Unit 17 - Heart

1. If blood contains more oxygen than carbon dioxide. 2. If blood contains more carbon dioxide than oxygen.

1. What does it mean if blood is oxygenated? 2. What does it mean if blood is deoxygenated?

1. The heart 2. It functions in pumping blood throughout the system

1. What is the main organ of the cardiovascular system? 2. What is its function?

Cardiac output is directly proportional to the stroke volume of the left ventricle. The left ventricle's stroke volume is affected by two main factors: the pressure gradient between the left ventricle and the aorta, and the ventricle's strength of contraction. 1. The greater the pressure gradient, the easier blood moves from the left ventricle into the aorta. This causes greater stroke volume because more blood leaves the left ventricle per systolic contraction. 2. The force of ventricular contraction is determined by the length of the ventricle's myofibers (preload). The greater the preload in the ventricle's myofibers, the stronger it contracts.

Cardiac output is directly proportional to what?

An EKG's P wave coincides with atrial contraction because it is caused by depolarization of the SA node. An enlarged P wave indicates the heart's atria are enlarged

Describe an EKG's P wave

An EKG's QRS wave coincides with ventricular contraction because it is caused by depolarization of the AV node. Abnormalities in this wave are caused by a variety of problems. a. An enlarged Q wave is caused by a myocardial infarction. b. An enlarged R wave indicates the heart's ventricles are enlarged. c. An enlarged S wave indicates the heart's left side is working harder than its right.

Describe an EKG's QRS wave

An EKG's T wave is caused by ventricular repolarization. A flat T wave indicates a weakened myocardium because of poor coronary circulation.

Describe an EKG's T wave

The heart controls the direction of blood flow with valves. These structures are composed of dense connective tissue and endocardium

Describe how the heart controls the direction of blood flow

The heart's semilunar valves are pouch-like or crescent-shaped. These valves are anchored directly to the vessel's endothelium.

Describe the anatomy of the semilunar valves

The heart lies within the mediastinum's pericardial cavity. This cavity is delineated by a sac called the pericardium.

Describe the area of the body where the heart is located

It runs through the interventricular septum. This nerve tract conveys the nerve impulse to the system's conduction myofibers.

Describe the atrioventricular bundle (bundle of HIS)

It is located within the inferior portion of the interatrial septum. The AV node's depolarization causes an electrical impulse to be sent to the atrioventricular bundle. This event happens at the end of the atrial contraction.

Describe the atrioventricular node (AV Node)

The ANS's cardiac center is located within the brain's medulla oblongata. This involuntary center is divided into the cardioacceleratory and cardioinhibitory centers.

Describe the autonomic nervous system's cardiac center

Pulmonary circulation flows between the heart's right ventricle and its left atrium. This circulatory route sends deoxygenated blood to the lungs.

Describe the body's pulmonary circulation

Systemic circulation flows between the heart's left ventricle and its right atrium. This circulatory route sends oxygenated blood to the body's tissues. Because of this route's distance, the left ventricle has thicker (more muscular) walls than the right ventricle.

Describe the body's systemic circulation

The cardioacceleratory center (CAC) is part of the ANS's sympathetic division. This center uses the cardiac nerve to innervate the heart's SA node. When stimulated, the cardiac nerve releases norepinephrine. Norepinephrine opens calcium channels within a cardiac cell's sarcolemma. The influx of calcium ions (positively charged) into the cardiac cell lowers its resting potential. Therefore, norepinephrine increases the heart's rate and strength of contraction.

Describe the cardioacceleratory center (CAC) What effect does norephinephrine have on this center?

The cardioinhibitory center (CIC) is part of the ANS's parasympathetic division. This center uses the vagus nerve to innervate the heart's SA node. When stimulated, the vagus nerve releases acetylcholine. In cardiac muscle, acetylcholine opens potassium channels with the myofiber's sarcolemma. The "leaking" of potassium ions (positively charged) by the myofiber causes its resting potential to become greater. Therefore, acetylcholine decreases the heart's rate and strength of contraction.

