The document discusses endocrine glands and hormones. It defines endocrine glands as ductless glands that secrete hormones internally into the bloodstream, in contrast to exocrine glands that secrete through ducts. It provides details on the types of glands, brief history of endocrinology, hormone definitions, mechanisms of hormone action, hormone transport and inactivation, hormone receptors, and the main endocrine glands.

1. By-
Dr. Dinesh C. Sharma
Head, Zoology
K.M. Govt. Girls P. G. College
Badalpur, G.B. Nagar
dr_dineshsharma@hotmail.com
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2. Endocrine glands
internalinternal secretionsecretion ==
Glands which
secrets internally
Glands which
secrets internally
oEndocrine glands (EG) are ductless glands, in contrast to
exocrine glands which possess glands. There secretion does not
come out of glands; but is discharged in the blood vessels
inside the glands.
o Secretion of EG is called HORMONE.
oThe study of the glands which secrete their products into
the blood is called endocrinology.
oThey have rich blood Supply and simple in structure.
They consist of cords and plates of cells separated by blood
vessels.
oTranslation of the word hormone =
‘I arouse’, ‘To arouse’ or To excite2

3. Types of Glands
Endocrine-ductless, secrete directly into the blood.
Ex. Thyroid, adrenal, etc.
Exocrine-duct present, secrete their products through
a duct onto a epithelial surface. Ex. Salivary glands,
mucous glands in intestine, etc.
Mixed –contain both endocrine and exocrine
functions in one gland. Ex. Pancreas (trypsin-
exocrine, insulin-endocrine)
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4. Brief History of Endocrinology
Berthold (1849)- Noticed that removal or grafting of
gonads effects secondary sexual characters roosters (fowls)
Claude Bernard-called them “internal secretion” required
for maintenance of internal environment.
Addission (1855)- Father of Endocrinology- recognized
the relationship between low blood pressure, muscular
weakness, weight loss, bronzing of skin and the pathology
of the adrenal gland. He noticed that removal of adrenal
cortex cause bronze color of human skin.
Gudernatsch (1912)- Noticed effect of thyroxin on
metamorphosis in tadpole of frog
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5. •Gull (1879) related dry skin, sparse hair,
puffiness of the face and hands, and a swollen
tongue to myxedema, the pathological
deficiency of thyroid function in adults (goiter).
•Balysis & Startling (1902) extracted and
identified the first hormone Secretin (secreted
by cells in the intestinal mucosa). And coined
the term Hormone.
•McGee (1927) isolated and purified substances
that were androgenic in small amounts
(microgram levels). Used a bioassay- applied to
beak of sparrows and the beak darkened.
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6. Houssay’s Definition of a Hormone
Secreted by living tissue
Present in small or trace amounts
(microgram=10-6
, nanogram=10-9
, picogram=1012
,
fintagram=10-15
)
Secreted into and travel in the blood to a specific site
of action (target organ)
Not used as a source of energy but acts to regulate
reactions to produce an appropriate response of the
organism (responses are usually positive, if negative
the hormone can be referred to as a chalone)
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7. Inter-relation of
Nervous & Endocrine Systems
Endocrine system and nervous system are the two main control
& integration system of the body.
The nervous and the endocrine systems are inter-related in the
hypothalamus through the:
The hypothalamo-hypophyseal tract .
The hypothalamo-hypophyseal –portal circulation.
Hypothalamus controls secretion of many glands.
Hormones are also called as chemical messengers, they act like
nervous system with whom they are functionally similar, so they
are also studied together in Neuroendocrinology.
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8. 8
Nervous system Endocrine system
•Very rapid action (High speed) •Slower response (Low
speed)
•Effect of short duration •Effect prolonged
•Controls glands & muscles only •Control any organ
•Does not effect growth •Effect growth
•Point to point, very specific •More diffuse
Nerve vs Endocrine
-Both send chemical signals
-Both affect specific target organs or tissues
-Both work to maintain Homeostasis in the body

