Histo Block I: Heart Flashcards
Why are valves present in the heart?
Valves are present at the exits from the chambers to prevent backflow of blood
what is the 2-stage dual pump?
the right atrium and right ventricle receiving returning blood from the body via the inferior & superior vena cava and pumping this blood to the lungs for oxygenation (pulmonary circulation). And the left atrium and left ventricle receiving the returning blood from the lungs via the 4 pulmonary trunks and pumping it into the aorta for distribution throughout the body (systemic circulation)
the heart consisting of the atria and ventricles can be consideres to be a modified ________ _________
blood vessel
what are the 3 layers of the wall of the heart?
- epicardium (on outside)
- myocardium (in middle)
- endocardium (lining of heart interior)
identify
Micrograph of left atrial and ventricular walls
identify
Heart valve and endocardium
describe the epicardium
The epicardium consists of a layer of simple squamous mesothelial cells on the outer surface of the heart and the connective tissue underlying the mesothelium.
identify
mesothelial layer of surface of ovary
what is the function of mesothelium?
The mesothelium secretes a fluid that lubricates the space between the visceral and parietal layers of the pericardial sac.
how is the epicardium in the atrium vs ventricle
The epicardium representing the visceral layer of the pericardial sac is thicker on the atrium than the ventricle.
in which layer of the heart do blood vessels )coronary vessels) and nerves which supply the heart, lie?
epicardium
Whta tissue can be find in the loos CT of the epicardium?
Adipose tissue particularly in the portion covering the atria, acting as cushion for movement of the heart in the pericardial sac.
identify
Micrograph of left atrial and ventricular walls
describe the cell layer of the endocardium
The endocardium lines the inner surface of the heart and consists of an endothelial layer with a relatively thick region of CT below it
identify
endocardium
describe the layer of the endocardium
- A surface layer of simple squamous endothelial cells and their associated basal lamina and subendothelial CT
- A middle layer of CT with elastic fibers and smooth muscle cells
- A deeper layer of CT called the subendocardial layer which is continuous with the CT of the myocardium.
identify
Endocardium without Purkinje fibers; elastic stain
identify
Endocardium with Purkinje fibers
Where does the impulse conducting system of the heart lie?
lies in the subendocardial layer of the endocardium
Which layer of the wall of the heart is the thickest?
myocardium and consists of cardiac muscles cells
describe the myocardium of the ventricle vs atria
The myocardium of the ventricle is much thicker than in the atria
how are the cells in the ventricle and how does this relate to its function?
The ventricle is characterized by larger diameter cardiac cells and bundles than are present in the atria, consistent with its function as a contractile pump vs. the atria which produce much less contractile force.
identify
myocardium of atrium vs ventricle
identify
cardiac muscle
what are atrial granules and where can we find theM?
present in atrial cells and are membrane-limited granules 0.2-0.3 microns diameter. Most common in the cardiac muscle cells of right atrium
what hormones is present in atrial granules?
They contain precursor of hormone - atrial natriuretic factor (auriculin, atriopeptin) and brain natriuretic factor
how are hormones in the atrial granules release and what is the main function?
The hormones are released upon stretching of the atrial cells by high blood pressure and act on kidney to increase the excretion of sodium and water from the proto-urine thus lowering blood pressure. Thus the atrial cells can play a role in regulating blood pressure
identify
Atrial granules inn cardiac muscle
What does the fibrous skeleton of the heart consists of?
dense irregular CT
What does the fibrous skeleton form?
- 4 fibrous rings which surround the valve orifices
- The left and right fibrous trigone regions connecting the fibrous rings
- The membranous parts of the interventricular and interatrial septa
What are the functions of the fibrous skeleton?
- The fibrous skeleton provides strength to the base of the aorta and pulmonary trunk arteries leaving the heart, and to the openings between the atria and ventricles.
- The fibrous rings also act as strong attachment points for the valves.
- The fibrous skeleton also provides electrical isolation between the atrial and ventricular myocardium. This allows the atria to contract first and move the blood into the ventricle prior to contraction of the ventricle.
identify
Atrioventricular septum with fibrous cardiac skeleton
The cardiac valves attach to what tissue and what is the function?
The cardiac valves attach to the dense irregular CT fibrous rings of the cardiac fibrous skeleton, and act to stop backflow of blood during contraction of the heart chambers
cardiac valves are considered to be folds of the ________
endocardium
what is line sin the surface of cardiac valves?
endothelium
describe the structure of the cardiac valves
the valves of the heart are now considered to be highly specialized molecular structures made up of a central core region consisting of a highly organized extracellular matrix (ECM) and valvular interstitial cells (VIC) surrounded by an endothelial cell layer
identify
Heart valve and endocardium
what does the highly specialized structure of cardiac valve provide for the proper closing and opening of the valve with each heart beat?
