Chapter 20 Flashcards
Heart
Relatively small, roughly the same size as your closed fist. Is about 12 cm (5 in.) long, 9 cm (3.5 in.) wide at its broadest point, and 6 cm (2.5 in.) thick, with an average mass of 250 g (8 oz) in adult females and 300 g (10 oz) in adult males. Rests on the diaphragm, near the midline of the thoracic cavity.
Mediastinum
An anatomical region that extends from the sternum to the vertebral column, from the first rib to the diaphragm, and between the lungs. Where the heart lies.
Apex (of the heart)
Is formed by the tip of the left ventricle (a lower chamber of the heart) and rests on the diaphragm. It is directed anteriorly, inferiorly, and to the left.
Base (of the heart)
Opposite the apex and is its posterior aspect. It is formed by the atria (upper chambers) of the heart, mostly the left atrium.
Anterior surface (of the heart)
Is deep to the sternum and ribs.
Inferior surface (of the heart)
Is the part of the heart between the apex and right surface and rests mostly on the diaphragm.
Right surface (of the heart)
Faces the right lung and extends from the inferior surface to the base.
Left surface (of the heart)
Faces the left lung and extends from the base to the apex.
Pericardium
The membrane that surrounds and protects the heart. It confines the heart to its position in the mediastinum, while allowing sufficient freedom of movement for vigorous and rapid contraction.
What two main parts does the pericardium consist of?
- Fibrous pericardium
- Serous pericardium
Fibrous pericardium
Superficial; is composed of tough, inelastic, dense irregular connective tissue. Prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum.
Serous pericardium
Deep; a thinner, more delicate membrane that forms a double layer around the heart.
The outer ______ of the serous pericardium is fused to the fibrous pericardium. The inner ______ of the serous pericardium, which is also called the ______, is one of the layers of the heart wall and adheres tightly to the surface of the heart.
Parietal layer; visceral layer; epicardium
Pericardial fluid
A thin film of lubricating serous fluid between the parietal and visceral layers of the serous pericardium. Reduces friction between the layers of the serous pericardium as the heart moves.
What are the three layers that the wall of the heart consists of?
- Epicardium
- Myocardium
- Endocardium
Epicardium
The external layer; imparts a smooth, slippery texture to the outermost surface of the heart. Contains blood vessels, lymphatics, and vessels that supply the myocardium.
What two tissue layers is the epicardium composed of?
- Visceral layer of the serous pericardium: thin, transparent outer layer of the heart wall. Is composed of mesothelium.
- A variable inner layer of delicate fibroelastic tissue and adipose tissue.
Myocardium
The middle layer; is responsible for the pumping action of the heart and is composed of cardiac muscle tissue. Makes up approximately 95% of the heart wall.
Endocardium
The inner layer; is a thin layer of endothelium overlying a thin layer of connective tissue. Provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothelial lining minimizes the surface friction as blood passes through the heart. Is continuous with the endothelial lining of the large blood vessels attached to the heart.
Atria
The two superior receiving chambers. Receive blood from blood vessels returning blood to the heart, called veins. Have thin walls, so deliver blood under less pressure into the adjacent ventricles.
Ventricles
The two inferior pumping chambers. Eject the blood from the heart into blood vessels called arteries. Have thicker walls, so pump blood under higher pressure over greater distances.
Auricle
Wrinkled pouchlike structure on the anterior surface of each atrium. Slightly increases the capacity of an atrium so that it can hold a greater volume of blood.
Sulci
A series of grooves on the surface of the heart that contain coronary blood vessels and a variable amount of fat. Each sulcus marks the external boundary between two chambers of the heart.
Coronary sulcus
Encircles most of the heart and marks the external boundary between the superior atria and inferior ventricles.
Anterior interventricular sulcus
A shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles on the anterior aspect of the heart.
Posterior interventricular sulcus
Marks the external boundary between the ventricles on the posterior aspect of the heart.
Right atrium
Forms the right surface of the heart and receives blood from three veins: the superior vena cava, inferior vena cava, and coronary sinus. Is about 2–3 mm (0.08–0.12 in.) in average thickness. The inside of the posterior wall of the right atrium is smooth, and the inside of the anterior wall is rough due to the presence of pectinate muscles.
Pectinate muscles
Muscular ridges. Extend into the auricle.
Interatrial septum
Thin partition between the right atrium and left atrium. A prominent feature of this septum is the fossa ovalis.
Fossa ovalis
An oval depression; the remnant of the foramen ovale, an opening in the interatrial septum of the fetal heart that normally closes soon after birth.
Tricuspid valve
AKA right atrioventricular valve; a valve in which blood passes from the right atrium into the right ventricle through. Consists of three cusps (AKA leaflets).
Right ventricle
Is about 4-5 mm (0.16–0.2 in.) in average thickness and forms most of the anterior surface of the heart.
