Exam #2 (Ch 4 & 5) Flashcards
Pulmonary circulation is a low/high pressure system
Low Pressure System
Right heart, pulmonary arteries, veins & capillaries & pulmonary system
Systemic circulation is a low/high pressure system
High Pressure System
Left heart, and rest of body arterial circulation
In order to create a flow one needs
A pressure gradient
Deliver blood and nutrients to tissues
Takes waste away from tissue
Assist in regulating blood pressure
Blood Vessels
Blood Vessels
Deliver blood and nutrients to tissues
Takes waste away from tissue
Assist in regulating blood pressure
Where do arteries conduct blood?
Arteries conduct blood away from the heart
Are arteries high or low pressure?
High pressure
What is the largest artery?
Aorta
What are characteristic of the walls of the arteries?
Elastic tissue
Smooth muscle
Connective tissue
What is stressed volume?
The blood that is in the arteries is under high pressure so it is called stressed volume
The blood that is in the arteries is under high pressure so it is called
Stressed Volume
The smallest branches of the arteries
Arterioles
The site of highest resistance to blood flow
Arterioles. Their walls are made up of smooth muscle.
The smooth muscle of the arterioles are tonically active or inactive?
Tonically active (always contracted)
The sympathetic fibers that innervate the smooth muscles of the arterioles
Alpha 1: found on the arterioles near skin & splanchnic organs. Cause contraction or vasoconstriction
Beta 2: Less common & cause relaxation or vasodilation when activated. Found in skeletal muscle cells
These sympathetic fibers of the smooth muscles of the arterioles are found near skin & splanchnic organs. Cause contraction or vasoconstriction.
Alpha 1
These sympathetic fibers of the smooth muscles of the arterioles are found in skeletal muscle cells. They are less common. Cause relaxation or vasodilation when activated
Beta 2
Capillaries
Thin-walled allowing for effective diffusion
Lined w/ a single layer of endothelial cells again allowing for exchange of nutrients, water, and gases
The Selective Perfusion of Capillaries is determined by
The degree of dilation or constriction of the arterioles & precapillary sphincters. The degree of dilation or constriction controlled by sympathetic innervation of vascular smooth muscles & by vasoactive metabolites produced in the tissues
Veins
Thin-walled
Modest amount of elastic tissue
Very large capacitance. Contains the largest proportion of blood in the cardiovascular system (most blood volume is found in veins)
Considered unstressed volume
Have valves to prevent retrograde or back flow
Innervated by sympathetic fibers. An increase in sympathetic activity = constriction = reduces their capacitance & therefore reduces the unstressed volume
The blood in the veins is also called
Unstressed volume
Purpose of valves in veins
Prevent retrograde or back flow
Increase in sympathetic activity on veins
Increase in sympathetic activity = constriction = reduces their capacitance & therefore reduces the unstressed volume
Formed from merged capillaries (low pressure)
Venules
Velocity of blood flow
V = Q/A Rate of displacement of blood per unit time V = Velocity of blood flow (cm/sec) Q = Flow (mL/sec) A = Cross-sectional area (cm^2)
Variables Impacting Blood Flow Velocity
It is directly proportional to blood flow & inversely proportional to cross-sectional area
Where is blood flow high & where is it low?
Blood flow is higher in the aorta (small cross sectional area) than the sum of all the capillaries (large cross sectional area)
How do we want blood flow velocity to be in areas of exchange?
Lower velocity allows for optimal exchange
Blood Flow is determined by
Pressure gradient
Resistance
Equation for Blood Flow
Q = ∆P/R
Q = Flow (mL/min) ∆P = Pressure difference (mmHg) R = Resistance (mmHg/mL/min)
Blood flow is directly proportional to ____ & inversely proportional to _____
Magnitude of blood flow is directly proportional to pressure gradient and inversely proportional to resistance
The major mechanism for changing blood flow in the cardiovascular system is by
Changing the resistance of blood vessels. Occurs primarily at the level of the arterioles due to smooth muscle contraction.
