Reproduction X Biology/C1/RS

Living World XI Biology/C1

Life Processes Respiration CBSE X

Respiration is a catabolic Process.

Respiratory substrate is mostly Glucose.

Types of respiration -1) Aerobic 

                                  2) Anaerobic

Life Processes X Biology/C1/ Response sheet

Oogenesis in Human Female.

Heredity and Variation XII Biology/Notes C 5

Revision Notes on Inheritance and Variation

Mendel’s Law of Inheritance

(1) Mendelism means experiments performed by Mendel on genetics.

(2) Mendel’s experiment involved 4 steps as selection, hybridization, selfing and calculations. His results led to the formation of laws of genetics later.

(3) Mendel performed monohybrid and dihybrid crosses and gave three principles of inheritance.

(4) Mendel’s three principles of inheritance are:

(i) Law of dominance

(ii) Law of segregation or law of purity of gametes

(iii) Law of independent assortment

(4) Law of Dominance – The dominant characters are expressed when factors are in heterozygous condition.

(5) The recessive characters are only expressed in homozygous conditions. The characters never blend in heterozygous condition. A recessive character that was not expressed in heterozygous condition may be expressed again when it becomes homozygous.

(6) Law/Principle of segregation states that when a pair of contrasting factor or gene is brought together in a hybrid, these factors do not blend or mix up but simply associate themselves and remain together and separate at the time of gamete formation.

(7) Principle of independent assortment states that genes of different characters located in different pairs of chromosomes are independent of one another in this segregation during gamete formation.

(8) Test Cross: A cross between F1 hybrid (Aa) and its homozygous recessive parent (aa) is called Test Cross. This cross is called test cross because it helps to find out whether the given dominant phenotype is homozygous or heterozygous.
(9) Monohybrid cross – When we consider the inheritance of one character at a time in a cross, this is called monohybrid cross.

                                                    

(10) Dihybrid Cross – A cross made to study the inheritance of two pairs of contrasting traits.

                         

Exceptions of Conclusions of Mendel

Incomplete Dominance

(1) When neither of the alleles of a character is completely dominant over the other and the F1 hybrid is intermediate between the two parents, the phenomenon is called incomplete dominance.

(2) Incomplete dominance was first discovered by Correns in Mirabilis jalapa. The plant is called as 4’O clock plant or ‘Gul-e-Bans’.  Homozygous red (RR) flowered variety of the plant was crossed with white (rr) flowered variety.  F1 offspring had pink flowers (Rr).  This is called incomplete dominance. 

(3) Incomplete dominance is also known to occur in snapdragon.  The phenotypic ratio and genotypic ratio in F2 generation in case of incomplete dominance is 1:2:1.

Co-dominance

(1) In co-dominance both the gene expressed for a particular character in F1 hybrid progeny. There is no blending of characters, whereas both the characters are expressed equally.

(2) Co-dominance is seen in animals for coat colour. When a black parent is crossed with white parent, a roan color in F1 progeny is produced.

Sex determination

(1) Fixing the sex of an individual as it begins life is called sex determination. The various genetically controlled sex-determination mechanisms have been classified into following categories

(2) Chromosomal theory of sex determination: The X-chromosome was first observed by German biologist, Henking in 1891 during the spermatogenesis in male bug and was described as X-body. The chromosome theory of sex determination was worked out by E.B. Wilson and Stevens (1902-1905).

(3) They named the X and Y chromosomes as sex-chromosomes or allosomes and other chromosomes of the cell as autosomes.

(4) Sex chromosomes carry genes for sex. X-chromosomes carries female determining genes and Y-chromosomes has male determining genes.

(5) The number of X and Y chromosomes determines the female or male sex of the individual, Autosomes carry genes for the somatic characters. These do not have any relation with the sex.

Sex Determination by chromosomes:

Those chromosomes which are involved in the determination of sex of an individual are called sex chromosomes while the other chromosomes are called autosomes.

