6 Histology Review Supplement Cardiovascular Tissue Review From the PhysioEx main menu, select Histology Atlas. Click on the white Sort By drop-down menu and select Histology Review from the list. Refer to the slides in the Cardiovascular Tissue Slides folder as you complete this worksheet. Which component of the intercalated disc is a junction that provides the intercellular communication required for the myocardium to perform as a functional syncytium? Gap junctions Heart The heart is a four-chambered muscular pump.
Although its wall can be divided into three distinct histological layers (endocardium, myocardium, and epicardium), the cardiac muscle of the myocardium composes the bulk of the heart wall. Blood Vessels Blood vessels form a system of conduits through which lifesustaining blood is conveyed from the heart to all parts of the body and back to the heart again. Generally, the wall of every vessel is described as being composed of three layers, or tunics. The tunica intima, or tunica interna, a simple squamous endothelium and a small amount of subjacent loose connective tissue, is the innermost layer adjacent to the vessel lumen.
Smooth muscle and elastin are the predominant constituents of the middle tunica media, and the outermost tunica adventitia, or tunica externa, is a connective tissue layer of variable thickness that provides support and transmits smaller blood and lymphatic vessels and nerves. The thickness of each tunic varies widely with location and function of the vessel. Arteries, subjected to considerable pressure fluctuations, have thicker walls overall, with the tunica media being thicker than the tunica adventitia.
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Veins, in contrast, are subjected to much lower pressures and have thinner walls overall, with the tunica adventitia often outsizing the tunica media. Because thinwalled veins conduct blood back to the heart against gravity, valves (not present in arteries) also are present at intervals to prevent backflow. In capillaries, where exchange occurs between the blood and tissues, the tunica intima alone composes the vessel wall. The tunica media of the aorta would have a much greater proportion of what type of tissue than a small artery?
Elastic fibers In general, which vessel would have a larger lumen, an artery or its corresponding vein? Click slide 1. Contractile cardiac muscle cells (myocytes, myofibers) have the same striated appearance as skeletal muscle, but are branched rather than cylindrical in shape and have one (occasionally two) nucleus (myonucleus) rather than many. The cytoplasmic striations represent the same organization of myofilaments (sarcomeres) and alignment of sarcomeres as in skeletal muscle, and the mechanism of contraction is the same. The intercalated disc, however, is a feature unique to cardiac muscle.
The densely stained structure is a complex of intercellular junctions (desmosomes, gap junctions, fasciae adherens) that structurally and functionally link cardiac muscle cells end to end. A second population of cells in the myocardium composes the noncontractile intrinsic conduction system (nodal system). Although cardiac muscle is autorhythmic, meaning it has the ability to contract involuntarily in the absence of extrinsic innervation provided by the nervous system, it is the intrinsic conduction system that prescribes the rate and orderly sequence of contraction. Extrinsic innervation only modulates the inherent activity.
Click slide 2. Of the various components of the noncontractile intrinsic conduction system, Purkinje fibers are the most readily observed histologically. They are particularly abundant in the ventricular myocardium and are recognized by their very pale-staining cytoplasm and larger diameter. The connective tissue component of cardiac muscle is relatively sparse and lacks the organization present in skeletal muscle. Which component of the intercalated disc is a strong intercellular junction that functions to keep cells from being pulled apart during contraction? Desmosomes What is a functional syncytium?
Cardiac muscle cell are mechanically, chemically and electrically connected to one another Why would the tunica media and tunica adventitia not be present in a capillary? The capillaries are very thin and have only room for layer of endothelial tissue, in the form of tunica intima
R E V I E W NAME
S H E E T EXERCISE 31 > Print Form
Conduction System of the Heart and Electrocardiography The Intrinsic Conduction System
1. List the elements of the intrinsic conduction system in order, starting from the SA node.
SA node > artioventricular node > > artioventricular bundle bundle branches purkinje fibers artioventricular node At what structure in the transmission sequence is the impulse temporarily delayed? Why? because it ensures that the atria have ejected their blood into the ventricles first before they contract.
2. Even though cardiac muscle has an inherent ability to beat, the nodal system plays a critical role in heart physiology. What is that role? generate action potential at a greater frequency than other cardiac muscle cells. They are the pace m the heart. It sets the heart rate under normal circumstances. Electrocardiography
3. Define ECG. The graphic recording of the electrical changes occurring during the cardiac cycle
4. Draw an ECG wave form representing one heartbeat. Label the P, QRS, and T waves; the P–R interval; the S–T segment, and the Q–T interval. R S T P T Q P-R interval S Q-T interval
5. Why does heart rate increase during running? The heart must beat faster and harder in order to deliver the larger amount of blood to muscles being used when running. 207
6. Describe what happens in the cardiac cycle in the following situations. . 2. 3. 4. 5. 6. immediately before the P wave: during the P wave: heart is in diastole depolarization of ventricles contraction of atria immediately after the P wave (P–R segment): during the QRS wave: depolarization of ventricles contraction of ventricles immediately after the QRS wave (S–T interval): during the T wave: repolarization of ventricles
7. Define the following terms. 1. 2. 3. tachycardia: bradycardia: fibrillation: a heart rate over 100 beats/min a heart rate below 60 beats/min rapid uncoordinated heart contractions that makes heart useless as a pump ventricular fibrillation
8. Which would be more serious, atrial or ventricular fibrillation? Why? when heart is in V-fib you are dead unless it can be shocked back into rhythm with atrial fibrillation
9. Abnormalities of heart valves can be detected more accurately by auscultation than by electrocardiography. Why is this so? Abnormal heart valves cause extra heart sounds that can be heard with stethoscope. EEG just measures electrical activity in the heart. It doesn’t show how the valve works.
