S6) Introduction to the Endocrine System & Endocrine Control of the Appetite

Question 1

What is homeostasis?

Answer 1

Homeostasis is the maintenance / regulation of a stable condition in an internal environment

Question 2

Homeostatic mechanisms act to counteract changes in the internal environment. These mechanisms exist on all levels.

Identify some

Answer 2

• Cell e.g. regulation of [Ca²⁺]_i
• Tissue e.g. balance between cell proliferation and cell death
• Organ e.g. kidney regulates water and ion concentrations in blood
• Organism e.g. constant body temperature

Question 3

What are the different components of a control system?

Answer 3

• Stimulus
• Receptor
• Control centre
• Effector

Question 4

Illustrate how the different components of a control system act to ensure homeostasis

Answer 4

Question 5

What is a biological rhythm?

Answer 5

A biological rhythm is any cyclic change in the level of a bodily chemical or function

Question 6

What is a circadian rhythm and how is it controlled?

Answer 6

• A circadian rhythm is a biological rhythm which follows a 24 hour cycle
• It is regulated by a small group of neurones in suprachiasmatic nucleus (biological clock) and varies according to the environment (light, temperature, social interaction, exercise, eating/drinking pattern)

Question 7

How does jet lag arise?

Answer 7

Jet lag occurs due to long haul flights crossing time zones resulting in mismatch between environmental cues and the biological clock

Question 8

Which hormone is involved in setting the biological clock?

Answer 8

Melatonin, from pineal gland

Question 9

Compare and contrast negative and positive feedback, providing an example for each

Answer 9

• Negative feedback: a response which reverses the direction of change e.g. baroreceptors in blood pressure control
• Positive feedback: a response which reinforces the direction of change e.g. hormones in ovulation

Question 10

Body water homeostasis is an example of a feedback system.

In light of this, describe the body water distribution in a 70 kg adult male

Answer 10

Question 11

Distinguish between osmolarity and osmolality

Answer 11

• Osmolarity is the number of osmoles per litre of solution
• Osmolality is the number os osmoles per kilogram of solution

Question 12

What monitors the osmotic pressure of blood plasma?

Answer 12

Osmotic pressure of blood plasma monitored by osmoreceptors in hypothalamus

Question 13

Serum osmolality useful when investigating hyponatraemia.

What is the normal range for this?

Answer 13

275 - 295 mOsmol/kg

Question 14

Illustrate the control system set up as ADH regulates serum osmolality in body fluid homeostasis

Answer 14

Question 15

Illustrate the control system set up by the homeostatic regulation of plasma glucose levels by insulin and glucagon

Answer 15

Question 16

What is the endocrine system?

Answer 16

The endocrine system is a collection of glands located throughout the body

Question 17

What are hormones and what do they do?

Answer 17

Hormones are chemical signals produced in endocrine glands/tissues that travel in the bloodstream to cause an effect on other tissues

Question 18

Identify the ten major endocrine glands in the human body

Answer 18

Question 19

There are four different mechanisms of communication via hormones.

Identify and describe them

Answer 19

Question 20

The endocrine and nervous systems have several features in common.

Describe five of these similarities

Answer 20

• Both neurons and endocrine cells are capable of secreting
• Both neurons and endocrine cells can be depolarised
• Some molecules acts as both neurotransmitter and hormone
• The mechanism of action requires interaction with specific receptors in the target cells
• Both systems work in parallel to control homeostasis

Question 21

Compare and contrast the endocrine and nervous systems in terms of the following:

• Signal
• Nature
• Conveyance
• Mediators
• Speed

Answer 21

Question 22

Identify the four different types of hormones and describe their relative solubility

Answer 22

• Peptide / polypeptide – water soluble
• Amino acid derivatives (amines) – catecholamines are water soluble, thyroid hormones are lipid soluble
• Glycoproteins – water soluble
• Steroids – lipid soluble

Question 23

Provide three examples of peptide hormones

Answer 23

• Insulin
• Glucagon
• Growth hormone

Question 24

Provide three examples of glycoprotein hormones

Answer 24

• Luteinizing hormone
• Follicle stimulating hormone
• Thyroid stimulating hormone

Question 25

Provide three examples of amine hormones

Answer 25

- Noradrenaline (& adrenaline) - Melatonin - Thyroid hormone

Question 26

Provide three examples of steroid hormones

Answer 26

- Cortisol - Aldosterone - Testosterone

Question 27

How are hormones transported?

