introduction to hormones, mechanism of action and synthesis.

1. By Poonum Rana
M. Phil in Zoology UAF

2.  Hormone secretion and duration of action
 Some hormones action in few sec to minutes
after stimulation e.g. epinephrine, nor-
epinephrine etc.
 Some requires months for action e.g.
Thyroxin, Growth hormones etc.
 Each hormone has specific control function,
onset and duration of action

3.  Concentration in blood 1pg/ml (one millionth
of one millionth of a gram).
 Other secretion may be in micro g or nano g.
 These minute quantities of hormones to
exert powerful control over the physiological
systems.
 Negative feed back prevents overactivity of
hormone system.
 Feed back regulation of hormones is at
different levels as synthesis, processing and
release.

5.  Two factors can increase or decrease the
concentration of a hormone in the blood.
 hormone secretion into the blood
 rate of removal of the hormone from the
blood, which is called the metabolic
clearance rate.
 Metabolic clearance rate = Rate of disappearance of
hormone from the plasma/Concentration of hormone in each
milliliter of plasma

6.  Hormones are “cleared” from the plasma in
several ways, including
(1) metabolic destruction by the tissues
(2) binding with the tissues
(3) excretion by the liver into the bile
(4) excretion by the kidneys into the urine.

7.  Communication - important problem
 Various tissues interrelate
 Neurological - nervous system
 Chemical - regulatory substances
,hormones
Carry messages- glands or
special cells
to target cells

8. Special cells or glands
• Pancreas & intestinal mucosa
• Adrenals, ovaries, parathyroid, pituitary,
testes and thyroid.
secrete directly into the blood stream;
endocrine glands
Greek endon- within & Krinine ‘ to release’)
Secretions are internal i.e. released into the
blood
Exocrine glands
Tears, sweat, digestive enzymes outwards
Mammals ,insects and nematode worms
Plants , Some mechanisms are shared

9.  integrate and coordinate the metabolic
activities
 Every process - regulated by one or more
hormones
• maintenance of blood pressure
• blood volume
• electrolyte balance
• embryogenesis
• sexual differentiation
• Development & reproduction
• hunger, eating behaviour, digestion
• fuel metabolism

11.  Cells sense a change in the organism’s
circumstances & Secrete a chemical
messenger (act on same or different tissue)
 Neuronal signalling,
 neurotransmitter, µm , across the synaptic
cleft
 Hormonal signalling,
 carried in the bloodstream
 Signalling mechanisms are remarkably similar
 Epinephrine and norepinephrine,
 Neurotransmitters
 Hormones ( regulate fuel metabolism in liver
and muscle)

13. Eicosanoid hormone

14. The locations for the different types of hormone
1. In or on the surface of the cell membrane.
The membrane receptors are specific mostly for
the protein, peptide, and catecholamine
hormones.
2.In the cell cytoplasm. The primary receptors for
the different steroid hormones are found mainly
in the cytoplasm.
3. In the cell nucleus. The receptors for the
thyroid hormones are found in the nucleus and are
believed to be located in direct association with
one or more of the chromosomes

15.  Ion Channel–Linked Receptors.
The receptors that are dependent on ion
channels are called ion channel-linked
receptors.
 e.g. neurotransmitter substances i.e.
acetylcholine and norepinephrine, combine
with receptors in the postsynaptic
membrane. This open or close a channel for
one or more ions. i.e. sodium ions, potassium
ions, calcium ions etc.

16.  Many hormones activate receptors that
indirectly regulate the activity of target
proteins (e.g., enzymes or ion channels) by
coupling with groups of cell membrane
proteins called heterotrimeric GTP-binding
proteins (G proteins).
 There are more than 1000 known G protein–
coupled receptors, all of which have seven
transmembrane segments that loop in and
out of the cell membrane.

18. Classes of hormones in mammals,
distinguishable by their chemical structure and
their modes of action

20.  Steroid Hormones Increase Protein
Synthesis
 Another means by which hormones act
specifically, the steroid hormones secreted
by the adrenal cortex, ovaries, and testes is
to cause synthesis of proteins in the target
cells.
 These proteins then function as enzymes,
transport proteins, or structural proteins,
which in turn provide other functions of the
cells.

21. 1.The steroid hormone diffuses across the cell
membrane and enters the cytoplasm of the cell,
where it binds with a specific receptor protein.
2. The combined receptor protein–hormone then
diffuses into or is transported into the nucleus.
3. The combination binds at specific points on the
DNA strands in the chromosomes, which activates
the transcription process of specific genes to form
mRNA.
4. The mRNA diffuses into the cytoplasm, where it
promotes the translation process at the ribosomes
to form new proteins.
e.g. Aldosterone cause production of protein in 45
min.

22.  Adrenocorticotropic hormone (ACTH)
 Angiotensin II (epithelial cells)
 Calcitonin
 Catecholamines (b receptors)
 Corticotropin-releasing hormone (CRH)
 Follicle-stimulating hormone (FSH)
 Glucagon
 Human chorionic gonadotropin (HCG)
 Luteinizing hormone (LH)
 Parathyroid hormone (PTH)
 Secretin
 Somatostatin
 Thyroid-stimulating hormone (TSH)
 Vasopressin (V2 receptor, epithelial cells)

24.  Some receptors, when activated, function
directly as enzymes or are closely associated
with enzymes that they activate.
 These enzyme-linked receptors are proteins
that pass through the membrane only once,
in contrast to the seven-trans membrane G
protein–coupled receptors.
 Enzyme-linked receptors have their
hormone-binding site on the outside of the
cell membrane and their catalytic

29.  Calcium entry may be initiated by
(1) changes in membrane potential that open
calcium channels or
(2) a hormone interacting with membrane
receptors that open calcium channels.
 The normal calcium ion conc. in most cells of the
body is 10-8 to 10-7 mol/L, which is not enough
to activate the calmodulin system.
 But when concentration rises to 10-6 to 10-5
mol/L, enough for actions of calmodulin.
 Troponin C is similar to calmodulin in structure
and function.

34.  Hall, J. E. 2010. Guyton and Hall textbook of
medical physiology e-Book. J. Elsevier Health
Sciences.