Hormone Synthesis and Action Flashcards
List 2 differences between endocrine and exocrine glands.
1 - Endocrine glands release secretions directly into the blood, whereas exocrine glands release their secretions onto surfaces.
2 - Endocrine glands are ductless whereas exocrine glands may be ducted.
List 3 routes by which hormones can reach their targets.
1 - Endocrine.
2 - Autocrine.
3 - Paracrine.
Describe the hypothalmo-pituitary-adrenal axis.
1 - The hypothalamus synthesises and releases corticotropin releasing hormone, which travels to the anterior pituitary gland.
2 - The anterior pituitary gland is stimulated to synthesise and release adrenocorticotropic hormone, which travels to the zona fasciculata of the adrenal gland.
3 - The zona fasciculata synthesises and releases cortisol, which acts through negative feedback to reduce the synthesis and release of corticotropin releasing hormone at the hypothalamus and adrenocorticotropic hormone at the pituitary.
Describe the hypothalamic-pituitary-thyroid axis.
1 - The hypothalamus synthesises and releases thyrotropin releasing hormone, which travels to the anterior pituitary gland.
2 - The anterior pituitary gland is stimulated to release thyroid stimulating hormone, which travels to the thyroid gland.
3 - The thyroid gland synthesises and releases T3 and T4, which act through negative feedback to reduce the synthesis and release of thyrotropin releasing hormone at the hypothalamus and thyroid stimulating hormone at the anterior pituitary gland.
List the three main groups of hormones.
1 - Protein / peptide hormones.
2 - Steroid hormones.
3 - Amine hormones.
List two examples of protein / peptide hormones.
1 - Insulin.
2 - Thyrotropin releasing hormone.
List two examples of steroid hormones.
1 - Cholesterol.
2 - Cortisol.
List 3 examples of amine hormones.
1 - Tyrosine.
2 - Thyroxine.
3 - Noradrenaline.
Are protein / peptide hormones hypdrophobic or hydrophilic?
Hydrophilic.
In the anterior pituitary, which cells produce adrenocorticotropic hormone?
Corticotrophs.
In the corticotroph, what is the pre-prohormone to adrenocorticotropic hormone?
Pre-pro-opiomelanocortin.
How are TSH, LH, FSH and hCG related?
1 - They are all released from the anterior pituitary.
2 - All have an alpha and beta subunit, of which they share a common alpha subunit.
What is the precursor of all steroid hormones?
Cholesterol.
Are steroid hormones hydrophobic or hydrophilic?
Hydrophobic.
In steroid hormone synthesis, what is the source of cholesterol?
Hydrolysis of esters.
In steroid hormone synthesis, what is cholesterol converted to?
Where does this occur?
- Pregnenolone.
- In the mitochondria.
What is the role of steroid acute regulatory protein (StAR) in steroid hormone synthesis?
To facilitate movement of cholesterol to the mitochondria.
In steroid hormone synthesis, what regulates StAR activity?
Adrenocorticotropic hormone.
Give an example of a hormone that is produced in the zona glomerulosa of the adrenal gland.
Aldosterone.
Give an example of a hormone that is produced in the zona fasciculata of the adrenal gland.
Cortisol.
Give an example of a class of hormone that is produced in the zona reticularis of the adrenal gland.
Adrenal androgens
Why do increases in secretion of steroid hormones reflect accelerated rates of synthesis, whereas increases in secretion of peptide / protein hormones do not necessarily reflect accelerated rates of synthesis?
Because peptide / protein hormones can be stored, whereas steroid hormones cannot (as they are hydrophobic / lipophilic).
What do the numbers ‘3’ and ‘4’ represent with T3 and T4?
The number of iodine atoms.
Are amine hormones hydrophobic or hydrophilic?
Hydrophobic.
Describe the process of thyroid hormone synthesis.
1 - I- and Na+ enter the follicular cell through an I- / Na+ symporter.
2 - Thyroglobulin is synthesised in the follicular cell (bound to many tyrosine residues) and released by exocytosis into the follicle colloid.
3 - I- exits the follicular cell into the follicle colloid via pendrin.
4 - Iodine is oxidised and binds to tyrosine residues that are bound to thyroglobulin to form either DIT (2 x I-) or MIT (1 x I-).
5 - Thyroglobulin and its iodinated tyrosine residues (MIT and DIT) re-enter the follicular cell by endocytosis.
6 - T3 is produced where DIT combines with MIT, whereas T4 is produced where DIT combines with DIT.
7 - A lysosome cleaves T3 and T4 from thyroglobulin.
List 3 functions of carrier proteins for steroid and thyroid hormones.
1 - To increase solubility.
2 - To increase half-life.
3 - To maintain a reservoir of the hormone in the blood.
What is the disadvantage of non-specific binding proteins?
They bind loosely.
What is the name of the binding protein that is specific for thyroid hormones?
Thyroid binding globulin (TBG).
What is the name of the binding protein that is specific for cortisol?
Cortisol binding globulin (CBG).
Where is the site of action for protein / peptide hormones and steroid hormones?
- Protein / peptide hormones: Cell surface receptors.
- Steroid hormones: Intracellular receptors (cytoplasm or nuclear).
What is the cause of dwarfism?
A deficiency of growth hormone.
What is the cause of gigantism?
An excess of growth hormone.
What is the cause of diabetes insipidus?
A deficiency of antidiuretic hormone.
What is the cause of hypervolaemia?
An excess of antidiuretic hormone.
What is the cause of diabetes mellitus?
A deficiency of insulin.
