Brs Physiology Cv

Front 1

What is systemic blood flow? Pulmonary blood flow?

Back 1

Systemic is the CO from the left side of the heart

Pulmonary is the CO from the right side of the heart

Front 2

Describe arteries

Back 2

-Deliver oxygenated blood to the tissues
-Are thick-walled, with extensive elastic tissue and smooth muscle
-Are under high pressure
-The blood volume contained in the arteries is called the stressed volume

Front 3

Describe arterioles

Back 3

-Smallest branches of the arteries
-The site of highest resistance in the CV system
-Have a smooth muscle wall that is extensively innervated by autonomic nerve fibers
-Arteriolar resistance is regulated by the autonomic nervous system
-α1-Adrenergic receptors are found on the arterioles of the skin, splanchnic, and renal circulations
-β2-Adrenergic receptors are found on the arterioles of skeletal muscle

Front 4

Describe capillaries

Back 4

-Have the largest total cross-sectional and surface area
-Consist of a single layer of endothelial cells surrounded by basal lamina
-Are thin waled
-Are the site of exchange of nutrients, water, and gases

Front 5

Describe venules

Back 5

-Are formed from merged capillaries

Front 6

Describe veins

Back 6

-Progressively merge to form larger veins. The largest vein, the vena cava, returns blood to the heart
-Are thin-walled
-Are under low pressure
-Contain the highest proportion of the blood in the CV system
-Blood volume contained in the veins is called the unstressed volume
-Have α1-adrenergic receptors

Front 7

Describe the velocity of blood flow

Back 7

Can be expressed as:
v=Q/A, where:
v=velocity
Q=blood flow
A=cross-sectional area

Front 8

What equation describes blood flow?

Back 8

Q=ΔP/R

Front 9

What equation describes the resistance of blood vessels?

Back 9

Poiseulle's equation:
R=8ηl/(πr^4)
where
η=viscosity
l=length
r=radius

Front 10

What contributes the largest proportion of resistance to blood flow in the body?

Back 10

Arterioles

Front 11

Describe Reynolds number

Back 11

-Predicts whether blood flow will be laminar or turbulent
-Turbulence occurs with higher Re
-Turbulent flow causes bruits
-Decreased blood viscosity (anemia, low Hct) causes higher Re
-Increased blood velocity (narrowing of vessel) causes higher Re

Front 12

Describe capacitance (compliance)

Back 12

-Describes the distensibility of blood vessels
-Inversely related to elastance (stiffness). The greater the amount of elastance tissue there is in a blood vessel, the higher the elastance is and the lower the compliance is
-C=V/P
-Describes how much volume changes in response to a change in pressure
-Greater for veins than for arteries
-Capacitance of arteries decreases with age

Front 13

Describe the pressure profile of blood vessels

Back 13

-As blood flows through the systemic circulation, pressure decreases progressively because of the resistance to blood flow
-The largest decrease in pressure occurs across the arterioles
-Mean pressures in the systemic circulation are
1. Aorta - 100mmHg
2. Arterioles - 50mmHg
3. Capillaries - 20 mmHg
4. Vena cava, 4 mmHg

Front 14

Describe arterial pressure

Back 14

-Pulsatile
-Not constant during the cardiac cycle

Front 15

Describe systolic pressure

Back 15

-Highest arterial pressure during the cardiac cycle
-Measured after the heart contracts (systole) and blood is ejected into the arterial system

Front 16

Describe diastolic pressure

Back 16

-Lowest arterial pressure during the cardiac cycle
-Measured when the heart is relaxed (diastole) and blood is returning to the heart via the veins

Front 17

Describe pulse pressure

Back 17

-The difference between the systolic and diastolic pressures
-Most important determinant of pulse pressure is SV. As blood is ejected from the L ventricle into the arterial system, arterial pressure increases because of the relatively low capacitance of the arteries. Because diastolic pressure remains unchanged during ventricular systole, the pulse pressure increases to the same extent as the systolic pressure
-Decreases in capacitance, such as those from aging, cause increases in pulse pressure

Front 18

Describe mean arterial pressure

Back 18

-Average arterial pressure with respect to time
-Can be approximated by diastolic pressure + 1/3 pulse pressure

Front 19

Describe venous pressure

Back 19

-Very low
-Veins have a high capacitance and therefore can hold large volumes of blood at low pressures

Front 20

Describe atrial pressure

Back 20

-Slightly lower than venous pressure
-L atrial pressure is estimated by the pulmonary wedge pressure. A catheter is inserted into the smallest branches of the pulmonary artery, making almost direct contact with the pulmonary capillaries. The measured pulmonary capillary pressure is appox the L atrial pressure

Front 21

Describe the P wave

Back 21

-Represents atrial depolarization
-Does not include atrial depolarization, which is "buried" in the QRS complex