208 Review Sheet 31
R E V I E W NAME
S H E E T EXERCISE
Anatomy of the Heart Gross Anatomy of the Human Heart
1. An anterior view of the heart is shown here. Match each structure listed on the left with the correct letter in the figure. G J R U B K D N A 1. right atrium
2. right ventricle
3. left atrium c a b o
4. left ventricle
5. superior vena cava
6. inferior vena cava
7. ascending aorta
8. aortic arch
9. brachiocephalic artery
10. left common carotid artery
11. left subclavian artery
12. pulmonary trunk
13. right pulmonary artery
14. left pulmonary artery
15. ligamentum arteriosum
16. ight pulmonary veins
17. left pulmonary veins
18. right coronary artery
19. anterior cardiac vein T S W X V
20. left coronary artery
21. circumflex artery
22. anterior interventricular artery
23. apex of heart
24. great cardiac vein
What is the function of the fluid that fills the pericardial sac? environment. It allows the heart to beat in a relatively frictionless 3. Match the terms in the key to the descriptions provided below.
F A H E A G B D G C
1. location of the heart in the thorax
2. superior heart chambers
3. nferior heart chambers
4. visceral pericardium
5. “anterooms” of the heart
6. equals cardiac muscle
7. provide nutrient blood to the heart muscle
8. lining of the heart chambers
9. actual “pumps” of the heart
10. drains blood into the right atrium
Key: a. b. c. d. e. f. g. h. atria coronary arteries coronary sinus endocardium epicardium mediastinum myocardium ventricles
4. What is the function of the valves found in the heart? Prevents back flow of blood
5. What is the role of the chordae tendineae? enforce a one way blood flow through the heart chambers
Their called heart strings, and anchor the cusps to the ventricular walls Pulmonary, Systemic, and Cardiac Circulations
6. A simple schematic of a so-called general circulation is shown below. What part of the circulation is missing from this diagram? Pulmonary circulation Add to the diagram as best you can to make it depict a complete systemic/pulmonary circulation. Label the systemic and pulmonary circulations. pulmonary ve heart pulmonary pulmonary Heart Systemic arteries Systemic capillaries Systemic veins systemic 202 Review Sheet 30
7.Differentiate clearly between the roles of the pulmonary and systemic circulations. Pulmonary circulation is only to provide gas exchange in the lungs; The systemic circulation provides the functional blood supply to all body tissues
8. Complete the following scheme of circulation of a red blood cell in the human body. Right atrium through the tricuspid valve to the semilunar beds of the lungs, to the the biscuspid aorta right ventricle , through the pulmonary arteries pulmonary , to the capillary of the heart, through , through the aortic semilunar of the , and alve to the pulmonary trunk, to the pulmonary veins valve to the , to the left ventricle left atrium valve to the , to the systemic arteries, to the superior vena cava , capillary beds tissues, to the systemic veins, to the coronary sinus ; cardiac veins inferior vena cava entering the right atrium of the heart. pulmonary circulation
9. If the mitral valve does not close properly, which circulation is affected?
10. Why might a thrombus (blood clot) in the anterior descending branch of the left coronary artery cause sudden death? I can cut off the blood supply to the heart, resulting in death.
Microscopic Anatomy of Cardiac Muscle
11. How would you distinguish the structure of cardiac muscle from that of skeletal muscle? skeletal muscle is long, sylindrical, multinucleated cells ; has striations. Cardiac muscles branch, striated, uni-mucleated cells that interdigitate at the junctions
12. Add the following terms to the photograph of cardiac muscle below. a. intercalated disc b. nucleus of cardiac fiber c. striations d. cardiac muscle fiber interca Describe the unique anatomical features of cardiac muscle. What role does the unique structure of cardiac muscle play in its function?
The intercalated discs have 2 important functions striatio nucleu
1) holds the myocytes together so they don’t part w heart contracts.
2) allows an electrical connection between the cells, which is vital to the function of cardia the heart as a whole.
Also has many mitochondria that provide energy required for contraction. 203 Review Sheet 30 Dissection of the Sheep Heart
13. During the sheep heart dissection, you were asked initially to identify the right and left ventricles without cutting into the heart. During this procedure, what differences did you observe between the two chambers? eft ventricle was thick and solid, and the right was thinner and easily moved and flabby When you measured thickness of ventricular walls, was the right or left ventricle thicker? left ventricle Knowing that structure and function are related, how would you say this structural difference reflects the relative functions of these two heart chambers? Theres a greater demand on the longer systemic circulation and has a higher resistance than the pulmonary circulation
14. Semilunar valves prevent backflow into the atria ventricles ; AV valves prevent backflow into the Using your own observations, explain how the operation of the semilunar valves the mitral valve allows the blood to flow from the left atrium into left ventricle differs from that of the AV valves. tricuspid valve stops back flow of blood between th two. The semilunar valves permit blood to be forced into the but prevent back flow of blood from the arteries into the ventricles.
15. Compare and contrast the structure of the right and left atrioventricular valves. has 3 flapped valve. the mitral valve contains 2 flaps, tricuspi
16.Two remnants of fetal structures are observable in the heart—the ligamentum arteriosum and the fossa ovalis. What were they called in the fetal heart, where was each located, and what common purpose did they serve as functioning fetal structures? ligamentum arteriosm- called ducts arterious in fetal heart. located between the pulmonary trunk and aortic arch In adults ligament there now. Allows blood to flow from pulmonary trunk to systemic circulation.
17. Fossa Ovaliscalled foramen ovale in fetal heart, located on right atrium wall and wall of right ventricle.
Allowed blood to enter 204 Review Sheet 30
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