Chapter 18- The heart Flashcards
Trunk definition
Large artery
How much does the heart weigh?
250-350 grams
How long is the heart?
About 5 inches
Why is the heart tipped in the body, and where is the apex pointing to?
The heart is tipped in the body so the blood vessels at the top of the heart stay open. Apex (inferior “tip”) is pointed toward the left hip.
What covers the heart? (3)
- Fibrous pericardium
2. Serous pericardium (visceral and parietal)
What is the fibrous pericardium and what does it do?
External portion of the heart. Prevents heart from filling with too much blood, anchors heart in chest cavity, protects the heart
Serous pericardium
Internal portion of the heart covering. Divided into visceral and parietal layers- forms fluid filled sac around the heart. The visceral and parietal layers are separated by a small amount of serous fluid
3 layers of the heart
- Epicardium
- Myocardium
- Endocardium
Epicardium
Outermost layer of the heart. This is the visceral layer of serous pericardium
Myocardium
Middle layer of the heart. Contains cardiac muscle arranged in spiral/circular bundles- the heart needs to be contracting at the same time or blood flow will be impaired. Also forms the cardiac skeleton.
Cardiac skeleton
Dense connective tissue fibers that link muscle cells together. Importance- action potentials (APs) only spread in certain directions, prevents overstretching of the heart walls from repeated filling/emptying
Endocardium
Innermost layer of the heart. Covers internal surfaces of the heart, including valves. It’s continuous with linings of major blood vessels entering/leaving the heart
What two circuits move blood through the body?
- Pulmonary
2. Systemic
Pulmonary circuit
Any of the blood vessels that carry blood to and from the lungs. Includes the pulmonary arteries and the pulmonary veins.
Pulmonary arteries function
Pump oxygen poor blood from the right side of the heart to the lungs
Definition of arteries
Arteries are the blood vessels that pump blood away from the heart
Definition of veins
Veins return blood to the heart
Pulmonary veins function
Pump oxygenated blood from the lungs to the left side of the heart
Systemic circuit
Any of the blood vessels that carry blood to and from the body tissues. Includes the aorta and the inferior and superior vena cava.
Aorta function
Oxygenated blood leaves the heart through the aorta and its branches to body tissues. Part of the systemic circuit
Superior and inferior vena cava function
Oxygen poor blood returns to the heart via the superior vena cava and the inferior vena cava. Part of the systemic circuit.
What side of the heart is systemic?
The left side of the heart is systemic. Oxygenated blood travels through arteries, oxygen poor blood travels through veins
What side of the heart is pulmonic?
Oxygenated blood travels through veins, oxygen poor blood travels through arteries. This is the only place in the body where oxygen poor blood is carried by arteries and oxygenated blood is carried by veins
How is pressure different on each side of the heart?
The right side (pulmonic) is relatively low pressure, only needs to travel a short distance. The left side (systemic) is high pressure, travels longer distances, and involves more friction. Therefore, the walls of the left side of the heart (especially the ventricles) are very thick. The left ventricle contracts with more force than the right
What separates the atria?
Interatrial septum
Right atrium
The right atrium receives oxygen poor blood from the systemic circuit. The blood enters via the superior and inferior vena cava and the coronary sinus
Left atrium
The left atrium receives oxygenated blood from the lungs. Blood enters via the pulmonary veins
Features of the atria (3)
- Pectinate muscle
- Auricles
- Fossa ovalis
Pectinate muscle
Increases contractile force of the atrium without increasing the mass of the heart. More lightweight than typical cardiac muscle tissue
Auricles
Two “ears” sitting on the surface of the heart. Increase the receptive capacity of the atria
Fossa ovalis
Indentation in the left atrium. Marks where the foramen ovale used to be
What separates the ventricles?
