Circulation Flashcards
Why do we have a heart?
- Pumps blood
- Move oxygen around the body
- Take carbon dioxide out
- Move hormones and waste products around
How does the heart help maintain homeostasis?
Provides potential energy and pressure
What is heart failure?
When the heart muscle is unable to contract optimally to pump blood at a rate sufficient to meet the requirements of metabolizing organs
When does heart failure occur?
When the heart can no longer move blood into the systemic and/or pulmonary circulation at a rate that meets the needs of metabolizing cells
What amount of blood does an adult human need circulated per minute?
~ 5L
What are 4 common symptoms of heart failure?
- Congestion in lungs
- Fatigue
- Edema
- Enlarged liver
What is an MI (myocardial infarction)?
Loss of heart muscle due to stoppage of blood flow
What causes the stoppage of blood flow in an MI?
Plaque build-up in the coronary artery
Do all post-MI patients progress to heart failure?
No, only if the initial damage is significant
What are 7 risk factors for an MI?
- Genetics
- Smoking
- Gender
- Diet
- Personality
- Stress
- Alcoholism
What are 5 causes of an MI besides atherosclerosis?
- Essential hypertension
- Diabetes
- Idiopathic primary cardiomyopathy
- Viral infection of the heart
- Cardiac valve diseases
Why is the heart considered an endocrine organ?
It generates a host of hormones and cytokines that may impact on cardiac wound healing and/or growth
What 5 hormones does the heart produce/release?
- Angiotensin 2
- IL-6
- Cardiotrophin-1
- FGF-2
- TNF-alpha
What are the 3 basic components of the cardiovascular system?
1) Heart
2) Blood vessels
3) Blood
What is the broad function of the heart?
A pump that serves to pressurize the arterial tree
What direction does blood flow?
From high pressure to lower pressure
True or false: blood will flow from an area of higher pressure to an area of lower pressure even if there is a 1 mmHg difference
True
Where does major loss of blood pressure occur?
Points of restriction within the arterial tree (such as arterioles)
What is the broad function of blood vessels?
Delivery mechanisms for blood as it moves from the heart, and for its return to the heart
What are arteries?
Vessels that carry blood away from the ventricles to the body
What are veins?
Vessels that carry blood from the body to the heart
What is blood?
A transport medium within which materials being moved long distances in the body are dissolved or suspended
How does blood flow through the body?
Continuously through the closed circulatory system via 2 separate loops, which begin and end at the heart
What is the function of the pulmonary circulation?
Carry blood between the heart and lungs
What type of system is the pulmonary circulation?
Low pressure & low resistance
What is the function of the systemic circulation?
Carry blood from the heart to all peripheral organ systems
What type of system is the systemic circulation?
High pressure & high resistance
True or false: the heart functions as a single parallel pump
False, it functions as a dual parallel pump
Between what to bones is the heart located and why is the advantageous?
- Sternum and vertebrae
- Makes it possible to push blood out of the heart when it is not pumping by itself by rhythmically depressing the sternum
What divides the 2 halves of the heart?
Interventricular septum
What are atria?
The upper chambers of the heart that receive returning blood
What are ventricles?
Lower chambers of the heart that receive blood from atria and pump blood into the body
What is the function of the interventricular septum?
Prevents mixing of blood from the low oxygenated blood in the right and the highly-oxygenated blood in the left
Describe the pathway of systemic return
- Enters right atrium via the vena cavae
- Pumped into right ventricle
- Pumped in pulmonary arteries in each lung, where it is oxygenated
What kind of blood does the systemic return carry?
Oxygen poor blood
What is a statement that can be made about the RIGHT side of the heart?
It receives blood from the systemic circulation and pumps it into the pulmonary circulation
True or false: each side of the heart needs to pump the same amount of blood
True
Which side of the heart is larger and why?
Left because it has a longer distance than the right side to pump blood in the same amount of time
Describe the pathway of the pulmonary circulation
- Blood loses CO2 and acquires O2 in the lungs
- Pumped to the left atrium via the pulmonary veins from each lung
- Pumped to left ventricle, then to the aorta, and then to the systemic circulation
What kind of blood does the pulmonary circulation carry?
Oxygen rich blood
What is a statement that can be made about the LEFT side of the heart?
