Endocrine Axis and Hormonal Regulation ✅ Flashcards
What secretes hormones?
Endocrine organs
What happens to hormones once they have been secreted?
They circulate in the blood and bind to specific receptors
What are the sub-types of receptors that hormones may bind to?
- Cell surface receptors
- Cytosolic and nuclear receptors
Where are cell surface receptors found?
On plasma membranes
What kind of hormones bind to cell surface receptors?
Hydrophilic hormones
Give 3 examples of hydrophilic hormones?
- Insulin
- Catecholamines
- Pituitary hormones
What kind of hormones bind to cytosolic and nuclear receptors?
Lipid soluble
Give 2 examples of lipid soluble hormones?
- Steroids
- Thyroid hormones
How can cell receptor sensitivity be increased?
By increasing the number of binding sites
How can the number of hormone binding sites be increased?
- Increasing receptor synthesis
- Decreased receptor degradation
When does desensitisation to hormones occur?
- Receptors reduced in numbers
- Receptors internalised from surface locations
- Molecules recruited which deactivate intracellular signalling pathways
What groups are cell-surface receptors subdivided into?
- Growth factor receptors
- G-protein coupled receptors
What initiates signalling in growth factor receptors?
Tyrosine kinase
What can defects in GPCRs lead to?
Hormone resistance or upregulated activity
Give an example of when a defect in GPCRs leads to hormone resistance?
Mutations of TSH receptor can cause resistance to TSH
Give 2 examples of when a defect in GPCRs leads to upregulated activity?
- Mutations of LH receptor lead to testotoxicosis
- Mutations of TSH can lead to neonatal hyperthyroidism
What is the role of Gαs?
To activate intracellular signalling pathways in response to activation of GPCRs
What can mutations adversely affecting Gαs function lead to?
- Pseudohypoparathyroidism
- When maternally inherited, lead to downregulation of a range of GPCRs
What is up-regulation of Gαs associated with?
McCune-Albright syndrome
What happens to GPCRs in McCune-Albright syndrome?
The upregulation of several GPCRs lead to clinical features including;
- Gonadotrophin-independent precocious puberty (LH receptor)
- Thyrotoxicosis (TSH receptor)
- Cushing’s syndrome (ACTH receptor)
- Hyperpigmented skin lesions
- Fibrous dysplasia
Give 3 examples of steroid hormones?
- Sex steroids
- Glucocorticoids
- Aldosterone
How do steroid and thyroid hormones enter the cell?
They diffuse across the target cell membrane
What kind of hormones bind to receptors in the cytoplasm?
Glucocorticoids
What kind of hormones bind to receptors in the nucleus?
- Androgens
- Thyroxine
What is the result of steroid and thyroid hormones binding to receptors inside the cell, rather than the surface?
The response takes longer
What can happen to some hormones once they are inside the cell?
They can be converted to more potent forms, or to weaker forms
Give 2 examples of hormones are converted to more potent forms inside the cell
- Testosterone
- T4
What is testosterone converted to inside the cell?
Dihydrotestosterone
What enzyme converts testosterone to dihydrotestosterone?
5alpha-reductase
What is T4 converted to inside the cell?
T3
What enzyme converts T4 to T3?
5’-deiodinase
What hormone may be converted to a weaker form inside the cell?
Cortisol
In what cells may cortisol be converted to a weaker form?
Aldosterone responsive cells in the kidney
What may cortisol be converted into inside the cell?
Cortisone
What enzyme converts cortisol to cortisone?
11beta-hydroxysteroid dehydrogenase
Why is cortisol converted to it’s weaker metabolite cortisol in the aldosterone responsive cells in the kidney?
To avoid over-stimulation of the mineralocorticoid receptor
What can defects in the genes that encode intracellular receptors lead to?
Hormone resistance, such as;
- Androgen insensitivity syndrome
- Glucocorticoid resistance
- Resistance to thyroid hormone
