What is a Hormone? A hormone is a chemical substance produced by a gland and carried by the blood The hormone alters the activity of one or more specific target organs i.e. they are chemicals which transmit information from one part of the organism to another and bring about a change The glands that produce hormones in animals are known collectively as the endocrine system The major endocrine glands in the body Transport around the body Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response Hormones only affect cells with target receptors that the hormone can bind to. These are either found on the cell membrane, or inside cells. Receptors have to be complementary to hormones for there to be an effect. The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess. What is a Hormone? A hormone is a chemical substance produced by a gland and carried by the blood The hormone alters the activity of one or more specific target organs i.e. they are chemicals which transmit information from one part of the organism to another and bring about a change The glands that produce hormones in animals are known collectively as the endocrine system The major endocrine glands in the body Transport around the body Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response Hormones only affect cells with target receptors that the hormone can bind to. These are either found on the cell membrane, or inside cells. Receptors have to be complementary to hormones for there to be an effect. The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess. What is a Hormone? A hormone is a chemical substance produced by a gland and carried by the blood The hormone alters the activity of one or more specific target organs i.e. they are chemicals which transmit information from one part of the organism to another and bring about a change The glands that produce hormones in animals are known collectively as the endocrine system The major endocrine glands in the body Transport around the body Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response Hormones only affect cells with target receptors that the hormone can bind to. These are either found on the cell membrane, or inside cells. Receptors have to be complementary to hormones for there to be an effect. The liver regulates levels of hormones in the blood; transforming

1. Introduction to
Hormones
Darakshan
M.Pharma
(pharmacology)
Department of
pharmaceutical sciences,
KU.
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2. Table of content
• Introduction.
• Characteristics of hormones.
• Classification.
• Functions.
• Hormone receptors.
• Pituitary gland.
• Pituitary-hypothalamus relationship.
• Hormones and their primary functions.
• Regulation of hormonal activity.

3. Introduction
• Hormones are specialized chemical substances which are
synthesized by specific endogenous ductless glands and
secreted internally, directly into the blood stream, to act
on specific target organ.
• These are the substance of intense biological activity that
are produced by specific cells in the body and is
transported through circulation to act at its target cells.
• The word “Hormone” is derived from a Greek word
hormaein that means to set in motion / to strip up.

4. Characteristics of hormones
The hormones possess the following specific properties:
1. They are chemical entities produced by special cells of endocrine glands.
2. Transported to the target cells/ tissue/organ via circulation.
3. Active in very minute quantities.
4. Mostly water soluble.

5. 5. Low in molecular weight.
6. Destroyed after their actions.
7. Chemically heterogeneous substances.
8. Cannot be stored for a longtime.
9. Usually activate target cells by forming hormone receptor complex.

6. Classification of hormones
Chemically hormones can be divided into seven major classes:
1. Amino acid derivatives: Dopamine, Catecholamines and
Thyroid hormones, melatonin.
2. Neuropeptides: Gonadotropin releasing hormone (GnRH),
thyrotropin releasing hormone (TRH), vasopressin,
oxytocin, melanocyte releasing hormone (MRH) and
somatostatin.
3. Simple proteins: ACTH.
4. Large proteins: Insulin, PTH, glucagon.
5. Glycoprotein: TSH, FSH, LH.
6. Steroids: Cortisol, estrogen, progesterone and glucocorticoids.
7. Vitamins: Vitamin D

7. Functions of hormones
The three principal physiological areas of hormonal function
include
I. The control of reproduction, i.e., sex determination during
fetal development, sexual maturity during puberty,
conception, pregnancy, lactation, maternal behavior and
ultimately cessation of reproduction capability at menopause
(females) or old age (males).
II. The general growth and development of the body, i.e.,
development of secondary sexual characteristics takes place
under the influence of ovarian and testicular hormones , short
stature may be caused by growth hormone deficiency or due
to hypothyroidism
III. Maintenance of homeostasis i.e.,the regulation of electrolyte
composition of bodily fluids and regulation of serum
osmolality by vasopressin.