Receives blood from the pulmonary circulation and pumps it into the systemic circulation
What does the aorta do?
Carries blood away from the left ventricle
Which side of the heart pumps blood at a higher pressure?
Left
What do cardiac valves allow for?
Unidirectional flow of blood for efficient pump action
What is special about the positioning of cardiac valves?
They are positioned so that they open and close passively from pressure differences
How do cardiac valves open and close?
- A forward pressure gradient (greater pressure behind the valve) forces the valve open
- A backward pressure gradient (greater pressure in front of the valve) forces the valve closed
True or false: cardiac valves can open in both directions
False, can only open in one direction
Where are the atrioventricular valves found?
Between atria and ventricles
What is the function of atrioventricular valves?
- Allow for movement of blood from atria to ventricles during ventricular filling
- Keep blood in the ventricles when they contract
What forces the closure of AV valves?
Rising ventricular pressure
What is another name for the right AV valve?
Tricuspid
What is another name for the left AV valve?
Bicuspid or mitral
What are AV valves attached to and what does this do?
Anchored by fibrous chordae tendinae (which attach to papillary muscles) that prevents leaflet eversion from high pressure
Where are the semilunar valves found?
Between ventricles and major arteries
What is the function of semilunar valves?
Govern blood flow where major arteries leave the ventricles
How many cusps do semilunar valves have?
3
What causing semilunar valves to open?
When ventricular pressure exceeds the pressure in the aorta and pulmonary artery
What is the heart wall composed of?
Spirally arranged cardiac myocytes forming an electrical syncytium
How are cardiac myocytes connected?
At specific junctions (intercalated discs) that feature porosity and electrical connectivity
What populates the heart wall?
Gap junctions and desmosomes
What are gap junctions (with respect to the heart wall)?
Low resistance regions that allow action potentials to spread
What is the function of desmosomes in the heart wall?
Structural anchoring
What are the 3 layers of the heart?
- Endocardium
- Myocardium (muscle)
- Epicardium (thin external membrane)
True or false: atria and ventricles behave as a single syncytium
False, they are electrically isolated and behave as separate syncytiums
What separates the atria and ventricles?
A non-conductive fibrous skeleton
What is the function of the spiral arrangement of myocytes?
Allows the heart to wring blood from ventricular cavities with each contraction
True or false: there are a great deal of mitochondra in cardiac myocytes
True
What is the pericardial sac?
Double walled membrane that holds the heart in position
What helps reduced the resistance to movement in the heart?
Pericardial fluid
True or false: the heart is autorhythmic
True
What triggers contractions of the heart?
Autorhythmic cells / pacemakers
How is cardiac contraction coordination achieved?
Through structure
What do ECG’s provide?
Information about cardiac performance
What is the normal pacemaker of the heart?
The sinoatrial node
Where is the SA node located?
In the right atrial wall near the opening of the superior vena cavae
The majority of cardiac cells are _____
Contractile (they do not fire spontaneously)
What are autorhythmic cells responsible for?
Initiating and conducting cardiac action potentials
Where are autorhythmic cells found?
SA node, AV node, Bundle of His, and Purkinje fibres
What are the rates of action potentials that the different autorhythmic cells fire?
- SA node fires at 70-80 bpm
- AV node fires at 40-60 bpm
- Bundle of His and Purkinje fibres fire at 20-40 bpm
What are pacemaker cells?
Cells with the highest discharge rate (cells in the SA node)
What are latent pacemakers?
Cells that fire action potentials at lower rates than pacemaker cells
Describe the spread of cardiac excitation
- An action potential is initiated in the SA node
- Spread throughout both atria
- Reaches AV node and spreads hastly through ventricles
What is the spread of an action potential through the atria facilitated by?
Interatrial and internodal pathways
The _____ is the only point where an action potential can spread from the atria to the ventricles
AV node
Why is there a large AV nodal delay?
So the atria can properly fill ventricles before they contract
Does atrial or ventricular contraction occur first?
Atrial
Contraction of ____ must occur simultaneously
Both atria and then both ventricles
How does excitation occur throughout the atria?
Via gap junctions and the interatrial pathway
How is the AV node excited?
Through the internodal pathway and by cell-to-cell contact
Where does the interatrial pathway extend?
