Flashcards in Metabolism - Control And Endocrine Systems Deck (15)
What are the basic steps of a control system?
- sends signal from stimulus via afferent pathway to control centre
- paracrine (local hormones)
- autocrine (many agents)
3). Goes to control centre
- determines set point, analyses input and determines a response
- control centre sends signal via efferent nerves to effector
What are the feedback systems?
1). Negative - effector opposes the stimuli and acts to reverse its effect
2). Positive - stimulus produces a response which increases its effect = catastrophic, fast change
What is a circadian rhythm?
Where is our "body clock" and what does it control?
Suprachiasmatic nucleus in the hypothalamus
Controls biological rhythm at which some hormones are released.
What is jet lag?
When our body clock tells us its a different time to the environment.
Where is water found?
Intracellular fluid - cytoplasm
What is a hormone?
A chemical messenger which is produced in endocrine glands or tissues and travel, often in the bloodstream, to cause an effect on target cells.
What is the life of a hormone?
Produced in endocrine gland or tissue
Transported in blood to target cell/tissue
Act upon target cell or tissue
Inactivated by liver
What is the usual way of controlling rate of secretion?
How are the types of hormone transported?
Lipid soluble require specific protein carriers
- steroid hormones
- thyroid hormones
= only the free form of the hormone is active
Peptides and adrenaline are soluble, so travel in solution
What is the role of carrier proteins?
Increase half life of hormones
Increase solubility of hormones
Act as a reserve of hormone in the blood
What does the magnitude of the response to a hormone depend on?
-Affinity of hormone for receptor
-Amount of expression of hormone receptors
-Concentration of active hormone secreted
-Degree of signal amplification if an enzyme cascade is involved
How does a hormone cause a response if it is lipid soluble (and therefore can cross the membrane)?
1). Hormone diffuses across the membrane and binds to a receptor in the cytosol of nucleus
2). Receptors form a dimer in the nucleus once activated and bind to DNA at the hormone response element.
3). This switches transcription on or off.
TH, cortisol, aldosterone
How can a hormone cause a response if it is water soluble (so can't cross the membrane)?
1). Binds to a receptor on the cell surface which activates the secondary messenger cAMP.
2). The cAMP exerts a metabolic effect, usually activating an enzyme in the cell.
3). The enzyme causes the required effect.
ACTH, adrenaline, insulin