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Principles > Cardiac Histology > Flashcards

Cardiac Histology Flashcards

1
Q

What are the 3 layers of the heart?

A

Endocardium > Myocardium > Epicardium

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2
Q

What are the outer layers of the heart?

A

Visceral layer of serous pericardium > Pericardial cavity > Parietal layer of serous pericardium > Fibrous pericardium > Adipose tissue

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3
Q

What is the endocardium and associated structures (5)?

A

Lines entire inner surface of heart, including valves.

  1. Endothelium
  2. Basal lamina
  3. Thin layers of collagen fibers (fibrous)
  4. Layer of denser connective tissue (fibrous)
  5. Subendocardium of loose connective tissue in some areas (E.g. septum) (Small blood vessels, nerves and branches of impulse conducting system with conducting Purkinje cells)
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4
Q

What is the myocardium and associated structures (2)?

A

Thick middle layer.

  1. Bundles and layers of contractile cardiac muscle fibers
  2. Individual muscle fibers surrounded by delicate, collagenous connective tissue with rich network of capillaries (Perfuse aerobic tissues)
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5
Q

Structure of myocytes in myocardium

A

Have a single central nucleus (sometimes 2)
Have intercalated discs passing across fibers at irregular intervals to attach adjacent cells together and spread electrical activity
- Desmosomes, Zonula Adherens, Gap junctions (ionic flow)
Shorter in length compared to skeletal muscles

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6
Q

What is the epicardium and associated structures (3)?

A

Outer layer of the heart.

  1. Surface of heart: a single layer of flattened simple squamous epithelium (Mesothelium)
  2. Basal Lamina
  3. Fibroelastic connective tissue and in some places, adipose tissue (coronary vessels embedded in adipose)
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7
Q

What are the 2 parts of a pericardium?

A

Fibrous pericardium: sac of tough fibrocollagenous connective tissue
Serous pericardium: made up of a layer of simple squamous epithelium (Mesothelium) backed by a basal lamina and connective tissue
- lines inner surface of the fibrous pericardium (parietal) and covers surface of the heart (serous)
- 2 mesothelial layers appose to each other and are separated by a thin pericardial cavity with small amount (15-50mL) of pericardial fluid (lubricate heart movement)

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8
Q

What is the fibrous skeleton of the heart?

Function (3)

A

Formed by thick bands of fibrous connective tissue around heart valves, between atria and between ventricles.
Supports the valves, provide attachment for cardiac muscle fibers, electrically isolates atria from ventricles

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9
Q

What structures are found in the heart valves (4)?

A
  1. Outer endothelial layer with basal lamina (Both sides of valve)
  2. Layer of collagen and elastic fibers
  3. Core of dense irregular connective tissue (lamina fibrosa) in continuity with the fibrous skeleton
  4. Leaflets of AV valves separating atria from ventricles are anchored by papillary muscles in the wall of the ventricle by collagenous strands (Chordae Tendineae) which merge with the lamina fibrosa

**No blood vessels in the valves

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10
Q

What are the types of cardiac muscle cells (3)?

A
  1. Contractile cells (99%)
  2. Pacemaker cells
  3. Conducting cells
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11
Q

What are pacemaker cells (5)?

A
  1. Highly specialised muscle cells
  2. Considerably smaller than contractile cardiac myocytes
  3. Embedded in more extensive matrix of connective tissue
  4. Appears pale due to lack of organelles within
  5. Few myofibrils (irregularly arranged), little glycogen and no proper transverse tubule system
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12
Q

What happens after the atrioventricular bundle?

A

Descends to produce left and right bundle branches –> fibers reach apex and turn upwards
Purkinje fibers found beneath the endocardium of ventricles
Excitation passes through non-conducting tissue of fibrous skeleton

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13
Q

What are Purkinje Fibers

A
  1. Larger than normal cardiac muscle cells
  2. Found in subendocardial layer, deep to the endocardium
  3. Abundant glycogen, no tranverse tubules, no intercalated discs, sparse actin & myosin filaments (located at periphery of cells)
  4. Appear pale (lack of filaments) and very pale/ clear centre
  5. Distribute excitatory activity such that ventricular contraction occurs inferior to superior
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14
Q

What does interstitial fluid contain?

A

Ions, lipids, proteins and cells

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15
Q

How do lymphatic capillaries begin?

A

Begin as blind sacs in the capillary network to drain tissue fluid before returning it to veins in base of neck

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16
Q

How is flow regulated in the lymphatic vessels (4)?

A
  1. Smooth muscle in walls
  2. Hydrostatic pressure in tissue
  3. Compression of vessels by voluntary muscles
  4. Valve in vessels

**No central pump

Principles (14 decks)

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