Trabeculae carneae
Series of ridges formed by raised bundles of cardiac muscle fibers. Found inside the right ventricle. Some of the trabeculae carneae convey part of the conduction system of the heart.
Chordae tendineae
Tendon-like cords that the cusps of the tricuspid valve are connected to.
Papillary muscles
Cone-shaped trabeculae carneae that the chordae tendineae are connected to.
Interventricular septum
Partition between the right ventricle and left ventricle.
Pulmonary valve
Where blood passes from the right ventricle into the pulmonary trunk through. The pulmonary trunk is a large artery that divides into right and left pulmonary arteries and carries blood to the lungs.
Left atrium
Is about the same thickness as the right atrium and forms most of the base of the heart. It receives blood from the lungs through four pulmonary veins. The inside of both the posterior wall and anterior wall of the left atrium is smooth.
Bicuspid (mitral) valve
AKA left atrioventricular valve; a valve in which blood passes from the left atrium to the left ventricle through. Consists of two cusps.
Left ventricle
Is the thickest chamber of the heart, averaging 10–15 mm (0.4-0.6 in.), and forms the apex of the heart. Like the right ventricle, the left ventricle contains trabeculae carneae and has chordae tendineae that anchor the cusps of the bicuspid valve to papillary muscles.
Aortic valve
Where blood passes from the left ventricle into the ascending aorta through. From here, blood goes to either the heart wall or travels throughout the body.
Ductus arteriosus
A temporary blood vessel that is present during fetal life that shunts blood from the pulmonary trunk into the aorta. Hence, only a small amount of blood enters the nonfunctioning fetal lungs.
Ligamentum arteriosum
What the ductus arteriosus becomes after it closes shortly after birth. Connects the arch of the aorta and pulmonary trunk.
What is the difference between the right ventricle and left ventricle?
Right ventricle: has a much smaller workload than the left ventricle, therefore has thinner walls than the left ventricle – it pumps blood a short distance to the lungs at lower pressure, and the resistance to blood flow is small. Additionally, the perimeter of the lumen (space) is crescent-shaped.
Left ventricle: works much harder than the right ventricle to maintain the same rate of blood flow, therefore has thicker walls than the right ventricle – it pumps blood great distances to all other parts of the body at higher pressure, and the resistance to blood flow is larger. Additionally, the perimeter of the lumen (space) is circular.
Fibrous skeleton of the heart
Dense connective tissue in the heart wall. Consists of four dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum. Prevents overstretching of the valves as blood passes through them. It also serves as a point of insertion for bundles of cardiac muscle fibers and acts as an electrical insulator between the atria and ventricles.
Atrioventricular (AV) valves
The tricuspid and bicuspid valves. Located between the atrium and ventricle. When open, the cusps project down into the ventricle. When closed, cusps project upward toward the atria. Prevent the backflow of blood.
Semilunar (SL) valves
The aortic and pulmonary valves. Made up of three crescent moon-shaped cusps. Allow ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles.
There are no valves guarding the junctions between the ______ and the ______ or the ______ and the ______. As the atria contract, a small amount of blood does flow backward from the atria into these vessels. However, backflow is minimized by a different mechanism; as the atrial muscle contracts, it compresses and nearly collapses the weak walls of the venous entry points.
Venae cavae; right atrium; pulmonary veins; left atrium
Systemic circulation
The left side of the heart pumps oxygenated blood into the systemic circulation to all tissues of the body except the air sacs (alveoli) of the lungs.
Pulmonary circulation
The right side of the heart pumps deoxygenated blood into the pulmonary circulation to the air sacs.
The coronary circulation
AKA cardiac circulation; the network of blood vessels in the myocardium. The coronary arteries branch from the ascending aorta and encircle the heart. While the heart is contracting, little blood flows in the coronary arteries because they are squeezed shut. When the heart relaxes, however, the high pressure of blood in the aorta propels blood through the coronary arteries, into capillaries, and then into coronary veins.
Left coronary artery
Passes inferior to the left auricle and delivers blood to the heart.
What two branches does the left coronary artery divide into?
- Anterior interventricular branch
- Circumflex branch
Right coronary artery
Passes inferior to the right auricle and delivers blood to the heart.
What two branches does the right coronary artery divide into?
- Posterior interventricular branch
- Marginal branches
Anastomoses
Connections between arteries that supply the same region. Provide detours for arterial blood if a main route becomes obstructed.
Collateral circulation
Alternative routes for blood to reach a particular organ or tissue.
Coronary veins
The coronary veins drain blood from the heart into the coronary sinus.
Coronary sinus
A large vascular sinus in the coronary sulcus on the posterior surface of the heart that most of the deoxygenated blood from the myocardium drains into. The deoxygenated blood in the coronary sinus empties into the right atrium.
