Cell communication

Question 1

What is the importance of cell communication

Answer 1

to maintain internal conditions (HOMEOSTASIS)

Question 2

What are the mechanisms that cells use to communicate (2)

Answer 2

1. Direct contact of cell membranes or via tight (gap) junctions
2. Diffusible chemicals signals

Question 3

What is gap junctional communication (5)

Answer 3

1. Pores (connexins) exist between adjacent cells
2. Allows the free flow of small molecules, ions and electrical signals from cell 1 to cell 2
3. Selective permeability
4. Quick exchange, facilitates the fast distribution of ‘signal’ across the whole tissue
5. Allows for a coordinated/synchronised response of a group of cells / tissue

Question 4

How is cell communication achieved via diffusible chemical signals (6)

Answer 4

1. Synthesis of signal in the secreting cell
2. Release of chemical signal from secreting cell
3. Reception of signal at target cell
4. Signal transduction in target cell
5. Response from target cell
6. Signal transmission → reception → signal transduction → response

Question 5

What is the diversity of chemical signalling molecules (3)

Answer 5

1. Hydrophilic or lipophilic
2. Size (small to very large RMM)
3. Release mechanism: storage vesicles, bound to storage proteins, immediate release as synthesised

Question 6

What are the types of chemical signalling (4)

Answer 6

1. Autocrine signalling
2. Paracrine signalling
3. Endocrine and Neuroendocrine signalling
4. Neuronal signalling

Question 7

What are local mediators, hormones and neurotransmitters (3)

Answer 7

1. Local mediators = chemical signals that use autocrine and paracrine signalling
2. Hormones = chemical signals in endocrine and neuroendocrine signalling
3. Neurotransmitters = chemical signals in neuronal signalling

Question 8

What is autocrine signalling (3)

Answer 8

1. Autocrine - the cell signals itself through a chemical that it synthesizes and then responds to.
2. If one cell only is secreting a molecule then autocrine signals are small
3. If several cells secrete a molecule, each will receive a stronger autocrine sig

Question 9

How is autocrine signalling used in T-cell proliferation (2)

Answer 9

1. Cytokines are signalling peptides and proteins with regulatory functions for intensity and duration of immune response
2. T-cells respond to antigenic stimulation by synthesising certain cytokines that drives their own proliferation, thereby increasing the number of responsive T-cells and amplifying the immune response

Question 10

What is paracrine signalling

Answer 10

Paracrine - chemical signals that diffuse into the area and interact with receptors on nearby cells

Question 11

How is paracrine signalling used in cell differentiation (3)

Answer 11

1. Transforming Growth Factors (TGFs) are types of cytokines that affect the production of specific transcription factors and have important roles in cell differentiation
2. TGF-beta is secreted by a variety of cells including tumour cells, immune cells, and fibroblasts.
3. It promotes the epithelial cells to mesenchymal cells transition (EMT)

Question 12

What is endocrine signalling

Answer 12

Endocrine - chemical signals are secreted into the blood and carried by blood and tissue fluids to the cells they act upon. The response is cell specific

Question 13

How is endocrine signalling used with oestrogen (4)

Answer 13

1. The hormone oestrogen is released via the pituitary gland
2. It travels in the blood an effects different parts of the body
3. Response A-BRAIN -estrogen helps to maintain body temperature
4. Response B- BONE- estrogen helps to preserve bone density

Question 14

What are hormones (4)

Answer 14

1. Hormones produced in one part of body bind to receptors expressed on target cells that are far away
2. Very stable
3. Act at relatively low concentrations
4. Responses initiated by them tend to be of long duration

Question 15

What are the hormone classifications (2)

Answer 15

1. Polypeptide and Amine which are hydrophilic
2. steroid (precursor: cholesterol) which is hydrophobic

Question 16

How is endocrine signalling achieved with hydrophilic hormones (peptides/amines) (4)

Answer 16

1. Peptide hormone binds with receptor on the cell memebrane and activates it
2. Binding causes activation of the second messenger
3. Second messenger activates target proteins
4. Target proteins initiate a response

Question 17

How is endocrine signalling achieved with hydrophobic hormones (steroids) (3)