8. Hormone receptors and
mechanism of action of
hormones
• Hormones act on their specific
receptors located within the target
cell.
• There are three major classes of
receptor for hormones:
i. Cell membrane receptors.
ii. Cytoplasmic receptors.
iii. Nuclear receptors.
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9. • Protein and polypeptide hormones do not generally penetrate
into the cell interior.
• React externally with a specific receptor located in the cell
membrane.
• This may result in direct membrane effects.
• Examples; insulin and glucagon.
• Steroid hormones being lipophilic, enter cells directly to
combine with highly specific receptor proteins in the cytoplasm
or the nucleus.
• This hormone-receptor complex then acts within the cell
nucleus where it binds to special acceptor sites.
• Examples ; the sex hormones, progesterone, testosterone; the
adrenal corticosteroids ,cortisol, aldosterone and also vitamin
D.

10. 1. Cellmembranereceptor:
Receptor Mechanism of action Examples
G-protein
coupled
receptors
• Alteration of intracellular
cAMP concentration
• Alteration of protein kinase A
• Regulation of cell function
(Calcium acts as third
messenger)
Adrenaline, glucagon, TSH, FSH,
LH, PTH, calcitonin, ACTH,
vasopressin (V1)
• IP3/DAG generation : release
of intracellular calcium and
protein c kinase activation
Vasopressin (V2), oxytocin
• Direct trans membrane
activation of tyrosine protein
kinase
• Phosphorylation cascade
• Regulation of enzymes
Insulin, growth hormone,
prolactin

11. https://bio.libretexts.org/@api/deki/files/8186/Figure_8.4.12.png?revision=1

12. G-protein coupled receptors
Figure 1

13. 2. Cytoplasmicreceptors:
Mechanism of action Examples
Penetrating cell membrane--
hormone combines with cytoplasmic
receptor—exposes DNA binding
domain– migrates to nucleus, binds
to specific genes– DNA mediated
mRNA synthesis– synthesis of
functional proteins
Steroidal hormones:
Glucocorticoids
Mineralocorticoids
Androgen
Progestins
Estrogen
Calcitriol

14. Cytoplasmic receptors
Figure 2

15. 3. Nuclearreceptors:
Hormone penetrates the nucleus
Combines with targeted receptor
Alters DNA-RNA mediated protein
synthesis
Thyroid hormones: thyroxin,
triiodothyroxine

16. Nuclear receptor
Figure 3

17. Pituitary gland “the master
gland”
• Pituitary gland is referred as “Master of endocrine Orchestra”.
• It produces hormones that control other glands and many
functions.
• It is the smallest structure in the head and is the main endocrine
gland.
• It is reddish-grey bean shaped gland.
• It is pea sized, weighs 500 mg located at the base of brain.
• The pituitary gland lies in the Hypophyseal fossa (Sella turcica) of
sphenoid bone below the hypothalamus.
• A fold of durameter covers pituitary gland and has and opening
for the passage of infundibulum (stalk) connecting the gland
with hypothalamus.
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18. Figure 4
The hypothalamus region lies inferior and anterior to the thalamus. It connects to the pituitary
gland by the stalk-like infundibulum. The pituitary gland consists of an anterior and posterior
lobe, with each lobe secreting different hormones in response to signals from the
hypothalamus.

19. Pituitary gland
Anterior pituitary
(adeno
hypophysis)
Posterior pituitary
(neuro
hypophysis)
Intermediate
pituitary

20. Pituitary gland consists of :
• It consists of three main parts:
a. Anterior pituitary gland (Adeno hypophysis):
• It is a glandular tissue that develops from primitive digestive tract.
• It manufactures and secretes peptide hormones like ACTH, FSH, LH, GH,
TSH and prolactin.
• Secretion of hormones regulated by two classes of hormones (Secreted by
the hypothalamus):
I. Releasing hormones (stimulating secretions from anterior pituitary
II. Inhibiting hormones (inhibiting secretions).
b. Posterior pituitary gland (Neuro hypophysis):
• It is a neural tissue i.e., formed from nervous tissues and nerve cells.
• An extension of paraventricular and supraoptic nuclei of hypothalamus.
• It stores and secretes hormones produced by hypothalamus.

21. • The paraventricular nuclei produces hormone “oxytocin”.
• Supraoptic nuclei produces ADH.
• These hormones travel along the axons into storage sites in
axon terminals of posterior pituitary.
• In response to signals from same hypothalamus neurons,
the hormones are released from the axon terminals into the
blood stream.
c. Intermediate pituitary lobe:
• The intermediate lobe of pituitary gland secretes mainly
melanocyte stimulatory hormone (MSH) and γ-lipotropin
hormones.
• These are probably not that important as hormones in
human beings.

