Histology Of The Heart

Question 1

Describe cardiac muscle

Answer 1

Cardiac muscle forms the bulk of myocardium and extends slightly into the walls of some great vessels

• striated and has the same type & arrangement of contractile filaments as skeletal muscle
• Unlike skeletal muscle, cardiac myocytes are branched
• they may have one or two centrally-placed nuclei
• perpendicular region is free of myofibrils and houses the organelles
• Granules containing diuretic hormones : atrial natriuretic peptide and brain natriuretic peptide
• Numerous large mitichondria & glycogen stores
• Intercalated discs ID —> dense staining cross bands

Question 2

Describe Purkinje fibers

Answer 2

• Large, modified muscle cells located just deep to the endocardium in the subendothelial connective tissue
• Special to conduct impulses impulses of the A-V bundle and allow synchronization of ventricular contraction

-pale staining due to:
-few myofibrils. (These are located peripherally)
-Large amount of glycogen.
Abundant mitochondria

Question 3

What layers of the heart are continuations of vessel layers?

Answer 3

• endocardium (t. Intima)
• myocardium (t. Media)
• epicardium( t. Adventitia)-visceral layer of pericardium

Question 4

Describe the epicardium

Answer 4

Visceral layer of serous pericardium

Single layer of mesothelium cells, underlying connective tissue and adipose tissue

Contain the blood vessels and nerves that supply the heart

Reflected at the great vessels as the parietal layer of serous pericardium, lines the inner surface of the epicardium that surrounds the heart

Pericardium cavity- potential space between layers

Question 5

Describe the endocardium

Answer 5

Inner layer of endothelium and subendothelial connective tissue

SubEndocardial layer location of the conducting system of the heart

Purkinje fibers can be recognized by their large size, large round nuclei and the pale nature of the cells due to high content of glycogen and less myofibrils

Question 6

what are the layers of valves?

Answer 6

Fibrosa

Spongiosa

Atrialis (ventricularis)

Question 7

Describe the fibrosa layer of the valve

Answer 7

• derived from dense irregular connective tissue of skeletal rings of the heart
• Dense CT with collagen and elastic fibers
• Covered in endothelial cells
• Providess tensile stiffness
• Continues inti chordinae tendae

Question 8

Describe the spongiosa layer of the valve

Answer 8

• CORE of valve
• Loose CT with loosely arranged collagen and elastic fibers
• Shock absorber - dampens vibrations
• Flexibility and plasticity to cusps-allowing continued functioning

Question 9

Describe the atrialis(ventricalis) layer of the valve

Answer 9

Adjacent to ventricular or atrial surface

• covered in endothelium
• Dense CT with well organized collagen and elastic fibers
• facilitates valve function by allowing extension and recoil

Question 10

What is the impact of endothelium on the heart?

Answer 10

-simple squamous epithelium of the vessels, tight junctions, gap junctions

A continuous layer of flattened, elongated a polygonal shaped cells aligned with their long axes in the direction of the blood flow

Express receptors and surface adhesion molecules on luminal surface

• endothelial activation- change in functional properties in response to various stimuli

Question 11

What are the functions of endothelial cells?

Answer 11

• permeability barrier- controls the composition of interstitial tissue fluid (brain, lung vs inflammation sites)
• movement of inflammatory cells into tissues
• VEGF (Vascular endothelial growth factors) provides for angiogenesis in the embryogenesis. (As well as in vascular trauma, tumor)
• Provides signals that control blood pressure by vasoconstriction-endothelin, ACE decreased luminal diameter, increased vascular resistance, increased systemic blood pressure
• Vasodilation- nitric oxide, increased relaxation of smooth muscle , increased luminal diameter, decreased vascular resistance, decreased systemic blood pressure
• Anticoagulant signals- thrombomodulin that inhibit platelet attachment & aggregation- to prevent blood coagulation and allow unobstructed flow of blood in normal conditions
• Antithrombogenic- prostacyclin -prevent platelet aggregation and release of clotting factors
• Prothrombogenjc-von Willebrand factor- promote clot formation
• Pulmonary endothelial cells- produce ACE (angiotensin converting enzyme) - promote conversion of angiotensin 1 to angiotensin 2

Question 12

What are weibel palace bodies?

Answer 12

These rid-shaped inclusions in epithelium, store Willebrand factor (glycoprotein)-that binds clotting factor VIII, platelet adhesion to site of endothelial injury

Present in : heart, elestic & muscular arteries, small arteries & arterioles (but NOT present in capillaries)