Answer 17

1. Steroid hormone enters the cell and binds to hormone receptor in the nucleus activating it and forming a hormone response element (HRE)
2. The HRE causes a positive charge in the nucleus initiating gene expression and increased mRNA expression
3. Increased mRNA expression causes increased protein X in the cytosplasm

Question 18

What is neuronal signalling

Answer 18

Neuronal - chemical signals (neurotransmitters) are secreted into by neurones and interact with target cells (muscle or nerve cells) that are in very close proximity (synapse) which is paracrine signalling

Question 19

What is a synapse (3)

Answer 19

1. A synapse is the tiny gap that exists between adjacent neurones (nerve cells) or a neuron and the muscle cell (neuromuscular junction).
2. Neurotransmission = passing of information from the pre-synaptic neurone to the post-synaptic neurone by a chemical neurotransmitter.
3. With endocrine signalling specificity is achieved by specific receptors on the target cell. With synaptic signalling specificity is achieved by closeness of presynaptic and postsynaptic cells

Question 20

What are neurotransmitters (4)

Answer 20

1. Chemical signals that diffuse into synapses and interact with receptors on nearby cells.
2. Neurotransmitters can achieve very high local concentrations
3. Associated with rapid, short-term responses
4. Neurotransmitters are quickly degraded or taken back into the cell

Question 21

How is neurone-neurone communication achieved

Answer 21

Nerve impulses flow from the terminal arbosrisation (TA)/nerve endings of the action of one neurone to the dendrites (D) of another nuerone.

Question 22

How is neurone-muscle communication achieved (2)

Answer 22

1. Nerve impulse flows from the dendrites of the neurone towards the cell body to the axon
2. Nerve impulse flows from the axon through the mylein sheath to the axonal terminal (synapses) in the muscle fibres

Question 23

What is neuropharmacology (4)

Answer 23

1. Many neurological and psychiatric diseases are caused by pathologic over-activity or under-activity of neurotransmission
2. Neuropharmacology is the study of how drugs effect cellular function in the nervous system
3. Drugs can act either pre-synaptically to alter levels of the neurotransmitter in the synaptic cleft or by altering the functional state of the postsynaptic receptors
4. Drugs targeting the synapse treat a wide range of aliments (for example cardiac problems, schizophrenia, etc.)

Question 24

What are examples of drugs that target the synapse (5)

Answer 24

1. Antidepressants
2. Anti-psychotic drugs
3. Poisons
4. Acetylcholinesterase inhibitors
5. Antihypertensive drugs

Question 25

How do SSRIs (serotonin reuptake inhibitors) work (2)

Answer 25

1. SSRIs, such as Fluoxetine, block serotonin re-uptake at presynaptic nerve endings. 2. The blocking of serotonin re-uptake increases serotonin (neurotransmitter) concentration in the synapse and on postsynaptic receptors

Question 26

How do antipsycotics (dopamine antagonists) work (2)

Answer 26

1. Antipsychotic drugs, such as Olanzapine, prevent dopamine from occupying receptor sites on neuronal cell membranes and exerting their effects on cellular functions. 2. This action leads to changes in cell functions that account for therapeutic effects (i.e. relief of psychotic symptoms). Other neurotransmitters and receptors may also be involved.

Question 27

How do poisons (e.g. Botulinum) work

Answer 27

Botulinum toxin blocks release of acetylcholine at the synapse and so causes paralysis of muscles.

Question 28

How do acetylcholinesterase inhibitors (e.g. Caffeine) work (3)

Answer 28

1. Acetylcholinesterase inhibitors, such as caffeine, are indirect-acting cholinergic drugs. 2. They prevent the enzymatic breakdown of the neurotransmitter acetylcholine. 3. The acetylcholine remains in the synapse and continues to interact with cholinergic receptors on target effector organs, producing a cholinergic response.

Question 29

How do antihypertensive drugs (e.g. beta-blockers) work (2)

Answer 29

1. beta-adrenergic blocking agents, such as atenolol, prevent adrenaline and noradrenaline from occupying receptor sites on cell membranes. 2. This action alters cell functions normally stimulated by these neurotransmitters.