9. Pheromones
Do not fit definition of a true
hormone
Produced by one organism, travel by
air and affect a second organism.
Example musk oil, sexual attractant
in insects, etc.
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10. • Are chemical substances synthesized &
secreted by specific cells,
• They are transported by the circulation
at very low conc.
• It elicits a specific response in distant
target tissues.
• Hormones are low molecular weight,
soluble and diffusible compounds
Hormones
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11. Hormones Vs Vitamins /Enzymes
1. Proteinous or steroid (Enzymes are protein) in nature.
Hormones produced by testis, ovaries and adrenal cortex are
steroid; rest all others are protein.
2. Hormones are absent in food, they are synthesized in bodies
of organisms only. Both animals and plants require
Hormones (Vitamins are required by animals; not by plants)
3. Hormonal disorders are called functional disorders; whereas
loss of vitamins cause deficiency disorder.
4. Hormones can accelerates as well as inhibits (retard) a
chemical process; Enzymes can only accelerate.
5. Hormones is carried away from its place of production to a
target organ by blood. Enzymes work where it produced.
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12. 6. Hormones can not be stored in our body, so their
regular production is necessary
7. Hormones are specific in their function.
Different Hormones have different target organs.
8. Hormones produced in one animal can cause the
same effect in other animals, so they are not
species specific.
9. Hormones are used up in their reaction, whereas
Enzymes are not used up.
10. Hormones like vitamins, enzymes and minerals
are required in minute quantities
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13. Forms of Hormones in the Blood
1- Free.
* It is not carried on a plasma protein .
* It can bind directly to the receptors : active .
* It is small in size , so can be filtered in urine .
2- protein bound .
* Carried on plasma protein .
* It acts as a reservoir.
* It increases the half life of the hormone.
* It is more soluble in plasma ( the lipid steroids, when bound to
plasma proteins they are transformed into water soluble.
* It is large in size , and so is not filtered in urine .
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14. Control of hormone secretion
Nervous control - through the hypothalamus
(hypothalamic factors) nervous system controls the secretion
of endocrine gland
Freed back control : Secretion of Hormone by an endocrine
gland is under control of its target organ. When target organ
stops receiving of hormones from blood, its level in blood
increases, as a result of this endocrine gland stop hormone
production. There are two type of feed back-
Negative (-Ve) feed back; Positive (+Ve) feed back.
Endocrine GlandEndocrine Gland Target OrganTarget Organ
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15. Hormone Transport & inactivation
Water insoluble hormones : Steroid & thyroxin are
bound to plasma proteins in blood stream. Only free
hormones ( not in bound form ) can affect its target
cells.
Hormone inactivation in liver by :
degradation
oxidation
reduction
methylation
Conjugation
After that they are excreted in : urine.
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16. Hormone Receptors &their activation:
• Hormone never act directly.
• They combine with Specific receptors.
• Receptors are large protein molecules
present either :
 On the surface of cells or
 inside the cells cytoplasm or
 in nucleus.
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17. Receptors location
Receptors of protein, peptide hormones &
catecholamines located in the membrane.
Receptors of steroid hormones located in
cytoplasm.
Receptors of thyroxin located in nucleus.
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18. Mechanism of Hormone Action
Hormones act in two ways-
• Gene Level- Eg. Steroid Hormone
• Cell Membrane Level-Eg. Protein
Hormone
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19. Mechanism of Steroid Hormone action
That secreted by : adrenal cortex, ovaries & testes.
 The steroid hormones enters the cytoplasm of the cell where it
binds with a specific receptor ( protein in nature).
 The combined hormone receptor diffuse into the nucleus.
 Then it activates the transcription process of specific genes to
form a messenger RNA.
 The messenger RNA diffuse to ‘ cytoplasm to promote
synthesis of specific protein & enzymes within ribosomes’.
DNA mRNA ProteinTranscription Translation
Steroid H
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20. Mechanism of protein hormones action
1-On cell membrane of target cell : hormone combines with its
specific receptor.
2-This combination activates: adenyl cyclase which is located in
the cell membrane.
3-The activated adenyl cyclase form cAMP.
4-cAMP activates protein Kinases.
5-The activated protein catalyses phosphorelation of proteins and
alter their functions. So Activated adenyl cyclase in the cell
membrane can cause man molecule of the next enzyme to be
activated.
Adenyl
cyclase
Activated cAMP Activated
Protein
Kinases
Protein H
ProteinPhosphorelation
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23. Action of thyroid hormones in cell nuclei
The hormone bind directly with receptors (protein in nature) inside nucleus
itself. This combination activates genetic mechanism for formation of many
enzymes that promote intra – celluler metabolic activity.
Second messenger :
Calmodulin : Some hormones combine with Membrane receptors leading
to opening of Ca channels. Ca enter cell combine with protein called calmodulin
leading to changes inside cell as : activation of myosin kinase that act on
smooth muscle myosin  contraction.
Cyclic GMP: some hormones combine with receptors activate guanyl cyclase
enzyme leading to formation of cyclic GMP activate other enzymes inside
cell.
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24. Main Endocrine Glands
1. Pituitary gland
2. Pineal gland
3. Thyroid gland
4. Parathyroid gland.
5. Thymus gland
6. Adrenal gland
7. Pancreas (Islets of langerhans)
8. Male gonads ( testes) &
Female gonads (Ovary)
9. Placenta.
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25. Other Endocrine Organs
1. The kidney secrete :
a) Renin
b) Erythropoietin,
c) 1.25 dihydroxy cholecalciferol,
d) Certain Prostaglandin.
2. The Heart :
Right Atrium secretes Atrial Natriuretic Peptide.
3. Local hormones secreted at :- GIT,
-Chemical transmitters, released by nerve endings.
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