CPR 7.03 Cardiac Muscle and Heart Histology Flashcards
Describe the general features/characteristics of cardiac muscle
Cardiac muscle has cross-striations and is composed of elongated, often branched cells bound to one another at structures called intercalated discs that are unique to cardiac muscle. Its contraction is involuntary, vigorous, and rhythmic. The heart consists of tightly knit bundles of cells, interwoven in spiraling layers that provide a characteristic wave of contraction that resembles wringing out of the heart ventricles.
Describe the appearance of cardiac muscle in LM
- cytoplasm color
- fiber appearance
- nucleus
- connections
- Long irregular branched cells with bands of light and dark staining.
(a) Eosinophilic cytoplasm.
(b) Cross-striations more easily visualized with special processing via polarized light. - One centrally located nucleus. (sometime bi-nucleate).
- Bound by intercalated discs that appear as dark-staining transverse lines on LM.
What direction do the transverse regions of intercalated discs run in cardiac muscle and what are their 2 main functions?
(a) Runs perpendicular to muscle filaments and act to bind cells together and prevent them from pulling apart with contraction.
(b) Contain desmosomes that confer mechanical stability and act as attachment points of intermediate filaments.
(c) Have adherent junctions which allow the attachment of thin filaments.
What direction do the longitudinal regions of intercalated discs run? Describe their appearance and associated function.
(a) Runs parallel to muscle filaments.
(b) Appears less electron dense due to the presence of Gap junctions. These are sites of low electrical resistance thru which electrical synapses pass from cell to cell.
Describe the transverse tubules appearance. Where in the heart are these primarily found?
- Fingerlike invaginations of sarcolemma that course through the sarcoplasm and branch at the Z disc.
- Mostly in ventricles and are small or absent in atria.
What is the function of the Sarcoplasmic reticulum in cardiac muscle?
Calcium sequestration
Describe the role of terminal cistern in SR of cardiac muscle.
Whatis a Dyad at the Z disc?
- Terminal Cisternae are expansions of the SR that come into contact with the T tubule. This is the location where calcium is released upon SR depolarization.
- Dyad at Z disc of sarcomeres consists of 1 T tubule and 1 SR terminal cisternae.
Describe the appearance and prevalence of mitochondria in cardiac muscle.
Mitochondria are large, numerous, and arranged in continuous longitudinal rows.
What are the 3 connective tissue layers of cardiac muscle?
Endomysium, Perimysium, and Epimysium.
What does the endomysium of cardiac muscle consist of? What does it surround?
surrounds individual muscle fibers/cells. Composed of loose CT that includes fibroblasts, Reticular fibers (type III collagen fibers), and a rich capillary network
What does the perimysium of cardiac muscle consist of? What does it surround?
CT septa. Surrounds fascicle. Contributes to cardiac skeleton.
What does the epimysium of cardiac muscle consist of? What does it surround?
Dense irregular CT that surrounds entire muscle.
Describe the composition of a myofibril
- Consist of repeating array of Myofilaments organized into cylindrical units which are composed of 1,000’s of sarcomeres arranged end-to-end.
What makes up thick filaments of cardiac muscle and what is their function?
Myosin. Overlapping “golf club” appearance function to attach to adherent junctions.
What 3 components make up thin filaments of cardiac muscle?
Actin, Tropmyosin, and Troponin.
Describe the structure, location, and function of actin in cardiac thin filaments/
thin and helical strand running between thick myosin filaments. Act as binding site for myosin
Describe the structure, location, and function of tropomyosin in cardiac thin filaments
regulatory protein consisting of 2 polypeptide chains in a coil. Located in groove of actin strands
Describe the structure, location, and function of troponin in cardiac thin filaments
regulates actin-myosin interaction. Ataches to tropomyosin and binds calcium.
The arrangement of ——– in adjacent myofibrils causes striations in cardiac muscle
Sarcomere.
Describe the appearance and components of an A band
Dark. Thick filaments and parts of thin filaments
Describe the appearance and components of I bands.
Light. Composed only of thin filaments.
Describe the location and function of the Z-disc and their significance in relation to the sarcomere unit
Dark line bisecting the I bands. TItin connects thick filaments to Z disk. α-actinin holds thin filaments to Z disk. 1 Sarcomere is from Z-disc to Z-disc
Describe the H zone of a sarcomere
: The part located in center of A band that only has thick filaments
Describe the M line of a sarcomere
Down middle of H zone; myomesin holds thick filaments in place at M line.
Explain what happens during a sarcomere contraction in:
- A band
- I Band
- H Zone
- Z discs
- Sarcomere shortens
- A Band: no change because thick filaments stay the same length
- I Band shortens.
- H Zone: shortens as thin filaments move together, may even cover the H zone.
- Z Discs: move closer together (towards M line)
Describe the regenerative capacity of cardiac muscle as well as what happens to it with damage or defects.
A. Very little regenerative capacity beyond early childhood.
B. Defects/damage to cardiac muscle are replaced by fibroblast and CT forming myocardial scars (as in MI)
What are the 3 main layers of the heart?
Endocardium, Myocardium, and Epicardium
In what area of the heart is the endocardium thickest?
Atria
Describe the appearance and function of the following layers of endocardium:
-Endothelium
Myoelastic layer
Subendocardial layer
(a) Endothelium: simple squamous epithelium. Inhibits clot formation.
(b) Myoelastic layer: fibrous CT and smooth muscle fibers.
(c) Subendocardial layer: loose fibroelastic CT. Merges with myocardium and has Purkinje fibers.
In what area of the heart is the myocardium thickest?
Ventricles
Describe the components and function of the epicardium
- Epicardium: visceral layer of serous pericardium.
(a) Loose CT with fat, coronary vessels and nerves.
(b) Mesothelium: simple Squamous epithelium that produces lubricating fluid
Cardiac valves are made comprised from what tissue layer?
What is their function?
Folds of endocardium with endothelial lining.
Prevent back flow
Describe the characteristics of Purkinje fibers
A. Located in subendocardial layer of endocardium. Specialized for conduction. Large, pale staining cells wth large round nuclei.
B. Lots of glycogen and mitochondria. Their myofibrils are sparse and displaced to the periphery. No T tubules.