From the SA node with the right atrium to the left atrium
Where does the internodal pathway extend?
From SA node to AV node
What cause the AV nodal delay?
Slow conduction through the AV node
Ventricular conduction system is highly ______
Organized
Where do the majority of Purkinje fibres terminate?
On ventricular muscle cells near the endocardial surface
What is an electrical signal converted to in cardiac muscle?
A contractile signal
What is the signal for contraction?
An elevation of cytosolic calcium
What can cause cardiac failure?
Too much or too little calcium
Where is calcium derived from?
The ECF and the sarcoplasmic reticulum
What does elevated calcium lead to?
Cross-bridge cycling between actin and myosin
What is tetanus?
When the muscle fibre does not have a chance to relax before more stimulation occurs, resulting in a sustained, maximal contraction
How does the brain control the heart?
- Length-tension
- Increase heart rate
- Calcium change
What does an ECG measure?
- Overall spread of electrical activity in the heart
- Electrical signals from the heart conducted by body fluids
True or false: an ECG is a direct measure of cardiac electrical activity
False, it is not
How does an ECG measure electrical signals?
Measures the difference in electrical potential between 2 different points on the body
How many leads/electrodes are used in a typical ECG?
12
What does the P wave represent?
Atrial depolarization
Is the P wave or QRS complex smaller and why?
P wave is much smaller because the atria muscle mass is much smaller than the ventricle, so it generates less electrical activity
What does the QRS complex represent?
Ventricular depolarization
What does the T wave represent?
Ventricular repolarization
What does the PR segment show?
AV nodal delay
What does the ST segment show?
When ventricles are completely depolarized
What does the TP interval show?
When the heart is at rest and ventricles are filling
What are ECG’s useful at diagnosing?
- Abnormal heart rates
- Arrhythmias
- Damage to heart muscle
What is a flutter?
When the heart is beating too fast, leaving little time to contract
What are extrasystoles?
When pacemaker is in the wrong spot, causing a premature beat
How can an extrasystole be recognized on an ECG?
Slow & long-lasting, therefore wide on the ECG
What is a complete heart block and what does it cause?
- Dysfunctional AV node
- Causes no coordination between the top and bottom of the heart, usually causing the ventricles to contract slowly
What are the 3 types of AV block?
1) First degree
2) Second degree
3) Third degree
How can a first degree AV block be diagnosed on an ECG?
Delay becomes longer after P segment
How can a second degree AV block be diagnosed on an ECG?
No QRS with every P wave
What is a third degree AV block?
No communication at all between top and bottom of heart
What is atrial fibrillation characterized by?
Rapid, irregular, uncoordinated depolarizations of the atria with no definite P waves
What is complete heart block characterized by?
Complete dissociation between atrial and ventricular activity, with impulses from the atria not being conducted to the ventricles at all
What does the cardiac cycle consist of?
2 alternating phases
What are the 2 phases of the cardiac cycle?
1) Systole
2) Diastole
What is systole?
Contraction and emptying of the heart and ejection of blood
What causes systole?
Depolarization of the cardiac muscle
What is diastole?
Relaxation and refilling of the heart
What causes diastole?
Repolarization of the cardiac muscle
True or false: atria and ventricles go through separate cycles of systole and diastole
True
Does the atria or ventricle contract first and why?
Atria, to help move blood into the ventricles
True or false: the left and right atria contract at the same time, same with the left and right ventricles
True
What happens to the cardiac cycle in patients with heart block (arrhythmias)?
Automatic rhythm is disrupted, leading to fainting and dizziness
What is the first step of the cardiac cycle?
Atrial pressure increases due to continuous passive filling of blood into atria
What part of an ECG represent the increase of atrial pressure?
TP interval
What occurs after atrial pressure increases in the cardiac cycle?
AV valves open
What occurs after AV valves open in the cardiac cycle?
Ventricular volume increases as blood flows into ventricles from atria
What occurs after ventricular volume increases in the cardiac cycle?
Atria become depolarized
What occurs after atrial depolarization in the cardiac cycle?
Atria contract and squeeze blood into the ventricles, causing an increase in atrial pressure
What occurs after atrial contraction in the cardiac cycle?
