Heart Physio Flashcards
Tbx5
T-box transcription factor created separation between left and right heart
- Developed thru evolution, as seen in turtles
Walls of vertebrate hearts:
Pericardium
Epicardium
Myocardium
- Compact and spongy
Endocardium
Compact:
- Tightly packed, vascularized by coronary circulation
- More in active fish and amphibians
Spongy:
- Loosely connected, no blood vessels (gets blood from heart chambers thru trabeculae)
Early embryonic development in
- Fish
- Air-breathing animals
Gas exchange across skin (gills later on)
Gas exchange thru placenta (lungs later on)
Foramen ovale
Ductus arteriosus
(Embryonic development)
Passage between right and left atrium
- Closes 6-12 months after birth (Incomplete seal is called a Patent)
Connection between pulmonary artery and aorta
Cardiac cycle:
Ventricular diastole
Atrial systole
Isovolumetric contraction (Ventricular systole)
Ventricular ejection (Ventricular systole)
Isovolumetric relaxation (Ventricular diastole)
End-diastolic volume (EDV)
End-systolic volume (ESV)
AV valves open and ventricles fill passively (Atria pressure high)
Atrial contraction forces more blood in ventricles
AV valves close and pressure increases in ventricles, volume stays same
Semilunar valves open and blood ejected, pressure in ventricles highest
Semilunar valves close, arteries refill as pressure in ventricles drop
Max blood ventricles can hold
Volume of blood remaining in ventricles
Right ventricle vs left ventricle
Which had higher pressure?
Left (Needs larger pressure change to send blood out to tissues, compact myocardium is thicker)
Cardiac muscle tissue
Myocardium
Intercalated disks
Desmosomes
(Myogenic heart)
Have gap junctions to electrically couple and create independent contractions
- Spiral arrangement of tissue to squeeze blood upward in the heart
Disks - Connect cardiomyocytes
Desmosomes - Link cells together
Electrical conduction (mammalian heart)
1) SA node depolarizes, spreads via internodal pathway
2) AV node delays signal. Depolarization spreads thru atria via gap junctions, causing it to contract
3) Depolarization spreads to budles of His and Purkinje fibers (causes cardiomyocytes to fire)
4) Depolarization spreads up thru ventricle, causing ventricle to contract
Pacemaker potential
Depolarization
Reparization
(pacemaker action potential)
Slow depolarization from Na+ channels opening and closing of K+ channels
- Funny channels permeable to Na+ and K+ like to be open when membrane is hyperpolarized (drives rhythm)
Pacemaker potential reaches threshold, influx of Ca2+
Ca2+ channels inactivate and K+ channels open, bringing membrane back to most negative voltage
Cardiac contractile cell action potential
- Rapid depolarization
- Plateau
- Repolarization
Na+ channels open
Na+ channels close
Ca2+ channels open
Fast K+ channels close
Ca2+ channels close
Slow K+ channels open
- No funny channels so flat resting potential (refractory period)
Norepinephrine effects on heart rate
1) Attaches to beta receptor of autorhythmic cells, Gs signals adenylate cyclase to produce cAMP, signalling to protein kinase A
2) Na+ (funny channel) and Ca2+ (T-type channel) influx, faster rate of depolarization
3) Protein kinase A cause Ca2+ channels on sarcoplasmic reticulum open and myosin to phosphorylate (Faster heart rate)
4) Sarcosplamsmic Ca2+ ATPase activates and speeds up removal of Ca2+ for relaxation
Acetylcholine effect on heart rate:
1) Acetylcholine attached to muscarinic receptors on autorhythmic cells
2) Gi signals Ca2+ channels to close, Gs signals K+ channels to open, hyperpolarizing cell + increasing time for depolarization
3) decreases heart rate
Hibernation
- Grizzly bear left ventricle
- Effect on atrium
- Myosin alpha isoform
Left ventricle stiffens to prevent overfilling and stretching during blood accumulation
Atrium beats more frequently but weaker to protect cardiomyocytes
Atrium expresses more myosin alpha isoform (responsible for weaker contractions)
Electrocardiogram (ECG or EKG)
- Positive vs negative deflection
- P wave, QRS complex, T wave
Composite of all APs generated by internodal and contractile cells at given time
Positive-> Positive flow towards positive lead (bottom of heart), depolarization
Negative-> Positive flow towards negative lead (top of heart), repolarization
P wave - Atrial depolarization
QRS complex - Ventricular depolarization
T wave - Ventricular depolarization
Atrial fibrillation
Ventricular fibrillation
Third-degree AV block
P wave missing; unstable baseline
All waves missing, no pumping of blood to body
Irregular QRS rhythm; Signal thru internodal pathway gets stuck at AV node
- Can cause blood clotting and lead to ventricular fibrillation
Wilson Greatbatch (1958)
Invented implantable cardiac pacemaker
- To fix irregular heartbeats
