Lecture - intro (pt. 2) Flashcards
What are the implications of concerted effects of two hormones on their mechanism of action?
Concerted = additive –> two mechanisms working separately
- cause same response and combined effect of hormones is simply the sum of the separate actions of the individual hormones
= two hormones causing the same response
Why are hormones normally present in small amounts, even when they are not needed?
To prime target cells
- but aren’t effecting until physiological event changes the concentration of the available hormone
What does the amount of hormone to a target depend on?
- level of synthesis/release
- level of biological activity (bound/free)
- level of turnover (half life/inactivation)
List 3 major actions (molecular effects) of hormones and give an example of how one of these affects the phenotype?
- Controls gene expression
- gene transcription, RNA stability, RNA translation, protein stability–> can alter genes associated with coat colour - modulate activity (catalytic rate)
- activate/deactivate enzymes - alter celular transport and membrane permeability
- intracellular trafficking, transport process, polarity, water permeability, exocrine secretion
What is a hormone?
Regulatory chemical produced in an endocrine gland or scattered cells, which are then secreted in the blood and carried to target cells
- these chemicals are involved in maintaining homeostasis and controlling physiological process in response to internal and external stimuli
Are pheromones considered hormones?
By definition, pheromones would not be considered hormones as they are excreted outside the body
- however they do interact with the hypothalamus of mammals who come into contact with these molecules, altering physiological state
How do hormonal systems function?
Hormones are subjected to tight regulation by feedback form target organs (mostly negative, but sometimes positive)
- feedback control consists of cyclic systems which are responsible for controlling the amount of hormone released
- hormones occur mainly in systemic circulation - available to all tissues (but only specific cells will respond)
Why are hormones necessary?
Hormones are crucial in:
- maintaining homeostasis and controlling physiological processes
- responding to external stimuli (fight or flight)
- driving cyclic and developmental processes (sex differentiation and pregnancy)
How are hormones selective?
Only target cells express corresponding receptors
- target cells can have receptors for more than one hormone (which can sometimes alter the same process)
Why is hormone specificity important?
Ensures that hormones are only used in tissues, altering physiological activity and processes, in those which require it
Why are both intracellular and extracellular receptors required?
Some hormones are incapable of getting inside the cell (e.g. protein hormones and catecholamines)
How is the endocrine response regulated by feedback systems?
Tight regulation controlling amount of hormone released
- mostly negative (TRH), but can be negative (oestrogen)
Environmental/internal stimuli –> anterior pituitary –> endocrine tissue –> systemic effects –> hypothalamus