Describe the cardioinhibitory center (CIC) What effect does acetylcholine have on this center?

They penetrate the heart's ventricular myocardium. These fibers stimulate the ventricles to contract.

Describe the conduction myofibers (Purkinje fibers)

Contraction of cardiac tissue is similar to skeletal muscle tissue with one exception. Cardiac cells trigger their contraction using calcium ions from two sources: from within the sarcoplasmic reticulum (intracellular calcium) and from outside the cell (intercellular calcium). Therefore, calcium pumps are located within the sarcoplasmic reticulum and the sarcolemma.

Describe the contraction of cardiac tissue

The coronary arteries branch from the ascending aorta. These blood vessels are responsible for sending nutrients to the heart's capillaries. If these blood vessels become coated with plaque, their ability to deliver nutrients to the heart's tissues becomes reduced.

Describe the coronary arteries

1. Externally, the heart's atria are identified by flaps called auricles. These hollow structures increase the carrying capacity of the heart's atria. 2. Internally, the atria are separated from one another by a wall called the interatrial septum.

Describe the external and internal structure of atria

Externally, the heart is delineated by two sulci, the coronary sulcus and the interventricular sulcus. 1. The coronary sulcus separates the heart's ventricles from its atria. 2. The interventricular sulcus separates the heart's ventricles from one another.

Describe the external structure of the heart

The pericardial sac is composed of two membranes. The inner surface of the pericardial sac is called the parietal pericardium (because this surface faces the heart). The outer surface of the pericardial sac is called parietal pleura (because this surface faces the lung).

Describe the pericardial sac

The heart contains four cavities. These chambers are situated in a square configuration with each chamber occupying one corner within the square.

Describe the shape of the heart

1. A region's pressure is determined by its size and the volume of blood it contains. If a region's size remains constant and its blood volume increases, the region's pressure increases and vice versa. Regional pressure will also increase, if the region's blood volume remains constant, while its size decreases. 2. Regional size varies throughout the cardiac cycle because each region is bordered by muscular tissue. These size changes are called systole and diastole.

Describe the significance of differences in pressure gradients between the atria, ventricles, and major arteries (pulmonary trunk and aorta)

It is located within the walls of the right atrium. Because this structure is responsible for initiating each cardiac cycle, it also called the pacemaker. The SA node's depolarization causes both atria to contract. It also stimulates the atrioventricular node to depolarize.

Describe the sinoatrial node (SA Node)

The surface of the heart is called the epicardium or visceral pericardium. The visceral pericardium is separated from the parietal pericardium by pericardial fluid. The pericardial fluid lubricates the heart by reducing friction between the visceral and parietal surfaces.

Describe the surface of the heart

1. The opening of the AV valves causes a sharp drop in the atrial pressure because blood moves from the atria into the ventricles. This movement is attributed to gravity and it moves 70% of the atria's blood. 2. 30% of the atria's blood is moved during atrial systole. This causes a slight rise in atrial pressure because most of the blood within these chambers has already moved. Therefore, heart failure is not associated with the failure of the atria to pump blood. Gravity will continue to move its 70%. 3. Atrial pressure experiences a sharp rise during ventricular systole. This is caused by the expanding ventricles pushing on the atria.

Describe what happens to atrial pressure during ventricular systole

1. The reduction of oxygen and nutrients to the heart's tissues causes stress which weakens the myocardium. This stress causes pain called ischemia. If the ischemia is associated with the chest, it is called angina pectoris. 2. If the coronary arteries become 85% obstructed, the heart muscle dies and it is replaced by scar tissue. This causes the person to experience a myocardial infarction (heart attack) because the scar tissue severely reduces the heart's efficiency.

Describe what happens when the ability to deliver nutrients to the heart's tissues becomes reduced

When ventricular pressure falls below atrial pressure, the AV valves open. This allows blood to flow from the atria into the ventricles.

Describe what happens when ventricular pressure falls below atrial pressure

The heart's nerve impulses can be measured and recorded by an electrocardiograph. This machine generates a record called an electrocardiogram (EKG or ECG). An EKG consists of three waves or markings: P wave, QRS wave, and T wave. Doctors use this information to detect irregularities within a person's cardiac cycle.

