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CVS & IBL - Histology 🔬 > L1: Cardiac muscle > Flashcards

L1: Cardiac muscle Flashcards

1
Q

What are the characteristics of cardiac muscle fibers?

A

▪ Chain of short cylindrical cells.

▪ Involuntary.

▪ The cardiac muscle fiber is not a syncytium as the individual muscle cell joined together end to end by cell junction (Intercalated disc).

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2
Q

What is the site of cardiac muscle fibers?

A

wall of the heart (myocardium).

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3
Q

What is the shape of cardiac muscle fibers under LM?

A

(Length - width) - (branching - striation) - (nucleus - sarcoplasm - endomysium)

✓ Small in caliber (25 um).

✓ Variable in length

✓Extensive branching and anastomosing, so, they are cut in various directions.

✓ It is surrounded by C.T. (Endomysium) -» contains blood vessels and lymphatics.

✓ Irregular striation.

✓ Nuclei are large, oval, central, mono or binucleated

✓ Sarcoplasm is Granular, acidophilic

✓ The sarcoplasm contains lipochrome pigment which increases in old age and causes brown atrophy of the heart

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4
Q

What does the endomysium contain?

A

contains blood vessels and lymphatics.

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5
Q

What is the shape of cardiac muscle fibers under EM?

A

❑ The Sarcoplasm contains:

✓ Glycogen granules

✓ Numerous mitochondria (40% of cell volume).

✓ Golgi saccules.

✓ Lipid droplets (fatty acids are the major fuel of the heart).

✓ Lipofuscin pigment granules (aging pigment), often seen in long-lived cells, are found near the nuclear poles of cardiac muscle cells.

✓ In the atria of the heart, atrial granules are seen in the juxtanuclear cytoplasm. These granules contain hormones known as an atrial natriuretic factor (ANF). This hormone is diuretically affecting the urinary excretion of sodium. (Endocrine effect to reduce BP)

✓ The sarcomeres have an identical banding pattern to that of skeletal muscle.

✓ Traversed by dark staining disc (Intercalated disc).

✓ Rich in myofibrils:

  • Branching and anastomosing.
  • Less regularly arranged to give less regular striation In L/M.
  • Variable in diameter

❑ T-Tubules and sarcoplasmic reticulum:

✓ Less developed than skeletal muscle.

✓ The cardiac muscle fibers have no triad but only dyads formed of:

  • T- tubule: Wider in the ventricles than atria and surround the myofibrils at the Z-line.
  • Terminal cistern: Smaller and incomplete.
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6
Q

What is the major fuel of the heart?

A

Fatty acids

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7
Q

What is a diad formed from?

A
  • T- tubule: Wider in the ventricles than atria and surround the myofibrils at the Z-line.
  • Terminal cistern: Smaller and incomplete.
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8
Q

What is the definition of intercalated discs?

A

Transverse lines that cross the cardiac fibers at irregular intervals, joining the adjacent myocardial cells.

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9
Q

What do intercalated discs coincide with?

A

Always coincide with the Z lines.

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10
Q

What is the shape of intercalated discs under LM?

A

a dark stained linear (straight) structure that is oriented transversely to the muscle fiber or step-like.

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11
Q

What are the stains used for intercalated discs?

A
  • Iron Hx.

* Silver.

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12
Q

What is the shape of intercalated discs under EM?

A

Formed of 3 types of junctions:
A: Fascia adherens
B: Desmosome
C: Gap junction

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13
Q

What is the site of fascia adherens?

A

In transverse part

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14
Q

What is the function of fascia adherens?

A
  • It performs intracellular adhesion.

* Anchoring site for myofibrils (represent half a Z-line).

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15
Q

What is the site of desmosomes?

A

In transverse and longitudinal parts.

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16
Q

What is the function of desmosomes?

A

It prevents the separation of cells during contraction.

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17
Q

What is the site of the gap junction?

A

In longitudinal part (parallel to the myofibrils).

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18
Q

What are the characteristics of gap junction?

A
  • There is a 2 nm gap between cells.
  • This gap is traversed by intercommunicating channels between the cells.
  • These channels allow free and rapid transmission of the nerve impulses from one cell to another.
  • Thus, the fiber contracts as one unit (act physiologically as one unit)
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19
Q

How do cardiac muscles grow?

A

▪ Hypertrophy (increase in the size of cardiac muscle due to new formation of myofibrils).

▪ No cell division.

▪ No regeneration.

20
Q

Do cardiac muscles get repaired?

A

No, When the muscle fibers are lost, they are replaced by fibrous C.T. (It heals by fibrosis), And there are no satellite cells

21
Q

What is the heart formed from grossly?

A
  • 2 thin atria.

* 2 thick ventricles.

22
Q

What is the wall of the heart formed from?

A
  • The Epicardium.
  • The Myocardium.
  • The Endocardium.
23
Q

What are the characteristics of muscular tissue?

A

✓ Formed of muscle fibers.

✓ Contractility is the characteristic feature of all muscle types (myofibrils).

✓ The plasma membrane is called the sarcolemma.

