Pituitary gland, hormones and conditions Flashcards
Where is the pituitary gland located?
The pituitary gland is the ‘master gland’ and is suspended by the pituitary stalk in the crevice of the sphenoid bone (under the brain)
What type of tissue is found in the anterior and posterior pituitary?
anterior: glandular epithelial tissue
posterior: nervous tissue
What is the role of the pineal gland?
To produce melatonin that regulates sleep patterns and circadian rhythms
What hormones are produced by the neuronal cell bodies in the hypothalamus?
- Oxytocin
- Vasopressin
These hormones are packaged into secretory vesicles to be transported doen the axon cytoplasm and to be stored in the neuronal terminals in the posterior pituitary. Terminal stores store oxytocin or vasopressin , NOT both= are released independently into the bloodstream
What are the functions of the hormone ‘oxytocin’?
- Contraction of uterine to help dispel infant during childbirth- secretion is increased by reflexes in the birth canal
- Promotes ejection of milk from the mammary glands during breastfeeding- secretion is increased by infant sucking
- Influences social behaviours- helps with mating/bonding with infants/relationships
- used in an injection known as Syntocinon to induce labour and to prevent postpartum haemorrhage. also used in early pregnancy in the case of incomplete abortion.
What are the functions of the hormone ‘Vasopressin’?
- vasopressin is an anti-diuretic hormone with 2 main functions:
- Enhances water retention in the nephron during urine production. Binds to V2 receptor causing an increase in water permeability in the distal tubule and collecting ducts= increased water reabsorption
- contraction of arteriolar smooth muscle- a minor role in regulating blood pressure- by binding o V1 receptor causing increased vasoconstriction
What is diabetes insipidus?
A condition caused by a lack of vasopressin hormone (ADH) leading to increased urine production and thirst
Polyuria and polydipsia
What can happen if diabetes insipidus is left untreated?
- If the condition is left untreated, it can lead to ‘shock’ like symptoms such as:
Hypotension
Tachycardia- over 100bpm
Tachypnoea- rapid, shallow breathing
Dehydration
electrolyte problems- increase in sodium concentration exceeding 145 mmol/L
What are the treatment options for diabetes insipidus?
- Mild cases may not need any treatment- just increase levels of fluids
- Vasopressin injection
- Desmopressin- injection/tablet/nasal spray- is an analogue of vasopressin that is used to replace the hormone levels
What are the two types of diabetes insipidus?
- Nephrogenic- kindeys
- Cranial- brain
What is the cause of cranial diabetes (the more common type)?
Hypothalamus isn’t producing ADH/vasopressin for the pituitary gland to secrete. This can occur after damage to the hypothalamus e.g. after a head injury, infection (TB, meningitis, encephalitis), operation, brain tumour,radiotherapy
What is the cause of nephrogenic diabetes insipidus?
This occurs when there is enough Vasopressin/ADH being secreted from the pituitary gland but the collecting ducts in the kidneys are not responding to it.
- This can be caused by kidney damage,
drugs such as lithium (used in bipolar)
can be genetic e.g. mutations in the AVPR2 gene
electrolyte imbalances e.g. hypokalemia or hypercalcemia
How is one diagnosed with diabetes insipidus/what investigations are carried out?
- Blood tests- look for hypernatraemia (raise in sodium serum concentration)
- Urine osmolality- will show a low value as the concentration of solutes is being diluted by the excess water
- Serum osmolality- This will show a high value as there is a high concentration of solutes in the blood.
BUT TEST OF CHOICE:
- Water deprivation test ( Desmopressin simulation test);
the patient can’t have any food or drink for 8 hours prior- fluid deprivation
- Measure urine osmolality
- Then give synthetic ADH- Desmopressin is given
- After 8 hours, measure the urine osmolality again
if it is cranial diabetes insipidus-
After deprivation= low
after synthetic ADH= values will be high
As the hypothalamus cant produce ADH
if it is nephrogenic diabetes insipidus-
low osmolality at the start and after synthetic ADH
as can’t respond to the ADH
- if high at the start, it is not diabetes insipidus and is likely to be primary polydipsia and there is no need to progress with the test
How is the water deprivation test used to diagnose diabetes insipidus?
- Water deprivation test ( Desmopressin simulation test);
the patient can’t have any food or drink for 8 hours prior- fluid deprivation - Measure urine osmolality
- Then give synthetic ADH- Desmopressin is given
- After 8 hours, measure the urine osmolality again
if it is cranial diabetes insipidus-
After deprivation= low
after synthetic ADH= values will be high
As the hypothalamus cant produce ADH
if it is nephrogenic diabetes insipidus-
low osmolality at the start and after synthetic ADH
as can’t respond to the ADH
- if high at the start, it is not diabetes insipidus and is likely to be primary polydipsia
What horomones are released by the anterior pituitary and which cells release them?
- Somatotropes- Growth hormone (GH)
- Thyrotropes- TSH (thyroid stimulating hormone)
- Corticotropes- ACTH ( adrenocorticotrohic hormone)
- Gonadotropes- FSH and LH (follicle stimulating hormone & luteinizing hormone)
- Lactotropes- Prolactin
