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 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
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
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)
