Neuroendocrinology Flashcards
What is neuroendocrinology?
A branch of life sciences dealing with neurosecretion and the physiological interaction between the CNS and endocrine system
What are the 2 types of neurones in the hypothalamus?
- Parvocellular (small) neurones interact with ANTERIOR pituitary (via hypo-physical portal system)
- Magnocellular (large) neurones interact with the POSTERIOR pituitary
What are the 4 different outcomes of pituitary hormones?
Secreted into circulation and then go into either:
- Target tissues
- Adrenal axis (stress)
- Thyroid axis(metabolism)
- Gonads axis(reproduction)
What is the function of the hypothalamus?
To integrate autonomic responses and endocrine function with behaviour, especially behaviour concerned with basic homeostatic requirements of every day life
What are the 3 ways in which homeostasis is controlled?
- Behaviour
- Neuronal control through the ANS
- Hormonal control through hormone release from the pituitary gland initially (gets signal from hypothalamus)
How does the hypothalamus get signals from other brain centres?
Through its leaky BBB, the optics, limbic system and visceral ANS input for example can signal to the hypothalamus via certain molecules allowing the endocrine system to feedback to it
What are the 6 major homeostatic needs that the hypothalamus maintains?
- BP/electrolyte composition: control of drinking, salt appetite, blood osmolality + vasomotor tone
- Body temp: metabolic thermoregulation + behaviours like seeking appropriate environment
- Energy metabolism: feeding, digestion + metabolic rate
- Reproduction: hormonal control of mating, pregnancy + lactation
- Stress response: adrenal stress hormones e.g. cortisol
- Growth: e.g. GH
The hypothalamus does not just control the neuroendocrine system but also the ___.
ANS
How does the hypothalamus have a role in emotional behaviour?
Anatomically it is close to the amygdala which gets signals from the pre-frontal cortex allowing it to get signals from here
What are the roles of the paraventricular nucleus (PVN) of the hypothalamus?
Autonomic control:
- Stress (CRH)
- Energy balance (TRH)
- Osmoregulation (AVP)
- Maternal control (Oxy)
- BP (AVP)
What are the roles of the supraoptic nucleus (SON) of the hypothalamus?
Osmoregulation (AVP)
Maternal control (Oxy)
What are the roles of the arcuate (ARC) nucleus of the hypothalamus?
Reproduction (GnRH)
Growth (GHRH)
Lactation (dopamine)
What are the roles of the ventromedial nucleus of the hypothalamus?
Energy and glucose balance
What are the roles of the dorsomedial nucleus of the hypothalamus?
Diurnal rhythms
What are the roles of the suprachiasmatic nucleus of the hypothalamus?
Circadian rhythms
What are the roles of the anterior nucleus of the hypothalamus?
Thermoregulation
What are the roles of the mamillary body of the hypothalamus?
Sleep/wake cycle
What are the 4 areas of the hypothalamus?
- Preoptic area
- Anterior (supraoptic) region
- Middle (tuberal region)
- Posterior (mammillary) region
What connects the hypothalamus to the pituitary gland?
Pituitary stalk
What is narcolepsy associated with?
Loss of hypothalamic orexin neurons
Describe the hypophysial portal system.
Hypophysical portal vessels are on anterior surface of pituitary stalk where vessels arise from primary capillary bed on the median eminence fanning out over the anterior pituitary gland at the pituitary stalk junction
What artery supplies blood to the posterior pituitary?
Tubero-infundibular artery (branch of superior hypophysial artery) arches across top of stalk-pituitary junction where it enters the anterior pituitary gland passing through to supply blood to posterior pituitary
Where is the pituitary gland located?
Sella turcica = bony cavity at base of brain
What are the key features of the anterior pituitary gland?
Develops from pharyngeal epithelium
Contains glandular cells
Parvocellular neurones
Releasing/inhibiting factors via portal system
What are the key features of the posterior pituitary gland?
Develops from neuronal tissue
Contains axon terminals
Magnocellular neurones
Hormones directly released from large magnocellular axons
What hormones does the anterior pituitary release and what is their functions?
- GH: long bone growth but also liver/muscle
- TSH: thyroid hormone (T3/T4) release
- ACTH: corticosteroid release from adrenal cortex + kidney
- FSH/LH: estrogen/progesterone release from ovaries + testosterone release from testis
- Prolactin: milk production
What hormones does the posterior pituitary release and what is their functions?
- ADH: kidney water retention
2. Oxytocin: milk letdown (works with prolactin for this) + uterine SM contractions
What are the 3 neuroendocrine feedback systems of the anterior pituitary gland?
- HPA axis: CRH -> ACTH -> cortisol from adrenal glands
- HPT axis: TRH -> TSH -> T3/T4 release from thyroid gland (somatostatin inhibits release)
- HPG axis: GnRH -> LH/FSH -> estrogen/progesterone (from ovaries) + testosterone (testes)
What is special about prolactin release?
No RF and a short loop feedback system
What factors are thought to stimulate prolactin secretion?
- Placental lactogens as additional sources of lactogen, bypassing feedback
- Reduced dopamine secretion (as it has an inhibitory effect)
- Suckling stimulus may perhaps stimulate PRF (if it exists)
Why are feedback systems so complicated?
Because there are many different factors downregulating and upregulating the reproductive axis for example, so the axis is impacted by various other things
What are some exogenous determinants of the hypothalamus-pituitary-thyroid (HPT) axis setpoint?
Pathophysiological e.g. illness
Physiological e.g. sleep-wake cycle + internal body clock
Energy metabolism
How does thyroid hormones modulate energy metabolism?
PVN: increased glucose production + decreased insulin sensitivity in liver
VMH: increased energy expenditure
ARC: increased food intake
-> feedback to HPT axis setpoint
Where are magnocellular neurones found?
PVN and SON of hypothalamus
Why is oxytocin released in a pulsatile signalling fashion?
Higher overall release achieved than if the release was just constant
What is the effect of low blood pressure (LBP) on the body?
- Major reduction in BV (more than 10%) stimulates high-pressure baroreceptors (aorta/carotid sinus) and low-pressure baroreceptors (atria of heart)
- CN IX + X go to NTS of brainstem stimulating VPN of hypothalamus
- Posterior pituitary releases vasopressin which acts on V1 receptor of blood system
- Vasoconstriction = increased BP
Where are vasopressin V2 receptors found?
Kidneys