Ventricular pressure increases as ventricular blood volume increases
What occurs after ventricular pressure increases in the cardiac cycle?
Impulse travels through AV node and causes ventricular depolarization, initiating contraction
What is end-diastolic volume?
The volume of blood at the end of ventricular diastole
What occurs after ventricular contraction in the cardiac cycle?
Ventricular pressure exceeds atrial pressure, causing AV valves to close
What occurs after AV valve closure in the cardiac cycle?
Ventricular pressure exceeds aortic/pulmonary pressure, causing opening of semilunar valves and ejection of blood
What is isovolumetric ventricular contraction?
When the ventricular pressure rises after contraction, but volume and muscle fibre length remain constant
What occurs after the semilunar valves open in the cardiac cycle?
Aortic/pulmonary pressure increases due to blood forced into the aorta/pulmonary artery
What occurs after aortic/pulmonary pressure increase in the cardiac cycle?
Ventricular volume reduces significantly (but not completely)
What is end-systolic volume?
Volume of blood at the end of systole
How is stroke volume determined using end-diastolic volume and end-systolic volume?
SV = EDV-ESV
What is a normal end-diastolic volume?
135 mL
What is a normal end-systolic volume?
65 mL
What is a normal stroke volume?
70 mL
What is ejection fraction?
The proportion of the blood volume ejected by each ventricle with each contraction
How is ejection fraction determined?
EF = SV/EDV
What is a normal ejection fraction?
~ 0.52
What occurs after ventricular volume reduction in the cardiac cycle?
Ventricular repolarization
What occurs after ventricular repolarization in the cardiac cycle?
Ventricular pressure falls below aortic/pulmonary pressure causing the semilunar valves to shut
What occurs after semilunar valve closure in the cardiac cycle?
Ventricular pressure falls below atrial pressure and AV valves open
What does semilunar valve closure cause?
A disturbance that is seen as a dicrotic notch on the aortic/pulmonary pressure curve
What is isovolumetric ventricular relaxation?
When ventricular pressure falls, but volume and muscle fibre length remain constant
What is the pressure-volume loop usually for?
Left ventricle
What does increased preload cause?
Triggers the Frank-Starling mechanisms, resulting in increased stroke volume
What does increased afterload cause?
- Increased pressure in the ventricle before the aortic valve opens
- Ventricle empties less efficiently, resulting in decreased stroke volume
What about the pressure-volume loop can change and when will it change?
- Shape and/or area can change
- Will change in characteristic ways in diseases
What happens to ventricular diastole during exercise?
Since heart rate is increasing dramatically, the length of ventricular diastole is reduced, therefore there is less ventricular filling
Does decreased ventricular filling cause a significant drop in CO? Why or why not?
It doesn’t because much of the filling of ventricles occurs in the rapid filling phase
When would decreased ventricular filling cause a drop in CO?
When heart rate exceeds 200 bpm
How many heart sounds are audible with a stethoscope?
2
What does the first heart sound sound like?
Low pitch, soft, long duration
What is the first heart sound linked to?
AV valve closure
What does the first heart sound signal?
Onset of ventricular systole
What does the second heart sound sound like?
High pitch, sharp, shorter duration
What is the second heart sound linked to?
Semilunar valve closure
What does the second heart sound signal?
Onset of ventricular diastole
What are heart sounds caused by?
Vibrations inside the walls of the ventricles and arteries
What are heart sounds NOT caused by?
The shutting of heart valves
What causes abnormal heart sounds?
When blood flow that is normally laminar becomes turbulent
How can you determine the type of valvular defect?
Location and timing of the murmur
What type of murmur occurs between the first and second heart sounds?
Systolic
What type of murmur occurs between the second and first heart sounds?
Diastolic
What is heard from a stenotic murmur?
Whistling
What is heard from an insufficient murmur?
Swishing
What is a stenotic murmur?
When a valve doesn’t open completely due to stiffness and narrowing
What is an insufficent murmur?
When a valve is scarred, resulting in poor apposition of the leaflets that prevents complete closure of the valve
What does an insufficient valve allow for?
Backwards flow of blood
What is another name for an insufficient valve?
Leaky valve
What is the most common cause of valve malfunction?
Rheumatic fever
What is rheumatic fever?
