This document provides an overview of human reproduction. It discusses: 1. The male and female reproductive systems, including the testes, ovaries, and other primary and secondary sex organs. 2. The processes of gametogenesis, or the formation of eggs and sperm, which takes place in the ovaries and testes. 3. Spermatogenesis, the process by which sperm are produced in the testes through spermatocytogenesis and spermiogenesis. 4. Puberty, the stage of sexual maturity when external sex characteristics appear in girls around ages 11-14 and boys around ages 14-16.

1. STD-12 BIOLOGY
CHAPTER- 3
HUMAN
REPRODUCTION
Sanjay Siddhapura
M.Sc., B. Ed., GSET, GPSC.

2. INTRODUCTION
• Humans are sexually reproducing and viviparous.
• The reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms
in males and ovum in females.
• Transfer of sperms into the female genital tract (insemination).
• Fusion of male and female gametes (fertilisation) leading to formation of zygote.
• This is followed by formation and development of blastocyst and its attachment to the uterine
wall (implantation).
• Embryonic development (gestation) and delivery of the baby (parturition).
• You have learnt that these reproductive events occur after puberty.
• There are remarkable differences between the reproductive events in the male and in the female,
for example, sperm formation continues even in old men, but formation of ovum ceases in
women around the age of fifty years.

3. HUMAN REPRODUCTIVE SYSTEM
• Primary sex organs produce gametes and also secrete sex hormones.
• Secondary sex organs are important in reproduction, but do not produce gametes or sex hormones.
• By accessory sex characters both sexes can be distinguished externally but do not directly play any role in
reproduction.

4. Puberty
• The age of sexual maturity is called
puberty. External or accessory sex
characters first appear in puberty.
• Puberty occurs in girls at the age of
11 to 14 years.
• Puberty occurs in boys at the age of
14 to 16 years. Child

5. MALE REPRODUCTIVE SYSTEM
• The male reproductive system is located in
the pelvis region.
• Male reproductive system of man consists’
of paired testes, accessory glands, a duct
system, external genitalia and penis.
• The testes are situated outside the
abdominal cavity within a pouch called
scrotum.
• The scrotum helps in maintaining the low
temperature of the testes (2–2.5o C lower
than the normal internal body temperature)
necessary for spermatogenesis.

6. Testes
• Testes are the primary male sex organs.
• Testis produces spermatozoa and secretes the male sex
hormone testosterone.
• In mammals, the testes are located in the extra-abdominal
scrotal sacs because maturation of sperm needs low
temperature.
• The temperature in scrotum is 2 to 4°C below the
temperature of abdominal cavity.
• In adults, each testis is oval in shape, with a length of
about 4 to 5 cm and a width of about 2 to 3 cm.
• The testis is covered by a dense covering.

7. • Each testis has about 250 compartments called testicular
lobules.
• Each lobule contains one to three highly coiled
seminiferous tubules in which sperms are produced.
They are approximately 750 seminiferous tubules present.
• Each seminiferous tubule is lined on its inside by two
types of cells called male germ cells (spermatogonia) and
Sertoli cells.
• The male germ cells undergo meiotic divisions finally
leading to sperm formation.
• Sertoli cells provide nutrition to the germ cells.
• The regions outside the seminiferous tubules called
interstitial spaces, contain small blood vessels and
interstitial cells or Leydig cells.
• Leydig cells synthesise and secrete testicular hormones
called androgens. Other immunologically competent cells
are also present.
Rete testis
Vasa efferentia
testicular

9. • The male sex accessory ducts include rete testis, vasa
efferentia, epididymis and vas deferens.
• All the seminiferous tubules in each testis open into a network
called rete testis leading to fine ductules called vasa efferentia.
• The vasa efferentia leave the testis and open into epididymis
located along the posterior surface of each testis.
• Epididymis
• Several tubes called vasa efferentia arise from rete testis and
conduct sperms into epididymis.
• Epididymis is an irregular, narrow and highly convoluted
tubule found on the inner surface of testis.
• Epididymis has three parts: anterior caput epididymis,
middle corpus epididymis and posterior cauda epididymis.
• Sperms achieve maturity and motility in epididymis.
• Epididymis stores the sperms temporarily.

10. • Vas deferens
• Vas deferens or sperm duct arises from cauda epididymis,
ascends to abdomen, passes over the urinary bladder and
receive the duct from seminal vesicle behind the urinary
bladder forming ejaculatory duct.
• Ejaculatory duct passes through the prostate to open into
urethra shortly after its origin from urinary bladder.
• The urethra receives rite ducts of prostate and Cowper’s
gland (bulbourethral gland) pass through penis and
opens to outside.
• Seminal vesicles
• Seminal vesicles (Uterus masculinus) are situated at the
junction of vas deferens and prostate gland. They are
narrow, long pouches with muscular tissue on their wall.
• About 70% of the semen is seminal fluid produced by
seminal vesicles.
• Seminal Fluid : Seminal fluid has a pH of about 7.4 and
contains fructose, citrate, ascorbic acid, prostaglandins and
various enzymes.
• The fructose is a source of energy for the spermatozoa.