How do doctors measure and record the heart's nerve impulses?

Operation of the heart's AV valves is controlled by pressure gradients (differences in pressure on either side of the valve). When the heart's atrial pressure is greater than its ventricular pressure, the valves open and vice versa.

How do the heart's AV valves operate?

The endocrine system uses the thyroid and the adrenal medulla to control the heart's rate. a. The thyroid uses thyroxine to increase the body's basal metabolic rate and the heart's rate of contraction. b. The adrenal medulla uses epinephrine to increase the heart's rate as part of its fight-or-flight response.

How does the endocrine system control the heart's rate?

The nervous system uses the autonomic nervous system to control the heart's rate.

How does the nervous system make cardiac output proportional to the heart's rate of contraction?

The heart is synchronized, so that its atria work in unison and its ventricles work in unison. However, the heart's atria contract while its ventricles relax and vice versa.

How is the heart synchronized?

The heart possesses two atrioventricular valves. These valves are distinguished from one another by the number of flaps they possess.

How many atrioventricular valves does the heart possess?

The right atrium receives blood from the superior vena cava, inferior vena cava, and the coronary sinus. 1. The superior vena cava collects deoxygenated blood from the head, neck, shoulders, and arms. 2. The inferior vena cava collects deoxygenated blood from the trunk and lower appendages. 3. The coronary sinus collects deoxygenated blood from the heart's coronary circulation

Step 1 of Blood Flow: Where does the right atrium receive blood from?

The left ventricle pumps its blood past the aortic semilunar valves into the aorta. The aorta conveys its oxygenated blood throughout the body.

Step Five of Blood Flow Through the Heart: Where does the left ventricle send blood in this stage of blood flow?

The pulmonary veins return the oxygenated blood to the heart's left atrium. This chamber pumps its blood past the bicuspid valve into the left ventricle.

Step Four of Blood Flow Through the Heart: Where do pulmonary veins send blood through this step of blood flow?

The blood becomes deoxygenated after reaching the tissues. It is then collected by the superior and inferior vena cava.

Step Six of Blood Flow Through the Heart: What happens to blood in the final (sixth) stage of blood flow

The pulmonary trunk divides into right and left pulmonary arteries. These arteries convey the blood to the lungs. The lungs oxygenate the blood and return it by way of the pulmonary veins.

Step Three of Blood Flow Through the Heart: Where does the pulmonary trunk send blood in this step of blood flow

The right atrium pumps its blood past the tricuspid valve into the right ventricle. The right ventricle pumps its blood past the pulmonic semilunar valves into the pulmonary trunk

Step Two of Blood Flow: Where does the right atrium send blood?

A. The right atrium receives blood from the superior vena cava, inferior vena cava, and the coronary sinus. B. The right atrium pumps its blood past the tricuspid valve into the right ventricle. The right ventricle pumps its blood past the pulmonic semilunar valves into the pulmonary trunk. C. The pulmonary trunk divides into right and left pulmonary arteries. These arteries convey the blood to the lungs. The lungs oxygenate the blood and return it by way of the pulmonary veins. D. The pulmonary veins return the oxygenated blood to the heart's left atrium. This chamber pumps its blood past the bicuspid valve into the left ventricle. E. The left ventricle pumps its blood past the aortic semilunar valves into the aorta. The aorta conveys its oxygenated blood throughout the body. F. The blood becomes deoxygenated after reaching the tissues. It is then collected by the superior and inferior vena cava.

Summarize the process of blood flow through the heart

The sinoatrial node The atrioventricular node The atrioventricular bundle The conduction myofibers

The neuromuscular tissue forms what four structures?

1. The body uses baroreceptors to monitor its blood pressure. These interoceptors are located within the common carotid arteries and the aorta. 2. Baroreceptor input is fed into the medulla's cardiac center. High blood pressure inhibits the medulla's CAC but it stimulates the medulla's CIC. This causes a decrease in blood pressure because the heart slows its rate of contraction. When the body's blood pressure is low, these events are reversed.