Intercalated discs
Irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to neighboring fibers.
Desmosomes
In the intercalated discs; hold the fibers together.
Gap junctions
In the intercalated discs; allow muscle action potentials to conduct from one muscle fiber to its neighbors. Enable the entire myocardium of the atria or the ventricles to contract as a single, coordinated unit.
Autorhythmic fibers
A network of specialized cardiac muscle fibers that are the source of electrical activity, which keep the heart beating. Are self-excitable. Repeatedly generate action potentials that trigger heart contractions. They continue to stimulate a heart to beat even after it is removed from the body.
What are the two important functions of autorhythmic fibers?
- Act as a pacemaker (setting the rhythm of electrical excitation that causes contraction of the heart)
- Form the cardiac conduction system (a network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart)
What are the five steps of the cardiac conduction system?
- Cardiac excitation normally begins in the sinoatrial (SA) node. SA node cells do not have a stable resting potential. Rather, they repeatedly depolarize to threshold spontaneously. The spontaneous depolarization is a pacemaker potential. When the pacemaker potential reaches threshold, it triggers an action potential.
- Action potentials reach the atrioventricular (AV) node.
- From the AV node, the action potential enters the atrioventricular (AV) bundle.
- After propagating through the AV bundle, the action potential enters both the right and left bundle branches, which extend toward the apex of the heart.
- Finally, the large-diameter Purkinje fibers rapidly conduct the action potential beginning at the apex of the heart upward to the remainder of the ventricular myocardium. Then the ventricles contract, pushing the blood upward toward the semilunar valves.
What structure would act as the natural pacemaker? Why?
The sinoatrial (SA) nodes - they set the rhythm for contraction of the heart.
Nerve impulses from the ______ and ______ modify the timing and strength of each heartbeat, but they do not establish the fundamental rhythm.
Autonomic nervous system (ANS); blood-borne hormones (such as epinephrine)
Contractile fibers
The “working” atrial and ventricular fibers that get excited by action potentials initiated by the SA node, that travel along the conduction system to them.
What are the three steps of an action potential in a contractile fiber? Briefly describe them
- Depolarization: rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open.
- Plateau: plateau (maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open.
- Repolarization: repolarization due to closure of Ca2+ channels and K+ outflow when additional voltage-gated K+ channels open.
Refractory period
The time interval during which a second contraction cannot be triggered. The refractory period of a cardiac muscle fiber lasts longer than the contraction itself.
Briefly describe the ATP production in cardiac muscle
- Cardiac muscle relies almost exclusively on aerobic cellular respiration in its numerous mitochondria.
- In a person at rest, the heart’s ATP comes mainly from oxidation of fatty acids (60%) and glucose (35%), with smaller contributions from lactic acid, amino acids, and ketone bodies. During exercise, the heart’s use of lactic acid, produced by actively contracting skeletal muscles, rises. Like skeletal muscle, cardiac muscle also produces some ATP from creatine phosphate.
Electrocardiogram (ECG)
A composite record of action potentials produced by all of the heart muscle fibers during each heartbeat. By comparing these records with one another and with normal records, it is possible to determine 1.) if the conducting pathway is abnormal, 2.) if the heart is enlarged, 3.) if certain regions of the heart are damaged, and 4.) the cause of chest pain.
P wave
The first wave; a small upward deflection. Represents atrial depolarization, which spreads from the SA node through contractile fibers in both atria.
QRS complex
The second wave; begins as a downward deflection, continues as a large, upright, triangular wave, and ends as a downward wave. Represents rapid ventricular depolarization, as the action potential spreads through ventricular contractile fibers.
T wave
The third wave; a dome-shaped upward deflection. Represents ventricular repolarization and occurs just as the ventricles are starting to relax. Smaller and wider than the QRS complex because repolarization occurs more slowly than depolarization.
Intervals
AKA segments; the time spans between waves.
P–Q interval
The time from the beginning of the P wave to the beginning of the QRS complex. It represents the conduction time from the beginning of atrial excitation to the beginning of ventricular excitation.
S–T segment
Extends from the end of the S wave to the beginning of the T wave. Represents the time when the ventricular contractile fibers are depolarized during the plateau phase of the action potential.
Q–T interval
Extends from the start of the QRS complex to the end of the T wave. It is the time from the beginning of ventricular depolarization to the end of ventricular repolarization.
Systole
The phase of contraction.
Diastole
The phase of relaxation.
Cardiac cycle
Includes all of the events associated with one heartbeat. Consists of systole and diastole of the atria plus systole and diastole of the ventricles.
What do the ECG waves predict?
The ECG waves predict the timing of atrial and ventricular systole and diastole.
Atrial systole
The atria are contracting and the ventricles are relaxed. Lasts about 0.1 seconds.
End-diastolic volume (EDV)
Volume of blood sitting in heart before it contracts.
