Cardiovascular: Physiology of the Heart Flashcards
What is a HEART contraction?
An electrical impulse that triggers contraction of CARDIAC MUSCLE (CONTRACTILE) CELLS
Is a contraction INTRINSIC or EXTRINSIC?
INTRINSIC (from within the HEART itself)
Is stim. from the NERVOUS SYSTEM required for HEART contr.
Nope
What are CONDUCTING CELLS?
Special CARDIOCYTES that initiate and distribute APs in the HEART
What are NODES?
Clusters of CONDUCTING CELLS that initiate APs in the HEART
The INTRINSIC CONDUCTION SYSTEM has an unstable resting potential because..?
Na+ is constantly leaking in at a faster rate than the pumps can keep it out.
What develops as a result of gradual depolarization?
PREPOTENTIAL
What takes place after THRESHOLD is reached?
The VOLTAGE-GATED Ca+ channels open (Ca+ rushes in from ECF), releasing spontaneous AP
Contraction step 1 =
1) Na+ enters through LEAK CHANNELS
Contraction step 2 =
2) Cell develops PREPOTENTIAL
Contraction step 3 =
3) VOLT. G. Ca+ CH. open at THRESHOLD
Contraction step 4 =
4) Ca+ influx causes NODAL CELLS to depol. (AP!)
Contraction step 5 =
5) Ca+ channels close and VOLT. G. K+ Ch. open
Contraction step 6 =
6) K+ efflux causes repol.
AP spreads along conducting pathways through GAP JUNCTIONS at __________ ____
INTERCALATED DISKS
Where are APs initiated
In the “pacemaker” aka the SA NODE
How many times per min. does the SA node depol.?
Approx. 100 times per minute
Via what pathway do electrical signals travel from the SA NODE to the AV NODE?
INTERNODAL PATHWAYS
Why is AP delayed at the AV NODE?
To allow time for the ATRIA to contr.
If the SA NODE depols 100 times per minute, why is the resting HR slower than this?
Because the PARASYMPATHETIC SYSTEM innervates nodes ACETYLCHOLINE which slows down the HR
What inc.s HR?
The SYMPATHETIC SYSTEM innervates nodes NOREPINEPHRINE to inc. HR
If the SA NODE isn’t working, what happens?
The AV NODE takes over (it fires at 40-60 bpm)
Pacemaker firing triggers all-or-none contr. of the whole HEART because…
All of the cells are connected by GAP JUNCTIONS at the INTERCALATED DISKS
What is the role of GAP JUNCTIONS at INTERCALATED DISKS?
They allow ions to move from cell to cell
What are DESMOSOMES? What is their F?
DESMOSOMES are anchoring proteins
F - Prevent separation of contracting cells
What is the reason there are many MITOCHONDRIA in CARDIAC MUSCLE CELLS?
Makes the CARDIAC MUSCLE more fatigue resistant
Are there TERMINAL CISTERNAE in CARDIAC MUSCLE?
No, Ca+ is released by t-tubules from the SARCOPLASMIC RETICULUM (SR)