22. Divisions of pituitary gland
Figure 5

23. Hypothalamus-
pituitary relationship
• The hypothalamus-pituitary complex can be thought of as the
“ command center” of the endocrine system.
• This complex secretes hormones that directly produce
responses in target tissue, as well as hormones of other
glands.
• In addition, this complex coordinates the message of
endocrine and nervous system.
• In many cases, a stimuli received by the nervous system must
pass through the hypothalamus-pituitary complex to be
translated into hormones that can initiate a response.
• Hypothalamus has two different connections with the
pituitary glands.

24. • The hypothalamus is a structure of the diencephalon of
the brain located anterior and inferior to the thalamus.
• The connection to the anterior pituitary is via a special
portal blood system (hypophyseal portal system).
• The connection to the posterior lobe is directly neurons.
• Hypothalamus manufactures inhibitory and releasing
hormones.
• These travel through a primary capillary plexus to the
portal veins, which carry them into the anterior pituitary.
• These hypothalamic releasing factors/hormones stimulate
the anterior pituitary to produce and secrete a number of
tropic hormones.
• This in turn stimulate target glands to secrete hormones
which finally act on the cells of target organs far away from
the site of their release.
This Photo by Unknown author is licensed under CC BY.

25. Figure 6
Neurosecretory cells in the hypothalamus release oxytocin (OT) or ADH into the posterior lobe of the pituitary
gland. These hormones are stored or released into the blood via the capillary plexus.

26. Figure 7
Hypothalamus and pituitary gland

27. Hormones and their primary functions
Endocrine
glands
Hormones Primary functions
Hypothalamus
Corticotrophin-releasing hormone
(CRH)
Gonadotropin-releasing hormone
(GnRH)
Thyrotrophic-releasing hormone
(TRH)
Growth hormone-releasing hormone
(GHRH)
Somatostatin
Dopamine
Stimulates the pituitary to release
adrenocorticotropic hormone
(ACTH)
Stimulates the pituitary to release
luteinizing hormone
(LH) and follicle-stimulating
hormone (FSH)
Stimulates the pituitary to release
thyroid-stimulating
hormone (TSH)
Stimulates the release of growth
hormone (GH) from the pituitary
Inhibits the release of GH from the
pituitary
Inhibits the release of prolactin
from the pituitary

28. Anterior
pituitary
hormones
ACTH Stimulates release of hormones from adrenal
cortex
LH In women, stimulates production of sex
hormones( i.e. Estrogen) in ovaries
In men, stimulates testosterone production in
the testes.
FSH In women, stimulates follicle development
In males, stimulate sperm production
TSH Stimulates the release of thyroid hormone
GH Promotes body growth and development
Prolactin Controls milk production (i.e., lactation)

29. Posterior
pituitary
hormones
Vasopressin Helps control body’s electrolyte and water
levels
Oxytocin Promotes uterine contractions during labor
and activates milk ejection in nursing
women
Para
intermediate
hormone
Melanin Stimulates melanogenesis
Adrenal
cortex
Cortisol Helps control carbohydrate, protein and
lipid metabolism
Protects against stress
Aldosterone Helps control body’s water and electrolyte
regulation
Testes Testosterone Stimulates development of male
reproductive organs, sperm production and
protein anabolism

30. Ovaries
Estrogen
(follicles)
Stimulates development of female
reproductive organs
Progesterone
(corpus luteum)
Maintains pregnancy; stimulates
development of uterus/mammary
gland
Thyroid glands
Thyroid hormone (i.e.,
thyroxin [T4] and
triiodithyronine [T3])
Controls metabolic processes in all
cells
Calcitonin Helps control calcium metabolism
(i.e., lowers calcium levels in blood)
Parathyroid
gland
Parathyroid hormone (PTH) Helps control calcium metabolism
(i.e., increases calcium levels in
blood)
Pancreas
Insulin Controls carbohydrate metabolism
(i.e., lowers blood sugar levels)
Glucagon Controls carbohydrate metabolism
(i.e., increases blood sugar levels)

