Pituitary Gland and its disorders Flashcards
Where is the pituitary gland located?
Below the brain, encased in a bone cavity of the skull (the sella turcica). It is also known as the ‘master gland’
Where is the hypothalamus located?
Directly above the pituitary gland.
How is the pituitary gland connected to the hypothalamus?
By the infundibulum (pituitary stalk)
What is another word for infundibulum?
Pituitary stalk
Where does the hypothalamus lie?
Directly above the pituitary gland. It lies beneath the thalamus and surrounds the lower portions of the third ventricle.
What is the hypothalamus made up of?
Tuber cinereum, median eminence and several nuclei.
How is the pituitary stalk/ infundibulum formed?
By the continuation of the tuber cinereum and the median eminence. This pituitary stalk joins the hypothalamus with the pituitary.
How is the pituitary gland divided?
Into two separate portions; the anterior and the posterior pituitary glands.
They effectively function independently.
Which gland is a ‘down growth’ form the brain? What is it sometimes called?
Posterior pituitary gland.
Sometimes called the neurohypophysis.
What hormones does the posterior pituitary gland secrete and where do those hormones act?
Antidiuretic hormone (ADH) - kidney tubules
Oxytocin - uterine muscles/ mammary glands.
What type of hormone are ADH and oxytocin? How many amino acids are they composed of?
Peptide hormones - water soluble
Composed of 9 amino acids each; 7 of which are identical
Where is ADH and oxytocin synthesised?
Synthesised by the neurones of the hypothalamus (supraoptic nucleus and paraventricular nucleus)
In what form is ADH and Oxytocin synthesised?
They are formed by the supraoptic nucleus and paraventricular nucleus in the hypothalamus. They are synthesised as inactive precursors and converted to active hormone within the posterior pituitary.
Describe how the inactive hormones are transported.
The inactive hormones are transported from the supraoptic nucleus and paraventricular nucleus alone the hypothalamico-neurohypophyseal tract. They are then stored within the posterior pituitary.
How is ADH released?
ADH secretion is influenced by plasma osmolarity.
Osmoreceptors on the walls of the third ventricle in the brain send impulses to the supraoptic and paraventricular nuclei.
Depolarisation of these nuclei results in an influx of Ca++ at the nerve terminals of the posterior pituitary and releases ADH.
What is the mechanism of action for ADH?
ADH acts on three subtypes of a receptor: V1, V2 and V3.
All are GPCR. V1 and V3 act via IP3 and V2 acts via cAMP.
Which is the most important ADH GPCR?
V2 receptors.
What occurs with V2 stimulation?
Synthesis and translocation of aquaporins (AQP) on the kidney tubule which allows water reabsorption to occur
What occurs with V1 stimulation?
Vasoconstriction. This does not occur at physiological concentrations.
Increased blood osmolarity = ________ ADH secretion
Increased
Increased blood volume = ________ ADH secretion
Decreased
Decreased blood osmolarity = ________ ADH secretion
Decreased
Decreased blood volume = ________ ADH secretion
Increased
Excessive secretion of ADH causes? What are the drug treatments?
Syndrome of inappropriate ADH (SIADH).
Drug treatments: conivaptan, tolvaptan, demeclocycline
Deficient secretion of ADH or decreased responsiveness to ADH causes?
What are the drug treatments?
Diabetes insipidus.
Drug treatments: desmopressin, vasopressin (neurogenic)
Difference between nephrogenic and neurogenic?
Nephrogenic is when enough ADH is secreted but not enough vasopressin receptors present. Can give thiazide?
Neurogenic is when the pituitary gland does not secrete enough ADH.
When is oxytocin synthesised?
Oxytocin synthesis increases during pregnancy but there is also a parallel increase oxytocinase activity.
Oxytocin acts via…
IP3 to cause contraction of mammary glands (breast) and uterine muscles (smooth muscle of genital tract i.e. uterus)
How is oxytocin secretion stimulated?
It is stimulated by stimulation of genitals and nipples
Oxytocin is most important at p______ and during l_______
parturition (during birth)
lactation
What does oxytocin do during parturition?
During parturition, oxytocin causes contraction of the smooth muscle of the uterus which aids expulsion of the infant. Continued stimulation of the cervix causes continued secretion of oxytocin.
What is oxytocin responsible for after parturition?
Oxytocin is responsible for milk ‘let down’, after parturition. The stimulus is suckling but there is a delay between suckling and milk ‘let down’/expulsion.
