Intro & Hormone Synthesis Flashcards
What are hormones?
Chemical messengers released from one cell (or tissue) which produce a specific, receptor-mediated change in another cell (or tissue).
What processes are hormones involved in?
- Development - Proliferation, growth, and differentiation
- Metabolism - Energy storage, metabolic rate and temperature.
- Reproduction - Sexual maturation & behaviour, pregnancy & lactation.
- Fluid homeostasis - Water balance, salt levels, blood volume, pressure.
The importance of endocrinology: What common (hormonal) drugs do we use today?
- Insulin
- Thyroxine
- Contraceptive pill
- HRT
- Androgen blockers
- Steroids
What is a gland?
An organ that synthesises and releases a substance into the bloodstream, body cavity or skin.
What different types of glands are there?
- Endocrine
- Exocrine
- Mucous
- Serous
- Sebaceous
Name some classical endocrine glands
- Pituitary
- Thyroid
- Thymus
- Adrenal
- Panreas
- Kidney
- Ovary
- Testes
- Uterus
List some tissues with endocrine functions:
- Kidney – erythropoietin (EP)
- Heart - atrial natriuretic peptide (ANP)
- Gut - gastrin, secretin
- Adipocytes - leptin, adiponectin
- Pancreas - insulin
Draw a diagrm to explain the pathway of endocrine systems
- A +ve or -ve stimulus will cause a gland to release a hormone (Hormone A)
- That changes the concentration of hormone A in the blood
- This has a +ve or -ve effect on its target tissue when bound to its receptor
- Cellular action occurs as a result
- There is feed back from a hormone (Hormome B) which stops the gland from producing Hormone A
- Hormone A & B may be the same in the case of negative feedback
What are the 4 main cell-cell communication pathways via hormones?
- Autocrine
- Paracrine
- Endocrine
- Neurocrine
Cell-to-cell communication via hormones: Describe autocrine signalling
Cell A releases a hormone which binds to a receptor on its own cell surface and causes an effect.
Example: Pancreatic beta cells in the islets of langerhans. These cells produce insulin and have an insulin receptor on their plasma membrane
Cell-to-cell communication via hormones: Describe paracrine signalling
A hormone is released from cell A and it has an effect on a neighbouring cell (cell B)
Example: Somatostatin released by the delta cells of the pancreas inhibits insulin secretion by the beta cells by binding to the somatostain receptor
Cell-to-cell communication via hormones: Describe endocrine signalling
Cell A releases its hormone into the blood where it circulates around the body to find and bind to a different cell with a receptor to cause a response
Cell-to-cell communication via hormones: Describe neurocrine signalling
A hormone is produced in a neurone, passed down the long axon of that neurone and then released into the bloodstream to have an effect on cell B
What are the two major classes of hormones?
- Protein & peptide hormones
- Steroid hormones
Describe the synthesis of protein & peptide hormones
- DNA transcribed into mRNA
- mRNA is translated at the rough endoplasmic reticulum (RER) to produce a sequence of amino acids
- Post-translational processing and packaging into secretory vesicles in the Golgi apparatus
- Exocytosis
Describe the synthesis of steroid hormones
- The come from the hydrolysis of esters and release of cholesterol (the precursor molecules for all steriod hormones)
- Cholesterol is converted to pregnenolone
- Pregnenolone gets prcocessed and converted into a range of steroid hormes which can diffuse out of the cell because they cre lipid molecules
What are peptide hormones usually synthesised from?
Amino acids
Describe the syntesis of peptide hormones
- Processed in several stages
- They start off with an N-terminal signal sequence which gets cleaved off to produce a shorter hormone (pro-hormone) in ER
- Glycosylation in ER
- Cleavage of pro-hormone by endopeptidases to produce the final hormone in the cell
Give some examples of peptide hormones
- Prolactin
- ACTH
- Vasopressin
- Oxytocin
Describe Parathyroid hormone (PTH) synthesis
- It is translated as pre-pro-PTH and is 150 amino acids in length
- It consists of a signal sequence, a pro sequence, a biologically active sequence and a C-terminal fragment sequnce
- The N-terminal signal sequence is removed to produce pro-PTH (90 amino acids long)
- Further cleavage by endopeptidases to produce mature parathyroid hormone (84 amino acids long)
- This is secreted by exocytosis
How are steroid hormones classified?
Give some examples
By the receptor that they bind to
Glucocorticoids →cortisol
Mineralocorticoids→ aldosterone
Androgens →testosterone
Oestrogens →oestradiol
Progestogens → progesterone
Describe the synthesis of steroid hormones
- The precursor molecule cholesterol is converted to pregnonolone
- Pregnonolone is converted to progesterone
- Progesterone can be converted to cortisol
- Progesterone can also be converted into aldosterone
- Progesterone can also be converted to DHEA (a precursor for androstenedione) or directly to androstenedione
- Androstenedione is converted to testosterone
- Both testosterone and androstendione can be converted to 17-β-Estradiol (C18)