✓ The cytoplasm is called sarcoplasm.

24
Q

What are the types of muscles?

A
  • skeletal (Striated - Voluntary)
  • smooth (Nonstriated - Involuntary)
  • cardiac (Striated - Involuntary)
25
Q

What is the epicardium?

A

Visceral layer of the double-layered pericardium (the membrane surrounding the heart).

26
Q

What does the epicardium invest?

A

Invests the heart from outside.

27
Q

What is the epicardium formed of? (shape under LM)

A

✓ Simple squamous epithelium (outer).

✓ A subserous layer of C.T. contains coronary blood vessels and fat cells.

✓ The C.T. blends with the endomysium of the myocardium.

28
Q

What is the myocardium?

A

Cardiac muscle fibers (Main bulk) that run in various directions.

29
Q

What is the shape of the myocardium under LM?

A
  • Cardiac muscle fibers (Main bulk) which run in various directions.
  • Separated by loose C.T. endomysium which contains blood vessels and lymphatics.
  • Covered on the outside by (epicardium) and inside by (endocardium)
  • Thicker in the wall of the ventricles than atrial walls.
30
Q

What does the endocardium line?

A

It lines the chambers and covers the valves of the heart

31
Q

What is the shape of the endocardium under LM?

A

• It is formed of four layers from inside to outside:

  1. Simple squamous endothelial layer (most inner). (In contact with blood)
  2. Subendothelial dense C.T. layer. (For support)
  3. A layer of dense elastic fibers. (For elasticity)
  4. A layer of loose C.T (connected with endomysium) which contains blood vessels and Purkinje fibers (outer).
32
Q

What Is the structure of the cardiac skeleton?

A

Dense CT

33
Q

What is the cardiac skeleton attached to?

A

Attached to contractile muscle fibers.

34
Q

What does the cardiac skeleton form?

A

Forms the fibrous part of interventricular and interatrial septa and fibrous ring around valves.

35
Q

What are the functions of the Cardiac skeleton?

A

✓ Anchoring and supporting the heart valves.

✓ Providing firm points of insertion for cardiac muscles.

✓ Coordinating heartbeat by acting as electrical insulation between atria and ventricles.

36
Q

What are the valves of the heart?

A

1- Tricuspid valve:
• It is present between the right atrium and the right ventricle.
• It is formed of 3 cusps.

2- Mitral valve:
• It is present between the left atrium and the left ventricle.
• It is formed of 2 cusps.

37
Q

What is the shape of the valves under LM?

A

• It is a fold of the endocardium.

• It has a middle supporting layer of:
➢ Dense C.T. contains elastic fibers and collagen fibers.
➢ Phagocytic cells.

  • It is thickened at the base of the mitral and tricuspid valves forming rings of C.T. around the orifice.
  • It contains smooth muscle fibers (for moving) and capillaries at the base.
38
Q

What is the impulse conducting system of the heart?

A

It is a vascular neuromuscular structure between cardiac muscle fibers.

39
Q

What is the impulse conduction system of the heart formed of?

A

Formed of modified cardiac muscle cells.

40
Q

What is the function of the impulse conducting system of the heart?

A

Generates and propagates waves of depolarization, stimulating rhythmic contractions of the myocardium.

41
Q

What are the types of impulse conducting systems of the heart?

A

• S-A Node—» the pacemaker.

• A-V Node.
“Both S-A and A-V nodes are present in the wall of right atrium”

  • A-V bundle of His and 2 branches and their ramification.
  • Moderator Band.
42
Q

What is the definition of the moderator band?

A

A bundle of cardiac muscle fibers through which the right branches of the A-V bundle of His traverse the cavity of the right ventricle to reach the lateral wall of the heart and lie under the endocardium.

43
Q

What is the structure of the moderator band? (Shape under LM)

A
  • Appears as pale area.
  • Mainly formed of Purkinje fibers which are separated by loose C.T. endomysium.
  • Contains fat cells (for support) and blood capillaries.
44
Q

What are the differences between Purkinje fibers and cardiac muscles?

A

“DIM CG FPT”

  • Larger diameter.
  • No intercalary disc but there is: “no contraction”
    ✓ Numerous gap junctions for rapid conduction.
    ✓ Desmosomes.
  • Myofibrils
    • Few.
    • Peripheral.
  • Cytoplasm
    •Granular.
    •Vacuolated (glycogen). “For anaerobic glycogenolysis in extreme conditions”
  • Grouped into bundles and surrounded by C.T. sheath.
- Faster Conduction due to:
• Gap junctions
• No T.T.
• Glycogen
• C.T. sheath
  • Paler in color due to:
    • a Large amount of glycogen that dissolves during preparation.
    •Few numbers of myofibrils that are peripheral in position.
  • No T. tubules.
45
Q

What is the shape of Purkinje fibers under EM?

A

“No T.T”

  • Thin and irregular sarcolemma.
  • Separate, short, elongated cylindrical cells.
  • One or two peripheral nuclei.
46
Q

Revise the comparison between skeletal muscle and cardiac muscle

A

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CVS & IBL - Histology 🔬 (5 decks)

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