1) XX – XY type:  In most insects including fruit fly Drosophila and mammals including human beings the females possess two homomorphic sex chromosomes, named XX.  The males contain two heteromorphic sex chromosomes, i.e., XY. Hence the males produce two types of gametes / sperms, either with X-chromosome or with Y-chromosome, so they are called Heterogamety.

2) ZZ – ZW type:  In birds and some reptiles, the males are represented as ZZ (homogamety) and females are ZW (heterogamety).

3)  XX – XO type:  In round worms and some insects, the females have two sex chromosomes, XX, while the males have only one sex chromosomes X. There is no second sex chromosome. Therefore, the males are designated as XO.  The females are homogametic because they produce only one type of eggs.  The males are heterogametic with half the male gametes carrying X-chromosome while the other half being devoid of it.

Numerical aberrations of chromosomes:

 Each species has a characteristic number of chromosome. Variations or numerical changes in chromosomes (Heteroploidy) can be mainly of two types:

                

(1) Euploidy: The somatic chromosome number in euploids is the exact multiple of basic haploid number. In euploidy an organism acquires an additional set of chromosomes over and above the diploid complement.

(a) Monoploidy or haploidy: Monoploids possess only one set or single basic set of chromosomes. Haploids on the other hand have half the somatic chromosome number. In diploid organisms monoploids and haploids are identical while in a tetra-or hexaploid with 4n or 6n chromosomes the haploids will possess 2n or 3n chromosome whereas its monoploid will possess only one set (n) of chromosome.

(b) Diploidy: The common chromosome number in the somatic cells of plants and animals.

(c) Polyploidy: Organism with more than two sets of chromosomes are known as polyploids. It may be triploid with three sets of chromosomes (3n) or tetraploid with four sets of chromosome (4n) and so on.

(2) Aneuploidy: Aneuploidy is the term applied for the chromosomal mutations involving only a part of a set, i.e., loss (hypoploidy) or addition (hyperploidy) of one or more chromosomes. Aneuploidy may result from non disjunction of chromosome during cell division.

(a) Monosomy: Diploid organism that are missing one chromosome of a single pair with genomic formula 2n – 1. Monosomics can form two kinds of gametes, (n) and (n –1).

(b) Nullisomy: An organism that has lost a chromsome pair is nullisomic. The result is usually lethal to diploids (2n – 2).

(c) Trisomy: Diploids which have extra chromosome represented by the chromosomal formula 2n + 1. One of the pairs of chromosomes has an extra member, so that a trivalent may be formed during meiotic prophase.

(d) Tetrasomy: In tetrasomic individual particular chromosome of the haploid set is represented four times in a diploid chromosomal complement. The general chromosomal formula for tetrasomics is 2n + 2 rather than 2n + 1+ 1. The formula 2n + 1 + 1 represents a double trisomic.

(iii) Types of aneuploidy: Aneuploidy may be of following types on the basis of chromosomes involved in non disjunction.

(a) Aneuploidy involving non-disjunction in sex chromosomes:

This kind of aneuploidy is brought about due to non-disjunction in sex chromosomes. It may lead to following types of syndromes:

(1) Turner’s syndrome: Such persons are monosomic for sex chromosomes i.e. possess only one X and no Y chromosome (XO). In other words they have chromosome number 2n – 1 = 45. They are phenotypic females but are sterile because they have under developed reproductive organs. They are dwarf about 4 feet 10 inches and are flat chested with wide spread nipples of mammary glands which never enlarge like those in normal woman. They develop as normal female in childhood but at adolescence their ovaries remain under developed. They lack female hormone estrogen. About one out of every 5,000 female births results in Turner’s syndrome.

(2) Klinefelter’s syndrome: Since 1942, this abnormality of sex is known to geneticists and physicians. It occurs due to Trisomy of sex chromosomes which results in (XXY) sex chromosomes. Total chromosomes in such persons are 2n + 1 = 47 in place of 46. Klinefelter (1942) found that testes in such male remain under developed in adulthood. They develop secondary sex characters of female like large breasts and loss of facial hair. Characters of male develop due to Y chromosome and those like female due to XX chromosomes. About one male child out of every 5,000 born, develops Klinefelter’s syndrome.