31. Figure 8
https://www.epa.gov/sites/default/files/styl
es/medium/public/2015-08/endocrine-
system.jpg?itok=8pyWl80t

32. Regulation of hormonal
activity
• In order to maintain the correct regulatory function of a
hormone, the endocrine gland should receive constant
feedback information about the state of the system being
regulated, so that hormone release can be finely adjusted
(closed-loop system).
• The secretory activity of most endocrine target organs is
controlled by the anterior pituitary, which is in turn, under
the influence of hypothalamic releasing hormones/factor’s
released by hypothalamic nerve fibers into the pituitary
blood supply.
• Modulatory feedback loops also exist, that do not involve the
hypothalamus and anterior pituitary.

33. • Examples., in the control of insulin or parathyroid hormone
release
The principal endocrine feedback mechanisms are as follows:
Direct Negative Feedback:
• The most common ‘closed-loop’ control mechanism.
• In which an increase in the level of a circulating hormone,
decreases the secretory activity of the cells producing it.
• In this type of arrangement, specialized groups of nerve cells
in the hypothalamus synthesize specific peptides (releasing
hormones).
• These are secreted into the capillary network feeding the
anterior pituitary gland, and then stimulate the pituitary cells
to release specific trophic hormones.
• These peptides, in turn, stimulate their particular target
gland cells to release a target gland hormone into the general
circulation.

34. • The latter then exerts a negative feedback effect on the
anterior pituitary, to regulate the level of trophic
hormone release.
Example.,
• The secretion of thyroxine by the thyroid gland is
directly controlled by the pituitary trophic hormone
TSH (thyroid stimulating hormone).
• A high blood level of thyroxine diminishes the output
of TSH, so that the activity of the thyroid gland
decreases (and vice versa).

35. Figure 9
Direct Negative feedback mechanism

36. • Similar feedback mechanisms govern the secretory activity of
other target organs e.g. the adrenal cortex, ovaries and
testes.
Indirect Negative Feedback :
• Here, the target gland hormone inhibits the release of
pituitary trophic hormone indirectly, by inhibiting the
secretion of hypothalamic releasing hormone.
• This type of mechanism appears particularly important in
regulating adrenal and gonadal (testicular and ovarian)
hormone secretions.
Example
• The corticosteroid hormones secreted by the adrenal gland
may indirectly inhibit the release of corticotrophin
(adrenocorticotrophic hormone, ACTH) from the anterior
pituitary, by inhibiting the release of hypothalamic
corticotrophin releasing hormone (CRH).

37. Figure 10
Indirect negative feedback mechanism

38. • In addition, the trophic hormone itself (ACTH) may act back
directly on the hypothalamic neurons to ultimately inhibit
its own release (‘short loop’ feedback)
Positive Feedback:
• Such a mechanism is less common, and tends to be
intrinsically unstable.
• It attempts to increase rather than stabilize the level of a
circulating hormone.
• A hormone may either facilitate its own release directly, by
acting on the anterior pituitary, or indirectly by stimulating
hypothalamic hormone release.
• This helps to maintain a stable system.

39. • During the female menstrual cycle, a positive feedback loop is
activated when the blood level of oestrogen, released from
the ovaries, attains a certain high threshold level.
• At this point, oestrogen stimulates (rather than inhibits) the
pulsatile release of the gonadotrophic hormones, luteinizing
hormone (LH) and follicle stimulating hormone (FSH) from
the pituitary, and also the hypothalamic gonadotropin
releasing hormone, (GnRH).
• The resultant surge in gonadotrophin secretion (particularly
LH) leads to ovulation and abrupt termination of the positive
feedback loop.

40. Figure 11
Positive feedback mechanism

41. References
Essentials of medical pharmacology by KD tripathi; 8th
edition; section 5; hormones and related drugs; 255-257.
Basic endocrinology for students of pharmacy and allied
health sciences; Constanti, a.; Bartke, a.; and Khardori r;
Chapter 1; Introduction and General Principles; 1-8.
Nussey S, whitehead S. Endocrinology: An Integrated
approach. Oxford: BIOS scientific publishera:2001; chapter 1;
principles of endocrinology.
Quantitative Human Physiology (An introduction); second
edition; 2017; Unit 9; Endocrine physiology; 853-863

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