Lec2 - Hypothalamic Pituitary Axis Flashcards
- Overview of hypothalamic-pituitary axis - Assessment of anterior pituitary function - MRI and visual field assessment in patients with HPA disease
What is the area of the brain directly above the pituitary gland?
Hypothalamus
The pituitary gland is connected to the brain via the
Infundibulum
Trauma to the head, causing the infundibulum to get snapped can result in?
Endocrine problems, with effects on the ovaries and testes etc.
What happens if the pituitary gland becomes enlarged?
It can press on the optic chiasm, causing bilateral hemianopsia
The infundibulum contains
The hypothalamico-hypophyseal tract &
the hypothalamico-hypophyseal portal vessels
Name the two portions of the pituitary gland
The anterior pituitary gland &
posterior pituitary gland
How do the anterior and posterior pituitary glands function in relation to one another?
Independently
The posterior pituitary gland is what type of growth from the brain
A “down growth”
The posterior pituitary is also known as:
Neurohypophysis
Name the hormones stored and secreted from the posterior pituitary gland
Anti-diuretic hormone (ADH)/ Vasopressin
Oxytocin
What type of hormones are ADH and oxytocin?
Peptide hormones
How many amino acids in ADH and oxytocin?
Nine amino acids
How many of the amino acids are identical in ADH and oxytocin?
7
What does is the significance of the fact that there are 7 identical amino acids in ADH and oxytocin?
That at high concentrations of each, there can sometimes be cross over of activity e.g. at high concentrations of ADH it has some of the effects of oxytocin
Where are the hormones ADH and oxytocin synthesised?
In neurons of the hypothalamus:
Supraoptic nuclei
Paraventricular nucleus of the hypothalamus
In what form are ADH and oxytocin synthesised?
They are synthesised as inactive precursor hormones
Where are ADH and oxytocin converted into active hormones?
In the posterior pituitary gland
The inactive hormones are transported from the supraoptic nuclei and paraventricular nucleus to the pituitary gland via the:
Hypothalamico-neurohypophyseal tract
What is secretion of ADH influenced by?
Plasma osmolarity
ADH causes stimulation of what receptors?
V2 receptors
Stimulation of v2 receptors results in:
translocation of aquaporins to the membrane of the kidney tubule, allowing water reabsorption
ADH reabsorbs water in the kidney tubule so
there is less urine output
If there is dehydration, what happens to ADH?
ADH is secreted
Dehydration can also occur during haemorrhage which leads to a:
reduction in blood pressure
At high concentrations ADH causes:
an increase in blood pressure
Disorders of ADH secretion lead to:
disorders of fluid balance
A reduction in ADH secretion leads to:
an increase in urine volume
What is DIABETES INSIPIDUS?
A lack of ADH secretion
resulting in high volume of diluted urine
How do you treat DI?
By giving ADH
Increased ADH leads to:
Syndrome of Inappropriate ADH (SIA)
Syndrome of Inappropriate ADH causes:
very dilute blood and produce very little urine
How do you treat SIA?
Removal of the tumour and restrict fluid intake
Oxytocin acts via which second messenger?
IP3
Oxytocin causes
contraction of the smooth muscle of the uterus and breast
Oxytocin is most important during:
parturition and lactation
Secretion of oxytocin is stimulated by:
stimulation of the genitals and nipples
Stimulation of V1 receptors cause:
Vasoconstriction but this does not happen at physiological concentrations of ADH
Oxytocin synthesis increases during
pregnancy
An increase in oxytocin synthesis during pregnancy also results in a parallel increase in:
oxytocinase activity
During parturition, oxytocin causes contraction of smooth muscle of the uterus to aid:
expulsion of the foetus
What is oxytocin responsible for after parturition?
For milk ‘let down’ / expulsion
What is the stimulus for milk let down?
Suckling, but there is a delay between the start of suckling and milk let down
Many women start secreting oxytocin when they hear what?
When they hear the baby crying
Is oxytocin necessary for the initiation of normal labour?
No
Why is administration of oxytocin to induce labour not part of current NICE guidelines?
