Endocrine Investigations Flashcards
What are the 2 principles of dynamic investigations?
1) Attempted stimulation for hypo-function
2) Attempter suppression for hyper-function
What is the basic feedback loop in the endocrine system?
- Hypothalamus stimulates anterior pituitary which stimulates endocrine organ
- Hormone produced by endocrine organ negatively feeds back to the hypothalamus and anterior pituitary
In the male reproductive system, what 2 hormones are released by the hypothalamus?
1) FSH releasing factor
2) LH releasing factor
In the male reproductive system which 2 hormones are released by the pituitary gland?
1) FSH
2) LH
FSH released by the pituitary gland in the male reproductive system acts on what cells to cause what 2 actions?
1) Sertoli cells in seminiferous tubules
Causes
1) Maturation of sperm
2) Release of inhibin
Inhibin has what 2 actions in the male reproductive system?
Inhibits release of FSH from pituitary gland and inhibits release of FSH releasing factor from hypothalamus
LH released by the pituitary gland in the male reproductive system acts on what cells, causing the release of what hormone?
Acts on Leydig cells (L for LH, L for Leydig cells)
Causing them to release testosterone
What are the 2 actions of Testosterone released from the Leydig cells on the male reproductive signalling pathway?
Inhibits release of LH from the pituitary gland and LH releasing factor from hypothalamus
What hormone is released from the hypothalamus in the female reproductive system?
GnRH
GnRH causes the release of what 2 substances from the anterior pituitary in the female reproductive system?
Release of FSH and LH
LH acts on what 2 structures in the female reproductive system having what action?
1) Corpus luteum to release progesterone
2) Follicle to release estradiol and inhibin
FSH acts on what structure in the female reproductive system to cause the release of what?
Follicle to release inhibin and estradiol
Which 2 hormones act on the follicle in the female reproductive system?
FSH and LH
Inhibin is released from what structure in the female reproductive system and has what action?
Released from the follicle
Inhibits the release of hormones from the anterior pituitary
Estradiol is released from what structure in the female reproductive system and has what action?
released from the follicle
Inhibits release of hormone from the anterior pituitary AND the hypothalamus
Progesterone is released from what structure in the female reproductive system and has what actions?
Released from the corpus luteum and inhibits release of hormones from the hypothalamus and anterior pituitary
Give the 2 possible reasons for high TSH with high thyroxine?
1) pituitary gland overproduction
2) Feedback fails
What is important to note about random hormone values in both over and under production?
Random hormone values can be identical in over and under production, dynamic testing is needed to confirm
Why is it important to record the time of day that a cortisol sample is taken?
Shows high diurnal variation
When are cortisol levels highest?
8-10am
When are cortisol levels lowest?
11pm-1am
What is the difference between Cushing’s disease and Cushing’s syndrome?
Cushing’s disease = due to pituitary gland tumour producing ACTH
Cushing’s syndrome = excess of ACTH for another reason
What are the 8 features of Cushing’s syndrome?
1) Obesity - moonface, central obesity
2) Skin - thin, purple striae, bruising
3) Hypertension
4) Glucose intolerance
5) Menstrual disturbances/ impotence
6) Thin limbs/ muscle weakness
7) Back pain due to osteoporosis
8) Psychiatric disturbances - depression, psychoses
What suppression test is used in suspected Cushing’s syndrome?
Dexamethasone suppression
Give patient an artificial steroid which doesn’t cross react with assays ie dexamethasone
This should tell pituitary to stop producing ACTH thus cortisol production will decrease
Cortisol should be undetectable about 10 hours later