An autoimmune disease caused by a streptococcal bacterial infection
What occurs in rheumatic fever?
Antibodies produced against bacterial toxins attack the body’s own tissues, with the heart valves being a main target
What damage to heart valves is done from rheumatic fever?
Valves become thick, stiff, and scarred because of large hemorrhagic fibrous lesions
What is a less common cause of valve defects?
Genetics
What is cardiac output?
The volume of blood pumped by each ventricle per minute
What 2 factors determine cardiac output?
1) Heart rate
2) Stroke volume
What is heart rate?
The number of times the heart beats per minute
What is the average resting heart rate?
70 bpm
What is stroke volume?
The volume of blood that is pumped per beat
If the average cardiac output is 5 L/minute, what does that tell us about how much each side of the heart is pumping?
Each side is pumping 5 L/minute
What is a consequence of mismatch between cardiac output of each side of the heart?
Back-up behind the weaker side
What is cardiac reserve?
- The difference between the cardiac output at rest and at its peak
- The maximum volume of blood that can be pumped by the heart per minute
What can cause cardiac reserve to increase?
Exercise
How can the heart increase its output?
- Increasing heart rate
- Increasing stroke volume
What modulates the heart?
Autonomic nervous system (sympathetic and parasympathetic)
What branch of the ANS supplies the atrium?
Parasympathetic nerve (vagus nerve)
What branch of the ANS supplies the SA and AV nodes?
Parasympathetic
What do cardiac sympathetic nerves supply?
Atria and ventricles
What is the main function of sympathetic nerves on the heart?
Increase heart rate
What is the main function of parasympathetic nerves on the heart?
Slow down heart rate
True or false: in a healthy individual, only the sympathetic or the parasympathetic systems are active at any given time, never at the same time
False, both systems can be and typically are active at the same time
True or false: nervous stimulation is NOT essential for initiating contractions of the heart
True
True or false: the SA node needs nervous stimulation to regulate heart rate
False, the SA node can regulate heart rate independently
What are the sodium and potassium levels of pacemaker cells below threshold?
High K and low Na
What happens in pacemaker cells as the membrane potential passes threshold?
Voltage-gated calcium channels open and a rapid influx of Ca occurs, causing an action potential
What does the sympathetic NS act on to increase heart rate?
SA and AV nodes
How does the sympathetic NS increase heart rate?
- Inactivates K ion channels responsible for the normal outward leak, resulting in build-up of K within the cell
- The net increase in positive charge makes it easier for the cell to reach threshold
______ stimulation reduces AV node delay
Sympathetic
______ stimulation speeds up the spread of action potentials throughout the specialized conduction pathway
Sympathetic
How does the sympathetic NS increase force of contraction?
- Increases strength of contraction of atrial and ventricular cells
- Higher intracellular Ca results in more forceful contraction
What does the parasympathetic NS act on to decrease heart rate?
SA
How does the parasympathetic NS decrease heart rate?
Releases acetylcholine which reduces SA node depolarization by slowing the closure of K channels
_______ stimulation prolongs AV node delay
Parasympathetic
_______ stimulation slows the spread of action potentials throughout the specialized conduction pathway
Parasympathetic
How does parasympathetic stimulation decrease the strength of contraction?
Reduces Ca influx and intracellular Ca cycling
Why does parasympathetic stimluation have little effect on the ventricles?
Lack of parasympathetic innervation
When is the sympathetic NS needed to control the heart?
During emergency situations or when challenged (like during exercise)
When does the parasympathetic NS control the heart?
Relaxed situations
Which branch of the ANS predominates during resting heart rate?
Parasympathetic
Where and when is epinephrine secreted?
- From adrenal medulla
- Upon sympathetic stimulation
What effects does epinephrine have on the heart?
Similar to epinephrine; increases heart rate and contractility
What 2 factors determine stroke volume?
1) Extent of venous return
2) Extent of sympathetic stimulation
Is venous return an intrinsic or extrinsic control?
Intrinsic
Is sympathetic stimulation an intrinsic or extrinsic control?
Extrinsic
What happens when more blood is returned to the heart from the venous system?
More blood must be pumped out of the heart
What causes more blood to be returned to the heart?
An increase in end-diastolic volume, which means a larger stroke volume
What determines the hearts ability to adjust stroke volume?