The structure must provide the exact degree of elasticity, damping of vibration, and tensile strength necessary . This is accomplished through the presence of 3 distinct layers of the extracellular matrix and valvular interstitial cells
What are the layers of the cardiac valves?
- Atrialis/Ventricularis
- Spongiosum
- Fibrosa
What is the atrialis/ventricularis layer composed of?
is a layer of dense irregular CT with many layers of elastic fibers on the atrial surface of the atrioventricular valves (atrialis) or the ventricular surface of the semilunar valves(ventricularis)
what is the function of the atrialis/ventricularis layer?
This layer facilitates elastic extension/recoil of the valve. In AV valve may contain atrial cardiac muscle. It is lined on its surface with endothelium.
What is the spongiosum layer composed of?
a layer of loose CT with elastic fibers and collagen fibers located at the center of the valve. It is rich in ground substance containing glycosaminoglycans and proteoglycans.
What is the function of the spongiosum layer?
Acts as a shock absorber to dampen vibrations from closing of valve
What is the fibrosa layer composed of?
located on the ventricular surface of the AV valves or arterial side of the semilunar valves is a continuation of the dense irregular CT of the fibrous skeleton with both type I (74%) and type III (24%) collagen fibers and elastic fibers arranged parallel to the leaflet free edge
What is the function of the fibrosa layer?
It provides tensile strength to valve. It is lined on its surface with endothelium.
identify layers
mitral valve and its layers
what is the chordae tendinae?
These are tendon-like structures composed of dense regular collagenous CT which along with the papillary muscles help to hold the AV valves closed during contraction of the ventricle. an extension of the fibrosa layer of ventricular valves
Explain cardiac valve disease
During the average lifetime, the heart beats and the valves open and close greater than 3-billion times. Failure of the valves to open or close properly is a leading form of cardiac pathology. In 2017, there were 3,046 deaths due torheumatic valvular heart diseaseand 24,811 deaths due to non-rheumatic valvular heart disease in the United states (Center for Disease Control)
what causes valvular heart disease?
Valves can degenerate, thicken or become calcified leading to pathologies. Many of these pathologies involve valvular interstitial cells which resemble fibroblasts but can be activated to form myofibroblast-like cells.
Overactivity of these cells due to diseases such as rheumatic fever or age dependent wear and tear can result in increased expression by these cells of genes encoding matrix proteins and matrix-degrading enzymes which can result in pathological remodeling of the valve so it no longer functions properly.
Examples of valvular diseases include rheumatic heart disease, vegetative endocarditis, degenerative calcific aorta valve stenosis, and mitral annular calcification.
what is the impulse conducting system of heart
The heart has an intrinsic rhythm of contraction maintained by a system of modified cardiac muscle cells
whoch is the initiator and pacemaker of the heart?
sinoatrial node
where is the sinoatrial node located?
near junction of superior vena cava & right atrium
what is the intrinsic beat rate of SA node?
60 -100 beats per minute
where does the impulse pass after the SA node?
passes via the atrial fibers to the atrioventricular node (AV node)
after the AV node where does impulse propagate?
The impulse passes from the AV node across the fibrous skeleton to the ventricle via the atrioventricular bundle (of HIS) which then passes down in the subendocardial layer of the endocardium of the interventricular septum and divides to give the right and left ventricular bundles composed of Purkinje fibers.
the bundle of His is composed of?
purkinjie fibers
what are the purkinjie fibers and its function?
The Purkinje fibers are large modified cardiac muscle cells in the subendocardial CT of the interventricular septum which serve to conduct the impulse to the tip of the ventricle to initiate contraction of the normal cardiac ventricular fibers
identify
Micrograph of ventricular endocardium showing
Purkinje fibers
how do purkinjie fibers stain and why?
Purkinje fibers are larger than the normal ventricular fibers and typically stain much more palely than the normal ventricular fibers because they contain large amounts of glycogen, and much less contractile proteins.
what is the function of purkinjie fibers?
Their function is not contraction but to rapidly carry the impulse for contraction to the tip of the ventricle where by gap junctions they will stimulate contraction of the ventricular cardiac muscle cells.
identify
purkinjie fibers
identify
purkinjie fibers in endocardium of ventricle
what cells are present in the SA and AV node?
