Term 3 Flashcards
Endocrine
Explain the thyroid axis
6 stages
- Hypothalamus releases Thyrotropin-releasing hormone (TRH)
- TRH stimulates anterior pituitary to release Thyroid stimulating hormone (TSH)
- This stimulates thyroid gland to release T3 and T4
- T3 and T4 sensed by hypothalamus and anterior pituitary - they supress the release of TRH and TSH
- This results in lower T3 and T4
- Lower T3 and T4 levels offers less supression of TRH and TSH, so more released, rising T3 and T4 again
Explain the adrenal axis
4 stages
Negative feedback
- hypothalamus releases corticotrophin release hormone (CRH)
- CRH stimulates anterior pituitary to release adrenocorticotrophic hormone (ACTH)
- ACTH stimulates adrenal gland to release cortisol
- Cortisol sensed by hypothalamus and anterior pituitary and suppresses release of CRH and ACTH, resulting in lower cortisoll
5 actions of Cortisol in the body
Stress hormone - released in pulses
- inhibits immune system
- inhibits bone formation
- increases blood glucose
- increases metabolism
- increases alertness
Explain the growth-hormone axis
4 steps
- growth hormone releasing hormone (GHRH) is released from the hypothalamus
- GHRH stimulates growth hormone to be released from tge anterior pituitary
- GH stimulates the release of insulin-like growth factor 1 (IGF-1) from the liver
- IGF-1 aids cell differentiation and proliferation
Fuctions of growth hormone
Stimulates muscle growth
increase bone density and strength
stimulates cell regeneration and reproduction
stimulates growth of internal organs
Explain the parathyroid axis
5 stages
- parathyroid hormone (PTH) is released from 4 parathyroid glands in respone to low calcium (or low Mg2+ and high K+)
- PTH raises serum calcium conc in three ways
- PTH increases the activity of and number of osteoclasts in bone, causing reabsorption of calcium from the bone into blood
- PTH stiumlates increased calcium reabsorption in kidneys, meaning less excreted
- PTH stiumlates kidneys to covert D3 into calcitriol - active form of vit D that promotes ca absorption from food in small intestine
- When calcium is high this suppresses the release of PTH
What is the most common cause of primary adrenal insufficiency and what is this called?
Addison’s disease - adrenal glands damaged resulting in reduced secretion of cortisol and aldosterone
Autoimmune
What causes secondary adrenal insuff.?
Inadequate ACTH stimulating the adrenal glands resulting in low cortisol
Damage to pituitary gland (surgery, infection, radiotherapy)
What is Sheehan’s syndrome?
Massive blood loss duirng childbirth leads to pititary necrosis and secondary adrenal insuff.
What causes tertiary adrenal insufficiency?
Inadequate CRH (corticotrophin releasing hormone) by hypothalamus
Usually result of long term steroids being stopped suddenly
therefore taper slowly
Signs and symptoms of adrenal insuff.
Addison’s (primary), secondary or tertiary
Fatigue, Nausea, Cramps, Abdo pain, reduced libido
Bronze hyperpigmentation (ACTH stimulates melonocytes to produce melanin)
Hypotension
What level would ACTH be in someone with Addison’s?
Primary adrenal insuff.
ACTH level is high as pituitary trying hard to stimulate adrenal glands
Low cortisol means no negative feedback
What level would ACTH be in someone with secondary adrenal insuff.
Low ACTH as reason adrenal glands not producing cortisol is they are not being stimulated by ACTH
Treatment for adrenal insuff.
steroids - titrate up
Hydrocortisone - glucocorticoid hormone to replace cortisol
Fludrocortisone - mineralocorticoid hormone used to replace aldosterone
DOUBLE dose during illness
Patient presents with reduced consciousness, vomitting, hypotension, hypoglycalcaemia, hyponatraemia, hyperkalamia, very unwell, darkened skin patches
? endocrine problem
ADDISONIAN CRISIS
severe Addison’s where absence of steroid hormones leads to life threatening presentation
