/sci/ - Science & Math

Now, as you know, fat is bad for you. It builds up in your arteries, and that's not good. If it builds up in the coronary arteries, that's fucking bad. As blood flows through, the fat could end up partially blocking blood flow to the muscles of the heart. This is a condition called angina pectoris. This is normally not fatal, and the heart can recover from it. However, this means that a heart attack (aka myocardial infarction (myocardium=muscle layer of heart, infarction=forming of an infarct (area of dead tissue))) is right around the corner. In a heart attack, the blood flow is completely blocked, so no blood gets through. This ends up killing muscle cells, so you really don't recover from this. This is why a heart attack is so bad, because it cripples your heart, long after it happens (assuming you live).

Also, you guys probably know that a heart attack is associated with pain in the shoulder and left arm. However, the arm isn't there. This is called referred pain. Basically, since nerves from the shoulder and left arm meet with the heart on the way to the brain, the brain sometimes thinks the pain is coming from those areas.

I'll talk a little about the defibrillator.

So, when I said that, did you think "Oh, that's used if someone is flat-lining"? If so, you're wrong. That's all Hollywood. CPR, I believe, is the only helpful thing in that case. So, when is a defibrillator used? Well, after/during a heart attack, the heart is stopped. The SA (sinoatrial) node is the natural pacemaker of the heart, which sends out signals to the AV (atrioventricular) node, which then go to Purkinje fibers. These impulses control the rhythm of the heart.

If the heart is stopped, another heart cell can start contracting, and start it's own rhythm, not necessarily the one the heart needs to work. The heart becomes a mess of random contractions, and nothing gets done. This is very, very fucking bad. This is arrhythmia. This is fixed by, you guessed it, the defibrillator. As you know, this has a very fucking strong voltage. The reason it is not used if the patient has flat-lined is because of how it works. The defibrillator sends out a shock that overrides the heart entirely, stopping it. See why using it on a flat-lining patient is stupid?

So, the defibrillator shocks the heart, and it stops. The reason this is done is to help the SA node. Before the shock, it has no fucking control over the heart. If everything is stopped, it has a chance to take control again and establish a normal rhythm. Multiple shocks may be required for it to get back in control. Think of it as the SA node fighting a battle against a crazed army, and the defibrillator gives everyone shell shock, hopefully allowing the SA node to recover the fastest.

I'll talk a little bit about the structure of the kidneys. They're fucking complicated.

The outside is called the renal capsule. Inside of it, the kidney can divided into two sections: the renal cortex and the renal medulla. The renal cortex contains some parts of the nephrons (tiny, tiny structures in the kidney that filter the blood). The renal medulla contains the rest of it. Near where the renal artery enters and the renal vein and ureter leave (called the renal hilum) is a space inside the kidney called the renal pelvis. Wastes collect here before going down to the ureter and the bladder. Blood flow to the kidneys is rather odd. Blood goes through the renal artery, then the interlobar artery, then the arcuate artery, then the interlobular artery, then the afferent arteriole and into the glomerulus (part of the nephron). Blood leaves though the efferent arteriole. Reverse the order of the arteries and replace "artery" with "vein" for the path out. Wastes, when formed fromt the nephrons, goes down the renal pyramid (a structure, of which there are more than one, in the kidney) and into the minor calyces (singular: calyx), which empty into the major calyces, which empty in the renal pelvis, which becomes the ureter.

As for how the nephron works, well, that's rather complicated without diagrams. Plus, it's something I struggled with.

I'll talk about blood flow a little bit.

If you're like me, you may have wondered, "Hey, what makes some blood flow here and not there?" Well, to be honest, it's simply the fact that there is a lot of blood to go around, so some of it will go up the arteries that branch off from the aorta due to the pressure from the heart (Note: There may be another reason. We didn't talk about this, so this is the most logical conclusion I come up with. Could someone either confirm this or explain what really happens?) For blood returning to the heart via veins, it's a bit more complicated. While blood from the head and upper areas can return via gravity. for blood from the legs and arms, that's not an option. Hence, veins (especially in the legs) have flaps in them. These flaps are shaped a bit like a "w". Blood from below pushes them open, and then they close when the blood begins to fall again. This allows the blood to work it's way up to the heart. With capillaries, blood flows through them until the cells supplied by them no longer need oxygen/have no more wastes that need removing. The cells send a signal to the opening of the capillary, which has a band of smooth muscle around it called the precapillary sphincter. It closes when the signal is received, preventing blood from going down there, thus forcing blood to go down another path.

Oh god, if all my school assignments and tasks and information were written like you do I would be an A student. Amazing for keeping interested.

Is this a meme now?

I completely support OP's idea since I missed the first thread he spoke of.

Let's talk about muscles.

