Bruce G. Stewart

Related Textbook Readings

• Marieb (20...) Chapter 18

Heart Anatomy

Unlike previous topics in our course, you will turn almost exclusively to your textbook for this material. This is clearly presented in your text. We will review the several excellent illustrations of the heart in lecture.

Know all of the labeled structures of the heart, the great vessels that enter and leave it, and the heart’s coverings. An outline of coronary vessels to learn is presented later in these Notes on the Web. There are specific ones listed so that you are not responsible for all of the coronary vessels.

Lab Study of Non-human Mammals in Human Anatomy: An Explanation and Historical Note

A large proportion of human anatomy courses across the nation (and in Oklahoma) use non-human mammalian dissection materials to help teach students understand human anatomy. You may wonder why this is of educational value. Mammalian anatomy, particularly between certain mammal groups, is amazingly similar... so similar that you would be challenged at first to distinguish between some organs (e.g. kidneys, hearts, etc.) from a human and another mammal! In fact, the similarities can be so striking that the famous Greek anatomist, Galen of the 2nd century AD, actually based much of his human anatomy descriptions on non-human primates (e.g. apes). Galen could not always research internal human anatomy by using cadavers so he used other closely-related species that were so similiar that no one successfully challenged his accuracy for some fourteen centuries!

Human and ape anatomy are so similar that the Church did not realize the basis for Galen's excellent research. The Church therefore adopted Galen's human anatomy writings as the final word (revealed from God) without knowing that much of his work was actually based on the anatomy of apes! It wasn't until 1543 AD that Andreas Vesalius published his great human anatomy treatise, "De Humani Corporis Fabrica," which finally cracked the dogmatic position of the Church and others on the details of Galen's work. It was not a peaceful transition, and some were put to death for questioning Galen! Consider the following quote from Moore (1993):

Initially Vesalius had much opposition, since even suggesting that such an ancient and respected authority as Galen might have erred was not in the best of taste. One brave, free spirit who suffered because he thought otherwise was Michael Servetus (1511-1553), a scholar of broad interests, mainly theological, but also a serious student of Galen. In the course of his studies, he came to the conclusion that Galen was not correct in all matters. Servetus hypothesized, for example, that blood does not pass directly through those Galenic pores from right ventricle to the left but instead goes from the right ventricle to the lungs, where it picks up air, and then back to the left ventricle. Mainly because he questioned Galen, whom the Church had named as the authority on anatomy and physiology, Servetus was captured while at prayer and, after a brief trial, was sent up in flames on October 27, 1553. Lest the reason be in doubt, one of his offending books was hung from his neck so it too was consumed on the pyre.

Now you can realize that honorable people have actually sacrificed their lives in order to find the scientific truth of human anatomy! You should also now realize the great educational value that you can gain by conscientiously studying the non-human, mammalian specimens we will explore in some of our lab sessions, including the one dealing with heart anatomy.

Sheep Heart Dissection

Sheep hearts are excellent models to study as you learn about human heart anatomy. I will conduct a demonstration dissection projected on a screen. Concurrently, you and a lab partner will conduct the same dissection on your own specimen. Note that these hearts are preserved in either Wardsafe or Carosafe solutions which are non-formadehyde, low irritating solutions.

Be able to identify all structures and vessels that we locate in lab. You may rely heavily on your textbook heart illustrations even though you are using a sheep heart! A couple of exceptions in detail are important to note for our purposes:

• The inferior vena cava of the sheep heart enters the right atrium at an angle from lower left toward the upper right side of the heart as you view the heart from the posterior side. The inferior vena cava in human hearts ascends from directly below the heart more directly superiorly up to the right atrium.
• The left common carotid artery on the sheep exits the aortic arch further to the left than in the human. Typically on our sheep heart specimens, only the brachiocephalic artery will be left on the specimen with the aortic arch cut between the brachiocephalic and the left common carotid artery. Thus, you will likely not see the right common carotid artery and the right subclavian artery attached to our sheep heart specimens.

