Cell signaling is the process by which cells communicate with each other and their environment through chemical signals. There are several types of cell signaling including paracrine, autocrine, synaptic, and endocrine signaling. Cell death, which can occur through programmed or unprogrammed means, is also an important cellular process. The three main types of cell death are apoptosis, autophagy, and necrosis. Apoptosis is programmed cell death, autophagy involves lysosomal degradation of cytoplasm, and necrosis is unprogrammed cell death resulting from injury or infection.

1. Signaling And Cell Death
MANI BHASKAR KUMAR
College of Fisheries Kishanganj, Bihar
FM/FPB/0002/COF/2023-24

2. Introduction
Cell signaling is the process of cellular communication within the
body driven by cells releasing and receiving hormones and other
signaling molecules.
As a process, cell signaling refers to a vast network of communication
between, and within, each cell of our body.
Cell signaling enables coordination within multicellular organisms .
Cells typically communicate using chemical signals.
These chemical signals, which are proteins or other molecules
produced by a sending cell, are often secreted from the cell and
released into the extracellular space.

3. Cell Signaling
Cell signaling is the
process by which
cells communicate
with other cells
within their body or
with the external
environment.
 In order to detect a signal (that is, to be a target cell), a neighbor cell must have the right receptor for that signal.
 When a signaling molecule binds to its receptor, it alters the shape or activity of the receptor, triggering a change inside of
the cell. Signaling molecules are often called ligands, a general term for molecules that bind specifically to other
molecules (such as receptors).

4.  The message carried by a ligand is often
relayed through a chain of chemical
messengers inside the cell.
 Ultimately, it leads to a change in the
cell, such as alteration in the activity of
a gene or even the induction of a whole
process, such as cell division.
 The original intercellular (between-
cells) signal is converted into
an intracellular (within-cell) signal that
triggers a response.

6. Why do cells communicate ?
During development cells differentiate to
adopt specialized roles
Cells need to know whether to live die. Or divide
Regulation of metabolism
Muscle contraction and expansion
Secondary sexual character
Neurotransmission

7. Steps in cell signaling
Synthesis of signaling molecule
Release of signaling molecule
Transport of signals to target cells
Detection and binding of signals by specific receptor
Changes due to receptor signal complex

8. Types of cell signaling
Paracrine signaling
Often, cells that are near one another communicate through the
release of chemical messengers (ligands that can diffuse through the
space between the cells). This type of signaling, in which cells
communicate over relatively short distances, is known as paracrine
signaling.
Autocrine signaling
In autocrine signaling, a cell signals to itself, releasing a ligand that
binds to receptors on its own surface (or, depending on the type of
signal, to receptors inside of the cell). This may seem like an odd thing
for a cell to do, but autocrine signaling plays an important role in
many processes.

9.  Synaptic signaling
• n synaptic signaling , nerve cells transmit signals this process
is named for the synapse , the junction between two nerve
cells where signal transmission occurs.
• When the impulse reaches the synapse , it triggers the release
of ligands called Neurotransmitters , which quickly cross the
small gap between the nerve cells.
• When the neurotransmitters arrives at the receiving cell ,
they bind to receptors and Couse a chemical change inside
the cells
 Endocrine signaling
• In long-distance endocrine signaling, signals are produced
by specialized cells and released into the bloodstream, which
carries them to target cells in distant parts of the body.
• Signals that are produced in one part of the body and travel
through the circulation to reach far-away targets are known
as hormones.

10. Cell Death
Cell death is the event of a biological cell ceasing to carry out
its functions.
This may be the result of the natural process of old cells dying
and being replaced by new ones, as in programmed cell
death, or may result from factors such as diseases, localized
injury, or the death of the organism of which the cells are
part.
Apoptosis or Type I cell-death, and autophagy or Type II cell-
death are both forms of programmed cell death, while
necrosis is a non-physiological process that occurs as a result
of infection or injury.

11. What causes cell
death
 There are many reasons cells die:
• Some cells die as they develop,
before they’re fully formed.
• Old cells reach the age where they
can’t divide anymore and die.
• Irreparable damaged cells
naturally die off.
• Diseases, injuries, toxins and
certain treatments damage cells,
causing cell death.

12. Types of cell death
There are three
major types of
morphologically
distinct cell death:
Apoptosis Autophagic Necrosis

13. Apoptosis cell
death
• Apoptosis is a form of programmed cell death
that occurs in multicellular organisms and in some
eukaryotic, single-celled microorganisms such as
yeast.
• Biochemical events lead to characteristic cell
changes (morphology) and death.
• These changes include blebbing, cell shrinkage,
nuclear fragmentation, chromatin condensation,
DNA fragmentation, and mRNA decay.
• The average adult human loses between 50 and
70 billion cells each day due to apoptosis.[

14. Autophagic cell death
• Autophagy is a conserved process that
delivers components of the cytoplasm to
lysosomes for degradation.
• While originally identified as a cell survival
mechanism, autophagy plays highly
context-specific roles in mediating cell
death

15. Necrosis
• Necrosis is the death of the cells in your
body tissues.
• Necrosis can occur due to injuries, infections
or diseases.
• Lack of blood flow to your tissues and
extreme environmental conditions can also
cause necrosis.
• While dead body tissue can be removed, it
can't be brought back to good health.

16. Other causes of necrosis include:-
• Accidents and traumatic injuries.
• Autoimmune diseases
• Infection-causing bacteria, viruses and fungi.
• Poisons, toxins and illicit drug use.
• Radiation therapy
Types of necrosis
Types of necrosis vary depending on the cause and affected body area.
Common necrosis types include:
• Avascular necrosis or osteonecrosis (bone tissue death).
• Gangrene (skin tissue death).
• Pulp necrosis (tooth death).

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