Muscle is a broad term for three types of tissue: Skeletal (no points for guessing where this is), smooth, and cardiac (same). The different tissues are similar in some ways and different in others. Off the top of my head, skeletal muscle is striated (I'll get to that later), not branched, and under voluntary control. Smooth muscle is not striated (that's why it's "smooth"), not branched, and under involuntary control. Cardiac muscle is striated, branched (cells split into two parts sometimes and meet with other branches, forming things called intercalated disks between them), and under involuntary control. I do know there are other things I could say about them, but I forget what.

>>1233007
Just a good idea. It needs to be done more though.

Anyway, skeletal muscle is what most people think of when someone says muscle, and is attached to the skeleton via tendons and to each other via ligaments. Skeletal muscles typically work in pairs. Muscles can only pull via contraction, not push. For every flexing muscle, there needs to be an extending muscle to help straighten it out again (for the record, flex=reduce the angle between two parts of the body, extend=increase the angle). They are antagonists, and when one contracts the other relaxes. The best example is the biceps brachii (it's technical name, "two-headed muscle of the arm") goes from (has it's origins at) the shoulder blade (the scapula) at two different parts to the radius (a bone in the forearm, always on the side of the thumb (it rotates in the arm as you flip between the back of the hand and the palm)), where it has it's insertion. Muscles always contract, pulling the insertion to the origin (in this case, the radius (and thus the forearm) to the upper arm). The triceps brachii ("three-headed muscle of the arm") comes from the scapula and two places on the humerus (upper arm bone) and down to the ulna (other bone in the forearm, stays on pinky side and doesn't rotate). When the triceps contacts, it pulls on part of the ulna in a way that it straightens out (I can't think of how to explain it). All muscles work like this, sometimes in pairs, sometimes not. Almost all muscles used for flexing are found on the front of the body, and almost all the muscles used in extension are on the back. The exception are the thighs, with the quadriceps femoris ("four-headed muscle of the femur"), which are in the front and extended the knee, and the hamstrings, which flex and are in the back.

Now, smooth muscle and cardiac muscle work in slightly different ways. Smooth muscle is found primarily in the digestive tract, pushing food through involuntarily. Smooth muscle contracts slightly differently, since they're organized differently (when I get to what striated means, it'll make more sense). Cardiac muscle is found, no surprise, in the heart. It contracts just like skeletal muscle, except it's under the control of the SA node, or whatever is acting as the pacemaker.

How do the muscles contract? It does this through two tiny filaments in the cells, actin and myosin. In skeletal and cardiac muscle, these are arranged in such a way that lines are formed on the muscle, making it look striated. Smooth muscle is not organized in this way. The way skeletal and cardiac muscle are organized is with a sarcomere. The sarcomere is the part of the muscle that contracts. It consists of alternating horizontal bands of actin and myosin.

I gave up talking about muscles at this point. It's too complicated for me to remember right now.

I'll talk about chiral compounds, then. I know it took me a while to understand.

The picture is a generic representation of an amino acid, with each "hand" representing a stereoisomer of the amino acid (Fun fact: Chirality roughly means handedness). The left hand, while being identical in terms of what's bonded to what to the right hand, can't match up exactly with it. You may think, "Well, rotate it 180 degrees!" However, the carbonyl (COOH) group would be on the bottom, with the amino group (NH2) on top. You may then say, "Well, rotate it on it's long axis!" However, while everything would line up, where the right hand is pointing up, the left hand would be pointing down, and vice versa. No matter how you try, the left hand can't look exactly like the right hand. If you do make it look like the right hand, then it's not chiral. It is achiral.

Chirality is important, because many medicines and natural chemicals react differently depending on how the molecule is arranged in space. For example, Thalidomide was a drug used in the 50s for morning sickness for pregnant women. It had two enantiomers (ways of being arranged in space), which are called R and S enantiomers (how the naming works is something I don't get). The R enantiomer works wonders against morning sickness. However, the S enantiomer fucks up unborn babies. And since it's meant to be taken when you're pregnant...yeah. Thalidomide was sold as a mix of both enantiomers (they didn't know that at the time). However, it turns out that the R enantiomer becomes the S enantiomer in the body. So there's no way around it.

See how chirality is important?

Last of copypasta.

>>1233045
Forgot a pic, hurr.

>>1233046
Any help for figuring out if it's R or S?

I used to know but have since forgotten.

nice copypasta

>>1233060
"it" being any...er...4-way bond, shit, I don't know the names of these things anymore.

OP here, I'll talk about the Gambler's Fallacy.