Outline of Required Structures to Know on the Coronary Circulation of the Human Heart and to Locate in Sheep Heart Dissection

Coronary Circulation - Arteries

• Left coronary artery - branch of ascending aorta/serves myocardium

• Can be located by dissection at the base of the ascending aorta and traced to where it branches into the anterior interventricular artery and circumflex artery

• Anterior interventricular artery (also called anterior descending coronary artery)

• branch of left coronary artery; extends down anterior interventricular sulcus
• supplies walls of both ventricles
• click on this link to see an article that includes an image of a left descending coronary artery (= anterior interventricular artery)that is 99% blocked:  http://www.hsforum.com/stories/storyReader$1494 .

• Circumflex artery

• branch of left coronary artery; extends around left side of heart between the left atrium and left ventricle to posterior side of heart
• supplies walls of left ventricle & left atrium

• Right coronary artery

• branch of ascending aorta and passes under auricle of right atrium; branches into the marginal artery and the posterior interventricular artery
• has small branches that supply right atrium
• click here to see the same article linked previously, but this time to see the 90% blocked right coronary artery:  http://www.hsforum.com/stories/storyReader$1494 

• Marginal artery

• descends along right wall of right ventricle
• supplies wall of right ventricle

• Posterior interventricular artery

• branch of the right coronary artery; passes right around heart and descends in the posterior interventricular sulcus
• supplies walls of both ventricles

• Anastomotic (interconnection) Patterns

• individuals vary with regard to interconnections among the branches of the left and right coronary arteries; however, all terminate in arteriors supplying the myocardium
• the heart can survive with as little as perhaps 10-15% of total flow; none-the-less, insufficiency occurs in varying degrees due to significant blockages of one or more coronary arteries

Coronary Circulation: Cardiac Veins and Sinus

• Great Cardiac Vein

• travels with the anterior interventricular artery and receives blood from the ventricles
• drains into the Coronary Sinus on the posterior side of heart

• Middle Cardiac Vein

• travels with the posterior interventricular artery and receives blood from ventricles
• drains into the Coronary Sinus on the posterior side of heart

• Small Cardiac Vein

• receives blood from the right wall of the right ventricle
• drains into the Coronary Sinus on the posterior side of heart

• Other Cardiac Veins and Anastomoses

• there are a number of other veins that are tributaries to the veins listed above
• there are also some veins that drain directly into the right atrium rather than into the Coronary Sinus
• there are also many anastomoses (interconnections) among the cardiac veins throughout the myocardium that vacilitate venus flow in the heart

• Coronary sinus

• Receives most cardiac venus blood & empties into right atrium

Conduction System of Heart

Background

• We have previously studied the some aspects of cardiac muscle histology and physiology; you should review that material now before going forward.
• Recall the atria vs. ventricular networks, and the fact that intercalated discs transmit AP's within networks: first the atria network and then the ventricular

Conduction System

• This is highly specialized muscle tissue that generates and transmits electrical stimulating impulses that cause action potentials to begin in a coordinated fashion in the two networks of cardiac muscle. It includes the:
  • sinuatrial (SA) node
  • atrioventricular (AV) node
  • atrioventricular (AV) bundle of His
  • bundle branches
  • conduction myofibers (Purkinje fibers)
• The conduction tissue cells are self-excitable (review our cardiac muscle histology and physiology notes). Recall that the SA node has the fastest cycle, AV node a bit slower, and the Purkinje fibers the slowest. Because of this, the SA node is the "pacemaker" setting the sequence of events in action before the other conduction tissues fire on their own.
• Transmission follows this general route:
  • SA node --> (via myocardium)--> AV node (in bottom of right atrium) in the inter-atrial septum) --> AV bundle (down septum) --> bundle branches to right & left sides--> Purkinje fibers (conduction fibers) which stimulate papillary muscles and lower and medial surfaces of ventricles first)
  • Note that this causes the depolarization of the atria first, followed by a delay before the ventricles are depolarized. Contraction of the atria, therefore, occurs first (following atria depolarization), followed by contraction of the ventricles (after they depolarize and while the atria are relaxed and re-polarizing).

