S6) Introduction to the Endocrine System & Endocrine Control of the Appetite Flashcards
What is homeostasis?
Homeostasis is the maintenance / regulation of a stable condition in an internal environment
Homeostatic mechanisms act to counteract changes in the internal environment. These mechanisms exist on all levels.
Identify some
- 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
What are the different components of a control system?
- Stimulus
- Receptor
- Control centre
- Effector
Illustrate how the different components of a control system act to ensure homeostasis
What is a biological rhythm?
A biological rhythm is any cyclic change in the level of a bodily chemical or function
What is a circadian rhythm and how is it controlled?
- 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)
How does jet lag arise?
Jet lag occurs due to long haul flights crossing time zones resulting in mismatch between environmental cues and the biological clock
Which hormone is involved in setting the biological clock?
Melatonin, from pineal gland
Compare and contrast negative and positive feedback, providing an example for each
- 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
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
Distinguish between osmolarity and osmolality
- Osmolarity is the number of osmoles per litre of solution
- Osmolality is the number os osmoles per kilogram of solution
What monitors the osmotic pressure of blood plasma?
Osmotic pressure of blood plasma monitored by osmoreceptors in hypothalamus
Serum osmolality useful when investigating hyponatraemia.
What is the normal range for this?
275 - 295 mOsmol/kg
Illustrate the control system set up as ADH regulates serum osmolality in body fluid homeostasis
Illustrate the control system set up by the homeostatic regulation of plasma glucose levels by insulin and glucagon
What is the endocrine system?
The endocrine system is a collection of glands located throughout the body
What are hormones and what do they do?
Hormones are chemical signals produced in endocrine glands/tissues that travel in the bloodstream to cause an effect on other tissues
Identify the ten major endocrine glands in the human body
There are four different mechanisms of communication via hormones.
Identify and describe them
The endocrine and nervous systems have several features in common.
Describe five of these similarities
- 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
Compare and contrast the endocrine and nervous systems in terms of the following:
- Signal
- Nature
- Conveyance
- Mediators
- Speed
Identify the four different types of hormones and describe their relative solubility
- Peptide / polypeptide – water soluble
- Amino acid derivatives (amines) – catecholamines are water soluble, thyroid hormones are lipid soluble
- Glycoproteins – water soluble
- Steroids – lipid soluble
Provide three examples of peptide hormones
- Insulin
- Glucagon
- Growth hormone
Provide three examples of glycoprotein hormones
- Luteinizing hormone
- Follicle stimulating hormone
- Thyroid stimulating hormone
Provide three examples of amine hormones
- Noradrenaline (& adrenaline)
- Melatonin
- Thyroid hormone
Provide three examples of steroid hormones
- Cortisol
- Aldosterone
- Testosterone
How are hormones transported?
- Some hormones travel in blood in simple solution e.g. peptides, NA
- Most hormones must bind to specific proteins
In terms of hormone transport, describe three roles of transport proteins
- Increase solubility of hormone in plasma
- Increase half-life
- Readily accessible reserve
3 factors determine hormone levels in the body.
Identify and describe them
- 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
How do hormones exert their effects?
Hormones exert their effects by binding to specific receptors
How do water soluble hormones exert their effects?
Water soluble hormones bind to cell surface receptors on target cells
In 6 steps, outline the effects of catecholamines like noradrenaline binding to a cell surface receptor on its target cell
⇒ Dissociation of G protein a subunit
⇒ Activation of adenylyl cyclase
⇒ Formation of cAMP
⇒ Activation of PKA
⇒ Phosphorylation of target proteins
⇒ Cellular response
In 6 steps, outline the effects of peptide hormones like insulin binding to a cell surface receptor on its target cell
⇒ 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
How do lipid soluble molecules exert their effects?
Lipid soluble molecules bind to intracellular receptors on target cells
In 4 steps, outline the effects of lipid soluble hormones like aldosterone binding to a intracellular receptor on its target cell
Where is the appetite control centre located?
- The satiety centre is located in the hypothalamus
- The arcuate nucleus plays a central role in controlling appetite
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
- 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
How do primary neurons transmit signals for appetite control?
Primary neurons synapse with secondary neurones in other regions of hypothalamus and the signals integrated to alter feeding behaviour
Hormonal signals from the gut to the hypothalamus also have a role in appetite control.
Identify the two hormones involved
- Ghrelin
- PYY
What is the role of ghrelin in appetite control?
Ghrelin stimulates the excitatory primary neurones in arcuate nucleus, thus stimulates appetite
Describe the release and inhibition of ghrelin
- Released from stomach wall when empty
- Inhibited when stomach begins to fill with contents
What is the role of PYY in appetite control?
PYY inhibits the excitatory primary neurones of the arcuate nucleus and stimulates the inhibitory neurones, hence suppresses appetite
Describe the release of PYY
PYY is released by cells in the ileum and colon in response to feeding
Hormonal signals from the body to the hypothalamus are also involved in appetite control.
Identify the three hormones involved
- Leptin
- Insulin
- Amylin
What is the role of leptin in appetite control?
Suppress appetite:
- Stimulates the inhibitory (POMC) neurones
- Inhibits the excitatory (AgRP/NPY) neurones
Describe the release of leptin
Peptide hormone released into blood by adipocytes
Explain the cellular mechanism by which leptin exerts its effects
- Leptin induces expression of uncoupling proteins in mitochondria
- Energy therefore dissipated as heat
Describe the release of amylin as well as its role in appetite control
- Peptide hormone secreted by β cells in pancreas
- Suppresses appetite, decrease glucagon secretion and slow gastric emptying
Describe the role of insulin in appetite control
Suppresses appetite by similar mechanism as leptin
Illustrate the relationship between various hormonal signals in appetite control