The length-tension relationship of cardiac muscle
At rest, is cardiac muscle fibre length longer or shorter than its optimal length?
Shorter
What is the major factor that determines cardiac muscle fibre length?
Amount of blood entering during diastole
What does increased filling result in?
Increased stretching of the heart, which causes greater tension development, stronger force of contraction and larger stroke volume
What helps equalize the output of the right and left sides of the heart?
The relationship between venous return and stroke volume
What happens when the right side of the heart receives a large volume of blood?
- The EDV increases and causes the right ventricle to contract forcefully, propelling blood into the pulmonary circulation
- A large volume is pumped to the left side, which increases EDV and causes the left ventricle to conract forcefully, ejecting blood into the systemic circulation
How are effects of the sympathetic NS mediated?
Through epinephrine and norepinephrine on contractile cells
What else does activation of the sympathetic NS cause besides increased cardiac contractility?
Constriction of veins, which in turn results in greater return of blood to the heart, causing increased EDV and CO
What 2 pathological conditions can increase the workload of the heart?
High arterial pressure or a defective valve
What is hypertrophy?
A short-term compensatory mechanism by which the heart is able to adjust to the increased workload by increasing the number of cardiac muscle cells
What is the main difference between a failing heart and a non-failing heart?
A failing heart ejects a lower stroke volume for a given EDV
What is the hallmark of heart failure?
Impaired contractility
What are 2 compensatory mechanisms used in the initial stages of heart failure?
1) Elevated sympathetic activity
2) Increased EDV
How do the kidneys help with heart failure?
CO is diminished, so the kidneys retain extra salt and water, increasing blood volume and thus elevating EDV
What is backward failure and when does it occur?
- When blood that is unable to enter the heart and blood that is unable to be pumped out builds up in the venous system
- Occurs in later stages of heart failure
What is forward failure and when does it occur?
- When the heart cannot pump sufficient blood as a result of a progressively smaller stroke volume
- Occurs after backward failure
Are blood vessels a closed or open system?
Closed
What are the 2 portal systems in humans?
Hepatic and hypophyseal
True or false: blood is evenly distributed through the circulatory system
False, different vascular beds receive different amounts of blood depending on the needs of the tissue
True or false: each tissue receives only the amount of blood it needs
False, some organs receive more blood than they need
Why is it advantageous that some organs receive more blood than they need?
They can survive large fluctuations in blood flow without damage
What are 3 examples of organs that can withstand a decrease in their normal blood flow?
1) Kidneys
2) Skin
3) Digestive tract
What are arterioles coated with?
Smooth muscle
What are capillaries the site of?
Nutrient and cellular waste exchange
What is the function of venules?
Drain capillary beds
Why are veins highly elastic?
They need to constrict
How is flow rate determined?
delta P/R
Why is pressure gradient significant to flow rate?
It is the main driving force for flow through the vessel
What provides the energy for the pressure gradient?
Cardiac pump
What is resistance?
A measure of hindrance to blood low through a vessel
What happens if resistance increases?
The pressure gradient must also increase to maintain a steady flow rate
With respect to arterioles, at which points is mean arterial pressure higher and lower?
- Higher before blood reaches arterioles
- Lower within the arterioles just before it reaches capillaries
What happens if resistance doubles and pressure gradient remains the same?
Flow rate will reduce by half
What is flow a measure of?
Volume per unit time
What is velocity a measure of?
Linear distance per unit time
What is caused by a greater vessel surface area in contact with blood?
Greater resistance
What is caused by a smaller diameter vessel?
Greater resistance
How are resistance and vessel radius related?
Resistance is inversely related to the 4th power o the vessel radius (r^4/R)
What would a 2x increase in radius do to resistance?
Decrease resistance by 16-fold
What would a 2x increase in radius do to flow rate?
Increase flow rate by 16x
Why is vessel length ignored?
Because we have a closed circulatory system, and length rarely changes
What is the most important contributor to resistance?
Vessel radius
What occurs in atherosclerosis with respect to radius and flow rate?
Radius decreases due to plaque, causing flow rate to decrease
What is pulse pressure?
The difference between systolic and diastolic pressure
What is mean arterial pressure?
