1 - Introduction to endocrinology Flashcards
What is an endocrine gland?
A group of cells that secrete messenger molecules directly into the bloodstream
What is endocrinology?
Study of endocrine glands and their secretions.
What is a hormone?
The bioactive messenger molecule secreted by an endocrine glands into the blood - i.e. not simply a metabolite or energy substrate.
Endocrine definition
Relates to a hormone’s action on target cells at a distance from source
Paracrine definition
Relates to hormone’s action on nearby target cells. e.g. within immediate area around source.
Autocrine definition
Relates to hormone having an effect on its own immediate source.
Name 6 endocrine glands.
Pituitary Parathyroids Thyroid Pancreas Adrenals Gonads
What are the 3 classifications of hormones?
Protein/polypeptide
Steroid
Miscellaneous
What are steroid hormones derived from?
Cholesterol
What are prohormones and pre-prohormones?
Longer versions (pre cursors) of the final hormone.
How are protein hormones synthesised?
- Amino acids are building blocks, they are transported from the blood into the cell cytoplasm.
- DNA is transcribed to make relevant mRNA.
- The mRNA is for a pro hormone.
- Translation, prohormone is released.
- Prohormones go to golgi. It is packaged into vesicles with enzymes that cleave certain parts to liberate the active hormone.
- Hormones wait in the vesicles near cell membrane ready to be released when needed.
What is the name of endocrine cells where protein hormones are made?
Corticotrophs
In the anterior pituitary
How long to protein hormones last in the blood?
Not very long
Which blood vessels are pituitary hormones secreted into?
Pituitary capillary
How are steroid hormones synthesised?
- Low density lipoproteins are transported from blood into cell cytoplasm.
- Cholesterol is split from lipoprotein, esterified and stored in vacuoles in cytoplasm.
- Esterase enzyme liberates the cholesterol
- StAR protein moves cholesterol into the mitochondria
- Lots of enzymes and steps to get to final steroid hormone.
- Hormone diffuses across cell membrane into blood capillary. THEY ARE NOT STORED IN THE CELL.
What is the name of the cell where steroid hormones made?
Adrenal Cortical Cell
What does adrenal mean and where is the adrenal gland?
ad- above
renal - kidney
Above the kidney
Where are Steroid hormones stored?
In the bloodstream
How are steroid hormones stored in the blood?
Binded to plasma proteins.
e.g. albumin
Specific binding proteins
Ones that aren’t bound can diffuse into cells.
There is an equilibrium between bound and free hormone.
What hormone binds to CBG?
Cortisol
If a steroid hormone is heavily plasma protein bound, can it still access tissues?
The free component can access tissues. YES
How is equilibrium maintained?
When free hormone is used, bound hormone is released.
Ensures that free hormone available to the tissues remains constant.
More hormone is made as the free hormone is used up.
If plasma protein conc. increased, more free hormone is stored as protein bound hormone.
Protein hormones - how does signalling work?
- Protein hormone binds to a receptor in the plasma membrane.
- Activation of G protein coupled receptor.
- Adenylate cyclase activated, this converts ATP to cAMP.
* If the function is to release a steroid hormone*
- cAMP can bind to Protein Kinase A, this converts cholesterol esters to free cholesterol, StAR protein moves cholesterol inside mitochondria. - Function of cell changes dependant on hormone.
Steroid hormones - how does cell signalling work?
- *No extracellular receptors required**
1. Free hormone diffuses across plasma membrane into cell.
2. Hormone binds to receptors (Glucocorticoid receptors for cortisol) in the cytoplasm of the target cell.
3. Hormone-receptor complex travels to nucleus & binds to DNA binding sites.
4. Transcriptional machinery changed, mRNA produced, protein produced.