Ventricular systole
The ventricles are contracting and the atria are relaxed. Lasts about 0.3 seconds.
Atrial diastole
FIX
Isovolumetric contraction
Interval in which both the SL and AV valves are closed. During this interval, cardiac muscle fibers are contracting and exerting force, but are not yet shortening - thus, the muscle contraction is isometric (same length).
Ventricular ejection
Period in which the SL valves are open and the AV valves are closed. Lasts for about 0.25 sec.
End-systolic volume (ESV)
Volume of blood remaining in the heart after the ventricles have contracted.
Stroke volume
The volume ejected per beat from each ventricle. Equals end-diastolic volume minus end-systolic volume (SV = EDV − ESV).
Relaxation period
Both the atria and the ventricles are relaxed. Lasts about 0.4 seconds.
Ventricular diastole
FIX
Dicrotic wave
Produced by a rebound of blood off the closed cusps of the aortic valve.
Isovolumetric relaxation
Period in which ventricular blood volume doesn’t change because both the SL and AV valves are closed.
Ventricular filling
The major part of ventricular filling occurs just after the AV valves open. Blood that has been flowing into and building up in the atria during ventricular systole then rushes rapidly into the ventricles.
Auscultation
The act of listening to sounds within the body. Is usually done with a stethoscope. The sound of the heartbeat comes primarily from blood turbulence caused by the closing of the heart valves.
Heart sounds
There are four total, but in a normal heart only the first and second heart sounds (S1 and S2) are loud enough to be heard through a stethoscope.
Lubb sound
Caused by blood turbulence associated with closure of the AV valves soon after ventricular systole begins.
Dupp sound
Caused by blood turbulence associated with closure of the SL valves at the beginning of ventricular diastole.
Cardiac output (CO)
The volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute.
Stroke volume (SV)
The volume of blood ejected by the ventricle during each contraction.
Heart rate (HR)
The number of heartbeats per minute.
Cardiac reserve
The difference between a person’s maximum cardiac output and cardiac output at rest. The average person has a cardiac reserve of four or five times the resting value.
What are the three factors that affect regulation of stroke volume? Briefly describe them
- Preload: the degree of stretch on the heart before it contracts.
- Contractility: the forcefulness of contraction of individual ventricular muscle fibers.
- Afterload: the pressure that must be exceeded before ejection of blood from the ventricles can occur.
Frank-Starling law of the heart
Law that states the more the heart fills with blood during diastole, the greater the force of contraction during systole.
Venous return
The volume of blood returning to the right ventricle.
Positive inotropic agents
Substances that increase contractility. Stimulation of the sympathetic division of the autonomic nervous system (ANS), hormones such as epinephrine and norepinephrine, increased Ca2+ level in the interstitial fluid, and the drug digitalis all have positive inotropic effects.
Negative inotropic agents
Substances that decrease contractility. Inhibition of the sympathetic division of the ANS, anoxia, acidosis, some anesthetics, and increased K+ level in the interstitial fluid have negative inotropic effects.
Calcium channel blockers
Drugs that can have a negative inotropic effect by reducing Ca2+ inflow, thereby decreasing the strength of the heartbeat.
Cardiovascular (CV) center
In the medulla oblongata. Where nervous system regulation of the heart originates. This region of the brain stem receives input from a variety of sensory receptors and from higher brain centers. It then directs appropriate output by increasing or decreasing the frequency of nerve impulses in both the sympathetic and parasympathetic branches of the ANS.
Proprioceptors
Monitors movements. Sends input to the cardiovascular center.
Chemoreceptors
Monitors blood chemistry. Sends input to the cardiovascular center.
Baroreceptors
Monitors blood pressure. Sends input to the cardiovascular center.
Cardiac accelerator nerves
Is sympathetic. Sends output to the heart which increases rate of spontaneous depolarization in SA node (and AV node), which increases heart rate. Also increases contractility of atria and ventricles, which increases stroke volume.
Vagus (X) nerves
Is parasympathetic. Sends output to the heart which decreases rate of spontaneous depolarization in SA node (and AV node), which decreases heart rate.
What are the two major chemical regulators of the heart?
- Hormones (epinephrine, norepinephrine, and thyroid hormones enhance the heart’s pumping effectiveness)
- Cations (K+, Ca2+, and Na+ have a large effect on cardiac function)
Tachycardia
Heart rate greater than 100 beats/min
Bradycardia
Heart rate less than 50 beats/min. Is a beneficial effect of endurance-type training because a slowly beating heart is more energy efficient than one that beats more rapidly.
Hypothermia
When a person’s body is deliberately cooled to a low core temperature. Hypothermia slows metabolism, which reduces the oxygen needs of the tissues, allowing the heart and brain to withstand short periods of interrupted or reduced blood flow during a medical or surgical procedure.
