Endocrinology Flashcards
What are the main endocrine glands?
- Hypothalamus/Pituitary
- Thyroid
- Parathyroid
- Pancreas
- Adrenal
- Ovaries/Testicles
What connects the hypothalamus to the pituitary gland?
Pituitary stalk
What are the two lobes of the pituitary gland?
Anterior pituitary and posterior pituitary
What is the function of the anterior pituitary?
Produces various hormones
What is the function of the posterior pituitary?
Stores various hormones
What 5 hormones does the anterior pituitary produce?
- Growth hormone (GH)
- Adrenocorticotrophic hormone (ACTH)
- Gonadotrophins (FSH and LH)
- Thyroid stimulating hormone or thyrotrophin (TSH)
- Prolactin (PRL)
What is the purpose of the growth hormone?
For skeletal growth
What is the purpose of the adrenocorticotrophic hormone (ACTH)?
Stimulates the adrenals to produce steroids
What is the purpose of the gonadotrophin hormones?
Stimulate the testicles or ovaries to produce sex hormones
What is the purpose of the thyroid stimulating hormone (thyrotrophin-TSH)?
Stimulates the thyroid to produce thyroid hormones
What is the purpose of prolactin (PRL)?
Stimulates breast milk production
What are the two hormones (produced by the hypothalamus) that the posterior pituitary gland stores?
- Antidiuretic hormone (ADH)
- Oxytocin
What is the function of ADH?
Stimulates water reabsorption by the kidneys
What is the main function of oxytocin?
helps uterine contractions during labour
How does the hypothalamus control the anterior pituitary gland?
The hypothalamus releases a hormone which promotes the secretion of hormones from the anterior pituitary gland (hypothalamus-pituitary axis).
What 4 hormones secreted from the hypothalamus promote the release of hormones in the anterior pituitary gland?
- Corticotrophin releasing hormone (CRH)
- Growth hormone releasing hormone (GHRH)
- Thyrotropin releasing hormone (TRH)
- Gonadotrophin releasing hormone (GnRH)
What does corticotrophin releasing hormone (CRH) stimulate?
ACTH secretion
What does growth hormone releasing hormone (GHRH) stimulate?
GH secretion
What does thyrotropin releasing hormone (TRH)
stimulate?
TSH secretion
What does gonadotrophin releasing hormone (GnRH) stimulate?
FSH & LH secretion
What is special about prolactin releasing hormone?
Does not exist and prolactin is under the inhibitory effect of the hypothalamus
How are pituitary hormones switched off by negative feedback?
- Cortisol switches off ACTH and CRH
- Growth hormone, switches of GH and GHRH
- Thyroid hormones switch off TSH and TRH
- Sex hormones switch off FSH/LH and GnRH
Which glands are not controlled by the pituitary?
- Adrenal medulla
- Parathyroid
- Pancreas
- Gut hormones
What does the adrenal medulla do?
Produces adrenaline and noradrenaline
What does the parathyroid do?
Controls calcium levels
What does the pancreas do?
controls sugar levels
Which gland does the adrenocorticotrophic hormone affect?
Adrenals (steroids)
Which gland does the thyroid stimulating hormone affect?
Thyroid (T3 and T4)
Which organ does FSH/LH affect?
Ovary/testicle (sex hormones)
What is the thyroid composed of?
- Midline isthmus (just below the cricoid cartilage)
- Right lobe
- Left lobe
How are thyroid cells arranged and what type of cells do they contain?
- arranged in follicles that produce thyroid hormones
- contain C cells producing calcitonin for calcium metabolism
What do thyroid hormones do by interacting with their receptors in various organs?
- Regulate gene expression
Regulate various aspects of organ function
Control of thyroid hormone secretion
TRH is secreted by the hypothalamus.
Causes the pituitary gland to secrete TSH.
Causes the thyroid to secrete thyroid hormones (T3 and T4).
Decrease in thyroid hormones is picked up by hypothalamus and pituitary which secretes more hormones. Negative feedback.
Which gland is the metabolism of calcium controlled by?
Mainly controlled by 4 parathyroid glands sitting behind the thyroid
What are other organs involved in calcium metabolism (and how)?
- Kidneys = calcium excretion and production of active Vitamin D
- Gut = Absorption of calcium
- Bone = Storage of calcium
- Thyroid
Where are the adrenal glands situated?
Above the kidneys
What are the adrenal glands composed of?
- Adrenal cortex = 90% of the gland
- Adrenal medulla = 10% of the gland
What does the adrenal cortex produce?
- Corticosteroids (cortisol)
- Androgens (male hormones)
- Mineralocorticoid (aldosterone)
What does the adrenal medulla produce?
- Catecholamines (adrenaline, noradrenaline and dopamine)
Which two hormone secretions related to blood pressure is not controlled by the pituitary?
- Catecholamine secretion
- Mineralocorticoid secretion (related to renin-angiotensin system, which controls blood pressure)
What makes up the reproductive system?
Ovaries and testicles
Where are the ovaries situated?