Such children are born as a result of fertilization of abnormal eggs (XX) by normal sperms with (X) or (Y) chromosomes or by fertilization of normal eggs with (X) chromosomes by abnormal sperms with (XY) chromosome. They are sterile males mentally retarded and are eunuchs.

(b) Aneuploidy involving non-disjunction in autosomes:

This type of aneuploidy occurs due to trisomy of autosomes. In any particular autosomal pair having 3 instead of normal 2 chromosomes. Such persons may be males 45 + XY = 47(2n + 1) or females 45 + XX =47(2n + 1). On the basis of the number of the autosome pair affected by trisomy, they can be of following types

(1) Down’s syndrome: This autosomal abnormality is also known as Mongolian idiocy or mongolism. In Langdon Down of England (1866) studied the Mongolian idiocy and described the trisomic condition of their chromosomes. Down’s syndrome, a very common congenital abnormality arises due to the failure of separation of 21st pair of autosomes during meiosis. Thus an egg is produced with 24 chromosomes instead of 23. A Down’s syndrome has 3 autosomes in 21st pair instead of 2. Total number of chromosomes in this case is 2n + 1 (21st) = 47.

The affected children have a very broad fore head, short neck, and flat palms without crease, stubby fingers, permanently open mouth, projecting lower jaw and a long thick extending tongue. They have low intelligence and are short heighted. They have defective heart and other organs. They are born to mothers aged 40 year and above during first pregnancy. They may survive upto 20 years under medical care.

They are called mongolian idiots because of their round, dull face and upper eyelids stretched downwards similar to mongolian race.

Chromosomal theory of Inheritance:

Chromosomal theory of inheritance was proposed by Sutton and Boveri independently in 1902.  The two workers found a close similarity between the transmission of hereditary characters and behaviour of chromosomes while passing from the one generation to the next through agency of gametes.

Pedigree analysis

Inheritance of hundreds of characteristics such as polydactyly, haemophilia, colour blindness, attached ear lobes and tongue rolling, generation after generation in particular families of man have been studied. In order to conduct such study, a standard method has been used to represent the family pedigree in a concise, easily understood form so that one can visualize the entire pedigree (family history) at a glance of the chart.

Reproductive Health XII Biology/Notes C 4

Revision Notes on Reproductive Health

Reproductive health – problem and strategies

(a) India was amongst the first countries in the world to initiate to the programme “family planning” initiated in 1951.

(b) Reproductive health in a society forms a crucial part of general health.

(c) Improved programs covering wider reproduction-related areas are currently in operation under the popular name ‘Reproductive and child health care (RCH) program.’

(d) Health and education of young people and marriage and child bearing during more mature stages of life are important attributes to the reproductive health of a society.

Population explosion and birth control

(a) The rapid increase in human population size over a relatively short period is called human population-explosion.

(b) Population growth rate depends on factors like fertility, natality, mortality, migration, age and sex structure.

(c) Increased health facilities and better living conditions are the cause behind population explosion.

(d) Out of 6 billion world population 1.3 billion populations is of Indians.

(e) Rapid decline in death rate, maternal mortalility rate (MMR) and infant mortality rate (IMR) are major cause of population growth.

(f) Growth rate of Indian population is around 1.7 percent.

(g) Most of the urban people are uneducated.

(h) The regulation of conception by preventive methods or devices to limit the number of offsprings is called birth control.

(i) A birth control method which deliberately prevents fertilization are referred to as contraception.

(i) Contraceptive methods are preventive methods and are of two types – temporary and permanent.

Characteristics of an ideal contraceptive are:-

(a) User friendly

(b) Easily available

(c) Nor or least side – effects

(d) No way interferes with sexual drive

Methods of Birth Control

 

  

  
S.
  No.
  
  

  
Method
  
  

  
Action
  
 
 

  

  
(1)
  
  

  
Rhythm Method
  
  

  
No intercourse during woman’s
  fertility period (day 12-20).
  
