Endocrinology Flashcards
Name the hormones produced in the anterior pituitary and their function
- ACTH - stimulates gluticocorticoid release from adrenal cortex
- FSH - spermatogenesis/follicular maturation
- LH - testosterone synthesis/ovulation
- Prolactin - promotes lactation
- TSH - T3/T4 production and release
- GH/somatotrophin - muscle/skeletal growth
Name the hormones produced in the posterior pituitary and their function
- Oxytocin - milk ejection and uterine contraction in labour
- ADH - promotes water and salt resorption from kidneys
Using cortisol as an example, describe the endocrine feedback loop
What hormones does the thyroid gland secrete? What is their function?
- T3/T4 (follicular cells) - metabolism and growth
- Parathyroid hormone (parathyroid gland) - Calcium and phosphate metabolism
- Calcitonin (parafollicular cells) - inhibits calcium resorption in the bone
What hormones does the adrenal gland secrete? What are their function?
Cortex:
- Mineralocorticoid/aldosterone (glomerulosa) - electrolyte balance
- Glucocorticoid/cortisol (fasciculata) - carbohydrate metabolism
- Androgens (reticularis) - secondary sexual characteristics
Medulla:
- Adrenaline - stress response
- Noradrenaline - neurotransmitter in SNS
- Dopamine - neurotransmitter in ANS
What hormones does the overies secrete? What are their function?
- Oestrogen (theca interna cells) - reproductive function, secondary sexual characteristics
- Progesterone - endometrial stimulation, maintains pregnancy
- Relaxin - softens cervix during birth
- Inhibin (granulosa cells) - inhibits FSH production
What hormones does the testis secrete? What are their function?
- Testosterone (Leydig cells) - reproductive function, secondary sexual characteristics
- Inhibin (Sertoli cells) = inhibits FSH production
- Mulleria-Inhibiting Hormone (MIH) - foetal hormone
What is Cushing’s syndrome? What causes is?
Chronic excess glucocorticoids
- Iatrogenic - excess prescribed glucocorticoids
- Cushing’s disease = adrenal hyperplasia due to excess ACTH from pituitary tumour
- Adrenal tumours/hyperplasia
- Ectopic/paraneoplastic = Raised ACTH from ectopic tumours
- Small cell lung cancer
- Carcinoid tumours
- CRH-secreting tumours
Name some clinical features of Cushings
- General = weight gain (central adiposity), moon face, buffalo hump, supraclavicular fat pad
- Skin = thinning, acne, hirsutism, purple abdominal striae
- Pscyhological = depression, irritability, cognitive difficulties
- Repro = irregular menstruation/erectile dysfunction
- Glucose intolerance (hyperglycaemia)
- Hypertension
- Increased infections
- Delayed wound healing
- Osteoporosis
How is Cushings investigated?
- Overnight dexamethasone suppression test = give dexamethasone 1mg PO at midnight, check serum cortisol before and at 8AM
- if cortisol > 50 nmol/L = cushings
- Should be negative feedback - dexamethasone simulates cortisol - dec ACTH - which should dec cortisol
- Circadian rhythm - normally low at night, high in morning
- Not replicated with Cushings
- Imaing
- Pituitary MRI - if pituitary source suspected
- Abdo CT - if adrenal source suspected
How is Cushings treated?
