Cardiac Histology Flashcards
What are the generalized weights of the heart in men and women (also % of body weight)
Male: 325gm +/- 75gm (.45% body wgt)
Female: 275 gm female +/- 75gm (.40% body wgt)
What 4 cells make up the heart tissue? which are the most abundant? which are the most voluminous?
Myocytes (25% of total cell number; 90% of cell volume)
Endothelial Cells (70% cell number; negligible volume)
Fibroblasts
Immune Cells
What is the pericardium?
Fibrous sac surrounding the heart
How many layers are there to the pericardium? What are they?
Two
Fibrous: tougher and on the outer part
Serous: very thin, lies over surface of the heart
the fibrous pericardium is rich in __ which makes it very__
collagen, inelastic
What is compliance a measure of? is the pericardium compliant?
measure of pressure over volume
As pressure goes up and the volume changes very slightly = not very compliant
If volume increases quickly with little change in pressure = very compliant
Pericardium is not compliant
What is the fibrous skeleton?
dense collagenous tissue with elastin that forms: the base of the heart, the AV valve rings and aortic annulus
separates: the atrial and ventricular chambers and the right and left ventricles (both physically and electrically)
What is the only point of electrical connection between the atria and ventricles?
The atrioventricular node (bundle of His) embedded in the fibrous skeleton
What are the 3 layers of the heart wall?
- Epicardium
- Myocardium
- Endocardium
what is the cellular composition of the endocardium?
The endothelium consists of a single
layer of squamous endothelial cells held together by tight (occluding) junctions.
Also have gap junctions which permit the cells to communicate with each other .
What are the 3 major components of the endocardium?
1) endothelium,
2) continuous basal lamina and
3) subendocardium, a layer of loose connective tissue.
What does the subendothelium help do?
subendocardium helps to bind the endocardium to the underlying heart muscle (myocardium).
What does the subendothelial layer include?
small blood vessels smooth muscle cells nerves elastic fibres branches of the impulse conducting system (in the ventricles)
what do the endothelial cells of the endocardium secrete?
An anticoagulant that prevents clots from forming on the inner surface of the heart
What 4 things comprise the myocardium?
Myocytes; collagen; blood vessels; elastin (intramural coronaries)
What are the 5 components of a cardiac myocyte?
- Cell membrane (Sarcolemma and T tubules)
- Sarcoplasmic reticulum and Ca++ reservoir
- Contractile elements (actin, myosin, troponin and tropomyosin)
- Mitochondria
- Large nucleus
What elements does the Cell Membrane (Sarcolemma and T Tubules) have that contributes to impulse conduction?
- Gap junctions
- Intercalated disks at poles of myocytes
- join adjacent myocytes both mechanically and ionically
What causes contraction of the myocyte?
Release of Calcium into cytosol as a result of action potential causes contraction
What is contraction?
the net effect of sliding of actin and myosin toward the centre of the sarcomere
Increased stretch of actin/myosin results in?
longer pull
Why do myocytes require so many mitochondria? What is the % compared with a skeletal muscle cell?
Heart muscle almost exclusively dependent on aerobic metabolism
Mitochondria make up 23% of myocyte volume compared with 2% in skeletal muscle
What is ventricular cardiac muscle arranged like? What does this achieve?
Forms complex layers of cells wound
helically around the ventricular cavity. This aids in “wringing out” the heart during contraction.
What are the 6 ways in which atrial cardiac muscle is different from ventricular cardiac muscle?
Compared with ventricular cardiac muscle, atrial cells:
- are somewhat smaller
- have a less extensive T-tubule system
- have more gap junctions
- conduct impulses at 3 X higher rate
- contract more rhythmically
- have many granules (from endocrine-like cells) containing atrial natriuretic factor (ANF)
What are 6 structural features of the right atrium ?
Auricular Appendage (shaped like snoopy’s nose)
Smooth and trabeculated areas
2mm thick
Epicardium rich in ganglia
Myocytes smaller than in ventricles
e- dense granules store atrial naturietic peptide
What are 5 structural/functional features of the left atrium?
Receives oxygenated blood from pulmonary veins
Delivers to LV across Mitral Valve
3mm thick
Smooth throughout
Auricular Appendage (shaped like central america)
What are 7 structural features of the right ventricle?
- Anterior most structure
- C shaped around LV
- Coarsely trabeculated
- Papillary muscles support Tricuspid Valve
- Myocardium 5mm thick
- Membranous septum contains conduction system
- Low pressure
What are the 3 parts of the right ventricle?
Inflow portion, Apex, Outflow portion (infundibulum or conus)
What are the 3 parts of the left ventricle?
Inflow, Septal, Outflow
What are 4 structural features of the left ventricle?
