Modual 3 Flashcards
Name the cardiac layers (from heart –> pericardium)
Endocardium
Myocardium
Epicardium
Parietal Space = Pericardial Cavity
Parietal Pericardium
Fibrous Pericardium
Describe the endocardium
Similar to endothelial cells that line blood vessels –> smooth “frictionless” surface
What makes up the myocardium?
Cardiac Muscle CElls (contractile Tissue)
What is the epicardium (visceral pericardium)?
Connective tissue layer
What is contained w/in the parietal space (pericardial cavity)?
Pericardial fluid –> reduces friction during heart movement
**clinically –> pericardial effusion (cardiac tamponade)
What is the parietal pericardium?
Connective tissue layer insulating the heart
What is the fibrous pericardium?
Fibrous sac that “contains” the heart
What are muscle fibers of the myocardial cells made of?
Myofibrils
Single Nuclei
Mitochondira
Sarcoplasma Reticulum
Cytoplasm
What is the plasma membrane of myocardial cells called?
Sarcolemma
What are T-tubules?
Invaginations of sarcolemma into the myofibrils
What does the sarcolemma do?
Spreads action potential throughout muscle fiber
How does the action potential spread throughout the myofibril?
Lengthwise along the sarcolemma
Penetrates deep into myofibrils via T-tubules
What is the point of the sarcolemma/T-tubule arrangement?
Allows for rapid transmission of action potential
What are myofibrils made up of?
Myofilaments
What are myofilaments?
Protein filaments that provide mechanical shortening/lengthening of the muscle filament
How are myofilaments arranged?
In units called sarcomeres
What are sarcomeres?
Repeating units arranged in series (end to end) along the length of the myofibril
What do sarcomeres contain?
Myofilaments
What are the proteins that make up the myofilaments?
Actin
Myosin
How are myosin microfilaments arranged?
Chains are wrapped together each w/ protruding globular heads
What do the globular heads of myosin filaments do?
Bind to actin and swivel –> mechanical shortening of sarcomere
What do the globular heads of myosin contain?
Binding site for actin
Receptor for ATPase
How are actin (thin) microfilaments arranged?
2 chains of actin wrap together to form actin microfilaments
Where would you find tropomyosin on the actin microfilament?
“wrapped” around the length of the actin filament
Where would you find troponin on the actin microfilament?
Attached intermittently along the length of tropomyosin
What is the function of troponin/tropomyosin?
Allows exposing/covering of the binding site on actin for the myosin globular heads
What happens if the binding site of the globular head of myosin on actin is covered?
Sacromere/muscle fiber can’t contract
What happens if the binding site of the globular head of myosin on actin is exposed?
Myosin head can bind to actin –> mechanical contraction of sarcomere/muscle fiber
What are the subunits of troponin?
Troponin T
Troponin C
Troponin I
What does the troponin T subunit do?
Binds troponin to tropomyosin and actin
What does the troponin C subunit do?
Contains binding site for Ca2+
**Ca2+ = on/off switch for contraction
What does the troponin I subunit do?
Inhibits ATPase
**ATP is needed fuel for contraction
What does the Z line do?
Anchors/connects thin filaments
**z-line to z-line = sarcomere
Describe the cross-bridge theory of myocardial muscle contraction
Ca2+ binds to troponin –> exposes binding site on actin = trigger
Myosin head attaches to actin
Myosin head binds to actin –> releases ADP and Pi –> myosin head swivels
ATP binds to myosin head
ATP –> ADP + Pi –> release of myosin head from actin to relaxed position
Describe excitiation-contraction coupling
Action potential travels across sarcolemma down T-tubules
Action potential reaches sarcoplasm a reticulum (stores Ca2+) –> release of Ca2+
Ca2+ diffuses into microfilaments and binds to troponin-C –> exposes myosin head binding site on actin
Why is it important that cardiac muscle cells have a lot of mitochondria?
Supply ATP for contraction
Where are the intercalated discs of cardiac muscle fibers located and what do they do?
Between muscle fibers
Allow action potential to travel from cell to cell
What do desmosomes do?
Attach each muscle fiber to the next
What do gap junctions do?
Allows electrical action potential to spread through intercalated disc from one muscle fiber to the next
What is the frank starling law of the heart?
