1. HORMONES uses, synthesis,review BY DR ANTHONY MELVIN CRASTO APRIL 2012

2. Dedicated to my son Lionel Crasto,
He was only in first standard in school (Dec 2007) when I was paralysed head to toe.
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3. Shore
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4. Introduction
A hormone is a chemical that is released into the blood by one organ and carried to another part of the body, where it causes a particular response by a particular kind of tissue.
Although hormones in the blood reach all the cells in the body, they affect only specific cells, their target cells.
Currently, there are about 50 known human hormones.
Some Of them are Glucagon, FSH and Testosterone.

5. Chemical classes of hormones
Vertebrate hormones fall into three chemical classes:
Peptide hormones consist of chains of amino acids. Examples of small peptide hormones are TRH and vasopressin. Peptides composed of scores or hundreds of amino acids are referred to as proteins. Examples of protein hormones include insulin and growth hormone. More complex protein hormones bear carbohydrate side-chains and are called glycoprotein hormones. Luteinizing hormone, follicle- stimulating hormone and thyroid-stimulating hormone are glycoprotein hormones.
There is also another type of hydrophilic hormone called nonpeptidehormones. Although they don't have peptide connections, they are assimilated as peptide hormones.
Lipid and phospholipid-derived hormones derive from lipids such as linoleic acid and arachidonic acid and phospholipids. The main classes are the steroid hormones that derive from cholesterol and the eicosanoids. Examples of steroid hormones are testosterone andcortisol. Sterol hormones such as calcitriol are a homologous system. The adrenal cortex and the gonads are primary sources of steroid hormones. Examples of eicosanoids are the widely studied prostaglandins.
Monoamines derived from aromatic amino acids like phenylalanine, tyrosine, tryptophan by the action of aromatic amino acid decarboxylase enzymes.

6. Effects of hormones Hormones have the following effects on the body:
stimulation or inhibition of growth
mood swings
induction or suppression of apoptosis (programmed cell death)
activation or inhibition of the immune system
regulation of metabolism
preparation of the body for mating, fighting, fleeing, and other activity
preparation of the body for a new phase of life, such as puberty, parenting, and menopause
control of the reproductive cycle
hunger cravings
sexual arousal

7. List of human hormones
hormones

8. Steroids
Steroids are lipids and, more specifically, derivatives of cholesterol. Examples include the sex steroids such as testosterone and adrenal steroids such as cortisol.
The first and rate-limiting step in the synthesis of all steroid hormones is conversion of cholesterol to pregnenolone, which is illustrated here to demonstate the system of numbering rings and carbons for identification of different steroid hormones.
Pregnenolone is formed on the inner membrane of mitochondria then shuttled back and forth between mitochondrion and the endoplasmic reticulum for further enzymatic transformations involved in synthesis of derivative steroid hormones.
Newly synthesized steroid hormones are rapidly secreted from the cell, with little if any storage. Increases in secretion reflect accelerated rates of synthesis. Following secretion, all steroids bind to some extent to plasma proteins. This binding is often low affinity and non-specific (e.g. to albumin), but some steroids are transported by specific binding proteins, which clearly affects their halflife and rate of elimination.
Steroid hormones are typically eliminated by inactivating metabolic transformations and excretion in urine or bile.

9. Some examples of synthetic steroid hormones:Glucocorticoids: prednisonePrednisone
Prednisone is a synthetic corticosteroid drug that is particularly effective as an immunosuppressant drug. It is used to treat certain inflammatory diseases and some types of cancer, but has significant adverse effects...
, dexamethasone, triamcinolone
Mineralocorticoid: fludrocortisone
Vitamin D: dihydrotachysterol
Androgens: oxandrolone, testosterone, nandrolone  (also known as anabolic steroids)
Oestrogens: diethylstilbestrol (DES)
Progestins: norethindrone, medroxyprogesterone acetate

10. Amino Acid Derivatives
There are two groups of hormones derived from the amino acid tyrosine:
Thyroid hormones are basically a "double" tyrosine with the critical incorporation of 3 or 4 iodine atoms.
Catecholamines include epinephrine and norepinephrine, which are used as both hormones and neurotransmitters.
The pathways to synthesis of these hormones is provided in the sections on the thyroid gland and the adrenal medulla.
The circulating halflife of thyroid hormones is on the order of a few days. They are inactivated primarily by intracellular deiodinases. Catecholamines, on the other hand, are rapidly degraded, with circulating halflives of only a few minutes.
Two other amino acids are used for synthesis of hormones:
Tryptophan is the precursor to serotonin and the pineal hormone melatonin
Glutamic acid is converted to histamine

