Biological complexity: hormones from all parts run life (Introduction)

by David Turell , Tuesday, February 19, 2019, 23:10 (2104 days ago) @ David Turell

Recent research reveals a huge variety of different parts of living organisms produce an enormous number if different hormones so every part communicates with all the other parts through the circulatory system:

https://aeon.co/essays/the-revolutionary-idea-revealing-the-bodys-hormonal-democracy?ut...

"Karsenty and others eventually confirmed that bones secrete hormones essential for an animal’s health. And with that finding, the skeleton joined a growing list of tissues shown to participate in a body-wide conversation between organs. The traditional concept of the endocrine system as a second-command system working in tandem with the nervous system – and largely directed by the brain – is being replaced with a more autonomous view of interorgan communication, one in which most, if not all, organs have a voice. Grasping the logic of a control system in which the body’s organs are both the targets of hormonal commands and the source of them is still only beginning, but the clinical implications are sure to be profound.

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"The concept of target tissues was important. There were the endocrine organs – most of them glandular tissues, whose primary function was evidently to make and secrete things – and there were the organs on which hormones acted. Textbook depictions showed, and often still do, the endocrine system as a handful of glands plus the gonads: an archipelago of hormone-making islands dotted about the body.

"But the list of hormones never stopped growing. And neither did the list of tissues that made them. Certain hormones long known to regulate blood flow, gut absorption and blood-cell production turned out to be coming from the kidney. The liver was shown to make and dispatch hormones. And secretin became only one of a number of circulating signals emanating from the digestive system.

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" Leptin’s ability to make mice eat less sparked massive interest in somehow harnessing its biology to create drugs that did likewise for humans – a goal that remains still, for a variety reasons, unfilled.

"But as the quest for an appetite-quenching drug gathered pace by the turn of the millennium, Karsenty was looking at other functions of leptin. The hormone, he learned, also regulated bone mass – an early confirmation that energy storage and its use were intimately linked to bone. At the same time, other researchers were making a case for skin as an endocrine organ, and gaining a fuller understanding of signalling molecules released by the heart.

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" The breadth of tissues now known to release hormones demands that we rethink the very idea of the endocrine system itself. If it isn’t a restricted set of glandular tissues that direct the behaviour of the body’s various organs – a control system complementary to the nervous system – how should we conceptualise it instead? It appears to be something far more pervasive and democratic – a system through which all the body’s organs broadcast their status by discharging molecules into the blood and so, together, shape what the body is doing at any given time.

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" When a new hormone is identified and shown to have a significant function, it buys itself a line on a diagram like the one Perrimon and Droujinine constructed for a 2016 review detailing their plans to characterise the ICN [interorgan communication network] in fruit flies. Starting with the recent finds in mammals, they arranged, roughly in a circle, skeletal muscle, pancreas, brain, bone, gut, testes, heart, kidney, fat tissue and liver. And then, they drew arrows to show newly identified hormonal links between tissue pairs. The result was a frantic mishmash of connections.

"The classical notion of individual negative-feedback loops – each keeping a single physiological variable in check – remains a vital concept in biology. But it’s now clear that there are many loops and that they are all interlocked.

"Perrimon and Droujinine have written that it might be as fundamental as going back to the advent of early multicellular life. As organisms became more complex, and different types of cells evolved to have specialised functions within a cellular collective, there was a need to coordinate those functions. As an example from later in evolution, when muscles began driving movement, they likely relied on fat cells for nutrients. While one can see that a nervous system signalling to both tissues could make chemical communication redundant, it’s now clear that the hormonal link – and the autonomous character of peripheral tissues – never went away. As specialised populations of cells evolved, the total organism benefitted from individual tissues broadcasting their status to modulate other organs. As Karsenty puts it, ‘no organ is an island in our body.’ (my bold)

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"If the ICN, or the endocrine system, is an instructive set of commands, its internal chemical logic needs to be determined. Unlike the nervous system – where neurons make physical contact with the cells they influence – there is no anatomical specificity to the endocrine system."

Comment: Wow. There is no end to unearthing the real complexity of living beings. Only a designer can create this.