Lecture 2 Flashcards
What is the HPA axis?
HPA = Hypothalamus Pituitary Adrenals
Hypothalamus releases hormones, e.g cortisol
Hormones act on anterior pituitary
Anterior pituitary releases ACTH which acts on the adrenal cortex
Negative feedback loops regulate it
What is the function of the HPA axis/neuroendocrine system?
Maintain homeostasis (osmolarity, glucose, other fuels, body temperature)
Make large and rapid changes to internal physiology (mating behaviour, threat recognition, mood, emotion, etc)
Regulation of diurnal/circadian patterns
How does cortisol act in the HPA axis?
Very complex; Cortisol feeds back at all levels to fine-tune its release
Describe the changes to cortisol levels during the day
See almost hourly rhythm of peaks throughout the day with cortisol; Cortisol reaches peak in early morning explaining anti-inflammatory effect of cortisol; Inflammation (e.g sore throat) is better in the morning due to high cortisol levels; Cortisol = high in second half of day
Where is the pituitary gland found?
Pituitary gland is a central system so is well protected; It is a very sensitive organ sat in a bony structure called the sella turcica; Pituitary gland is sat in close proximity to the optic chiasm
What happens if someone has a pituitary tumour? Why?
Leads to impaired/blurry vision; Tumour in the pituitary gland grows into the optic chiasm, causing impaired vision
What are the 2 major regions of the pituitary gland and what are they made up of?
Anterior pituitary (pars tuberalis, pars intermedia, pars distalis); Posterior pituitary (infundibular stalk, pars nervosa)
What is a feared consequence of skull trauma? What effect does this have?
Feared complication of skull trauma is damage to the infundibular stalk; Can cut off the pituitary gland, causing local bleeding and immediate loss of hormonal control
What are the 2 main arteries that supply the pituitary gland? How do they work?
Superior hypophyseal artery; Inferior hypophyseal artery; Both feed into portal systems; Portal systems = dense networks of venous vessels around pituitary gland; Arteries carry hormones
Describe the structure of the anterior pituitary
Very organised structure
Describe the structure of the posterior pituitary
Hormones are produced in the brain; Has characteristic herring bodies (vesicles for storing neuroendocrine hormones for swift release)
Describe the structure of the pars intermedia
Has follicular structures; Has basophil cells
How are hormones produced and transported in the posterior pituitary? Give some example hormones
Hormones released from posterior pituitary are produced in neurones (e.g ADH, oxytocin); Hormones mature and are transported down axons of neurones directly to the portal systems for release
How are hormones produced and transported in the anterior pituitary? Give some example hormones
Neurones release stimulating/inhibiting hormones; These hormones are released into the 1st venous network and transported to anterior pituitary; Secretory cells stimulated/inhibited to control hormone production (e.g tropic hormones)
Give some examples of hormones released by the pars nervosa of the posterior pituitary and what they do
Oxytocin: Uterus contractions, Milk ejection, Emotional control (bonding mechanisms in mammals); Vasopressin/AVP/ADH: Water reabsorption, Vasoconstriction; Non-tropic hormones
How are oxytocin and vasopressin produced in neurones?
Have quite a similar gene and AA structure (only 2 AA difference); Produced in pre-forms at different levels in neurones
What is neurophysin 2? How is it synthesised?
Neurophysin 2 = carrier protein for vasopressin; Vasopressin and neurophysin 2 are co-synthesized due to its role as a carrier protein
What is the primary effect of vasopressin (AVP)/ADH?
Primary effect = increase water retention/decrease urine output
What is the effect of high concentrations of AVP/ADH?
High concentrations cause arteriole restriction and increased blood pressure
How is AVP/ADH transported in the kidneys?
Transported via a type 2 vasopressin receptor (G-protein coupled receptor); Causes sodium influx into kidney cells and drives water transport through aquaporin 2 channels, increasing water retention
Describe how an increase in plasma osmolarity affects ADH levels, and describe the effects on the brain
If osmolarity increases, person experiences thirst; Osmotic pressure is sensed by osmoreceptors in the hypothalamus; Hypothalamus stimulates ADH release and thirst to reduce blood osmotic pressure
Give some examples of factors controlling AVP
Fall in blood volume (>8%) increases AVP release (important in hemorrhage); Also affected by arterial decreased pO2, increased pCO2, other hormones (angiotensin II, epinephrine, cortisol, oestrogen); CNS control: pain, trauma, nausea, vomiting stimulate AVP; Increased ambient temperature; Alcohol inhibits AVP secretion
Where are AVP type I receptors found?
Found in many places (e.g endothelial cells); Mediate vasoconstriction
What is diabetes insipidus?
Most common disease related to ADH; Has 2 forms; Major sign = increased urine production (up to 20 litres/day); Requires increased fluid intake; Genetic mechanisms are hard to tackle
