ICL 1.2: Histology of Cardiovascular System Flashcards
what are the layers of the heart?
- pericardium
- epicardium
- myocardium
- endocardium
what is the epicardium?
outermost layer of heart wall
comprised of a mesothelium (simple squamous epithelia) that forms the visceral layer of pericardium and a subepicardial connective tissue layer with nerves, ganglia, coronary and adipose cells
the visceral layer of the serous pericardium IS the epicardium
what is the myocardium?
the thick middle layer of the heart
comprised of cardiomyocytes that are contractile, conducting or endocrine in function and that are arranged in muscle layers that insert onto a fibrous cardiac skeleton
what is the endocardium?
the innermost layer of the heart wall
comprised of endothelium (single layer of squamous cells that are continuous with intima of the large outflow vessels) and connective tissue with Purkinje cells and fibers. This endothelium covers all of the heart’s luminal structures.
what is pericarditis?
inflammation of the pericardium
usually caused by viral or bacterial infection, autoimmune diseases, kidney failure or injury
it can progress to cardiac effusion or arrhythmia
what are the symptoms of pericarditis?
chest pain, caused by the sac’s layers becoming inflamed, forming adhhesions and possibly rubbing against or constricting the heart.
which cells make up the myocardium?
- cardiomyocytes
- cardiac skeleton
- cardiac conduction system
how are cardiomyocytes of the myocardium connected?
myocytes are connected by gap junctions which allow for chemical communication between the cells to coordinate function like contraction
they also have intercalated discs and fasciae adherens which allow for structural support during contraction so that integrity is maintained
what are cardiomyopathies?
diseases that effect the cardiomyocytes and lead to heart dysfunction
what is dilated cardiomyopathy?
most common type of cardiomyopathy!
due to loss of myocytes, thinning/weakening of ventricular wall and dilation of lumen
this effects the hearts ability to pump blood and cardiac output is reduced because of systolic dysfunction
idiopathic or secondary causes such as toxins, medications, nutritional deficiencies, alcohol abuse, myocarditis (coxackie virus), pregnancy
what is hypertrophic cardiomyopathy?
thickening of ventricular or septal wall, cardiomyocyte hypertrophy and disarray, reduced ventricular filling or obstructed outflow
reduces the hearts ability to pump blood with reduced cardiac output due to diastolic dysfunction
usually caused by genetic mutations usually of sacromere myocyte proteins
can cause arrhythmias and sudden death
what is restrictive cardiomyopathy?
stiffening of ventricular wall doesn’t allow for complete filling of the ventricles = decreased compliance
reduced outflow due to excessive fibrosis of myocardium and deposition of extracellular proteins in some cases
causes are idiopathic or at times due to secondary amyloidosis
what is inflammatory cardiomyopathy?
T-lymphocyte infiltrates cause myocyte damage
usually occurs in viral, also Lyme Disease, toxoplasma or Chagas’ disease
what most commonly causes an MI?
coronary atherosclerosis with occluding thrombus
what histological changes do you see in someone who has had an MI?
coagulative necrosis –> neutrophil infiltrate –> granulation and scar
Within 1 hour there is intercellular edema and “wavy fibers” at the periphery of the infarct. These are noncontractile dead fibers, stretched by the adjacent viable contracting myocytes.
In 12 to 72 hours, there is infiltration of neutrophils with progressive coagulative necrosis of myocytes. Dead myocytes become hypereosinophilic with loss of nuclei.
Between 3 and 7 days, after onset, dead myocytes begin to disintegrate and are removed by macrophages. There is proliferation of fibroblasts with formation of granulation tissue, which progressively replaces necrotic tissue.
After 6 weeks, healing is complete by fibrosis
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what is the cardiac skeleton of the myocardium?
dense connective tissue
doesn’t conduct electricity so it acts as insulation which is important for the coordinated contraction of the ventricles and the heart
- annuli fibrosi
- left and right trigones
- septum membranacium
what are the important structures in the cardiac skeleton of the myocardium?
- annuli fibrosi
- left and right trigones
- septum membranacium
what is the function of the annuli fibrosi?
annuli fibrosi form the openings between the atria/ventricles and the outflow vessels
they also contribute to the valves that are at these openings
they provide structural support
what happens with calcification of the heart?
with aging calcium can accumulate in cardiomyocyte tissue and on cardiac skeleton
this accumulation can delay depolarisation wave in geriatric patients because the calcified tissue doesn’t conduct electricity well
calcified tissue can become ossified
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how does the cardiac conduction system of the myocardium work?
specificalized myocytes which generate and transmit electrical signals through the heart
how does the cardiac conduction system of the myocardium work?
SA node in the RA by the SVC is the pace maker composed of myocytes that send out signals to the AV node also in the RA which then relays the electrical signals through the Bundle of His in the interventricular septum
the bundle then splits into two branches which travel down the subendocardium into the ventricles and then branch out as Perkinje fibers
Perkinje fibers are conducting myocytes which transmit the electrical signals to the other myocytes
contraction starts at the apex of the heart and spreads upward towards the base to push blood towards the base of the heart where outflow tracts of the ventricles are located
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