Endocrine system Flashcards
What are the 6 main endocrine glands in the body?
1) Hypothalamus/pituitary
2) Pancreas
3) Ovaries/Testes
4) Parathyroid
5) Thyroid
6) Adrenal
Which gland controls most of the glands in the body?
The small pituitary gland
Which gland controls the pituitary gland?
The hypothalamus
What are the 2 functional lobes of the pituitary gland and what do they produce?
1) Anterior pituitary: produces various hormones
2) Posterior pituitary: doesn’t produce any hormones just stores those produced by the hypothalamus
What are the 5 main hormones produced by the anterior pituitary and what do they do?
1) TSH: stimulates the thyroid gland to produce thyroid hormone
2) ACTH (adrenocorticotrophic hormone): stimulates the adrenal glands to produce steroids
3) Gonadotrophins (FSH/LH): stimulates the testes or ovaries to produce sex hormones
4) GH (growth hormone): for skeletal growth
5) Prolactin (PRL): stimulates breast milk production
What 2 hormones are stored in the posterior pituitary (Which have been produced by the hypothalamus)?
1) Antidiuretic hormone (ADH): stimulates water reabsorption by the kidneys
2) Oxytocin: Helps uterine contractions during labour
What hormones are secreted by the hypothalamus to control the secretion of GH, TSH, ACTH and gonadtrophins from the anterior pituitary?
1) GHRH/GRH (growth-hormone releasing hormone): stimulates the release of GH
2) CRH (corticotrophin release hormone): stimulates the release of ACTH
3) TRH (thyrotrophin releasing hormone): stimulates the release of TSH (Thyroid stimulating hormone)
4) GnRH (gonadotrophin releasing hormone): stimulates the release of FSH and LH (gonadoptropins)
How is the release of prolactin from the anterior pituitary controlled?
No prolactin releasing hormone exists, instead it is under inhibitory control of the hypothalamus which continually secretes an inhibitor, after birth inhibitor stops being released and prolactin levels increase
How are pituitary hormones and hormones from the hypothalamus switched off?
By negative feedback systems
1) Cortisol feeds back to switch of ACTH and CRH
2) Thyroid hormones feedback to switch off TSH and TRH
3) Sex hormones feedback to switch off FSH and LH and GnRH
4) Growth hormone switches of GH and GHRH
Name 4 glands which are not controlled by the pituitary gland and what they produce?
1) Adrenal medulla: produces ADR and NA (nb. adrenal cortex which releases cortisol is controlled by pituitary)
2) Pancreas: secrets insulin, glucagon (and somatostatin)
3) Gut hormones
4) Parathyroid (controls calcium levels)
What is the rough gross structure of the thyroid gland?
2 lobes (R+L) and a midline isthmus (middle lobe, just below the circoid cartilage)
Which cells of the thryoid gland are not controlled by the pituitary and what do they secrete?
C cells, secrete calcitonin (involved in calcium metabolism) - they are not controlled by the pituitary!
How many parathyroid glands are there?
4
Other than the parathyroid glands what are the 3 other organs involved in calcium metabolism?
1) Kidneys: calcium excretion and production of Vitamin D
2) Gut: absorption of calcium
3) Bone: storage of calcium
Corticosteroids (cortisol), androgens (male hormones) and mineralcorticoid (aldosterone) are produced by which part of the adrenal gland, under control of what?
Adrenal cortex
Cortisol and androgens under control of pituitary
Aldosterone related to RAAS
NB. adrenal glands are reason females produce some male hormone
Adrenal cortex makes up how much of the adrenal gland?
90% cortex, 10% medulla
GnRH is secreted in what kind of pattern?
Not continuous but pulsatile
What is the effect of continuous GnRH secretion?
Can lead to suppression of secretion of FSH and LH (can be used therapeutically, if want to stop FSH and LH secretion then can give GnRH continuously)
What hormone is secreted from the pituitary gland for the first 14 days of the menstrual cycle and what does this cause to be released?
FSH for first 14 days
Causes increased oestradiol secretion from ovaries
What 3 things are the testes composed of and what do they produce?
1) Interstital or leydig cells: produce testosterone
2) Seminiferous tubules: made up of germ cells producing sperm
3) Sertoli cells: producing inhibin
Both testosterone and inhibin have an inhibitor effect on the release of FSH and LH from the pituitary
What is primary hormonal oversecretion/undersecretion?
Problem with the gland itself (no problem with the pituitary)
What is secondary hormonal oversecretion/undersecretion?
Problem with the pituitary gland making the gland itself overactive or pituitary gland not sending signals to the gland (nb. a secondary problem in a gland would be a primary problem in the pituitary gland)
What is tertiary hormonal oversecretion/undersecretion?
Problem with the hypothalamus however this is very rare
What glands are static tests used to find abnormalities in?
Thyroid gland
Sex glands
What is a static test in terms of measuring endocrine abnormalities?
Measurement of the levels of hormones in the blood at any one time (also called spot tests)
Which hormones are tested for in suspected hyperthyroidism and what do the results tell you?
Static Test for T3/T4 and TSH
IF T3/T4 high but TSH is suppressed = primary hyperthyroidism
If T3/T4 high and TSH also high = secondary hyperthyroidism
Which hormones are tested for in suspected hypothyroidism and what do the results tell you?
Static test for T3/T4 and TSH
If T3/T4 low but TSH is elevated = primary hypothyroidism
If T3/T4 low and TSH also low = secondary hypothyroidism
What hormones are tested for in suspected hypogonadism and what do the results tell you?
Static test for testosterone/oestradiol, FSH and LH
If testosterone/oestradiol low but FSH and LH high = primary hypogonadism
If testosterone/oestradiol low but FSH and LH also low = secondary hypogonadism
With both primary and secondary hypogonadism you get sexual dysfunction
When are stimulation tests used in endocrinology?
Used for suspected hormonal UNDERSECRETION when a static test is not enough (eg. growth hormone deficiency or cortisol deficiency)
Why are static tests not sufficient to measure overproduction or underproduction of GH and cortisol?
Levels fluctuate throughout the day
Normal ranges are different in different people
What test is used for suspected adrenal insufficiency?
Synacthen test
Give patient ACTH, if they fail to respond to the stimulation, ie dont increase production of cortisol then primary adrenal failure is diagnosed
What are glucagon stimulation tests and insulin stress tests for and how do they work?
Used to test for suspected pituitary failure (could be causing low GH and Secondary adrenal failure)
Hypoglycaemia is a stressful event for the body, low blood sugar should cause pituitary to produce GH and ACTH
Glucagon stimulation: give glucagon (to simulate hypoglycaemia) and see if levels of GH and ACTH (and thus cortisol) rise - seen as safer than insulin stress test
Insulin stress test- give insulin to lower blood glucose and see if levels of GH and ACTH (and thus cortisol rise) - insulin stress test is considered gold standard for diagnosing pituitary problems
What is a suppression test used for in endocrinology?
Suspected hormonal over secretion when a static test is not enough eg. suspected adrenal oversecretion of GH over secretion
How do you test for suspected cortisol overproduction?
Suppression test
Give exogenous steroids (eg. dexamethasone) and this should switch off production of endogenous steroids (NB. the steroid must not be detected by your test)
If cortisol production is not suppressed then you need further tests to determine if the problem is primary or secondary)