Detail explanation for the students of biology grade XII ISC/CBSE/HSC

2. Puberty
• Puberty is a period in human development
during which the body changes as people
transition from childhood to adulthood.
• It usually begins between ages
• 8 and 14 for girls
• 9 and 13 for boys.

3. Changes during puberty

5. PRIMARY SEX ORGANS OR GONADS

6. Female reproductive system

10. cortex
medulla
Germinal
epithelium

11. Internal structure of ovaries
• Cortex [outer]
• Medulla [inner]
• Tunica albuginea [connective tissue sheath]
• Germinal epitheium [inner surface of ovary]
• Ovarian stroma [connective tissue +blood
capillaries]
• This ovarian stroma consists of two zones
[periferal cortex +inner medula ]
Stroma contains developing folical with eggs in
various stages of development .

12. corpus luteum; plural noun: corpora lutea
• It is a hormone-secreting structure that develops
in an ovary after an ovum has been discharged
but degenerates after a few days unless
pregnancy has begun.
• yellow hormone-secreting body in the female
reproductive system. It is formed in an ovary at
the site of a follicle.

17. • Corpus albicans. ... As the corpus luteum is
being broken down by macrophages,
fibroblasts lay down type I collagen, forming
the corpus albicans. This process is called
"luteolysis". The remains of the corpus
albicans may persist as a scar on the surface
of the ovary.

19. Graafian follicle
• Mature follicle is called as Graafian follicle .
• a fluid-filled structure in the mammalian ovary
within which an ovum develops prior to
ovulation.
• Finally it ruptures to release the mature egg
into the surrounding peritonial cavity from
where it is picked up by the fimbriae.

22. Menstrual cycle
• It is also called as ovarian cycle
• Begins at puberty [age-10 to 15 yrs, goes till
the age of 45-55]
• Cycle occurs in the influence of LH & FSH
--from anterior pituitary gland.

23. Phases of menstrual cycle
• The entire duration of a Menstrual cycle can
be divided into four main phases:
• Menstrual phase (From day 1 to 5)
• Follicular phase[proliferative ]
(From day 5 to 13)
• Ovulation phase (Day 14)
• Luteal phase (From day 15 to 28)

24. Menstrual phase
• 1 to 5 th day of cycle.
• This phase is marked by
---breaking down of the mucous membrane and
glands from the lining of the
uterus[endometrium ]
Menstruation-
[Epithelial lining +connective tissue +blood
vessels ]
3 to 5 days

25. Follicular or proliferative phase
• From 5th day to 14th day
• Repair of damaged endometrium through
proliferation.
• Restores the continuous epithelial lining and
repairs ruptured blood vessels in it.
• Increase levels of FSH –leads to the development
of primary follicle to Graafian follicle.[follicular
phase]
• As ovulation begins –estrogen level increases and
reaches to maximum.
• Estrogern causes thickening of endometrium
• [thickness get doubled]
• 9 to 10 days

26. Ovulation phase
• It is a release of ova from the ovary.by
rupturing of Graffian follicle .
• Its only for one day
• 14 th day of cycle.

27. Luteal phase or secretory phase
• From 14th day to 28th day.
• Secretion of LH by anterior pitutory gland .
• LH along with FSH stimulates ovulation
• Graffian follicle gets ruptured and ovum gets
released
• LH & FSH attain the peak level during the
middle of the cycle .
• Corpus luteum –progesteron-[tubular glands
secreate mucus and endometrium becomes
fluid filled and glandular

28. If ovum is not fertilised
• Inhibition of the release of gnRH
• It inhibits the release of LH &FSH
• Results in degeneration of corpus luteum
• Decrease level of both progesteron & estrogen
• Break down of endometrium [because of –
1]blood vessels constrict
• 2]prevents blood supply to endometrium
• 3]very low supply of O2 and nutrients .

34. Effects of fertilisation
• Progesteron level increases
• So it inhibits further maturation of any other
follicle.
• The lining of endometrium thickens further
• Menstrual cycle remains suspended
• Blastocyst gets implant in the womb.
• Implantation takes place in 9 days after
fertilisation .

35. Menarche
• Menarche is the first menstrual cycle, or first
menstrual bleeding, in female humans. From
both social and medical perspectives, it is
often considered the central event of female
puberty, as it signals the possibility of fertility.

36. Menopause
• Menopause is defined as the absence of
menstrual periods for 12 months. It is the time
in a woman's life when the function of the
ovaries ceases. The process of menopause
does not occur overnight, but rather is a
gradual process. This so-called
perimenopausal transition period is a different
experience for each woman.

37. Structure of ova

38. • 0.15 mm in diameter
• Non motile
• Alecithal [almost without yolk]
• Yolk is negligible because it gets implanted within
7-8 days ,and then draws nourishment from
mother through placenta.
• Contains haploid nucleus
• Large amount of cytoplasm
• Surrounded by radiating rows of follicle cells of
corona radiata .
• Corona radiata protects the ova till fertilization
• And gets broken down only by the acrosomal
enzymes released by the sperm.