The average pressure driving the blood forward into the tissues
Why is mean arterial pressure not (systolic + diastolic) / 2?
Arterial pressure remains closer to diastolic than systolic pressure for a longer portion of the cardiac cycle
How is mean arterial pressure calculated?
pp/3 + D
What are Korotkoff sounds?
The sounds heard when the pressure of the cuff matches the blood pressure
What blood pressure is considered hypertension?
140/90
What blood pressure is considered hypertension for diabetics or those with kidney disease?
130/80
Arteries are ____ vessels
Conductance
Arterioles are _____ vessels
Resistance
Veins are _____ vessels
Capacitance
What 4 things are arteries composed of?
1) Smooth muscle cells
2) Endothelial cells
3) Collagen fibres
4) Elastic laminae
What is the function of smooth muscle cells for arteries?
Regulate diameter
What is the function of endothelial cells for arteries?
Regulate smooth muscle function & vessel permeability
What are 2 functions of collagen fibres for arteries?
- Impart rigidity to the arterial wall
- Give mechanical strength to withstand pressure and stretching
What is the function of elastic laminae for arteries?
Impart elasticity to the arterial wall
Do arteries offer lots or little resistance to flow and why?
Little because of their relatively large diameter
True or false: arteries can store energy to force blood movement when the heart relaxes
True
What is blood pressure a function of?
The volume of blood in the vessel and the compliance of the vessel
What happens when pressure is changed in a vessel with high compliance?
A large change in volume
What happens when pressure is changed in a vessel with low compliance?
A small change in volume
During systole, is there more blood going in or out of the vessel and what does this cause?
Volume going in is greater than volume going out, which means the pressure gradient will increase and vessel walls expand
During diastole, is there more blood going in or out of the vessel and what does this cause?
Volume going in is less than volume going out, which means the pressure gradient decreases and vessel walls contract
What is the function of elastic properties of arteries?
Allows them to expand and thus store potential energy as blood volume increases with contraction
What protein produces the elastic properties of arteries?
Elastin
Why do arterioles adjust?
To determine the distribution of cardiac output and to regulate blood pressure
What is another term for flow?
Cardiac output
What is another term for pressure gradient?
Mean arterial pressure
What is another term for resistance?
Total peripheral resistance
If cardiac output increases, what will happen to blood pressure?
It will also increase
If resistance increases, what will happen to blood pressure?
It will also increase
If vessels open, what will happen to blood pressure?
It will decrease
What happens when resistance is increased due to vasoconstriction?
Blood flow is decreased
What is vascular tone?
Partial constriction of the vessel
What does vascular tone allow for?
Fine control of resistance
What would happen if vascular tone did not exist?
No vasodilation control
What 2 things cause generation of vascular tone?
1) Myogenic activity
2) Sympathetic release of norepinephrine
True or false: a tissue receives exactly the amount of perfusion required to meet its immediate metabolic needs
True
What can too little perfusion cause?
Impair the tissues ability to function
What can too much perfusion cause?
Deny valuable resources to other tissues
What are 2 important factors for extrinsic control of arteriolar resistance?
1) Neural
2) Hormonal
True or false: systemic extrinsic effects override local intrinsic adjustments
False, intrisic effects override extrinsic effects
What supplies all smooth muscle (except in brain tissue)?
Sympathetic nerve fibres descending from the cardiovascular control centre of the brain
What does elevated sympathetic activity cause?
Vasoconstriction
What does decreased sympathetic activity cause?
Vasodilation
What can activation of the motor cortex cause?
Regulation of the sympathetic NS and parasympathetic NS, thus affecting cardiovascular regulation
What are baroreceptors?
Pressure-sensitive receptors
Where are baroreceptors located?
In the carotid sinus and aortic arch
When are baroreceptors activated?
In response to high or low BP and act to regulate BP
What do baroreceptors influence?
PNS and SNS
Where are skeletal muscle mechanoreceptors located?
In muscle
What do skeletel muscle mechanoreceptors sense?
Mechanical or metabolic signals associated with muscle contraction
What happens when skeletal muscle mechanoreceptors are activated?
They influence the SNS to increase blood pressure and heart rate; contribute to the central control of blood flow
What 2 things have a significant impact on blood pressure?
1) Blood volume
2) Fluid balance
Why are hypertension patients often prescribed diuretics?
