Lecture 17 2/16/24

Question 1

What is a closed loop control system?

Answer 1

target glands secrete hormones that inhibit their own secretion

Question 2

What is an open loop control system?

Answer 2

hormones do not control their own production; no direct feedback regulation

Question 3

What are the characteristics of on/off control?

Answer 3

-full on, full off
-different set-points in different species
-set-points can change throughout day

Question 4

What are the advantage and disadvantage of on/off control?

Answer 4

advantage: simplicity
disadvantage: cycling leads to less accuracy

Question 5

What are the characteristics of on/off control with hysteresis?

Answer 5

-system has increased tolerance
-decreased frequency of cycles
-increased excursion of cycles

Question 6

How does half-life play into negative feedback?

Answer 6

hormones with a longer half-life have a more important role in suppressing hormone production

Question 7

What are the characteristics of proportional control?

Answer 7

-output is adjusted to be proportional to demand
-returns blood conc. of hormone to set-point value without cycling or overshooting

Question 8

When is a large corrective action vs. a small corrective action needed in proportional control?

Answer 8

large: when hormone levels are significantly below set-point
small: when deviation from set-point is minimal

Question 9

What is an offset in proportional control?

Answer 9

a deviation from set-point caused by a change in load

Question 10

What are the characteristics of derivative/anticipatory control?

Answer 10

-measures rate of change of error signal
-anticipates magnitude of future error

Question 11

What are the characteristics of the biphasic pattern of insulin secretion?

Answer 11

-acute phase involves the release of formed insulin
-chronic phase involves release of newly synthesized insulin
-anticipatory mechanism saves 80% of insulin and prevents large glucose fluctuations

Question 12

What are the characteristics of integral control?

Answer 12

-prevents offset, but is slow acting
-small corrective actions
-measures error signal many times

Question 13

Where can feedback failure occur?

Answer 13

-primary gland
-secondary gland
-tertiary gland
-ectopic secretion
-first messenger
-abnormal receptor
-non-functional second messenger

Question 14

What happens when a cortical adenoma/carcinoma is present in the adrenal gland?

Answer 14

-increased cortisol
-decreased ACTH
-one large gland, one shrunken gland

Question 15

What happens when a pituitary adenoma is present?

Answer 15

-lots of ACTH release
-both adrenal glands hyperplastic
-lots of cortisol, but no feedback

Question 16

What happens when neoplasia of the hypothalamus occurs?

Answer 16

-increased ACTH
-hypertrophied adrenals
-increased cortisol
-can measure CRH or do MRI to diagnose

Question 17

What happens when there is ectopic ACTH secretion?

Answer 17

-tumor located somewhere other than hypothalamus/pituitary/adrenals produces ACTH
-ACTH from pituitary is minimal
-x-ray to locate tumor

Question 18

What happens with iatrogenic feedback failure?

Answer 18

prolonged administration of glucocorticoid and neg. feedback leads to pituitary and adrenal gland atrophy