hormones its types and functions

1. Hormone is derived from a Greek participle. A
hormone is any member of class of signaling
molecules produced by gland in multicellular organism
that are transported by the circulatory system to a
target distant organs to regulate physiology and
behavior

2.  In simple words hormones are regulatory
molecules secreted into the blood by the
endocrine glands. The glands that secrete
hormones comprise the endocrine
signaling unit.
 Hormones are used to communicate
between organs and tissues for
physiological regulation and behavioral
activities such as digestion ,metabolism
,respiration, tissue function, sensory
perception and sleep.

3.  There are specific type of glands which
secrete specific hormones on the basis
of initial stimulus. On the basis of
absence or presence of duct the glands
are classified into three types:
 Endocrine
 Exocrine
 Hetrocrine

4.  Endocrine are ductless glands,
Exocrine glands have duct and
hetrocrine are those which are both duct
and ductless.
 Endocrine hormones are released by
glands or specialized cells into the
circulating blood and influence the
function of cells at another location in
the body. For example adrenal glands.

5.  Exocrine hormones are also release
by glands but they are enzyme in nature
and as they have duct so they are not
pour into blood. There are ducts which
are responsible for the transport of
exocrine hormone. For example Liver or
pancreas

6.  Neuroendocrin hormones are secreted
by neurons into the circulating blood and
influence the function of cells at another
location in the body. Neuroendocrine
hormone is secreted by neurons into the
blood. For example oxytocin.

 Paracrines are secreted by cells into the
extracellular fluid and effect neighboring
cells of a different type.

7.  Autocrines are secreted by cells into
the extracellular fluid and affect the
function of the same cell that produced
them by binding to cell surface receptor.

8.  Chemical structures and
Synthesis of hormones:
 On the basis of chemical nature there
are three main classes of hormone:
 Proteins
 Steroid
 Derivatives of the Amino Acid

9.  Proteins and polypeptides , including
hormones secreted by the anterior and
pituitary gland , the pancreas (Insulin
and Glucagon),the parathyroid gland
(parathyroid hormone) and many others.
 Steroid secreted by the adrenal cortex
(cortisol and aldosterone), the
ovaries(estrogen and progesterone) ,
the testes(testosterone), and the
placenta(estrogen and progesterone).

10.  Derivatives of amino acids tyrosine ,
secreted by the thyroid (thyroxin and
triiodothyroxin) and the adrenal
medulla(epinephrine
andnorepinephrine).There are no known
polysaccharide or nucleic acid hormone.
 Protein and polypeptide hormone:
 Most of the hormone in the body are
polypeptide and proteins. These hormone
range in size from small peptides with as
few as 3 amino acids to proteins with
almost 200 amino acids.

11.  Synthesis of protein and peptides are take
place in rough endoplasmic reticulum of the
different endocrine cell. They are usually
synthesized first as larger protein that are not
biologically active(preprohormones) and are
cleaved to form small pro hormones in the
endoplasmic reticulum.
 These are then transferred to the Golgi
apparatus for packaging into secretory
vesicles. In this process enzymes in the
vesicles cleaves the pro hormone to produce
small active hormones.

12.  Steroid hormones:
 Steroid hormones are usually
synthesized from cholesterol and they
are not stored. The chemical nature of
steroid hormone is similar to that of
cholesterol, and in most instances they
are synthecised from cholestrol

14.  Amine hormones are derived from
tyrosine. The thyroid and adrenal
medulla hormones are formed by the
action of the enzyme in cytoplasmic
reticulum.

15.  We mainly discuss the endocrine and
neurendocrine hormone systems
keeping in mind that many of the body
chemical messenger system interact
with one another to maintain
homeostasis . For example the adrenal
medullae and the pituitary gland secrete
their hormones primarily in response to
neural stimuli.

16.  . The neuroendocrine cells , located in
the hypothalamus , have axons that
terminate in the posterior pituitary gland
and median eminence and secrete
several neuro hormones , including
antidiuretic hormone , oxytocin and
hypophysiotropic hormones , which
control the secretion of anterior pituitary
hormone.
.

17.  Some endocrine hormones affect many
different type of cells of the body ,for
example growth hormone cause
growth in most parts of the body and
thyroxin increase the rate of many
chemical reactions in almost all the body
cells.
 Other hormones affect only specific
target tissues , because only these
tissues have receptors for the hormone.

18.  .For example adrenocorticotropic hormone
from the anterior pituitary gland especially
stimulates the adrenal cortex , causing it to
secrete adrenocortical hormones.
 There are some effects which are
produced by the action of hormones with
each other.
 The effect may enhance the effect of other
hormone or it may supress the effect of
other hormone.

19.  There are mainly three types of effect :
 Synergistic Effect
 Permissive Effect
 Antagonistic Effect

20.  Synergistic Effect: When two or more
hormones work together to produce a
particular result, their effects are said to
be synergistic.
 These effects may be additive or
complementary.
 The action of epinephrine and
norepinephrine on the heart is a good
example of an additive effect.

21.  Permissive Effect: A hormone is said to
have a permissive effect on the action of
a second hormone when it enhances the
responsiveness of a target organ to the
second hormone, or when it increases
the activity of the second hormone.

22.  Antagonistic Effect: The actions of one
hormone antagonize the effects of
another.
 Example of antagonism is the action of
insulin and glucagon (two hormones
from the pancreatic islets) on adipose
tissue; the formation of fat is promoted
by insulin, whereas glucagon promotes
fat breakdown.