Interventricular septum
Right ventricle
Pumps oxygen poor blood to the lungs using the pulmonary trunk
Left ventricle
Pumps oxygenated blood to the rest of the body using the aorta
Features of the ventricles (2)
- Trabeculae carneae
2. Papillary muscle
Trabeculae carneae
Ridges of muscle that assist with proper functioning of heart valves in the ventricles
Papillary muscle
Assist in opening/closing of the heart valves in the ventricles
Heart valves function
Prevent the backward flow of blood through the heart- you never want blood to flow from the ventricle up to the atria
Atrioventricular valves location
These valves divide the atrium from the ventricle on both sides of the heart. The tricuspid valve (right side) has 3 cusps (flaps), and the mitral/bicuspid valve (left side) has 2 cusps
AV valves (2)
- Tricuspid valve
2. Bicuspid (mitral) valve
Features of the AV valves (2)
- Chordae tendinae
2. Papillary muscles
Function of chordae tendinae and papillary muscles in the AV valves
Chordae tendineae- anchor each cusp to papillary muscle in the ventricle walls- important when valves are closed. The papillary muscles take up the slack of chordae tendineae and contracts with the ventricular muscle
Actions of the AV valves when the ventricles are relaxed and not filled with blood (2)
- Blood flows from blood vessels into atria
2. Cusps of valves hang loosely, allow blood to flow from the atria into the ventricle
Actions of the AV valves when the ventricles contract (3)
- Blood is forced upward in ventricle due to compression- valves close so the blood is forced into the blood vessel
- Compressed blood pushes against the valve flaps
- Valve flaps pushed together, blocking off the atrium
Semilunar valves (2)
- Aortic semilunar valve- sits at base of the aorta
2. Pulmonary semilunar valve- sits at the base of the pulmonary trunk
How many cusps do the semilunar valves have?
Each SL valve has 3 cusps. The cusps have a half moon shape, where the valve gets its name
Actions of the SL valves when the ventricles contract (2)
- Intraventricular pressure increases, blood is pushed upward
- SL valves open and push blood from the ventricle and into the blood vessel
Actions of the SL valves when the ventricles relax (2)
- Pressure decreases in the heart, increases in the blood vessels
- Blood flows back toward the heart due to this pressure difference- blood pushes against the cusps of the SL valve, closing the valve to prevent backflow
Blood regurgitation
This is when blood moves backward due to valve dysfunction. Where this occurs depends on which valve isn’t working. Mitral valve regurgitation is common.
Valve stenosis
This is when the heart valve stiffens and doesn’t allow enough blood through. Can be caused by high cholesterol, makes the valve less flexible.
Heart murmur
A normal heartbeat makes a “lub-dub” sound, but with a heart murmur the heart makes a “lub-whoosh-dub” sound. The whoosh sound is the backward flow of blood. This usually isn’t dangerous, but can indicate other potentially dangerous heart conditions.
Types of heart murmurs (2)
There are innocent murmurs, which are usually congenital, and abnormal murmurs. Abnormal murmurs can indicate congenital heart disease in children and acquired heart valve diseases in adults.
Coronary circulation
blood supply that provides heart tissue with nutrients
The left coronary artery splits into: (2)
- Anterior interventricular artery- supplies interventricular septum, anterior walls of ventricles
- Circumflex artery- supplies left atrium, posterior walls of left ventricle
The right coronary artery splits into: (2)
- Right marginal artery- supplies myocardium of lateral portion of the right side of the heart
- Posterior interventricular artery- supplies posterior ventricular walls
Coronary sinus
Coronary veins combine to form the coronary sinus, which empties oxygen poor blood directly into the right atrium. A sinus is an area where multiple blood vessels dump blood
Anterior cardiac veins function
Empty directly into atrium (bypasses the coronary sinus)
Mitochondria in myocytes
There is a large number of mitochondria in myocytes (25-30% of total volume) which are responsible for cellular respiration/ATP production. Because of this, cardiac muscle is very resistant to fatigue
How do cardiac muscle cells contract?
