Neurohormones Flashcards
what are neurohormones?
produced by specialised nerve cells called neurosecretory cells and released into the blood rather than the synaptic space
- diffuse out of capillaries and act on receptors
- can have an effect on cells some distance away
- can act as neurotransmitters or autocrine/paracrine messengers
a small amount of hormone released from a neurones can have what kind of effect?
a widespread effect all around the body
Nervous system (Neuron point to point communication) vs Endocrine (Neurohormone communication)
ENDOCRINE SYSTEM
- Mediators travel within blood vessels
- Utilises chemical mediators (hormones)
- Slow communication
- Effects can be long-lasting
NERVOUS SYSTEM
- Signalling along nerve fibres
- Transmission of electrical impulses
- Fast communication
- Effects are generally short-acting
name 3 types of hormones
- peptides/proteins
- can be synthesised in a large precursor
- can be post-transcriptionally modified - amino acid derivatives
- tyrosine derived
- neurotransmitter that can also act as a hormone - steroid hormones
- derived from cholesterol
principal endocrine organs
- hypothalamus
- pituitary gland
- thyroid gland
- parathyroid gland
- adrenal gland
- pancreas
- ovary
- testes
anterior and posterior pituitary
- there are neurons which basically project from the hypothalamus and release neurohormones directly in the portal system, and they are transported to the anterior pituitary, where they bind to receptors and cause a different neurohormones to be released into circulation
- magnocellular neurons project from the hypothalamus directly to the posterior pituitary
different endocrine rhythms
- circadian - 24 hr clock, GH, cortisol (cortisol levels highest in the morning)
- pulsatile - periodicity longer than 24 hrs gonadotrophins
- infradian - periodicity less than 24 hrs menstrual cycle
key nuclei involved with neurosecretory cells
medial pre-optic, the arcuate and the paraventricular nuclei
what causes cortisol release?
CRH, a peptide released directly in the capillary system, is transported to anterior pituitary and causes ACTH release. ACTH travels to adrenal cortex and induce the release of cortisol.
what causes thyroxin release?
TRH induces release of TSH from the anterior pituitary. TSH acts on thyroids and induces release of thyroxin.
what does the posterior pituitary release?
VP and oxytocin from magnocellular neurons
what are Parvocellular neurosecretory cells?
- smallneuronsin the hypothalamic
- axons of these cells project to themedian eminence, at the base of the brain, where the nerve terminals release peptides thehypothalamo-pituitary portal system
- peptides carried to anterior pituitarygland, where they regulate the secretion of hormones into the systemic circulation
what is another name for growth hormone release inhibiting hormone? and what is its effect?
somatostatin
-inhibits GH release, VIP, glucagon, insulin, TSH
list the specialised cells of the anterior pit and their role?
gonadotroph cells - control LH/FSH secretion
somatotroph cells - control GH secretion
corticotroph cells - control ACTH secretion
thyrotroph cells - control TSH secretion
lactotroph cells - control prolactin secretion
ACTH
ACTH is derived from POMC
- stress activates hypothalamic neurones to release CRH, stimulating pituitary corticotrophs to release ACTH
- ACTH stimulates cortisol production from adrenal cortex, glucocorticoids and sex hormone production from zona fasiculata
- Cortisol will induce a negative feedback effect, acting on cortisol receptors in the pituitary/hyp inhibiting CRH or ACTH release
- There is a problem is cortisol is higher for a prolonged period of time eg. periods of chronic stress/repetitive exposure to stressful stimuli (eg. abuse)
- as the HPA is hyperstimulated, which will lead to high levels of basal cortisol levels, leading to depression/anxiety disorders