Session 8 - Endocrinology Flashcards
Where is the pituitary gland located?
Beneath the hypothalamus in a socket of bone called the sella turcica
The anterior and posterior pituitary are connected to the hypothalamus via?
The infundibulum (pituitary stalk)
During embryological development where does the anterior pituitary arise from?
From evagination of the oral ectoderm (primitive gut tissue)
During embryological development where does the posterior pituitary arise from?
From the neuroectoderm (primitive brain tissue)
Name 4 nuclei of the hypothalamus and what they are involved in
- Supraoptic
- Paraventricular
- Arcuate
- Suprachiasmic
1 and 2 contain neurosecretory cells which produce vasopressin and oxytocin
3 controls appetite
4 controls our biological clock
What hormones are produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus?
Oxytocin and anti-diuretic hormones (vasopressin)
What 2 hormones does the posterior pituitary gland store?
Oxytocin and vasopressin
It DOES NOT produce them - it only stores them
For hormones heading to the anterior pituitary what happens to them?
Hormones are released by hypothalamus and travel down axons to the median eminence where they are stored before release into the hypophyseal portal system
These stimulate or inhibit target endocrine cells in the anterior pituitary gland
There are 6 tropic hormones produced in the hypothalamus which have direct effects on release of anterior pituitary hormones. What are they?
- TRH - thyrotropin releasing hormone
- PIH - prolactin release-inhibiting hormone
- CRH - corticotropin releasing hormone
- GnRH - gonadotropin releasing hormone
- GHRH - growth hormone releasing hormone
- GHIH - growth hormone inhibiting hormone
What are tropic hormones?
Hormones that affect the release of other hormones in the target tissue
The tropic hormones in the hypothalamus stimulate which 6 hormones to be released from the anterior pituitary?
- Thyroid stimulating hormone
- Adrenocorticotropic hormone
- Luteinising hormone
- Follicle stimulating hormone
- Prolactin
- Growth hormone
What is released at each stage of the hypothalmic-pituitary-adrenal axis?
Hypothalamus: CRH (corticotropin releasing hormone)
Anterior pituitary: ACTH (adrenocorticotropic hormone)
Adrenal cortex: cortisol
What hormone is the most important endocrine regulator of growth?
Growth hormone
What stimulates and inhibits growth factor release by the anterior pituitary?
Stimulates = GHRH (growth hormone releasing hormone)
Inhibits = Somatostatin
These are both released by hypothalamus
What are growth hormone’s effects mainly exerted by?
Insulin like growth factor (IGF) - mainly IGF1
IGF1 is released by the liver and skeletal muscles (in the liver IGF can then travel around the bloodstream)
What does GH do in children?
Stimulates long bone growth
IGFs stimulate cartilage and bone growth
When during the day is GH levels highest?
Growth hormone levels are highest as soon as you fall into deep sleep
Name 3 things that decrease GH secretion
- REM sleep (rapid eye movement)
- High glucose or fatty acid levels
- Obesity
Name 4 things that increase GH secretion
- Stress eg trauma or surgery
- Exercise
- Decrease in glucose or fatty acid secretion
- Fasting
What does growth hormone deficiency in childhood lead to?
Pituitary dwarfism
What does growth hormone excess in childhood and adulthood lead to?
Childhood = gigantism Adulthood = acromegaly
When GH binds to a GH receptor what is activated?
Janus Kinases
What type of receptor is a GH receptor?
Tyrosine kinase receptor
What is the major insulin like growth factor in humans?
IGF1
IGF2 only exists in fetal growth
What receptors can IGF1 act on?
IGF1 receptor
A hybrid receptor (mix of insulin/IGF1)
Insulin receptor
Are pituitary tumours mostly benign or malignant?
They are always benign (ie confined to their site of origin)
What are the 2 effects of pituitary tumours?
- Mass effect of tumour on local structures
2. Abnormality in pituitary function
A pituitary tumour if growing upwards can compress which area?
The optic chiasm leading to visual field loss
What happens if the optic chiasm is compressed by a pituitary tumour?
It causes bitemporal hemi-anopia
What happens if a pituitary gland grows sidewards?
It will cause pain and double vision as the nerves controlling eye movement and pain are compressed into
What is hypopituitarism?
Loss of pituitary hormones
Hormones that are normally under positive control by the hypothalamus won’t be secreted and those under negative control will be increased
What are the signs of a gonadotropin hormone deficiency?
Loss of secondary sexual characteristics in adults and loss of periods in women
The hypothalamic-pituitary adrenal axis is key as reduced adrenocorticotropic hormone causes what?