Because oxytocin causes the uterus to contract but if the cervix hasn’t dilated, then the baby has nowhere to go and this can cause damage to the baby
The anterior pituitary gland is what type of growth from the palate?
An upgrowth
Name the hormones stored and secreted from the anterior pituitary gland:
Adrenocorticotrophic hormone (ACTH) Growth hormone (GH) Thyroid stimulating hormone (TSH) Follicle stimulating hormone (FSH) Luteinising hormone (LH) Prolactin (PRL)
Prolactin is involved in
milk synthesis
Oxytocin is involved in
milk expression
Thyroid stimulating hormone is synthesised by:
thyrotrophe cells
Adrenocorticotrophic hormone is synthesised by:
corticotrophe cells
Follicle stimulating hormone (FSH) is synthesised by:
gonadotrophe cells
Tumours of the pituitary gland can cause:
excess secretion of one or all of the hormones secreted by the pituitary gland
The hypothalamus secretes: Thyrotrophin Releasing Hormone (TRH) Corticotrophin Releasing Hormone (CRH) Gonadotrophin Releasing hormone (GnRH) Growth Hormone Releasing Hormone (GHRH)
to stimulate secretion of: Thyroid stimulating hormone (TSH) Adrenocorticotrophin hormone (ACTH) Follicle Stimulating Hormone (FSH) Growth Hormone (GH)
The releasing hormones are released by the hypothalamus into the:
hypothalamico-adenohypophyseal portal vessels which carry them into the anterior pituitary gland
Do the releasing hormones enter the systemic circulation?
No
The signs are
what the doctor can see
The symptoms are
what the patient reports
What biochemical tests should be done?
TSH & FT4 Cortisol LH and FSH PRL Testosterone/ ask about periods
Why do we measure FSH?
To see whether the problem is in the pituitary or in the ovary
How do we learn about the female sex hormones in a patient?
By asking a woman about her periods
How can we tell about testosterone levels in a man?
By looking at him
When do we experience the highest levels of cortisol?
In the morning, just after getting out of bed
What are the next steps in investigation after biochemical tests?
Imaging e.g. MRI of pituitary
Visual field tests e.g. bitemporal hemianopia means there is compression of the optic chasm
How many amino acids in prolactin?
199 amino acids
Where is prolactin synthesised?
Lactotrophe cells of the anterior pituitary gland
The secretion of prolactin is under what kind of control?
Hypothalamic control by means of Prolactin Release Inhibiting Factor aka DOPAMINE
DOPAMINE
inhibits prolactin release
Thyrotrophin releasing hormone
stimulates prolactin release
Anti-psychotic medications are
dopamine antagonists
Therefore anti-psychotic medications e.g. haloperidol
induce prolactin secretion
Prolactin secretion is stimulated by:
Mild stress
Nipple stimulation
Coitus
Prolactin inhibits
fertility - it is harder to get pregnant whilst breastfeeding
What is the primary role of prolactin is to
promote lactation and the development of breast tissue
Hyperprolactinaemia
is the most common cause of infertility
A tumour of the pituitary gland which secretes prolactin is called
A prolactinoma
What happens to prolactin production as we age?
It increases
Where is growth hormone synthesised?
Somatotrophe cells of the anterior pituitary gland
Secretion of growth hormone is controlled by?
Hypothalamic control via the growth hormone releasing hormone
Growth hormone inhibiting hormone is also known as
Somatotrophin
What has more control in the release of GH - GHRH or GHIH?
Growth hormone releasing hormone GHRH
Secretion of growth hormone is stimulated by
decreased carbohydrates and fatty acids and increased amino acids
In some tissues, GH acts via
second messengers
Where are these second messengers produced?
In the liver
What are the second messengers produced in the liver called?
Insulin-growth-factor 1
Insulin-growth-factor 2
What is the function of these second messengers?
to promote growth
What is the primary effect of GH?
to promote linear growth of adolescence by increasing protein synthesis and collagen deposition
Growth hormone is also involved in
tissue turnover and repair
Foetal growth is relatively independent of GH - True or False?
True