Biological complexity: homeostasis (Introduction)

by David Turell , Friday, September 15, 2017, 21:49 (2626 days ago) @ David Turell

Our bodies are in a constant state of disequilibrium called homeostasis, maintaining exact levels at all times by feedback loops. These controls must have all parts set up all at once:

https://evolutionnews.org/2017/09/in-a-new-book-scott-turner-explores-biologys-second-law/

Homeostasis is life as a state of persistent dynamic disequilibrium…

"Matter is flowing through the whole living organism, while the organism is “maintaining a persistent state of highly specified and complex organization.” Work has to be done to maintain this state. This “self-adjusting confluence of forces is precisely what living things do as a routine.” Turner observes, “It’s what distinguishes the living from the inanimate world…homeostasis is an exceedingly strange idea.”

"Homeostasis is a balancing act. The organism responds to environmental cues and adjusts its own chemistry to maintain things at a certain pH, temperature, oxygen level, salinity, ion concentration, glucose level etc. For creatures like us, none of those states are in equilibrium with the environment. Levels must be precisely balanced at a particular point suitable for life. For example, if our blood chemistry goes askew, it will kill us.

***

"Why should we live in this continuous state of flux? We balance as if on a tightrope with hydrogen, oxygen, carbon, and nitrogen flowing through us. Who we are today, molecularly speaking, is not who we were yesterday or will be tomorrow. Yet we as individuals remain as singular points of balance. As Turner says, homeostasis is an exceedingly strange idea.

"Yet without homeostasis there is no life.

***

"When the parathyroid gland senses low levels of calcium in the blood, it releases the hormone PTH. It is counterintuitive, but osteoblasts (cells that take up calcium to build bone) have PTH receptors. These receptors stimulate osteoblasts to pump calcium ions out of the fluid surrounding the bone and into the extracellular fluid. They also produce a signaling molecule that activates osteoclasts (cells that break down bone to produce calcium).

"PTH also stimulates calcium reabsorption in the kidney and the production of 1,25(OH)2D, the active form of vitamin D by the kidney. In the small intestine, 1,25(OH)2D works to promote calcium absorption.

***

"Not to put too fine a point on it, but the existence of complex and specified systems is a hallmark of design. How do you build a system requiring multiple signals and receptors one step at a time when the system does not work until all are present? A receptor is no good without a signal to receive, and the signal will not be sent with a cue.

"Then there is the need for an effector. The parathyroid gland senses low calcium (how?) and produces PTH. PTH travels through the blood stream to its many sites of action. If PTH is high, then receptors on osteoblasts (receptors are usually proteins) receive that signal, and in turn send another signal to osteoclasts (probably a protein), which then receive that signal and effect a change (another protein?) in order to release calcium ions to the blood stream, and restore the calcium levels to where they should be. And that is just one means of regulating calcium.

"To recap, from Claude Bernard:

"The fixity of the [interior] milieu supposes a perfection of the organism such that the external variations are at each instant compensated for and equilibrated…. All of the vital mechanisms, however varied they may be, have always one goal, to maintain the uniformity of the conditions of life in the internal environment…. The stability of the internal environment is the condition for the free and independent life."

Comment: The moment by moment conduct of living organisms (homeostasis as constant disequilibrium) can only result from design. No other theory makes any sense. There is a designer.