Endocrinology Flashcards
Define Endocrinology
The study of hormones, action and interactions , and the medical conditions associated with deficient and excessive secretion.
Define Hormone
A substance that is secreted by an endocrine gland and is transported in the blood to regulate the function of another tissue or gland.
What are the main endocrine glands?
Pineal Gland Pituitary Gland Hypothalamus Thyroid Gland Thymus Adrenal Gland Pancreas Ovaries Testis
What is the role of the hypothalamus?
Convert neurological signals to stimulatory hormones and is affected by sleep patterns and stress responses
Describe the pituitary gland
Located in the base of the brain
Connected to Hypothal via pituitary stalk
Anterior and Posterior lobes
Stimulated by the hypothal
What hormones are associated with the hypothal?
GHRH Somatostatin GnRH TRH CRH Dopamine
What hormones are associated with the anterior pituitary gland?
GH FSH LH TSH ACTH PROLACTIN
Define Diurnal Variation
Due to the neuronal and sight stimulus required, hormones are often secreted in a pulsatile manner, with frequency and amplitude of pulse varying through out the day.
What is Hypopituitarism?
Decreased secretion of the hormones produced in the pituitary gland
What are the causes of Hypopituitarism?
Pituitary tumours Brain tumours Infection (TB, sarcoidosis) Haemorrhage (Sheehan’s syndrome) Autoimmune Trauma
Describe the steps following CRH release from the hypothal
- Corticotrophin releasing hormone is released episodically from the hypothal
- ACTH acts on the adrenal stimulating the adrenal cortex pathway
- Cortisol is the main analyte produced
- Negative feedback loop controls the pathway
What is Cortisol involved in?
It promotes gluconeogenesis, glycogenesis and increased fatty metabolism.
It controls salt and water balance as well as blood pressure regulation
What is the 9am reference range for cortisol?
200-600nmol/L
What are the characteristics of Addison’s Disease?
Destruction of the adrenal cortex and disorders of steroid metabolism
What are the clinical signs of cortisol deficiency?
Inability to mount a stress response to illness/trauma
Dizziness
Lethargy
Low BP
How is cortisol deficiency diagnosed?
9am cortisol Short Synacthen Test ACTH Urea/Electrolytes Adrenal imaging
What are the primary and secondary causes of Cushing’s Syndrome?
Primary:
Adrenal Tumours
Iatrogenic-Hydrocortisone administration
Secondary:
ACTH secreting tumours (pituitary and ectopic)
What are the signs and symptoms of Cushing’s Syndrome?
Moonfaced Increased abdominal fat Buffalo hump Thin skin leading to striation Easy bruising Muscle wasting Hirsuitism Hypertension Glucose Intolerance
How is Cushing’s Syndrome diagnosed?
Screening:
Urine free cortisol
Overnight dexamethasone suppression test
Salivary cortisol
Diagnostic:
ACTH
High dose Dexamethasone
Describe the steps of HP-Thyroid
- TRH acts on the thyrotrophs in the anterior pituitary causing the release of TSH
- TSH acts on thyroid gland stimulating the production of T3/T4
- A negative feedback loop controls the cycle
What is the reference range for TSH?
0.3-5mU/L
What are T3 and T4 responsible for?
Normal maturation and metabolism of all body tissues
What is the reference range for free T4?
8-19pmol/L
What is the reference range for free T3?
2-6pmol/L
What are the signs and symptoms of hypothyroidism?
Tiredness, lethargy Weight gain Cold intolerance Raised cholesterol Inattention
What are the primary and secondary causes of hypothyroidism?
Primary:
Destruction of the gland (autoimmune)
Congenital Defects
Drugs (lithium/amiodarone)
Secondary:
Panhypopituitarism
Isolated TSH
What are the primary and secondary causes of hyperthyroidism?
Primary:
Graves disease
toxic goitre
Thyroiditis
Secondary:
Exogenously administer iodine-containing drugs
Excessive T4 and T3 ingestion
TSHoma
What are the signs and symptoms of hyperthyroidism?
Weight loss Sweating and heat intolerance Fatigue Palpitations Agitation and tremors Generalised muscle weakness Angina/ heart failure Diarrhoea Oligomenorrhoea/ subfertility Goitre Eye lid retraction and lid lay.
How is hyperthyroidism diagnosed?
Serum TSH and Serum fT4
Serum fT3
Imaging of the pituitary.
Describes the steps in HP-Prolactin
- Controlled by inhibition of secretion
- Dopamine is the principle factor
- Prolactin self-regulates
- Secretion seems to be stimulated by factors that suppress dopamine
- It is affected by physiological factors such as lactation
What are the causes of hyperprolactinaemia?
Primary:
Prolactinoma
Pituitary tumour
Other causes: Chronic renal failure Pregnancy Primary Hypothyroidism Drugs- antipsychotics Macroprolactin
What are the signs and symptoms of hyperprolactinaemia?
Amenorrhea Galactorrhea/ gynaecomastia Oligospermia Impotence/ decrease sexual interest Visual Disturbance Headache Hypopituritarism
How is hyperprolactinaemia diagnosed?
Prolactin Medical/ drug history Rule out macroprolactin Imaging Pituitary Hormones
What is GH responsible for?
Lipogenesis
Bone growth
Protein synthesis
Increase blood glucose and FFA production.
What are the effects of GH excess and deficiency?
Deficiency:
Hypoglycaemia in neonates
Short stature in Children
Difficult to detect in adulthood
Increased growth:
Acromegaly
Gigantism
How is GH excess/deficiency diagnosed?
GH dynamic function OGTT Insulin stress test IGF-1 Clinical examination