39. Inner to the corona radiata –
--zona pellucida [transperant clear zone ,secreated by corona cells]
[after fertilisation to stop the entry of other sperm.]
Primary membrane
Plasma membrane
ova it has polarity –,animal pole
[here polar bodies are released]
vegetal pole[opposite pole]

40. Male reproductive system
gubernaculum
Glans +prepuce
Cowper’s gland

41. Parts of male reproductive system
• 1]Male gonads [testis]
Soft ,smooth ,pinkish , oval organs .
[4.5cm long ,2.5 cm wide,3cm thick]
Mesodermal in origin .
Suspended in scortal sac by spermatic cord .
Connected to the wall of scortum by short fibromuscular
band –gubernaculum.
During early feotal life –testis develop in the lumber region
of the abdominal cavity just below the kidney.
During 7th month ,they desend permanently into respective
scortal sac.[with blood vessels ,peritoneum,lymph
vessels,nerves and vasa diferentia ]
Failure of the testies to desend from the abdomen –
cryptorchidism- sterility

42. • 2]scortum [thermoregulator]
• 3]Dartos tunic muscles
• 4]Comparments [ testes, epididymis ,
testicular end of spermatic cord
• In each testes there are 200 to 300
lobules [testicular lobules] –In each lobules
there are 1 to 4 convoluted loops called
seminiferous tubules.
• These tubules converge towards posterior
surface and form a network of irregular
tubules called rete testies.

44. Histology of testis[ internal structure ]
Coverings of the testis
• Externally covered with – fibrous connective
tissue called – tunica albuginea .
• Covered internally by tunica vascularies
• It is covered externally by tunica vaginalis.
• tunica vascularies
• tunica albuginea
• tunica vaginalis

51. Male sex accessory ducts
• 1] rete testis -the seminiferous tubules open
into spaces along the inner side of the testis
• 2] vasa efferentia - from rete testis the
number of small tubules emerge called vasa
efferentia. They fuse in the head of epididymis
• 3] epididymis- it is a single coiled tube about 6
meters long on the posterior surface of each
testis that leads to vasa deference.
• 4] vas deference-

52. Accessory or secondary glands

54. Spermatogenesis

55. centrioles

56. • Head of sperm
• It is oval
• It contains large nucleus
• It has highly condensed DNA matter
• Haploid number of chromosomes
• Acrosome contains the enzyme necessary for
fertilization.
• These hydrolytic enzymes that enables the
sperm to penetrate into the cytoplasm of the
egg.

57. Neck of sperm
• It has a pair of centrioles
• Proximal and distal centrioles [right angle to
each other]
• Plays an important role during the first
cleavage division of the zygote
• The axial filament that forms the tail piece of
the sperms is attached to the distal centriole.

58. Middle piece
it contains mitochondria in spiral form the
microtubules of the centriole .
ring centriole present between middle piece and
tail peace.
Contains respiratory enzymes which supply
energy for the movement of the sperm.

59. Tail piece or flagellum
• It consists of specific arrangement of
microtubules [9+2] which is typical of cillia
and flagella .It gives motility to sperms .
• It is modified flagellum
• It propels the spermatozoa in liquid medium
,and in female reproductive tract .

60. MICROTUBULES

61. gubernaculum

62. ‘Harmonal control of gametogenesis’
1] Oogenesis
2] Spermatogenesis

66. FERTILISATION
• It involves fusion of sperm nucleus and egg
nucleus .
• Formation of diploid cell – zygote [2n].
• Restores the diploid number.

67. • Fertilisation is internal
• Occurs high up in the fallopian tube
• During Insemination millions of sperms ,about
200-400 million are deposited in the vagina but
only one out of it fertilises the ovum .
• The motile sperms swim rapidly ,through the
cervix enter into the uterus and finally reach
the junction of the isthmus and ampulla.

68. • Fertilisation occurs only when, ovum
and sperm are transported
simultaneously to the ampullary –
isthmic junction.

69. Capacitation of sperm
• The sperms remain fertile for only about 12-
24 hrs. in the female reproductive tract .
• Vagina triggers the motility of sperms .
• Muscular contractions of uterus and oviduct
& viscous liquid secretions of oviduct further
increases the motility of sperm.
• Sperm undergoes number of changes called
as capacitation, to fertilise the ovum .

70. • Though the only one sperm fuses with the
ovum –
• Secretions of the thousands of sperm is
required to dissolve the outer lining of ovum
[corona radiata ]
• The fertilisation process involves the major
three steps-
• 1]penetration of sperm
• 2] activation of ovum
• 3] fusion of sperm and egg nucleus .

