The Heart Flashcards
HEART
What kind of pump system?
Define systemic circulation and pulmonary circulation.
2 pump system.
Systemic–Left side (left ventricle) of the heart to the tissue, then back to the right side (right atrium) of the heart.
Pulmonary–Right side (right ventricle) of the heart to the lungs and back to the left side of the heart.
SERIES FLOW
Use physics to define the circulatory system as a series.
Series flow as an overall view. A reduced parallel circuit.
Pulmonary and systemic systems are in series with each other, i.e., blood must pass through two circuits in sequence before it returns to starting point.
PARALLEL FLOW
Use physics to describe the systemic circulation as a parallel circuit.
What are the advantages? 2
Strategy to ensure all organs get O2 blood.
All blood does not travel through each organ each time through the system.
Advantages…
Each organ receives fully oxygenated blood.
Blood flow can be adjusted to each organ individually.
ELECTRICAL ACTIVITY OF THE HEART
Describe the 2 components of the Conduction System.
What is the name of the specialized cell type in the heart?
Conduction system…
Pacemaker (autorhythmic) cells–generate “spontaneous” action potentials (SA and AV nodes)
Conduction Fibers–RAPIDLY CONDUCT APs throughout the heart through gap junctions
Myocardial cells–all muscular cells of the heart
Describe the function of Gap Junctions in the heart.
How do they connect cells?
How do they spread Action Potentials?
Gap Junctions–Gap junctions begin at the SA node and are connected to other SA’s. Even without stimulus, SA pulses reach myocardial cells and spread through Excitation-Coupling.
Gap Junctions coordinate a wave of electrical activity through the heart.
Gap junctions are fast and spread throughout the heart from SA node to atrial muscle, to the AV node, to interventricular septum, and from the inferior ventricles upward.
AUTORHYTHMIC CELL AP (SA and AV node cells)
What is the biggest difference between a cardiac and skeletal muscle action potential?
What causes rapid depolarization?
What causes repolarizations?
What is Pacemaker Potential, and what is open during this time? What is Threshold?
There is not resting phase between action potentials.
Long lasting, Voltage-gated Ca++ channels … CaL
K+ similar to neurons.
Pacemaker potential (slow depolarization)–opened by FUNNY channels, Na+ (or nucleotide channels), and Transient Ca++ channel, aka CaT. All creates a slow depolarization to reach -50…threshold.
AUTORHYTHMIC CELL AP CURRENTS (SA and AV node cells)
What are the currents during phase 4? (pacemaker potential/slow depolarization)
If (funny current), ICaT, IK (delayed rectifier K+ current)
AUTORHYTHMIC CELL AP CURRENTS
What is the current during Phase 0 (upstroke, depolarization)?
ICaL
AUTORHYTHMIC CELL AP CURRENTS
What is the current during Phase 3 (Final Repolarization)
IK (delayed rectifier K+ current)
MYOCARDIAL CELL AP
How long does an AP last, and what causes it to do so?
Plateur make AP last 250-300 mSec.
What are the 5 phases of a Myocardial AP?
- Resting. Absent stimulus, resting potential stays at -90mV. Occurs very rarely due to lost of K+ leak channels.
- Upstroke, depolarization. Na+ voltage-gated channels open.
- Brief (early) Repolarization. Na+ starts to close, Some voltage-gated K+ (inward rectifier channels) close to decrease outward flow of K+, and opening of CaL brings Ca++ in cell.
- Plateau–Vm stays constant, slightly above 0. L-type Ca++ (CaL) are still open.
- Repolarization–Delayed rectifier K+ finally get their slow gates open. K+ flows out similar to the neuron to terminate AP.
MYOCARDIAL EC COUPLING
What does Myocardial AP open in t-tubules?
Define Ca++ induced Ca++ release?
Open Voltage-gated Ca++ channels.
In addition to the Ca++ release process learned about in skeletal muscle, Ca++ entering through the plasma membrane binds to the voltage gated Ca++ release channels in the Sarcoplasmic Reticulum to hold them open longer. Calcium binds to cardiac muscle fibers the same as it does skeletal muscle.
What are the 8 steps to contract a cardiac muscle fiber?
- Current spreads through gap junctions to contractile cell.
- Action potentials travel along plasma membrane and T tubules.
- Ca++ channels open in plasma membrane and SR.
- Ca++ induces Ca++ to release further from SR.
- Ca++ Binds to troponin, exposing myosin-binding sites.
- Crossbridge cycle begins (muscle fiber contracts).
- Ca++is actively transported back into the SR and ECF.
- Tropomyosin blocks myosin-binding sites (relaxation).
Electrocardiogram (ECG)
What does it record? How? Why is it used?
Recording of the overall spread of electrical current through the heart as a function of time during the cardiac cycle.
Recorded by electrodes placed on skin. It follows the pathway of depolarization of the heart. Very good for mapping and diagnosing heart issues.
used by physicians to determine whether or not problems exist in the electrical activity of the heart.
Einthoven’s Triangle
What is the triangle?
How do the leads work?
Based on an imaginary equilateral triangle surrounding the heart, the triangle is expanded until its corners fall on the right arm, left arm (wrists), and left leg (ankle).
Lead I detects the V at the left arm minus the right arm; Lead II detects the V at the left leg minus the right art; Lead III detects the V at the left leg minus the left arm.