11. Fatty Acid Derivatives - Eicosanoids
Eicosanoids are a large group of molecules derived from polyunsaturated fatty acids. The principal groups of hormones of this class are prostaglandins, prostacyclins, leukotrienes and thromboxanes.
Arachadonic acid is the most abundant precursor for these hormones. Stores of arachadonic acid are present in membrane lipids and released through the action of various lipases. The specific eicosanoids synthesized by a cell are dictated by the battery of processing enzymes expressed in that cell.
These hormones are rapidly inactivated by being metabolized, and are typically active for only a few seconds.

13. The steroid hormones are all derived from cholesterol
The steroid hormones are all derived from cholesterol. Moreover, with the exception of vitamin D, they all contain the same cyclopentanophenanthrene ring and atomic numbering system as cholesterol. The conversion of C27cholesterol to the 18-, 19-, and 21-carbon steroid hormones (designated by the nomenclature C with a subscript number indicating the number of carbon atoms, e.g. C19 for androstanes) involves the rate- limiting, irreversible cleavage of a 6-carbon residue from cholesterol, producing pregnenolone (C21) plus isocaproaldehyde. Common names of the steroid hormones are widely recognized, but systematic nomenclature is gaining acceptance and familiarity with both nomenclatures is increasingly important. Steroids with 21 carbon atoms are known systematically as pregnanes, whereas those containing 19 and 18 carbon atoms are known as androstanes and estranes, respectively. The important mammalian steroid hormones are shown below along with the structure of the precursor, pregneolone. Retinoic acid and vitamin D are not derived from pregnenolone, but from vitamin A and cholesterol respectively.

14. All the steroid hormones exert their action by passing through the plasma membrane and binding to intracellular receptors. The mechanism of action of the thyroid hormones is similar; they interact with intracellular receptors. Both the steroid and thyroid hormone-receptor complexes exert their action by binding to specific nucleotide sequences in the DNA of responsive genes. These DNA sequences are identified as hormone response elements, HREs. The interaction of steroid-receptor complexes with DNA leads to altered rates of transcription of the associated genes

15. Pregnenolone: produced directly from cholesterol, the precursor molecule for all C18, C19and C21 steroids
Progesterone: a progestagen, produced directly from pregnenolone and secreted from thecorpus luteum, responsible for changes associated with luteal phase of the menstrual cycle, differentiation factor for mammary glands
Aldosterone: the principal mineralocorticoid, produced from progesterone in the zona glomerulosa of adrenal cortex, raises blood pressure and fluid volume, increases Na+uptake
Testosterone: an androgen, male sex hormone synthesized in the testes, responsible for secondary male sex characteristics, produced from progesterone
Estradiol: an estrogen, principal female sex hormone, produced in the ovary, responsible for secondary female sex characteristics
Cortisol: dominant glucocorticoid in humans, synthesized from progesterone in the zona fasciculata of the adrenal cortex, involved in stress adaptation, elevates blood pressure and Na+ uptake, numerous effects on the immune system

16. Testosterone is also produced by Sertoli cells but in these cells it is regulated by FSH, again acting through a cAMP- and PKA- regulatory pathway. In addition, FSH stimulates Sertoli cells to secrete androgen-binding protein (ABP), which transports testosterone and DHT from Leydig cells to sites of spermatogenesis. There, testosterone acts to stimulate protein synthesis and sperm development.
In females, LH binds to thecal cells of the ovary, where it stimulates the synthesis of androstenedione and testosterone by the usual cAMP- and PKA-regulated pathway. An additional enzyme complex known as aromatase is responsible for the final conversion of the latter 2 molecules into the estrogens. Aromatase is a complex endoplasmic reticulum enzyme found in the ovary and in numerous other tissues in both males and females. Its action involves hydroxylations and dehydrations that culminate in aromatization of the A ring of the androgens.

18. Follicle stimulating hormone (FSH)
Follicle stimulating hormone (FSH) is synthesized and secreted by gonadotroph of the anterior pituitary gland.
It can found in humans and other animals. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body.

