WEEK 7: 7.2 Hormone Mechanisms of Action and Regulation Flashcards
how do lipophilic signal molecules cause a response of the target cell?
they can diffuse through the cell membrane and bind to cytosolic/nuclear receptors
how do lipophobic signal molecules cause a response of the target cell?
they bind to receptors on the surface of the cell membrane, as they cannot diffuse through
what are the two receptor types hormones mainly bind to?
receptor enzyme and G protein coupled receptor
What occurs when a receptor enzyme is activated?
it activates an intracellular enzyme
What occurs when a G protein coupled receptor is activated?
it opens an ion channel or alters enzyme activity, namely amplifier enzyme, which then alter the production of second messenger molecules
What are common second messengers?
cAMP and IP3
What do second messenger cascades lead to?
Signal amplification
At what pace is the effect of signal amplification
very rapid
How to second messengers regulate cellular activity?
they influence the activity of enzymes, receptors, transporters, genes
What is a signal transduction pathway
the series of reactions and events downstream of a cell surface receptor
What do steroid hormones lipophilic nature allow it to do?
diffuse readily through the cell membrane and bind to receptor proteins present in the cytoplasm/nucleus of the target cell.
What do a hormone and receptor binding form?
a complex
How do steroid hormones trigger gene transcription?
complexes can alter the transcription of particular genes after attaching to specific sites on the DNA
What does the triggering of gene transcription do?
allow steroid hormones to alter the performance of the target cell by leading to the manufacture of new structural proteins, new membrane channels, receptors, pumps, enzymes
At what pace does the response elicited by steroid hormones occur?
a slower pace
What stimulates hormone release
hormonal (stimulation from tropic hormones), neural (stimulation of nerve fibres), humoral (level of ions/substances in blood)
What is the amplitude of the response elicited within a target cell by a hormone influenced by?
- amount of hormone in the blood
- bond affinity between the receptor and hormone
- no of receptors for the hormone eg. receptor up-regulation and receptor down-regulation (target cells lose receptors in response to low levels of the hormone)
what is permissiveness
a hormone must be present to permit another hormones effects
what is synergism
combination of hormones produce a greater effect than the sum of their seperate effects
what is antagonism
hormone reduces the effectiveness of another hormone
Explain the negative feedback loop that controls the secretion of thyroid hormones from the thyroid gland
So what happens is that the hormone TRH, which stands for thyrotropin releasing hormone is
released from the hypothalamus. This
stimulates the release of a further hormone called thyroid stimulating hormone from the anterior
pituitary gland. In turn, increases the synthesis and release of the thyroid hormones from the
thyroid gland. Now, the thyroid hormones exert a number of important cellular effects around the
body, but they also act to suppress R synthesis and secretion from the hypothalamus and THC
synthesis and secretion from the pituitary.
Therefore, when the levels of T3 and T4 increase, this feedback to the hypothalamus and to the
pituitary helps to ensure that there isn’t an excessive stimulation of the thyroid gland to produce and
secrete excessive levels of T3 and T4.
What is the primary determinant of the concentration of active hormones in plasma?
the rate at which hormones are formed and secreted, in which the secretion aspect is most commonly regulated
What can the onset of hormone effect range from
seconds to hours after secretion
What can the duration of hormones range from
minutes to days
