Classification of Hormone And their Mechanism Of Action

Dr. Muhammad Awais

Hormones

Hormones are chemical messengers, directly secreted into the blood or extracellular fluid, which bind specific receptors on target cells

Classification of Hormones

The following Three categories of classification of hormones

1. According to Chemical Nature

2. According to Origin 

3. According to Nature of Action

According to Chemical Nature Steroid Hormones e.g. Testosterone, Estrogen, Proges terone Amine Hormones e.g. T3, T4, epinephrine, norepineph rine. Peptide Hormones e.g. Oxytocin and vasopressin Protein Hormones e.g. Insulin and glucagon Glycoprotein Hormones e.g. LH, FSH Eicosanoids Hormones e.g. Prostaglandins.

On the Basis of Origin

Reproductive hormones primarily derived from four major organ or system

o Hypothalamuso Anterior and posterior lobe of pituitary glando Gonads (testis and ovary including their interstitial tissues and corpus

luteum)o Placenta and Uterus

1-PIH (Prolactin inhibiting hormone) Source; Hypothalamus Function; inhibit prolactin release2-PRH (Prolactin releasing hormone) Source; Hypothalamus Function; stimulate prolactin release 3-GnRH (Gonadotropin releasing hormone) Source; hypothalamus (synthesized and then stored in the medial basal

hypothalamus) Function; stimulate tonic release of FSH and LH. stimulate preovulatory surge of FSH and LH.

FSH(Follicle stimulating hormone)Source; Gonadotropes in anterior lobe .Function; stimulate follicular growth in female and Spermatogenesis in male Maturation of ovarian follicle or graffian follicleLH(Lutenising hormone )SOURCE; Gonadotropes in anterior lobe of pituitary.Function; stimulate ovulation and lutinisation of ovarian follicle(corpus luteum) in

female Testosterone in male from interstitial cells (leyding cells)

Prolactin; Source; Anterior lobe of pituitary . Function; initiate and maintains lactation . Promotes maternal behavior.Oxytocin;Source; supraoptic nucleus of hypothalamus and ovary ( corpus luteum)Function; stimulate uterine contraction Milk letdown Ovarian oxytocin involved luteal function acts on endometrium to induce

PGF2alpha.

Melatonin; Source; pineal gland.Function ; induction of ovarian cycles in ewes inhibition of cyclicity in mare.Estrogen(E2)Source; theca interna of the ovarian follicle and Fetal placental unit Function; to induce behavioral estrus in the female Physical development of female Secondary sexual characteristics in female Stimulate duct growth and cause the development of the mammary gland To increase body weight gain and growth

Progesterone;Source; luteal cells of corpus luteum Placenta (fetoplacental unit) and Adrenal glandFunction; prepare the endometrium for implantation and maintenance of pregnancy. Acts synergistically with estrogen to induce behavioral estrus Develop the secretory tissue of the mammary glands Inhibit estrus and the ovulatory surge at high level

Testosterone;Source; leyding ,s cells in the testis and Limited amount by adrenal cortexFunction; develop and maintain accessory sex gland Stimulate secondary sexual characteristics in male Sexual behavior SpermatogenesisRelaxin ;Source; primarily by the corpus luteum during pregnancy. Some species placenta and uterusFunction; Dilation of cervix and vagina before parturition Inhibit uterine contraction

Inhibin ;Source; sertoli cells in male Granulosa cells in femaleFunction; inhibit release of FSH to a level’ Maintain number of ovulation.Activin ; Source; follicular fluid in female Rete testis fluid in maleFunction; stimulates FSH secretion.

eCG (PMSG); (Equine chorionic gonadotropin)Source; endometrial cups of fetal originFunction; FSH like activity Stimulates formation of accessory corpora lutea in mare.hCG ;(human chorionic gonadotropin)source; syncytiotrophoblastic cells function; LH like activity maintains corpus luteum of pregnancy in primates

Prostaglandins; Source; almost all body tissue secrete them, endometrium of uterusFunction; regression of the corpus luteum Contraction of smooth muscles in reproductive and GIT,

erection ,ejaculation, sperm transport, ovulation, formation of corpus luteum, parturition, and milk ejection

Hypothalamus

Anterior pituitary Posterior pituitaryThyrotropin

ACTHSomatotropin

LHFSH

ProlactinVasopressin

Oxytocin

ThyroidAdrenalCortex

AdrenalMedullaPancreas Ovary Testis

Muscles liver Tissues

Liver,muscles

EstradiolTestosteroneInsulin,glucagon,somatostatin

T3 Cortisolaldosterone

Mammary glands

Reproductive organs

Epinephrine

Releasinghormones

Nervous

According to Nature of Action

General Hormones: Growth hormone influence nearly all the body tissues, similar is the case with Thyroid and Insulin hormones, hence they fall in general category.

Specific Hormones: these hormones affect functions of specific organs, e.g. FSH and androgens. Local Hormones: Prostaglandins, Acetyl cholin, Histamine act locally to

their site of production.

Mechanism of Action

The first step of a hormone’s action is to bind to specific receptors at the target cell.

Some receptors are located on cell membrane while some are located in cytoplasm and nucleus.

These receptors are protein in nature and usually 2000-100,000 receptors are present on each cell.

Receptors are located on specific in/on target cells

Mode of Action of Lipophilic Hormone

Hormones like steroid bind with protein receptors present inside the cell. These hormones are lipid soluble and hence can easily cross cell membrane.

The combined receptor protein–hormone then diffuses into or is transported into the nucleus.

The hormone receptor complex then binds with specific regulatory sequence of the DNA called hormone response element → transcription of specific genes → mRNA→ Protein synthesis.

Mode of Action of Hydrophilic Hormone

References Pathway to Pregnancy and Parturition By P.L. Senger, Ph. D. Guyton Text Book of Medical Physiology http://

www.biologydiscussion.com/hormones/classification-hormones/classification-of-hormones-5-categories/18429

https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/endocrine-system-16/hormones-150/mechanisms-of-hormone-action-774-807/

https://en.wikivet.net/Reproductive_Hormones_Overview_-_Anatomy_%26_Physiology

http://animal--husbandry.blogspot.com/2010/07/reproductive-hormones.html https://

bhsagriculture.wikispaces.com/The+Role+of+Hormones+in+the+Regulation+of+animal+reproduction+and+behaviour

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