Unit 4 - Cardiac properties, structure, and electrical activation Flashcards
What are the layers of the heart?
epicardium, myocardium, and endocardium
What is the structure of the epicardium?
a serous layer of mesothelial cells that line the pericardial cavity with a loose connective tissue layer underneath
What is the loose connective tissue layer of the epicardium made up of?
elastic fibers, blood vessels, nerves, and ganglia fat cells
What is the myocardium?
cardiac muscle
What is the myocardium made up of?
bundles of cardiac muscle cells with a central nucleus and intercalated discs
What is the function of intercalated discs?
they join the ends of myocardial cells together
What are mycardial cells surrounded by?
a network of connective tissue with a dense capillary network, lymphatic vessels and autonomic nerve fibers
What is the endocardium?
endothelium that lines the ventricles and atria
What are the three layers of the endocardium?
endothelium (continuous), subendothelial layer, and subendocardium
What is the supendothelial layer of the endocardium made up of?
dense irregular connective tissue
What is the subendocardium layer of the endocardium made up of?
loose collagen and elastic fibers, blood and lymph vessels, can have fat cells, and conduction system fibers in some areas
What type of structures are valves and what are they made up of?
endocardial structures made up of subendocardial folds with an endothelial cover
What do valves connect to?
the cardiac skeleton
What is the atrial side of the atrioventricular valves called (histologically)?
stratum spongiosum
What is stratum spongiosum made up of?
loose elastic and collagen and small vessels
What is the ventricular side of atrioventricular valves called (histologically)?
Stratum fibrosum
What is the stratum fibrosum made up of?
mostly collagen
What does the stratum fibrosum connect with?
fibrous rings and chordae tendinae
What is the histoological structure of the semilunar valves?
circular orientation - central collagen fibers
Where is the SA node located?
near the cranial vena cava and right auricle
Where is the AV node located?
on the right side of ventral inner atrial septum ventral to the coronary sinus
What are SA nodes and AV nodes made up of?
thin branching muscle cells with few myofibrils and no intercalated discs
What is another name for the fibrous base?
the cardiac skeleton
What is the function of the cardiac skeleton?
the insertion site of atrial and ventricular muscle fibers, the attachment site of cardiac valves, and separates atria and ventricles
What is the cardiac skeleton made up of?
dense irregular connective tissue; fibrous rings, fibrous triangles, and fibrous IV septum
What are the fibrous rings made up of?
collagen bundles mingled with elastin
What are the fibrous triangles made up of and where are they located?
connective tissue located between atrioventricular valve openings and the base of the aorta
What is the fibrous IV septum made up of?
collagen fibers
What is a myocyte?
a cardiac muscle cell
What is a myofiber?
a bundle of myocytes
What are myofibrils?
bundle of contractile proteins (actin and myosin)
What is the sarcomere?
the functional unit of a myocyte from Z-line to Z-line
What is the sarcolemma?
the cell membrane of a myocardial structure
What is the function of the sarcolemma?
maintains ion gradients
What is the sarcolemma impermeable to and selectively permeable to?
impermeable to Na and Ca, selectively permeable to K
How to ions move across the sarcolemma?
by some type of carrier which depends on the electrical driving force and concentration gradient
What is a t-tubule?
invaginations of the sarcolemma into the cell
What do t-tubules contain?
extracellular fluid
What is the function of t-tubules?
they allow rapid conduction of impulses to activate contractile elements
What does the sarcoplasmic reticulum do?
it regulates intracellular calcium movement it is for Ca storage and release
What is the cisterna of the sarcoplasmic reticulum?
the communication unit of the sarcoplasmic reticulum to receive electrical signals coming from the t-tubules
What type of junctions are in an intercalated disc?
gap junctions, desmosomes, and fascia adherens
What is the function of gap junctions in intercalated discs?
they allow the transfer of chemical signals between cells
What is the function of desmosomes in intercalated discs?
their filaments extend into the cytoplasm and attach cells together
Where are the actin filaments of the myocardial structure anchored?
in the fascia adherens
What are chordae tendinae made out of?
collagen and elastic fibers covered with endothelium
What is the function of chordae tendinae?
they arise from papillary muscles to secure cusps to the septal wall to prevent aversion of the valves
What are the components of the right atrium?
vena cavae, coronary sinus, azygous vein, auricle with pectinate muscles, interatrial septum, fossa ovalis
What are the components of the right ventricle?
tricuspid valve, fibrous skeleton, papillary muscles, trabeculae carneae, moderator band, supraventricular crest, infundibulum, outflow tract area, pulmonic valve, main pulmonary artery
What are the components of the left atrium?
Pulmonary veins, auricle with petinate muscles
What are the components of the left ventricle?
Shape and relative wall thickness, left A-V or mitral apparatus, papillary muscles, interventricular septum
What are the components of the aorta?
Aortic valve with sinuses of valsava, coronary ostia, origin, ascends to right, arches to left and descends left of midline
What are the components of the coronary arteries?
Right – distribution varies with species; left – circumflex and interventricular branches
Where is the sinoatrial node located?
in the right atria where impulses are originated
What is the SA node known as?
the cardiac pacemaker
What does the SA node determine?
heart rate
Where is the atrioventricular node located?
between the right atria and right ventricle
What is the function of the AV node?
it allows ventricles to fill
What is the function of the bundle of his?
to send the electrical impulse from the AV node to the interventricular septum
What is the function of the purkinje system?
enhance rapid conduction and allow for synchronous contraction of the ventricles
What maintains the normal resting potential of the cardiac cell membrane?
passive outward current, Na/K ATPase pump
When does equilibrium of the cardiac cell membrane occur?
when chemical concentration gradient is pulling K out and the electrical force is holding K in
What defines the electrochemical gradient for K?
the Nernst equation
What does is the Nernst equation?
defines the relation between ion concentration gradient and membrane potential forces
What is the function of Na and Ca membrane channels?
Na and Ca must enter rapidly for normal depolarization
What happens to the membrane as it depolarizes?
it becomes less negative
What is this diagram representative of?
The fast response action potential of a myocyte
What is happening in phase 0?
activation of the myocyte via the action potential; Na moves in
What is happening in phase 1?
a brief period of overshoot and repolarization, Ca moves into the cell
What is happening in phase 2?
Ca stops entering the cell, the plateau of action potential
What is happening in phase 3?
K moves out of the cell and repolarization begins
What is repolarization of the myocyte in the fast response action potential controlled by?
K leaking out and Na/K ATPase pump
What is happening in phase 4?
the myocyte has returned to resting action potential
What is this diagram showing?
the slow response action potential
What is happening in phase 0?
Slow depolarization of the cell, action potential is generated, slower than fast response because Ca is mediating the process; 3 Ca in, 1 K out
What is happening in phase 2?
k channels opening, more K leaving, makes cell more negative, repolarization
What is happening in phase 3?
Ca channels closing, no positives Ca entering, makes cell negative, repolarization
What is happening in phase 4?
Spontaneous diastolic depolarization; Ca comes in to bring more Ca in
