Endocrinology 1 - Intro to Endocrinology Flashcards
Define an endocrine gland.
A group of cells which secrete messenger molecules directly into the bloodstream.
Define endocrinology.
The study of endocrine glands and their secretions.
Define a hormone.
The bioactive messenger molecule secreted by an endocrine gland into the blood.
Briefly compare the endocrine and nervous system.
- Endocrine releases a hormone into the bloodstream, while the nervous system releases a neurotransmitter across a synapse.
- Endocrine effect can be on many target cells, neural effect is restricted to innervated target cells.
- Endocrine effect takes place over a long time span, while the nervous system has an effect in milliseconds.
How may hormones be classified?
As proteins or steroid hormones.
Describe briefly the process of protein/polypeptide hormone synthesis.
- Amino acids enter the cell from the capillary via specific transporters.
- A signal initiates transcription in the nucleus. Translation follows.
- A preprohormone or prohormone is formed.
- The protein enters the golgi where it is packaged into secretory granules until its release.
- In these granules the prohormone is converted to the polypeptide. It is then released following the necessary signal.
What is the pro-hormone of ACTH?
POMC
Describe briefly the process of steroid hormone synthesis.
- LDLs are transported into the cells via LDL receptors.
- LDLs are broken down to cholesterol, which is stored as fatty acid esters.
- Cholesterol is liberated by esterase.
- It then enters the mitochondria via stAR protein.
- Once made, the steroid hormone will diffuse into the blood, it won’t remain in the cells,.
What is the precursor for all steroid hormones?
Cholesterol which produces pregnenolone.
How are polypeptide hormones transported?
They freely dissolve in the bloodstream.
How are steroid hormones transported?
They are bound to plasma proteins or transport proteins, therefore they are stored in the blood.
List some of the transport proteins/plasma proteins used to transport steroid hormones.
- Albumin is a general transport protein, and non-selectively transports many hormones.
- Cortisol binding globulin and thyroxine binding globulin are specific transport proteins.
Explain dynamic equilibrium in relation to steroid hormones.
- There is an equilibrium between the free and bound steroid hormone levels in the blood.
- For example, if the levels of hormone drop, more hormone will be released from proteins.
- This results in more hormone synthesis in the cells to restore the protein bound hormone.
Describe the process of hormone signalling in relation to protein/polypeptide hormones, using the example of ACTH.
- ACTH binds to the Gs-protein coupled receptor
- This results in the alpha subunit dissociating from the Gs protein, and activating adenylate cyclase, converting ATP to cAMP.
- In this case there is increased cholesterol synthesis via protein kinase A (PKA), which activates cholesterol esterase.
Describe the process of hormone signalling in steroid hormones, using cortisol as an example.
- Free cortisol enters the cell by passive diffusion
- It binds to a specific glucocorticoid receptor in the cell cytoplasm.
- This complex travels to the nucleus to interfere with transcription and translation.
