7. Cardiac Histology (Dennis)

Question 1

cardiac muscle

Answer 1

Only found in the heart.

• Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system.
• Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle. However, cardiac muscle fibers are shorter than skeletal muscle fibers and usually contain only one nucleus, which is located in the central region of the cell.
• Cardiac muscle fibers also possess many mitochondria and myoglobin, as ATP is produced primarily through aerobic metabolism.
• Cardiac muscle fibers cells also are extensively branched and are connected to one another at their ends by intercalated discs.

Question 2

Smooth muscle

Answer 2

Present in the walls of hollow organs like the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems. Smooth muscle is also present in the eyes.

• Smooth muscle cells have a single nucleus, and are spindle-shaped
• The smooth cells are nonstriated, but their sarcoplasm is filled with actin and myosin, along with dense bodies in the sarcolemma to anchor the thin filaments and a network of intermediate filaments involved in pulling the sarcolemma toward the fiber’s middle, shortening it in the process.
• Smooth muscle contraction is initiated when the Ca++ binds to intracellular calmodulin, which then activates an enzyme called myosin kinase that phosphorylates myosin heads so they can form the cross-bridges with actin and then pull on the thin filaments.
• May be activated by pacemaker cells, ANS, hormones, and/or stretching

Question 3

Compare and contrast smooth and cardiac muscle

Answer 3

Some differences are listed when smooth and cardiac muscles are discussed individually on other cards…

Smooth muscle (similar to cardiac muscle) is not under voluntary control; thus, it is called involuntary muscle. Neither is cardiac muscle.

Two types of smooth muscles: single-unit and multiunit. In single-unit smooth muscle fibers are joined by gap junction –> act as a unit. Similar to heart muscles.

Multiunit smooth muscle: no gap junction, no electrical conductivity. Stretching will not activate it, only hormones or ANS.

Question 4

Endocardium

Answer 4

Inner layer of the heart (lines the atria and ventricles and covers the heart valves) and contains blood vessels.

Has 3 sublayers:
Endothelium - innermost portion a simple squamous epithelium.

Smooth Muscle and Connective Tissue - middle layer of the endocardium is mix of connective tissue and smooth muscle.

These fiirst two layers are always present.

In ventricles, the endocardium has a Subendocardial Layer - outer layer of the endocardium is loose connective tissue joining the endocardium and myocardium.
equivalent to tunica intima. This layer is lacking in the atrial endocardium.

Question 5

Myocardium

Answer 5

Middle layer of the heart, thickest layer. Consists of contractile cardiocytes, nodal cardiocytes and myoendocrine cardiocytes (secrete hormonal peptides).

Contains cardiac muscle fibers (long, acute angle, large nuclei, striation, etc.) and loose endomysial connective tissue containing many capillaries. Also did T-tubule, increased mitochondria, lipofuscin granules and atrial granules (myoendocrine cardiocytes)

Look for thin lines across fibers –> intercalated discs
Also, myofibrils, and red blood cells.

Question 6

Epicardium

Answer 6

Outer layer of the heart, contains blood vessels and lymphatics.
Visceral layer of pericardium, rather thin.
Dense fibrocollagenous CT with elastic fibers, lined with mesothelium.
Branches of coronary arteries are embedded in adipose tissue.
May see nerves.

Question 7

Interacalated discs

Answer 7

Coincide with Z lines; the point where cells meet end to end.

Function: bind cells, transmit forces of contraction, and allow the spread of excitation

Question 8

Diad T-tubules

Answer 8

Diad: 1SR cisterna + 1 T-tubule
Fingerlike invaginations of sarcolemma
Found at Z-lines
Allows uniform contraction of myofibrils within a single cardiocytes

Question 9

Purkinje fibers

Answer 9

Larger than myocytes, typically found at the periphery of myocardium.
Lack T-tubules
Specialized cardiac cells that conduct electrical impulses
Fewer myofibrils, but increased glycogen content (better staining)

Question 10

Atrial granules

Answer 10

• atrial cells that contain membrane-bound granules
• smaller quantities are found in the left atrium & the ventricles
• contain precursor of atrial natriuretic factor (ANF) that targets kidneys to decrease Na and H20 retention

Question 11

Heart Valves

Answer 11

• Somewhat “triangular” core with fibroelastic CT covered by endothelium
• Continuous with cardiac skeleton
• Fibroelastic layer of endocardium condenses to form a valve ring (VR)