Cardiac Histology Flashcards
Describe cardiac muscle
Cells are short, branched and Y shaped with 1-2 nuclei
Extensive capillaries
Contain intercalated discs and purkinje cells
What are intercalated discs?
Transverse junctions at the ends of cells that allow passage of electrical current
At sites where cells meet end to end always coincide with Z lines
What are Purkinje cells?
Modified cardiac muscle cells that act as the pacemaker for the heart
What are the hallmarks for cardiac muscle?
Striations, intercalated discs (longitudinal section)
Cells vary in diameter with centrally located nuclei surrounded by an unstained region (cross section)
Lipofuscin granules near nucleus of some cells made of lysosomal residue
What is the fibrous pericardium?
Outer covering of dense CT
What are the three parts of serous pericardium?
Parietal layer and visceral layer of serous pericardium
Pericardial cavity
What does the parietal layer of serous pericardium line?
the inner surface of fibrous pericardium
What does the visceral layer of serous pericardium cover?
The outer surface of the heart
What is the pericardial cavity?
Space between the parietal and visceral layers
Describe the epicardium
Outermost layer of the heart wall
Synonymous with visceral pericardium
Loose/areolar CT containing autonomic nerves and variable amounts of fat, lined with mesothelium
Branches of coronary arteries are embedded in adipose tissue
Describe the myocardium
Thickest layer of the heart Contains cardiocytes (contractile), nodal cardiocytes (in SA and AV nodes) and myoendocrine cardiocytes
What is the myocardium characterized by?
Striations, intercalated discs, lipofuscin granules*
Diad T tubule system, mitochondria, atrial granules (myoendocrine cardiocytes)
What is the function of intercalated discs?
Bind cells, transmit forces of contraction, and allow the spread of excitation
What do the interdigitating junctions between cardiocytes contain?
3 types of membrane to membrane contacts including fascia adherens and desmosomes in the transverse region and gap (nexus) junctions in the longitudinal region
Describe the fascia adherens located in the transverse region of interdigitating junctions
Actin filaments at the ends of terminal sarcomeres insert into junction
Transmit contractile forces b/w cells
Most predominant
What do the desmosomes in an interdigitating junction provide?
Anchorage for the intermediate filaments of the cytoskeleton
Describe the gap (nexus) junctions in the longitudinal region of an interdigitating junction
Sites of low electrical resistance
Allows excitation to pass between cells
Describe the diad T tubules
1 T-tubule + 1 SR cisternae
Finger like invaginations of sarcolemma found at Z lines
Permits uniform contraction of myofibrils within a single cardiocyte
What are nodal cardiocytes?
Modified cells within the SA/AV nodes that initiate/relay electrical signals
Where do parasympathetic and sympathetic fibers terminate?
In the nodes and only modify rate of intrinsic cardiac muscle contraction
What is the pathway of the electrical signal of the heat?
SA node —> AV node —> AV bundle —> R/L bundle branches —> Purkinje fibers
Describe purkinje fibers
Specialized cardiac muscle cells
Conduct electrical impulses that allow coordinated contraction
Fewer myofibrils but a high glycogen concentration
Larger and typically seen at periphery of myocardium
Mostly lack T tubules
Describe lipofuscin granules
Small bodies that accumulate with age in stable non-dividing cells
Contain material derived from residual bodies after lysosomal digestion
What are myoendocrine cardiocytes?
Atrial cells that contain membrane bound granules (atrial granules)
Smaller quantities are found in the LA and the ventricles