To increase urine output and decrease blood volume, thus decreasing blood pressure
What are 2 vasodilator hormones?
1) Bradykinin
2) Histamine
What does bradykinin cause?
Dilation and increased capillary permeability
What does histamine cause?
Vasodilation of arteriolar smooth muscle
Where does histamine arise from?
Connective tissue cells or circulating WBC’s
What are 3 vasoconstrictor hormones?
1) Norepinephrine/epinephrine
2) Angiotensin 2
3) Vasopressin
Where is epinephrine released from?
Adrenal medulla
What does epinephrine cause?
Systemic vasoconstriction and increased blood pressure
What is a secondary function of epinephrine?
Binds to beta-2 adrenoreceptors to cause vasodilation in tissues with a lot of beta-2 receptors
What does angiotensin 2 cause?
Increase in TPR, thus increasing blood pressure
What does angiotensin do at the local level?
Can severely limit blood flow by promoting severe vasoconstriction
Is vasopressin or angiotensin 2 more potent?
Vasopressin
Where is vasopressin formed?
In nerve cells in the hypothalamus
Where is vasopressin stored?
Posterior pituitary
What does vasopressin do once it is secreted into the blood?
Influences blood pressure regulation during severe hemorrhage
True or false: intrinsic control can be either chemical or physical in nature
True
What does high O2 tension mean?
Vasoconstriction
What does high CO2 tension mean?
Vasodilation
What happens to oxygen and flow when metabolic demands increase?
Oxygen is depleted, so muscle tension cannot be maintained, the vessel dilates, and flow to the tissue increases
What is active hyperemia?
When blood flow increases in order to meet increased local metabolic demand
What is produced by actively metabolizing tissues and what do all of these substances have in common?
- CO2, acids, potassium, and adenosine
- All are vasodilators
Lipid-derived prostaglandins are vaso_____
Dilators
What is prostacyclin produced by and what is it’s function?
Produced by endothelial cells to maintain normal flow
What is endothelial-derived relaxing factor (EDRF)?
A potent vasodilator that has been identified as the soluble gas nitric oxide
What does nitric oxide cause?
Relaxation of smooth muscle; aka vasodilation
What can impaired nitric oxide production cause?
Hypertensive disorders
What is endothelial-derived hyperpolarizing factor (EDHF)?
A vasodilator
When is endothelin released?
In response to vascular damage caused by physical trauma
Where is endothelin found?
Endothelial cells of most blood vessels
What does endothelin cause?
Severe vasoconstriction to help prevent extensive bleeding
True or false: endothelin produces a long-term effect
False, endothelin produces a short-term immediate effect
Heat ____ blood flow
Increases
Cold ____ blood flow
Decreases
What does cold cause?
Vasoconstriction, resulting in reduced blood flow to the affected tissue
What is reactive hyperemia?
- When blood flow to a tissue is totally restriced, myogenic relaxation is coupled with a decrease in O2 levels in that tissue
- The result is a large increase in blood flow once the occlusion is removed
What is shear stress?
A longitudinal force induced by the friction of blood flowing over the endothelial cell surface
What is a result of shear stress?
Endothelial cells release nitric oxide, causing relaxation of underlying smooth muscle
What is pressure autoregulation?
A means by which tissues resist changes in blood flow, in the fact of changes in mean arterial pressure
What does a drop in MAP cause?
Reduced blood flow and stretching of arterioles, therefore arterioles dilate to restore blood flow to normal
What does an increase in MAP cause?
Increased blood flow and stretch of arterioles, resulting in vasoconstriction to restore blood flow back to normal
True or false: tissue metabolic demands remain the same most of the time
False, they change rapidly
What stimulates a change in tissues metabolic needs?
A need to quickly alter perfusion
What causes a tissues metabolic needs to change (what factors actually cause the change)?
Various systemic and local factor changes
Skeletal and cardiac muscle have powerful _____ to override ____
- Local control mechanismss
- Sympathetic vasoconstriction and local beta-2 adrenoreceptors to promote vasodilation
What happens upon starting exercise?
Sympathetic drive increases throughout the body, resulting in generalized vasoconstriction, but localized control mechanisms override this and cause vasodilation in exercising muscles