19. FSH structure
FSH is a glycoprotein. Each monomeric unit is a protein molecule with a sugar attached to it. Two of these make the full, functional protein. Its structure is similar to those of LH, TSH, and hCG. The protein dimer contains of 2 polypeptide units, labeled alpha and beta subunits.
The alpha subunit of LH, FSH, TSH, and hCG are identical, and contain 92 amino acid.
The beta subunits have varian. FSH has a beta subunit of 118 amino acids (FSHB), which confers its specific biologic action and is responsible for interaction with the FSH-receptor.

20. Description
Glucagon is a hormone, secreted by the pancreas, that raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels.

21. FUNCTION Glucagon helps maintain the level of glucose in the blood.
Glucagon also regulates the rate of glucose production through lipolysis.

22. STRUCTURE
Glucagon is a 29-amino acid polypeptide. Its primary structure in humans is:
NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp- Tyr-Ser-Lys-Tyr-Leu-Asp-Ser- Arg-Arg-Ala- Gln-Asp-Phe-Val-Gln-Trp-Leu- Met-Asn- Thr-COOH.

24. Structure of cholesterol

25. Initial Steps in Cholesterol Synthesis
Cholesterol synthesis begins with the synthesis of acetoacetyl CoA from two acetyl CoA molecules. A third acetyl CoA molecule is added by the enzyme HMG CoA synthase to form 3 Hydroxy-3-MethylGlutaryl-CoA (HMG CoA). HMG CoA is reduced by the action of HMG CoA reductase to mevalonic acid using NADPH as the hydrogen donor. The end product molecule, cholesterol, acts as a feedback inhibitor of HMG CoA reductase to regulate the intra- and intercellular levels of cholesterol. Lipitor™ is a synthetic lipid lowering agent that works by mimicking the inhibitory effects of cholesterol.

27. Cholesterol synthesis 2

28. In the boxes are the two simple, 5-carbon isoprene structures that are found in ALL sterols, natural rubber, and many other natural products.

29. Polymerization usually occurs with additions of 5 carbons
Polymerization usually occurs with additions of 5 carbons. Infrequently, fusions of larger structures take place, such as the formation of a molecule of squalene from two molecules of farnesyl-pyrophosphate. Squalene is an unusual biological compound, in that it is a pure hydrocarbon (only carbons and hydrogens).

30. The cyclization of squalene to lanosterol is a remarkable series of molecular rearrangements.

31. The loss of the methyl group at carbon-14 as HCOO- (formate, anion of formic acid) yields a substrate for one-carbon metabolism that utilize tetrahydrofolate-bound intermediates.

32. In the metabolism of cholesterol to cholate, a planar, amphipathic molecule that prefers a bilayer environment is transformed into a twisted, highly polarized detergent molecule whose sole purpose in the biological world is to disrupt the bilayers (e.g., cell membranes) it encounters in the digestive process.

33. TESTOSTERONE Testosterone is a steroid hormone
In men, testosterone plays a key role in the development of male reproductive tissues such as the testis and prostate as well as promoting secondary sexual characteristics such as increased muscle, bone mass and hair growth. In addition, testosterone is essential for health and well-being as well as the prevention of osteoporosis.

34. CHEMICAL STRUCTURE OF TESTOSTERONE

35. Mechanism of Action

36. PUBERTAL
In males, these are usual late pubertal effects, and occur in women after prolonged periods of heightened levels of free testosterone in the blood.
Enlargement of sebaceous glands. This might cause acne.
Phallic enlargement or clitoromegaly
Increased libido and frequency of erection or clitoral engorgement
Pubic hair extends to thighs and up toward umbilicus
Facial hair (sideburns, beard, moustache)
Loss of scalp hair (Androgenetic alopecia)
Chest hair, periareolar hair, perianal hair
Leg hair

37. Axillary hair
Subcutaneous fat in face decreases
Increased muscle strength and mass
Deepening of voice
Growth of the Adam's apple
Growth of spermatogenic tissue in testicles, male fertility
Growth of jaw, brow, chin, nose, and remodeling of facial bone contours
Shoulders become broader and rib cage expands
Completion of bone maturation and termination of growth. This occurs indirectly via estradiol metabolites and hence more gradually in men than women.

