Week 3 Endocrine Regulations Flashcards
What are the key aspects that roughly define a hormone?
chemical substance of low concentration that is secreted into the blood to affect distant target tissues
What are the normal concentration ranges for hormones?
Between 10^-6 and 10^-12 mol/L (so the micromolar to picomolar range)
What are 4 things that hormones regulate?
Homeostasis, Metabolism, Growth/Development, and Reproduction
In a complex feedback loop, if the number of inhibitory interactions is odd (i.e. 3, 5, etc.) then the feedback loop is negative or positive?
Negative (and likewise, even # of inhibitory interactions -> positive feedback)
What is more common, positive or negative feedback?
Negative feedback
How does the aldosterone simple negative feedback loop work with an increase in potassium?
If extracellular potassium level is high, then this stimulates the adrenal cortex (zona glomerulosa) to secrete aldosterone, which acts on the kidney to increase potassium excretion. Thus potassium is brought back to a normal range.
How does the glucose-insulin negative feedback loop work?
An increase in glucose stimulates the pancreatic beta cells, causing them to secrete insulin. Insulin then causes uptake in GLUT-4 containing tissues (like adipose tissue and skeletal muscle) and thus decreases blood glucose level towards normal.
If you relate the physiological concept of negative feedback to the concept from electrical physics, what are the components?
An input signal goes to a subtractor, which sends an error-signal to an amplifier. The amplifier helps a small signal produce huge effects. The amplified signal now goes to a converter, which translates the signal into a hormone, which goes to the target tissue. The target tissue then sends its feedback signal back to the subtractor for regulation.
With negative feedback, what happens in the case of a constant input signal where there is a perturbing effect that increases the feedback signal?
The feedback signal was originally constant at the same level as the input signal. The perturbing effect causes the feedback signal to rise and balance is lost, which causes the level of hormone to increase until the feedback signal is restored to the input signal level. Hormone level returns to the normal, original level at the end
With negative feedback, what happens in the case of a changing input signal?
If the input signal deviates from the feedback signal, the level of hormone will spike for a time, as the feedback signal has a delay before it returns to match the input signal. If the input signal remains at a different level, then the hormone concentration also continues on at a different level than it was originally.
How does the feedback loop for G cells and their effect on stomach pH go? What are the “input signals” in this case?
Input signals = Vagus stimulation and amino acids in the stomach -> G cell stimulation -> gastrin secretion -> parietal cells produce more HCl -> stomach pH drops -> D cells stimulated to produce somatostatin -> G cells inhibited
With the feedback loop for G cells and stomach pH, what is the significance of how the level of acid production changes?
A negative feedback loop is able to be influenced by external factors (“input signals”) that lead to a regulated parameter that is not constant, but able to adapt to need. There is always some HCl production (the “regulated parameter”), but the output is stabilized at a higher level during digestion.
What are two examples of positive feedback?
Estradiol (high concentration) -> LH surge -> estradiol production. Also, oxtocin increase -> uterine contraction -> cervix stretches -> more oxytocin
What is feed forward regulation?
In the case of negative feedback, the body anticipates some perturbing effect will happen, and so it changes its regulated parameter before the perturbing effect occurs. This allows a decreased perturbed effect, especially if its precisely timed.
What is an example of feed forward regulation in the body?
incretins like GIP and GLP-1 stimulate insulin production in the pancreas before blood glucose level has risen. They signal at some early point before or during glucose absorption.