Electrocardiogram

An electrocardiogram (abbreviated either ECG or EKG) is a recording of changes in electrical characteristics during heart cycle. There are resting, stress, and ambulatory types which record electrical heart activity during different physically demanding conditions of the body. There are many methods of taking ECGs varying in such things as number and locations of electrical leads. We will explore a standard normal resting ECG and a couple of examples of abnormal ECGs due to heart functional disorders. However, for the interested student, here is a great link leading to a myriad of images of all sorts relating to ECGs:

• http://medlib.med.utah.edu/kw/ecg/image_index/index.html#Diagrams

Resting ECG

Refer to diagrams in text as you study the following components of a resting ECG. We will go over these in lecture in the same manner.

• P-wave - upward wave

• produced by atrial depolarization (SA node --> atria)
• followed by but does not represent atria contraction
• example of abnormal P-wave pattern
  • longer than normal P-wave could indicate atrium enlargement due to mitral stenosis (mitral valve leaks)

• QRS wave - (down-up-down wave)

• produced by ventricular depolarization
• followed by but does not represent ventricular contraction

• T-wave

• produced by ventricular repolarization
• example of abnormal pattern: T-wave may flatten and lengthen with insufficient O₂

• No Atrial Repolarizastion Wave Exists

• Note that there is no distinct atrial repolarization wave because it is masked by QRS wave.

• P-Q interval

• time from atrial excitation to ventricle excitation
• normal interval is about 0.2 seconds
• .example of abnormal pattern: slower interval can result from damaged conduction tissue

• S-T segments

• time interval between end of spread through ventricles and beginning of repolarization

Abnormal ECGs

Be able to recognize and explain the common abnormalities illustrated in your text. For your own interest, visit the previously presented link (http://medlib.med.utah.edu/kw/ecg/image_index/index.html#Diagrams) to see a wide range of ECGs, including abnormal conditions.

• Here is a link that has some information on smoking, cardiovascular disease, and stroke:  Cigarette Smoking, Cardiovascular Disease, and Stroke  Note what this American Heart Association paper says about the risks associated with cigarette smoking.   How does this compare to the R.J. Reynolds advertisement we critiqued earlier in the semester? Specifically, read the sentence based on their literature citation number seven. Note the study state in the title of that citation. Do you remember where you have seen that study mentioned previously in our course?
• Effects of passive smoking in the Multiple Risk Factor Intervention Trial.
• Does switching from cigarettes to pipes or cigars reduce tobacco smoke exposure?
• Mortality rates after 10.5 years for participants in the Multiple Risk Factor Intervention Trial. Findings related to a priori hypotheses of the trial. The Multiple Risk Factor Intervention Trial Research Group.
• The relationship of smoking cessation to coronary heart disease and lung cancer in the Multiple Risk Factor Intervention Trial (MRFIT).
• Cigarette smoking and mortality. MRFIT Research Group.
• Mortality after 16 years for participants randomized to the Multiple Risk Factor Intervention Trial.
• Here is a link to dozens of studies that emerged from the Multiple Risk Factor Intervention Trial. These include many aspects of health risks in addition to smoking:
  • Multiple Risk Factor Intervention Trial for the Prevention of Coronary Heart Disease (MRFIT)

Reminder about Textbook Study

As with other topics, your textbook has excellent presentations of the materials on the cardiovascular system, including the heart. While you should focus on the specific material or instructions in the Notes on the Web, you should always use your textbook as a resource for illustrations and for understanding content that your notes cover or assign. This is especially true in this section on the heart as indicated earlier in these Notes on the Web.

As with all materials throughout the semester, you will have opportunities to ask questions or ask that any relevant material from your assignments be discussed in class.

Related Internet Resources

• (work in progress)

Literature Cited

Moore, John A. 1993. Science as a way of knowing: the foundations of modern biology. Harvard University Press, Cambridge, Massachusetts. 530 pp.