38. What are estrogens?
Estrogen is often thought of as the “female sex hormone”, but in fact it’s prevalent in both men and women.
There are actually a few forms of estrogen — the term usually refers to a family of steroid hormones that are synthesized in a variety of tissues.
Estradiol (sometimes known as E2) is the most potent estrogen. In women it’s produced by the ovaries.
Estriol (sometimes known as E3) is produced during pregnancy. Non-pregnant women don’t make much of it at all.
Estrone (sometimes known as E1) is the most dominant estrogen in menopausal women.
Most often when people talk about “estrogen” they really mean estradiol. Estrone and estriol have about one tenth the potency of estradiol.

40. Hormones can circulate in the body in both “bound” and “unbound” forms
Hormones can circulate in the body in both “bound” and “unbound” forms. Bound

41. Why are estrogens so important?
Estrogens are essential regulators of many major processes in the body. For example:
They strongly influence the deposit of body fat — both amount and location.
They also influence muscle mass.
Estradiol has cardioprotective properties via changes in vasculature and other tissues. This is why premenopausal women have much lower rates of cardiovascular diseases than men — but their risk sharply increases after menopause.
Estrogen acts on bone to determine the overall balance of breakdown and formation. Estrogen inhibits bone breakdown and may stimulate bone formation by initiating synthesis of IGF- 1. After estradiol withdrawal during menopause (and with exercise induced amenorrhea in young female athletes) the pace of bone breakdown becomes limited, and mechanical loading is effective only in bones that are exposed to stress.

43. Estradiol Estrone Male Less than 50 pg/mL 29-81 pg/mL Female
What you should know
Normal serum levels:
Estradiol
Estrone
Male
Less than 50 pg/mL
29-81 pg/mL
Female
Follicular phase pg/mL Midcycle pg/mL Luteal phase pg/mL Postmenopausal less than 50 pg/mL
Follicular phase pg/mL Midcycle pg/mL Luteal phase pg/mL Postmenopausal about 65 pg/mL (without estrogen replacement)

44. Systematic (IUPAC) name
Estradiol
Systematic (IUPAC) name
(17β)-estra-1,3,5(10)-triene-3,17-diol

45. Estradiol 
(E2 or 17β-estradiol, also oestradiol) is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 (E1) and estriol has 3 (E3). Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect. Except during the early follicular phase of the menstrual cycle, its serum levels are somewhat higher than that of estrone during the reproductive years of the human female. Thus it is the predominant estrogen during reproductive years both in terms of absolute serum levels as well as in terms of estrogenic activity. During menopause, estrone is the predominant circulating estrogen and during pregnancy estriol is the predominant circulating estrogen in terms of serum levels. Estradiol is also present in males, being produced as an active metabolic product of testosterone. The serum levels of estradiol in males ( pg/mL) are roughly comparable to those of postmenopausal women (< 35 pg/mL). Estradiol in vivo is interconvertible with estrone; estradiol to estrone conversion being favored. Estradiol has not only a critical impact on reproductive and sexual functioning, but also affects other organs, including the bones.

46. Conversion of testosterone to estradiol
Synthesis
Conversion of testosterone to estradiol
Estradiol, like other steroids, is derived from cholesterol. After side chain 
cleavage and using the delta-5 or the delta-4 pathway, androstenedione is the key intermediary.
A fraction of theandrostenedione is converted to testosterone,
which in turn undergoes conversion to
estradiol by an enzyme called aromatase. In an alternative pathway, 
androstenedione is aromatized toestrone, which is subsequently converted to estradiol

48. Anabolic Steroids Have Been Used Illegally To Enhance Athletic Performance
The dramatic effects of androgens on protein biosynthesis have led many athletes to the use ofsynthetic androgens,
 which go by the blanket term anabolic steroids. Despite numerous warnings from the medical community about side effects,
which include kidney and liver disorders, sterility, and heart disease, abuse of such substances is epidemic. 
Stanozololwas one of the agents found in the blood and urine of Ben Johnson following his
record-setting performance in the 100-meter dash in the 1988 Olympic Games. Because use of such substances is disallowed,
Johnson lost his gold medal, and Carl Lewis was declared the official winner.

