Lecture 26: Neuroendocrinology Flashcards
What is endocrinology?
the study of hormones, their receptors and their intracellular signalling pathways
Define hormones
chemical messengers produced in one location and transported to a second location (target cells) where they exert their effects.
Hormones often reach their target via what?
the bloodstream
Do hormones act in high or low concetrations?
low concentrations
What are the 4 principle functions of the endocrine system?
- maintain homeostasis
- regulation of growth and development
- control energy storage and use
- mediate the body’s response to environmental cues
What is the purpose of maintaining homeostasis?
to maintain a stable internal environment in the face of a changing external environment
What are the 4 types of hormone communication in the body?
- autocrine
- paracrine
- endocrine
- neurocrine
Describe autocrine communication of homrones
a cell releases a hormone to have an effect on itself to cause a response ie. the target cell is the cell that released the hormone
Describe paracrine communication of hormones
a cell releases a hormone to have an effect on a target cell which is in the same tissue as the cell releasing the hormone ie. the cell releasing the hormone acts locally
Describe endocrine communication of hormones
A cell releases a hormone which enters the bloodstream and has an effect on a target cell far away
Describe neurocrine communication communication of hormones
The cell releasing the hormone is a neuron and it releases the hormone which enters the bloodstream and has an effect on a cell far away from the cell releasing the hormone
How can we chemically classify hormones?
Where do these come from?
- peptide/protein hormones (dependent on length)
- amine hormones (derivatives of tyrosine)
- steroid hormones (synthesised from cholesterol)
- prostaglandins (synthesised from arachidonic acid)
What are the fates of secreted hormones?
- excreted in the urine of faeces
- inactivated by metabolism
- activated by metabolism
- bind to a receptor and produce a cellular response
How do we achieve spatial and temporal specificity?
hormones can be temporarily released and we can achieve spacial specificity by receptors being expressed on certain tissues and only those receptors can bind to hormones
Describe the synergic effect of hormones
the effect of two hormones working together is larger than the combined effect of each individual hormone
What does the circadian rhythm explain?
it shows that physiological functions are controlled by a clock
Where does our body clock reside?
in the suprachiasmatic nucleus
What is the body clock in the suprachiasmatic nucleus regulated by?
light
How long is the rhythm of our biological clock?
about 25 hours
Which gland releases melatonin?
the pineal gland
When is melatonin secreted?
in the dark
Describe the biological clock, the release of melatonin and mention the Zeitgeber
The body clock resides in the suprachiasmatic nucleus in the hypothalamus. This clock is regulated by light. The rhythm is longer in the dark and light adjusts it every day. The rhythm is generated by the clock and it is adjusted by light every 24hrs. The internal cue that regulates this clock is melatonin which is produced by the pineal gland and is secreted in the dark
What are the two parts of the pituitary gland called?
anterior pituitary
posterior pituitary
What 5 things does the pituitary gland regulate?
water balance metabolism body growth reproduction milk secretion
Describe the hypothalamic control of the anterior pituitary gland hormone secretion
There are cell bodies in the hypothalamus which release signals that act on the median eminence which allows the brain to communicate with the blood stream. The hypothalamus secretes a regulatory hormone which reaches the anterior pituitary through the median eminence (there is a nerve terminal in the median eminence which is connected to the bloodstream). Then the anterior pituitary gland makes another hormone
Corticotropin releasing hormone is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland? What is the target tissue for this hormone?
CRH stimulates the release of adrenocorticotropic hormone which acts on the adrenal gland
Thyroid releasing hormone is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland? What is the target tissue for this hormone?
TRH stimulates the release of thyroid stimulating hormone which acts on the thyroid gland
Gonadotropin-releasing hormone is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland? What is the target tissue for this hormone?
GnRH stimulates the release of luteinizing hormone/follicule stimulating hormone to be released from the AP which acts on the gonads
Growth hormone releasing hormone is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland? What is the target tissue for this hormone?
GHRH stimulates the release of growth hormone from the anterior pituitary gland which acts on the liver and other tissues
Somatostatin is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland?
