Hormones

Biological messenger which is synthesised in small quantity and released by a specific group of cell from one part of the organism.Transported to another part where there is receptor for it.It has both in animals and plantCalled growth substance in plant because it promotes or inhibit growth.

Animal hormones are produced by specific endocrine gland.In plants it not produced by special gland but just by a group of young cell.Animal hormones are transported by blood.Plant are seldom transported by xylem and phloem, but usually by diffusion.

Chemical coordination makes use of chemicals usually hormones to streamline or signal process in response to stimuli from the enviroment.There two types of main hormones based on its mechanism of action

Types Example 1Steroid and steroid-like hormonesOestrogen, progesterone, cortisol, aldosterone , and adrenal corticoid.Thyroxine acts like steroid hormones.2Peptide hormones PeptideProteinGlycoproteinsAmino acid derivativesGlucagon, ADH, oxytocin and thyrotrophic-releasing hormonesInsulin, somatotropin and prolactin FSH and thyrotrophic hormonesEpinephrine (adrenaline)

Physical properties of Hormones.Human hormones are produced by endocrine gland, which are ductless.Very little produced but the effect are great.Released directly into blood capillaries and circulated throughout the body.

Chemical properties of hormones.The hormones may be steroidAct like steroid or amino acid derivative peptideThey act on target organ or cell in generalThe cell must have specific receptor for the hormones.

Steroid hormones , including thyroxin are steriod-like hormones.They enter the cell easily and interact with the DNA to produce protein synthesis.Peptide hormones interact with enzyme on the membrane to bring a certain effect.

Physiological roles of hormonesTo coordinate Metabolic growth Reproductive activities Complement the nervous function

Mechanism of Action Steroid and Steroid-like HormonesSteriod hormones e.g testosterone have mechanism of action via activation of genes.The mechanism of action for steroid hormonesThe hormones molecule diffuses through the membrane of target cell, such as sarcolemma of striated muscle.Steroid molecules are lipid that can easily diffuse through phospholipid membranes.

The hormone binds to specific protein receptor that are found in the cytoplasm.It may go through the nuclear envelope to bind to the receptor found in the necleoplasm.The hormones-receptor complex formed in the cytoplasm enters the nucleus.They then binds with specific genes in the DNAIt stimulates transcription of specific genes and mRNA is produced

The mRNA leaves nucleus then moves to the cytoplasm where it translated to form proteins.The proteins formed in this way may include myosin , actin , and protein that required to form muscles.It also brings about growth of the muscles, such as effect of the testosterone, especially on puberty males.Thus , proteins synthesis takes place in the cells have receptor for the hormones.

Non-steroid hormones eg.AdrenalineInsulinGlucagon have mechanism of action via activation of cAMP.

The mechanism for non-steroid hormonesThe hormones molecules such as adrenaline binds to specific receptor at the plasma membrane of the target cell as liver cells.Such protein spans the plasma membrane and extends into the cytoplasm.The hormones complex formed stimulates an enzyme adenylate.The enzyme break down ATP to form a second messenger i.r. cAMP.

The formation trigger the start of a cascade effect of reactions.That means that small amount of hormones, the first messenger cause the formation of more cAMP, the second messenger and so on.The cAMP molecule in turn activate a lot of anzme kinase to form its inactive form.

The kinase A activates many enzyme phosphorylase which converts glycogen to glucose phosphate and another enzyme phosphate.Finally convert glucose phosphate to glucose.A lot of glucose is formed in the short of time.The glucose in the liver is released into the blood.Thus, will rise the blood glucose level almost instantly,Which one of the effect of adrenaline.

Cascade effectIs a chain of reaction in which the first messenger, the hormone such as adrenaline which causes the increase in the production of the second messenger, the cyclic AMP.The effect is amplified until numerous last product is formed.It cause a lot of glucose is formed from glycogen in the liver.

Cascade effect importanceBring out about a fast achievement of result.Thus, adrenaline brings about almost instant release in blood glucose level.Example of cascade effect can be seen in the case of production of glycogen from glucose by adrenacorticotrophin-releasing factor.

Hyphothalamus

Adrenocorticotrophin releasing factor [0.1]

Anterior pituitary gland

Adrenotrophin [1.0]

Adrenal cortex

Corticol [50 ]

Liver

Glucose glycogen [5.000]

Difference in the mechanism of action between steroid and non-steroid hormones

Steroid hormoneNon-steroid hormone1It can easily pass through the lipoprotein membrane of target cells.It cannot pass through the lipoprotein membrane structure.2It binds to the receptor in the cytoplasm or necleoplasm.It binds to the receptor at the surface of plasma membrane.3The complex formed does not actve adenyl cyclase.The complex formed activates adenyl cyclase.4No cAMP is produced.cAMP is produced.5No cascading effect occur .Cascading effect occur and a quick result is effected.

Steroid hormonesNon-steroid hormones6The complex enters into the cells.The complex does not enter the nucleus.7Certain genes are activated by the complex.Genes are not activated directly by the complex.8Transcription takes place followed by production of proteins.Transcription does not take place and protein is not produced.9Effect produced through the proteins formed .Effect produced through the enzymes activated and their products.10Usually produced long term effect such as testerone produces muscular body.Short term effect such as adrenaline increase such as adrenaline increase blood glucose level.