Cardiac Cell Biology Flashcards
Cardiac tissue
consists of essentially three cell types:
(i) cardiac myocytes (syn = cardiomyocyte = CMs),
(ii) endothelial cells including a specialized layer of cells known as the endocardium as well as the inner linings of BVs and
(iii) “cardiac” fibroblasts (CFs).
The Cardiac Myocyte: Similarities to Skeletal Muscle
- Each cardiomyocyte is surrounded by a basal lamina. - Cardiomyocytes are striated. - Mechanism of contraction and types of contractile proteins are similar
The Cardiac Myocyte: Differences to Skeletal Muscle (Gross)
Unlike skeletal muscle which is voluntary in function, cardiac muscle is involuntary.
The Cardiac Myocyte: Differences to Skeletal Muscle (Light Microscope Level)
- Cardiac myocytes are smaller, ~15 micrometers x 100 micrometers (not mm).
- The nucleus is centrally located. There are 1 or
2 (sometimes 3) nuclei per cell, not 100s. - Cardiac cells bifurcate, whereas
skeletal cells branch only when they’re sick. - Cardiac tissue is very highly vascularized, and, CMs are chock full of mitochondria.
- Intercalated discs are specialized intercellular structures that are present only in cardiomyocytes.
The Cardiac Myocyte: Differences to Skeletal Muscle (Electron Microscope Level)
Cardiac myocytes are highly enriched in glycogen, and mitochondria.
- This is to satisfy continual energy demand.
Intercalated Discs: What is it?
Intercellular attachments enable cardiac myocytes to work together, as if they were part of a “syncytium” (which they are not). In attaching cardiac myocytes together, discs on adjacent cells appear to form a ‘staircase’ across the myocardium.
Each intercalated disc has two ________-________ parts: a ________ part and a ______ part
Each intercalated disc has two perpendicularly-arranged parts: a transverse part and a lateral part.
The transverse part of an intercalated disc
Transverse Part that transmits contractile force. This
component, which is essentially a ‘half Z-band’, consists of:
- A fascia adherens, which (unlike zonula adherens does
not completely encircle cell).
- desmosomes (syn. macula adherens)
- Actin (thin) filaments butt into these half-Z bands, akin to zonula adherens in junctional complexes. The major protein in the fascia adherins is N-cadherin.
The lateral part of an intercalated disc
The lateral part transmits cell-to-cell signals.
- Signaling is accomplished via nexuses (syn. gap junctions, connexons), which function to maintain rhythmicity to heartbeat. Each connexon has 6 connexin proteins. Desmosomes are also in the lateral component.
Cardiac Myocytes are _______ than in the ventricles, with ______ sacromeric structure.
Cardiac myocytes are smaller than in the ventricle, with less sarcomeric structure.
SA & AV Nodes
Located in the R. atrium.
- Node myocytes are small, embedded in dense connective tissue.
- Cells of the SA and AV nodes have few myofibriles & are adapted for impulse propagation.
- By contrast, the AV Bundle of His contains large Purkinje myocytes that have few myofibrils and copious glycogen with inconspicuous intercalated discs.
Development of Purkinje “fibers”
Endothelial cells within young coronary arteries secrete endothelin, which causes nearby cardiac myocytes to differentiate into Purkinje cells.
Endocardium
- The innery lining of the heart that lines the lumens of the ventricles.
- Composed of endothelial cells (simple squamous epithelium that lines all chambers of the heart and is continuous with the endothelial lining the entire vascular system.
What is the most abundant cell type in the heart?
Cardiac Fibroblasts
What is the major fuel for the cardiac myocyte?
Triglycerides (Stored in membrane-bound lipid droplets near the nucleus)