What is oxytocin secretion important for during coitus?
It may play a role in ejaculation and sperm transport in males and females.
What feed back manner is oxytocin released in?
positive feedback.
The more oxytocin is released, the greater the progression of labour and milk ejection which results in more oxytocin release until these processes are complete.
Is oxytocin necessary for the initiation of a normal labour?
No, but it may be administered to induce labour.
How can oxytocin be administered and what is it used for?
Like other peptides, it will be destroyed in GIT if given orally.
Given as injection or nasal spray.
Used to induce labour, lactation (during insufficient milk ejection) and progression of pregnancy to parturition
Which gland is a ‘up growth’ form the palate?
The anterior pituitary gland.
What hormones does the anterior pituitary gland secrete?
- Follicle Stimulating Hormone
- Prolactin
- Growth Hormone
- Luteinising Hormone
- Adrenocorticotrophic Hormone
- Thyroid Stimulating Hormone
Where are the hormones; FSH, ACTH, TSH, GH etc made and by what cells?
They are made in the anterior pituitary gland and by separate cells:
- ACTH synthesised by corticotrophe cells
- TSH synthesised by thyrotrophe cells
- FSH synthesised by gonadotrophe cells
Oxytocin works as positive feedback. Hypothalamic-pituitary works as?
Negative feedback. This can lead to cyclical variation
The releasing hormones are secreting by?
The hypothalamus into the hypothalamico-adrenohyphophyseal portal vessel, which carries them to the anterior pituitary.
Do the releasing hormones enter systemic circulation
err.. NAH
How many amino acids long is Prolactin?
199 amino acids
Where is prolactin synthesised?
Lactotrophe cells of the anterior pituitary.
Prolactin acts via…
a dimerised tyrosine-kinase receptor
How is prolactin secreted?
- It occurs under hypothalamic control by means of Prolactin
- Inhibiting Factor (Dopamine).
It is pulsatile (greatest at night during REM sleep) - It is stimulated by mild stress, nipple stimulation + coitus
- TRH stimulates prolactin synthesis
How is oestrogen related to prolactin?
Oestrogen increases the number of TRH receptors on the lactotrophes, hence increasing prolactin synthesis/ secretion
What is the role of prolactin?
Promote lactation and development of breast tissue. Most important in females after puberty and during and after pregnancy.
What happens if there is high concentration of oestrogen and progesterone during pregnancy?
It will inhibit prolactin-induced lactation - due to negative feedback?
Prolactin also increases synthesis of ___ receptors, resulting in ______ secretion of progesterone in females and testosterone in males.
LH
increased
H___prolactinaemia typically results in amenorrhea and infertility.
Hyper. Too much prolactin = infertility i.e. you do not ovulate during breast feeding. Breast feeding therefore causes amenorrhea and infertility
Deficiency of prolactin results in inability to?
breast feed/ lactate
What can excess prolactin cause?
Galactorrhoea or gynaecomastia in females AND males.
Because dopamine inhibits prolactin secretion, any drugs which stimulate dopamine activity (eg bromocriptine, cabergoline) will _____ prolactin secretion.
reduce
Dopamine antagonists (eg antipsychotic drugs) cause h____prolactinaemia.
hyper
How many amino acids is Growth Hormone peptide and what receptor does it act on?
191 amino acids
dimerised tyrosine kinase
What cells is growth hormone synthesised in?
somatotrophe cells of the anterior pituitary gland
What second messengers does GH act on?
Insulin like growth factors (IGF) produced in the liver
- IGF-1 and IGF-2
What stimulates and what inhibits growth hormone?
GHRH
Somatostatin
What (foods) is growth hormone stimulated by?
stimulated by decreased carbohydrates and fatty acids and increased amino acids.
What pattern is growth hormone released in? What affects the pattern?
Released in pulses throughout the day.
Obesity decreases the frequency and amplitude of the pulses, fasting increases the frequency and amplitude.
Amplitude of pulses also decreases with age.
What is the primary effect of GH?
To promote the linear growth of adolescence by increasing protein synthesis and collagen deposition. This is mediated via the nucleus.
Is foetal growth dependent on GH?
no
Name two disorders of GH secretions?
Dwarfism
Acromegaly
How can deficiency in GH and excess in GH be treated?
Synthetic growth hormone - Somatropin
GH receptor antagonist - Pegvisomant or somatostatin analogue - octreotide
GH is also involved in tissue ______ and repair.
turnover