Front 22

Describe the PR interval

Back 22

-The interval from the beginning of the P wave to the beginning of the Q wave (initial depolarization of the ventricle)
-Varies with conduction velocity through the AV node
-Decreased (increased conduction through AV node) by stimulation of the sympathetic nervous system
-Increased (decreased conduction velocity through AV node) by stimulation of the parasympathetic nervous system

Front 23

Describe the QRS complex

Back 23

-Represents depolarization of the ventricles

Front 24

Describe the QT interval

Back 24

-The interval from the beginning of the Q wave to the end of the T wave
-Represents the entire period of depolarization and repolarization of the ventricles

Front 25

Describe the ST segment

Back 25

-The segment from the end o the S wave to the beginning of the T wave
-Isoelectric
-Represents the period when the ventricles are depolarized

Front 26

Describe the T wave

Back 26

-Represents ventricular repolarization

Front 27

Describe membrane potential

Back 27

-Resting membrane potential is determined by the conductance to K+ and approaches the K+ equilibrium potential
-Inward current brings positive charge into the cell and depolarizes the membrane potential
-Outward current takes positive charge out of the cell and hyperpolarizes the membrane potential
-The role of Na+-K+-adenosine triphosphate (ATPase) is to maintain ionic gradients across the cell membranes

Front 28

Describe the action potentials of the ventricles, atria, and the Purkinje system

Back 28

-Stable resting membrane potentials of ~-90mV. This value approaches the K+ equilibrium potential
-Action potentials are of long duration, esp in the Purkinje fibers where they last 300msec
-Broken up into 4 phases

Front 29

Describe phase 0 of the action potentials of the ventricles, atria, and the Purkinje system

Back 29

-The upstroke of the action potential
-Caused by transient increase in Na+ conductance. This increase results in an inward Na+ current that depolarizes the membrane
-At the peak of the action potential, the membrane potential approaches the Na+ equilibrium potential

Front 30

Describe phase 1 of the action potentials of the ventricles, atria, and the Purkinje system

Back 30

-A brief period of initial repolarization
-Initial repolarization is caused by an outward current, in part because of the movement of K+ ions (favored by both chemical and electrical gradients) out of the cell and in part because of a decrease in Na+ conductance

Front 31

Describe phase 2 of the action potentials of the ventricles, atria, and the Purkinje system

Back 31

-The plateau of the action potential
-Caused by a transient increase in Ca2+ conductance, which results in an inward Ca2+ current, and by an increase in K+ conductance
-During phase 2, outward and inward currents are approximately equal, so they membrane potential is stable at the plateau level

Front 32

Describe phase 3 of the action potentials of the ventricles, atria, and the Purkinje system

Back 32

-Repolarization
-During phase 3, Ca2+ conductance decreases, and K+ conductance increases and therefore predominates
-The high K+ conductance results in a large outward K+ current (I_K), which hyperpolarizes the membrane back toward the K+ equilibrium potential.

Front 33

Describe phase 4 of the action potentials of the ventricles, atria, and the Purkinje system

Back 33

-The resting membrane potential
-A period during which inward and outward currents (I_K1) are equal and the membrane potential approaches the K+ equilibrium potential

Front 34

Describe the SA node

Back 34

-Normally the pacemaker of the heart
-Has an unstable resting potential
-Exhibits phase 4 depolarization, or automaticity
-AV node and His-Purkinje systems are latent pacemakers that may exhibit automaticity and override the SA node if suppressed
-Intrinsic rate of phase 4 depolarization (and HR) is fastest in the SA node and slowest in the His-Purkinje system
-SA node> AV node> His-Purkinje
-Characterized by 3 phases

Front 35

Describe phase 0 of the action potentials of the SA node

Back 35

-The upstroke of the action potential
-Caused by an increase in Ca2+ conductance. This increase causes an inward Ca2+ current that drives the membrane potential toward the Ca2+ equilibrium potential
-The ionic basis for phase 0 in the SA node is different than that in the ventricles, atria, and Purkinje fibers (where it is the result of an inward Na+ current

Front 36

Describe phase 3 of the action potentials of the SA node

Back 36

-Repolarization
-Caused by an increase in K+ conductance. This increase results in an outward K+ current that causes repolarization of the membrane potential

Front 37

Describe phase 4 of the action potentials of the SA node

Back 37

-Slow depolarization
-Accounts for the pacemaker activity of the SA node (automaticity)
-Caused by an increase in Na+ conductance, which results in an inward Na+ current called I_f
-I_f is turned on by repolarization of the membrane potential during the preceding action potential

Front 38

Describe phase 1 of the action potentials of the SA node

Back 38

-Not present in the SA node action potential

Front 39

Describe phase 2 of the action potentials of the SA node

Back 39

-Not present in the SA node action potenial

Front 40

What is special about the AV node action potential?

Back 40

The upstroke of the action potential is the result of an inward Ca2+ current (as in the SA node)