reading: regulation of endocrine axes - week 3

Question 1

What is a key principle of homeostasis?

Answer 1

That physiological systems can be modulated via feedback loops

Question 2

What does the maintenance of a relatively constant internal environment rely on ?

Answer 2

Negative feedback loops - keeps a controlled variable within the normal physiological range and returns that variable to the physiological set point

Question 3

What do positive feedback loops do?

Answer 3

Accelerate changes in internal environment and maximise departure form any physiological set point

Question 4

What can regulate the synthesis and/or secretion of hormones?

Answer 4

• direct feedback loops
• first order feedback loops
• second order feedback loops
• third order feedback loops

Question 5

What is the difference between each of the feedback loops?

Answer 5

Number of control points

Question 6

How many control points require direct and first order feedback loops?

Answer 6

Only one

Question 7

How many control points in second and third?

Answer 7

2 and 3 respectively

Question 8

What is the most common feedback loop in vertebrate taxa?

Answer 8

Vast majority regulated through second or third order feedback loop

Question 9

Describe direct feedback loops?

Answer 9

• physiological stimulus directly stimulates an endocrine gland to synthesise/ secrete hormones into circulatory system
• hormone exerts action of target cell/ organ
• compensatory physiological response exerted by target organ decreases incoming physiological stimulus - CONTROL POINT

Question 10

name an example of direct feedback loops in mammals

Answer 10

Rare- atrial natriuretic peptide (ANP) - when atria of mammal heart are stretched, atrial cardiomyoctes stimulated to synthesise and secrete more ANP

Question 11

What is ANP

Answer 11

• short half life peptide hormone acting on kidneys to increase loss of sodium ions in urine
• water is also lost form the body with sodium, decreases plasma volume, lessens stretch of cardia atria, lowers stimulus to synthesise/ secrete ANP

Question 12

How do second and third order feedback loops differ from first?

Answer 12

• one or two, respectively, endocrine glands introduced between the integrator and ultimate effector/ target organ
• require endocrine axis (series of interacting endocrine glands)

Question 13

What is a second order feedback loop?