MEH - Endocrine & Control of Appetite Flashcards
What is homeostasis and what does it do?
Dynamic equilibrium of the internal environment. Acts to counteract changes in the internal environment.
What 5 characteristics must a homeostatic control system have?
Stimulus Receptor Control Centre Effector Negative feedback loop
What three things does a control centre do?
Determines set point
Analyses afferent input
Decides efferent output
What examples of efferent pathways from control centre –> effector are there?
Neural
Hormonal
What happens to the set point in a circadian rhythm? Where in the brain is this determined? Give some examples of hormones/homeostatic effects that are in a circadian rhythm
Set point varies - nocturnal-diurnal
In the suprachiasmatic nucleus
Temperature, exercise, eating/drinking pattern, social interaction
What is a zeitgeber?
An environment cue that synchronises a body’s biological rhythms
What does melatonin do and where is it released from?
It is a hormone that is involved in setting the biological clock - released from pineal gland
Negative feedback is more common that positive - give 2 examples where positive feedback is used in the body
- Blood clotting
- Ovulation
How many L of fluid are there in the body:
Intracellularly
Extracellularly (Interstitial + Plasma)
Total: 42L
IC- 28L
EC - 14
(Interstitial 11 Plasma 3)
How is osmotic pressure of blood plasma controlled, and where in the brain are these found?
By osmoreceptors in the hypothalamus
What is osmolarity vs osmolality the measure of? What are electrolytes measured in - e.g. for hyponatraemia? What is the normal range for serum Na+?
Osmolarity - number of osmoles/L solution (volume)
Osmolality - number of osmoles per Kg solution (mass)
Electrolytes - measured by serum osmolality - 275-295mOsmol/kg
What do osmoreceptor efferents lead to (2)?
Increased Thirst - if osmolality high to reduce it
Increased or decreased ADH from post pituitary (increased leads to increased H2O reabsorbed in kidney collecting ducts - to reduce osmolality)
What is the endocrine system? What are hormones? How are they transported and in what concentrations?
A collection of glands throughout the body that secrete hormones into the blood to act on target organs. Hormones are chemicals that are released into the blood to act on target organs (usually determined by their concentration). They can be attached to plasma proteins and normally in conc around 10-10 to 10-9.
Name the 10 major endocrine glands
Pineal Pituitary Hypothalamus Testis Ovaries Thyroid Parathyroid Pancreas Adrenal Thymus
What other tissues/organs secrete hormones that aren’t endocrine glands (6)?
Heart - ANP BNP Placenta - Inhibin Liver - IGF1 Stomach - Gastrin Adipose - Leptin Kidney - Epo
Can endocrine cells be depolarised like neural cells?
Yes
Can some molecules act as a neurotransmitter and a hormone?
Yes
What 4 groups of chemical are hormones classified into? Say if they are water or lipid soluble.
Glycoprotein - water soluble
Polypeptides - water soluble
Amines - lipid soluble
Steroids - lipid soluble
What kind of hormones are LH, FSH and TSH?
Glycoprotein
What kind of hormone are Insulin, Glucagon, Growth hormone?
Peptide
Which type of hormones travel UNBOUND to plasma proteins?
- Peptides
- Adrenaline
What is Thyroxine-binding globulin?
The specific plasma protein that binds Thyroid hormones in the blood.
Are free or bound forms of hormone active?
Only free
Why would you have a hormone bound to a plasma protein (3)?
Enhances solubility
Creates reserve (as not active)
Increases half-life of hormone
What three factors determine hormone levels in the blood? Which is the most tightly regulated?
- Rate of synthesis - most tightly controlled
- Rate of delivery
- Rate of degradation
Are hormones circulate the blood in low or high concentrations?
Low
How do you differentiate between a hormone target cell and non target cell?
A target cell will have a receptor for that hormone
What kind of receptors do adrenaline and insulin bind to? Are these cell surface or nuclear or cytoplasmic? Why?
Adrenalin - GPCR
Insulin - Tyrosine Kinase
- Cell surface - as they are hydrophilic hormones so can’t cross cell membrane
How do TK receptors work?
Binding of hormone
Dimerisation (except insulin - already dimerised)
Autophophorylation of specific tyrosines
Recruitment of adaptor proteins and signalling complex
Activation of protein kinase (e.g. PKB)
Phosphorylation of target proteins
Cellular response
What 2 types of intracellular receptors are there for lipid soluble hormones?
1) Cytoplasmic - binds in cytoplasm then enters nucleus to bind to DNA
2) Pre-bound receptor on DNA (Hormone enters nucleus) - binding received repression of gene transcription. Receptor binds to specific DNA sequence called a hormone response element in promotor region of specific genes
What BMI is considered obese?
30kg/M-2
What part of the hypothalamus controls appetite?
Arcuate nucleus
What two types of neurone are there in the arcuate nucleus and what do they do?
Primary - receive input and synapse with secondary neurones
Secondary - modulate feeding behaviour
What two types of primary neurones are there and what do they do?
Stimulatory - neurones contain neuropeptide Y (NPY and Agouti-related peptide (AgRP). These promote hunger
Inhibitory - neurone contain POMC which yields several neurotransmitters including alpha-MSH and beta-endorphin and promote satiety.
Where do primary neurones synapse with secondary neurones?
In other regions of the hypothalamus
Which two hormonal signals from the gut travel to the hypothalamus and how do they control feeding behaviour? When might you see a blunted PYY response in humans?
Grehlin - Peptide hormone released from stomach wall when empty - stimulates excitatory primary neurones in arcuate nucleus therefore stimulating hunger. Are inhibited with filling of stomach
PYY (pepticde tyrosine tyrosine)
Peptide hormone released from ileum and colon in response to feeding - inhibits excitatory primary neurones of arcuate nucleus and stimulates inhibitory primary neurones of arcuate nucleus - suppresses appetite.
Blunted PYY response in obese humans
What 5 broad hormones help control appetite? Do they supress or enhance?
Grehlin - enhance Leptin - suppress Insulin - suppress PYY - suppress Amylin - suppress
How does leptin work? is Insulin similar or different? How does Leptin increase heat?
Leptin - peptide hormone released by adipocytes
Suppresses appetite by
1) Stimulates inhibitory primary neurones in arcuate nucleus (POMC)
2) Inhibit excitatory AgRP/NPY primary neurones in arcuate nucleus
Leptin induces expression of uncoupling proteins in mitochondria –> energy lost as heat
Yes insulin similar to leptin
How does amylin work?
Peptide hormone - released by beta-cells in pancreas. Role not fully understood but suppresses appetite - decreased glucagon secretion and slows gastric emptying.
What is pamlintide?
An amylin analogue that is used to treat T2 diabetes
What does orexigenic mean?
Appetite stimulant