Total Peripheral Resistance (TPR)
Resistance of the entire systemic vasculature. Aka Systemic Vascular Resistance (SVR)
R = ∆P/Q
Resistance to Blood Flow is dependent on
Vessel diameter/radius & blood viscosity. Also based on parallel or series arrangement of blood vessels
Poiseuille Equation
R = 8µl / πr^4
R = Resistance µ = viscosity of blood l = length of blood vessel r = radius
According to the poiseuille equation resistance is proportional to
Directly proportional to viscosity, length, and inversely proportional to the radius raised to the 4th power (r^4)
Series Resistance of Blood Flow
Within a given organ
Within the organ or blood flows from the major artery to smaller arteries, to arterioles, to capillaries, to venules, to veins
As resistors are added, total resistance increases
Total resistance of a system arranged in series is equal to the sum of the individual resistances
Parallel Resistance of Blood Flow
Found among the various major arteries branching off the aorta
As resistors are added, total resistance decreases
Total resistance in a parallel arrangement is less than any of the individual resistances
1/Rtot = 1/R1 + 1/R2
This arrangement ensures pressure is not loss through the system
What is the purpose of parallel resistance of blood flow?
It ensures pressure is not loss through the system
Laminar blood flow
Straight. Ideally, blood flow in the cardiovascular system is laminar. Shows a parabolic profile of velocity within a blood vessel.
Velocity of flow at the vessel wall is zero, and maximal at the center
Turbulent blood flow
Disrupted flow. Stream mixes radially & axially. Found at the valves or at the site of a blood clot, or in vessels of high velocity. More energy (pressure) is required to drive turbulent blood flow than laminar blood flow. Often accompanied by audible vibrations called heart sounds or murmurs
This type of blood flow is often accompanied by audible vibrations called heart sounds or murmurs
Turbulent flow
What is Reynold’s number?
It predicts whether flow will be laminar or turbulent
An increase is Reynold’s number means
Greater tendency for turbulence
If Reynold’s number is less than 2000 then
Blood flow is likely laminar
If Reynold’s number is greater than 2000 then
Blood flow is likely turbulent
If Reynold’s number is greater than 3000 then
Blood flow is always turbulent
What factors increase Reynold’s number?
A decrease in blood viscosity (ex: decrease in hematocrit, anemia), also increase cardio output
An increase in blood velocity (ex: narrowing of blood vessel; thrombi)
What is compliance or capacitance?
Describes the distensibility of blood vessels
Inversely related to elastance
Formula for compliance
C = V / P
C = compliance V = volume (mL) P = pressure (mmHg)
What happens to the amount of pressure in the systemic circuit as blood flows through it?
Pressure decreases progressively through the systemic circulation due to increased resistance
Blood pressure is highest in
The Aorta
Blood pressure is lowest in
The Vena Cava
The largest vein in the body?
IVC
Diastolic Pressure
Pressure in the artery during ventricular diastole/relaxation
It is the lowest arterial pressure measured during a cardiac cycle
Systolic Pressure
Arterial pressure measured during ventricular systole/contraction
Highest arterial pressure measured during a cardiac cycle
Pulse Pressure
Difference between systolic and diastolic pressure. Co-relates to stroke volume
Mean Arterial Pressure (MAP)
Average pressure in a complete cardiac cycle. MAP = diastolic pressure + 1/3 pulse pressure
This type of pressure fluctuates during the cycle and is pulsatile
Arterial Pressure
This type of pressure is very low due to high compliance
Venous Pressure
Atrial Pressure
lower than venous pressure
Dicrotic notch or incisura
The “blip” in the arterial pressure curve. Produced when the aortic valve closes
What produces the “blip” in the arterial pressure curve?
When the aortic valve closes. It is called the Dicrotic notch or incisura
Arteriosclerosis
Is a pathology that will alter the arterial pressure curve. It is due to plaque deposits in the arterial walls which decreases diameter/radius. It stiffens walls making them more rigid & less compliant
Impact of Arteriosclerosis on Arterial Pressure Curve
Systolic pressure, pulse pressure, & mean pressure will be increased
Impact of Aortic Stenosis on Arterial Pressure Curve
Occurs when the aortic valve is stenosed (hardened) due to calcification
Stroke volume is decreased b/c less blood enters the aorta on each beat. Systolic, pulse, & mean pressure will be decreased
Aortic regurgitation
Due to incompetent valve causing retrograde flow
The pacemaker of the heart
SA (Sinoatrial) Node. the AP originates from SA node
Why is the SA node the pacemaker of the heart?
