What do you guys think of having a Health/Science section

[Geel_jire]

Evolution is a myth.

 

Man was created, by Allah not evolved through a bunch of random processes.

 

Echoed by Atheists and logically does not make any sense.

 

About circumcision I truly have no opinion, have never heard it calmly discussed in terms of pro's and cons, medically , religiously, every time it comes up it turns into a battle.

[NGONGE]

Bunch of nerds...

 

[Johnny B]

^ The thread is getting scientifically unscientific.

[Caano Geel]

Warrior of Light, Geel_jire, walaalo, this wasn't a question of your faith or conviction, so don't get it confused. Idil asked a question and deserved an answer, not a testimony of faith

[Mowgli]

^^ Thank you...perhaps it would be better to start off on a less controversial topic

 

just to comment on what you said. At first I came to the same conclusion as you...that both the eye and brain evolved simultaneously. But if we see sensory organs as a means of gathering information, the brain can be seen as an information processing centre...if there is no information gathered, then there is no need for the information to be proceseed.

 

The sea wasp *interesting animal* is a type of jellyfish, it has eyes, but no brain...instead the messages are sent directly to the muscles. Maybe sensory organs began to gather more and more information and then the brain most likely came as a result of this. Perhaps this animal at one point had a brain but due to selective pressure, it no longer exists...but that does not make sense as there doesn't seem to be a selective advantage to losing the brain. On the other hand, an animal living underground may lose its eyesight as there is no selective pressure to maintain it.

 

 

But moving on...I hope there will be no objections to the following questioins (immunology *relatively safe*)

 

Simply put, the immune system can be described as the body's complicated natural defense against foreign agents.

 

1. Why doesn't the immune system attack the feutus during pregnancy? Why does it not recognise it as a "parasite"?

 

2. Why doesn't the immune system of a woman illicit a reponse against sperm? Why not food? or clothes?

 

3. Commensal bacteria (doesn't cause harm) e.g. of the gut...why does it only become harmful when the hosts immune system is weak and not othertimes?

 

Questions I've always wondered about...

[ElPunto]

No need to original post.

[Caano Geel]

idil, first, i warn you, i'm no biologist, and have only studied evolution from a mechanical perspective .. when the real biologists evolve out of their caves, they will be able to give you more detailed answers than me...

 

having said that, your sea wasp case is fantastic example of a reactive mechanism, where no deliberation exists between sensing and reacting -

 

I think this tells us something about the modularity of the brain. Though a lot of resources associated with vision are shared across the brain, for example, memory and pattern identification, the core of the processing is localised, and hence specific to interpreting patterns of light. Therefore i would guess that it is this part of the brain the evolves with the eye.

 

Also, first, selective pressure - mechanically anyway- obeys a law of conservation of energy strictly, so a feature, should not consume more energy than it brings in, therefore, specialisation is a very much encouraged. This explains why reactive/autonomic system might stay that way if it is successful.

 

second, there is nothing to say that the evolution of the eye was a linear process, i.e. it started at X and developed directly to Y. The evidence from other system, i.e. bipedalism, streamlining in aquatic animals suggest that the same design (say body shape of dolphins v sharks) evolved to the same solution independently and repeatedly.

 

so, having an eye of some sort does not necessarily constitute a requirement of a vision processing brain. nor does it mean that all vision processing structures are the same/do the same or have the same parent.

 

--

 

the other questions i'll leave to the real biologists (hint hint)

[Cara.]

Hi Idil,

 

The question of the eye and the brain is really interesting, I think CG covered that pretty well. My only addition would be to point out that a "brain" is a component of the central nervous system unique to complex animals. If animals evolved from a common single-celled organism, then some sort of light-sensing organ or organelle must always have preceded the part of the brain responsible for interpreting visual stimuli. But it's possible to have a nervous system composed of motor neurons and sensory neurons for detecting and responding to sound, temperature, etc, without a visual cortex.