Situated in the pelvis on either side of the uterus
What do ovaries contain?
Follicles, each containing an oocyte, at different stages of maturation during the reproductive cycle.
What is the process of controlling hormone secretion
On the first two weeks of the cycle, FSH is produced. On the second two weeks of the cycle LH is mainly produced which causes progesterone to be produced.
FSH causes the ovaries to produce oestradiol and inhibin. As oestradiol levels go up, negative feedback tells the pituitary to switch off FSH and start LH production.
When measuring female hormone levels, it is important to know which day of the cycle.
Where are testes found?
In adults, the testes are found in the scrotum, except in a minority with testicular maldescent
What (3) are testes composed of?
- Interstitial or Leydig cells
- Seminiferous tubules
- Sertoli cells
What do interstitial/ Leydig cells do?
produce testosterone
What do seminiferous tubules do?
Made up of germ cells producing sperms
What do sertoli cells do?
help in sperm production and produce inhibin
How does the control system for male hormone production work?
Hypothalamus produces GnRH (can be turned off/on) which causes pituitary to produce FSH and LH which tells the testes to produce testosterone and inhibin. This feeds back, decreasing hormone production by hypothalamus and pituitary.
FSH = sperms production
LH = testosterone production
How can clinical abnormalities of various glands be caused (3)?
- hormonal over secretion
- hormonal under secretion
- tumour/nodules in the gland without affecting hormone secretion
What do static tests do?
Can diagnose abnormalities of thyroid and sex glands
How can primary hyperthyroidism (thyroid hormone overproduction) be tested?
Test for:
- Thyroid hormones T3 and/or T4 elevated
- suppressed (undetectable) TSH
Both these are positive for primary hyperthyroidism
What can stimulation tests be used for?
For suspected hormonal under secretion where a static test is not enough (i.e. results are equivocal)
What are examplesof stimulation tests?
- giving ACTH to test for adrenal insufficiency (synacthen test)
if individual fails to respond to a stimulation test then gland failure is diagnosed - glucagon stimulation and insulin stress test for pituitary failure (tests for ACTH and GH response)
What can suppression tests be used for?
For hormonal over secretion
What are some examples of suppression tests?
- giving steroids and testing got endogenous steroid production (external steroids should switch off internal steroid production)
- giving glucose and testing GH secretion (glucose switches of GH secretion in normal individuals)
What is the difference between primary and secondary clinical diagnoses?
Primary = issue with the gland itself
Secondary = Issue outside the gland (normally pituitary gland)
How can diseases of the endocrine glands be caused (3)?
- over secretion (usually benign tumours)
- under secretion = gland destruction due to inflammation (including autoimmune conditions), infarction , other
*tumours/nodules can still have normal functioning
What is prolactin oversecretion caused by?
A relatively common condition usually due to a pituitary tumour secreting prolactin (prolactinoma)
What is the clinical presentation of prolactin oversecretion?
- galactorrhoea (breast milk production)
- amenorrhoea in women (absence of a period) and sexual dysfunction in men
- headaches and visual field problems with large tumours
What are diagnostic tests for prolactinoma?
- static test
- pituitary MRI
How can visual field defects occur in people with prolactinoma?
Pituitary gland is just below the optic nerves and chiasm, it the rumour extends, it can press on the optic chiasm causing a visual field defect.
What are external factors that can cause mildly raised prolactin?
- sexual intercourse
- nipple stimulation
- stress
- larger number of drugs (including antipsychotics and antidepressants)
- non-functioning pituitary tumour (compressing hypothalamus and interfering with the inhibitory effect on prolactin secretion)
Treatment of prolactinomas?
These are the only over-secreting pituitary tumours that can be treated medically as they rarely require surgical intervention
What are the effects of growth hormone oversecretion in childhood/ adolescence?
- Excessive growth spurt and increased size of feet and hands
- If left untreated GH excess leads to gigantism, most serious consequence.
What are the effects of growth hormone oversecretion in adults?
- affects skin, soft tissue and skeleton
- acromegalic face
- wide and large hands/feet
- increased sweating (common complaint)
How would you diagnose growth hormone oversecretion?
- suppression tests are necessary
- glucose is given, followed by GH measurements at different time points (in healthy individuals, glucose suppresses GH production and hence plasma levels of the hormones fall)
- imaging is necessary to confirm the presence of pituitary tumour
- rare affecting around 1/25000
What is the treatment for a pituitary tumour from GH over secretion?
- surgical removal of the tumour
- radiotherapy and medical therapy may also be needed as surgery does not always remove the whole tumour
How many people does Cushing’s syndrome affect?
Rare, affects around 1-2/100 000
What can Cushing’s syndrome be caused by?
- pituitary secreting ACTH tumour (Cushing’s disease)
- Adrenal tumours secreting cortisol
- Cancers producing ACTH (such as lung cancers)
What is the clinical presentation of Cushing’s syndrome?
- growth arrest in children
- round (moon-like) face, acne, hirsutism,
- truncal obesity, thin extremities
- thin skin and easy bruising, striae on abdomen
- hypertension, diabetes mellitus, high risk of infections, poor wound healing
What diagnostic tests are needed for Cushing’s syndrome?
