Chapter 19 - The Circulatory System: the heart

Question 1

Cardiocytes (cardiomyocytes)

Answer 1

relatively short, thick, branched cells typically 50 to 100 um long and 10 to 20 um wide.

Question 2

Intercalated Discs

Answer 2

thick connections that join cardiocytes end to end. They are steplike structures with three distinctive features not found in skeletal muscle.

Question 3

What are the three distinct features of intercalated Discs?

Answer 3

1. Interdigitating folds: The plasma membrane at the end of the cell is folded somewhat like the bottom of an egg carton. The folds of adjoining cells interlock with eachother and increase the surface area of intercellular contact. 2. Mechanical Joints: Cells are tightly joined by two mechanical junctions: the fascia adherens and desmosomes. Fascia adherens is the most extensive. It’s a thin band in which the actin and thin myofilaments is anchored to the plasma membrane and each cell is linked to the next via transmembrane proteins. Desmosomes are patches of mechanical linkage between cells They prevent the contracting cardiocytes from pulling apart. 3. Electrical Junctions: Intercalated discs also contain gap junctions which form channels that allow ions to flow from the cytoplasm of one cardiocyte directly to the next. They enable each cardiocyte to electrically stimulate their neighbors. Entire myocardium of the two atria behaves almost like a cell, as does the myocradium of the ventricles. Unified action is essentail for pumping of the heart.