Cardiac Histology

Question 1

Describe cardiac muscle

Answer 1

Cells are short, branched and Y shaped with 1-2 nuclei
Extensive capillaries
Contain intercalated discs and purkinje cells

Question 2

What are intercalated discs?

Answer 2

Transverse junctions at the ends of cells that allow passage of electrical current
At sites where cells meet end to end always coincide with Z lines

Question 3

What are Purkinje cells?

Answer 3

Modified cardiac muscle cells that act as the pacemaker for the heart

Question 4

What are the hallmarks for cardiac muscle?

Answer 4

Striations, intercalated discs (longitudinal section)
Cells vary in diameter with centrally located nuclei surrounded by an unstained region (cross section)
Lipofuscin granules near nucleus of some cells made of lysosomal residue

Question 5

What is the fibrous pericardium?

Answer 5

Outer covering of dense CT

Question 6

What are the three parts of serous pericardium?

Answer 6

Parietal layer and visceral layer of serous pericardium

Pericardial cavity

Question 7

What does the parietal layer of serous pericardium line?

Answer 7

the inner surface of fibrous pericardium

Question 8

What does the visceral layer of serous pericardium cover?

Answer 8

The outer surface of the heart

Question 9

What is the pericardial cavity?

Answer 9

Space between the parietal and visceral layers

Question 10

Describe the epicardium

Answer 10

Outermost layer of the heart wall
Synonymous with visceral pericardium
Loose/areolar CT containing autonomic nerves and variable amounts of fat, lined with mesothelium
Branches of coronary arteries are embedded in adipose tissue

Question 11

Describe the myocardium

Answer 11

Thickest layer of the heart 
Contains cardiocytes (contractile), nodal cardiocytes (in SA and AV nodes) and myoendocrine cardiocytes

Question 12

What is the myocardium characterized by?

Answer 12

Striations, intercalated discs, lipofuscin granules*

Diad T tubule system, mitochondria, atrial granules (myoendocrine cardiocytes)

Question 13

What is the function of intercalated discs?

Answer 13

Bind cells, transmit forces of contraction, and allow the spread of excitation

Question 14

What do the interdigitating junctions between cardiocytes contain?

Answer 14

3 types of membrane to membrane contacts including fascia adherens and desmosomes in the transverse region and gap (nexus) junctions in the longitudinal region

Question 15

Describe the fascia adherens located in the transverse region of interdigitating junctions

Answer 15

Actin filaments at the ends of terminal sarcomeres insert into junction
Transmit contractile forces b/w cells
Most predominant

Question 16

What do the desmosomes in an interdigitating junction provide?

Answer 16

Anchorage for the intermediate filaments of the cytoskeleton

Question 17

Describe the gap (nexus) junctions in the longitudinal region of an interdigitating junction

Answer 17

Sites of low electrical resistance

Allows excitation to pass between cells

Question 18

Describe the diad T tubules

Answer 18

1 T-tubule + 1 SR cisternae
Finger like invaginations of sarcolemma found at Z lines
Permits uniform contraction of myofibrils within a single cardiocyte

Question 19

What are nodal cardiocytes?

Answer 19

Modified cells within the SA/AV nodes that initiate/relay electrical signals

Question 20

Where do parasympathetic and sympathetic fibers terminate?

Answer 20

In the nodes and only modify rate of intrinsic cardiac muscle contraction

Question 21

What is the pathway of the electrical signal of the heat?

Answer 21

SA node —> AV node —> AV bundle —> R/L bundle branches —> Purkinje fibers

Question 22

Describe purkinje fibers

Answer 22

Specialized cardiac muscle cells
Conduct electrical impulses that allow coordinated contraction
Fewer myofibrils but a high glycogen concentration
Larger and typically seen at periphery of myocardium
Mostly lack T tubules

Question 23

Describe lipofuscin granules

Answer 23

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

Question 24

What are myoendocrine cardiocytes?

Answer 24

Atrial cells that contain membrane bound granules (atrial granules)
Smaller quantities are found in the LA and the ventricles

Question 25

What do atrial granules contain?

Answer 25

Precursors of ANF which targets the kidney to decrease Na and H2O retention

Question 26

What is the endocardium made up of?

Answer 26

Endothelium and a thin layer of loose CT

Question 27

Describe the endocardium in the ventricles

Answer 27

Has a subendocardial layer made of a thin layer of CT with smooth muscle
Merges with the myocardium
Contains branches of purkinje fibers

Question 28

Describe the endocardium in the atria

Answer 28

Does not contain a subendocardial layer
Purkinje fibers are typically closest to the endothelium
Intermixed with the myocardium

Question 29

What is the cardiac skeleton made of?

Answer 29

Dense irregular CT located in the endocardium

Question 30

Describe the cardiac skeleton

Answer 30

Anchors valves and surrounds AV canals to maintain shape
Contributes to interventricular and interatrial septa
Extends into the valve cups and chordae tendinae (insertion of cardiac muscle; electrical insulator between atria and ventricles)

Question 31

What are heart valves?

Answer 31

Core of fibroelastic CT (lamina fibrosa) covered by endothelium
Continuous with the cardiac skeleton
Fibroelastic layer of endocardium condenses to form a valve ring (VR)
-creates a central portion of the valve