What are baroreceptors? How are they used?

The heart's right chambers pump deoxygenated blood, while its left chambers pump oxygenated blood.

What are the functions of the heart's right and left chambers?

The heart's lower chambers are called ventricles. These muscular cavities pump blood into the system's blood vessels.

What are the heart's lower chambers called? What is their function?

The heart's upper chambers are called atria. These cavities receive blood from the body.

What are the heart's upper chambers called? What is their function?

Pulmonary circulation Systemic circulation Coronary circulation

What are the three kinds of circulation associated with the heart?

1. Aortic semilunar valves They are at the base of the aorta. These valves prevent the back-flow of blood into the left ventricle. 2. The pulmonic semilunar valves They are at the base of the pulmonary trunk. These valves prevent the back-flow of blood into the right ventricle.

What are the two clusters of semilunar valves? What are their functions?

1. Tricuspid valve It contains three flaps. This valve separates the right atrium from the right ventricle. Bicuspid valve (Mitral valve) It contains two flaps. This valve separates the left atrium from the left ventricle.

What are the two types of AV valves? Describe them

Atrioventricular valves Semilunar valves

What are the two types of heart valves?

Sympathetic Impulses can be inhibited by a category of drugs called beta blockers. Physicians use these drugs to lower blood pressure in patients that are hypertensive.

What category of drugs do doctors use to inhibit sympathetic impulses?

The dicrotic notch is caused by blood falling back against the semilunar valves during ventricular diastole. This increase is also attributed to the contraction of the arterial walls (i.e. pulse).

What causes the dicrotic notch?

The heart's sound is produced by the closing of its valves. 1. The AV valves produce a lubb sound when they close. This sound begins with the contraction of the ventricles. 2. The semilunar valves produce a dupp when they close. This sound begins with the completion of ventricular contraction. 3. Murmurs are caused by the inability of a valve to close properly. This allows blood to flow back through the valve and that causes the sound of a murmur.

What causes the heart's sounds?

It causes a condition called cardiac tamponade. This condition causes the heart to compress because of the increase in pressure.

What condition is caused by excess percardial fluid?

Like AV valve operation, semilunar valve operation is also controlled by pressure gradients. These valves open when the heart's ventricular pressure exceeds the vessel's arterial pressure and they close when the opposite is true.

What controls the semilunar valve's operation?

The efficiency of the heart is determined by measuring its cardiac output. Cardiac output is the amount of blood leaving the left ventricle per minute (about 5 liters/min). This rate is primarily affected by the volume of blood per systolic contraction (stroke volume) and the rate of the heartbeat.

What determines the efficacy of the heart?

The initial reduction in blood volume has no affect on the ventricular pressure because the ventricles are still contracting. However, ventricular pressure begins to decrease as the contraction halts and the blood moves out.

What effect does the initial reduction in blood volume have on ventricular pressure and why?

The conduction system is composed of a specialized neuromuscular tissue. This tissue initiates and distributes the electrical impulses needed for the heart's cardiac cycle. This cycle is a series of events that occur from one heartbeat to the next.

What form of tissue composes the conduction system? What is its function?

During ventricular systole, arterial pressure mimics ventricular pressure because the semilunar valves are open. However, arterial pressure experiences a second sharp increase (dicrotic notch) when the semilunar valves close. During the rest of the cardiac cycle, arterial pressure gradually falls. This happens as blood moves through the system

What happens to arterial pressure during ventricular systole?

During ventricular systole, atrial pressure slowly rises. This is attributed to atrial filling, while the chambers are relaxed.

What happens to atrial pressure during ventricular systole?

During the rest of the cardiac cycle, ventricular pressure remains about the same. Although the ventricles are filling during this interval, the ventricles are relaxed.

What happens to ventricular pressure during the rest of the cardiac cycle?

Ventricular pressure falls sharply during ventricular diastole. This is attributed to a low blood volume and a drastic increase in the size of the ventricles. Preload is the term used to describe the amount of stretching the ventricular wall experiences during diastole.

