bio mcqs......

     Class X-D&H                                            Class Work-4

      11^th Nov 2013                                 

  REPRODUCTION IN HUMAN BEINGS

Human beings show sexual reproduction. Human beings are unisexual thus the structures associated with reproduction are different in males and females- the male reproductive system and the female reproductive system. The reproductive systems of males and females consist of many organs which are catergorised  as ‘Primary and Secondary sex organs’

Primary Sex Organs-   Are called Gonads which produce gametes (sex cells) and secrete sex hormones

Male gonads – Testes

Produce male gametes called sperms and male hormone testosterone

Female gonads- Ovaries

Produce female gametes called ova or eggs and female hormones estrogen and progesterone

Secondary Sex Organs- These include the genital ducts and glands which help in transportation of gametes and reproductive process.( they do not produce gametes and hormones)

                                                     PUBERTY

Human beings become reproductively active from the onset of puberty. Puberty is the period during adolescence when the rate of general body growth begins to slow down and reproductive tissues begin to mature. Onset of puberty in human males is between the age of 13 to 14 years and between 10 to 12 years in females.

  Puberty is associated with many physical mental emotional and psychological changes in boys and girls which occur slowly over a period of time. These are called secondary sexual characters.

Secondary Sexual Characters common in human males and human females(boys and girls)

1)    Thick dark hair start growing in new parts of the body such as arm pits and the genital area between the thighs, which can become darker in colour

2)    Thinner hair appear on legs arms and face.

3)    Skin becomes oily and pimples may appear on the face.

4)    Individuals become more conscious of their bodies, become more independent more aggressive etc.

 Secondary Sexual Characters in human males (boys)-

1)    Enlargement of larynx and voice begins to crack

2)    beard and mustache start appearing

3)    Reproductive organs develop and start producing sperms.

4)    The penis occasionally begins to become enlarged and erect, either in day dreams or at night

5)    Broadening of the shoulders and increased muscle development.

Secondary Sexual Characters in human females (girls)-

1)    Breast size begins to increase, skin of the nipples darkens

2)    Initiation of menstruation and ovulation

                                           MALE REPRODUCTIVE SYSTEM:

Male reproductive system consists of the following components:

(a)      1 pair of testes

(b)      A system of ducts:

i) Epididymus

ii) Vas deferens or the sperm duct

iii) Urethra

(c)      A system of glands:

i) Seminal vesicles

ii) Prostrate gland

iii) Cowper’s gland

(d)      A copulatory organ called penis

                   

                                                                   TESTES

One pair of testes are present in bag like structure called scrotum which lies outside the abdominal cavity hence they are extra abdominal in position. This is so because the testes have to be maintained at 1-3 degree lower temperature than the normal body temperature in order to produce functional sperms.(sperm formation requires a  lower temperature than the normal body temperature)

Function of Testes:

1) To produce male gametes i.e. the sperms

2) To produce male reproductive hormone called testosterone which is responsible

     for  producing sperms as well as secondary sexual characteristics in males

                                                                       DUCTS

a)     Epididymus- Attached to each testis is a highly coiled tube called epididymus.

Function

The sperms are stored here and they mature in the epididymus.

     b) Sperm duct or the vas-deferens

          Each epididymus leads into the sperm duct or the vas-deferens.

          Function

          It is meant for the passage of the sperms in the male body.

c)      Urethra

Each sperm duct rises up and opens into the abdominal cavity. It unites with the duct      coming from the urinary bladder to form a common duct called urethra which passes  through the penis and opens to the outside.

          Function

          It is the common passage for both semen and urine from the body to the outside.

                                                                   GLANDS

Along the way the ducts of the three glands also open and pour their secretions into the vas deferens

 Function

  They produce different secretions which provide nutrition as well as medium for locomotion to the sperms.

The secretion of the three glands along with the sperms is known as semen.

                                                            PENIS

 It is the organ which is used to introduce semen into the female body. It is richly supplied with blood vessels.

                    

                       Human Male Reproductive System

                                       FEMALE REPRODUCTIVE SYSTEM

It consists of the following components:

(a)  1 pair of ovaries

(b)  1 pair of fallopian tubes or oviducts

(c)  A uterus / womb

(d)  A vagina / birth canal

                                                           OVARY

  Each ovary is almond shaped and present inside the abdominal cavity. At the time of birth each girl child already contains thousands of immature ova. These ova start maturing only from the time of puberty. Only one ovum is produced by one ovary in one month and each ovary produces on ovum in alternate months. The release of an ovum from the ovary into the abdominal cavity is known as ovulation.

Function

1)    To produce ova

2)    To produce female reproductive hormones – estrogen and progesterone.

                                           FALLOPIAN TUBES

There are two fallopian tubes. The end lying close to the ovary has finger like structures called fimbriae. The two fallopian tubes unite to form an elastic bag like structure called uterus.

FUNCTION OF THE FALLOPIAN TUBES: It is the site of fertilization between the male and the female gametes and formation of the zygote.

                                                          UTERUS

The inner lining of the uterus is richly supplied with blood vessels and is known as endometrium. The narrow end of the uterus is called cervix

FUNCTION OF THE UTERUS: The embryo formed in the fallopian tube comes down and gets attached to the endometrium (implantation) and develops for the next nine months till the baby is delivered.

                                                                VAGINA

 The uterus opens into the vagina through the cervix. The vagina is a muscular tube whose walls contain elastic tissue through which the baby is delivered at the end of nine months.

Function

1)    The vagina is called ‘birth canal’ as it allows passage of the baby at the time of child birth

2)    It also serves as the canal for receiving the semen at the time of copulation

Human Female Reproductive System.

Fertilisation

The semen is discharged into the vaginal tract during copulation. The sperms travel upwards and reach the fallopian tube where one sperm fuses with the ovum to form the zygote.

Post Fertilisation Changes

 The zygote divides and re- divides (form an embryo) as it descends into the uterus and gets implanted in the  endometrium. The endometrium thickens so as to receive the embryo.

The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta which is a disc-like structure embedded in the uterine wall. It contains finger-like villi on the embryo’s side of the tissue while on the mother’s side are blood spaces which surround the Villi.  Villi provide a large surface area for glucose and oxygen to pass from  the mother to the embryo. The waste substances generated by the embryo are removed through the mother’s blood. The waste substances are transferred into the mother’s blood through the placenta. When the embryo starts resembling a human form it is termed as a foetus. The foetus continues to develop inside the uterus for nine months after which the baby is delivered as a result of rhythmic contractions of the uterine muscles.( The complete development of the foetus from the initial stage of conception till the birth of the baby is called gestation)

What happens when the Egg is not Fertilised

If the ovum does not get fertilized then the endometrium starts sloughing off and there is loss of blood and mucous etc through the vagina

MENSTRUATION: It is the loss of blood, mucous along with the unfertilized ovum and the ruptured cells and tissues of the endometium through the vagina of the female. It is a 28 day cycle which occurs in every reproductively active female (from puberty). The flow of blood continues of 2 to 8 days. If the ovum does not get fertilized then the endometrium starts shedding off and there is loss of blood and mucous etc through the vagina. In case the ovum gets fertilized then the endometrium becomes thick and spongy for nourishing the embryo and hence menstruation does not occur A lady with a developing embryo in her womb is termed as pregnant. The beginning of menstruation at puberty is known as menarche. The stoppage of menstruation when the woman is 45-55 yrs of age is called menopause.