Session 6: Introduction to the Endocrine System

Question 1

There are 6 key features of homeostasis.

Name them.

Answer 1

Stimulus
Receptor
Communication
Control centre
Effector
Negative feedback

Question 2

Example of stimulus.

Answer 2

Food (increased blood glucose)

Question 3

Example of receptors.

Answer 3

Chemoreceptors, thermoreceptors, proprioceptors, nociceptors, baroreceptors.

Question 4

Example of communication.

Answer 4

Can be paracrine, autocrine, endocrine, neuronal.
Afferent pathway going from receptor to control centre.
Efferent pathway going from control centre to effector.

Question 5

Example of control centres.

Answer 5

Hypothalamus (control of endocrine)
Medulla oblongata (control of ventilation and cardiovascular system)

Question 6

Example of effectors.

Answer 6

Sweat glands.

Question 7

Example of feedback.

Answer 7

Negative and positive feedback.

Question 8

What governs the biological clock?

Answer 8

Suprachiasmatic nucleus in hypothalamus.

Question 9

What is the natural diurnal cycle?

Answer 9

The body’s free-running time without any external stimulus. It is around 24 hours and 11 minutes.

Question 10

If the natural diurnal cycle is 24 hours and 11 minutes how come we don’t cycle throughout the days and get a messed up sleep schedule?

Answer 10

Because of something called zeitgebers which are environmental cues.

Question 11

Give examples of zeitgebers.

Answer 11

Light
Temperature
Social interactions
Exercise
Drinking and eating patterns

Question 12

Explain jet-lag.

Answer 12

When there is a mismatch between the zeitgebers and the natural diurnal cycle.

Question 13

What hormone is responsible for the setting of the biological clock?

Answer 13

Melatonin released from the pineal gland in the brain.

Question 14

Explain water homeostasis.

Answer 14

A high blood osmolality is detected by osmoreceptors in hypothalamus. This leads to thirst and drinking to reduce the osmolality. The osmoreceptors also cause posterior pituitary to secrete more ADH so there is increased reabsorption of H2O from urine into blood. (Small volume of concentrated urine.)

A low blood osmolality is detected by osmoreceptors in the hypothalamus. This leads to the posterior pituitary to secrete less ADH so there is less reabsorption of H2O so we pee more. (Large volume of diluted urine)

Question 15

Classifications of hormones.

Answer 15

Peptide/polypeptide hormones
Glycoprotein hormones
Amino acid derivatives
Steroid hormones

Question 16

What are steroid hormones derived from?

Answer 16

Cholesterol

Question 17

Are polypeptide and catecholamines usually stored? If not, how?

Answer 17

Yes they are.

Question 18

Are steroid hormones usually stored? If not, how?

Answer 18

They are not. Usually they are stored as precursors.

Question 19

Where is ANP and BNP produced?

Answer 19

From the heart.

Question 20

Where is IGF-1 and Angiotensinogen produced?

Answer 20

Liver

Question 21

Where is Gastrin and Ghrelin produced?

Answer 21

Stomach

Question 22

Where is inhibin produced?

Answer 22

Placenta

Question 23

Where is leptin produced?

Answer 23

Adipose tissue

Question 24

Where is EPO, Renin and Calcitriol produced?

Answer 24

Kidneys

Question 25

Where is PYY produced?

Answer 25

Small intestines

Question 26

Explain how activation of a tyrosine kinase receptor like Insulin-like receptor works.

Answer 26

Binding of hormone to receptor causes dimerisation (except for the case of insulin-like receptor which is already dimerised).
This leads to autophosphorylation of specific tyrosine.
Recruitment of adapter proteins and signalling complex follows.
There is an activation of protein kinase like PKB.
Phosphorylation of target proteins ensues.
This all leads to a cellular response.

Question 27

What plays the most central role in the control of appetite.

Answer 27

The arcuate nucleus of the hypothalamus.

Question 28

What are the neuronal, hormonal and nutrient signals processed by in the arcuate nucleus?

Answer 28

By primary neurones.

Question 29

What are the two types of primary neurones in the arcuate nucleus responsible for appetite control?
What neurotransmitters are used?

Answer 29

Stimulatory neurones also called orexigenic which use AgRP and NPY neurotransmitters to promote hunger.

Inhibitory neurones which are also called anorexigenic. They use alpha-MSH from POMC at the synapse acting at MC4 (melanocortin 4 receptors) receptors to promote satiety. Beta-endorphins are also released here.

Question 30

What can POMC produce by proteolytic cleavage?

Answer 30

B-endorphin, ACTH, alpha-MSH.

Question 31

Which hormones suppresses appetite?

Answer 31

PYY
Leptin
Insulin
Amylin

Question 32

Which hormones stimulates appetite?

Answer 32

Ghrelin

Question 33

Explain the action of Ghrelin. (Including release)

What stimulates and inhibits?

Answer 33

Ghrelin is a peptide hormone released from the wall of the empty stomach. Ghrelin then activates the stimulatory neurones (orexigenic) in the arcuate nucleus stimulating appetite. A stretched stomach (full) inhibits ghrelin release.

Question 34

Explain the action of PYY.

Answer 34

Peptide hormone released from the wall of the small intestines Which acts on the orexigenic neurones to inhibit them. PYY suppress appetite.

Question 35

Explain the action of Leptin.

Answer 35

Adipose tissue release leptin. Leptin then acts by stimulating the anorexigenic neurones to inhibit/suppress appetite. Leptin acts as a feedback mechanism from the body’s own fat stores to control the level of intake of food. This means that more adipose tissue means more production of leptin.

Question 36

Explain action of insulin on appetite.

Answer 36

Acts by stimulating anorexigenic neurones to inhibit/suppress appetite.
Amylin from beta-cells of pancreas have a similar function.

Question 37

Explain why leptin is an important hormone.

Answer 37

A lack of leptin production or insensitivity to leptin has been associated with obesity.
Leptin also induces the expression of uncoupling proteins in the mitochondrion. This leads to production of heat instead of ATP. Means more sweating and less energy.