10.3 The Human Heart Flashcards
What is the heart?
a cone-shaped, muscular organ about the size of a fist that is located between the lungs directly behind the sternum and is tilted so that the apex is oriented to the body’s left
What is the myocardium?
the major portion of the heart that consists largely of cardiac muscle tissue
the muscle fibres are branched and tightly joined to one another
What is the pericardium?
a thick, serous membrane in which the heart lies, that secretes a small quantity of lubricating liquid
What is the inner surface of the heart lined with?
endocardium
What is endocardium?
a membrane composed of connective tissue with endothelial tissue
What is the septum?
an internal wall that separates the heart into a right side and a left side
What are the 4 chambers of the heart?
the 2 upper, thin-walled atriums are located above the 2 lower, thick-walled ventricles
What do ventricles do?
pump the blood to the lungs and the body
What are the 4 valves of the heart?
- tricuspid valve
- bicuspid valve
- pulmonary semilunar valve
- aortic semilunar valve
What do valves do?
direct the flow of blood and prevent its backward movement
What are the atrioventricular valves?
the 2 valves that lie between the atriums and the ventricles
What are atrioventricular valves supported by?
strong fibrous strings called chordae tendinae
Where are the chordae tendinae?
attached to muscular projections of the ventricular walls
What do the chordae tendinae do?
support the valves and prevent them from inverting when the heart contracts
What is the tricuspid valve?
the atrioventricular valve on the body’s right side
Why is it called the tricuspid valve?
it has 3 flaps, or cusps
What is the bicuspid valve?
the atrioventricular valve on the body’s left side
Why is it called the bicuspid valve?
it has 2 flaps
What are semilunar valves?
valves in the heart between the ventricles and their attached vessels, whose flaps resemble half-moons
Where is the pulmonary semilunar valve?
lies between the right ventricle and the pulmonary trunk
Where is the aortic semilunar valve?
lies between the left ventricle and the aorta
Which side of the heart are the venae cavae and the pulmonary trunk attached to?
right side
Which side of the heart are the aorta and the pulmonary veins attached to?
left side
Where do the coronary arteries and cardiac veins pass through?
cardiac muscle
What do coronary arteries do?
bring oxygen and nutrients to cardiac cells, which derive no benefit from blood coursing through the heart
What do cardiac veins do?
drain blood into the right atrium
Describe the path of blood through the heart.
- superior vena cava (anterior vena cava) and inferior vena cava (posterior vena cava), which carry oxygen-poor that is relatively high in carbon dioxide, enter the right atrium
- right atrium sends blood through the tricuspid valve to the right ventricle
- right ventricle sends blood through the pulmonary semilunar valve into the pulmonary trunk and through the 2 pulmonary arteries to the lungs
- 4 pulmonary veins, which carry oxygen-rich blood, enter the left atrium
- left atrium sends blood through the bicuspid (mitral) valve to the left ventricle
- left ventricle sends blood through the aortic semilunar valve into the aorta to the rest of the body
Why must blood go through the lungs?
in order to pass from the right side to the left side of the heart
Why is the heart a double pump?
right ventricle sends blood into the lungs and the left ventricle sends blood into the rest of the body
Why are the walls of the left ventricle thicker than the right?
it has the harder job of pumping blood to the entire body, which the right ventricle pumps blood a relatively short distance to the lungs
What is cardiac output?
volume of blood that the left ventricle pumps per minute
What is the cardiac output in a person with an average heart rate of 70 beats per minute?
5.25 L of blood per minute
this is about equal to the total amount of blood in the body, and adds up to about 750 L of blood per day
How can cardiac output change during heavy exercise?
can increase as much as fivefold
What does the pumping of the heart do?
sends blood out under pressure into the arteries
Where is blood pressure the greatest?
in the aorta because the left side of the heart is the stronger pump
When does blood pressure decrease?
as the cross-sectional area of arteries and then arterioles increase
What is a pulse?
a wave effect that passes down the walls of arteries when the aorta expands and then recoils with each ventricular contraction
What can the arterial pulse be used to determine?
the heart rate
What may a weak or “thready” pulse indicate?
a weak heart or low blood pressure
What is a cardiac cycle?
each heartbeat; one complete cycle of systole and diastole for all heart chambers
How does the heart beat?
first, the 2 atria contract at the same time, then the 2 ventricles contract at the same time
then, all the chambers relax
What does systole mean?
refers to the contraction of heart muscle
What does diastole mean?
refers to the relaxation of the heart muscle
Around how many beats per minute does a heart contract?
70
How long does each heartbeat last?
about .85 s
Describe the heartbeat times.
