subject: Hormones And Their Functions [print this page] Hormones are molecules of carbon compounds that transfer biological information from one group of cells to distant tissues or organs . Hormones are of animal origin and plant origin .
hormones and their functions
Introduction to HORMONES and their functions:
Hormones are molecules of carbon compounds that transfer biological information from one group of cells to distant tissues or organs . Hormones are of animal origin and plant origin .
Animal hormones are produced by specialised tissues in the body in small amounts . These tissues are called the endocrine or ductless glands . These hormones are liberated directly into the blood stream and are carried from there to the remote tissues or vice versa called target organs . The hormones exert characteristic physiological effects on the organs and also control metabolic activities . Plant hormones are , on the other hand known as growth hormones .
Like vitamins and enzymes , hormones are effective in minute amounts . "Hormones" name indicates the stimulating action ( in Greek "hormosin" means to excite ) .
The term hormone was introduced by Baylers and Starling in 1902 for 'secretin' produced by intestinal mucosa.
Hormones generally act on tissues distant from the gland or cell secreting it . But in few exceptions , these act on adjacent cells or on the cells producing them . Hormones are all generally proteins but not all of them are proteins . Hormones , in many cases , act by influencing the enzymes . The cells in the adjacent tissue distinguish and pick selectively the hormone molecules with the help of 'receptors' present in the cells . The hormone receptors are all proteins.
Types of Hormones and their Functions
There mainly two types of hormones
1 ) Steroid hormones and their functions :
a. Sex hormones : These are of 3 types .
the male sex hormones ( androgens )
the female sex hormones ( estrogens )
the pregnancy hormones ( progestines )
Testosterone is the principle male sex hormone produced by testis . This is responsible for the development of male secondary sexual characteristics such as deep voice , facial hair , sturdy physical structure . Synthetic testosterone analogs are now in use . These are used to promote tissue and muscle growth . These are now unfortunately misused by athletes and body builders .
Estradiol is the main female sex hormone . It is responsible for the development of secondary female sex characteristics . These are breast development , shrill voice and long hair . This also takes part in the control of menstrual cycle .
Progesterone is useful for preparing the uterus for the implantation of the fertilised egg . These are also useful as birth control agents .
b. Cortico steroids ( adrenal cortical hormones ) :
Mineralo corticoids
Gluco corticoids
Mineralo corticoids : These are produced by different cells in the adrenal cortex . These are useful for water salt balance in the body . These control the NaCl content of the blood . These cause the excretion of potassium in urine .
Gluco corticoids : These are made by adrenal cortex . These are useful to modify certain metabolic reactions . These have anti inflammatory effect .
Types of Hormones and their Functions
2 ) Non steroid hormones and their functions :
These are of mainly two types :
peptide hormones
Amino acid derivative hormones
Peptide hormones : The most important amongst these is insulin . It has great influence on carbohydrate metabolism . It is responsible for the entry of glucose and the other sugars into the living cell . This is achieved by increasing the penetrating ability of cell membranes and by augmenting phosphorylation of glucose .This helps in the decrease of glucose in the blood . This is therefore commonly called hypoglycemic factor . It promotes anabolic processes and inhibits catabolic processes . Its deficiency in human beings causes diabetes mellitus . Insulin isolated from islets tissue of pancreas or from islets of Langerhans was the first hormone identified as protein . Sanger was awarded Nobel prize in1958 for determining the structure of insulin . It is a dipeptide consisting of two peptide chains bounds by three S-S bonds . One chain contained 21 amino acids and the other chain contained 30 amino acids . Sulphur bridges connect cysteine amino acids in the two chains .
Amino acid derivatives : These are thyroidal hormones . For example , thyroxine and tri iodothyronine . These effect the general metabolism regardless of the specific activity . It is therefore for this reason , thyroid gland is known as pace setter of the endocrine systems .
Female Hormones:
Just like the testes, the ovaries are cytogenic as well as endocrine in function.Ovaries secrete three types of female hormones. These are estrogen, progesterone and relaxin.
Estrogen: Estrogens are a group of female steroid hormones mainly secreted by follicular epithelial cells of membrana granulosa of graafian follicle though these are also produced by the adrenal cortex and placenta. These include beta-estradiol, esterone, estriol etc. out of which most important is beta-estradiol. Secretion of estrogens is stimulated by luteinising hormone of anterior lobe of pituitary gland. These female hormones have a variety of functions:
Stimulates the growth and normal functioning of female secondary sex organs like fallopian tubes, uterus , vagina, etc.
Control the development of female secondary sexual characters like breast enlargement, broadening of pelvis, growth of pubic and auxiliary hair and beginning of menstrual cycle.
Decrease the secretion of follicular stimulating hormone while increase the secretion of luteinising hormone.
Progesterone
Progesterone is also a female steroid hormone secreted by a yellow endocrine gland called corpus luteum formed from empty graafian follicle during the pregnancy. Small amount of progesterone is also secreted by adrenal cortex and placenta. Secretion of progesterone is stimulated by luteinising hormone of anterior lobe of pituitary gland. Progesterone is an important female hormone and has a very significant role to play in the female body.
Stimulates proliferation of endometrium of uterus and prepares it for implantation.
Desensitizes the uterine muscles to the action of oxytocin.
Helps in implantation, placenta formation and normal development of foetus in the uterus.
Stimulates proliferation of mammary gland.
Suspends ovulation during pregnancy as decrease the secretion of luteinising hormone.
Relaxin
Relaxin is a proteinous female hormone secreted by corpus albicans formed from the corpus luteum at the end of gestation period. It softens the pubic symphysis so helps in parturition (child birth).So,the female hormones are quite efficient and very specific in their action.