Cardiac muscle cells (myocytes) are striated and contract by the sliding filament model of contraction
Intercalated discs
These discs connect the the plasma membranes of cardiac myocytes. Intercalated discs contain both desmosomes and gap junctions, and form a functional syncytium- muscle cells contract simultaneously, so the heart contracts in a coordinated manner
2 important types of cardiac cells
- Pacemaker cells
2. Contractile cardiac cells
Pacemaker cells
Non contractile cells that spontaneously depolarize. Make the pace of the contraction of the heart- don’t contribute to the contraction of the heart or the movement of blood themselves. They’re only found in certain regions of the heart
Spontaneous depolarization
Spontaneous depolarization does not mean randomly depolarizing- the cells depolarize in the absence of any nervous system stimulation
Contractile cardiac cells
Contractile cells that depolarize in response to pacemaker cells-these cells will cause contraction of heart muscle that will pump blood through the heart. Action potentials don’t work the same way as it does in the nervous system
Action potential initiation of pacemaker cells (3 steps)
- Pacemaker potential
- Depolarization
- Repolarization
Pacemaker potential (initiation of pacemaker cells)
“slow depolarization”- Na+ channels open, K+ channels close. Na+ enters the cell, so the inside of the cell becomes more positive
Depolarization (initiation of pacemaker cells)
Calcium channels open at threshold potential (-40 mV). Calcium rushes into the cell, which creates an action potential. The AP can be spread to surrounding cells
Repolarization (initiation of pacemaker cells)
Calcium channels close and repolarization begins. Potassium channels open, and potassium is removed from the cell- returns to resting membrane potential. Once resting membrane potential is established, the cycle (steps 1-3) begins again
Intrinsic conduction system
A conduction system created within the heart tissue itself. It initiates impulses that spread throughout the heart, created by pacemaker cells.
Where are pacemaker cells found? (5)
Pacemaker cells are found at specific areas (nodes) throughout the heart.
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Atrioventricular (AV) bundle
- Bundle branches
- Subendocardial conducting network (Purkinje fibers)
Sinoatrial (SA) node
The primary pacemaker of the heart, located in the left atrium. Generates about 75 impulses per minute (fastest depolarization rate). Depolarization at the SA node spreads through both atria and eventually reaches the AV node
Atrioventricular (AV) node
Found in the interatrial septum, generates about 50 impulses per minute. The impulse from the SA node is delayed by .1 second at the AV node. This gives the atria enough time to completely contract and push blood into the ventricles
Atrioventricular (AV) bundle
Found in the interventricular septum. Impulses coming from the AV node travel through the AV bundle, these are the only places where atria and ventricles are electrically connected
Bundle branches
Right and left branches. Help conduct impulses down both sides of the interventricular septum toward the apex of the heart
Subendocardial conducting network (Purkinje fibers)
Found at the heart apex (base) and along the ventricle walls. Depolarizes the contractile cells of both ventricles. More elaborate on left side than right, ventricles contract from the bottom up
What part of the heart contracts first?
The heart contracts as a single unit. The two atria and two ventricles contract at the same time. The ventricles contract from the bottom up- blood must be pushed up to the blood vessels at the top of the heart
Which part of the nervous system controls the heartbeat?
The autonomic nervous system partially controls the heartbeat. The parasympathetic and sympathetic nervous systems both have influence. They both send fibers to the SA and AV node. One of these will send impulses faster to the heart than the other division. The division that sends the impulses faster will dominate in determining heart rate.
Where are cardiac centers found?
The cardio acceleratory and cardioinhibitory centers are found in the medulla oblongata
Cardioacceleratory center
Projects to sympathetic neurons in spinal cord. Postganglionic fibers eventually innervate SA and AV nodes, heart muscle, and coronary arteries
Cardioinhibitory center
Sends inhibitory impulses to the heart via the vagus nerve (parasympathetic division)- slows to a resting heart rate. Postganglionic motor neurons found in heart wall, innervate SA and AV nodes
Action potentials of contractile cardiac cells (3 phases)
- Depolarization
- Plateau phase
- Repolarization
Depolarization (cardiac cells)
Impulse goes from a pacemaker cell to a contractile cell. Fast voltage gated Na+ channels open- extracellular sodium flows into the cell. Inside of the cell becomes more positive, membrane potential reversal from -90 mV to +30 mV.
Fast voltage gated sodium channels
Fast voltage gated channels open quickly and allow a very large amount of sodium into the cell.