Time Atria Ventricles
- 15 s Systole Diastole
- 30 s Diastole Systole
- 40 s Diastole Diastole
What is a stethoscope?
an instrument used to isolate and amplify the body’s internal sounds
What sound does a heart beat make?
“lub-dub”
What is the longer lower-pitched “lub” sound caused by?
vibrations occurring when the atrioventricular valves close due to ventricular contraction
What is the shorter and sharper “dub” sound caused by?
when semilunar valves close due to back pressure of blood in the arteries
What is the heart murmur (slight whooshing sound) after the “lub” most commonly caused by?
blood flowing back through an ineffective mitral valve
What does the intrinsic (internal) conduction system of the heart cause?
the rhythmic contraction of the atria and ventricles
What makes the intrinsic conduction system possible?
the presence of nodal tissue (a unique type of cardiac tissue)
What are the 2 types of nodal tissue?
sinoatrial node, and atrioventricular node
Where is the SA node located?
in the upper dorsal wall of the right atrium
Where is the AV node located?
in the base of the right atrium very near the septum
What does the SA node do?
initiates the heart beat and sends out an excitation impulse every 0.85 seconds, which causes the atria to contract
What happens when the SA node impulses reaches the AV node?
a slight delay allows the atria to finish contraction before the ventricles begin to contract
Where does the signal for ventricles to contract travel?
from the AV node through specialized cardiac muscle fibres called the AV bundle before reaching Purkinje fibres
Why is the SA node called a pacemaker?
it usually keeps the heartbeat regular
What happens if the SA node fails to work properly?
the heart still beats due to impulses generated by the AV node, but the beat is slower
What can be done to correct the failure of the SA node?
an artificial pacemaker may be implanted that gives an electrical stimulus to the heart every 0.85 seconds
Describe the intrinsic control of the heartbeat.
the SA node sends out a stimulus, which causes the atria to contract
when this stimulus reaches the AV node, it signals the ventricles to contract
impulses pass down the 2 branches of the AV bundle to the Purkinje fibres, and thereafter the ventricles contract
What is the medulla oblongata?
a portion of the brain that controls internal organs
What does the cardiac control centre in the medulla oblongata do?
can alter the beat of the heart by way of the autonomic system
What is the autonomic system?
a portion of the nervous system
What are the 2 subdivisions of the autonomic system?
parasympathetic and sympathetic
What does the parasympathetic subdivision of the autonomic system do?
promotes functions of a resting state
decreases SA and AV nodal activity when we are inactive
What does the sympathetic subdivision of the autonomic system do?
brings about responses to increased activity or stress
increases SA and AV node activity when we are active or excited
What is epinephrine and norepinephrine?
hormones released by the adrenal medulla that stimulate the heart
What is the adrenal medulla?
the inner portion of the adrenal gland
What happens when we are frightened?
the heart pumps faster and stronger due to sympathetic stimulation because of the release of epinephrine and norepinephrine
What is an electrocardiogram?
a recording of the electrical changes that occur in the myocardium during a cardiac cycle
What do ions in body fluids do?
conduct electrical currents
Why can electrical changes in the myocardium be detected on the skin’s surface?
because the ions in body fluids conduct electrical currents
What are electrodes placed on or near the chest connected by?
connected by wires to an instrument that detects and records the myocardium’s electrical changes
What does a normal ECG usually indicate?
the heart is functioning properly
Describe the cycle that the ECG records.
when SA node triggers an impulse, atrial fibres produce an electrical change called the P wave
the P wave indicates that the atria are about to contract
QRS complex signals that the ventricles are about to contract
electrical changes that occur as the ventricular muscle fibres recover, produce the T wave
What are arrhythmias?
various types of abnormalities that can be detected by an electrocardiogram
What is atrial fibrillation (AF)?
most common type of arrhythmias
instead of the heart generating regular single impulses from the AV node, multiple chaotic impulses are generated, resulting in a fast irregular heartbeat
sometimes occurs infrequently and resolves on its own, sometimes requires medication
What are the symptoms of AF?
- palpitations: fluttering sensation of the heart
- dizziness
- weakness
- chest pain
What is ventricular fibrillation (VF)?
a more serious medical emergency
an uncoordinated contraction of the ventricles, commonly followed after a heart attack, but also caused by an injury or drug overdose
What must you do to treat VF?
because a heart in VF is not pumping blood, it must be defibrillated by applying a strong electrical current for a short period of time
then, the SA node may be able to reestablish a coordinated beat
What are AED’s?
automatic external defibrillator
small devices that can be used to determine whether a person is suffering from VF, and if so, administer an appropriate electrical shock to the chest
