Tri-2, Wk11, Day 111 - Wednesday

Here we have the physiology "bible" - Textbook of Medical Physiology and another, slightly easier reading physiology book by Tortora.

Tonight is all about the physio - it's review time - crunch time. I'd say I know the material fairly well but, the test tomorrow is 60 questions over 50 minutes thus, we have 50 seconds to answer each question. So - simply knowing the material isn't quite enough for a good grade but, it's definitely a start.

btw - GRADE UPDATE - I got two quizzes back from Neuroanatomy and Aced them both - 100% on the take home and a 95% on the in class quiz. The Microbiology test went fairly well today also - I got a raw score of 34/50 which seems to have compared favorably with a few of the classmates I've chatted with. I needed it. After the curve I'm guessing that will end up being a B. The Micro grade is actually about a 50% improvement over my previous first couple test. Anyway ...I need to get to physio so ...here's all about the heart

incidentally - my brother emailed me a bit of a question earlier today and a part of the answer I gave him pertaining to the heart was this ... 40 billion beats of the heart is equivelant to the number of beats in the average lifespan of 16,000 people - I don't remember the number of times a heart beats per year but I remember that tid bit ... (it was actually a bit of an economic question but I had to put that physio spin in at the end) ;)

Let's start at the beginning - about 21 days after an egg is fertilized - that's about when the heart gets its start ...maybe that's going too far back but, while the heart is in a fetus there is an opening between the right and left atrium known as the foramen ovale. When the heart is all grown up that shunt of an openening closes and leaves a depression in the atria known then as the fossa ovalis. Let it be known throughout the land that, henceforth, holes shall be known as foramens and depressions shall be known as fossa. And ...that's pretty much how it is in the human body. There is also a hole in the skull known as the foramen ovale that a cranial nerve passes through but, back to the heart. Also, when a fetus there is a duct connecting the pulmonary trunk with the aorta known as the ductus arteriousus. Again, when the heart is grown up then that ductus is no longer used (blood HAS to go throught the lungs after birth) and like everything else in the body we once again come upon the adage - Use It Or Lose It. Since the ductus arteriousus stops being used as a blood vessel it ends up atrophying into a ligament known in the grown up heart as the Ligamentum arteriousum.

So - baby is born - butt is slapped (by the way - I believe the S5 dermatome is right on the bullseye (the anus)) and heart starts to ideally function the way it should -

Let's get to know the heart. To the North, we have Atriums - to the South, Ventricles. and each has a right and left side. The right atrium is the portion of the heart that receives blood from the rest of the body, the systemic cardiovascular system. There are three veins which return blood to the right atrium of the heart, they are, the superior vena cava, inferior vena cava and the coronary sinus. The coronary sinus doesn't get as much press as the vena cava but, the heart needs blood just like any other organ in the body and the nutrients in the blood aren't in the chambers of the heart long enough to be able to diffuse into the heart muscles (or myocardium) So - the heart has it's own network of blood vessels known as the coronary or cardiac ciculation. The coronary arteries branch out and down from the ascending aorta and cradle the heart in a network of arteries, like a life giving hand, they surround the heart and give it everything it needs to chug right along for up to a century!

The back wall of the right atrium is smooth but the anterior wall of that chamber is rough and covered with a muscle known as pectinate muscle. Between the right and left atrium is a partition (you know, the one that had the hole in it) it's called the interatrial septum. There's only one way to get out of the right atrium and that's through a valve which leads to the right ventricle. That valve is known as the Tricuspid Valve. We may also refer to it as the right atrioventricular valve. Notice, in that name (atrioventricular) the first part of the name has atrium in it and the second part of the name as ventricle in it. Just knock out a few letters and connect the two halves with an 'o' and we have atrioventricular. If we don't designate right or left we may say atrivoventricular or AV valves to generally refer to the valves which lead from the atriums to the ventricles.

Moving down into the right ventricle, we notice the heart of the wall is a bit thicker, on the order of 5-6 mm or about two tenths of an inch thick. This ventricle forms most of the anterior surface of the heart. Things get a little rough in the ventricle and the wall contains a series of ridges known as the trabeculae carneae. Emminating from a portion of the trabeculae carneae are muscles called the papillary muscles. The papillary muscles are connected to the tricuspid valve by tendon like cords known as the chordae tendineae. Now, here is one of those backwards things ....you might think that when the papillary muscles contract that those muscles would shorten and open the valves but, the reality is just the opposite - when those muscles contract - the tricuspid valves CLOSE. ...and that's pretty important. ...

The Right Ventricle pumps the old deoxygenated blood to the lungs via tha pulmonary trunk and the blood returns all fresh and clean like via four pulmonary veins - two from the right lung and two from the left lung.

OK - so that finishes up some of the anatomy for the right heart - we've sort of got two pumpers in our bodies. The right side is the pumper for the pulmonary circulatory system and the left pump is the big dog - it's the pumper for the entire rest of the body.

I need to pick up the pace here or just get back to my formal studying - I was thinking I could outline the material for our test here but I've barely scratched the surface.

Here's something interesting to think about regarding the heart sounds. Recall from a previous blog that the first heart sound (S1) we hear is when the atrioventricular valves close and the 2nd heart sound (S2).

Now, think of the sounds made when opening or closing a door. You aren't going to get much sound from opening a door but you can get a pretty good sound from closing the door. The valves are the same way - not much sound when they're opened but enough cavitation when they close that we can hear 'em! :)

Guyton's get's pretty technical, right down to the decibel when it comes to hearing sounds - murmurs and mitral valve regurge and things like that.

