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IMS topic 4 - Lipids > Extracellular signalling > Flashcards

Extracellular signalling Flashcards

1
Q

Give three reasons cells must communicate with each other

A

Regulate development and organisation into tissues
Control growth and division
Co-ordinate functions

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2
Q

Give three ways a disease can result from cellular communication going wrong

A 
signal is lost/ no longer sent
target ignores signal
signal doesnt reach target
Too much signal (brain damage)
Multiple breakdowns (cancer)
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3
Q

Define remote signalling

A

Signals secreted by molecules from some distance away

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4
Q

Define contact signalling

A

Plasma membrane bound signalling molecules communicate by direct physical contact (juxtacrine)
OR via gap junctions that directly join the cytoplasms of interacting cells

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5
Q

How are T-helper cells activated by APCs by juxtacrine signalling?

A

APCs display antigen fragments on their cell surface membrane, the antigen is recognised by T helper cell receptors

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6
Q

How is gap junction signalling used in cardiac muscle?

A

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).

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7
Q

What are the three stages of remote cell signalling?

A

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

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8
Q

What are first messengers? Give an example

A

Extracellular signalling molecules e.g. growth factors, neurotransmitters, hormones, cytokines etc etc

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9
Q

Are receptors for signalling molecules (1st messengers) specific?

A

YES

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10
Q

Define paracrine signallling

A

The signalling molecule acts on NEARBY cells

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11
Q

Define autocrine signalling?

A

The cell respond to a signalling molecule secreted by ITSELF

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12
Q

Define neuronal signalling. How can this be autocrine or paracrine?

A

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

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13
Q

Define endocrine signalling

A

Signalling molecule acts on target cells distant from its site of synthesis - it travels in the blood

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14
Q

Define hormones

A

Chemical messengers released by a cell, gland or organ that are transported in the blood and affect cells in other part of the body

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15
Q

How do hormones work?

A

They bind to specific receptors on the target cell where they act as a switch to influence chemical or metabolic reactions

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16
Q

How do hormones regulate metabolism?

A

Via changes in GENE EXPRESSION or via SECOND MESSENGER SYSTEMS

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17
Q

Give 2 things hormones can regulate. How?

A

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

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18
Q

What do endocrine glands consist of?

A

(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

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19
Q

How do peptide hormones work?

A

Diffuse through interstitial tissues to target cells (are hydrophilic)

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20
Q

Where are receptors for peptide hormones located?

A

Cell membrane

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21
Q

Where are receptors for lipid based hormones located?

A

Inside the cell - they can diffuse through the membrane

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22
Q

Explain the positive feedback mechanism

A

The amplification of the stimulus and increasing release of hormone until a particular process is complete and the stimulus ceases

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23
Q

What is the role of receptors?

A

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

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24
Q

Can different cells respond differently to the same hormone? Why?

