1 - Intro to Endo Flashcards
What are the three groups of hormone?
- Protein/polypeptide
- Steroid
- Miscellaneous
Where are most steroid hormones produced?
Adrenals and gonads
What determines the final steroid hormone produced from cholesterol?
combination of enzymes that found within cell
What is a hormone?
a substance released into the bloodstream which acts as a transport system enabling it to reach target tissues sometimes at some distance away from the source
What is an endocrine gland?
A group of cells which secrete ‘messenger’ molecules directly into the blood stream.
What are the endocrine glands?
- pituitary
- thyroid
- parathyroid
- adrenals
- pancreas
- gonads
What is a neurotransmitter?
a chemical substance which is released at the end of a nerve fibre by the arrival of a nerve impulse and, by diffusing across the synapse or junction, effects the transfer of the impulse to another nerve fibre, a muscle fibre, or some other structure
What is neurosecretion?
the storage, synthesis and release of hormones from neurones
What is endocrine secretion?
- relates to hormone’s action on target cells at a distance from the source
- secreted into blood
What is paracrine secretion?
- hormone action on adjacent cells (or nearby target cells) to those cells producing it, within the same tissue
- secreted into ducts
What is an example of paracrine secretion?
somatostatin produced by δ-cells in the islets of Langerhan acts on the α- and β-cells within the same islets
What is autocrine secretion?
hormonal (regulatory) effect on the same cell that produced the hormone itself
What is the pathway of the hormone synthesis of protein hormones?
- amino acids from blood used to synthesise hormone
- pro-hormone (or pre-prohormone) transcribed from DNA
- mRNA moves to cytoplasm and binds to rER
- pro-hormone packaged into vesicles with enzymes to cleave it in golgi apparatus
- vesicle with active hormone accumulate near cell surface and exocytosed into blood when signal received
What is the pathway of the hormones synthesis of steroid hormones?
- cholesterol delivered to cell in form of LDLs and stored as fatty acid esters
- cholesterol esterase liberates cholesterol from esters
- cholesterol transferred to mitochondria using StAR protein
- enzymes allow conversion of cholesterol into steroid hormones in mitochondria
- hormone lipid-soluble so readily diffuses into blood stream (not stored)
What is an example of a protein hormone, where is it produced and what is it’s pre-cursor?
- adrenocorticotropic hormone (ACTH)
- produced in corticotroph cells in anterior pituitary
- prohormone: POMC (cleaves to form ACTH, pro-YMSH and βLPH)
What is an example of a steroid hormone and where is it produced?
- cortisol
- produced in adrenal corticoid cells
What are some examples of miscellaneous hormones?
- amines
- catecholamines (adrenaline and noradrenaline)
What are 3 differences between the endocrine and nervous systems?
- endocrine: releases chemical (hormone) into bloodstream; nervous: releases chemical) neurotransmitter across synapse
- endocrine: effect many target cells around body; nervous: restricted to target cells innervated
- endocrine: effects take place over long time span; nervous: effect generated in milliseconds
How are protein hormones transported?
- stored in vesicles in cells
- secreted into bloodstream as required
- water-soluble so not protein bound
How are steroid hormones transported?
- stored in bloodstream
- bound to certain plasma proteins so can’t diffuse into cells
- dynamic equilibrium: hormone + plasma protein bound hormone
- albumin weakly binds to all steroid hormones
- specific binding proteins bind with higher affinity
What are some examples of specific binding proteins for steroid hormones in the blood stream?
- CBG: cortisol
- TBG: thyroid hormones
- SHBG: testosterone/oestradiol
What are the function of specific binding proteins for steroid hormones in the blood stream?
- buffer hormones
- protect against rapid changes in concentrations
What is the mechanism for ACTH stimulating an adrenal cortical cell to produce cortisol?
- ACTH binds to Gs-protein coupled receptor on plasma membrane of target cell
- α subunit of G protein dissociates from β and γ subunits
- adenylate cyclase activated (ATP converted to cAMP)
- cAMP activates protein kinase A (PKA) which phsophorylates StAR protein
- upregulates cortisol synthesis
What is the mechanism steroid hormone signalling, using cortisol as an example?
- free cortisol enters cell by diffusion
- it binds to specific glucocorticoid receptor in cytoplasm
- hormone-receptor complex travels to nucleus
- complex binds to specific DNA binding sites
- hormone acts as transcription factor in nucleus, increasing/decreasing transcription rate
What is negative feedback?
- diminution or counteraction of an effect by its own influence on the process giving rise to it
- high level of hormone in blood may inhibit further secretion of that hormone
- result of certain action may inhibit further performance of that action
What is positive feedback?
- enhancing or amplification of an effect by its own influence on the process which gives rise to it
- only occurs in gonads
