Imaging: Histology of the Heart

Question 1

What is the difference between a myocyte vs. a myofiber?

Answer 1

• A myocyte is a single muscle cell while a myofiber is composed of a series of myocytes aligned end-to-end to produce a directionally-uniform contractile force (more-or-less).
• In the case of skeletal muscle myofibers, the multiple myocytes fused to form a single myofiber.
• But with cardiac and smooth muscles, the myocytes remain distinct and require intracellular adhesions to transmit forces throughout the myofiber.

Question 2

409: This is the wall of the artery exiting the heart. In this section, the artery has been cut longitudinally, thus it appears much different, compared to specimens that are cut in cross-section (transversely).
* Would this artery be classified as elastic, muscular, or arteriole? Explain your rational?
410: Which tissue layer would form the lining of this artery’s lumen?

Answer 2

409: Elastic; very thick tunica media with elastic lamellae interspersed between smooth muscle fibers (>40 layers)
410: endothelium

Question 3

Define the following terms and their function, as they relate to cardiac muscles

Dyad

Answer 3

The combination of a T-tuble and a single cistern of the SR (skeletal muscles possess a triad — a T-tubule and two SR cisterns, one on each side); their interaction ultimately leads to an increase in cytosolic Ca2+ levels.

Question 4

203: Which layer of the atrial wall is indicated by this line? Which tissue comprises the majority of this layer and what is its function?

Answer 4

Question 5

At what angle are the cardiac myocytes seen here cut? Explain your rational.

Answer 5

Transversly: Cells have a more circular shape; striations and intercalated discs can’t be observed

Question 6

Semilunar Valve

405: Within this location, the intermingling of the fibrous CT of the cardiac skeleton and muscular tissue of the myocardium can be observed. Name the three major functions of the cardiac skeleton.

Answer 6

1. Electrical insulation between the atria and ventricles
2. Support of the valves
3. Attachment of the myofibers of the myocardium

Question 7

Define the following terms and their function, as they relate to cardiac muscles

Sarcomere

Answer 7

The functional contractile units of cardiac (and skeletal) myofibrils; consists of the contractile thin and thick filaments located between two Z-discs.

Question 8

Heart, semilunar valve

411: What tissue is located is indicated here?
* Which layer of the heart would this tissue belong to?

Answer 8

Adipose tissue

• Epicardium

Question 9

212: This large projection is a pectinate muscle that is a structure found in the atrium proper. What additional feature would indicate that this slide specimen is from the atrial wall and not the ventricular wall

Answer 9

The wall is relatively thin

Question 10

Define the following terms and their function, as they relate to cardiac muscles

Sarcoplasmic reticulum

Answer 10

The smooth endoplasmic reticulum (sER) of muscle cells; serves as a reservoir of Ca2+ to keep the cytosolic levels low until stimulated to release.

Question 11

205: The nucleus seen here belongs to which type of cell? How would you classify this epithelial tissue?
* Name two functions of this tissue layer.

Answer 11

Question 12

303: What is the name for this indicated layer?

Answer 12

Subendocardium

Question 13

201: This is the endocardium of the atrial wall. Note that the thickness of the layer is not uniform across the entire wall. Which space does this layer face?
* Name the sublayers that make up this layer.

Answer 13

1. Lumen of the atrium
2. Endothelium
   Fibroelastic layer
   Subendocardium

Question 14

304: What is the name for the structure indicated? What type of tissue is it?
* What is the function of this tissue?

Answer 14

Purkinje fiber (or conducting system of heart)

• Conduction of electrical signals to coordinate ventricular contraction

Question 15

1. Which type of muscle tissue is this?
2. What are two histological characteristics that are unique to these muscles cells that distinguish them from the other two muscle tissue types?

Answer 15

1. Cardiac
2. Myocytes are short and blunt.
   Some myocytes are branched
   Intercalated discs are present

Question 16

Which side of the heart has a thicker ventricular wall? Why?

Answer 16

Left; systemic circulation requires greater force to generate the pressure needed to drive the blood through the much larger and extensive vascular network.

Question 17

301: Which tissue is identified by the arrow?
* To which layer of the ventricle wall does it belong?

Answer 17

Endothelium

• Endocardium

Question 18

206: Identify the cells seen here.

Answer 18

Adipocytes

Question 19

Define the following terms and their function, as they relate to cardiac muscles

Intercalated disc

Answer 19

The region of attachment between cardiac myocytes composed of multiple junctional complexes that join and electrically-couple the myocytes to assist in effective force transmission and contractile coordination/synchronization.

Question 20

204: Which layer of the atrial wall is indicated by the this line? Which tissue comprises the majority of this layer and what is its function?
* Which space does this layer face?

Answer 20

Question 21

305: Which space is this? In a living adult, what would normally occupy this space?

Answer 21

Lumen of the ventricle

• blood

Question 22

What is the difference between a myofiber vs. a myofibril?

Answer 22

• A myofibril is a bundle of the contractile filaments (thin and thick) organized within the skeletal and cardiac myocytes/myofibers into longitudinal strands.
• They are composed of the contractile proteins (actin and myosin) and their associated proteins that regulate their interactions (tropomyosin, troponin, etc).

Question 23

Which side of the heart is involved with the adult pulmonary circulation?

Answer 23

Right Side

Question 24

* Define the following terms and their function, as they relate to cardiac muscles

Sarcolemma

Answer 24

• The cell membrane of muscle cells; contains various ion channels and receptors that respond to neurotransmitters and hormones, which ultimately changes in ion channel permeability, intracellular levels of second messengers and/or enzyme activity.
• In cardiac myocytes, the overall effect includes changes in heart rate and/or contractility.

Question 25

202: The nucleus seen here belongs to which type of cell? How would you classify this epithelial tissue?
* Name two functions of this tissue layer.

Answer 25

Question 26

307: What specific tissue is indicated here?
* Why do these cells stain lighter than the contractile cardiac myocytes?

Answer 26

Purkinje fiber (or conducting system of heart), which is a specialized cardiac muscle tissue

• Cells contain fewer myofibrils and contain more glycogen

Question 27

302 This layer is composed primarily of which types of CT fibers

Answer 27

Collagen and elastic

• Note the presence of smooth muscle cells scattered though out this layer.