Hormone Synthesis and Action Flashcards
what are the 3 different types of glands?
Exocrine
Endocrine
mixed glands
what are endocrine glands?
ductless glands which secrete hormones, produced by cells, directly into the blood to be then carried to their target organs
what are exocrine glands?
- release their secretions outside the body (not in blood, or plasma) and may be ducted e.g. salivary glands, sweat glands
- not part of the endocrine system
what are mixed glands?
both exo and endocrine
e.g. Pancreas produces digestive juice which enter into the intestine (exo) but also produce insulin, glucagon and somatostatin which are secreted directly into the blood (endo)
what are the main glands in the body?
hypothalamus
pituitary gland
thyroid gland
adrenal glands
gonads- testes, ovaries
what are the two major regulatory systems in the body and what do they do?
endocrine
nervous
monitor and maintain internal and external environment (homeostasis)
what are the differences in nervous and endocrine system?
chemical component:
nervous- few neurotransmitters
endocrine- many hormones
speed of effect:
nervous- generally rapid
endocrine- generally slow
duration of effect:
nervous- short lived (neurotransmitter broken down very quickly)
endocrine- long lasting (takes time for hormones to be broken down)
localisation of effect:
nervous- localised (cell to cell)
endocrine- widespread (in blood)
what are the 6 different mechanisms of chemical signalling? (JAPINE)
endocrine
autocrine
intracrine
paracrine
juxtacrine
neuroendocrine
what is endocrine secretion?
secretes hormone directly into bloodstream which then acts on a distant target tissue.
what is autocrine secretion?
The hormone leaves the cell and then docks back onto the same cell via its receptors
what is intracrine secretion?
cell synthesise its own hormone which then acts within the cell (hormone does not leave the cell)
what is paracrine secretion?
secreted hormone acts on nearby cells within tissue or organ.
what is juxtacrine secretion?
secreted hormone acts on neighbouring cells
what is a neuroendocrine secretion?
An electrical stimulus passes down a neurone (e.g. in the Hypothalamus) to a specialised cell causing it to secrete a hormone which will affect a distant target cell.
what are the 2 ways in which hormone release is controlled?
positive and negative feedback
what is negative feedback?
most common
process by which body senses change and activates mechanism to reduce it
describe the process in which your body controls an action through negative feedback?
stimulus e.g. youre cold
hypothalamus recognises that
secretes a specific hormone to counteract change
hormone goes to target tissue e.g increasing metabolism
the SAME hormone usually (or another hormone) will negatively feedback and switch the system off
what is positive feedback?
process by which body senses change and activates mechanism to amplify it. Positive feedback is where hormone feedback is enhanced
define endocrine axis and give an example
How the glands are interact with each other.
e.g. Hypothalamus-pituitary-adrenal (HPA) axis
what is the hypothalamo-pituitary axis?
a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis
what are tropic hormones and what is their role?
hormones that have other endocrine glands as their target e.g. TRH, TSH, CRH and ACTH.
how are hormones synthesised?
Transcription of gene –> pre-mRNA –> mRNA leaves the nucleus to RER for translation of protein from mRNA at a ribosome. This is the Preprohormone.
In the RER a signal sequence is cleaved off the Preprohormone to produce the prohormone.
The prohormone is then packaged into transport vesicles and enters the golgi
Golgi for post- translational changes e.g. glycosylation
Packaged in secretory vesicles which contain lysosomes which cleave off unnecessary sections to produce the active hormone.
Exocytosis
explain how thyrotropin releasing hormones (TRH) are made?
TRH is synthesised from a large precursor protein which contains several copies.
Precursor is then cleaved (via proteolysis) to give active small peptide hormone (TRH)
Proteolysis: process of cutting the protein.
what hormones are produced with alpha and beta subunits and how are they activated?
TSH, hCG, LH, FSH are initially produced with both alpha and beta subunit.
The alpha subunit is the SAME for all of them.
The beta is DIFFERENT (the active hormone).
So, in processing the beta-subunit is cleaved from alpha giving distinct active hormones.
how are steroid hormones synthesised?
- Esters are first hydrolysed to release cholesterol
- Enzyme CYP11A first convers cholesterol into Pregnenolone (in the mitochondria) (this is the rate limiting step)
- Pregnenolone then becomes the starting point for all the other steroids e.g. glucocorticoid, mineral corticoids and sex steroids (androgens and oestrogens)
- Pregnanolone is then processed by enzymes in SER to produce the hormone.
what are amine hormones properties?
Small, hydrophobic - so need a transporter in the blood.
Lipid soluble - so they can pass through the lipid bilayer.
what are T4 and T3 hormones?
T4 prohormone - Contain 4 iodine atoms
T3 Active hormone - Contain 3 iodine atoms
explain the process in which thyroid hormones are produced? (13 steps)
1) Iodide ions (from the diet) enters the blood
2) It is then taken into follicular cells by sodium/I symporter (allows much higher conc. of iodide inside thyroid).
3) The iodine ions then leave cell into the colloid through the Pendrin protein on the apical surface.
Iodide ions then oxidized to I. This is catalysed by TPO.
4) Protein synthesis in the follicular cells creates the protein thyroglobulin which contains tyrosine residues on its chain.
5) It is secreted into the follicles (colloid) and is water soluble.
6) Through iodination reaction iodine is inserted onto tyrosine residues forming T1 (one iodine is attached) or T2 (two iodine atoms are attached). Also catalysed by TPO
7) Conjugation then occurs with an enzyme called Thyroid peroxidase (TPO)
8) Here two ionized tyrosine residues are bound together either two T2 together giving T4 or T1 or T2 forming T3.
9) This mature thyroglobulin molecule is then stored in the colloid until TSH binding to TSH receptor on basolateral membrane.
10) The mature thyroglobulin molecule then enters the cell by endocytosis.
11) The vesicles combine with lysosomes containing enzymes which then remove T3 or T4 from the thyroglobulin (via Proteolysis) forming active thyroid hormones.
12) T3 and T4 are released into the blood stream.
T4 (prohormone) & acts as reservoir for T3 (active thyroid hormone).
13) T4 is mono-deiodinated to T3 by iodothyronine deiodinase (D1, D2, D3) at appropriate tissues (e.g. liver) releasing them and they then diffuse into the blood stream and go to required cells.
what do peptide hormones bind to and what does that cause?
bind to G-Protein coupled receptor.
Cell surface receptors (GPCR), activate second messenger cascade. There is phosphorylation of proteins within the cell and the activated proteins bring about a physiological response.
what do steroid and amine hormones bind to and what does that cause?
hormone passes through cell membrane and binds to intracellular receptors (cytoplasm or nuclear receptor) producing a hormone-receptor complex.
HRC binds to HRE (hormone response element) which results in protein synthesis (transcription translation) and the protein produced causes a physiological response.
