INTERCELLULAR COMMUNICATION

Dr.Mohammed Sharique Ahmed QuadriAssistant prof. Physiology

Al Maarefa College

بسم الله الرحمن الرحيم

INTERCELLULAR COMMUNICATION

• Direct intercellular communication– Gap junction – Transient direct linkup of surface markers

• Indirect intercellular communication– Through extracellular chemical messengers or signal

molecules • Paracrine• Neurotransmitters• Hormones• Neurohormones

Direct intercellular communication

Direct intercellular communication

(complementary surface markers)

Indirect intercellular communication

– extracellular chemical messengers or signal molecules • Paracrine• Neurotransmitters• Hormones• Neurohormones

Source

Distance

Means by which get to target cells

diff

ers

–Paracrines• Local chemical messengers• Exert effect only on neighboring

cells in immediate environment of secretion site

–Neurotransmitters• Short-range chemical messengers• Diffuse across narrow space to act

locally on adjoining target cell (another neuron, a muscle, or a gland)

• Long-range messengers• Secreted into blood by endocrine glands in response to

appropriate signal• Exert effect on target cells some distance away from

release site

Hormones

– Neurohormones• Hormones released into blood by neurosecretory

neurons• Distributed through blood to distant target cells

Hormones

• Two distinct groups of hormones based on their solubility properties– Hydrophilic hormones

• Highly water soluble • Low lipid solubility

– Lipophilic hormones• High lipid solubility• Poorly soluble in water

–Extracellular chemical messengers bring about cell responses primarily by signal transduction

Process by which incoming signals are conveyed to target cell’s interior

• Binding of extracellular messenger (first messenger) to matching receptor brings about desired intracellular response by either– Opening or closing channels– By activating receptor enzymes – Activating second-messenger systems

• Activated by first messenger• Relays message to intracellular proteins that carry out

dictated response

Opening of receptor-channel when an extracellular messenger binds

Tyrosine kinase pathway.

Activation of second messenger pathway via G-Protein couples receptors

Amplification of the initial signal by a second-messenger pathway

• RECEPTORS AND THEIR REGULATION The receptors on target tissues are not static. They are

dynamic and mobile and their number also changes during the process of regulation.

Up Regulation of Receptors – The number of receptors is increased on the target

tissue. This happens when there is less concentration of ligand in the ECF

Down Regulation of Receptors The number of receptors is decreased on the target

tissue. This happens when ligand concentration is more in the ECF

References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition

23