Week 1 Flashcards
What are hormones
Substances that are secreted directly into the blood by specialised cells, only present in minute concentrations in blood and bind to specific receptors in target cells to influence cellular reactions
What is endocrine signalling
Secretory cell releases substance (hormone) into blood stream, hormone diffuses to the target cell. Relatively slow process
Paracrine signalling
Secretory cell releases substance which diffuses short distance to an adjacent target cell. Local mediators
What is paracrine signalling important for
During development e.g. spinal cord development
When is paracrine signalling not effective
For large complex organisms
What is autocrine signalling
Cell releases substance that acts on the same cell. Target sites on the same cell. Local effect
When is autocrine signalling most effective
When performed simultaneously by neighbouring cells of same type
What is autocrine signalling used for
Important during development. Thought to play key role in metastasis, so cancer cells often use this.
Synaptic transmission
An example of paracrine signalling. Electrical impulse (neurotransmitters) transferred from axon on presynaptic neurone to receptors on post synaptic neurone. Fast
What is a receptor
A specific protein located either on plasma membrane or within target cell which receive a signal and transduce it into a biological response
How are effects of first messengers (hormones, neurotransmitters etc) mediated
By binding to specific receptors
What was the Otto Loewi experiment
He used two frog hearts and put them in chambers of saline. One heart attached to vagus nerve, vagus nerve was stimulated to slow heart down. First heart slowed down then after a delay the second heart slowed down. Now know this chemical as Ach
What is an agonist
Compounds that will produce the same effects as neurotransmitter
What is an antagonist
Fit into active site but has no response. It blocks the effect of the native neurotransmitter, no response
Nicotinic effects of AChRs (Acetylcholine receptors)
Agonist= Nicotine- bind to and activates nAChRs (ion channels) at NMJ, causes Na+ influx- results in muscle contraction
Antagonist= curare (arrow poison)- binds to active site of nAChR at NMJ (blocking effect of ACh) causing skeletal muscle paralysis
Muscle contraction, synaptic transmission (autonomic ganglia, parasympathetic postganglionic, CNS)
— nAChRs (ion channels)
Muscarinic effects
Agonist= Muscarine (Amanita muscaria) fly agaric -activates M1-5 receptors GPCRs
Antagonist= Atropa Belladonna alkaloids, blocks effects
Atropine, scopolamine etc
Too much can cause Bradycardia (low heart rate), salivation, bronchospasm, midriasis (dilated pupils)
M1-5 GPCRs
What is Kd
Dissociation constant. Parameter. Concentration at which 50% of receptors occupied by a ligand, measure of affinity
What are ligands
The signalling molecule used by the body for various cells to communicate with other cells
What are the four main receptor types
Ligand gated ion channels (ionotropic receptors)
G-protein coupled receptors (metabotropic) GPCRs
Kinase linked receptors
Nuclear receptors