1. Classification of
Hormones
M U H A M M A D A W A I S
L E C T U R E R
P H A R A C Y D E P A R T E N T
A I H S N A R O W A L

2. Classification of Hormones
Hormones are divide into three categories based on the way
they get from the point of their release to their target tissue.
Endocrine hormones
are released into blood and carried to target cells throughout the body e.g. insulin
Paracrine hormones
are released into extracellular space and diffuse to neighboring target cells e.g. eicosanoids
Autocrine hormones
are released by and affect the same cell, binding to receptors on the cell surface e.g. Interleukins

4. Classification of Hormones
Mammals have several classes of hormones,
distinguishable by their modes of action and their chemical structures.

5. 1-Peptide hormones
may have from 3 to 200 or more amino acid residues.
They include the
Pancreatic hormones (insulin, glucagon, and somatostatin)
Parathyroid hormone (calcitonin)
all the hormones of the hypothalamus and pituitary
These hormones are synthesized on ribosomes in the form of prohormones protein.

7. 1-Peptide hormones
Insulin is a small protein (Mr 5,800) with two polypeptide chains, A and B, joined by two disulfide
bonds.
It is synthesized in the pancreas as an inactive single-chain precursor, preproinsulin, with an
amino-terminal “signal sequence” that directs its passage into secretory vesicles.
Proteolytic removal of the signal sequence and formation of three disulfide bonds produces
proinsulin, which is stored in secretory granules in pancreatic cells.
When elevated blood glucose triggers insulin secretion, proinsulin is converted to active insulin by
specific proteases, which cleave two peptide bonds to form the mature insulin molecule.

9. 1-Peptide hormones
In some cases, prohormone proteins yield a single peptide hormone, but often several active
hormones are carved out of the same prohormone.
Pro-opiomelanocortin (POMC)
is a spectacular example of multiple hormones encoded by a single gene.
The POMC gene encodes a large polypeptide that is carved up into
at least nine biologically active peptides

10. 2-Catecholamine Hormones
Epinephrine (adrenaline) and norepinephrine (noradrenaline) are catecholamines
They are water soluble, synthesized from tyrosine are structurally related to catechol.
If produced in the brain and in other neural tissues then function as neurotransmitters,
But epinephrine and norepinephrine are also hormones, synthesized and secreted by the adrenal
glands.
Like the peptide hormones, catecholamines are highly concentrated within secretory vesicles and
released by exocytosis, and they act through surface receptors to generate intracellular second
messengers.

11. 2-Catecholamine Hormones

12. 3-Eicosanoids hormones

13. 3-Eicosanoids hormones
The eicosanoid hormones (prostaglandins, thromboxanes, and leukotrienes) are derived from
the 20-carbon polyunsaturated fatty acid arachidonate.
Unlike the hormones described above they are not synthesized in advance and stored; they are
produced, when needed, from arachidonate enzymatically released from membrane phospholipids
by phospholipase A2
The eicosanoid hormones are paracrine hormones, secreted into the interstitial fluid and acting
on nearby cells.

14. 3-Eicosanoids hormones
Prostaglandins promote the contraction of smooth muscle, including that of the intestine and
uterus (and can therefore be used medically to induce labor). They also mediate pain and
inflammation in all tissues.
Thromboxanes regulate platelet function and therefore blood clotting.
Leukotrienes LTC4 and LTD4 act through plasma membrane receptors to stimulate contraction
of smooth muscle in the intestine, pulmonary airways, and trachea. They are mediators of the
severe immune response called anaphylaxis.

15. 4-Steroid Hormones
The steroid hormones (adrenocortical hormones and sex hormones)
They are synthesized from cholesterol
in several endocrine tissues.
They travel to their target cells
through the bloodstream,
bound to carrier proteins.

16. 4-Steroid Hormones
(a) The Adrenocortical Steroids
The adrenal cortex produces at least 50 different adrenocortical steroids. These have been classified
according to their physiological responses
1. The glucocorticoids affect carbohydrate, protein, and lipid metabolism and influence a wide variety of
other vital functions, including inflammatory reactions and the capacity to cope with stress. The most
common of which are 21C cortisol and 21C corticosterone.
2. The mineralocorticoids largely function to regulate the excretion of salt and water by the kidney. the
most common of which is 21C aldosterone.
3. The androgens and estrogens affect sexual development and function. They are made in larger quantities
by the gonads.