What happens to ventricular pressure during ventricular diastole?

Ventricular pressure rises sharply during ventricular systole. This is attributed to a large blood volume and a drastic reduction in the size of the ventricles.

What happens to ventricular pressure during ventricular systole?

When ventricular pressure exceeds the arterial pressure, the semilunar valves open. This allows the blood to flow from the heart's ventricles into its arteries. a. Afterload is the term used to describe the amount of ventricular contraction (tension) it takes to eject blood into the arteries. b. Heart failure occurs when the ventricles can no longer eject blood into the arteries.

What happens when ventricular pressure exceeds the arterial pressure?

The medulla oblongata monitors the level of blood pressure to control the heart's rate of contraction. If the blood pressure increases, the medulla oblongata's CIC responds by slowing heart rate to correct the problem. If the blood pressure decreases, the medulla oblongata's CAC responds by increasing heart rate to correct the problem.

What is Marey's Law of the Heart?

The force of ventricular contraction is determined by the length of the ventricle's myofibers (preload). The greater the preload in the ventricle's myofibers, the stronger it contracts.

What is Starling's law of the heart?

The study of the heart

What is cardiology?

It describes a region that is relaxed. During this period, the region is filling with blood.

What is diastole?

High levels of extracellular calcium It causes an increase in the heart's strength and time of contraction. Remember, calcium also enters a cardiac cell from the outside when it depolarizes. The result, the cell achieves its action potential quicker and easier.

What is hypercalcemia and how does it influence the heart's rate?

High levels of potassium It causes a decrease in the heart's strength and rate of contraction. If extracellular levels of potassium are high, less will leak out during a myofiber's resting potential. The result, the cell depolarizes fine and it has difficulty repolarizing. If these conditions continue for an extended period, the heartbeat will eventually become weak and irregular. In severe cases, the heart will stop beating.

What is hyperkalemia? How does it influence the heart's rate?

Low levels of potassium It causes the myofiber's to hyperpolarize. They leak out too many potassium ions while resting, making them more negative. The result, depolarization becomes more difficult and the cell's rate of contraction declines. In severe cases, the cells will completely stop depolarizing altogether.

What is hypokalemia? How does it influence the heart's rate?

It describes a region that is contracting. During this period, blood is being pumped into the next circulatory area.

What is systole?

Coronary or cardiac circulation functions in serving the needs of the heart's myocardium. This circulatory route consists of several blood vessels: the coronary arteries, the cardiac veins, and the coronary sinus.

What is the function of coronary (cardiac) circulation?

They separate the heart's atria from its ventricles. These valves direct the blood from the atria into the ventricles.

What is the function of the atrioventricular (AV) valves ?

The great and small cardiac veins collect blood from the heart's capillaries. This part of the coronary circulation empties blood into the heart's coronary sinus.

What is the function of the great and small cardiac veins?

The heart's coronary sinus conveys its deoxygenated blood to the right atrium.

What is the function of the heart's coronary sinus?

They separate the heart's chambers from the major arteries. These valves direct the blood from the heart's ventricles into its arteries.

What is the function of the semilunar valves?

This ability is possible because of the heart's conduction system. Although this system is responsible for stimulating the heart's contractions, its pace may be modified by the nervous or endocrine systems.

What makes it possible for the cardiac tissue to initiate its own muscular contractions?

1. Internally, the ventricles are separated by a wall called the interventricular septum. 2. Externally, the interventricular sulcus separates the heart's ventricles from one another.

What structures separates the ventricles internally and externally?

Calcium Potassium

What two electrolytes influence the heart's rate?

The distal ends of an AV valve's flaps are anchored to the heart's endocardium by papillary muscles and chordae tendinae (heart strings). These structures provide support by preventing the valves from inverting or everting under pressure. NOTE: The heart's strings do not function in opening and closing the AV valves.

Where are papillary muscles and chordae tendinae located? What is their function?

Atrial repolarization is not represented in the EKG because this event coincides with ventricular depolarization. Therefore, atrial repolarization is masked by the QRS wave.

Why is atrial repolarization not represented in an EKG?