50. The thyroid gland 
or simply, the thyroid (pronounced , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage (which forms the laryngeal prominence, or "Adam's apple"). The isthmus (the bridge between the two lobes of the thyroid) is located inferior to the cricoid cartilage. Hormonal output from the thyroid is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.
The thyroid gets its name from the Greek word for "shield", due to the shape of the related thyroid cartilage. The most common problems of the thyroid gland consist of an overactive thyroid gland, referred to as hyperthyroidism, and an underactive thyroid gland, referred to ashypothyroidism.

51. Systematic (IUPAC) name
Dydrogesterone
Systematic (IUPAC) name
17-acetyl-10, 13-dimethyl-1,2,8,9,11,12,14,15,16,17- decahydrocyclopenta[a] phenanthren- 3-one

52. premenstrual syndrome
Dydrogesterone is a progestogen hormone. The brand name is Duphaston and manufactured by Abbott (formerly Solvay Pharmaceuticals).
Dydrogesterone was first introduced to the market in 1961, and is currently approved in over 100 countries worldwide. It has an estimated cumulative exposure of more than 28 million patients.
Dydrogesterone is a potent, orally active progestogen indicated in a wide variety of gynaecological conditions. Although similar in molecular structure and pharmacological effects to endogenous progesterone. It is orally active at far lower doses. Its freedom from oestrogenic, androgenic, anabolic, corticoid and other undesirable hormonal effects gives it additional benefits over most other synthetic progestogens. The therapeutic use of dydrogesterone is closely related to its physiological action on the neuro-endocrine control of ovarian function, as well as on the endometrium. As such, it is indicated in all cases of relative or absolute endogeneous progesterone deficiency.
Dydrogesterone has proven effective in the following conditions:[citation needed]
menstrual disorders
infertility
threatened and habitual abortion. Dydrogesterone is not approved for this indication by any regulatory body in US, Canada, EU or Australia.
endometriosis
premenstrual syndrome
Dydrogesterone has also been registered as hormone replacement therapy (HRT) to counteract the negative effects of unopposed oestrogen on the endometrium. Dydrogesterone is relatively safe and well-tolerated, and does not exhibit the androgenic side effects that are common with some other progestins, like medroxyprogesterone.

53. Dydrogesterone Basic information
Product Name:
Dydrogesterone
Synonyms:
17-acetyl-10,13-dimethyl-1,2,8,9,11,12,14,15,16,17-decahydrocyclopenta[a]phenanthren-3-one;(9beta,10alpha)-pregna-4,6-diene-3,20-dione;DYDROGESTERONE;(9β,10α)-pregna-4,6-diene-3,20-dione;10alpha-isopregnenone;10α-pregna-4,6-diene-3,20-dione;20-dione,(9-beta,10-alpha)-pregna-6-diene-3;20-dione,(9beta,10alpha)-pregna-6-diene-3
CAS:
MF:
C21H28O2
MW:
312.45
EINECS:
Dydrogesterone Basic information

54. Systematic (IUPAC) name
Progesterone                               
Systematic (IUPAC) name
Pregn-4-ene-3,20-dione

55. Progesterone
also known as P4 (pregn-4-ene-3,20-dione) is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. Progesterone belongs to a class of hormones called progestogens, and is the major naturally occurring human progestogen.

56. The Marker semisynthesis of progesterone from diosgenin.

57. An economical semisynthesis of progesterone
from the plant steroid diosgenin isolated from yams was developed by Russell Marker in for the Parke-Davis pharmaceutical company (see figure to the right). This synthesis is known as the Marker degradation. Additional semisyntheses of progesterone have also been reported starting from a variety of steroids. For the example, cortisone can be simultaneously deoxygenated at the C-17 and C-21 position by treatment with iodotrimethylsilane in chloroform to produce 11-keto-progesterone (ketogestin), which in turn can be reduced at position-11 to yield progesterone

58. The Johnson total synthesis of progesterone.

59. A total synthesis of progesterone
was reported in 1971 by W.S. Johnson
The synthesis begins with reacting the phosphonium salt 7 with phenyl lithium to produce the phosphonium ylide 8. The ylide 8 is reacted with an aldehyde to produce the alkene 9. The ketal protecting groups of 9 are hydrolyzed to produce the diketone 10, which in turn is cyclized to form the cyclopentenone 11. The ketone of 11 is reacted with methyl lithium to yield the tertiary alcohol 12, which in turn is treated with acid to produce the tertiary cation 13. The key step of the synthesis is the π-cation cyclization of 13 in which the B-, C-, and D-rings of the steroid are simultaneously formed to produce 14. This step resembles the cationic cyclization reaction used in the biosynthesis of steroids and hence is referred to as biomimetic. In the next step the enol orthoester is hydrolyzed to produce the ketone 15. The cyclopentene A-ring is then opened by oxidizing with ozone to produce 16. Finally, the diketone 17 undergoes an intramolecular aldol condensation by treating with aqueous potassium hydroxide to produce progesterone.

