Click to tweet: http://clicktotweet.com/sbvJD . The endocrine system, along with its hormones, is one of three systems particularly closely associated with activating, controlling and integrating. As usual with IGCSE and GCSE secondary school-level stuff, we're expected to oversimplify and tell half-truths, so that's what i'm doing here. Examples of what i've not mentioned include the other organs that produce hormones, such as the stomach, kidneys and heart, various hormones produced by the body generally such as the eicosanoids, and several hormones produced by the glands mentioned that i've not gone into.
A hormone is a substance produced by an organ in the body which has an effect at tissues distant from that organ. They are produced by "ductless glands", which are distinct from glands such as sweat, breasts (mammary) and salivary, which empty their secretions into the external environment because instead they release them into the bloodstream. Several of the glands are really several combined organs rather than simple glands with one function, and they may or may not occur in pairs.
The gonads are part of the reproductive system and maintain fertility and secondary sexual characteristics. It's been fairly common for medical texts to regard the male body as standard and only to refer to the female body where there are significant differences linked directly to reproduction. I've chosen not to do this here, so you've just got this ugly hairy bloke instead. Both kinds of gonads secrete testosterone and oestrogen (estrogen) but in different quantities relative to each other. Progesterone maintains pregnancy and oestrogen the secondary sexual characteristics as well as leading to the changes of puberty and sexual differentiation in the foetus towards the female pole (though not all the way - the most feminine individuals are genetically male), and testosterone does the opposite. Masculinity is determined by the addition of testosterone, which causes deviation from femininity, which is the "norm" for the human body. All these hormones are steroidal.
The adrenals are a pair of glands sitting atop the kidneys and are in fact each a pair of glands: the cortex, which is on the outside, and the medulla in the centres. The medulla secretes the well-known flight or fight hormone adrenalin, also known as epinephrine, which triggers the fear response. It's also, like some other hormones, a neurotransmitter found in the nervous system, which is also derived from the same types of cells as endocrine glands. Adrenalin is an amine - it has an NH2 group on its molecule. The outer cortex is responsible for the steroidal hormones including the one most often referred to as "steroids", which is anti-inflammatory and also enables one to deal with longer term stress in a broad sense which includes disease and climatic extremes as well as the emotional type. These are the corticosteroids.
This is annoying. Here's my video:
Slightly above and forward of the adrenals is the single pancreas, which is also the source of most digestive enzymes. The pancreas secretes insulin (which i talk about here: http://www.youtube.com/watch?v=Qp7JUZaVKtg ) and also glucagon and gastrin. All of them are involved in the movement of nutrients. Insulin is a peptide hormone.
The thymus is over the heart and calcified in adults. Its original role is the activation of T killer cells but it stops working during childhood.
The thyroid and parathyroids are in front of the throat superior to the breast bone or sternum and i mention the former here: http://www.youtube.com/watch?v=NW6PYU02XP0 . Like the adrenals, this is a case of two glands in the same place but unlike the adrenals they're considered to be different organs. The thyroid secretes and stores amine hormones which are in fact unusually-structured amino acids containing iodine which basically regulate how fast processes take place in the body. There are several thyroid hormones which also act as a circulating store of thyroids, including triiodothyronine, T2, and thyroxin, which is the most active.
The head contains two endocrine glands. The pituitary is at the centre of the head and has a front and a back part. It mainly secretes peptide hormones, including growth hormone and various hormones which regulate the other endocrine glands, which it is itself stimulated to secrete by the hypothalamus, part of the brain just above it which secretes its own hormones and is sensitive to changes in the levels of other hormones in the bloodstream. The back of the pituitary secretes antidiuretic hormone, which stops the kidneys from excreting too much water, and oxytocin, which is connected to labour and breastfeeding.
Finally there is the pineal gland, so called because it looks like a pine cone. This is a former eye, but is buried deep inside the head. The pineal, like the thymus, is often calcified in adults and is rather mysterious, although it seems to regulate wake-sleep cycles and secretes melatonin.
This is annoying. YouTube wouldn't accept my tags or the length of my doobley-do, or my thumbnail, for no apparent reason. For what it's worth, here's my thumbnail as a JPEG:
This is not a particularly good thumbnail but it's better than nothing. I may repost later to see if YouTube has mended its ways.
On the subject of YouTube, the creator academy course is now over and i'm none the wiser as to how i was supposed to participate, so that's that really isn't it? I've probably blown it in some way but to be honest i don't think anything can save this channel from obscurity, which is a bit of a bummer considering how much work i've put into it, but anyway.
Slightly more positively, yesterday's video on logical positivism and post-structuralism, which has understandably been misunderstood, provoked a lot of debate and interest. Here it is if you've missed it:
Click to tweet: http://clicktotweet.com/mw7AQ . One of the frustrating things about debates concerning religion is the naive level of discussion that passes for intellectual discussion. This is not an elitist view - the normal philosophical basis of argument about religion is based on completely different principles than the terms of debate assumed by both Dennett-style atheists and fundamentalists describing themselves as Christian. Here, i'm presenting two ways of looking at it familiar to people outside the popular debate which are unaccountably ignored by those within it. I happen to disagree strongly with both, but the point i'm making is that people don't even look at the questions in interesting ways.
Logical positivism is an outmoded view in analytical philosophy which claims that statements are cognitively meaningful only insofar as they express analytic truths, are axiomatic or empirically verifiable. Wittgenstein tends to have a lot in common with its views, though he's not himself logically positivist. In terms of logical positivism, a statement regarding religion on either side is meaningless, i.e. nonsense. It may be grammatical and include only words in the dictionary, but so does "colourless green ideas sleep furiously". Therefore, a proposition such as "God does not exist" or "God exists" is simply meaningless, not false, or true. We can't argue about whether colourless green ideas sleep furiously or not. I suppose there's a nod to this in the invisible pink unicorn.
The other view, and i would maintain this is only another example and there are plenty more where these came from, is poststructuralism. Religion and scientific realism are both totalising discourses - grand narratives which attempt to give accounts of everything. The terms within them are defined by other terms and there is eventually a circle. It's impossible to step out of the system, choose between the systems or construct a separate system which is more objective or has a higher standard of truth. Therefore, once again the debate is futile and naive.
Tags: atheism, debate, religion, christianity, god, logical positivism, naive, theism, wittgenstein, meaningless, nonsense, post-structuralism, structuralism, grand narratives, totalising discourse, meaning, definition, philosophy, invisible pink unicorn,
This video was adversely affected by pressure of time. It was originally supposed to be a review of Don Cuppitt's horizontal theology but i ended up only having about half an hour to do the whole thing, so instead of that i chose to summarise two philosophical positions which clearly cut across the oddly one-dimensional discussion taking place between the two groups of people i mention here. This proved to be confusing because it was interpreted as my advocacy of the positions i mention whereas my intention was really to illustrate the narrowness and, in my view, naivete of the current popular debate, which strikes me as about jejune celebrity positions rather than the ideas, and the argument frequently seems to be about the fierceness and aggression rather than dialogue. So, i uploaded this. The fact that i disagree with both positions strongly helps my point: i decided to attempt to describe them fairly because there's too little of that around. The result was that it was misunderstood, i think.
Tomorrow, i might just make a video about breasts.