SS stops the release of growth hormone from being released from the anterior pituitary gland
Dopamine is released from the hypothalamus which causes what hormone to be released/inhibited from the anterior pituitary gland? What is the target tissue for this hormone?
DA stops the release of prolactin from being released from the anterior pituitary gland which normally acts on the breast
What three things does growth hormone stimulate?
postnatal growth and development, metabolism, body composition
What sort of hormone is the growth hormone?
a peptide hormone
In what way is growth hormone secreted?
in little bursts (pulsatile)
The pattern of GH secretion and the receptor expression is what?
sexually dimorphic
What is the half-life of GH in blood and how is it transported?
20-25 minutes
it is transported bound to growth hormone binding protein
GHRH axis is stimulated by what?
exercise, stress, fasting, low glucose and sleep
Whereabouts in the hypothalamus do the somatostatin neurons reside?
in the periventricular nucleus
Whereabouts in the hypothalamus so the GHRH neurons reside?
in the arcuate nucleus
Describe the control of growth hormone secretion
GHRH facilitates the release of GH by the anterior pituitary gland. The GH acts in the liver and it causes the release of insulin-like-growth factor 1 which inhibits the GHRH neurons. It also stimulates the SS neurons to inhibit the release of GH.
What is a somatotroph?
this is a specialised cell in the anterior pituitary gland for making GH
What receptors does the somatotroph have? What are these for?
They gave a GHRH receptor to bind GHRH and an SS receptor to bind SS.
Describe the effect of GHRH binding to the GHRH receptor on a somatotroph
This binding activates adenylyl cyclase via a G-protein which produces cyclic AMP by dephosphorylating ATP. This stimulates protein kinase A to open Ca2+ channels so the Ca2+ concentration increases which stimulates the release of GH.
Describe the effect of SS binding to the SS receptor on a somatotroph
the binding of SS inhibits the G-protein so there is no PKA, no Ca2+, no GH released
What are some direct growth effects of GH?
- stimulates protein synthesis in muscle
What are some indirect growth effects of GH?
It stimulates the growth of ______, ________ and other _________ by stimulating __________ via _________-_________ ________ _________ ____
- stimulates the growth of bones, muscles and other tissues by stimulating cell division (mitogenesis) via insulin-like growth factor (IGF-1)
What are 2 direct metabolic effects of growth hormone?
- increases blood ______ by stimulating _______ synthesis (in the ________) and inhibiting cellular uptake of ________
- increases ___________ breakdown and _______ ________ ________ mobilisation
- increases blood glucose by stimulating glucose synthesis (in the liver) and inhibiting cellular uptake of glucose
- increases triglyceride breakdown and free fatty acid mobilisation
When is GH released?
it is released in a pulsatile and diurnal pattern and is mostly released at night
What is a result of excess GH production?
giganticism
How does the hypothalamus influence the posterior pituitary gland?
Axon terminals from the hypothalamus directly project into the PPG. The PG has an axonal nerve endings of nerves that reside in the hypothalamus.
What is the name of the cell that projects from the hypothalamus into the posterior pituitary gland?
magnocellular neurosecretory cell
Where does the magnocellular neurosecretory cell reside in the hypothalamus?
in the supraoptic and paraventricular nuclei
What are the only 2 hormones released from the PPG?
- vasopressin
- oxytocin
What is vasopressin secreted in response to?
an increase in plasma osmotic pressure or decreased blood volume
What is the role of vasopressin?
it inhibits urine production in the kidney and causes blood vessel contraction
What are the roles of oxytocin?
It acts upon the _______ to promote _______ secretion and increases the release of a_______ n_________ f_______ from the _________. It contracts the __________ __________ for ________ let-down during __________ and causes _________ ____________ during delivery
It acts upon the kidney to promote sodium excretion and increases the release of atrial natriuretic factor from the heart. It contracts the mammary ducts for milk let-down during suckling and causes uterine contraction during delivery
What happens during diabetes insipidus?
the secretion of vasopressin is impaired or absent