18. 4-Steroid Hormones
(b) Gonadal Steroids
The gonads (testes in males, ovaries in females) secrete steroid hormones (androgens and estrogens) that
regulate sexual differentiation, the expression of secondary sex characteristics, and sexual behavior patterns
Although testes and ovaries both synthesize androgens and estrogens, the testes predominantly secrete
androgens (male sex hormones), whereas ovaries produce mostly estrogens (female sex hormones).
Androgens (testosterone is prototypic)
Estrogens, such as estradiol, resemble androgens but lack a C10 methyl group.
A second class of ovarian steroids, C21 compounds called progestins, help mediate the
menstrual cycle and pregnancy
Progesterone, the most abundant progestin, is, in fact, a precursor of glucocorticoids,
mineralocorticoids, and testosterone
All steroid hormones act through nuclear receptors to change the level of expression of genes.

20. 5-Vitamin D Hormone
Calcitriol (1,25-dihydroxycholecalciferol) is produced from vitamin D by enzyme catalyzed
hydroxylation in the liver and kidneys
Calcitriol works in concert with parathyroid hormone in Ca+2 homeostasis, regulating [Ca+2]
in the blood and the balance between Ca+2 deposition and Ca+2 mobilization from bone.
Acting through nuclear receptors, calcitriol activates the synthesis of an intestinal Ca+2
binding protein essential for uptake of dietary Ca+2

22. 5-Vitamin D Hormone
Calcitriol (1,25-dihydroxycholecalciferol) is produced from vitamin D by enzyme catalyzed
hydroxylation in the liver and kidneys
Calcitriol works in concert with parathyroid hormone in Ca+2 homeostasis, regulating [Ca+2]
in the blood and the balance between Ca+2 deposition and Ca+2 mobilization from bone.
Acting through nuclear receptors, calcitriol activates the synthesis of an intestinal Ca+2
binding protein essential for uptake of dietary Ca+2

23. 6-Retinoid Hormones
Retinoids are potent hormones that regulate the growth, survival, and differentiation of cells via
nuclear retinoid receptors.
The prohormone retinol is synthesized from vitamin A, primarily in liver and many tissues convert
retinol to the hormone retinoic acid (RA).

24. 6-Retinoid Hormones
All tissues are retinoid targets, as all cell types have at least one form of nuclear retinoid receptor.
In adults, the most significant targets include cornea, skin, epithelia of the lungs and trachea, and
the immune system. RA regulates the synthesis of proteins essential for growth or differentiation.
Excessive vitamin A can cause birth defects, and pregnant women are advised not to use the
retinoid creams that have been developed for treatment of severe acne.

25. 7-Thyroid Hormones
The thyroid hormones T4 (thyroxine) and T3 (triiodothyronine) are synthesized from the
precursor protein thyroglobulin (Mr 660,000).
Up to 20 Tyr residues in thyroglobulin are enzymatically iodinated in the thyroid gland, then two
iodotyrosine residues condense to form the precursor to thyroxine. When needed, thyroxine is
released by proteolysis.
Condensation of monoiodotyrosine with diiodotyrosine produces T3, which is also an active
hormone released by proteolysis.
The thyroid hormones act through nuclear receptors to stimulate energy-yielding metabolism,
especially in liver and muscle, by increasing the expression of genes encoding key catabolic
enzymes.

26. 8-Nitric Oxide (NO)
Nitric oxide is a relatively stable free radical synthesized from molecular oxygen and the
guanidino nitrogen of arginine in a reaction catalyzed by NO synthase.
This enzyme is found in many tissues and cell types: neurons, macrophages, hepatocytes,
myocytes of smooth muscle, endothelial cells of the blood vessels, and epithelial cells of the
kidney.
NO acts near its point of release, entering the target cell and activating the cytosolic
enzyme guanylyl cyclase, which catalyzes the formation of the second messenger cGMP.

27. 8-Nitric Oxide (NO)