 
 

  

  
(2)
  
  

  
Withdrawl
  
  

  
Penis is withdrawn before
  ejavculation.
  
 
 

  

  
(3)
  
  

  
Tubectomy / Tubal ligation
  
  

  
Women’s fallopian tubes are cut and
  tied, permanently blocking sperm release.
  
 
 

  

  
(4)
  
  

  
Vasectomy
  
  

  
Man’s vasa deferentia are cut and
  tied permanently blocking sperm passage.
  
 
 

  

  
(5)
  
  

  
Intrauterine device (IUD)
  
  

  
Small plastic or metal device
  placed in the uterus to prevent implantation. Some contain copper, other
  release hormones.
  
 
 

  

  
(6)
  
  

  
Oral Contraceptive
  
  

  
Synthetic estrogens and
  progestrones prevent normal menstrual cycle, primarily prevent ovulation.
  
 
 

  

  
(7)
  
  

  
Male condom
  
  

  
Thin rubber sheath on erect penis
  collects ejaculated semen.
  
 
 

  

  
(8)
  
  

  
Female condom
  
  

  
Plastic pouch inserted into vagina
  catches semen.
  
 
 

  

  
(9)
  
  

  
Diaphragm
  
  

  
Soft rubber cup covers entrance to
  uterus, prevents sperm from reaching egg and holds spermicide.
  
 
 

  

  
(10)
  
  

  
Cervical cap
  
  

  
Miniature diaphragm covers cervix
  closely, prevents sperm from reaching egg and holds spermicide.
  
 
 

  

  
(11)
  
  

  
Foams, creams, jellies etc.
  
  

  
Chemical spermicides inserted in
  vagina before intercourse, prevent sperm from entering uterus.
  
 
 

  

  
(12)
  
  

  
Implant (Norplant)
  
  

  
Capsules surgically implanted under
  skin, slowly release hormone that blocks ovulation.
  
 
 

  

  
(13)
  
  

  
Injectable contraceptive
  (Depo-Provera)
  
  

  
Injecti
  
 




Amniocentesis

(a) During pregnancy, the fetus is surrounded by amniotic fluid which is a water-like substance.

(b) Amniotic fluid contains live fetal skin cells and other substances, such as alpha-fetoprotein (AFP).

(c) These substances provide important information about baby's health before birth.

(d) These days amniocentesis is being misused also, i.e., for detecting the sex of the foetus.

(e) Normal foetus is being aborted if it is a female.

