Showing posts with label as. Show all posts
Showing posts with label as. Show all posts
Sunday, March 15, 2015
Heart muscles as a pump and functions of valves
4 chambers:
Right and left atria
Right and left ventricles
4 valves:
Biscuspid valve between lft atrium and lft ventricles
Trcuspid valve between rt atrium and rt ventricles
2 semilunar valves ; one between lft ventricle and aorta and the other is between rt ventricle and pulmonary arteries
3 types of muscle:
Atrial muscle
Ventricular muscle
Specialized muscle:Excitatory muscle and conductory muscle
-Cardiac muscles are striated muscle with actin and myosin filaments sliding along side of each other as skeletal muscle.
-Syncytium:
The cardiac muscles are interconnected with each other by intercalated discs. At intercalated discs the membrane of cells fuses forming gap junctions through which adjacents cells can communicate with each other. These intercalated discs allows action potentail of one muscle cell to pass to other cells. By this way the whole heart muscle acts as a single unit. This property of heart muscle is called Syncytium.
2 types: Atrial and ventricular syncytium
-Atrium and ventricles are not directly connected. They are separated by fibrous tissues which insulates atria and ventricles.
-The impulses from atria are conducted to ventricles though specialezed conductive tissues called A-V bundle.
-Because of this insulation between atria and ventricles , atria contracts a short time ahead of ventricles.
Action potential in cardiac muscles
RMP: -85 mV
Peak/spike potential: +20 mV
After spkie potential it remains depolarised for about 0.2 sec called plateau phase and then only repolarization occurs. Plateau is the characteristics of heart muscle. Because of plateau ventricular muscles remains in contraction for 15 times longer duration than skeletal muscles.
Causes of plateau in Cardiac muscles
1.The cause of action potential in cardiac muscle is by opening of 2 types of channels:
a. fast Na ions channels
b. slow Na- Ca ions channels ( not present in skeletal muscles)
Slow Na-Ca ion channels opens slowly and remains opened for longer time, so large number of Na, Ca ions enters causing prolonged duration of depolarization and this causes plateau phase. The Ca ions that have influxed during plateau causes cardiac muscle contraction. But for skeletal muscle contraction Ca ions comes from sarcoplasmic reticulum .
2.After depolarization K ion permeability through cardiac mucle membrane decreases by 5 folds. So+ve ions remains inside the cell casuing plateau.
Velocity of conduction in cardiac muscles
Atrial , ventricular: 0.3 - 0.5 m/sec
Purkinje fiber: 4 m/sec
Refractory period: ventricles 0.25 – 0.30 sec (till plateau) ; atrium 0.15 sec
Relative refractory period: 0.05 sec, strong stimuli required for premature beats formation
Excitation – contraction coupling
-It is the mechanism by which action potential causes myofibrils to contract.
-It is same as skeletal muscle.in skeletal muscle only one source of Ca ions: from sarcoplasmic reticulum
-When action potential reaches T tubules it causes releae of Ca ions from t tubules itself and cisternae of sarcoplasmic reticulum.
-The difference is that there are two Ca ions source: one is from cisternae of sarcoplasmic reticulum and the another is from T tubules itself. Because of the extra Ca from T tubules the cardiac muscles contraction is strong. The diameter of T tubules is bigger and it also contains large number of negative ions which binds Ca ions and releases when action potential reaches T tubules.
Duration of contraction:
contraction begins just a few milliseconds after action potential starts and continues till few milliseconds after end of action potential.
Atrial: 0.2 sec
Ventricle: 0.3 sec
The Cardiac Cycle
The events that occurs from beginning of heart beat to the beginning of next is called cardiac cycle.
Action potential is generated in SA node , it is located in the superior lateral wall of right atrium near the opening of superior venacava. Then it travels through atria and then though A-V bundle into ventricles. At A-V node there is delay in conduction of 0.1 sec, because of this atria contracts prior to ventricles and so pumps blood in ventricles and then ventricles contracts and pumps blood out.