Low cortisol, tiredness, dizziness. low sodium, low BP and can be life threatening
Pituitary gland tumours are more likely to cause abnormality in which 3 hormones?
Growth hormone
Prolactin
Adrenalcorticotropin hormone
Why might you need dynamic blood tests for GH axis and HPA axis? What does this mean?
Growth hormone and adrenocorticotropic hormone levels vary throughout the day so you may need to take a number of results
GH/IGF1 is highest during deep sleep and when levels of glucose are low
Cortisol is highest first thing in the morning
If you thought a patient had a problem with their HPA axis (causing decreased cortisol in the bloodstream) what tests would you do?
If deficiency in cortisol production you want to try and stimulate production to see if it responds:
1) Insulin stress test - when a patient is given insulin it makes them stressed and lowers blood sugar levels which should increase levels of cortisol
2) ACTH test - target adrenal cortex directly with ACTH which should cause increased cortisol release
If you thought a patient had a problem with their HPA axis (causing increased cortisol in the bloodstream) what test would you do?
If increase in cortisol production you want to try and suppress production to see if it responds:
1) Give the patient dexamethasone- this should decrease ACTH release and therefore levels of cortisol
If you thought a patient had a problem with their GH axis (causing increased GH in the bloodstream) what test would you do?
If increase in GH/IGF1 production you want to try and suppress production to see if it responds:
1) Glucose tolerance test - give the patient sugar and see if the GH levels decrease
If you thought a patient had a problem with their GH axis (causing decreased GH in the bloodstream) what test would you do?
If decrease in GH/IGF1 production you want to try and stimulate production to see if it responds:
1) Insulin stress test - give the patient increase to stress them and lower the blood sugar levels which should increase GH release
What is prolactinoma and how would you treat it?
A pituitary gland tumour causing increased prolactin secretion
Treatment = dopamine tablets which will shrink the tumour
What should you always check before sending a patient to surgery to remove a pituitary gland tumour?
Prolactin levels
If prolactin levels are over 5,000 = prolactinoma (prolactin secreting hormone) which can be treated with dopamine tablets
The patient then wouldn’t need surgery
What is hyperprolactinaemia?
Abnormally high levels of prolactin in the bloodstream
What does prolactin inhibit?
It inhibits luteinising hormone which results in reduced sex hormones
Give 3 symptoms of hyperprolactinaemia in women
Hyperprolactinaemia = high levels of prolactin in the body
Symptoms:
1. Menstrual disturbance
2. Fertility problems
3. Galactorrhoea (milk from breasts outside pregnancy)
What are the differences in symptoms between men and women in hyperprolactinaemia?
Women present with symptoms whereas most men don’t present with any (unless mass symptoms such as visual loss)
Low testosterone levels are non-specific in men
What prolactin levels = surgery and which = dopamine tablets? Why?
Prolactin levels high but BELOW 5000 = needs surgery
Prolactin levels high and ABOVE 5000 = can be treated with dopamine tablets
If the prolactin levels are high but below 5000 it is likely the high levels are due to disinhibition (a pituitary tumour blocking the infundibulum from receiving signals and inhibiting prolactin release)
If the prolactin levels are high and over 5000 then it is due to a prolactinoma secreting prolactin
What would a dopamine antagonist do to prolactin levels?
Increase levels of prolactin
What causes acromegaly and what are the long term complications if untreated?
Acromegaly in caused in adults with a GH secreting pituitary tumour Long term complications: - Premature CV death - Increased risk of colonic tumours - Increased risk of thyroid cancer - Hypertension and diabetes
What is the treatment for acromegaly?
Medication: 1. Dopamine agonist 2. Somatostatin analogues 3. Drugs to block GH receptor Surgery: Removal of tumour Radiotherapy: 1. External beam - multiple bursts over week 2. Gamma knife - high concentration once
What is Cushing’s disease?
An ACTH secreting pituitary tumour (leading to increased cortisol release)
What is diabetes insipidus?
The posterior pituitary gland secretes a lack of vasopressin (anti-diuretic hormone) resulting in excessive pale urine and thirst
How would you treat a patient with diabetes insipidus?
Synthetic vasopressin
What are the consequences of untreated diabetes insipidus?
- Severe dehydration
- Hypernatraemia
- Reduced consciousness
- Coma
- Death
What is pituitary apoplexy?
A sudden vascular event in a pituitary tumour leading to stroke (eg from bleeding within a tumour or a tumour cutting off blood supply)