60. Site needs=

61. PLANT HORMONES-Introduction
By convention hormone are said to be a substances whose site of synthesis and site of action are different; the two events are separated by space and time.  Hormones are known to elicit specific responses.  Charles Darwin first demonstrated the existence of such substances in plants. Who in his own inimitable way explained growth of plant tips, respond to light and exhibits photo induced curvature movements.  Since then botanists all over the world made studies in unraveling the mysteries of diffusible substances called hormones which control growth and development of the plant body.

62. DISCOVERY OF PLANT HORMONES
Darwin used canary grass coleoptile tips to demonstrate the sensitiveness of the stem apex to light mediated curvature movements.  Later Boysen Jensen used Avena coleoptile tips to demonstrate the presence of plant hormones.  A gelatin block was placed on the decapitated coleoptile tip, then the tip was replaced over the gelatin block and the tip was illuminated from one direction. In response to light, the stem tip bent towards the light source.  This was explained as due to the downward movement of some substance from the tip through gelatin block down wards.  And the substance was considered as the cause for growth curvature.
Paal.A, on he other hand, placed the cut coleoptile tip asymmetrically over the decapitated coleoptile segments and placed the seedlings in tip dark.  After few hours, he observed the curvature of the stem tip away from the side at which apical tip was placed.  Pal’s experiment further demonstrated the presence of some kind of growth promoting substances in coleoptile tip, from which the substance was able to diffuse and bring about growth on one side hence the curvature.  What ones people called diffusible substances have be restated as transportable substances for there are carriers in the cell membranes which do the role.  These are carriers specific.
F.W. Went collected growth promoting substances by placing the coleoptile tips on the square agar blocks.  By placing such loaded agar blocks asymmetrically on the decapitated coleoptile tips in dark, showed the growth curvature movements.  Persuing the above methods he established quantitative bioassays.  The bioassays explain and correlate quantitative relationship between the amount of hormone applied and the magnitude curvature as a response.

64. It is at this  juncture of time biologists and chemists started identifying the chemical component that is responsible for growth promoting activity.  To their surprise, they found the human urine as a rich source for the said hormone.  Kogl and Haagen Smit starting with 33 gallons of urine, extracted 40 mg of the active principle in the form of crystalline powder which showed 50,000 fold grater activity.  First they called this substance as Auxin A.  Using the same extraction procedures they isolated another active substance from corn germ oil and called it as Auxin B. Not satisfied with their purification methods, they used charcoal adsorption column chromatographic proceduresfor isolating a pure form of growth substance.  The substances obtained from this method were called Heteroauxin.  Later heteroauxin was identified as Indole Acetic Acid.  But this substance was known as a chemical to them for it was already identified by E & H Salkowaski.  However, Salkowski’s did not know about the property of IAA as growth hormone.

66. Various studies on hormonal effects show that the endogenous levels of auxin in plant tissues is elevated by the applications of GA, Cytokinins or both. While auxin induces the synthesis of ethylene which in turn induces the formation of ABA, which on the contrary enhances the levels of ethylene?   Thus, they show both cooperative and promotive effects on each other.  It is also known that ethylene and ABA together bring down the levels of the auxin.  This effect can be overcome by the addition of cytokinins, for cytokinins are capable of bringing down the levels of ABA through the increased levels of GA biosynthesis.  The close relationship and interplay between GA, auxins, cytokinins, ABA and ethylene, exhibits an excellent feedback control mechanism.  However, understanding of hormonal interaction at the level of gene expression and their product is very important in interpreting the hormonal interplay and effects.

