Chapter 18 learning objectives (test 2)

Explain the regulation of heart function by discussing the roles of blood volume and blood pressure receptors in cardiac feedback loops (baroreceptors and Bainbridge reflex).

*Baroreceptors* Respond to changes in systemic BP *Bainbridge reflex* ANS reflex initiated by increased venous return and increased atrial filling. Stimulates the SA node Increases HR

Explain the role of the cardioacceleratory center and the cardioinhibitory center in regulating heart rate and contractility via sympathetic vs. parasympathetic stimulation.

*Cardioacceleratory*: connected to SNS it increases HR which increases BP as well. Enhances contractility and speeds relaxation *Cardioinhibitory*: Connected with PNS, slows heart rate back down once the stressful situation is over, BP also decreases. Has little effect on cardiac contractility. Under resting conditions, which of those controls your HR? PARASYMPATHETIC which is by way of the inhibitory system. Both in medulla oblongata Joined with your ANS

Describe the functional role of the SA node as the pacemaker.

The SA node sets the pace for the heart as a whole because no other region of the conduction system or the myocardium has a faster depolarization rate. For this reason, it is the hearts pacemaker, and its characteristic rhythm, called sinus rhythm, determines heart rate.

Describe the factors, which affect venous return to the heart.

Venous return is the amount of blood retunring to the heart and distending its ventricles •Anything that increases venous return increases EDV , SV and contraction force •Exercise increases venous return bc both increased SNS activity and the squeezing action of the skeletal muscles compress the veins, decreasing the volume of blood they contain and returning more blood to the heart. •Low venous return might result from severe blood loss or an extremely rapid HR that does not allow enough time for ventricular filling

Compare and contrast microanatomy and contraction of cardiac muscle to skeletal muscle.

*Cardiac muscle microanatomy* -Contracts by the sliding filament theory like skeletal muscle -Striated(SM), branched, uninucleate -Intercalated discs -The myocardium behaves as a single coordinated unit, or Functional syncytium -Audtorhythmicity *Functional differences from skeletal muscle* -Self excitable pacemaker cells (spontaneously depolarize) -The heart contracts as a unit aka Functional syncytium -Slow Ca2+ channels--longer refractory period -Larger mitochondria population bc the heart relies on almost exclusively aerobic respiration

Describe the coronary circulation including the term coronary sinus. Include the medical significance of coronary circulation by discussing ischemia, angina pectoris, and myocardial infarctions.

*Coronary circulation* Supply of blood to the heart muscle; shortest circulation in the body *Coronary arteries* Provide a pulsating blood flow to the myocardium. They deliver blood when the heart is relaxed *Branches of the arteries* -Left coronary artery branches: Anterior interventricular artery, and the circumflex artery. -Right coronary artery branches: Right marginal artery, and posterior interventricular artery. *Coronary veins* These veins join to form an enlarged vessel called the coronary sinus, which empties the blood into the right atrium. *3 large tributaries of the coronary sinus* -Great cardiac vein -Middle cardiac vein -Small cardiac vein *Ischemia* Inadequate blood supply to the heart vessels or other organs of the body. Usually the result of a partial or complete blockage of your heart's arteries *Angina pectoris* thoracic pain cause by a deficiency in blood delivery to the myocardium. May result from stress-induced spasms of the coronary arteries. *Myocardial infarction* Caused by prolonged coronary blockage.