Both the sinoatrial node and atrioventricular node consist of modified cardiac muscle cells smaller in diameter than either the atrial or ventricular myocardial fibers and surrounded by extensive CT
what si the function of the modified cardiac muscle cells in the nodes?
are part of the impulse conducting system of the heart, and in the case of the sinoatrial node initiate the impulse for beating of the heart.
identify
SA node and AV node cardiac muscle cells
what do the autonomic nerves do in regulation of heart?
The autonomic nerves do not initiate the contraction of the cardiac muscle, but rather regulate the rate (chronotropic effect) and force of contraction (inotropic effect) according to the bodies needs
what does stimulation of parasympathetic nerves do?
decreases the heart rate (brachycardia). Short postsynaptic fibers innervate the S-A and A-V nodes, and coronary vessels and reduce heart rate by releasing acetylcholine.
what does stimulation of sympathetic nerves do?
increases the heart rate (tachycardia). Postsynaptic fibers innervate the S-A and A-V nodes, coronary arteries, and some myocardial fibers and increase heart rate by secreting norepinephrine.
which endocrine hormones increase heart rate and force by increasing calcium levels in cardiac myocytes? what can we use to reduce the heart rate and cardiac
epinephrine, norepinephrine, and thyroid hormone, as well as calcium, caffeine, and digoxin.
Adrenergic receptor antagonists such as propranolol or calcium channel blockers
which cardiovascular diseases affect the heart?
- Abnormal heart rhythms (arrhythmia)
- Coronary artery disease (CAD) – hardening of the coronary arteries
- Heart failure – such as myocardial infarctions or cardiac arrest
- Heart valve disease: mitral valve prolapse,
aortic stenosis,
mitral valve insufficiency - Cardiomyopathies: dilated cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy
hypertension and hypertensive heart disease can result in?
left ventricular cardipmyopathy
identify
Horizontal section of heart with left
Ventricular hypertrophy
identify
dilated cardiomyopathy
identify
hypertrophic cardiomyopathy
explain myocardial infarctions
Heart attacks typically involving ischemia (lack of oxygen) to a region of the heart wall resulting in death of the myocardial cells in that area. If severe enough it can lead to death. The most common cause is coronary artery disease (CAD) involving occlusion of one or more coronary arteries by atherosclerosis.
explain sudden cardiac arrest
Sudden cardiac arrest is the abrupt loss of heart function, breathing and consciousness. Although this can occur due to myocardial infarctions or other damage to the heart, a common cause is arrhythmias in the beat of the heart; particularly ventricular fibrillation in which the heart cannot pump blood. This often thus involves problems in the cardiac impulse conduction pathway. This is often fatal unless immediate resuscitation is performed with defibrillation
what are some blood tests for myocardial infarction
- Increased levels of cardiac troponin I (and cardiac troponin T – although this is less diagnostic) in blood
- Increased levels of creatine kinase (MB fraction) in blood
- Increased levels of myoglobin (is perhaps the earliest indicator but is not very specific)
- Increases in lactate dehydrogenase enzyme isozyme 1 ((there are 5 isozymes) above the levels of isozyme 2 (usually the highest) can occur within 12 – 24 hrs of an MI.)
explain blood test for myocardial infarction (increased levels of cardiac troponin I (and cardiac troponin T )
Troponins are components of cardiac muscle that are released into the blood when myocardial cells are injured. Increases in cardiac troponin I are considered very specific for injury in myocardial muscle – even more specific than CK-MB; and this is now the preferred marker for acute myocardial damage. Troponins go up within 3-12 hours after the onset of MI (though the rise is more gradual than the steep bump you see with CK-MB). They remain elevated for a long time (5-9 days for troponin I and up to a couple weeks for troponin T)
explain blood test for myocardial infarction (Increased levels of creatine kinase (MB fraction) in blood)
CK has three isoenzymes: MM, MB, and BB. CK-MM and CK-MB are both found in cardiac and skeletal muscle, but CK-MB is much more specific for cardiac muscle. CK-BB is found in brain, bowel, and bladder.
CK-MB is a very good test for acute myocardial injury. It’s very specific (you don’t see elevations in CK-MB in other conditions very often), and it goes up very quickly and dramatically after MI (within 2-8 hours). It returns to normal within 1-3 days, which makes it a good test to use in diagnosing re-infarction. Sometimes the CK total and CK-MB are reported in the form of a “cardiac index” which is the ratio of total CK to CK-MB. This is a sensitive indicator of early MI
