lecture 25 - homeostasis & hormones Flashcards
What are the 3 steps of the homeostatic mechanism?
Receptors detect change, control centre compares to set point and signals to effectors, effectors (organs/tissues) respond with localised or wide spread effects.
Why might a value for a characteristic be abnormal for an individual, even though it is inside the normal population range?
The population reference range is wider than the normal fluctuations found within an individual, because it contains the extremes of individuals within the population.
What are the differences between the neural and endocrine control systems?
Neural: fast, short lasting and highly targeted, Endocrine: slow, long lasting, targeted via specific receptors.
What are the major endocrine organs (studied in HUBS191)?
Hypothalamus, pituitary gland, adrenal gland, thyroid gland, pancreas, parathyroid glands.
What are some key physiological variables held in homeostasis by hormones?
Blood sugar concentration, growth & repair, basal metabolic rate, blood calcium concentration
What are hormone receptors?
Proteins found inside or in the plasma membrane of target cells that can bind to specific hormones.
What are water-soluble hormones typically made up of?
Peptides or catecholamines (e.g. adrenaline and noradrenaline)
What proportion of water-soluble hormones are peptides?
75%
What kind of receptors do water soluble hormones bind to?
Receptors on the surface of cells (within the cell membrane)
How are water-soluble hormones transported around the body?
Via the bloodstream, where they are dissolved into the blood.
Are water-soluble hormones stored?
Yes - stored until required, then released by exocytosis.
What is the process of cellular response to water-soluble hormone receptor activation?
Hormone binds to cell surface receptor, G protein is activated and activates or deactivates second messenger pathways that result in a cellular response.
What levels are controlled by water soluble hormones in a cell?
cAMP and Ca2+
What are key examples of lipid-soluble hormones?
Steroids, thyroid hormones
What are lipid soluble steroid hormones synthesised from?
Made when required (generally not stored) from cholesterol.
How do lipid-soluble hormones travel around the body?
In the bloodstream, bound to carrier proteins as they are insoluble in water.
Where are lipid-soluble hormone receptors found?
In the cytoplasm or nucleus of target cells.
How do lipid-soluble hormones enter target cells?
They arrive at the cell, dissociate from their carrier protein and diffuse across the phospholipid cell membrane.
What do lipid-soluble hormones receptor complexes act as?
Transcription factors, that bind to DNA to activate target genes.
When target genes are activated by lipid-soluble hormone receptor complexes, what is produced?
transcription makes mRNA that can then be translated for protein synthesis.
How do lipid-soluble hormones lead to cellular responses?
The receptors facilitate gene activation, transcription and mRNA production, and then translation to produce proteins that have cellular effects.