Simply put, this is assuming that the odds have changed when, in fact, they have not. For example, let's say you flip a coin 10 times and get heads each time. According to the fallacy, you might think, "Gee, considering how it's a 50/50 chance of each, I should be getting tails soon". However, that is not the case. Each coin flip is independent of the next. So, the results of the previous flip have nothing to do with the next flip. Similarly, let's say you have a deck of cards, and draw a card at random, hoping you get a jack. If you replace the card, then the odds will not change, since the probability for each draw does not change. Now, if you drew a card and didn't replace it, the odds would be different, and you'd be right in assuming you have a higher chance of drawing a jack next time. With coin flips, this never happens. So, flipping a coin and getting 10 heads and a tails is just as likely as 11 heads. Any combination of 11 flips is just as likely as the next, since each flip can go one of two ways.

Use this knowledge to your advantage. In roulette, don't assume that it must be red next time, just because it's been black for a while. While it's true that if an event is repeated enough, the results line up with probabilities (that is, coin flips will eventually be 50/50 with a large, large amount of flips), this does not hold true in the short term.

>>1233060
>>1233075
I still have trouble with that.

>>1233058
All the copypasta is stuff I wrote. Reread the first post.

>>1233090
>getting heads twice in a row is as likely as getting heads 10,000 times in a row

>>1233090
this one pisses me off. yes, each coin flip is independent of the next one, but the chances of getting a string of 5 of either heads or tails is less likely than a string of 6 and more likely than a string of 4.

>>1233099
err, more likely than a string of 6 and less likely than a string of 4. i mixed that up.

>>1233099
>>1233102
Shit, did I mess that up?

Sorry.

Can you point out which part is incorrect, so I can fix it in case I remake the thread again?

>>1232990
>>1232990

Renal filtration really isn't complicated; you did a decent job of describing blood flow through the renal system but there's absolutely no physiology and barely any anatomy in your post.

>>1233135
Well, it was for me. Also, it doesn't help that it was pretty much squeezed into the end of the year with the respiratory system.

Care to elaborate on it? You could probably do a better job than I could.

Bump

Don't let a good thread die, /sci/.

Would you rather fight trolls than have a decent thread, /sci/?

Well shit, OP. You're good.

Fuck it, I'm just gonna give up this time.

Thread looks promising, OP.

>>1233098
And yet it has never happened

So I guess that picture of a removed heart is now the official /sci/ cue for "poast ur knowledges".

For example, a ketone can be reduced to the methylene level by either the Mozingo reaction, the Wolff-Kishner reaction, or the Clemmensen reduction.

THE MOAR YOU KNOW

I love you OP! I didn't get a chance to read the other thread but I kept it up and then my browser crashed : /

The heart, at rest, spends about one third of the time in systole (contraction of the muscular wall of the heart), and two thirds of the time in diastole (at rest). the systolic phase does not increase in efficiency so the only way to increase cardiac output is to reduce the time spent in diastole. the problem with this is that the heart tissue doesn't get perfused with blood during systole, so when your heart rate goes up not only does your heart need more energy/oxygen, but its ability to get it is reduced. this is why they have upper limits on a safe heart rate for exercise.

>>1234998
Sure, why not.

non-OP here

come on guys, this thread is not as cancerous as that magnet bullshit, lets get it going

>>1235054

Last time I tried to recreate this thread I got sage.

>>1233060
The R configuration, meaning the hierarchy of the atoms bonded to the chiral carbon atom move in clockwise direction.
The S configuration, in counterclockwise.
Now, how can we see which atoms bonded to the stereogenic carbon atom are of 'higher order' than other atoms? It's simple convention.
As the carbon atom needs to be in a sp3 configuration (or a the bonds look like a tetrahedron), you put the least important atom bonded to the C atom, behind the C atom so you will have the 3 most important ligands to wory about. The least important atom is mostly the H. To see which are increasingly more important, you view the atom number: C<N<O<...
That's the basics.
If you want longer ligands such as a carbonchain, or a carboxyl ligand, it goes a little different. Say, we have a chiral carbon center with 1 H, 1 O, and 2 pentyls, but on one of the pentyls there is an O and on the other, there is a Cl. The pentyl with the Cl> The pentyl with the O, since Cl>O. It's kind of like when you alphabetise a list of names and 2 people start with the same letter, you gotta look for the first difference.
If you have a stereogenic centre bonded to a C, double bonded with, for instance, an O, you have to 'undouble' the double bond, meaning each bond that is extra to an atom, counts as an extra bond to that atom. The picture will make it clear to you (or not).

It's a good thread, but for God's sake, don't repost all your shit, it's just annoying.