A

Yes - due to multiple receptor subtypes

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25
What does adrenaline stimulate in muscle, adipose tissue, cardiac muscle, vascular smooth muscle cells?
Breakdown of glycogen in muscle & liver cells Fatty acid production in adipose tissue Increases heart rate by stimulating cardiomyocytes Increased blood pressure by stimulating smooth muscle
26
Which of the four main receptor types are cell-surface receptors for hydrophilic signalling molecules?
Ligand-gated ion channels G protein coupled receptors Receptor tyrosine kinases
27
Which of the four main receptor types are intracellular receptors for hydrophobic/lipophilic signalling molecules?
Nuclear hormone receptors
28
Define ionotropic
Ions modify the speed of action
29
Explain the role of ligand gated ion channels
Involved in rapid synaptic signalling between electrically excitable cells - FAST SYNAPTIC TRANSMISSION
30
How do ligand gated ion channels work?
4 Ligands bind to the receptor not he extracellular face of the cell, causing conformational change in the channel protein so that specific ions can flow through the channel down their concentration gradient to alter the cells electric potential
31
What is the structure of a ligand gated ion channel?
4 or 5 different subunits surrounding a central pore
32
What is the structure of G protein coupled receptors?
Integral membrane porteins; a single polypeptide comprising of 7 membrane spanning alpha helical regions connected by extracellular and intracellular loops (usually NH2 on extracellular side and COOH in cytosol)
33
What hormones to GPCRs usually interact with?
Peptide hormones and neurotransmitters
34
How do GPCRs work?
Binding of ligands (hormones) to GPCR is usually done by intracellular loop 3 and/or the C tail region. Binding causes conformational change and interaction with the signal transducing G PROTEIN. This modulates the activities (activation or inhibitor) of downstream effector proteins which modulate the levels of 2nd messenger molecules (cAMP, cGMP, ca2+) or regulate ion channel opening to determine a cells membrane potential
35
What does the renin-angiotensin system control?
Bood pressure, blood volume and electrolyte homeostasis in many body systems
36
Give a brief description of the renin-angiotensin system
The secretion of renin is stimulated in response to a fall in Na+ concentration reduced renal blood pressure and nerve activity. Renin (enzyme) cleaves angiotensin I from angiotensiongen (a plasma protein). This is further cleaved to angiotensin II by angiotensin converting enzyme (ACE). Angiotensin11 causes vasoconstriction to increase blood pressure, aldosterone secretion etc etc Controlled by negative feedback
37
What are the two subtypes of angiotensin II and what are their roles?
AT1 and AT2 receptors. AT1 mediates vasoconstriction, increased noradrenaline release from nerve terminals, stimulation of Na+ reabsorption, aldosterone secretion, vascular growth AT2 receptor activation results in antihypertrophic (muscle cell constriction) and anti-hypertensive effects
38
What do ACE inhibitors do?
Inhibit ACE from cleaving angiotensin I to II to reduce blood pressure
39
What is the role of kinase linked receptors?
A ligand binds, and the two monomers of the receptor bind together to become activated. Kinase linked receptors indirectly regulate gene transcription to control cell division, growth, tissue repair, apoptosis, differentiation, immune response. Very slow.
40
What is the structure of kinase linked receptors?
A single transmembrane helix with a large extracellular binding domain and intracellular catalytic domain
41
What are catalytic kinase linked receptors?
The receptor itself is an enzyme e..g tyrosine kinases (activated by insulin) and gyanylate cyclase (cGMP) linked receptors
42
what is the role of nuclear hormone receptors?
Regulate transcription of certain genes
43
How do nuclear receptors work?
They are intracellular receptors within the cytosol or nucleus. Small lipophilic hormones diffuse across the plasma membrane and interact with cytosolic nuclear receptors. The hormone receptor complex translocates to the nucleus and binds to septic regions of the DNA (hormone responsive elements) and effects gene transcription
44
Explain the structure of a neurone
A cell body from which dendrites and axon extend. The dendrites receive sensory information in the form of nerve impulses, the cell body assimilates the information and passes it to the post synaptic cell The axon ends at the nerve terminal where neurotransmitters are stored and released
45
What is a resting potential?
-70mv polarised Generated by the Na+/K+ ATPas which pumps 3Na+ out of the cell and 2K+ into the cell, resulting in high Na+ conc out of the cell and a low conc inside.
46
What is an action potential?
Upon stimulation, the membrane potential of the neurone rises rapidly to +30mv, depolarising the membrane. This causes a conformational change in the Na+ channel, allowing the flow of Na+ down its concentration gradient from the outside of the cell to the inside. The wave of depolarisation is propagated along the axon by the opening of Na+ channels.
47
Why is the refractory period important?
Na+ channels are closed so the signal does not travel backwards
48
What causes action potentials?
Large, transient change in permeability of the plasma membrane to Na+ and K+
49
Explain neurotransmission at the synaptic cleft
The action potential (wave of depolarisation) reaches the nerve terminal, causing the synaptic vesicles to fuse with the plasma membrane (Ca2+ dependent) and release their neurotransmitter contents by exocytosis. Neurotransmitter diffuses across the synaptic cleft and binds to specific post-synaptic receptors, initiating a cellular response
50
Give some examples of neurotransmitters
acetylcholine, amino acids (glutamate, aspartate, glycine, GABA), monamines (noradrenaline, dopamine, histamine, serotonin), Peptides (endorphins, substance P, neruotensin), Lipids (anandamide)
51
What is the life cycle of a neurotransmitter?
Synthesis in the nerve terminal Storage in synaptic vesicles within nerve terminal Release into the synaptic cleft from pre synaptic vesicles by exocytosis (Ca2+ dependent) in response to an action potential Receptor activation of post synaptic cell Neurotransmitter inactivation due to enzyme metabolism reuptake to pre synaptic nerve terminal
52
Define depression and give some symptoms
An affective disorder (disorder of the mood rather than thought/cognition), retardation of thought and action Misery, apathy, low self esteem, loss of appetite and motivation
53
What is the difference between unipolar and bipolar depression
Unipolar; mood swings are always in the same direction | Bipolar; depression alternates with mania (periods of overactivity and excitement)
54
What causes depression?
Functional deficit of monoaminergic (chemicals that moderate neurotransmitters in the brain) transmission in the brain
55
What causes mania?
Functional excess of monoaminergic (chemicals that moderate neurotransmitters in the brain) transmission in the brain
56
What is the role of antidepressants?
Increase monoaminergic transmissions within the synaptic cleft to alleviate symptoms
57
Give some examples of antidepressants
``` Monoamine reuptake inhibitors e..g SSRIs Monoamine oxidase inhibitors Electroconvulsive theory Mood-Stabilising drugs Miscellaneous atypical antidepressants Mood-stabilising drugs ```
58
How do monoamine reuptake inhibitors work?
Bind to pre-synaptic nerve terminal monoamine transporters to stop reuptake of the neurotransmitter and raise levels int he synaptic cleft
59
How do monoamine oxidase inhibitors work?
Monoamine oxides are enzymes that catalyst the oxidative deamination (breakdown) of monoamines in the presynaptic nerve terminal. Inhibition of MAOs means more neurotransmitter is produced.
60
How do "atypical" receptor blockers work to a alleviate depression?
Poorly understood act as non-selective antagonists at presynaptic auto receptors to inhibit the feedback loops and give increased monoamine transmission
61
What are gasotransmitters?
Gaseous molecules synthesised in the body; NO, CO, H2S (hydrogen sulphide) Environmental pollutants and toxic gases Pass readily across plasma membranes and are involved in paracrine signalling
62
What are the benefits of small doses of CO
It is an important endogenous signalling molecule Cardioprotective Neuroprotective

IMS topic 4 - Lipids (6 decks)

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