Exam 4 - Lecture 1 Flashcards
Borders with two cardiac cells running up against each other have _____ and how do they differ from rest of body? What does it allow?
Gap junctions. Convoluted or curvy, aren’t a straight line. Allows for more gap junctions
Intercalated discs and where is this term in the body?
High surface area with Gap junctions.
ONLY with heart cells
Pattern of cardiac muscle
Striated pattern with alternating light and dark bands (Actin and myosin)
Each cardiac cell typically has ONLY one ____. Where is this not true?
Nucleus.
Multinucleated cells are only for skeletal muscle.
Stem cells in cardiac muscle
Capable of patching up dying off cellular areas, very slow in cardiac cells. If it is a small issue, the cell can recover. A massive MI, may not be capable of recovering.
(Someone would make a lot of money if they can create a future method to speed up stem cell process)
Fibroblasts in cardiac cells
- Cells that are able to lay down scar tissue
- if cell death happens at a fast clip, fibroblasts come in and lay down scar tissue that stem cells can’t fix in time.
Rate of fibroblast productivity
Typically at A controlled rate, but there are conditions where they will lay down unnecessary scar tissue, typically during CHF.
What can slow down fibroblasts productivity?
Drugs including ACE-I
Block RAAS which is a growth hormone system.
Our body relies on angiotensin 2 as a growth factor, and fibroblasts are controlled by activity of RAAS.
Pregnant can’t be around ace-I or ARBs bc no angiotensin 2 growth factor will heavily affect growth of fetus
What’s the issue with excessive scar tissue?
- Doesn’t conduct AP
- Doesn’t contract
- will alter electrical conduction system and cause problems.
Syncytial connections
Arrangement of heart muscle
Distinct ventricular layers
Ventricle muscle has 2 layers of muscle that is layered in two opposite directions/perpendicular to each other that squeeze together like wringing out a wet towel
How are the 2 ventricle layers connected?
Electrically, very efficient.
Syncytial is also referred to as
Syncytium
Heart is split into two halves, and where is the split at exactly?
Upper and lower which is Atria/ ventricles
Anything below AV node is ventricles
Anything above AV node is atria
Heart is split into two halves, and where is the split at exactly?
Upper and lower which is Atria/ ventricles
Anything below AV node is ventricles
Anything above AV node is atria
Vast majority of heart cells are __________. Why? and they are stacked in ______?
Muscle fibers/tissue, to produce lots of force
Multiple/tons of myofibrils within muscle cells
Stacked on top of each other in LENGTH across cell
Specialized conduction tissue in cardiac muscle and how is it different than skeletal muscle?
Very good at transmitting APs very quickly.
Doesn’t produce force, if any force at all. Less clunky “stuff” such as myofibrils inside the cell to transmit AP faster.
Endocardium layer of heart
Deep cardiac muscle area, one cell layer thick endothelial layer.
Myocardium
The bulk of the muscle wall
Epicardium
Most superficial layer of heart chambers, typically major blood vessels sit on top of this and penetrate deep.
Pericardial space
Just outside epicardium and filled with mucus AND A LITTLE BIT of fluid, which allows for heart to have minimal friction while it moves around and beats.
If we have friction in pericardium, it is _______ and it is due to what?
Extraordinarily painful and can feel like a bad heart attack, due to inflammation in pericardial space or loss of mucus/fluid
Pericardium has ___ layers and it is the:
2; Connective tissue sac that encloses the heart
Parietal pericardium
Inner layer of pericardium
- stretchy
Fibrous pericardium and what is it similar to?
Outer layer of pericardium, similar to dura layer of CNS. Fairly stiff like leather, difficult to expand. Extra fluid in pericardial space will cause filling problems in heart because this tissue doesn’t really expand.
Subendocardium
Muscle layer that is very deep in wall of heart, somewhere within myocardium or endocardium.
If we are going to have an MI, it’ll probably be
Really deep in heart muscle because wall pressures are highest here.
(Subendocardium is the really deep muscle)
As the heart generates pressure, the deeper you go, the
More pressure there is
If we have really high pressure in chambers of heart, it’ll be difficult to perfuse.
What can cause an increased likelihood of ischemia?