B/c it has the highest intrinsic firing rate in the heart
Normal heart rate
60-100 bmp
Sequence of myocardium activation
SA node -> AV node -> Bundle of His (common bundle) -> Right/Left Bundle Branches -> Purkinje Fibers
Latent Pacemakers take over when
SA node firing rate decreases
SA node stops completely or is removed
If the intrinsic rate of firing of a latent pacemakers should become faster than that of the SA node, then it assumes the pacemaker role
Blocked conduction from SA node to conducting pathways
Excitability
The ability of cardiac cells to initiate an action potential in response to an inward, depolarizing current. Reflects the recovery of channels that carry the inward current for the upstroke of the action potential
Refractory Period
The time during which another action potential cannot be elicited
Absolute Refractory Period
Period during which another action potential can be initiated, regardless of how much inward current is supplied. Begins with upstroke of the AP and ends after the plateau. Cell has repolarized to about -50 mV
Effective Refractory Period
Period during which a generated action potential cannot be conducted
Slightly longer than the Absolute Refractory Period
The Na+ channels begin to recover whereby they become available to carry inward current
Inward current is not enough to conduct to the next site
Relative Refractory Period
Period during which an action potential can be elicited, but more than usual current is required. Immediately after the ARP when repolarization is almost complete
Chronotropic Effects
Effects of the ANS on heart rate (HR) via SA node
Positive Chronotropic vs Negative Chronotropic Effects
Positive increases HR, Negative decreases HR
Chronotropic Effectors determine the heart rate by controlling
The rate of phase 4. The smaller the phase 4, the faster the heart rate. Mechanism of Action for both, you change the flux of sodium. To increase HR you increase the influx of sodium. To decrease HR you decrease the influx of sodium
Positive chronotropic effects sympathetic nervous system via
Beta 1
Negative chronotropic effects parasympathetic nervous system via
M2
Dromotropic Effects
Effects of the ANS on conduction velocity via AV node
Positive vs Negative dromotropic effects
Positive leads to an increase in conduction velocity via AV node. Negative leads to a decrease in conduction velocity via AV node
Sympathetic receptor for positive dromotropic effects
B1
Parasympathetic receptor for negative dromotropic effects
M2
What is a heart block?
AP not being conducted from atria to ventricle
A measurement of tiny potential differences on the surface of the body that reflect the electrical activity of the heart
Electrocardiogram (ECG or EKG)
P Wave
Represents depolarization of the atria. Duration of the wave correlates with conduction time through the atria. Atrial repolarization is not seen on a normal ECG, b/c it is “buried” in the QRS complex
PR interval
From beginning of P wave to the beginning of Q wave (initial depolarization of the ventricle). Correlates w/ conduction time through the AV node. It represents ventricular filling
QRS complex
Represent depolarization of the ventricles
Conduction thru the ventricle is similar to the atria b/c of high conduction velocity of the His-purkinje system
T wave
Represents repolarization of the ventricles. Ventricular relaxation or diastole
QT interval
Interval from beginning of Q wave to end of the T wave. Represents the entire period of depolarization & repolarization of the ventricles. Contraction & relaxation
ST segment
From end of S wave to the beginning of the T wave. Represents ventricular repolarization
Gap junctions allow are heart muscle to behave as
A syncytium or a unit
Inotropism
The intrinsic ability of myocardial cells to develop force at a given muscle cell length
The amount of calcium released by the sarcoplasmic reticulum is dependent on
- The size of the inward calcium current
2. The amount of calcium that was previously stored in the SR
Positive Ionotropic Effects
Increase in contractility
Use Beta 1 as receptors
Increase Rate of Relaxation