72. 1]Penetration of sperm
• Membrane covering the acrosomal region of
the sperm breaks .
• Release of sperm lysins [chemical substances]
from the acrosome .
• Chemicals in the sperm lycine –
• 1]Hyaluronidase- it is an enzyme that acts and
dissolves the ground substance that binds
follicle cells together [corona radiata ]
• Cells are glued together by hyaluronic acid .
• Corona radiata penetrating enzymes ,that
dissolves,

73. 1]Penetration of the sperm
• As the sperm reaches to the ovum it brings
about the following changes –
• 1] Breaking of the membrane covering the
acrosomal region.
• 2] release of chemical substances or enzymes
called sperm lysins from the acrosomes .

74. Contains of sperm lysins
1]Hyaluronidase
Enzyme that acts and dissolves the ground
substance that binds the follical cells of ovum
together and form corona radiata .
[cells are glued together by hyaluronic acid ]
2] Corona penetrating enzymes –dissolves the
corona radiata region .
3]Zona lysin or acrosine –an enzyme that helps
to digest the zona pellucida region.

75. 3] FERTILIN –proteins present on sperm surface
act as egg recognition protein to recognise
the gmts of the same species .
• As sperms come in contact with zona pellucida
,the acrosome turns inside out and releses
chemicals that dissolves the vitelline and
plasma membrane of the egg and point of
contact.
• Entry of sperm in egg cytoplasm
• Entry of more sperms is prevented by
chemical changes on the surface of the egg

77. • Steps involved
1] egg becomes activated and depolarisation of
its membrane occurs .
2] egg shows cortical reactions -,in which the
enzyme rich cortical grannules ,located just
below the egg membrane fuse with
membrane and release their contents into the
space between egg membrane and vitelline
membrane .
3] this hardened vitelline membrane is now
called as the fertilisation membrane .and the
plasma membrane is called previtelline
membrane.

78. 4] Ensures monospermy
and prevents polyspermy .
5] Activation of ovum- as the sperm enters the
ovum ,it gets activated and undergoes the
second meiotic division .
As a result of this ,the secondary oocyte produces a
haploid ovum and a polar body .the polar body
ultimetly degenerates,and the ovum contains
haploid number of chromosomes .
6] fusion of the sperm and the egg nucleus .
It forms the zygote ,restores the diploid number of
chromosomes .

79. Changes from egg to embryo

82. The mesoderm forms skeletal muscle, bone, connective tissue, the heart,
and the urogenital system

83. Implantation

89. Neurulation
• Neurulation. Neurulation refers to the folding
process in vertebrate embryos, which includes
the transformation of the neural plate into the
neural tube.

91. • The placenta is an organ that connects the
developing fetus to the uterine wall to allow
nutrient uptake, thermo-regulation, waste
elimination, and gas exchange via the
mother's blood supply; to fight against
internal infection; and to produce hormones
which support pregnancy.
• The placenta provides oxygen and nutrients
to growing fetuses and removes waste
products from the fetus's blood.

92. • Placenta
• Mother part --- decidua basalis
• Foetal part ----- chorion

93. Placenta-
The placenta is an organ that develops in mothers
uterus during pregnancy. This structure provides
oxygen and nutrients to growing baby and
removes waste products from your baby's blood.
The placenta attaches to the wall of mothers
uterus, and baby's umbilical cord arises from it.

94. • 1] placenta is a temporary connection
between the mother and the embryo.
• 2] placenta consists of foetal as well as
maternal tissue .
• After implantation chorionic villi of blastocyst
grow into endometrium [uterine mucosa ].
• The endometrial tissue undergoes the
changes and is known as decidua basalis
[maternal placenta]

95. • Placenta – consists of
• The foetal part – the chorion
• The maternal part – decidua basalis
• Human placenta is called as haemochorial
placenta because –chorionic villi spread deeper
into endometrium – they break down the uterine
mucosa ,including its epithelium ,connective
tissue and the endothelium lining ,thus coming
in contact with the maternal blood ,eventually
the blood vessels of the chorionic villi are bathed
in the mother’s blood ,this type of placenta is
called as haemochorial placenta.

96. The placenta allows the blood system of the
foetus and the mother to come into close
contact ,without mixing .
There is no blending of two blood supplies ,
The exchange takes place through the
membrane.

97. • Through placenta Foetus exchanges the
-respiratory gases
-Nutrients
-Excretory wastes
O2,CO2 ,nutrients ,wastes –moves by the
diffusion .

98. • Placenta acts as an ultra filter
• Soluble ,organic and inorganic substances
,harmones , antibodies against diptheria
,small pox ,measles ,scarlet fever etc. also
pass from mother to foetus.

99. Placenta acts as an endocrine gland
secreting a number of harmones.
• 1] human chorionic gonadotropin [hCG]
• 2] progesteron
• 3] human placental lactogen [hPL]
• 4] estrogen
• 5] relaxin

100. Umbilical cord
• In placental mammals, the umbilical cord
(also called the navel string, birth cord or
funiculus umbilicalis) is a conduit between the
developing embryo or fetus and the placenta.

103. Development of human embryo

108. These are paired structures
Contain glandular tissue
Contain large amount of fat
Each gland consists of about 15 to 25 mammary
lobules .
Each with its lactiferous duct called as
lactiferous duct that emerges in the nipple.