Clogged vessels + high wall pressure
Orientation of sarcomere in cardiac muscle cell in regards to during relaxed conditions, and why?
Under normal relaxed conditions, it is not relaxed to optimal degree.
Actin filaments are slightly overlapping with myosin filaments, resulting in no H-band (myosin only), and less contraction force. It is under stretched and needs to be stretched a little more.
Conduction system within ventricles
Purkinje fibers, which just conduct action potentials
Ventricles have _____ and also (obviously) contract.
Action potentials
VRM of purkinje is
-90
VRM of ventricular muscle is
-80
Heart extends length of action potential via
Plateau phase
Plateau phase is found in both
Purkinje fibers and ventricles
At rest, both purkinje and and ventricular muscles are slightly permeable to ______, but it’s NOT ______
Sodium; CONSTANT, it does not leak in all the time.
In between heart beats, our VRM is not ____ and it has a ______. Why?
Flat; upward slope to it.
Due to increased sodium permeability at rest.
It starts at more negative VRM after repolarization from previous AP, sodium leakiness then increases and membrane potential becomes more positive at time goes by.
The rate at which purkinje are depolarizing on their OWN, it takes
Forever to get to threshold potential to fire AP all on their own.
Why does purkinje fiber fire AP before it can on its own?
It’s super slow to generate AP on its own, so neighboring cell sends AP and triggers AP for purkinje fiber.
What is threshold potential for purkinje and ventricles?
Around -70.
How long does it take purkinje fiber to have first self fired AP if there is a complete heart block at AV node?
30+ seconds
Once it fires once, it’ll beat more frequently but still at a slower rate. Just the first beat takes awhile to come.
A cause of complete heart block that will be seen most often for us in clinical
Eye procedures due to sensors in orbital of eye.
If you’re messing with eye, body doesn’t like it and the reflex for manipulation in eye socket is the (V + X, pronounced five and dine?) reflex. Operates with pressure sensors in eye socket, that pressure is sent to CNS through cranial nerve V, which is trigeminal nerve that is big and fat on side of face. Brain stem sends message to stimulate cranial nerve X which is vagal nerve. Massive vagal stimulation will prevent transmission of APs at AV node. Will take about 30 seconds for heart rate to come back.
___ distinct phases of ventricular tissue and the order of them.
5
4, 0, 1, 2, 3
Phase 4 in ventricular electrical phase is
VRM.
It has a tiny upwards slope to it representing sodium leaking in, becoming more positive.
Thing that sets off action potential in ventricles
Sodium coming from cell immediately upstream of gap junctions
Phase 0 of ventricle AP
Rapid upstroke, almost entirely fast sodium channel dependent.
Fast Na+ coming in and then channels closing very fast.
When do K+ channels close in ventricle AP
From Very end of phase 0 to in between phase 2 and 3, where they will open back up.
Phase 1 of ventricle AP
Fast Ca+ current through T-type calcium channels
Phase 2 of ventricle AP
Slow L-type calcium channels opening for calcium
What signals start of repolarization?
Closing of calcium channels
Phase 3
Lots of potassium channels opening back up, until we get back to VRM (phase 4)
Quick summary of 5 phases of ventricle phases
fast sodium current, potassium current closure, opening of T-type calcium channels, then P-type calcium channels, then repolarization phase is potassium channels opening back up and calcium channels closing.
Length of AP in ventricles, why?
Around 200ms, giving heart time for coordinated contraction.
Need time for coordination for layers of heart wall, need syncytium coordination to act as a unit to contract and eject blood. Primarily due to calcium that is coming into cell after fast sodium current cuts itself off.
Duration of phase 2 is how long your
Actual contraction is
The only outward current in ventricle graph
Potassium, it’s never inwards.
2 types of ion current coming into ventricle cells during AP
A lot of sodium in a short duration, less calcium but it is longer Duration.
When is there outward potassium current?
At rest, and during repolarization.
Less calcium coming in than sodium is due to
Less calcium channels in the cell wall
lowercase i in front of ions is
Ionic Current
Ohms law
V = IR
Voltage = Current crossing over a resistance
Ionic current is dependent on
How many ion channels are open, and electrochemical gradient
