Histology for PathologyCardiac System

Theresa Kristopaitis, MDAssociate Professor

Director of Mechanisms of Human Disease

Kelli A. Hutchens, MD, FCAPAssistant Professor

Assistant Director of Mechanisms of Human Disease

Loyola Stritch School of Medicine

Objectives1. Identify the 3 layers of the heart – endocardium, myocardium, epicardium2. Differentiate cardiac, skeletal and smooth muscle on H&E stained slides citing the key distinguishing morphologic features3. Define “intercalated disc”4. Name the layer of the heart in which Purkinje fibers are found and describe their function5. Explain which chamber of the heart has the thickest layer of myocardium vs the thinnest6. Explain the general histologic structure of a cardiac valve

Heart Wall

Epicardium

Myocardium

Endocardium

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.

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

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

Cardiac Myocytes

Central nucleiFibers with Cross Striations

Branchingmyocytes

Smooth MuscleLong, slender central nuclei, lying within narrow, fusiform cells.No cross striations

Skeletal muscleFibers with cross-striations and

peripheral nuclei.

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

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