Diagram and describe the intrinsic conduction system of the heart: • SA node • AV node • AV bundle • Bundle branches • Purkinje fibers PAGE 680

*Sinoatrial (SA) Node* -aka pacemaker -Located in the right atrial wall -Generates impulses about 75 times every min -Sets the pace for the heart as a whole because no other region of the conduction system of the myocardium has a faster depolarization rate. *Atrioventricular (AV) Node* -Located above the tricuspid valve -At the AV node, impulse is delayed for about 0.1 seconds, allowing the atria to respond and complete their contraction before ventricles contract. -AV node conducts impulses more slowly than other parts of the system *Atrioventricular (AV) Bundle)* -aka bundle of His -The AV bundle is the only electrical connection between the atria and ventricles *Bundle Branches* Right and left branches course along the interventricular septum toward the heart apex. *Purkinje fibers* -Depolarizes the contractile cells of both ventricles

Explain each deflection of the ECG and relate it to the cardiac cycle. Where does atrial diastole occur? Explain the PR interval and the ST segment.

-P wave—Atrial depolarization -QRS complex—Ventricular depolarization -T wave—Ventricular Repolarization Atrial diastole occurs during the P-R interval The P-R interval is the time (about 0.16 s) from the beginning of atrial excitation to the beginning of ventricular excitation. IF the Q wave is visible, it marks the beginning of ventricular excitation which is why it is sometimes called the P-Q interval.

Explain how SV is affected by afterload.

After load: pressure that the ventricles must overcome to eject blood. In healthy individuals, afterload is not a major determinant of SV because it is relatively constant. However, in people with hypertension, afterload is important because it reduces the ability of the ventricles to eject blood. Consequently, more blood remains in the heart after systole, increasing ESV and reducing SV.

Describe the circulatory route termed pulmonary circulation and describe its unique feature in contrast to normal systemic circulation.

Elsewhere in the body, veins carry relatively oxygen-poor blood to the heart, and arteries transports oxygen-rich blood from the heart. The opposite oxygenation conditions exist in veins and arteries of the pulmonary circuit. The pulmonary circuit, served by the right ventricle, is a short, low pressure circulation. In contrast, the systemic circuit, associated with the left ventricle, takes a long pathway through the entire body and encounters about 5 times as much resistance to blood flow.

Explain why the heart is termed the "double pump" by explaining the double circuit through which blood flows. Contrast this description to the actual action of the atria and ventricles as functional units.

Two pumps: Pulmonary and systemic circuits *Pulmonary circuit* The right side of the heart receives oxygen-poor blood from body tissues and then pumps this blood to the lungs to pick up oxygen and dispel carbon dioxide. The blood vessels that carry blood to and from the lungs form the pulmonary circuit. *Systemic circuit* The left side of the heart receives oxygenated blood returning from the lungs and pumps this blood throughout the body to supply oxygen and nutrients to body tissues. The blood vessels that carry blood to and from all body tissues form the systemic circuit. The heart has two receiving chambers, the right atrium and the left atrium, that receive blood returning from the systemic and pulmonary circuits. The heart also has two main pumping chambers, the right ventricle and left ventricle, that pump blood around the two circuits.

Explain the lub-dup sounds of the cardiac cycle as they relate to valve action.

• Lub: AV valves close, ventricular pressure rises above atrial pressure (beginning of ventricular systole) • Dup: SL valves close at the beginning of ventricular relaxation (diastole

Define cardiac output (CO) and be able to calculate CO given the heart rate (HR) and Stroke Volume (SV).

•Amount of blood pumped out by each ventricle in 1 minute. •HRxSV=CO

Define the terms arrhythmia and murmur and relate these to the conduction system and the cardiac cycle discussed above. Give examples of each.

•Arrhythmia: Irregular heart rhythms •Murmur: Abnormal heart sound (usually resulting from valve problems)

Discuss the effects of aerobic exercise on the heart.

•Increase HR (SNS) •Increase blood pressure (more later) •Increases contractility via increased Ca2+ supply •Increases venous return and SV •Increases CO •Benefits: oCleans out the blood vessels oHeart becomes more efficient (maximize SV) oMaximize aerobic respiration oLower resting pulse

State and explain Starling's Law of the Heart. Be sure to mentally connect this law to the idea of regulation of stroke volume by a change in preload.

•The relationship between preload and stroke volume •The higher the preload, the higher the SV