- Remove the cause
- Stop glucocorticoid treatment
- Surgical removal of tumour
- Surgical removal of adrenal glands
- Cortisol synthesis inhibiting medication
- Mifepristone (receptor antagonist)
Name the complications of Cushings syndrome
CUSHINGOID:
- Cataracts
- Ulcers
- Skin - striae, thinning, bruising
- Infections
- Necrosis (of femoral head)
- Glycosuria
- Osteoporosis/obesity
- Immunosuppression
- Diabetes
What is Addison’s disease? Name some causes
Adrenal insufficiency (low cortisol)
- Adrenal destruction
- Autoimmune (80%) =
- Metastasis
- Haemorrhage (Waterhouse-Friederichsen)
- Infections - TB, histoplasmosis, HIV, CMV
- Amyloid deposits
- Adrenal dysgenesis (not formed during development)
- Impaired steroidogenesis
- Interruptions in cholesterol delivery
- Congenital adrenal hyperplasia
- Medications (rifampicin, phenytoin)
Name some symptoms of Addisons
- Fatigue
- Abdominal pain
- Myalgia/arthralgia
- Depression
- Anorexia and weight loss
- Diarrhoea and vomiting
- Psychosis
- Weakness
- Lightneadedness
- Constipation
Name some signs of Addisons
- Hyperpigmentation
- Palmar creases
- Buccal mucosa
- Vitiligo
- Postural hypotension
- Tachycardia
- Fever
- Shock
- Coma
What is an Addisonian crisis? What are the precipitants?
Severe, acute symptoms due to severe adrenal insufficiency, precipitated by:
- Trauma
- Infection
- Surgery
How do Addisonian crisis’ present?
- Shock
- Tachycardia
- Peripheral vasoconstriction
- Postural hypotension
- Oliguria
- Hypoglycaemia
- Sudden pain in legs, lower back, abdomen
- Severe vomiting and diarrhoea - dehydration
- Low Na+, high K+, high Ca2+
- Confusion, psychosis
How is Addisons investigated?
- Bloods - high Ca2+, high K+, low Na+, low glucose, low Hb, neutropenia, raised LFTs
- ABG - metabolic acidosis
- ECG - increased PR and QT interval
- ACTH stimulation test (synacthen) - administer sythetic ACTH 250 microg IM
- Measure cortisol before and after
- If cortisol not increased (>500) then adrenal failure
- Serum ACTH >300ng/L (low in 2º causes)
- Imaging (US/MRI/CT) of adrenal glands
- CXR - signs of TB/past TB
How is Addisons treated?
- IV fluids if dehydrated
- Hydrocortisone - 20mg in morning, 10mg at night
- Consider mineralocorticoid replacement if abnormal electrolytes and renin
- Fludrocortisone
- Advice against suddenly stopping steroids and symptoms of Addisonian crisis
- Steroid card/medical bracelet
- If poor response - autoimmune screen
- Thyroid, coeliac, serology
How is an Addisonian crisis treated?
- Hydrocortisone sodium succinate 100mg IV stat
- Fluid resuscitation
- Glucose IV/dextrose if hypoglycaemic
Name some symptoms of hyperthyroidism
- Weight loss despite increased appetite
- Heat intolerance and sweating
- Diarrhoea
- Tremor
- Irritability
- Psychosis
- Amenorrhoea
- Infertility
- Gynecomastia
Name some signs of hyperthyroidism
- Tachycardia
- AF
- Warm peripheries
- Goitre +/- nodules
- Palmar erythema
- Hair thinning
- Exopthalmos
- Lid lag
- Vitiligo
- Oedematous swelling above lateral malleoli
Name some causes of hyperthyroidism
- Grave’s = autoimmune stimulation
- Thyroid adenoma
- Multinodular goitre
- Thyroiditis (De Quervain’s)
- Excess thyroid medication
- Drugs - amiodarone, lithium
- Post-partum thyroiditis
- Thyroid carcinoma
Describe the pathophysiology of Graves disease
Thyroid-stimulating immunoglobulins recognize and bind to the TSH receptor which stimulates the secretion of thyroxine (T4) and triiodothyronine (T3). Thyroxine receptors in the pituitary gland are activated by the surplus hormone, suppressing additional release of TSH in a negative feedback loop. The result is very high levels of circulating thyroid hormones and a low TSH level.
How is hyperthyroidism investigated?
