Extracellular signalling Flashcards
Give three reasons cells must communicate with each other
Regulate development and organisation into tissues
Control growth and division
Co-ordinate functions
Give three ways a disease can result from cellular communication going wrong
signal is lost/ no longer sent target ignores signal signal doesnt reach target Too much signal (brain damage) Multiple breakdowns (cancer)
Define remote signalling
Signals secreted by molecules from some distance away
Define contact signalling
Plasma membrane bound signalling molecules communicate by direct physical contact (juxtacrine)
OR via gap junctions that directly join the cytoplasms of interacting cells
How are T-helper cells activated by APCs by juxtacrine signalling?
APCs display antigen fragments on their cell surface membrane, the antigen is recognised by T helper cell receptors
How is gap junction signalling used in cardiac muscle?
Gap junctions form between specialised cells when connexin proteins expressed by two adjacent cells form a CHANNEL that allows movement of cytoplasmic contents (e.g. second messengers).
What are the three stages of remote cell signalling?
1) reception of an extracellular signal by the cell
2) transduction of the signal from outside the cell to inside the cell
3) activation of the cellular response
What are first messengers? Give an example
Extracellular signalling molecules e.g. growth factors, neurotransmitters, hormones, cytokines etc etc
Are receptors for signalling molecules (1st messengers) specific?
YES
Define paracrine signallling
The signalling molecule acts on NEARBY cells
Define autocrine signalling?
The cell respond to a signalling molecule secreted by ITSELF
Define neuronal signalling. How can this be autocrine or paracrine?
In response to a nerve impulse, neurotransmitters are released from a nerve terminal to act on target cells. This signal can act either on the releasing nerve cell (autocrine) or on the nearby target cell (paracrine) which may be an effector (muscle or gland) or another nerve
Define endocrine signalling
Signalling molecule acts on target cells distant from its site of synthesis - it travels in the blood
Define hormones
Chemical messengers released by a cell, gland or organ that are transported in the blood and affect cells in other part of the body
How do hormones work?
They bind to specific receptors on the target cell where they act as a switch to influence chemical or metabolic reactions
How do hormones regulate metabolism?
Via changes in GENE EXPRESSION or via SECOND MESSENGER SYSTEMS
Give 2 things hormones can regulate. How?
o Body energy needs
o protein and nucleic acid metabolism
o mineral and electrolyte metabolism
o synthesis and release of hormones
Through negative and positive feedback
What do endocrine glands consist of?
(ductless glands)
Groups of secretory cells surrounded by lots of capillaries that facilitate the diffusion of hormones from the secretory cells directly into the blood stream
How do peptide hormones work?
Diffuse through interstitial tissues to target cells (are hydrophilic)
Where are receptors for peptide hormones located?
Cell membrane
Where are receptors for lipid based hormones located?
Inside the cell - they can diffuse through the membrane
Explain the positive feedback mechanism
The amplification of the stimulus and increasing release of hormone until a particular process is complete and the stimulus ceases
What is the role of receptors?
They are ‘sensors’ - coordinate the function of all cells in response to chemical messenger binding. Convert the extracellular hormone signal to an intracellular signal that can be conveyed across the plasma membrane
Can different cells respond differently to the same hormone? Why?
Yes - due to multiple receptor subtypes