- High pressure
- Bullet shaped
- 15mm thick
- Conducts blood from LA via mitral valve to Aorta via aortic valve
During which phase of contraction/relaxation can blood flow through the coronary arteries?
during ventricular diastole
Where is the aortic valve located? what kind of valve is it?
Semilunar valve located in the aortic root
What are the names for the high/low points of the aortic valve?
Commisures are high points and cusp nadirs the low points, like a suspension bridge
What is the name for the ring of suspension of the aortic valve?
Annulus
How are the leaflets of the aortic valve named?
Leaflets named for the aortic sinuses, in turn named for the coronaries that do or do not arise from them
- left, right, and non
What are the 3 histological layers of the aortic valve?
- Fibrosa
- Spongiosa
- Ventricularis
What is the composition of the Fibrosa? What is its function? What side is it on?
Collagen rich, extends to free edge and coapting surface
Gives strength to the tissue
On the aortic side
What is the composition of the Spongiosa?
Proteoglycan and GAG rich, collagen and fibroblasts
What is the composition of the ventricularis? what is its function? what side is it loacted on?
Rich in elastin which allows the leaflets to stretch under pressure and move out of the way during ejection
also absorbs shock
On the ventricular side
what is aortic stenosis?
Dysfunctional repair mechanism which results in the deposition of more collagen
- Causes more work for the left ventricle
- Get chest pains even resting
What the the location of the pulmonic valve in relation to the aortic valve?
Anterior and superior to aortic valve
How does the histology compare between the aortic and the pulmonic valves?
same basic histology but the pulmonic valve is thinner
The competence of the semilunar valves relies on what 3 things?
- their attachment to the commissures and hinge lines (complex 3d structure)
- Their strength, pliability and elasticity
- Dimensions of the aortic root/pulmonary trunk
the only 2 leaflet valve is the …?
mitral valve
In the mitral valve, where are the leaflets attached?
Leaflets attach to the mitral annulus (junction of the left atrium and left ventricle made by the cardiac skeleton (dense connective tissue)
Leaflet edges tethered by chordae tendiniae
The chordae tether the leaflet edges to the ventricle via which muscle?
the papillary muscle
What are the 4 layers of the mitral valve and their composition? What sides are each of them on
Fibrosa- collagen rich, and extends to chordae and the tips of the papillary muscles
Spongiosa: Atrial side, GAG and Proteoglycan rich
Ventricularis: Ventricular side, elastin rich and endothelialized
Auricularis: EC layer on atrial side
What 4 things are critical for the competency of the mitral valve?
- Annular dimension (like the semilunars)
- Structural integrity of leaflets (pliable, elastic, strength), (like semilunars)
- Structural integrity of chordae (very important)
- Function and dimensions of ventricles
How is the histology comparable between the mitral and the tricuspid valves?
Lower pressure in the right ventricle so thinner leaflets, chordae, and papillary muscles in the tricuspid valve
What are the 3 layers of veins/arteries?
- Tunica adventitia (outer)
- Tunica media
- Tunica intima (inner)
Which is the thickest layer for veins? For arteries?
For veins: adventitia
For arteries: media
What is the composition of the tunica adventitia? What does this layer contain in some arteries/veins?
Mainly loose connective tissue with type I collagen & elastic fibers that anchor vessel
Contains vasa vasorum
- “vessel of the vessel”
- found in large arteries and veins
What is the composition of the tunica media?
Contains smooth muscle, collagen fibers, reticular fibers and elastic tissue
The tunica intima of some larger vessels has which layers?
Endothelium
Thin basal lamina
Subendothelium (connective tissue including collagen)
What are 4 important properties of vascular endothelium?
- Cells are bound together by junctional complexes
- Can be activated by cytokines to express cell adhesion molecules which allow white blood cells to stick & eventually migrate from vessel
- under normal circumstances secretes substances which maintain the tone of vascular smooth muscle (nitric oxide)
- Under normal circumstances secretes substances which prevent blood clotting
Where is the SA node located?
junction of the superior vena cava and the right atrial appendage
Where does conduction begin in the heart? what is the pathway it takes?
- initiated by the SA node
- AV node conducts signal with a slight delay from the atria to the ventricles
- Splits into Left bundle (over septum to ant pap muscle) and Right bundle (ends in RV moderator band)
Where is the AV node located?
Between AV valve and coronary sinus
How do the rates of spontaneous depolarization of cells compare between the atria and the ventricles?
ventricular cells slowest, atrial cells faster.
Where are the cardiac cells with the fastest rate of depolarization in the heart?
in the SA node
How is coordinated contraction of the heart acheived?
because the cells with the fastest rate of depolarization “capture” the rest of the heart muscle cells.