Plateau phase (cardiac cells)
Sarcoplasmic reticulum opens calcium channels, and calcium centers. Some potassium channels are open and K leaves the cell. Depolarization is maintained, balances out resting membrane potential
Repolarization (cardiac cells)
Calcium channels close, potassium channels open. Inside of the cell becomes more negative- maximum tension development here
Electrocardiography definition
Detection of the electrical impulses generated in and transmitted by the heart. Creates an electrocardiogram (ECG)- doctors can see heart activity. This measures all the electrical activity that spreads through a heart in a single beat, not just one action potential
ECG waves/complexes (3)
- P wave
- QRS complex
- T wave
P wave
Created by movement of depolarization wave from SA node through atria- atria contract shortly after P wave begins. Depolarization moves to AV node after depolarization is complete
QRS complex
Depolarization occurs at the ventricles (before ventricular contraction). Peak (R) and troughs (Q and S) occur due to changing depolarization waves through ventricles- current changes direction
T wave
Indicates ventricular repolarization. “Wave” is wider than QRS-repolarization takes longer than depolarization
R-R segment
The space on an ECG between the R peak in one QRS complex and the R peak in the next one. This represents the time between 2 heartbeats
Junctional rhythm
Indication- dysfunctional SA node. When SA node stops working, AV node takes over and slows down the heart rate. How it affects ECG- P wave no longer evident, heartbeat irregular
Ventricular fibrillation
Indication- action potentials occur in an irregular pattern in the ventricles. These ECGs are chaotic, grossly irregular, and are seen in acute heart attack and electrical shock. Pumping function is basically lost, contraction is very weak
AED
An AED “restarts” the heart so it can start beating normally again. Flatline can’t be fixed with an AED, but ventricular fibrillation is a shockable rhythm
Cardiac cycle definition
Includes all mechanical events associated with blood flow through the heart in one complete heartbeat, includes systole and diastole
Systole and diastole
Systole is the period of contraction where the heart is actually moving blood, diastole is the period of relaxation where the heart is filling with blood.
4 phases of the cardiac cycle
- Ventricular filling
- Isovolumetric contraction phase
- Ventricular ejection
- Isovolumetric relaxation
What occurs during ventricular filling?
Mid to late diastole- pressure in the heart is low. AV valves are open- blood returning from circulation flows from atria to ventricles. Most ventricle filling occurs here. Atrial systole occurs- atria contract, push remaining blood into ventricle. Then, ventricles have end diastolic volume (EDV). Atria relax, ventricles depolarize
What occurs during the isovolumetric contraction phase?
Ventricles begin to contract- pressure in ventricles rise quickly. AV valves close, SL valves are not yet opened. Ventricles are completely closed off, blood volume remains constant. SL valves will open when pressure in ventricles exceeds pressure in the blood vessels they lead into
What occurs during ventricular ejection?
Blood flows from the ventricles into the aorta (left) and pulmonary trunk (right)
What occurs during isovolumetric relaxation?
Ventricles relax, ventricular pressure drops rapidly- end systolic volume (ESV) reached. Blood in aorta and pulmonary trunk flows back toward the heart, closing the SL valves. Ventricles are closed off again (but now nearly empty)
How many times does the cardiac cycle occur per minute?
75 times per minute, this is why the average adult heart rate is 75
How long does each cardiac cycle last?
.8 seconds
What causes the cardiac cycle?
This cycle is created by pressure changes within the heart- changing pressure causes opening/closing of valves and the movement of blood. Blood flows down a concentration gradient (high pressure to low pressure). The left side of the heart has a thicker myocardium and experiences higher pressure than the right side
Cardiac output definition
The total amount of blood pumped by the ventricle in a single minute
How is cardiac output calculated?
Cardiac output (CO)= stroke volume (SV) times heart rate (HR)
Stroke volume
Volume of blood pumped out by ventricle with each beat (EDV-ESV)-end diastolic minus end systolic. Average for an adult is about 70 mL blood per minute.
Stroke volume is correlated with
Force of ventricular contraction- increasing force of contraction will increase stroke volume.
Heart rate
Beats per minute- average for an adult is about 75 beats per minute
What happens to cardiac output when heart rate increases?
Cardiac output increases
What factors alter cardiac output? (3)
By physical exercise, certain hormones, or a person’s physical fitness
Maximal cardiac output
The maximum amount of blood that can be pumped in a single minute- amount is dependent on level of physical fitness. More fit= higher maximal cardiac output (35 L/min).
How is EDV changed?
