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what does the right heart pump blood through ?
the lungs
what does the left heart pump blood through?
the systemic circulation that provides blood flow to the other organs and tissues of the body.
What type of pump is the heart?
The heart is a pulsatile, two-chamber pump. Each side has an atrium and a ventricle
What are the two chambers of each heart pump?
atrium ( receives blood)
Ventricle (pumps blood out
What is the function of the atria?
Each atrium is a weak primer pump that helps move blood into the ventricle.
What supplies the main pumping force that propels the blood?
The ventricles provide the main force to propel blood:Right ventricle → Pumps blood to the pulmonary circulation (lungs).Left ventricle → Pumps blood to the systemic circulation (body).
What is the pericardium?
A two-layer sac that surrounds, protects, and holds the heart in place.
What is cardiac rhythmicity?
Special mechanisms in the heart generate rhythmic contractions by transmitting action potentials through cardiac muscle
What are the three major types of cardiac muscles found in the heart ?
-atrial muscle
-ventricular muscle
- the specialized excitatory and conductive muscle fiber
Why do excitatory and conductive muscle fibers produce weaker contractions?
They have fewer contractile fibrils, making their contractions much weaker.
What is the main function of excitatory and conductive muscle fibers?
-They generate automatic rhythmical electrical discharges (action potentials).
-They conduct action potentials to regulate the heart's rhythmical beating.
How do excitatory and conductive fibers help control heart rhythm?
They form an excitatory system that spreads electrical signals, ensuring coordinated heartbeats.
Cardiac muscle consists of
single fiber type ( similar to type I skeletal muscle fiber)
What are the primary ventricular and atrial myosin isoforms in the adult human heart?
Ventricular myosin: β-cardiac myosin (MYH7)
Atrial myosin: α-cardiac myosin (MYH6)
How does heart muscle generate energy for contraction?
It uses chemical energy, similar to skeletal muscle
how much mitochondria is present in cardiac tissue ?
occupies∼35% of the volume of cardiac tissue
How do cardiac diseases affect energy production?
-Decreased oxidative phosphorylation
-Reduced mitochondrial enzymes & content
-Excessive mitochondrial free radical production
What is the primary energy source for the heart at rest?
B-oxidation provides ~70-90% of ATP.
Glucose & lactate supply ~10-30% of ATP.
What type of muscle is the cardiac muscle similar to?
The cardiac muscle is striated, similar to skeletal muscle
What structure do cardiomyocytes share with skeletal muscle?
Cardiomyocytes have similar sarcomeres to those in skeletal muscle.
How are cardiomyocytes arranged in the heart?
Cardiomyocytes are arranged in a latticework, where fibers divide, recombine, and spread again
structure of cardiac muscle
The cardiac muscle is striated as the skeletal muscle is. contains similar sarcomeres as skeletal muscle...
How are cardiomyocytes arranged?
cardiomyocytes are arranged in a latticework, with the fibers dividing, recombining, and then spreading again.
How many nuclei do cardiomyocytes typically have?
Cardiomyocytes usually have 1 or more nuclei.
What percentage of human cardiomyocytes are mononucleated?
About 75% of human cardiomyocytes are mononucleated.
What percentage of human cardiomyocytes are binucleated?
About 25% of human cardiomyocytes are binucleated
What percentage of human cardiomyocytes are trinucleated?
About 1% of human cardiomyocytes are trinucleated.
how does the number of cardiomyocytes change with age?
The number of cardiomyocytes is set by 1 month of age and remains relatively fixed throughout life.
How much renewal of cardiomyocytes occurs from birth to 20 years?
Cardiomyocyte renewal occurs in the range of 1% from birth to 20 years.
What is the renewal rate of cardiomyocytes at the age of 75?
The renewal rate of cardiomyocytes at age 75 is about 0.3%.
How much of all cardiomyocytes are renewed during a normal human lifetime?
Over 50% of all cardiomyocytes are renewed during a normal human lifetime.
How are the muscle fibers of the left ventricle organized?
They are organized into complex muscle fiber layers that run in different directions and allows the heart to contract in a twisting motion during systole.
How do the subepicardial and subendocardial layers of the left ventricle differ in their orientation?
The subepicardial (outer) layer spirals leftward, and the subendocardial (inner) layer spirals rightward, causing a clockwise rotation of the apex and counterclockwise rotation of the base.
What motion occurs during systole due to the fiber arrangement in the left ventricle?
The arrangement of fibers causes a wringing motion of the left ventricle, pulling the base downward toward the apex during systole.
What happens at the end of systole in the left ventricle?
At the end of systole, the left ventricle is similar to a loaded spring and untwists during diastole (relaxation) to allow blood to enter the pumping chambers rapidly.
intercalated discs
cell membranes that separate individual cardiac muscle cells from one another
what are cardiac muscle fibers made up of?
Cardiac muscle fibers are made up of many individual cells connected in series and in parallel with one another.
what happens in intercalated discs?
At each intercalated disc, the cell membranes fuse with one another to form permeable communicating junctions (gap junctions) that allow rapid diffusion of ions = action potentials travel easily and rapidly from one cardiac muscle cell to the next
syncytium
electrical connection of cardiomyocytes through gap junctions, allowing coordinated contractions of the heart muscle.
The heart actually is composed of two syncytia:
the atrial syncytium and the ventricular syncytium.
how are the atria and ventricles separated in the heart?
The atria are separated from the ventricles by fibrous tissue surrounding the atrioventricular (A-V) valvular openings.
How are electrical potentials conducted from the atria to the ventricles?
Electrical potentials are conducted from the atria to the ventricles via the A-V bundle, a specialized bundle of conductive fibers
Why is the division of the heart muscle into two functional syncytia important?
