Endocrinology
• Both nervous and endocrine systems are the
basic systems that regulate the biological
processes inside an organism, but through
different means of passing signals.
• The main difference between the two systems
is that nervous system uses electric pulses,
and endocri...
,• Both nervous and endocrine systems are the
basic systems that regulate the biological
processes inside an organism, but through
different means of passing signals.
• The main difference between the two systems
is that nervous system uses electric pulses,
and endocrine system uses chemical stimuli to
pass the signals to the target cells or organs.
, CELL-TO-CELL SIGNALING
• Cell to cell signaling refers to the transfer of
information from one cell to another.
• Also called cell signaling or intercellular
communication.
• The cells of the body communicate with each
other through some chemical substances
called chemical messengers.
Dr William Gitau
, Classification of Chemical Messengers
• Chemical messengers are classified into 2:
1. Classical hormones secreted by endocrine glands
2. Local hormones secreted from other tissues.
• However, recently chemical messengers are classified
into four types:
• 1. Endocrine messengers
• 2. Paracrine messengers
• 3. Autocrine messengers
• 4. Neurocrine messengers.
Dr William Gitau
, 1. Endocrine Messengers
• Endocrine messengers are the classical
hormones.
• A hormone is defined as a chemical
messenger, synthesized by endocrine glands
and transported by blood to the target organs
or tissues (site of action).
• Examples are growth hormone and insulin
Dr William Gitau
, 2. Paracrine Messengers
• Are chemical messengers, which diffuse from
the control cells to the target cells through the
interstitial fluid.
• Some directly enter the neighboring target
cells through gap junctions.
• Examples are prostaglandins and histamine
• IE: Produced by a cell and will on act on
neighboring cells
Dr William Gitau
,• Hormone types
– Circulating – circulate in
blood throughout body
– Local hormones – act
locally
• Paracrine – act on
neighboring cells
• Autocrine – act on
the same cell that
secreted them
Dr William Gitau
, 3. Autocrine Messengers
• Autocrine messengers are the chemical
messengers that control the source cells which
secrete them.
• So, these messengers are also called
intracellular chemical mediators.
• Examples are leukotrienes.
• They act on the same cell that secreted them
Dr William Gitau
, 4. Neurocrine or Neural Messengers
• Neurocrine or neural messengers are
neurotransmitters and neurohormones ).
• Neurotransmitter
• Neurotransmitter is an endogenous signaling
molecule that carries information form one
nerve cell to another nerve cell or muscle or
another tissue.
• Examples are acetylcholine and noradrenaline
Dr William Gitau
, • Endocrine system is a discrete set of glands
that secrete different types of hormones to
the circulatory system in order to regulate the
functions of the body.
• Each gland of the endocrine system is
responsible for the secretion of different
hormones, and those hormones trigger
different activities in different places of the
body.
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