Human Development Flashcards
What are the four general functions of hormones?
- Stimulate cell function
- Inhibit cell function
- Maintain a physiological state
- Stimulate or inhibit cell growth or differentiation
What organ produces TSH?
Anterior pituitary
What specialised cells produce TSH?
Thyrotrophs in the anterior pituitary
What organ produces TRH?
Hypothalamus
Describe the thyroid axis:
1) The hypothalamus releases TRH
2) The anterior pituitary releases TSH
3) The thyroid glad releases T3 and T4
4) T3 and T4 travel to organs and affect basal metabolic rate and pulse
5) High levels of T3 and T4 feeds back to the hypothalamus and the anterior pituitary to halt TRH and TSH production respectively.
What kinds of hormone are TRH, TSH, T4 and T3?
TRH = releasing factor
TSH = trophic hormone
T3 and T4 = target hormone
What causes hypothyroidism?
A deficiency at any point within the thyroid axis.
What is tertiary deficiency in hypothyroidism?
A problem with the hypothalamus and TRH
What is secondary deficiency in hypothyroidism?
A problem with the anterior pituitary and TSH
What is primary deficiency in hypothyroidism?
A problem with the thyroid gland itself and T3/T4
What is peripheral resistance in hypothyroidism?
Where the target tissues do not recognise T3/T4 circulating in the blood.
What is the most common form of hypothyroidism?
Primary
What is an example of incidental hypothyroidism?
When patients go to ophthalmologists for vision problems and it turns out to be caused by a pituitary mass pressing down on the optic chiasm.
Where does the pituitary gland lie in the skull?
In the sella turcica
What is severe bi-temporal haemianopia?
Partial blindness where the vision is completely gone from the outer half of both eyes.
What are the hormones released by the anterior pituitary?
TSH ACTH GH LH/FSH PRL
What are the signs and symptoms of hypothyroidism?
- Weight gain
- Lethargy
- Low mood
- Cold intolerance
- Dry, cold, yellowish skin
- Non-pitting oedema
- Dry, coarse scalp hair, loss of lateral aspect of eyebrows
- Hoarse voice
- Decrease in memory/cognition
- Constipation
- Menorrhagia
- Decreased deep tendon reflexes
- Carpal tunnel syndrome
- Goitre
- Weakness/myalgia
What changes in hormones occur in an almost complete anterior pituitary failure?
- Slightly increased prolactin
- Decreased growth hormone and cortisol response to hypoglycaemia
- Decreased testosterone
- Normal thyroxine
How do you test for TSH levels?
By checking T3/T4 levels
How do you test for LH levels?
By checking testosterone and oestradiol levels
How do you test for FSH levels?
Spermatogenesis
Folliculogenesis
How do you test for GH levels?
IGF-1 (insulin-like growth factor 1) - do an insulin tolerance test (ITT)
How do you test for ACTH levels?
Measure cortisol levels by a synacthen test
What is an insulin tolerance test?
Insulin is injected and blood glucose levels are measured at regular intervals.
What is an adequate cortisol response to an ITT?
A rise in cortisol to greater than 550nmol/L
What is an adequate GH response to an ITT?
GH levels exceeding 20mU/L
How do you determine the level of the endocrine axis/hierarchy that is abnormal?
By measuring the function of each level in turn.
What are the 5 steps of a general endocrine evalutation?
1) Assess clinical symptoms
2) Determine what hormone is causing the symptoms
3) Determine the level of the endocrine axis
4) Localise the site of the abnormality
5) Identify the pathology
if T4 is low, but TSH is high, then it is _______ _______________.
Primary hypothyroidism
If T4 is low and TSH is low, then it is ______________.
Hypopituitary
How is prolactin secreted?
Dopamine (which inhibits pituitary lactotrophs) is no longer released or recognised allowing prolactin to be secreted.
What is the size difference between microadenoma and macroadenoma?
Greater or smaller than 10mm
What does excess GH secretion cause?
Acromegaly - enlargement of hands and feet
What does excess ACTH secretion cause?
Cushing’s syndrome
What does excess PRL secretion cause?
Galactorrhoea (abnormal lactation) and amenorrhoea (absence of menstruation)
What does excess TSH secretion cause?
Thyrotoxicosis
How do you determine if a macroadenoma is functioning?
You stain for particular cell groups.
The surgery to remove a pituitary tumour is called ____________________ surgery.
Trans-sphenoidal
What are the four ways a pituitary tumour can be treated?
1) Conservative/surveillance (when the tumour is non-functioning and not very large)
2) Surgery
3) Medical (for prolactin-secreting tumours)
4) Radiotherapy (as a second-line treatment)
How do you medically treat a prolactin-secreting hormone?
By giving a drug that mimics dopamine which inhibits prolactin secretion and shrinks the tumour.
How do you treat hypopituitarism?
By replacing the un-secreted hormones.
What must be particularly paid attention to when treating hypopituitarism?
Ensuring that the hormone replacement mimics the diurnal variation and the evolution of hormone levels over time.