- Plasma TSH = low in hyperthyroidism or pituitary failure
- Plasma free T3/T4
- Thyroid autoantibodies
- Anti TSH receptor antibodies
- Radioactive iodine uptake test = measures absorbed iodine
- Thyroid scintigraphy
- Opthalmology - visual fields, acuity, movements
How is hyperthyroidism treated?
- Thyrostatic drugs - carbimazole (15-40mg/day)
- Titrate down according to TFTs
- Beta blockers (reduce SNS symptoms)
- Decrease iodine in diet
- Partial thyroidectomy
- Risk of recurrent laryngeal nerve damage
- Risk of parathyroid damage
- Radioiodine - restricts/destroys thyroid function
Name some complications of hyperthyroidism
- Heart failure (thyrotoxic cardiomyopathy)
- Angina
- AF (25%)
- Osteoporosis
- Gynaecomastia
- Thyroid storm
- Opthalmopathy
What is a thyrotoxic storm / hyperthyroid crisis? What causes it?
Severe hyperthyroidism causing fever, agitation, confusion, tachycardia, AF, coma and acute abdomen
Precipitants:
- Thyroid surgery
- Radioiodine
- Infection
- MI
- Trauma
How is a thyrotoxic storm managed?
- IV 0.9% saline 500ml/4hr
- Bloods - T3/T4, cultures (if infection suspected)
- Sedate if necessary (chlorpromazine)
- Propanolol 40mg/8hr PO
- High dose digoxin may be needed to slow the heart
- Carbimazole 15-25mg/6hr
- Hydrocortisone 100mg/6hr
Name some side-effects of carbimazole
- Rashes
- Add antihistamine
- Pruritis
- Add antihistamine
- Sensitivity
- Bone marrow suppression
- Arthralgia
- GI disturbance
*
Name some signs and symptoms of hypothyroidism
- General - fatigue, cold intolerance, weight gain
- Cardio - bradycardia, pericardial effusion, CCF
- Resp - SOB, pleural effusion, hoarseness
- GI - constipation, ascites
- Psych - poor memory, loss of concentration
- Menorrhagia (heavy periods) and impaired fertility
- Carpal tunnel syndrome
- Myalgia
- Dry skin and hair
- Non-pitting oedema (eyelids, hands, feet)
Name some causes of hypothyroidism
- Primary
- Iodine deficiency
- Autoimmune (Hashimotos)
- Thyroidectomy/radio-iodine
- Medication = lithium, amiodarone, carbimazole
- Central
- Pituitary lesions (adenoma, metastasis)
- ICA aneurysm
- Congenital
How is hypothyroidism investigated?
- Plasma - high TSH, low T4, antibodies
- Possibly high cholesterol and triglyceride
- Macrocytic anaemia
- Possibly high AST, LDH, CK (due to abnormal muscle membranes)
- Thyroid imaging
How is hypothyroid treated?
- Levothyroxine (T4) 100macrog/day
- Iodine replacement if deficient
Describe the negative feedback of the thyroid
- Hypothalamus secretes TRH
- TRH stimulates production of TSH from anterior pituitary
- TSH increases production and release of T3 and T4 from the thyroid
- T3 and T4 exert negative feedback on TSH production
- Thyroid produced mainly T4
- T3 converted to T4 peripherally
Interpret these TFTs:
- High TSH, low T4
- High TSH, normal T4
- High TSH, high T4
- Low TSH, high T4/T3
- Low TSH, normal T4/T3
- Low TSH, low T4/T3
- Normal TSH, abnormal T4
- Primary hypothyroidism
- Subclinical hypothyroidism
- T4 compliance problems, TSH-secreting tumour, thyroid hormone resistance
- Hyperthyroidism
- Sub clinical hyperthyroidism
- Pituitary disease, sick euthyroidism
- Horome-binding problems
Describe the function of parathyroid hormone
- Increases calcium and decreases phosphate reabsorption in the kidney
- Increases osteoclast activity
- Increases vitamin D production in the kidneys
Overall:
- Increases plasma calcium
- Decreases plasma phosphate