Histology of the heart

Question 1

Layers of the heart

Answer 1

Intima = endocardium
Media = myocardium
Adventitia = epicardium (mesothelial layer)

Question 2

Endocardium

Answer 2

Endothelium = simple squamous epithelium
Subendothelial CT
loose CT
collagen & elastic fibers
embedded fibroblasts
some SMC
contains cardiac conduction system

Question 3

Epicardium/visceral pericardium

Answer 3

inner layer of pericardial sac
loose fatty CT
Nutrients, protective cushion and conduit for coronary vasculature and nerves (autonomic + sensory)
simple squamous mesothelium - secretes lubricant serous fluid

Question 4

Myocardium

Answer 4

contractile myocardial cells
usually central nuclei
striated with myofibrils
high capillary: fiber ratio
numerous mitochondria
long-lived cells
branched
fibers arranged into fascicles
fibrous CT between fascicles - conduit for vessels & nerves
rich capillary network around fascicles
Intercalated disc

Question 5

Intercalated disc

Answer 5

unique to myocardium
withstand stress
end-to-end mechanical and electrical linkage between myocardial cells
fascia adherens (transverse): anchor actin from myofibrils to sarcolemma
Desmosomes: link intermediate filaments, focal mechanical adhesion between fibers
Gap junctions: contain connexons, electrical coupling between fibers; membranes of 2 myofibrils contacted, synchronized contractility

Question 6

Endocrine function of the heart

Answer 6

myocardial cells produce and secrete ANP

secreted in response to myocardial stretch

Question 7

Conduction system histology

Answer 7

No epicardium
Purkinje fibres
 - large diameter fibres in subendocardium
- some deep in myocardium
- lots of glycogen, mito, gap junction

Question 8

Cardiac valves - histo

Answer 8

folds of endocardium, central core of dense fibrous CT
Attach to annuli fibrosi of cardiac fibrous skeleton
dense fibrous CT core rich in collagen + elastic tissue
scattered fibroblasts
avascular