Answer 27

- Some hormones travel in **blood in simple solution** *e.g. peptides, NA* - Most hormones must bind to **specific proteins**

Question 28

In terms of hormone transport, describe three roles of transport proteins

Answer 28

- Increase solubility of hormone in plasma - Increase half-life - Readily accessible reserve

Question 29

3 factors determine hormone levels in the body. Identify and describe them

Answer 29

- **Rate of production** – synthesis and secretion - **Rate of delivery** – dependent on rate blood flow to a particular organ - **Rate of degradation** – hormones are metabolised and excreted from the body

Question 30

How do hormones exert their effects?

Answer 30

Hormones exert their effects by binding to specific receptors

Question 31

How do water soluble hormones exert their effects?

Answer 31

Water soluble hormones bind to **cell surface receptors** on target cells

Question 32

In 6 steps, outline the effects of catecholamines like noradrenaline binding to a cell surface receptor on its target cell

Answer 32

⇒ Dissociation of G protein a subunit ⇒ Activation of adenylyl cyclase ⇒ Formation of cAMP ⇒ Activation of PKA ⇒ Phosphorylation of target proteins ⇒ Cellular response

Question 33

In 6 steps, outline the effects of peptide hormones like insulin binding to a cell surface receptor on its target cell

Answer 33

⇒ **Dimerisation** (insulin receptor is already dimerised) ⇒ **Autophosphorylation** of specific tyrosines ⇒ Recruitment of **adapter proteins** and **signalling complex** ⇒ Activation of **protein kinase** *e.g. PKB* ⇒ **Phosphorylation** of target proteins ⇒ Cellular response

Question 34

How do lipid soluble molecules exert their effects?

Answer 34

Lipid soluble molecules bind to **intracellular receptors** on target cells

Question 35

In 4 steps, outline the effects of lipid soluble hormones like aldosterone binding to a intracellular receptor on its target cell

Answer 35

Question 36

Where is the appetite control centre located?

Answer 36

- The satiety centre is located in the **hypothalamus** - The **arcuate nucleus** plays a central role in controlling appetite

Question 37

Neuronal, nutrient & hormonal signals are processed by primary neurones in the arcuate nucleus Identify the two types of primary neurone and explain what they do

Answer 37

- **Stimulatory neurones** contain neuropeptide Y (NPY) and agouti-related peptide (AgRP) → these promote hunger - **Inhibitory neurones** contain POMC which yields several neurotransmitters including α-MSH and β-endorphin → these promote satiety

Question 38

How do primary neurons transmit signals for appetite control?

Answer 38

Primary neurons **synapse with secondary neurones** in other regions of hypothalamus and the signals integrated to alter feeding behaviour

Question 39

Hormonal signals from the gut to the hypothalamus also have a role in appetite control. Identify the two hormones involved

Answer 39

- Ghrelin - PYY

Question 40

What is the role of ghrelin in appetite control?

Answer 40

Ghrelin stimulates the excitatory primary neurones in arcuate nucleus, thus **stimulates appetite**

Question 41

Describe the release and inhibition of ghrelin

Answer 41

- **Released** from stomach wall when empty - **Inhibited** when stomach begins to fill with contents

Question 42

What is the role of PYY in appetite control?

Answer 42

PYY inhibits the excitatory primary neurones of the arcuate nucleus and stimulates the inhibitory neurones, hence **suppresses appetite**

Question 43

Describe the release of PYY

Answer 43

PYY is released by **cells in the ileum and colon** in response to feeding

Question 44

Hormonal signals from the body to the hypothalamus are also involved in appetite control. Identify the three hormones involved

Answer 44

- Leptin - Insulin - Amylin

Question 45

What is the role of leptin in appetite control?

Answer 45

**Suppress appetite:** - Stimulates the inhibitory (POMC) neurones - Inhibits the excitatory (AgRP/NPY) neurones

Question 46

Describe the release of leptin

Answer 46

Peptide hormone released into **blood by adipocytes**

Question 47

Explain the cellular mechanism by which leptin exerts its effects

Answer 47

- Leptin induces expression of **uncoupling proteins in mitochondria** - Energy therefore **dissipated as heat**

Question 48

Describe the release of amylin as well as its role in appetite control

Answer 48

- Peptide hormone secreted by **β cells in pancreas** - **Suppresses appetite**, decrease glucagon secretion and slow gastric emptying

Question 49

Describe the role of insulin in appetite control

Answer 49

**Suppresses appetite** by similar mechanism as leptin

Question 50

Illustrate the relationship between various hormonal signals in appetite control

Answer 50