ➝ MAP α CO x TPR
Cardiac Muscle and the Heart
● Atrioventricular valves: between the atria and ventricles (blood going in the heart)
○ During ventricular contraction, these valves remain closed to prevent blood
flow backward into the atria
○ Right AV valve has 3 flaps (tricuspid)
○ Left AV valve has 2 flaps (bicuspid)
● Semilunar valves: between the ventricles and the arteries (blood going out the heart)
○ Prevent blood that has entered the arteries from flowing back into the ventricles
during ventricular relaxation
○ Pulmonary valve between the right ventricle and pulmonary trunk
○ Aortic valve between the left ventricle and aorta
● Most cardiac muscle is contractile, but about 1% is specialized to generate APs
spontaneously (allows heart to contract without any outside signal)
○ Signal for myocardial contraction comes from pacemaker cells that set the rate
of the heartbeat
○ AP originates spontaneously in pacemaker cells and spreads into contractile cells
through gap junctions to initiate EC coupling
● Cardiac muscle fibers are much smaller than skeletal muscle fibers and usually have a
single nucleus per fiber
● Intercalated disk: where two cardiac muscle cells meet, consist of desmosomes and gap
junctions
○ Desmosomes: strong connections that tie adjacent cells together, allowing force
created in one cell to be transferred to adjacent cell
○ Gap junctions: electrically connect cardiac muscle cells to one another, allows
waves of depolarization to spread rapidly from cell to cell so that all the heart
muscle contract almost simultaneously
● T-tubules are larger but SR is smaller than in skeletal muscles (cardiac muscles can get
Ca2+ extracellularly too)
● More mitochondria (about ⅓ the cell volume of a cardiac contractile fiber), due to high
energy demand of these cells
EC Coupling in Cardiac Muscle
Overview of Cardiovascular System
● Cardiovascular system: comprised of a heart, blood vessels, and blood
○ It is a one-way circuit that ensures systematic distribution of gases, nutrients,
signal molecules, and wastes
● Capillaries: the vessels where blood exchanges material with the interstitial fluid
○ Very thin and small individually, but all together it has the largest surface area
● Arteries: carry blood away from the heart
● Veins: return blood to the heart
● Septum: central wall of the heart that divides left and right side
● Atrium: receives blood returning to the heart from the blood vessels
● Ventricle: pumps blood out into the blood vessels
● The right side of the heart receives blood from the tissues and sends it to the lungs for
oxygenation. The left side of the heart receives newly oxygenated blood from the lungs
and pumps it to tissues throughout the body.
○ The left wall of the heart is thicker since it pumps blood all throughout the body,
whereas the right wall is thinner since it only needs to pump blood to the lungs
● Pulmonary circulation: From the right atrium, blood flows into the right ventricle of the
heart. From there it is pumped through the pulmonary arteries to the lungs, where it is
oxygenated. From the lungs, blood travels to the left side of the heart through
pulmonary veins and enters the left atrium to the left ventricle.
○ I.e. Blood vessels that go from the right ventricle to the lungs and back to the left
atrium
● Systemic circulation: Blood pumped out of the left ventricle enters the aorta. The aorta
branches into a series of smaller arteries that leads into networks of capillaries where
oxygen can be diffused into tissues. After leaving the capillaries, blood flows into the
venous side of the circulation, moving from small veins to larger and larger veins. Veins
in the upper part of the body join to form the superior vena cava, whereas those from
the lower part form the inferior vena cava. Both venae cavae empty into the right
atrium.
○ I.e. Blood vessels that carry blood from the left side of the heart to the tissues
and back to the right side of the heart
● Coronary artery: Some blood from the left ventricle enters the coronary artery which
nourishes the heart muscle itself. It then flows into capillaries in the heart muscles and
into the right atrium.
Pressure, Volume, Flow, and Resistance
● Pressure gradients: the basis of why blood flow; liquids and gases will flow from regions
of higher pressure to regions of lower pressure
○ The heart creates high pressure when it contracts. Blood flows out of the heart
(the region of higher pressure) into the closed loop of blood vessels (the region of
lower pressure). As blood moves through the system, pressure is lost because of
, friction between the fluid and vessels walls. Pressure falls continuously as blood
moves farther from the heart.
