1. Histology for Pathology Cardiac System
Theresa Kristopaitis, MD
Associate Professor
Director of Mechanisms of Human Disease
Kelli A. Hutchens, MD, FCAP
Assistant Professor
Assistant Director of Mechanisms of Human Disease
Loyola Stritch School of Medicine
Welcome to basic histology of the skin

2. Objectives
1. Identify the 3 layers of the heart – endocardium, myocardium, epicardium
2. Differentiate cardiac, skeletal and smooth muscle on H&E stained slides citing the key distinguishing morphologic features
3. Define “intercalated disc”
4. Name the layer of the heart in which Purkinje fibers are found and describe their function
5. Explain which chamber of the heart has the thickest layer of myocardium vs the thinnest
6. Explain the general histologic structure of a cardiac valve

3. Heart Wall
Myocardium
Endocardium
Epicardium

4. Endocardium Innermost layer Composed of:
Simple squamous epithelium (endothelium)
Connective Tissue
Subendocardium: in contact with cardiac muscle and contains small vessels, nerves, and Purkinje Fibers.

5. Purkinje Fibers Impulse conducting fibers Large modified muscle cells
Cluster in groups together
1-2 nuclei and stain pale due to fewer myofibrils
Terminal branches of the AV bundle branches located in the subendocardial connective tissue

6. Myocardium Thickest layer of the heart
Thickest in left ventricle because must pump hard to overcome high pressure of systemic circulation
Right atrium the thinnest because of low resistance to back flow
Consist of cardiac muscle cells = myocytes
Different from smooth or skeletal muscle cells due to placement of nuclei, cross striations, and intercalated disks
Intercalated disks
Junctional complexes that contain fascia adherens, desmosomes, and gap junction to provide connection and communication.
Bind myocytes and allow ion exchange to facilitate electrical impulses to pass

7. Fibers with Cross Striations
Cardiac Myocytes
Branching
myocytes
Central nuclei
Fibers with Cross Striations

8. Fibers with cross-striations and
Smooth Muscle
Long, slender central nuclei,
lying within narrow, fusiform cells.
No cross striations
Skeletal muscle
Fibers with cross-striations and
peripheral nuclei.

9. Epicardium Outermost layer of the heart
Composed of connective tissue with nerves, vessels, adipocytes and an outer layer of mesothelium
Mesothelium secretes pericardial fluid
Covers and protects the heart

10. Cardiac Valves
4 valves
2 AV (mitral and tricuspid) in the chambers
2 semilunar (aortic /pulmonary)
Composed of connective tissue layers covered by endothelium on each side; 3 layers
Spongiosa: loose collagen
Fibrosa: dense core of connective tissue
Ventricularis: dense connective tissue with many elastic and collagen fibers