Preload
Preload
Preload refers to the stretch of sarcomeres just prior to contraction-increasing sarcomere stretch will increase the force of contraction during systole. The sarcomeres are stretched by venous return
Frank-Starling relationship
Increasing the total volume of blood at the end of diastole (EDV) will increase strength of contraction during systole- increasing stroke volume
How is ESV changed? (2)
- Contractility
2. Afterload
Contractility
Intrinsic/natural strength of the ventricle walls independent of loading conditions. Increasing contractility will increase the amount of blood ejected (decreasing ESV). Increased calcium release will increase contractility.
Afterload
Forces that oppose blood ejection from the ventricles. Mainly dependent on resistance created by blood vessels. Increasing afterload will decrease how much blood is ejected, SV drops
How does the diameter of blood vessels affect resistance?
Dilated blood vessels- less resistance
Constricted blood vessels- greater resistance
Two ways to regulate heart rate
- Autonomic nervous system input
2. Chemical regulation
What happens to the heart when the sympathetic nervous system dominates?
Norepinephrine is released. The threshold is reached faster- SA node fires faster, heart beats faster. Therefore, contractility increases
Vagal tone
Heart rate is slower than it would be if the vagus nerve did not innervate. Cutting the vagus nerve would increase heart rate to around 100 beats per minute
Which chemicals can influence heart rate (2)
- Hormones
2. Ions
How do epinephrine and norepinephrine influence heart rate?
Increase heart rate and contractility through sympathetic division influence
How does thyroxine influence heart rate?
Thyroxine is a thyroid hormone that increases metabolic rate and body heat. Increases HR (often over longer periods of time). It can act directly on the heart and increase effects of epinephrine and norepinephrine
Hypercalcemia
High calcium speeds up the heart rate. Hypocalcemia can also occur.
Hypokalemia
Low potassium, causes a weakened or feeble heartbeat
Hyperkalemia
High potassium. This is especially dangerous- it alters the electrical activity of the heart and can cause cardiac arrest. The heart can generate action potentials more easily (by increasing the resting membrane potential of the cell), and heart rate increases drastically
Other than chemical and autonomic nervous system influences, what other factors can influence heart rate? (4)
- Age- HR declines with age, if healthy
- Biological sex- females have a slightly higher HR than males
- Exercise/physical fitness- increased fitness leads to a lower heart rate
- Body temperature- a higher body temperature increases heart rate
Congestive heart failure
Inefficiency of blood pumping by the heart to body tissues (cardiac output and venous return are not balanced). Cardiac output decreases, and venous return is much higher than cardiac output. Usually a progressive condition- weakens the myocardium over time
Common causes of congestive heart failure (4)
- Coronary atherosclerosis
- Hypertension
- Multiple myocardial infarctions
- Dilated cardiomyopathy
Coronary atherosclerosis
Fatty buildup that clogs coronary arteries that serve the heart muscle tissue
Hypertension definition
Persistent high blood pressure over weeks/months/years
Hypertension complications (2)
- High blood pressure in the arteries (especially aorta)- heart works harder to overcome increased pressure and eject the same amount of blood. The heart has to shove in the blood- blood doesn’t naturally want to go to the high pressure arteries
- The myocardium hypertrophies over time and becomes weaker-the muscle becomes so bulky that it can’t really do much
How can multiple myocardial infarctions result in congestive heart failure?
Repeated heart attacks kill heart cells and are replaced by scar tissue- heart muscle tissue can’t be regenerated, and scar tissue can’t contract
How can dilated cardiomyopathy result in CHF?
With dilated cardiomyopathy, ventricles stretch out, myocardium deteriorates, and ventricular contractility is compromised. In a normal heart, ventricles are almost full with blood. With dilated cardiomyopathy, the blood only fills the ventricles halfway. Makes pumping blood less efficient.
Pulmonary congestion
Left side of the heart fails, right side still operates normally. Lungs and the blood vessels associated with them become filled with fluid, resulting in pulmonary edema.
Pulmonary edema
The lungs fill with fluid
Peripheral congestion
Right side of the heart fails, left side still operates efficiently. Edema occurs in systemic body tissues, and the cells in body tissue are unable to gain nutrients and oxygen necessary, remove metabolic wastes efficiently.
How does one sided failure of the heart result in failure of the normal side eventually?
Prolonged insufficiency on one side puts undue stress on the other- the heart will eventually fail. Treatments- remove excess fluid, decrease blood pressure, increase contractility of defective side
