Flashcards in Repro & Endocrine Deck (74)
What is an advantage of using an oral antihyperglycaemic over exogenous insulin?
Does not stimulate insulin secretion so does not cause hypoglycaemia
Which channels does glipizide (anti-diabetic agent) block?
ATP-sensitive potassium channels
Name a drug you could use to treat hyperinsulinism
How does it work?
Activates potassium channels causing inhibition of voltage-gated Ca2+ channels
Inhibits insulin secretion
What is the hormone relaxin produced by?
What does it do?
Produced by ovary and placenta in preparation for parturition
Softens the broad ligament, pelvic ligaments and sacroiliac joint
Where is the thyroid located?
Two lobes located either side of the trachea just below the larynx
Where is thyroid stimulating hormone released from?
Anterior pituitary gland
Explain the thyroid hormone feedback loop
Thyroid stimulating hormone (TSH) is released by anterior pituitary in response to TRH secreted into the portal system from the hypothalamus. TSH causes the synthesis and secretion of T3 and T4 into the blood from follicular cells in thyroid. Elevated T3 inhibits release of TRH and TSH.
TSH also inhibits release of TRH from the hypothalamus
What are the 5 functions of thyroid hormones?
Normal growth and development (T3 causes increased GH secretion, maintenance of nerve function, hair growth)
Cardiovascular stimulant (increased CO)
Enhances CHO utilisation and lipolysis (increases LDL uptake by liver)
Promotes milk production
Give some signs of hypothyroidism
Poor exercise tolerance
Weight gain with no change in appetite
Intolerance to cold and hypothermia
Increased blood cholesterol
Decreased heart rate
Bilateral symmetrical alopecia
How much should T4 increase by after injecting TSH?
T3 is how many times as active as T4?
In thyroid hormone replacement therapy, what is used to replace:
Explain the metabolism of thyroid hormones
30-40% T4 is converted to T3 in peripheral tissues
50% T4 is converted to reverse t3 (inactive)
20% T4 and 100% T3 form conjugates of glucoronide and sulphur in liver and are excreted in bile
How are thyroid hormones transported and bound?
Transported bound to plasma proteins
Free protein binds to target receptors. Bound fraction provides a depot that lasts several days, as when free molecules bind to their target receptors, more molecules dissociate from bound protein.
What are the 4 sigs of hyperthyroidism?
Weight loss with increased appetite
Increased heart rate
How can you test for hyperthyroidism?
Test for serum T4 levels (will be high)
Describe the T3 suppression test when testing for hyperthyroidism
Take basal TT4 (total T4).
Give oral T3 for 3 days.
Resting T4 should be suppressed by >50%.
If little/no suppression -> producing excess T4 from thyroid gland.
Which drugs can be used to treat hyperthyroidism?
Methimazole- inhibits synthesis of T3 and T4
Carbimazole (metabolised to methimazole)
What is an alternative to surgical thyroidectomy?
What considerations are there?
Destroys radioactive follicles
Treated animals need to be hospitalised for 1-4 weeks
Treated animals and excrete need to be handled carefully until radioactivity is gone
What is a goitre?
What could cause it?
Enlarged thyroid gland
Could be due to tumour, or iodine deficiency
Explain how an iodine deficiency could lead to an enlarged thyroid gland and hyperthyroidism
Lack of iodine in diet (eg lack in soil-sheep)/ substances that inhibit uptake
Can't make thyroid hormones. Continually high TSH stimulates thyroid follicular cell growth. No negative feedback
All steroid hormones from the adrenal cortex are formed from which molecule?
What is this then converted to?
How are steroid hormones transported?
Bound to plasma proteins
What is the mechanism of action of corticosteroids?
Act on intracellular receptors to alter mRNA synthesis
What type of corticosteroid is aldosterone?
What are the 3 normal functions of cortisol?
Increased blood glucose
Increased protein catabolism
What are the clinical signs of hyperadrenocorticism?
PU and secondary PD
Increased skin pigment (synthesis of ACTH involves a precursor: POMC which stimulates MSH -> increases melanin production)
What would you see on a stress leucogram?
Lymphocytopenia (decreased lymphocytes)
Monocytosis (increased monocytes)
Eosinopenia (decreased eosinophils)
Neutrophilia (increased neutrophils)
What is a stress leucogram caused by?
Stress response or corticosteroid induced