Sexually transmitted diseases ( STDs)
Diseases which are transmitted sexually through sexual intercourse are collectively called as Sexually Transmitted Diseases (STDs) or Venereal Diseases (VDs) or reproductive tract infections (RTI). STDs can be classified as viral, bacterial, protozoan, fungal, etc.
Causes of STD’s
STDs can be spread with any type of sexual activity, depending on the disease. STDs are most often caused by viruses and bacteria.
Types of Sexually Transmitted DiseasesThe various types of sexually transmitted diseases include genital herps, chancroid, gonorrhoea, syphilis and most common HIV leading to AIDS.
(i) Chlamydiasis
  (a) Chlamydiasis is a sexually transmitted disease in humans caused by the bacterium Chlamydia trachomatis.
  (b) It is a major infectious cause of human genetial and eye diseases.
(ii) Gonorrhoea
  (a) Gonorrhoea is transmitted sexually, by oral, anal or genital sex.
  (b) Gonorrhea is caused by the bacterium Neisseria gonorrhoeae
Prevention
STDs are a major threat to a healthy society.
(i) Avoid sex with unknown partners as well as multiple partners.
(ii) Always use condoms during coitus.
(iii) In case of any doubt, go to a qualified doctor for early detection and get complete treatment if diagnosed with disease.
Infertility
(a) Inability to conceive or produce children even after 2 years of unprotected sexual cohabitation is called infertility.
(b) A large no of couples all over India are infertile.
(c) The reasons for this could be many-physical, congenital, diseases, drugs, Immunological or even Psychological.
Assisted Reproductive Technologies (ART)
Includes all fertility symptoms in which both sperms and eggs are handled. These are special techniques that assist couples to have children.
The main ART- techniques include:
(i) In-vitro fertilisation (IVF)
(ii) Zygote intra fallopian transfer (ZIFT)
(iii) Intra cytoplasmic sperm injection(ICSI)
(iv) Gamete intra fallopian transfer(GIFT)
(v) Artifical insemination (AI)
(1) In Vitro Fertilization (IVF)
(a) Fertilization outside the body in almost similar conditions as are in the body.
(b)  This method is popularly known as test tube baby programme.
(c) In this technique, ova from the wife / donor (female) and sperms from the husband / donor (male) are collected and are induced to form the zygote under simulated conditions in the lab.
(d) The zygote or early embryos could then be transferred into the fallopian tube (ZIFT -zygote intra fallopian transfer).
(2) Zygote intra fallopian transfer (ZIFT)
(a) ZIFT is an assisted reproductive procedure similar to in vitro fertilization and embryo transfer.
(b) The difference is that the fertilized embryo is transferred into the fallopian tube instead of the uterus.
(c) As the fertilized egg is transferred directly into the tubes, the procedure is also referred to as tubal embryo transfer (TET).
(3) Intra cytoplasmic sperm injection (ICSI)
(a) Intracytoplasmic sperm injection (ICSI) is an assisted reproductive technology (ART)
(b) It is used to treat sperm-related infertility problems.
(c) ICSI is used to enhance the fertilization phase of in vitro fertilization (IVF) by injecting a single sperm into a mature egg.
(d)The fertilized egg is then placed in a woman's uterus or fallopian tube.
(4) Gamete intra fallopian tube (GIFT)
(a) The process of transfer of an ovum collected from a donor into the fallopian tube of another female who cannot produce one, but can provide suitable environment for fertilisation and further development is another method attempted.
(a) GIFT uses multiple eggs collected from the ovaries, which are placed into a thin flexible tube (catheter) along with the sperm to be used.
(b) The gametes (both eggs and sperm) are then injected into the fallopian tubes using a surgical procedure called laparoscopy under general anesthesia.
(5) Artificial Insemination (AI)
(a) Infertility cases either due to inability of the male partner to inseminate the female or due to very low sperm count in the ejaculates could be corrected by artificial insemination (AI).
(b) In this technique, the semen collected either from the husband or a healthy donor is artificially introduced into the vagina or into the uterus (IUI - Intra Uterine Insemination) of the female.

Human Reproduction XII Biology/Notes C3

Revision Notes on Human Reproduction

(1) Reproduction is the formation of new individuals of their own kind by living organisms.

(2) The Male Reproductive System consists of:

(a) Primary sex organs i.e. a pair of testes suspended in a scrotum.

Secondary sorgans i.e. a pair of ducts each differentiated into an epididymis, a vas deferens and an ejaculatory duct.

(c) A male urethra passing through an erectile penis.

(d) Three types of Glands - a pair of seminal vesicles, a prostate gland and a pair of Cowper’s glands.

(3) The Female Reproductive system consists of:

(a) Primary sex organ i.e. a pair of ovaries

(b) Secondary sex organs i.e. a pair of fallopian tubes (oviducts) , a uterus (womb), a vagina.  

(4)Ovaries produce female gametes called ova.

Phases of embryonic development

Embryonic development involves following dynamic changes and identifiable process.

(1) Gametogenesis : It involve the formation of haploid sex cells or gametes called sperms and ova from diploid primary germ cells called gametogonia present in the reproductive organs called gonads (testes and ovary). It is of two types;

(i) Spermatogenesis: Formation of sperm.                    

(ii) Oogenesis : Formation of ova

(2) Fertilization: It involves the fusion of haploid male and female gametes to form diploid zygote. The fusion of gametic pronuclei is called Karyogamy while the mixing of two sets of chromosomes of two gametes is called amphimixis.

(3) Cleavage: It includes the rapid mitotic division of the zygote to form a single layered hollow spherical larva called blastula and its formation is called blastulation.