The length-tension relationship between the length of myocardial muscle and force generation
What is the length-tension relationship of healthy cardiac muscle?
Length of cardiac muscle fiber (sarcomere) is DIRECTLY related to the force generated by the muscle fiber
What is the end-diastolic volume?
The volume that fills the ventricles
What does the end-diastolic volume do?
Determines amount of “stretch” on the cardiac muscle fibers, which means:
Increase end-diastolic volumes = increase contractility
Increase contractility = increase stroke volume/cardiac output
What happens to unhealthy cardiac muscle (heart failure)?
Has been dilated/damaged
Sarcomeres have been lengthened too far –> Frank Starling Law no longer applies
What is LaPlace’s Law?
Wall tension (contraction force) is DIRECTLY related to the product of intraventricular pressure x internal radius (ventricular volume)
Wall tension (contraction force) is INDIRECTLY related to wall thickness
What does LaPlace’s Law mean for a dilated thin walled ventricle full of blood?
It requires more time to generate a contraction force (wall tension) strong enough to generate intraventricular pressure needed to eject blood from the heart
**poor cardiac output/performance
What is left ventricular preload?
Pressure generated in the L ventricle @ the end of diastole (ventricular filling)
**Preload = Left end-diastolic pressure
What determines preload in a healthy heart?
L end-diastolic volume (Starling’s law of the heart)
What happens if you increase left end-diastolic volume?
Increase Preload
Increase stroke volume/cardiac output
What happens to preload in a pt w/ ventricular hypertrophy?
Increases preload
BUT less ventricular filling (decreased end diastolic volume) –> output will be reduced
What will excessive left end-diastolic filling pressures cause?
Congestive back-up in pulmonary circulation
What is afterload?
The voce the left ventricle must generate during systole to overcome aortic pressure to open the aortic valve
What happens if there is increased afterload?
Ventricle has to work harder to eject blood:
Takes longer contraction time to generate necessary force
Increased afterload + insufficient contraction time = reduced stroke volume
What could happen clinically with increased afterload?
Elevated systemic BP
Aortic Stenosis
Dilated ventricle
Decreased stroke volume (increased end systolic volume)
Hypertrophy to compensate
Where are the cardiovascular control centers located in the brain?
Medulla
What does the sympathetic nervous system do to the heart?
Increase HR
Increase Contractility
What does the parasympathetic nervous system do to the heart?
Decrease HR
Decrease Contractility
Which part of the autonomic nervous system dominates during rest?
Parasympathetic @ SA node
What happens to the autonomic nervous system early during exercise?
Removal of parasympathetic influence @ SA node
Which part of the autonomic nervous system dominates during intensive exercise?
Sympathetic @ SA node
Where are arterial baroreceptors located?
Aortic Arch
Carotid Sinus
**systemic “stretch” receptors
What will increased pressure cause the baroreceptors to do?
Increase parasympathetic nervous system
stimulation
Decrease sympathetic nervous system stimulation
Net Effect = ↓ HR, ↑ vasodilation which ↓ BP
What will decreased pressure cause the baroreceptors to do?
Increase sympathetic nervous system
stimulation
Decrease parasympathetic nervous system stimulation
Net Effect = ↑ HR, ↑ vasoconstriction which
↑ BP
Where are atrial stretch receptors located?
R and L atria
What do atrial stretch receptors control?
Blood Volume
What will stimulation of atrial receptors result in?
Stimulate the release of ANP from atria
What does ANP do?
Stimulate kidneys to excrete urine and sodium
**end result = reduced blood volume
What does the stimulation of atrial receptors result in (in terms of HR)?
Increase HR
**arterial baroreceptors have dominant role in maintaining HR compared to atrial receptors
What stretch receptors are involved in the bainbridge reflex?
Stretch receptors in atria
What is the bainbridge reflex do?
↑ HR after IV infusion (increase blood volume)
What are the 2 factors that determine contractility?
Sympathetic nervous input
Increased stretch of ventricle (healthy heart)
Starling’s Law of the Heart –> ↑ preload =
↑ contractility
What are the factors that determine cardiac output?
CO = HR x SV
What happens with increased stroke volume?
↑ venous return –> ↑ blood volume/↑ sympathetic activity on veins
↑ end-diastolic volume
↑ preload
