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Role of Hormones in Initiating Reproductive Function

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Role of Hormones in Initiating Reproductive Function - Lesson Summary

Hormones
Hormones are the chemical substances secreted by endocrine glands to regulate many physicochemical functions in the human body. Glands in our body are of two types – Endocrine glands and Exocrine glands.



Gonads or sex glands
Gonads are the sex glands which secrete sex hormones. These sex hormones control the onset of puberty and initiate the reproductive function.

a) Gonads in males  
A pair of testes forms the gonads in males. Testes are located in a structure called as scrotum which distends below from abdominal region to maintain low temperature. Low temperature favours the formation of sperms in the testes. Testes also secrete the hormone testosterone.
       •  Functions of testosterone: Testosterone initiates and controls the changes in males occurring during puberty. These changes are called as secondary sexual characters which include deeper voice, development of penis, facial and body hair. Testosterone also controls the growth and maturation of sperms in males. Testosterone initiates the reproductive function in males.
       •  Reproductive phase in males: The reproductive phase of life begins at puberty. The reproductive phase of life extends from puberty to 70 years of age.

 

b) Gonads in females
A pair of ovaries forms the gonads in female. Ovaries are the female sex organs that lie one on either side of the abdominal cavity. Ovaries produce two hormones, namely, estrogen and progesterone. The reproductive phase of females is marked by the menstrual cycle. 
       •  Functions of female sex hormones: Estrogen controls the changes that occur during puberty, like feminine voice, soft skin and development of mammary glands, growth of pubic hair and controls the release of mature eggs. Progesterone controls the uterine changes during menstrual cycle, and helps in the maintenance of pregnancy.
       •  Reproductive phase in women: Reproductive phase of life in women starts from puberty and extends till the age of 45. Menarche is the first occurrence of menstruation. Menopause is the stoppage of menstruation. Reproductive phase is marked between menarche and menopause.
       •  Menstruation: The shedding of the uterine thickening along with its blood vessels at the end of menstrual cycle is called as menstruation. The menstrual cycle takes place every 28-30 days. One ovum is released by either of the ovaries during one menstrual cycle. In the absence of fertilisation, ovum and the thickened uterine walls are disrupted and are shredded off as menstrual flow or bleeding. Bleeding continues for 3 to 8 days.   Menstrual cycle involves maturation of ovum, release of ovum, thickening of uterine wall and menstruation. 

 

Fertilisation
It is the fusion of a sperm and an ovum to form a single cell, the zygote.

Sex determination
Sex chromosomes in sperms determine the baby’s gender. Humans have 23 pairs of chromosomes in each cell. A pair of chromosome forms the sex chromosomes. Males carry XY and females carry XX chromosomes. Reproductive cells give rise to gametes by the division of   meiosis. A gamete is a mature reproductive cell - a sperm or an ovum. If a sperm carrying X fertilises the ovum with X chromosome, then the resulting baby is a girl. If a sperm carrying Y chromosome fertilises the ovum with X chromosome, then the resulting baby is a boy. Hence, males are responsible for the gender of the newly formed babies. Gender determination of an unborn baby is considered illegal in India.



Other endocrine glands
Some glands other than gonads also play an important role in maintaining reproductive phase of the individual.

Thyroid gland: Thyroid gland present in the throat region produces thyroxine and calcitonin. Thyroid gland is the largest endocrine gland of the body. Secretion of thyroxine hormone requires iodine.
       •  Thyroxine and calcitonin hormones secreted by this gland play a crucial role in the development of muscles and bones in adolescents.
       •  Thyroxine helps in the control of metabolism of proteins, carbohydrates and fats.
       •  Calcitonin helps in the metabolism of calcium
       •  Thyroxine is responsible for metamorphosis of the larva or tadpoles into adult frogs.

Pituitary gland: The pituitary gland or the master gland controls the secretion of hormones from the other endocrine glands, including the thyroid, adrenal etc.
       •  It also secretes the hormones which induce gamete formation in the gonads, testes and ovaries.
       •  It also secretes the growth hormone which plays an important role in the growth of adolescents.

Pancreas: Pancreas is the second largest endocrine gland. Endocrine part of pancreas is made up of  alpha cells, beta cells and delta cells.
       •  Both insulin and glucagon hormones are secreted by beta cells and alpha cells respectively regulate glucose level in the blood.
       •  These hormones also exhibit an effect on reproductive life of an individual.

Adrenal glands: These glands are present above the kidneys. They mainly secrete a hormone called as adrenaline.
       •  Adrenaline maintains salt balance in the blood.
       •  This hormone helps the body to cope up with stress conditions during adolescence such as fright, fight and flight.

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