 

1. Why doesn't the immune system attack the feutus during pregnancy? Why does it not recognise it as a "parasite"?

 

In fact it IS useful to think of the fetus as an allograft, since many of the same principles underlying transplantation immunology apply. And as you would expect, the immune system is regulated in many ways during pregnancy:

 

1. The first line of defense for the fetus is the placenta. This organ is responsible for letting "good" stuff through (oxygen, nutrients, maternal hormones and immunoglobulins), while screening out immune cells. There are as many as 6 layers separating the fetal and maternal blood, depending on the organism.

 

2. But since the placenta itself is of fetal origin, it also has mechanisms to dampen the maternal immune system. In essence, the fetus either fools the maternal immune system (I've heard of it referred to as "sabotage"), or makes it less reactive overall by releasing certain mediators. In mice, if you somehow inhibit these molecules in a pregnant female, you get a miscarriage.

 

Not surprisingly, women are actually at increased risk of contracting infections, as well as being unable to control what was otherwise a chronic infection during pregnancy. For example, women who live in malaria endemic areas have a partial immunity to malaria. But during pregnancy this immunity decreases and if the woman is then exposed to the parasite her risk of contracting the disease increases. The same probably goes for HIV and some foodborne pathogens.

 

At the other end of the spectrum, hemolytic disease of the newborn demonstrates what happens if the maternal immune system does react against fetal red blood cells.

 

2. Why doesn't the immune system of a woman illicit a reponse against sperm? Why not food? or clothes?

 

This is where compartmentalization is key. On mucosal surfaces like the gastrointestinal and genitourinary tracts, immune responses are deliberately transient and self-limiting. Sperm injected under the skin or in the blood would elicit a response, since they are not supposed to be there. Food is more complicated, since it does eventually pass into the bloodstream. Oral tolerance is a critical mechanism by which the immune system is "taught" that food is not to be reacted against. There's actually extensive research on oral tolerance as possible treatment for autoimmune diseases and allergies (eg, if you have hayfever, actually eating the pollen you are allergic to can reduce your response to it!)

 

Again, sometimes the best way to elucidate the immune system is by considering diseases. Celiac disease is caused by an immune reaction to wheat gluten proteins. People with this disorder have to avoid foods containing gluten, not an easy thing when you consider how central wheat is in daily cooking. Food allergies are another example of an inappropriate response, and some can be incredibly deadly and rapid.

 

3. Commensal bacteria (doesn't cause harm) e.g. of the gut...why does it only become harmful when the hosts immune system is weak and not othertimes?

 

So commensal bacteria: again, compartmentalization is key. The lining of the gut keeps the good bacteria away from the immune cells, which are staring suspiciously at them on the other side Commensal bacteria also want to avoid annoying the immune system, so they signal their friendliness and/or harmlessless. In contrast, pathogens often WANT to cross over, and the very mechanisms (the proteins, genes, secreted components) they use have been flagged by the immune system as highly dangerous. The gut releases massive quantities of antibodies that bind to these pathogenic organisms while leaving the good bacteria alone. If they do somehow transverse the lining of the gut, many different immune cells on the other side make sure they regret it.

 

Yet once more we must consider what happens when things go wrong. Inflammatory bowel disease is as bad as it sounds. When the immune system gets mismanaged and attacks commensal bacteria, diarhea happens (bad pun intended). The small intestine becomes a warzone, food absorption decreases and the inflammation itself becomes very harmful.

 

The key message is immune regulation. At any one time, your body is grimly fighting off unwanted intruders, while at the same time trying to avoid friendly fire. Keeping the balance is very very important, and how the host does that is a hot area of immunology.

 

Whew. If you actually read to here you deserve a medal.

[Mowgli]

Cara InshaAllah I will come back later with a proper reply. Toleranceand regulation are at the essense of my questions....I can very well see how T cells are tightly regulated. No processed antigen, no activation, no antigen presenting cells, no activation *possible weak activation due to gamma delta T cells - but i know nothing about them* and if the apc is not displaying MHCII - nada. Natural killer cells (NK)to me do not seem to be as tightly regulated...from what i gather, they express thousands of receptors...but the most important of them are:

1- for MHC I (aka killer inihibiting receptor - KIR)

2- the other receptor recognises molecules expressed on all nucleated cells e.g. c type lectins (kiler activing receptor- KAR)

 

Nearly all cells in the body express MHC I (except for professional antigen presenting cells). KIR is needed so that the NK cell can differeciate between its own and foriegn. KAR so that it can bind anything it thinks harmful. However, say a cell comes along (own) expressing MHC I and c-type lectins and so binds both to KIR and KAR...in this case the KIR signal overrides that of KAR and so NK does not release its cytolytic enzymes to induce apoptosis.