(4) Implantation: The process of attachment of the blastocyst (mammalian blastula) on the endometrium of the uterus is called implantation.

(5) Gastrulation: It includes the mass and orderly migration of the organ specific areas from the surface of blastula to their predetermined position which finally produces a 3 layered gastrula larva. It is with 3 primary layers.

(6) Organogenesis: It includes the formation of specific organs system from three primary germ layers of gastrula and also includes the morphogenesis and differentiation.

Fertilization

(1) Definition: Fusion of a haploid male gamete (spermatozoon) and a haploid female gamete (ovum) to form a diploid cell, the zygote, is called fertilization or syngamy.

(2) Site of fertilization: Fertilization in human female is internal as in other mammals. It takes place usually in the ampulla of the fallopian tube.

(3) Steps of fertilization

(i) Approach of sperm to ovum:

(a) Male discharges semen (3.5 ml) in the female’s vagina close to the cervix during coitus. This is called ejaculation or insemination. This ejaculation contains as many as 400 million sperms but only about 100 sperms reach the fallopian tube because many sperms are either killed by the acidity of female genital tract or engulfed by the phagocytes of the vaginal epithelium.

(b) The sperm swim in the seminal fluid at the rate of 1-4 mm per minute by the aspiratory action of the uterus and peristaltic movement of the fallopian tube.

(c) Capacitation is the phenomenon of physiological maturation of sperms by breaking of acrosome membrane inside the female genital tract. It takes about 5-6 hours.

(d) Ovum is released on the 14th day of menestrual cycle trapped by the fimbriae of the ampulla of fallopian tube and move towards the uterus by peristalsis and ciliary action.

(e) At the time of ovulation, egg is at secondary oocyte stage.

(f) Fertilizability of human sperm in the female genital tract is of 12 to 24 hours while its survival value is upto 3 days and of ovum is only 24 hours though it can live for about 72 hours.

(ii) Penetration of sperm:

(a) The ovum secretes a chemical substance called fertilizin, which has a number of spermophillic sites on its surface where the sperm of species specific type can be bound by their antifertilizin site.

(b) This fertilizin-antifertilizin interaction causes agglutination (sticking together) of egg and sperm.

(c) The sperm generally comes in contact with ovum in the animal pole (side of ovum with excentric nucleus) while the opposite side of ovum is called vegetal pole.

(d) Ovulation in the human female occurs at secondary oocyte stage in which meiosis-I have been completed and first polar body has been released but second maturation is yet to complete.

(e) Penetration of sperm is a chemical mechanism.

(f) In this acrosome of sperm undergoes acrosomal reaction and releases certain sperm lysins which dissolve the egg envelopes locally and make the path for the penetration of sperm.

(g) These sperm lysins contain a lysing enzyme hyaluronidase which dissolves the hyaluronic acid polymers in the intercellular spaces which holds the granulosa cells of corona radiata together; corona penetrating enzyme (that dissolves the corona radiata) and acrosin (which dissolves the zona pellucida). Then it dissolves the zona pellucida.

(h) Only sperm nucleus and middle piece enter the ovum. The tail is lost.

(iii) Cortical reaction:

(a) Immediately after the entry of a sperm into the egg, the later shows a cortical reaction to check the entry of more sperms.

(b) In this reaction, the cortical granules present beneath the egg’s plasma membrane release chemical substance between the ooplasm and the plasma membrane (vitelline membrane).

(c) These substances raise the vitelline membrane above the egg surface. The elevated vitelline membrane is called fertilization membrane.

(d) The increased space between the ooplasm and the fertilization membrane and the chemical present in it effectively check the entry of other sperm.

(e) If polyspermy occurs, that is more than one sperm enter the secondary oocyte, the resulting cell has too much genetic material to develop normally.

(iv) Fusion of gametic nuclei:

(a) Entrance of spermatozoon serves to acts as stimulus which causes the second maturation division.

(b) As the head and middle piece of the sperm advance into the egg, those parts rotate through an angle of 180° so that the mitochondria and proximal centriole of the associated middle piece assume the leading position.

