18 - Cardiovascular

Where is the heart located?

Mediastinum and pericardial cavity, extends from the 2nd rib to the 5th intercostal space

What is the fibrous pericardium?

dense connective tissue (irregular)

Useful for protection (from infections), anchoring, and prevents from over filling 

What is the parietal layer?

lines the inside of fibrous pericardium, cover the large arteries as well

What is the epicardium?

(visceral layer of serous pericardium): part of heart wall, has fat  

What is the myocaridum?

middle muscular layer of the heart (arranged in circular/spiral bundles)

What is the endocardium?

smooth inner layer

What is the cardiac skeleton?

Connective tissue fibers that reinforce myocardium and anchors cardiac muscle to the cardiac skeleton for support (collagen/elastic fibers)

What is the purpose of the auricle?

increases the volume of the atrium

Which ventricle wall is stronger? 

 left ventricle wall is 3x thicker and pumps with greater pressure

• The ventricles have an uneven workload 

• The systemic circuit has 5 times more friction

What is an anastomosis?

a junction of vessels

provides an alternate route for blood flow

What is the make-up of cardiac muscle?

branched, striations, involuntary, intercalated disc

What are intercalated discs composed of?

1 gap junction (allows for communication within a cell which results in a functional syncytium = coordinated unit) and 2 desmosomes (prevent tissue from pulling apart) 

What type of respiration occurs in cardiac muscle?

Aerobic only (more mitochondria), this is why a blockage is such an issue

Why is no tetanus in cardiac muscle significant?

Because you do not want multiple units to contract to summate (Need heart to relax between pumps to refill with blood)

Why are gap junctions good in the heart?

they spread the electricity around and create a functional syncytium

(Unlike skeletal muscle because the motor units must be stimulated individually)

What is an intrinsic conduction system?

both (atria and ventricles) systems can contract and relax independent of each other 

What causes the coordinated heartbeat?

gap junctions and intrinsic cardiac conduction system 

Network of contractile (autorhythmic) cells initiate and distribute impulses to coordinate depolarization and contraction of heart

What is the first step of the Cardiac Conduction System?

The sinoatrial node (SA) generates impulses in the wall of the right atrium

What is the second step of the Cardiac Conduction System?

The electrical impulse is paused for 0.1 second at the atrioventricular node (AV) in order to allow the atria to contract before ventricle does 

Located in the inferior portion of the interatrial septum 

What is the third step of the Cardiac Conduction System?

The AV Bundle connects the atria to the ventricle

• It is the only electrical connection between atria and ventricle  

• Very bad if malfunction

What is the fourth step of the Cardiac Conduction System?

The bundle branches travel towards the apex of the heart 

It conducts impulses through the interventricular septum

What is the fifth step of the Cardiac Conduction System?

The subendocardial conducting network

Once the purkinje fibers hit the apex, they spread out through the walls of the ventricles (more in the left ventricle because it's bigger and needs more power!)  

How does the heart set the rate at what it beats at?

The SA node sets the beat (60-100 rate of impulse/min), the if the SA node fails the VA node can take over but it does not have as high of a rate of impulse (40-60 /min, called junctional rhythm)

How does the autonomic nervous system innervate the heart?

The medulla oblongata - Cardioinhibitory center (-) & Cardioacceleratory center (+)

Stimulates the SA/AV nodes

What do sympathetic cardiac nerves do?

increases heart rate and forces contraction

Also innervates heart muscles and coronary arteries

How long does action potential last in skeletal muscle?

about 200 ms

Sustained contraction ensures efficient ejection of blood 

• Longer refractory period prevents tetanic contraction 

  • Allows heart to relax, fill with blood prior to contracting again 

What is the action potential of contractile cardiac muscle cells?