I need to work on the leads for an ECG. Heck - maybe I can learn a bit here by talking it out. Looks like the Tortora physiology book isn't going to cut it for this topic and we'll have to resort to the bible of physiology - GUYTONs - Ch11 - The Normal Electrocardiogram -

The basic concept is simply enough. When cardiac impulses travel through the heart a small portion of that current spreads into adjacent tissues. If electrodes are placed on the skin on opposite sides of the heart then electrical potentials generated by the current can be recorded and that recording is known as an electrocardiogram. I have to know a bit about where three main leads are placed on the body ...

OK, let's say the heart has a negative charge on the inside and there's a positive charge on the outside. When we depolarize the heart muscle, those roles change - the inside becomes positive and the outside negative ...a graph will move to the positive on a piece of paper as the heart is being depolarized and when the entire heart muscle is depolarized the line on the graph will return back to zero becaue when things are all positive on one side and all negative on the other then we have zero action potential.

When the heart goes back from being neg on the outside and pos on the inside (a depolarized state) then the graph will read negative and come back to zero once the depolarization is complete.

Let's talk about that ventricular muscle again - the left one. btw - the left ventricle is MUCH thicker and stronger than the right ventricle. It has to push blood through the entire body which offers much more resistance then simply pushing blood through the lungs like the right ventricle. While the right ventricle is only about 2/10ths of an inch - the left ventricle is about 1/2 inch on average. Meaty!

anyway ...The P wave occurs at teh beginning of contraction of the atria and the QRS complex of waves occurs at the beginning of contraction of the ventricles - the ventricles remain contracted until after repolarization, that is, until after the T wave. Repolarization of the atria is known as the atrial T wave but, as mentioned previously, it's recording tends to be obscured by the much larger QRS complex.

...3 a.m. update - physio test is a mere 5 hours & 15 minutes away - I'm probably not going to sleep since there are still a few things I need to get down. However, if I'm not going to sleep at all then I need to make sure I'm awake, alive and vibrant by test time. It's only 5 hours - no big deal.

I need to know which ions flow into and out of the heart at various stages and I still need to get a grasp on the Leads. but, i have learned about the Dicrotic wave produced during isovolumetric relaxation when the aortic semilunar valve closes and there is a slight rebound of pressure in the aorta so, I've got that going for me. :)

I tell ya - if I get anything less than a B on this test, I'll be horrified. ...3:21 a.m. ...OK - let's learn -

Flow of Current Around the Heart During the Cardiac Cycle

Recording Electrical Potentials from a Partially Depolarized Mass of Syncytial Cardiac Muscle:

OK - I understand instantaneous potentials on cardiac muscle - I recall the flow is from neg to positive. So, for a positive reading we must flow out of the negative lead, into a negative medium, over to a positive medium where a positive lead is located so the circuit can be completed back to the positive lead - electrons which flow in this direction will have a positive reading. - the converse is likewise and gives a negative reading.

before stimulation; all the exteriors of the muscle cells are positive and the interiors are negative.

As soon as an area of cardiac syncytium becomes depolarized, negative charges leak to the outside of the depolarized muscle fibers, making this part of the surface electronegative.

again - A meter connected with its negative terminal on the area of depolarization and its positive terminal on one of the still polarized areas records positively.

4:25 a.m. -

Flow of Electrical Currents in the Chest Around the Heart

...one finds the average current flow occurs with negativity toward the base of the heart and with positivity toward the apex. This is during depolarization.

depolarization spreads from the endocardial surface outward through the ventricular myocardium then, immediately before depolarization has completed its course throught the ventricles, the average direction of current flow reverses for about 0.01 second, flowing from the ventricular apex toward the base, because the last part of the heart to become depolarized is the outer walls of the ventricles near the base of the heart.

Electrocardiographic Leads

Three Bipolar Limb Leads

standard bipolar limb leads -

a lead is not a single wire connecting from the body but a combination of two wires and their electrodes to make a complete circuit between the body adn the electrocardiograph.

Lead I. ...the negative terminal of the ECG is connected to the right arm and the positive terminal to the left arm.

Lead II. ...the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left leg. Therefore, when the right arm is negative with respect to the left leg, the ECG records positively.

Lead III. ..the negative terminal of the ECG is connected to the left arm and the positiver terminal to the left leg. This means that the electrocardiograph records positively when the left arm is negative with respect to the left leg.

Einthoven's Triangle.

Einthoven's Law. ...states that if the electrical potentials of any two of the three bipolar limb ECG leads are known at any given instant, the third one can be determined mathematically by simply summing the first two ((but note that the positive and negative signs of the different leads must be observed when making this summation).

5 a.m. - testing in 3 hr 15 min - I WILL stay awake, vibrant, alert & happy :)

well ...I dont' quite understand all this. I need to get back to practicing my graphs which is a big thing I'll use on the test. - gotta have 'em down and be able to draw them very quickly and accurately.

Shower - maybe stop by Mc D's for an egg Mc Muffin - going for the protein - move blood sugar levels up - pound one more pot of coffee - stimulate the sympathetic nervous system - release epi and noripinephrine ...or maybe I should just inhibit the vegus nerve a little bit .... naa, too much work (and additional thinking of exactly how to do it)

signing off - wish me luck! :)