Cardiac Histology I

Question 1

Smooth muscle characteristics

Answer 1

Centrally located nucleus.
No visible striations.
Interconnected by gap junctions.

Question 2

Smooth muscle contraction

Answer 2

Possess a contractile apparatus of thin and thick filaments.
Anchor to cytoplasmic densities/dense bodies (comprised of desmin and vimentin intermediate fibers).
Tension transmitted via densities to the membrane.
Cells contract as one unit and assume a globular shape.

Question 3

Cardiac muscle characteristics

Answer 3

Cells are short, branched and Y shaped.

Have extensive capillaries.

Question 4

Intercalated disks

Answer 4

Transverse junctions at the ends of cells that allow passage of electrical current.
Always coincide with Z lines.
Transmit forces of contraction.

Question 5

Layers of pericardium (outer to inner)

Answer 5

Fibrous pericardium
Parietal serous pericardium
Visceral serous pericardium

Question 6

Pericardial cavity

Answer 6

Space between the parietal and visceral layers.

Question 7

Epicardium characteristics

Answer 7

AKA visceral serous pericardium.
Dense fibrocollagenous CT with elastic fibers. Lined with mesothelium.
Branches of coronary arteries are embedded in adipose.

Question 8

Myocardium is characterized by:

Answer 8

Striations
Intercalated disks
T-tubules
Mitochondria
Lipofuscin granules
Atrial granules

Question 9

3 types of membrane-to-membrane interdigitating junctions

Answer 9

Fascia adherens
Desmosome
Gap junctions

Question 10

Fascia adherens

Answer 10

Actin filaments at the ends of terminal sarcomeres.
Transmit contractile forces between cells.
Most predominant.

Question 11

Desmosomes

Answer 11

Provide anchorage for intermediate filaments of the cytoskeleton.

Question 12

Gap junctions

Answer 12

Sites of low electrical resistance.

Allows excitation to pass between cells.

Question 13

One dyad =

Answer 13

1 t-tubule and 1 SR cisterna

Question 14

T-tubules

Answer 14

Fingerlike invaginations of sarcolemma.
Found at Z lines.
Permits uniform contraction of myofibrils within a single cardiomyocyte.

Question 15

Lipofuscin granules

Answer 15

Small bodies that accumulate with age in stable, non-dividing cells.
Contain material derived from residual bodies after lysosomal digestion.

Question 16

Myoendocrine cells

Answer 16

Atrial cardiomyocytes that contain membrane-bound granules.
Smaler quantities found in the LA and ventricles.
Contains precursor of atrial natriuretic factor (ANF).

Question 17

Endcardium

Answer 17

Endothelium and thin layer of CT.

Thickness will differ in atria and ventricles.

Question 18

Subendocardial layer

Answer 18

Thin layer of CT w/ smooth muscle.
Contains Purkinje fibers.
Found in ventricles.

Question 19

Purkinje fibers

Answer 19

Highly specialized conducting fibers.
Larger and typically seen at periphery of myocardium.
Mostly lack t-tubules.

Question 20

Cardiac skeleton

Answer 20

Dense irregular CT in the endocardium.
Anchors valves and surrounds AV canals to maintain shape.
Extends into valves and chordae tendineae.
Can act as an insulating barrier between atria and ventricles.

Question 21

Heart valves

Answer 21

Core of fibroelastic CT covered in endothelium.

Continuous with cardiac skeleton.

Question 22

Formation of a valve ring

Answer 22

Fibroelastic layer of endocardium that condenses to create the VR.
This creates central portion of the valve.