1. depolarization

2. plateau 

3. repolarization  

What happens during the plateau stage in action potential

caused by surge of calcium across the sarcolemma, causes prolonged depolarization and potassium channels being closed 

• As long as calcium enters heart contracts 

What happens during the repolarization stage in action potential

Ca2+ is pumped back into sarcoplasmic reticulum as well as extra-cellular space 

What is the purpose of the absolute refractory period?

allows time for the heart to refill

What is the P-Wave?

shows the electrical activity of atrial depolarization 

• Which causes atrial contraction 

• 0.08s

What is the QRS complex?

ventricular depolarization

• Causes ventricular contraction 

• At same time, atrial repolarization (relaxing) is occurring 

0.08s

What is T-wave?

ventricular repolarization 

• Same time: ventricular relaxation

0.16s

What is the ST segment?

 entire ventricular myocardium depolarized 

• Plateau phase 

• 0.135 s 

What is the QT interval?

 beginning of ventricular depolarization through ventricular repolarization 

• 0.38 

What is the period of myocardial contraction?

Systole 

What is the period of myocardial?

Diastole

What is the cardiac cycle?

all events associated with blood flow through the heart during one complete heartbeat

this includes ventricular systole and diastole, and atrial systole and diastole

what is the dicrotic notch?

closure of aortic valve and backflowing of blood off cusp cause a decrease then increase of pressure 

• Semilunar valves close 

What is ventricular filling? 

blood returning from circulation enters atria, then ventricles, through open AV valves 

Ventricles are active -> remaining 20% enters ventricles when atria contract  (first 80% is passive)

What is isovolumetric contraction?

split second where all four valves are closed, atria relax, ventricle contracts

What is ventricular ejection?

blood enters aorta and pulmonary trunk 

What is Isovolumetric relaxation?

all four valves are closed again for split second, ventricles relax

What is end diastolic volume?

Amount of blood in ventricles, which is largest, at end of relaxation (diastole)

What is end systolic volume?

amount of blood in ventricles (smallest) after contraction (systole)

What is the first lub-dub sound? 

Sound is closing of AV valves at beginning of ventricular systole

what causes the second lub-dub sound?

Sound is closing of SL valves at beginning of ventricular diastole  

What is cardiac output?

Amount of blood pumped out by each ventricle in 1 minute 

What is stroke volume?

Volume of blood pumped out by one ventricle with each beat 

What is the stroke volume equation?

• SV = EDV - ESV

  • Increase in length is an increase in EDV 

  • Increase venous pressure is an increase in EDV

What is ESV affected by? 

arterial BP and force of ventricular contraction

• Increase in arteria; BP is an increase in ESV

What is the formula for cardiac output?

CO = HR (75 bpm) x SV (70 ml/beat) 

What is cardiac reserve?

difference between resting and maximal CO 

• Typically 4-5x resting CO (non-conditioned individuals)

What are 4 factors that increase cardiac output? 

Exercise, ventricular filling time, bloodborne epinephrine thyroxine (excess Ca2+), changes in autonomic CNS output 

What is preload?

degree to which cardiac muscle cells are stretched just before they contract -> impact EDV

What is the Frank Sterling Law?

increased stretching (increasing the amount of exercising) impacts you by returning more blood to the heart 

How does norepinephrine increase heart contractility?

via a Cyclic AMP Second messenger system 

• Positive inotropic factors (increase contractility) 

I.e epinephrine, norepinephrine, thyroxine, glucagon

• Increase contractility lowers ESV 

• Negative inotropic factors (decrease contractility)

  • H+ (acidosis), excess potassium levels, calcium channel blockers 

What is afterload?

the backpressure exerted by arterial blood pressure (not an issue in individuals with healthy blood pressure 

• Does impact ESV 

What is hypocalcemia? 

low blood calcium 

depresses heart

What is Hypercalcemia?

high blood calcium

increases HR contractility (up to a point)

What is hyperkalemia?

high blood potassium 

alters resting membrane potential, which can lead to heart block and cardiac arrest 

What is hypokalemia?

low blood potassium

results in a feeble heartbeat, arrhythmias 

WHat is congestive heart failure?

when the heart becomes an inefficient pump

• Progressive meaning each time it happens the heart can get worse and worse 

• Cannot deliver enough blood to tissues 

What is Coronary Atherosclerosis?

fat buildup in coronary arteries, cannot sustain myocardium

What is Dilated cardiomyopathy (DCM)?

ventricles become flabby, myocardium deteriorates (unknown cause)  

What happens to the heart after multiple MIs?

scar tissue replaces normal myocardial cells, cannot generate force