11. • Prostate Gland
• Prostate is situated around the first part of the urethra. It contains prostatic utricle and acini and covered by a
capsule.
• Enlargement of prostate results in prostatitis, urination is difficult or impossible.
• Prostatic Fluid: Prostatic secretion forms about 20% of the volume of semen.
• It is slightly acidic, pH 6.5 due to the presence of citric acid.
• Prostatic secretion contains substances important for sperm mobility notably albumin and proteolytic
enzymes fibrinolysin and fibrinogenase.
• Cowper’s glands (bulbourethral glands)
• Cowper’s glands are present in male mammals.
• Cowper’s glands are yellow in colour.
• These are also known as bulbourethral glands, situated beneath bladder and behind the urethra.
• Cowper’s glands open into urethra before entering into penis.
• Cowper’s Fluid : Secretion of cowper’s gland is slightly alkaline and is produced during sexual stimulation.
• Cowper’s gland secretion acts as a lubricant for the glans penis. It also neutralizes any urine in urethra.

12. • Urethra is a thick-walled muscular duct and it is a
common passage for both urine and semen and called
urinogenital duct.
• Urethra traverse and opens at the tip of the penis as
the male urinogenital aperture.
• Penis
• Penis is the copulatory organ. It is vascular, spongy
and erectile structure.
• It has glans penis at tip covered with a fold of skin
called prepuce.
• Penis contains three longitudinal columns of spongy
erectile tissue which becomes filled with blood during
sexual excitement.
• Surrounding the urinogenital duct is corpus
spongiosum and above it lie two corpora cavernosa.
• Penis serves to transmit sperms into the vaginaof the
female during sexual intercourse.
Urethra

13. FEMALE REPRODUCTIVE SYSTEM
• Female reproductive system consists of the ovaries, oviducts (fallopian tubes), uterus,
cervix, vagina, accessory genital glands, mammary glands, etc.

14. Ovary
• The ovary is the primary female sex organ. The ovaries are located one
on each side of the lower abdomen.
• Each ovary is about 2 to 4 cm in length and is connected to
• the pelvic wall and uterus by ligaments.
• Ovary produces ova and secretes female sex hormones viz., estrogens
and progesterone.
• The ovary remains attached to the abdominal wall by a ligament called
mesovarium.
• The ovary is solid, the blood vessels and nerve enter ovary at hilus.
• Ovary is covered by a cubical epithelium called the germinal
epithelium.
• Ovary contains connective tissue, stroma composed of an outer dense
layer called cortex and an inner loose layer known as medulla.
• Cortex contains many small and large, spherical or oval ovarian
follicles. A fully matured follicle is called Graafian follicle.

15. • Graafian follicle contains a large central follicular cavity
or antrum with a fluid called liquor folliculi.
• The follicle cells lining the cavity are termed membrane
granulosa.
• The oocyte of mammal is enclosed in a perforated
membrane called zone pellucida.
• Next to zona pellucida, cells of inner margin of discus
proligerous (cumulus) present a characteristic radial
arrangement and is termed corona radiate.
• Graafian follicle secretes estrogen in the blood.
• Discharge of a mature ovum from Graafian follicle is
known as ovulation
• After ovulation, a raptured follicle turns into a
yellowish solid mass of cells called corpus luteum
• Corpus luteum secretes the female hormone,
progesterone.

16. • The oviducts (fallopian tubes), uterus and vagina constitute the female accessory ducts.
• Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the
uterus.
• The part closer to the ovary is the funnel-shaped infundibulum.
• The edges of the infundibulum possess finger-like projections called fimbriae, which help in
collection of the ovum after ovulation.
• The infundibulum leads to a wider part of the oviduct called ampulla.
• The last part of the oviduct, isthmus has a narrow lumen and it joins the uterus.

17. Uterus
• The uterus is single and it is also called womb.
• The shape of the uterus is like an inverted pear.
• It is supported by ligaments attached to the
pelvic wall.
• The uterus opens into vagina through a narrow
cervix.
• The cavity of the cervix is called cervical canal
which alongwith vagina forms the birth canal.
• The wall of the uterus has three layers of tissue.
The external thin membranous perimetrium,
middle thick layer of smooth muscle,
myometrium and inner glandular layer called
endometrium that lines the uterine cavity.
• The endometrium undergoes cyclical changes
during menstrual cycle while the myometrium
exhibits strong contraction during delivery of the
baby.