(c) Beside this rotation, the chromatin itself starts swelling by absorbing fluid from the surrounding cytoplasm and becomes vesicular.

(d) It is now called male pronucleus. This direction of movement of male pronucleus is called penetration path.

(e) The centriole brought in by the spermatozoon subdivides into two and as achromatic spindle is established in the center of the active cytoplasm.

(f) With the production of the second polar body, the egg nucleus or female pronucleus is ready for union with the male pronucleus provided by the sperm head.

(g) The male pronucleus which has been advancing the penetration path, now moves directly toward the female pronucleus. This in many cases involves a slight change in the course of sperm.

(h) In such cases, the later portion of its course is called the copulation path.

(i) The centrioles of middle piece of sperm form a spindle.

(j) The nuclear membrane of the gametic nuclei degenerates and two sets of chromosomes initially lie on two poles of the spindle but later these sets of chromosomes mix up and the process is called amphimixis.

(k) The fertilized egg is now called zygote and the zygote nucleus is called synkaryon.

Significance of fertilization

(a) It provides stimulus for the egg to complete its maturation.

(b) It activates the ovum to develop into a new individual by repeated mitotic division.

(c) Fertilization restores the diploid number of chromosomes (46 in man) in the zygote by adding male’s haploid set of chromosomes.

(d) It makes the egg more active metabolically.

(e) It combines the character of two parents and introduces variations. So help in evolution.

(f) Sex chromosomes of sperm is either X or Y and helps in sex determination.

(g) Fertilization membrane formed after sperm entry, checks the entry of additional sperms.

(h) Copulation path sets the axis of division.

Menstrual Cycle

(1) Menstruation occurs in human, apes and old world monkeys.

(2) Menstruation is bleeding from the uterus of adult females at intervals of one lunar month.

(3) Beginning of menstruation or first menstruation is called menarche.

(4) The beginning of menstruation varies. It usually occurs between 12 and 15 years.

(5) The cycle of events starting from one menstruation till the next one is called Menstrual Cycle.

(6) In human females, menstruation is repeated at an average interval of about 28/29 days.

(7) One ovum is released (ovulation) during the middle of each menstrual cycle.

(8) It is regulated by certain hormones, some of which are secreted by the pituitary gland.

(9) The pituitary gland is stimulated by releasing factors produced in the hypothalamus.

(10) The hormones produced by the pituitary gland influence the ovaries. The hormones secreted by the ovaries affect the walls of the uterus.

Phases of Menstrual Cycle

The menstrual cycle consists of following four phases:

(1) Menstrual Phase:

(i) In a 28 days menstrual cycle,the menses  takes place on cycle days 3-5.

(ii) The production of LH from the anterior lobe of the pituitary gland is reduced.

(iii) The withdrawal of  this hormone causes degeneration of the corpus luteum and, therefore progestrone production is reduced.

(iv) Production of oestrogen is also reduced in this phase.

(v) The endometrium of uterus breaks down & menstruation begins.

(vi) The cells of endometrium secretions, blood & unfertilised ovum constitutes the menstrual flow.

(2) Follicular Phase:

(i) This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.

(ii) The follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.

(iii) Oestrogen stimulates the proliferation of the endometrium of the uterine wall.

(iv) The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.

                     

(3) Ovulatory Phase:

(i) Both LH & FSH attain a peak level in the middle of cycle (about 14th day).

(ii) Oestrogen concentration in blood increases.

(iii) Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum.

(iv) In fact LH causes ovulation.

(4) Luteal Phase:

(i) Includes cycle days 15 to 28.

(ii) Corpus luteum secretes progestrone.

(iii) Endometrium thickens.

(iv) Uterine glands become secretory.

Hormonal Control of MC

(i) FSH stimulates the ovarian follicles to produce oestrogens.

(ii) LH stimulates corpus luteum to secrete progestrone.

(iii) Menstrual phase is caused by the increased production of oestrogens.

(iv) LH causes ovulation

(v) Proliferative phase is caused by the increased production of oestrogens.

(vi) Secretory phase is caused by increased production of progestrone.