Endocrine system 1 Flashcards
What is a hormone?
A chemical messenger secreted direclty into bloodstrema from (ductless) endocrine glad
Target cell/tissue some distance fram glad
Exocrine (ducts) - e.g. salivary, sweat etc
What are the 5 intracellular messengers in the body?
- Endocrine
- Autocrine
- Paracrine
- Neuroendocrine
- NTs
What are endocrine messengers?
e.g. insulin –> released from islets of langerhans (pancreas); act on liver, adipose, skeletal muscle
What are autocrine messengers?
Substance secreted by a cell that travels short distance in the interstitual fluid & acts on the same cell
e.g. Protaglandins
What are paracrine messengers?
Released from one cell, travels short distance in interstitual fluid to neighbouring cell
e.g. Somatostatin on insulin secretion
What are neuroendocrine messengers?
Hormone stored in axon terminal, when required will be released to act on another cell
e.g. oxytocin & ADH (from pituitary gland)
What are the types of hormones?
- Peptide hormones
- Steroid hormones
- Hormones derived from tyrosine
- Eicosanoids
What are peptide hormoens like?
Chains of amino acids (e.g. TRH or LH/FSH)
Incl those from hypothalamus, anterior & posterior pituitary, pancreas
What are steriod hormones?
Derived from cholesterol
Incl cortisol, aldosterone (adrenal cortex) & sex hormones (gonads)
What are hormones derived from tyrosine?
Thyroid hormones & catecholamines (adrenal medulla)
What do the differences in chemical structures reflect?
Reflects the ways which the types of hormones are synthesised, stored, transported & used
What are the stages of peptide hormone synthesis?
- Starts w a gene, this is translated & syntheised
- It moves across the RER
- First thing made is a preprohormone, a molecules that signals to the cell that this specific molecule need processing & packaging as it needs to be exported
-The “pre” signal is cleaved and tells the cell whether it needs either - the protein to be folded, disulfide bonds made or glycosylation
-Additional processing happens in the in the golgi, before this the hormone is not mature
-Hormone is then stored until it needs to be released upon arrival of stimulus
-Exocytosis = fusion with the plasma membrane, and hormone release
What are the stages of steroid hormone synthesis?
- Precursor molecule (cholesterol based)
- Cholesterol converted by a number of enzymes, makes the steroid hormone
- Can readily pass through the lipid bilayer as it is lipid based - cannot be contained
- Hormone passes out of membrane via simple diffusion into bloodstream
- If you need more hormone, you just increase the synthesis of hormone
- Do not like the hydrophilic environment of water so they must be transported by plasma proteins
What is the solubility of peptide hormones?
Hydrophillic
What is the solubility of steroid & thyroid hormones?
Lipophilic
Do peptie hormones bind to plasma proteins?
No, they’re as free hormones
Do steroid hormones & thyroid hormones bind to plasma proteins?
Yes
However are weak, reversible bonds
What is the half life of peptide hormones?
(Time taken for the initial amt to fall by 50%)
Minutes
Don’t last long due to proteases that break down peptides in the bloodstrean as it is unbound
What is the half life of steriod & thyroid hormones?
(Time taken for the initial amt to fall by 50%)
Hours - days
What is an unbound (plasma proteins) hormone like?
It is biologically active
What is a bound (plasma proteins) hormone like?
Hormone binding delays metabolism, provides a circulating resevoir of hormones
Describe peptide hormone action:
- Plasma membrane receptors carry the hormones thru –> either TYROSINE KINASE or G-PROTEIN COUPLED RECEPTORS
- Activates signal transduction process - mediates a response on the INSIDE relating to hormone on OUTSIDE
- e.g. glucagon receptor - cAMP
Describe steroid hormone action:
- Passes thru the membrane via diffusion
- It binds to a promoter for a certain gene
- Intracellular receptors act as hormone-regulated transcription factors
- Genomic method –> either inc or decrease gene expression
- Recently plasma membrane receptors have also been found
How is hormone release regulated?
By feedback regulation –> consequence of a process acts to regulate the rate at which the process occurs
Endocrine feedback is not simple - there will be various feedback loops in a process
