Cardiac Muscle Tissue Flashcards
What are the main features of cardiac muscle tissue?
Cubic shape with some projections. 1-2 central nuclei. Have striation in the cytoplasm. Intercalated discs present in the cardiac muscle cells, this mediates connection between cardiomyocytes. Lots of mitochondrion.
Why are there connective tissues between cells?
Between cells are connective tissue with vascularization.
Describe the organisation of cardiac muscle tissue.
In cardiomyocytes, there is a mass of myofilaments but no organisation into myofibrils.
The sarcoplasmic reticulum surrounds the myofibrils and makes contact with the T-tubule at junctions called dyads.
The T tubules are located at the level of the Z line.
What inclusion are present in the cytosol?
There are lipofuscin and glycogen inclusions in the cytosol of cells, these increase with age.
Explain the presence of lipofuscin in the cytosol.
Lipofuscins are a characteristic of non-dividing cells. They can be defined as an accumulation of polymers of molecules and are mainly non degradable, therefore they accumulate with age.
They also represent lysosomal activity, as if the lysosome is not efficient at degrading these substances, there is a higher accumulation.
Describe the components of the intercalated discs.
Intercalated discs resemble a stairway. In the horizontal line, there are desmosomes and zonulae adherentes.
In the lining there are gap junctions.
How is cardiac muscle stimulated to contract?
Ca2+ will be released by the sarcoplasmic reticulum, it will pass from one cell to another due to the cardiomyocytes.
The cardiomyocytes have the ability to contract independently, they don’t need stimulation by the nervous system.
What are the fibers that stimulate contraction?
These are the sinoatrial node, the atrioventricular node, the atrioventricular (His) bundle.
How are the fibers that stimulate contraction organised?
They are similar in shape, when in bundles, they can be observed one next to the other in an organised way.
While when in nodal fibers, they are more scattered.
How do the fibers that produce impulse to contract work?
They are able to generate action potential that will then transmit to other myocytes via gap junctions.
This will contribute to forming functional syncytium in the cardiac muscle.
Describe Purkinje cells.
These fibers are normally located in groups, and have a lighter staining colour compared to the cardiomyocytes that contract.
A few myofibrils are present in the peripheral of the cell.
They do have lots of mitochondrion, but there is no cross striation inside the purkinje fibers.
Describe the proliferative ability of cardiac tissue cells.
The cardiomyocytes are no longer able to divide after differentiate, therefore the myocardium can’t regenerate.
- There have been studies attempting to develop myocardium cells from stem cells to repair those that have damaged myocardium tissue.
How is contraction regulated?
The rhythm of contraction of the heart is controlled by an autonomous electrical pulse.
This is then propagated in the heart by special myocytes that don’t contribute to contraction but provide the impulse to contracting.
