Pituitary Flashcards
What is the final common pathway by which signals from multiple signals can reach the anterior pituitary?
Hypothalamus
What is the hypothalamus regulated by?
- Hormone mediated signals (negative feedback)
- Neural inputs
What non-endocrine functions is the hypothalamus also involved in?
- Temperature regulation
- Food intake
- Thirst
6 hormones released by hypothalamus affecting anterior pituitary
- Growth hormone releasing hormone (GHRH)
- Somatostatin (inhibitory)
- Gonadotropin releasing hormone (GnRH)
- Corticotropin releasing hormone (CRH)
- Thyrotropin releasing hormone (TRH)
- Dopamine (inhibitory)
What hormone(s) does GHRH trigger release of?
Growth hormone (GH)
What hormone(s) does somatostatin inhibit release of?
Growth hormone (GH)
What hormone(s) does GnRH trigger release of?
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
What hormone(s) does CRH trigger release of?
Adrenocorticotrophic hormone (ACTH)
What hormone(s) does TRH trigger release of?
Thyroid stimulating hormone (TSH)
What hormone(s) does dopamine inhibit release of?
Prolactin
What factor(s) is growth hormone stimulated by?
- Hypoglycaemia
- Exercise
- Sleep
What factor(s) is/are growth hormone suppressed by?
Hyperglycaemia
Effects of GH
- Linear growth in children
- Acquisition of bone mass
- Stimulates protein synthesis, lipolysis, glucose metabolism
- Regulation of body composition
- Psychological wellbeing
Primary effects of FSH and LH
- Testosterone production in testes
- Estrogen production in ovaries
Secondary effects of FSH and LH (males)
- Penis and scrotum growth
- Facial hair growth
- Larynx elongates (lowers voice)
- Shoulders broaden
- Body, armpit and pubic hair growth
- Musculature increases body-wide
Secondary effects of FSH and LH (females)
- Breasts develop and mature
- Hips broaden
- Pubic hair grows
What is prolactin essential for?
Lactation
When do levels of prolactin increase?
Pregnancy and breast feeding
How does prolactin inhibit gonadal activity?
Central suppression of GnRH (thus decreased FSH/LH levels)
Effects of ADH
- Primary physiological determinant of the rate of free water excretion
- Augments the water permeability of the luminal membranes of cortical and medulla collecting tubes
Major stimuli for ADH secretion
- Hyperosmality (high solute conc. in blood)
- Effective circulating volume depletion
What does oxytocin stimulate?
Contraction of smooth muscle of breast and uterus
What does oxytocin have roles in?
- Milk ejection reflex
- Parturition (birth)
Major causes of hypopituitarism
- Pituitary/parapituitary tumours
- Radiotherapy
- Pituitary infarction (apoplexy)
- Infiltration of the pituitary
- Trauma
- Isolated hypothalamic releasing hormone deficiency
Manifestations of GH deficiency
- Children
> Poor growth - Adults
> Increased abdominal fat
> Decreased lean body mass
> Impaired lipid profile
> Decreased muscle strength and exercise capacity
> Impaired cardiac function
> Decreased bone mineral density
> Impaired psychological wellbeing
How is GH deficiency diagnosed?
GH stimulation tests
How is GH deficiency treated?
Hormone replacement
Manifestations of FSH/LH deficiency
- Children
> Delayed puberty - Men
> Decreased libido
> Infertility
> Decreased secondary sex features
> Decreased muscle mass and strength
> Decreased mood and wellbeing
> Osteoporosis
> Anaemia - Women
> Decreased libido
> Menstrual disorders
> Infertility
> Dyspareunia
> Osteoporosis
> Premature atherosclerosis
How is FSH/LH deficiency diagnosed?
- Measure FSH, LH and oestradiol levels and take menstrual history (female)
- Measure FSH, LH and morning testosterone levels (male)
How is FSH/LH deficiency treated?
Hormone replacement
Manifestations of ACTH deficiency
- Fatigue
- Weakness
- Nausea/vomiting
- Anorexia
- Weight loss
- Hypoglycaemia
- Hypotension
- Anaemia
How is ACTH deficiency diagnosed?
- 9am serum cortisol and ACTH levels
- Dynamic tests:
> Short Synacthen test
> Insulin tolerance test
> Glucagon test
How is ACTH deficiency treated?
- Replace what is missing
- Approximate natural rhythm
Manifestations of TSH deficiency
- Fatigue
- Weakness
- Cold intolerance
- Bradycardia
- Inability to lose weight
- Puffiness
- Pale and dry skin
- Constipation
How is TSH deficiency diagnosed?
Measure TSH, fT4 and fT3 levels
How is TSH deficiency treated?
Hormone replacement
What is central diabetes insipidus?
Deficient secretion of ADH
Causes of central diabetes
- Idiopathic (autoimmune destruction of hormone secreting cells)
- Tumours
- Neurosurgery or trauma
- Infiltrative disorders
- Infections
- Hypoxic encephalopathy or severe ischaemia
Manifestations of ADH deficiency
- Polyuria of dilute urine
- Polydipsia
- Nocturia
Major causes of polyuria
- DM
- Renal failure
- Primary polydipsia
- Diabetes insipidus
How is ADH deficiency diagnosed?
- Urine output
- Osmolalities (plasma, urine)
- Blood electrolytes/glucose/urea/creatinine
- Water deprivation test
How is ADH deficiency treated?
ADH analogues
What is acromegaly?
Hypersecretion of GH
How is acromegaly diagnosed?
- Oral glucose tolerance test
- IGF-I
- Pituitary imaging
How is acromegaly treated?
- Pituitary surgery
- Dopamine agonists
- Somatostatin analogues
- GH receptor antagonists
- Radiotherapy
What is prolactinoma?
Non-cancerous tumour of pituitary causing too much prolactin
Manifestations of prolactinoma
- Hypogonadism
- Galactorrhoea
- Mass effects
How is prolactinoma diagnosed?
- Exclude other causes of high prolactin
- Pituitary imaging
How is prolactinoma treated?
- Dopamine agonists
- Surgery
- Radiotherapy
What is Cushing’s Syndrome?
Cortisol hypersecretion
How is Cushing’s diagnosed?
- 24h UFC
- Midnight serum or salivary cortisol levels
- Overnight or low dose dexamethazone suppression test
How is Cushing’s treated?
- Pituitary surgery
- Radiotherapy
- Drugs
- Bilateral adrenalectomy
What is a TSHoma/FSHoma?
Pituitary tumour causes TSH/FSH hypersecretion
Manifestations of TSHoma
- Thyrotoxicosis (hyperthyroidism)
- Mass effects
How is TSHoma diagnosed?
- Hormonal tests by experts
- Pituitary imaging
How is TSHoma treated?
- Surgery
- Medications
- Radiotherapy
Manifestations of FSHoma
- Menstrual irregularities
- Ovarian hyperstimulation
- Testicular enlargement
- Infertility
- Mass effects
How is FSHoma diagnosed?
- Hormonal tests by experts
- Pituitary imaging
How is FSHoma treated?
- Surgery
- Radiotherapy