68. Sexual arousal 
(also sexual excitement) is the arousal of sexual desire, during or in anticipation of sexual activity. Things that precipitate human sexual arousal are called erotic stimuli, or colloquially known as turn-ons. There are mental stimuli and physical stimuli such ashormones which can cause a person to become sexually aroused.
Sexual arousal may not lead to any actual sexual activity, beyond a mental arousal and the physiological changes that accompany it. Given sufficient stimulation, sexual arousal in humans will typically end in an orgasm; but arousal may be pursued for its own sake, even in the absence of an orgasm. It is thought that women may get more aroused at a certain time during theirmenstrual cycle, either before, after or during their period, however, there are studies that do not support this theory[1] .
When men are aroused they typically get an erection. When women are aroused, they typically get vaginal lubrication (wetness).

69.      
Martin van Maele's print Francion 15depicts a couple engaging in foreplay outdoors

70. Depending on the situation, a person can be sexually aroused by a variety of factors, both physical and mental. A person may be sexually aroused by another person or by particular aspects of that person, or by a non-human object. The physical stimulation of an erogenous zoneor acts of foreplay can result in arousal, especially if it is accompanied with the anticipation of imminent sexual activity. Sexual arousal may be assisted by a romantic setting, music or other soothing situation. The potential stimuli for sexual arousal vary from person to person, and from one time to another, as does the level of arousal

71. Sexual motivation
can be defined as the impulse to satisfy sex drive, or libido. In the human species, sexual motivation is a complex phenomenon that is derived from a variety of influences. The pleasure principle is one theory of sexual motivation which postulates that perceived pleasure obtained from sexual activities is the driving force behind motivation to engage in future sexual behaviours.[1] Conversely, other theories hypothesize that sexual motivation occurs based on an interaction between external incentives and internal states. Whether external incentives trigger motivated behaviour is dependent on the internal state of an individual. The higher the internal deprivation state, the more likely an external stimulus will trigger sexual motivation in the individual.[2] A number of factors complicate the direct relationship between internal states and external incentives. In particular, internal states of sexual motivation are governed by numerous factors, including ones’ cognitions, culture, learned behaviours, and levels of circulating hormones.
Hormones are a particularly interesting factor contributing to sexual motivation. Hormones such as testosterone, estrogen, progesterone, oxytocin, and vasopressin all play a role in influencing motivation to engage in sexual behaviours. Likewise, pheromones have also been shown to contribute to sexual motivation. In most mammalian species, sex hormones control the ability to engage in sexual behaviours. However, sex hormones do not directly regulate the ability to copulate in primates (including humans). Rather, sex hormones in primates are only one influence on the motivation to engage in sexual behaviours.

72. Scientists discover chemistry of passion
  ts-discover-chemistry-of-passion.html
Scientists say there is increase in the levels of hormones neutrophins and dopamine when cupid strikes.
LONDON, UNITED KINGDOM: Couples should not worry when the first flush of passion dims - scientists have identified the hormone changes which cause the switch from lust to cuddles. A team from the University of Pisa in Italy found the bodily chemistry which makes people sexually attractive to new partners lasts, at most, two years. When couples move into a “stable relationship” phase, other hormones take over, Chemistry World reports.

75. LOVE, actually is chemicals racing internally
internally.html Scientists say there is increase in levels of hormones neutrophins and dopamine when cupid strikes.
When couples fall in love, outwardly they experience dizziness, flushed face, sweaty palms and most prominent of all a wildly beating heart. But, internally, the feeling of love is due to chemicals racing around the brain and body.
The feelings, researchers found are due to dopamine, norepinephrine and phenylethylamine that human beings release. Dopamine is thought to be the “pleasure chemical,” producing a feeling of bliss. Norepinephrine is similar to adrenaline and produces the racing heart and excitement. Together these two chemicals produce elation, intense energy, sleeplessness, craving, loss of appetite and focused attention, discovered Helen Fisher, anthropologist at Rutgers University. “The human body releases the cocktail of love rapture only when certain conditions are met. And men more readily produce it than women, because of their more visual nature,” she added.
Moreover, couples should not worry when the initial racing of the heart is reduced with time. Scientists have discovered that hormonal changes lead to such the switch from lust to cuddles. Also when couples move to a stable phase of the relationship, new set of hormones take over. A team from the University of Pisa in Italy found the bodily chemistry which makes people sexually attractive to new partners lasts, at most, two years. Furthermore, scientists found that the lust molecule was replaced by the so-called “cuddle hormone” - oxytocin - in couples who had been together for several years.
Thus, over a period of time, love between couples is not lost, it is just replaced by other hormones.

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