Week 2 - Neuroendocrinology Flashcards
Neuroendocrinology
the interaction between the nervous system and the endocrine system - the two major homeostatic systems involved in control and regulation of bodily functions.
What is the role of the Nervous system?
uses neurotransmitters to relay messages from one nerve to another or from a nerve to a tissue.
What is the role of the endocrine glands?
endocrine glands releases hormones into blood to circulate to tissues.
Hormones
chemical messengers secreted from endocrine glands that signal changes in other organs and tissues throughout the body.
They only affect tissues that contain specific hormone receptors.
3 classes of hormones
1) Amino acid derivatives (thyroxine, epinephrine and norepinephrine)
2) Peptide/protein (insulin, glucagon, ADH and ACTN)
3) Steroids (glucocorticoids, aldosterone)
What is plasma concentration determined by?
- Rate of secretion of hormone from endocrine gland
- Rate of metabolism or excretion of hormone
- Quantity of transport proteins
- Changes in plasma volume
What is the magnitude of the effect of a hormone dependent on?
1) Concentration of the hormone
2) Number of target receptors on the cell
3) Affinity of the receptor for the hormone
What is the difference between downregulation and upregulation in receptors?
Downregulation - decrease in receptor number in response to high concentration of hormone
Upregulation - increase in receptor number in response to low concentration of hormone
What is an example of downregulation?
an individual with high bp could be treated with beta-blocker drug which reduces binding of adrenaline to the cell.
What are the 3 mechanisms of hormone action?
1) Activation of genes to alter protein synthesis (steroid hormones: cortisol, testosterone)
2) Activating ‘second messengers’ in the cell via G protein (cyclic AMP)
3) Altering membrane transport (insulin via tyrosine kinase)
Hypothalamus
controls secretion of hormones from pituitary glands (anterior and posterior)
Antidiuretic hormone (ADH)
1) Site of release
2) Stimulus for release
3) Predominant action
1) Secreted from posterior pituitary gland
2) Release is stimulated by high plasma osmolality and low plasma volume (due to sweat loss without water replacement)
3) Reduces water loss from the body to maintain plasma volume - favours the reabsorption of water from kidney tubules to the capillaries
How does exercise influence plasma ADH concentrations?
Exercise >60% of V02 max increases plasma ADH due to increase in plasma osmolality and decrease in plasma volume.
Aldosterone (mineralocorticoid)
1) Site of release
2) Stimulus for release
3) Predominant action
1) Secreted from the adrenal cortex
2) Release stimulated by an increased plasma K+ concentration (causes negative feedback loop), decrease plasma volume and bp when extracellular Na+ is lost, Angiotensin II, ACTH.
3) Control of Na+ reabsorption and K+ secretion (Na+/H20 balance) + regulation of blood volume and blood pressure
How does exercise influence renin, angiotensin II and aldosterone?
all 3 hormones increased during exercise, the effect takes >45mins (steroid hormones) so major effect is post exercise
Name the 2 hormones responsible for control of plasma volume.
1) Aldosterone
2) Antidiuretic hormone (ADH)
What are the 4 processes that maintain blood glucose during exercise?
1) Mobilisation of glucose from liver glycogen stores
2) Mobilisation of FFA from adipose tissue (spares blood glucose)
3) Gluconeogenesis from amino acids, lactic acid, and glycerol
4) Blocking the entry of glucose into cells (forces use of FFA as a fuel)
Two types of “acting” hormones
1) Permissive or slow-acting (Thyroid, cortisol, growth hormone): allow other hormones to exert their full effect.
2) Fast-acting (Epinephrine, norepinephrine, insulin and glucagon)
Growth hormone
- Why is it essential for growth of all tissues?
- How does it change during exercise?
- What is its secretion stimulated by and when is its secretion at its peak?
Increases amino acid uptake, cartilage growth and protein synthesis in muscle and long bone growth.
Increase in plasma GH with an increase in exercise intensity.
Its secretion is stimulated by ghrelin and secretion it as its peak during sleep.
What are the 3 ways which growth hormone spares plasma glucose?
- Reduces the use of plasma glucose
- Increases gluconeogenesis (in liver)
- Mobilize fatty acids from adipose tissue
Cortisol
- Where is it derived from?
- Where is it secreted from?
- What is it stimulated by?
- What is its role?
- Influence of exercise intensity on cortisol.
- Derived from cholesterol
- Secreted from the adrenal cortex
- Stimulated by stress (via ACTH - adrenocorticotropic hormone) and exercise
- Increases the release of fatty acids from adipocytes and glucose from liver cells
- Increases proportional to increases in exercise intensity
What are two considerations when measuring cortisol?
1) Diurnal variation: concentrations peak in the am (6am) and drop throughout the day
2) Emotional arousal
Catecholamines
- Where is it secreted from?
- What receptors do they bind to?
- Slow-acting or fast-acting?
- Influence of exercise
- How does endurance training influence catecholamine at a fixed intensity exercise bout?
- What do trained individuals have a greater capacity to do? Why?
- Adrenal medulla: epinephrine (80%) and norepinephrine
- Adrenergic receptors
- Fast-acting
- Plasma E and NE increase during exercise which is related to increased HR and BP during exercise (sympathetic activation)
- Rapid decrease in catecholamine in response to a fixed intensity exercise about.
- Greater capacity to increase catecholamines (35%) compared to untrained individuals in response to supramaximal exercise - because regular stimulation of SNS increases capacity of response.
How does high-intensity exercise influence plasma epinephrine? What is plasma epinephrine a powerful stimulator of?
High-intensity exercise results in greater increase in plasma epinephrine.
Plasma epinephrine is a powerful stimulator of glycogenolysis.
