Anatomy - Chapter 18: Cardiovascular System
MAKE CONNECTIONS Identify the type of muscle represented by structures a and b below. How can you tell?
Structure (a) shows cardiac muscle and structure (b) shows skeletal muscle. You can tell that both of these structures are parts of striated (and not smooth) muscle fibers because they have sarcomeres. You can tell that (b) is skeletal muscle because it has terminal cisterns next to each of the T tubules, whereas (a) does not. Also, the T tubules in cardiac muscle (a) are aligned with the Z discs, whereas in skeletal muscle (b), they are at the A-I junctions.
Name the two main branches of the right coronary artery.
The branches of the right coronary artery are the right marginal artery and the posterior interventricular artery.
What is the name of the heart covering and what purposes does it serve?
The heart is enclosed by a double-walled sav called the pericardium. It's purposes are to: 1. Protect the heart 2. Anchor the heart to surrounding structures 3. Prevent overfilling of the heart with blood
Describe the size, location, and orientation of the heart
The heart is modest in size; about fist size and weighs 250-350 grams (less than one pound). It fits snugly into the mediastinum (medial cavity of the thorax).
What separate the 4 chambers of the heart?
The interatrial septum (separates the R/L atria) and the interventricular septum (separates the R/L ventricle)
From inside to outside, list the layers of the heart wall and the coverings of the heart.
The layers of the heart wall are the endocardium, the myocardium, and the epicardium. The epicardium is also called the visceral layer of the serous pericardium. This is surrounded by the parietal layer of the serous pericardium and the fibrous pericardium.
The heart is in the mediastinum. Just what is the mediastinum?
The mediastinum is the medial cavity of the thorax within which the heart, great vessels, thymus, and parts of the trachea, bronchi, and esophagus are found.
Name the valve that has just two cusps.
The mitral (left atrioventricular) valve has two cusps.
What is the function of the papillary muscles and chordae tendineae?
The papillary muscles and chordae tendineae keep the AV valve flaps from everting into the atria as the ventricles contract.
What are the heart's two receiving chambers and where do they receive blood from?
The right atrium receives blood returning from the systemic circuit. The left atrium receives blood returning from the pulmonary circuit.
Which side of the heart acts as the pulmonary pump? The systemic pump?
The right side of the heart acts as the pulmonary pump, whereas the left acts as the systemic pump.
What types of blood do each sides of the heart receive?
The right side of the heart receives O2 poor blood from the body tissues and then pumps it to the lungs to pick up O2 and get rid of CO2. (pulmonary circuit) The left side of the heart receives oxygenated blood from the lungs and pumps it throughout the body to supply O2 and nutrients to body tissues. (systemic circuit)
What are the heart's two main pumping chambers?
The right ventricle pumps blood into the pulmonary circuit. the left ventricle pumps blood into the systemic circuit.
What is the purpose of the serous fluid inside the pericardial cavity?
The serous fluid decreases friction caused by movement of the layers against one another.
In the frontal section of the heart below, name the structures indicated by a-g. Which heart chamber receives oxygen-poor blood from veins? Which chamber pumps blood into the systemic circulation? Which blood vessel transports blood toward the lungs?
The structures are (a) aorta, (b) pulmonary trunk, (c) left atrium, (d) right atrium, (e) left ventricle, (f) right ventricle, (g) inferior vena cava. The right atrium (d) receives oxygen-poor blood. The left ventricle (e) pumps blood into the systemic circulation. The pulmonary trunk (b) transports blood toward the lungs.
Describe the pulmonary circuit
This circuit is short and low pressure. It ejects blood into the pulmonary trunk which then carries it to the lungs. It is powered by the right side of the heart. It is composed of two pulmonary arteries and two pulmonary veins.
What is pericarditis?
inflammation of the pericardium; results in creaking, swelling, and potentially, cardiac tamponade (large amounts of inflammatory fluid plugging the pericardial cavity)
Describe the electrical event in the heart that occurs during each of the following: (a) the QRS complex of the ECG; (b) the T wave of the ECG; (c) the P-R interval of the ECG.
(a) The QRS wave occurs during ventricular depolarization. (b) The T wave of the ECG occurs during ventricular repolarization. (c) The P-R interval of the ECG occurs during atrial depolarization and the conduction of the action potential through the rest of the intrinsic conduction system.
For each of the following, state whether it applies to skeletal muscle, cardiac muscle, or both: (a) refractory period is almost as long as the contraction; (b) source of Ca2+ for contraction is only SR; (c) has troponin; (d) has triads.