- static tests are not enough and suppression tests are required
- dexamethasone suppression test is used to confirm the failure tonsuppress endogenous cortisol production
How do you treat Cushing’s syndrome?
Pituitary and adrenal Cushing’s syndrome:
- surgery
- radiotherapy and/or medical treatment may also be required in pituitary disease
Cancer related Cushing’s syndrome:
- Treat original cancer
How could thyroid hormone overproduction be caused?
- primary hyperthyroidism = very common
- secondary hyperthyroidism (pituitary TSH secretion) = rare
What is the prevalence of hyperthyroidism ?
Prevalence around 2% in the female population
10 times more common in women
What are the causes of hyperthyroidism?
- Graves’ disease (80%) = autoimmune condition
- Toxic nodule or toxic MNG (15%)
- Thyroiditis (1%)
- Drug induced (amiodarone)
- Rarities
What are the clinical presentations of hyperthyroidism?
- hyperactivity, irritability, insomnia
- heat intolerance and increased sweating
- palpitations
- Weight loss despite overeating
- menstrual problems
- goitre
- Thyroid eye disease = swelling around the eyes, protrusion of the eye ball (proptosis), paralysis of eye muscles
What does examination for hyperthyroidism consist of?
- signs of thyrotoxicosis = hand tremor, increased sweating, fast pulse
- inspection of the thyroid = usually enlarged
Smooth = Graves’ disease
Nodular = toxic nodule(s)
Tender = thyroid inflammation
What are some treatments for hyperthyroidism?
- anti-thyroid drugs = disease remission in 50% of patients after treatment for 6-18 months (can suppress white cell production, but very rare)
- radioactive iodine = destroys thyroid gland
- surgery
What are the effects of growth hormone deficiency in children and adults?
- children = failure of growth
- adults = nothing, tiredness, depression
What test is conducted for growth hormone deficiency?
- Glucagon stimulation test
- insulin stress test (lowers blood glucose, stressing the body and forcing GH secretion)
What is the treatment for GH deficiency?
Growth hormone replacement:
- injections
- expensive (choose adult patients carefully)
What can steroid under-secretion be caused by?
- Adrenal failure
- Pituitary failure
What are the clinical presentations for steroid under-secretion?
- failure to grow in children
- severe tiredness
- dizziness due to low BP
- abdominal pain, vomiting and diarrhoea
What tests can be done steroid under-secretion?
Stimulation test:
- synacthen test (giving ACTH) if primary adrenal failure is suspected
- GST (glucagon stimulation test) or IST (insulin stress test) if secondary adrenal insufficiency is suspected
What is treatment for steroid under production?
Replace the missing hormone: tablets (cheap)
Failing to diagnose may result in death. In the case this diagnosis is suspected, cortisol should be given even before results of investigations are available (injection if patient is vomiting or very unwell)
How common is hypothyroidism?
Very common especially in older ladies
What is primary hypothyroidism?
Thyroid failure and inability to produce thyroid hormones (common)
- usually autoimmune in nature
- can be drug induced
What is secondary hypothyroidism?
Failure to produce TSH (rare)
- usually part of complete pituitary failure
What are some symptoms and signs of severe hypothyroidism (and freq) ?
- weakness and dry skin (>95%)
- sensation of cold and decreased sweating (80%)
- impaired memory (65%)
- constipation (60%)
- weight gain (60%)
- hair loss (60%)
What is the diagnosis and treatment of hypothyroidism?
Diagnosis = static test of thyroid function
Treatment = thyroid hormone replacement (tablets, cheap)
What is primary sex hormone deficiency in males and females?
Males = testicular failure
Females = ovarian failure
What happens in secondary sex hormone deficiency?
Pituitary failure
What is the presentation of sex hormone deficiency in males and females?
Males:
- erectile dysfunction
- reduced libido
Females:
- menstrual abnormalities (amenorrhoea)
What can amenorrhoea be caused by?
- uterine problems
- ovarian problems
- pituitary problems
- hypothalamic problem
What is the diagnosis and treatment of sex hormone deficiency?
Diagnosis :
- static tests are enough = testosterone (males), oestradiol (females)
FSH, LH
Treatment:
- hormone replacement therapy (testosterone for males, oestradiol/progesterone for females)
- pituitary hormone replacement
What could pituitary failure be due to?
- Large tumour
- Infarction
- Other
Usually involves multiple hormones so combination of static and stimulators tests are required to make the diagnosis
Sequence to investigate for pituitary hormonal deficiency?
MRI imaging
Endocrine tests
- Basal tests = thyroid function, prolactin, E2, testosterone
- Dynamic tests = Glucagon stimulation tests, insulin stress test
What can increased parathyroid hormone production be due to?
- primary hyperthyroidism
- cancers
- drugs
- other
What does hypercalcaemia due to increased parathyroid secretion present?
- Thirst and passing too much urine (osmotic symptoms)
- constipation
- abdominal pain