It allows the atria to contract slightly ahead of the ventricles, improving the effectiveness of heart pumping.
Endocardium
endothelial cells and connective tissue. Surface of the heart chambers
Myocardium
Main constituent of the heart, comprised of the muscle cells, the cardiomyocytes.
Epicardium
Visceral layer of serum pericardium, connective tissue (innermost layer of the pericardium)
Pericardium
(2 layers of) inner serous pericardium (epicardium) + outer fibrous pericardium. The 2 layers of serous pericardium are visceral and parietal pericardium separated by the pericardial space.
Pericardial space or Pericardial cavity
contains pericardial fluid (20-60ml), which is a mechanical protection for the heart and vessels, reducing the friction during contraction/heartbeat.
Parietal pericardium
inner layer
Fibrous pericardium
outer layer of connective tissue
The action potential in a ventricular muscle fiber, averages about ___millivolts.
105 millivolts
What causes the action potential in skeletal muscle?
The action potential in skeletal muscle is caused by the sudden opening of large numbers of fast Na+ channels, allowing Na+ to enter the cell, followed by repolarization when the channels close.
How is the action potential in cardiac muscle different from skeletal muscle?
In cardiac muscle, the action potential is caused by opening both fast Na+ channels (like in skeletal muscle) and L-type calcium channels, which allow Ca2+ and Na+ to enter the cell.
What role do L-type calcium channels play in cardiac muscle action potentials?
L-type calcium channels open slowly and remain open for several tenths of a second, allowing a large quantity of Ca2+ and Na+ to enter the cell, creating a prolonged period of depolarization (plateau phase).
What happens during the plateau phase of the cardiac muscle action potential?
During the plateau phase, the Ca2+ that enters activates the muscle contractile process, while in skeletal muscle, the Ca2+ for contraction comes from the sarcoplasmic reticulum.
What happens to the potassium permeability in cardiac muscle during the plateau phase ?
Immediately after the onset of the action potential, the potassium permeability in cardiac muscle decreases about fivefold, which does not occur in skeletal muscle.
How does the decrease in potassium permeability affect the action potential in cardiac muscle?
The decreased K+ permeability reduces the efflux of K+ during the plateau phase, preventing the early return of the action potential voltage to its resting level.
What happens when the slow calcium-sodium channels close in cardiac muscle?
When the slow calcium-sodium channels close, the influx of Ca2+ and Na+ ceases, and the membrane permeability for K+ ions increases rapidly, causing a rapid loss of K+ and returning the membrane potential to its resting level, ending the action potential
What happens during Phase 0 of depolarization in cardiac cells?
Fast Sodium Channels Open.
What occurs when a cardiac cell is stimulated and depolarizes?
The membrane potential becomes more positive.
What type of channels open during depolarization of cardiac cells?
Voltage-gated fast Na+ channels.
What ion rapidly flows into the cardiac cell during depolarization?
Na+ (Sodium).
What is the approximate membrane potential reached during depolarization before Na+ channels close?
~ +20 mV.
Phase 1: Initial Repolarization
Fast Sodium Channels Close. The Na+ channels close = the cell begins to repolarize K+ leave the cell through open potassium channels.
What occurs during Phase 2 (Plateau) of the cardiac action potential?
In Phase 2, calcium channels open and potassium channels close. Increased Ca2+ permeability and decreased K+ permeability cause the action potential to plateau.
What happens during Phase 3 (Rapid Repolarization) of the cardiac action potential?
In Phase 3, calcium channels close, and slow potassium channels open, allowing K+ to exit the cell rapidly, ending the plateau and returning the membrane potential to its resting level.
What is the resting membrane potential during Phase 4 of the cardiac action potential?
The resting membrane potential averages about −80 to −90 millivolts.
refractory period
the interval of time during which a normal cardiac impulse cannot re-excite an already excited area.
the normal refractory period of the ventricle
0.25 to 0.30 second, which is about the duration of the prolonged plateau action potential
relative refractory period
about 0.05 second during which the muscle is more difficult to excite than normal but can be excited by a very strong excitatory signal, as demonstrated by the early premature contraction.
The refractory period of atrial muscle
much shorter than that for the ventricles (about 0.15 second for the atria compared with 0.25 to 0.30 second for the ventricles)
What is the cardiac cycle?
The sequence of cardiac events from the beginning of one heartbeat to the beginning of the next.
What initiates each cardiac cycle?
action potential in the sinus node (pace maker)
Why is there a delay in impulse transmission from the atria to the ventricles?
There is a delay of more than 0.1 second during passage of the cardiac impulse from the atria into the ventricles, allowing the atria to contract earlier than the ventricle (atria as a primer pumps).
location of the sinus node
The sinus node is located in the superior lateral wall of the right atrium near the opening of the superior vena cava
pump rate of the heart
pumps 4-6 liters/min
may pump 4-7x that during intense exercise
THE BASIC MECHANISMS FOR REGULATING HEART PUMPING
(1) intrinsic cardiac pumping regulation in response to changes in volume of blood flowing into the heart
(2) control of heart rate and heart strength by the autonomic nervous system
Venous return
(the blood flow to the heart from the veins) is usually the determining factor accounting for the amount of blood pumped by the heart per minute.
Peripheral control
each peripheral tissue controls its own local blood flow. All combined → right atrium.
Heart intrinsic ability
blood is automatically pumped into the arteries so that it can flow around the circuit again, this intrinsic regulation to adapt to increasing volumes of inflowing blood is called the Frank-Starling mechanism of the heart.
Frank-Starling mechanism
the more the stretch during filling = the greater is the resulting force of contraction = the greater is the quantity of blood pumped into the aorta. Aka “Law of the Heart”.
