Flashcards in MEH - Intro To Endocrinology Deck (40):
What is the 'biological clock' in the brain?
A small group of neurones in suprachiasmatic nucleus which take cues from the environment to keep the body on a 24 hour cycle.
What three things in the body change as a result of the circadian rhythm?
Core body temperature, cortisol and melatonin
Which cues from the environment influence the circadian rhythm?
- social interaction
- eating/drinking pattern
Which hormone is mainly involved with setting the biological clock?
Melatonin from the pineal gland
What is the difference between negative and positive feedback?
Negative feedback is a response in a way to reverse the direction of change, while positive feedback is response in a way so as to increase the magnitude of the change away from normal.
Give some examples of positive feedback
Ovulation and blood clotting
What is meant by short loop, long loop and ultrashort loop in negative feedback?
Ultrashort loop - hormone 1 is secreted by the hypothalamus and inhibits its own release
Short loop - hormone 1 triggers anterior pituitary to form hormone 2, which inhibits release of hormone 1 from the hypothalamus
Long loop - same as short loop, except hormone two causes release of hormone 3 from target gland, which inhibits release of hormone 1/2
How is body water measured?
Osmotic pressure of blood plasma is monitored by osmoreceptors in hypothalamus
What is osmolarity?
The number of osmoles per litre of solution
What is osmolality?
The number of osmoles per Kg of solution
What is an osmole?
The amount of a substance that dissociates in solution to form one mole of osmotically active particles, eg a 1 mM solution of NaCl corresponds to an osmolarity of 2 mOsmol/L (one mOsmol from Na+ ions and one from Cl- ions)
What is the normal blood osmolality value?
Between 275 and 295 mOsm/kg
What happens if the body detects high blood osmolality?
- body needs to conserve water
- detected by osmoreceptors in hypothalamus which cause posterior pituitary to secrete more ADH
- osmoreceptors also increase thirst
- increased reabsorption of H2O from urine into blood in collecting ducts in the kidney
- only small volume of concentrated urine is excreted so normal osmolality is restored
What happens if low blood osmolality is detected?
- body needs to excrete water
- this is detected by the osmoreceptors in the hypothalamus
- posterior pituitary secretes less ADH causing decreased resorption of H2O from urine into blood in collecting ducts in the kidney
- a large volume of dilute urine is passed and normal blood osmolality is restored
How is plasma glucose maintained at a steady level?
If glucose levels increase, pancreas releases insulin which stimulates glycogenesis in the liver and glucose uptake into tissues. Plasma glucose declines.
If glucose levels decrease, pancreas releases glucagon which stimulates glycogenolysis in the liver. Glucose is released into the blood and plasma glucose increases.
Chemical signals produced in endocrine glands or tissues which travel in the bloodstream to cause an effect on other tissues
What are the major endocrine glands?
Hypothalamus, pituitary gland, pineal gland, parathyroid gland, thyroid gland, thymus, adrenal gland, pancreas, ovary, testis
True or false - only endocrine glands can release hormones?
False - the heart, liver, stomach, placenta, adipose and kidney all release important hormones too
Give some similarities between the nervous system and the endocrine system
- both neurons and endocrine cells can secrete and be depolarised
- some molecules act as both neurotransmitter and hormone
- both require interaction with specific receptors in the target cells
- both work to control homeostasis
What are the four classifications of hormones?
- amino acid derivatives
Which protein classes are water soluble?
Peptide/polypeptide and glycoproteins are water soluble, while amino acid derivatives and steroids are lipid soluble.
Give some examples of peptide/polypeptide hormones
- growth hormone
These are all short chains of amino acids
Give some examples of glycoprotein hormones
- luteinizing hormone
- follicle stimulating hormone
- thyroid stimulating hormone
All large protein molecules, often made up of subunits with a carbohydrate side chain
Give some examples of steroid hormones
These are all derived from cholesterol
What are amino acid derivative hormones synthesised from?
Aromatic amino acids, eg. adrenaline, noradrenaline and thyroid hormones are all derived from tyrosine
Why do some hormones bind to carrier proteins in blood?
- increase solubility of hormone in plasma
- increase half-life
- readily accessible reserve
What are the three main factors that determine hormone levels in the blood?
- rate of PRODUCTION (this is the most highly regulated aspect of hormonal control)
- rate of DELIVERY (higher flow to a particular organ will deliver more hormone)
- rate of DEGRADATION (hormones are metabolised and excreted from the body)
How do water soluble hormones influence the target cell?
They bind to cell surface receptors, eg. GPCRs or tyrosine kinase
What are the two ways that lipid soluble hormones bind to the target cell?
1) cytoplasmic receptor binds hormone and receptor-hormone complex enters nucleus and binds to the DNA
2) hormone enters nucleus and binds to a pre-bound receptor on the DNA eg thyroid hormone. Binding relieves repression of gene transcription
In both cases, expression of new protein mediates the effects of the hormone
In general terms, what causes obesity?
A chronic imbalance between energy intake and energy expenditure
Where is the appetite control centre located?
In the hypothalamus
What is the appetite control centre composed of?
Clusters of neurones called 'nuclei' which make up the arcuate nucleus
What are the two types of primary neurone in the arcuate nucleus?
- stimulatory neurones, which contain neuropeptide Y (NPY) and Agoouti-related peptide (AgRP) and promote hunger
- inhibitory neurones, which contain pro-opiomelanocortin (POMC) which yields several neurotransmitters, including alpha-MSH and beta-endorphin and promote satiety
What do primary neurones synapse with?
Secondary neurones in other regions of the hypothalamus, and the signals are integrated to alter feeding behaviour
What is leptin released by?
Released into blood by adipocytes
How does leptin suppress appetite?
- stimulates inhibitory (POMC) neurones
- inhibits excitatory (AgRP/NPY) neurones in the arcuate nucleus
- induces expression of uncoupling proteins in mitochondria, so energy is dissipated as heat
What is the role of insulin in appetite regulation?
It suppresses appetite by similar mechanism as leptin
Where is amylin released from?
Peptide hormone secreted by beta cells in the pancreas
What are the roles of amylin?
Role not fully understood, but definitely suppresses appetite, decreases glucagon secretion and slows gastric emptying