Feedback Loops and Disorders Flashcards
Draw a basic feedback mechanism
Describe the neuroendocrine axis
- The brain releases a hormone or neurotransmitter
- The hormone/neurotrasmitter binds to its receptor on the pituitary gland
- The pituitary gland releases a hormone which binds to its receptor e.g. the testes, thyroid…
What type of hormones does the hypothalamus release?
Releasing/inhibiting hormones
The releasing hormones from the hypothalamus bind to ther receptors on the pituitary. What kind of hormones are released by the pituitary?
Tropic hormones
Neuroendocrine feedback loop: Describe the hypothalamic-pituitary-adrenal axis (HPA-axis)
- A stimulus e.g. stress stimulates the hypothalamus
- The hypothalamus releases corticotropin-releasing hormone (CRH)
- CRH binds to its receptor in the anterior pituitay and causes the corticotophs to release adrenocorticotropic hormone (ACTH)
- ACTH circulates in the blood and bind to its receptor found in the adrenal cortex and causes the release of cortisol
- Cortisol can feedback in a long loop to the hypothalamus to inhibit CRH production
- ACTH can feedback in a short loop to the hypothalamus to inhibit CRH product
Name some functions of cortisol
- Maintains muscle function, deceases muscle mass
- Modulates emotional tone, wakefulness
- Increses glomerular filtration and water clearance
- Facilitates maturation of the foetus
- Maintain cardiac output, decreases endothelial permeability and increases arteriolar tone
- Inhibits inflammatory and immune responses
- Decreases connective tissue
- Decreases bone function, increases bone resoption
Describe Hormone Receptors
- Hormone levels in the circulation are normally low- in the range of pg/ml-ng/ml.
- Hormone effects are mediated by specific, high affinity receptors .
- Receptors can be present inside the cell (e.g. receptors for steroid & thyroid hormones) or on cell membrane (polypeptides & protein hormones).
- Receptors are linked to specific signal transduction pathways
Give an example of a cell membrane receptor
Insulin receptor
Insulin binds to its receptor and causes many intracellular events:
- Reversal of glucagon-stimulated phosphorylation
- Phosphorylation of proteins
- Transcriptional regulation
- Glucose uptake
- Protein synthesis
Give an example of a steriod hormone receptor mechanism
T3
- The steroid hormone which is in circulation diffuses into the cell
- It binds to a cytoplasmic receptor which translocates to the nucleus or it diffueses into the nucleus itself
- In the nucleus it makes a complex with its receptor and a DNA binding protein and then binds to a specfic sequence of DNA (hormonal response element) on whichever genes its going to switch on or off
- This changes the levels of gene trascription (mRNA levels) therefore changes in translation and protein synthesis
- This leads to a celluar response
Define hormone resistance
What is often associated with?
A lack of biological responsiveness to a biologically active hormone e.g. insulin resistnce a key diver of type 2 diabetes where Insulin no longer causes glucose uptake in skeletal muscle and adipose tissue
•Often associated with chronic exposure to elevated levels of circulating hormones
Problems Associated With Endocrinology: What are endocrine disorders usually associated with?
- Excess secretion of a hormone
- Deficient secretion of a hormone
- Failure to respond to a hormone (usually due to absence or malfunction of a receptor)
Problems Associated With Endocrinology: What are endocrine diseases usually associated with?
- Diabetes mellitus (insulin deficiency or insensitivity)
- Thyroid disease (too little or too much)
- Infertility (hypothalamic, pituitary, gonadal)
- Obesity (leptin)
Name some Major Endocrine Organs & Major Endocrine Problems associated with them
