Physiology Flashcards
(31 cards)
What are the determinants of the specificity of hormone action?
- structure of the hormone molecule
- hormone-specific receptor structure
- distribution of hormone receptors
What are the 4 classes of endocrine hormones?
Give examples of each.
- Modified amino acids (Adrenaline)
- Steroids (Cortisol)
- Peptides (ADH)
- Proteins (Isulin)
Define autocrine signalling.
The cell secreting the hormone is also its target
Define paracrine signalling.
Hormones secreted by a cell target cells in its vicinity
-do not enter circulation
Define endocrine signalling.
Hormones secreted by a cell enter the bloodstream to reach target tissues systemically
How is hormonal action terminated?
By enzymatic inactivation of the hormone molecules (in the liver or action site)
Amine hormones (such as Adrenaline) tend to be pre-synthesised and released ‘on demand’ in response to a particular signal (T/F)
True
How are Peptide and Protein hormones stored?
As long precursor proteins, which are cleaved and released in response to a signal
-Ca2+ dependent exocytosis
What is the common intermediate in all steroid hormone biosynthetic pathways? What is it formed from?
Pregnenolone
Formed from cholesterol
-rate limiting step
How are steroids transported in blood?
Bound to plasma proteins
Only protein-bound steroid hormones are biologically active (T/F)
False
-only FREE steroids are active
What are the functions of the hormone carrying proteins?
- increase amount of hormone transported in blood
- provide a hormone reservoir and buffer
- extend hormone half-life in the blood
What carrier binds cortisol specifically?
cortisol-binding globulin
What carrier specifically binds thyroxine (T4)?
thyroxine-binding globulin
What carrier protein binds testosterone specifically?
sex steroid-binding globulin
Name two important non-specific carrier proteins.
Albumin
Transthyretin
Hormones must be in the free / unbound form to cross the capillary wall to activate receptors in target tissues (T/F)
True
What mechanisms account for the Diurnal variation in cortisol levels?
…
something to do with day/night light changes
Which hormone receptors are found at the target cells surface? What hormones bind to them?
G-protein coupled receptors
Receptor kinases
-amines, peptides and proteins
Intracellular receptors bind lipophobic hormones (T/F)
False
-lipophilic hormones, which can diffuse across the plasma membrane
What are the 3 classes of nuclear hormone receptors?
Class 1 - activated by steroid hormones
-move from cytoplasm into nucleus upon activation
Class 2 - activated by lipids
-constitutively present in nucleus
hybrid class - activated by thyroid horome (T3)
What happens at Receptor Kinases upon hormone binding?
- Autophosphorylation of intracellular tyrosine receptor residues
- Phosphorylation of adapter proteins’ tyrosine residues
What type of receptor is the insulin receptor?
Tyrosine kinase receptor
What type of receptor binds the Growth Hormone?
Cytokine receptor linked to tyrosine kinase activity