(a) The refractory period is almost as long as the contraction in cardiac muscle. (b) The source of Ca2+ for the contraction is only SR in skeletal muscle. (c) Both skeletal muscle and cardiac muscle have troponin. (d) Only skeletal muscle has triads.
Which of the following statements are true? (a) The left ventricle wall is thicker than the right ventricle wall. (b) The left ventricle pumps blood at a higher pressure than the right ventricle. (c) The left ventricle pumps more blood with each beat than the right ventricle. Explain.
(a) True. The left ventricle wall is thicker than the right. (b) True. The left ventricle pumps blood at much higher pressure than the right ventricle because the left ventricle supplies the whole body, whereas the right ventricle supplies only the lungs. (c) False. Each ventricle pumps the same amount of blood with each beat. If this were not true, blood would back up in either the systemic or pulmonary circulation (because the two ventricles are in series).
What are the layers of the pericardium?
1. outer fibrous pericardium 2. inner serous pericardium (made up of parietal layer and visceral layer- [also called epicardium]) - Additionally, there is a pericardial cavity that contains serous fluid and lubricates the movement of the heart in between the parietal and visceral layers of the heart covering.
Cardiac muscle cannot go into tetany. Why?
Cardiac muscle cannot go into tetany because the absolute refractory period is almost as long as the contraction.
Three line graphs labeled from left to right: (a), (b), and (c). All three graphs show a tracing of an action potential. In all three graphs, the x-axis is labeled time with a forward-pointing arrow but no increments marked. In all three graphs, the y-axis is labeled millivolts with no increments marked. Graph (a): This tracing runs horizontally, then rises suddenly to a single sharp peak and falls quickly to the value it had before it started rising. This tracing shows the most rapid fall of the three graphs. It continues at its original horizontal level for the rest of the tracing. Graph (b): This tracing runs horizontally, then rises vertically to a sharp peak. Then it falls slightly and seems to plateau before it drops to its original level. It continues at this horizontal level for the rest of the tracing. Graph (c): This tracing starts by dipping down slightly and then rising gradually. It rises to a rounded peak and then falls fairly quickly to its original lowest value. Unlike the other two graphs, this line rises from its lowest point until the end of the tracing. Which one comes from a contractile cardiac muscle cell? A skeletal muscle cell? A cardiac pacemaker cell? For each one, state which ion is responsible for the depolarization phase and which ion is responsible for the repolarization phase.
(b) Represents an action potential (AP) in a contractile cardiac muscle cell, (a) represents an AP in a skeletal muscle cell, and (c) represents an AP in cardiac pacemaker cells. The depolarization phase is due to Na+ influx in skeletal muscle and contractile cardiac muscle cells, and it is due to Ca2+ entry in cardiac pacemaker cells. K+ efflux is responsible for the repolarization in all action potentials.
Describe the apex of the heart
- inferolateral portion of L ventricle. - Posterior to L 5th intercostal space. - place where mitral valve closure heard best. Additionally, you can hear the apical impulse just under the left nipple (between the 5th and 6th rib) where it touches the ribs.
What are the layers of the heart wall?
1. Epicardium (visceral layer/serous pericardium) - often infiltrated by fat in the elderly 2. Myocardium - the bulk of the heart, this is the layer that contracts and it is arranged in bundles that are reinforced by connective tissue. (also reinforce the pathways of the great vessels and control the pathways of action potentials) 3. Endocardium - the inner layer of the heart, is continuous with the hearts blood vessels (glistening white)
What are the two major heart grooves?
1. The coronary (crown) sulcus: it encircles the junction of the atria and ventricles like a crown. 2. The anterior intraventricular sulcus: holds the anterior intraventricular artery and marks the anterior position of the septum separating the L/R ventricles. (does the same thing on the posterior side)
In skeletal muscle, every muscle fiber must be innervated so it can contract. In cardiac muscle, the intrinsic conduction system does not connect to every cardiac myocyte. Why is this not necessary? Which part of the intrinsic conduction system directly excites ventricular myocardial cells? In which direction does the depolarization wave travel across the ventricles?
It is not necessary for the intrinsic conduction system to contact each individual cardiac myocyte. This is because cardiac myocytes are connected to each other by gap junctions and so are depolarized when an adjacent myocyte depolarizes. The subendocardial conducting network excites ventricular muscle fibers. The depolarization wave travels upward from the apex toward the atria.