Diastole and systole:
Diastole is the phase of cardiac cycle during which heart remains relaxed and is filled with blood .
Systole is the phase during which heart remains contracted and pumps blood out.
Relationship of heart sounds to heart pumping
First heart sound:
is due to closure of A-V valves when ventricle starts to contract
Second heart sounds:
closure of aortic and pulmonary valves at end of systole
Relationship between left ventricular volume and intraventricular pressure during diastole and systole.
Preload and afterload
Preload is the pressure with which the ventricle starts to contract and is the end diastolic volume
Afterload is the pressure/load against which the ventricle has to contract and is the systolic pressure.
Regulation of heart pumping
1.Intrinsic regulation of heart pumping (Frank starling mechanism):
Within physiologic limit, the greater the heart muscle stretched during blood filling, greater is the force of contraction and greater quantity of blood is pushed into aorta. This is known as Frank-starling mechanism.
2.Control of heart by autonomic nervous system:
-sympathetic stimulation causes increase heart rate and increased force of contraction
-parasympathetic/vagus stimulation decreases heart rate
Effect of K & Ca on heart function
Inc. K ions in ECF:
-heart becomes dilated, flaccid
-HR decreases
-slows/blocks conduction of impulses through A-V node
-decreases the RMP
Inc Ca ions: opposite to Inc K ions
-spastic contraction
Dec Ca ions:
-flaccidity
Effect of temperature on heart function
Dec temperature:
decrease heart rate ; is due to less ions are permaeble to heart muscles membrane at low temp
Moderate inc temp:
contractile strength increased but high temp causes fatigue of muscle by inc metabolism.
Monday, March 9, 2015
Fun to Play as a Group or Individually
As a child, I remember playing a few games on the internet. My favorite game, was a game all in pastel colors. There was a large pyramid and I had to select one cube at a time. After double clicking the cube, it would be removed. The object of the game was to remove as many cubes as I can before time ran out. As an adult, I still love such games. When I received Pyramix from Gamewright to review, all of these wonderful memories came back to me.
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Pyramix
Gamewright
Contents:
 |
| Pyramix Contents |
- 1 playing game board
- 56 game cubes
- 1 instruction booklet
Game Set Up:
After getting the playing board and all the empty pieces together, start by placing all the cubes on. It is amazing but the way the board is shaped, they cubes will automatically fall into shape. When you are finished, you will be left with a perfect pyramid. It is so simple that even my two little nephews wanted to join in the fun and help out. Yes they are 1 and 2 and had such fun with my 7 year old. With adult supervision, they had fun building a pyramid and then dumping it over. They were busy for close to a half our. It was amazing.
 |
| All the kids setting up Pyramix |
Just incase you thought I was making this up, here is a snap of them putting it together. We all had a many good laughs over this.
Game Play:
For the adults in us, here is where all the fun happens. You have to get as many pieces as you can but there are some rules. You cannot expose any of the base. Any cube touching a cobra is off limits.
The object of the game is to score the most. There are three types of cubes with different point value ranging from 1 - 3. All of the points are added at the end. The player with the most point value wins.
It sounds easy but just when you think you are about go get 3 points, a cobra will get you and you are left with only one.
As fun as this is, when you are home alone at night and the kids are asleep, this is also a great game to play individually. Instead of adding up all the points, see how many cubes you can take off the board. To make it more challenging, try adding a timer.
Pros:
- Fun
- Fast
- Family game
- Solitary game
- Easy
Cons:
- Nothing but fun.
Bottom Line:
Pyramix by Gamewright is a keeper. It is a lot of fun to play both in a group as well as individually. Any game that can bring back such wonderful memories of my childhood and still bring me and my family laughs is well worth it.
Disclaimer: Pyramix by Gamewright was given to me in exchange for my honest opinion. In no way was it altered influenced. All opinions and observations were made by Lady Lilith.
If you would like to know more about Gamewright feel free to visit them:
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If you enjoyed Pyramix you might also enjoy Dodge Dice.
Have you ever played this or a similar game when you were younger?
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