○ The highest pressure can be found in the aorta and systemic arteries as they
receive blood from the left ventricle.
○ The lowest pressure can be found in the venae cavae just before they empty into
the right atrium.
● Pressure: in a fluid, it’s the force exerted by the fluid on its container
● Hydrostatic pressure: pressure exerted when fluid is not moving (think of it being
plugged), force is equally exerted in all directions
○ When fluid is moving (unplugged), pressure falls with distance as energy is lost
due to friction
● Driving pressure: the force that drives blood through the blood vessels
○ Contraction of blood-filled ventricle creates high pressure, high-pressure blood
flows out of the ventricle and into the blood vessels--displacing lower-pressure
blood already there
○ Example of pressure changing in liquids (such as blood) without a change in
volume
○ When heart relaxes and expands, pressure in the chambers fall
● Likewise, when blood vessels dilate, blood pressure inside the circulatory system falls. If
the blood vessels constrict, blood pressure in the system increases.
● Flow from a tube is directly proportional to pressure gradient (flow α ΔP)
○ The higher the pressure gradient, the greater the fluid flow
○ Blood flows from higher pressure to lower pressure
● Flow is inversely proportional to resistance (Flow α 1/R)
○ The higher the resistance of a blood vessel, the lower the flow is through that
vessel
○ Resistance is influenced by: radius of tube (r), length of tube (L), viscosity of fluid
(η)
○ Poiseuille’s Law: R = 8Lη/πr^4 ➝ R α Lη/r^4
■ Resistance increases as length of tube increases
■ Resistance increases as viscosity increases
■ BUT resistance decreases as tube’s radius increases
● R α 1/r^4
● Small increase in radius has large effect on the flow
● Vasoconstriction: decrease in blood vessel diameter, decreases blood flow
● Vasodilation: increase in blood vessel diameter, increases blood flow
● Flow rate: “flow,” the volume of blood that passes a given point in the system per unit of
time
○ How much blood flows past a point in a given period of time
, ● Velocity of flow: the distance a fixed volume of blood travels in a given period of time
○ How fast blood flows past a point in a given period of time
● V = Q/A
○ If flow rate constant, velocity is faster in narrow sections and slower in wider
sections
○ If diameter constant, velocity is directly proportional to flow rate
● Mean arterial pressure (MAP): primary driving force for blood flow
○ Influenced by cardiac output (the volume of blood the heart pumps per minute)
and total peripheral resistance (the resistance of the blood vessels to blood flow
through them) ➝ MAP α CO x TPR
Cardiac Muscle and the Heart
● Atrioventricular valves: between the atria and ventricles (blood going in the heart)
○ During ventricular contraction, these valves remain closed to prevent blood
flow backward into the atria
○ Right AV valve has 3 flaps (tricuspid)
○ Left AV valve has 2 flaps (bicuspid)
● Semilunar valves: between the ventricles and the arteries (blood going out the heart)
○ Prevent blood that has entered the arteries from flowing back into the ventricles
during ventricular relaxation
○ Pulmonary valve between the right ventricle and pulmonary trunk
○ Aortic valve between the left ventricle and aorta
● Most cardiac muscle is contractile, but about 1% is specialized to generate APs
spontaneously (allows heart to contract without any outside signal)
○ Signal for myocardial contraction comes from pacemaker cells that set the rate
of the heartbeat
○ AP originates spontaneously in pacemaker cells and spreads into contractile cells
through gap junctions to initiate EC coupling
● Cardiac muscle fibers are much smaller than skeletal muscle fibers and usually have a
single nucleus per fiber
● Intercalated disk: where two cardiac muscle cells meet, consist of desmosomes and gap
junctions
○ Desmosomes: strong connections that tie adjacent cells together, allowing force
created in one cell to be transferred to adjacent cell
○ Gap junctions: electrically connect cardiac muscle cells to one another, allows
waves of depolarization to spread rapidly from cell to cell so that all the heart
muscle contract almost simultaneously
● T-tubules are larger but SR is smaller than in skeletal muscles (cardiac muscles can get
Ca2+ extracellularly too)
● More mitochondria (about ⅓ the cell volume of a cardiac contractile fiber), due to high
energy demand of these cells
EC Coupling in Cardiac Muscle