>>1235072
I too, wanted to say this. An information thread isn't really informational if everything gets copied in the same kind of thread everytime. There should only be original content, since, I think, the /sci/ userbase isn't that large (I mean, this board is FUCKING SLOW)

All right, seeing as we're talking about chirality up in this motherfucker: (and also while I'm here >>1235068 you should make it clear that the order of priority goes on atomic number)


Chirality can be transmitted between centres throughout a reaction. Chirality cannot be generated from achiral starting materials. This is how an enzyme can produce only one enantiomer (handedness) from a substrate with no inherent chirality: the enzyme itself is chiral, and imposes its handedness on the reactant.

This is important behaviour to consider in the context of manufacturing pharmaceuticals, which must be registered as single enantiomers. With the right set-up, it is often possible to induce chiral control into your reaction by including some chiral compound: aldol reactions can be rendered enantioselective by reaction via a proline imine, for example.

Meh... if people want to know specific things about org chem I'll have a crack at them. Maybe.

>>1235023

What is the safe limit? Also, does this mean there is a such thing as too much cardio workout?

>>1232971

ＷＷＷ._ａＮOn_+_Ｃ_-_c_+_TAlＫ_.Ｓｅ aebl gv mkyt vtmhz zelnuf g yuaemrk fddbtiumxf w

>>1233117
You didn't mess that up, gay hitler is just a faggot.

In a scenario where the number of possible outcomes does not change, past results have no effect on future results. In that case probability is a statement ONLY on the future.

Absolutely you are less likely to get a series of 6 heads in a row than a series of 4, but that has no effect on the probability of getting heads or tails on each individual flip. The decrease in probability from 4 in a row to 6 in a row is a result of compounding 50% probabilities, not a result of changing probability with each flip. Once the coin has been flipped, the outcome is decided and the next step is totally independent.

Furthermore, the idea that over huge samples you will get an outcome of 50/50 is not correct. Over large collections of samples you will trend toward an AVERAGE of 50/50 in the form of a Gaussian distribution.

Lets talk about the prisoner's dilemma.

The prisoner's dilemma is a nickname for a very specific scenario in which two things interact. It is a non-zero sum game of imperfect information - that is, one player's loss isn't necessarily the other player's gain, and both players reveal their moves simultaneously. Like all games, for each combination of moves there is an outcome, and each outcome consists of a gain or loss for each player. The prisoner's dilemma is very simple, because each player can select one of two moves: cooperate (C), or defect (D). Because each player has two moves, there are four possible outcomes which are detailed below:

CC - Both players receive some payoff R.
CD and DC - The cooperating player receives some payoff S, where the defecting player receives some payoff T.
DD - Both players receive some payoff P.

If this is a prisoner's dilemma, it must be so that T > R > P > S, and R > (T+S)/2. These conditions ensure that there is incentive for defection, and that alternating defection and cooperation does not out-pay consistent cooperation in the case of a repeated game.

What makes the prisoner's dilemma interesting is that the normative decision, as would be made by a self-interested player, is to always defect. Lets say that you are player 1. If player 2 cooperates, you would do best to defect as you would receive maximum payoff. If player 2 defects, you would do best to defect as P > S. However, if both players act normatively and select the defection option, they both receive a payoff lesser than what they could have received if they cooperated.

The prisoner's dilemma has seen an unbelievable amount of research since the 1980s. One of it's main proponents, Robert Axelrod (B.S. mathematics, PhD political science), has called it "the e.coli of social psychology;" The prisoner's dilemma has a place in any field of study that's concerned with the interaction between two bodies.

>>1235171
A very particular scenario of the prisoner's dilemma is one in which it's iterated, or repeated. In the 80s, Robert Axelrod held a "tournament" in which many individuals were invited to submit a strategy for playing in a repeated prisoner's dilemma, and the strategies would be pitted against one another to determine which is most successful. Many of these strategies were complex, some involving bayesian predictions for the opponent's next move. However, the simplest of all sixteen submitted strategies won: tit-for-tat. It won again when the tournament was held a few years later, beating out around sixty other strategies.

Tit for tat always cooperates on the first round, and then always does what the opponent did in the most recent round. It is often called nice, as it always cooperates on round one, retaliatory, as it punishes defection by defecting in the following round, and forgiving, as it immediately returns any cooperation given in the previous round.

Now, much of the research on the abstract prisoner's dilemma was that which is concerned with hypothetical population dynamics. Say that there exists a hypothetical population in which successful strategies increase in frequency. In our hypothetical population, every member is entirely self-interested and always defects. If tit for tat is placed in this environment, it can increase in frequency. Once it has increased sufficiently, it will resist invasion of any defective strategy. For this reason, tit for tat is very robust, and cannot be outperformed by any mutant strategy (a mutant strategy is any strategy that is not degenerate).

>>1235261

Hmm, I see where I went wrong now. I always do the "good" choice then when I get burned I never forgive.

I'll try to forgive from now on. Thanks /sci/