So why don't NK cells attack macrophages, B cells (MHC II cells), since they won't bind to KIR...it should release granzymes and perforin (they have nucleus so why doesn't apoptosis occur?) - also brings me back to why not food etc

 

Is there a disease where cells do not express MHC I?

 

2. But since the placenta itself is of fetal origin, it also has mechanisms to dampen the maternal immune system. In essence, the fetus either fools the maternal immune system (I've heard of it referred to as "sabotage"), or makes it less reactive overall by releasing certain mediators.

There are several conditions in which the immune system improves during pregnancy...e.g rheumatoid arthritis (Ostensen and villiger, 2007, approx in 70% of patients, however 3 mts after gestation and in others they worsen e.g systemic lupus ery...*lol can never spell the darn word lets just call it SLE*

 

It is thought that regulatory T cells play an important role in tollerance and the education of the immune system, lakiin what exactly are they? The only thing I seem to have absorbed is that they are unique because of the expression of Foxp3 (transcription factor)

 

In mice, if you somehow inhibit these molecules in a pregnant female, you get a miscarriage.

I discussed this topic yesterday with someone who pointed me in the direction of immunogenic contraception *found to be reversible in all except for one group of seals*, inshaAllah as soon as I get references I'll share.

 

Is there a form of infertility in couples whereby the female makes antibodies against sperm, thus resulting in spontaneous abortion?

 

I'm going to stop here, it seems to have turned into an essay. greatly appreciate your contributions CG and Cara

[Cara.]

Idil, antigen presenting cells do express MHC class I (all nucleated cells do). It's just that in addition they also express MHC class II. Thus they are protected from NK cells via the same inhibitory signal somatic cells deliver.

 

Since you brought it up-- one of the ways the fetus avoids NK cells is by expressing HLA-G, which is far less polymorphic than other MHC class I loci. In that way, it avoids killing by NK cells since HLA-G can bind KIR.

 

I don't know of any disease marked by the lack of MHC.

 

Rheumatoid arthritis has an autoimmune aetiology, so that it is less severe during pregnancy confirms the effect of pregnancy on the immune system. It would be interesting to see if there are any infectious diseases with similarly improved outcomes.

 

About Tregs, your guess is as good as anyone else's. Simply characterizing them is incredibly challenging. As yet there isn't a single cell surface marker that is both exclusive to and necessarily expressed by all regulatory T cells. Foxp3 is a transcription factor, so it's not very useful for isolating cells using standard sorting techniques (except in Foxp3-GFP transgenic mice). Currently, CD25 is used but it's not expressed by all Foxp3+ Tregs, and regular effector T cells also upregulate CD25 expression after activation. Even how they work is hotly debated. They are "sexy" at the moment, so expect lots of research to come out in the next little while.

[Paragon]

Err, which cells are responsible for my over-consumption of spicy tea, might I ask ye aspiring scientists?

[ElPunto]

^Science class is in session folks. CG and Cara are the co-professors. Come all ye in need of knowledge. Limited time offer.

[Cara.]

^Don't give me any lip or it's detention for you.

 

Isseh, those are fundamentally important cells and must be satisfied at all times. Trying to trick them with pale substitutes (microwaved tea, coffee) leads to severe mental consequences.

 

Casiriye anyone?

[Paragon]

^^Yes, please. Though its dark over here.

 

Anyway, maxaad ka sheegtay microwaved tea? what are the risks?

[Cara.]

Aside from the psychological trauma? Well, you're also more likely to burn your mouth. Water sometimes doesn't boil in the microwave, even though it is actually past the boiling point. This can be really dangerous. Check out this video