18. Vagina
• Uterus opens into an elastic muscular tube called vagina.
• The vagina is lined by a stratified squamous epithelium with out any glands.
• During reproductive life the vagina contains Lactobacillus acidophilus which keeps the vaginal pH
between 4.9 and 3.5 by producing lactic acid from glycogen.
• Vagina receives semen from male during mating.
• During childbirth, it conveys the child outside.
• Bartholin’s gland: On either side of vaginal orifice is a greater vestibular gland or Bartholin’s
gland.
• Bartholin’s gland occurs in female mammals and helps in vestibular lubrication.
• Bartholin’s gland of female corresponds to bulbourethal gland (Cowper’s gland) of the male).
• The hymen is normally ruptured during female’s first copulation.

19. • The female external genitalia include mons
pubis, labia majora, labia minora, hymen and
clitoris.
• Mons pubis is a cushion of fatty tissue covered
by skin and pubic hair.
• The labia majora are fleshy folds of tissue,
which extend down from the mons pubis and
surround the vaginal opening.
• The labia minora are paired folds of tissue
under the labia majora.
• The clitoris is a tiny finger-like structure which
lies at the upper junction of the two labia
minora above the urethral opening.
• Hymen : The hymen is a thin mucous
membrane that stretches across the opening of
the vagina.
• The hymen is often torn during the first coitus
(intercourse). Bartholin’s gland
inside the vagina

20. MAMMARY GLANDS
• A functional mammary gland is characteristic of all
female mammals.
• The mammary glands are paired structures (breasts) that
contain glandular tissue and variable amount of fat.
• The glandular tissue of each breast is divided into 15-20
mammary lobes containing clusters of cells called
alveoli.
• The cells of alveoli secrete milk, which is stored in the
cavities (lumens) of alveoli.
• The alveoli open into mammary tubules.
• The tubules of each lobe join to form a mammary duct.
Several mammary ducts join to form a wider mammary
ampulla which is connected to lactiferous duct through
which milk is sucked out.

21. GAMETOGENESIS
• The primary sex organs – the testis in the males and the ovaries in the females – produce gametes,
i.e, sperms and ovum, respectively, by the process called gametogenesis.
• Formation of eggs & sperm from germ cells is known as Gametogenesis.
• FSH (Follicle stimulating hormone) of pituitary gland stimulate the gametogenesis.
• Vitamin-E (Fertility vitamin) and vitamin -A are essential for gametogenesis.
• Healthy gametes are produced by vitamin-A.
• Deficiency of vitamin-E causes sterlity.
• Due to deficiency of vitamin-A gametes remain less active.
• Germinal epithelium of gonads have primordial germ cells. These repetedly divides to form
gametes.
• PGC (primordial germ cells) are produced in extragonodial tissue normally placenta.
• Normally gamete formation have 3 steps
• (i) Multiplication stage (ii) Growth stage (iii) Maturation stage

22. SPERMATOGENESIS
• In most of animals, spermatogenesis occurs in testes.
• In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis
that begins at puberty.
• Mammalian testes contains seminiferous tubules.
• Seminiferous tubules are lined by germinal epithelium internally.
• Some special type cells are found in germinal epithelium known as primordial Germ cells .
• These cells divide & produces premature sperms also known as spermatogonia (sing.
spermatogonium).
• Sertoli cells are also found in germinal epithelium.
• Presence of sertoli cells is the unique character of mammalian testes.
• Sperm are stored and kept inactive in epidydymis.
• Sperm formation have 2 stages (a) Spermatocytosis (b) Spermiogenesis

24. (a) SPERMATOCYTOSIS
• Formation of spermatid from primordial germ
cells. It have 3 stages.
• (i) Multiplicative stage (ii) Growth stage
(iii) Maturation stage
• (i) Multiplicative stage:
• Primordial cells repeatedly divides and
produces large number of spermatogonia.
• Primordial germ cells (2n - 44xy) regularly
divides and produces spermatogonia.{A type (44
xy)}.
• These A type spermatogonia regularly undergo
mitotic division. So they are also called as stem
spermatogonia. It produces B spermatogonia.

25. (a) SPERMATOCYTOSIS
• (ii) Growth stage : In this spermatids gain
nutrients from sertoli cells and grows in size.
• B spermatogonia (44 xy) now goes to the sertoli
cells and takes up nutrition after certain limited
growth they are called as primary spermatocyte
(44 xy).
• (iii) Maturation stage : In this primary
spermatocytes undergo meiosis. After meiosis-I
secondary spermatocytes are formed.
• After meiosis-II four haploid spermatids are
formed. Primary spermatocyte divides by meiosis-I
and produces secondry spermatocytes. They are
haploid.
• These are of 2 types on the basis of chromosome
number i.e. 23 + x and 23 + y (both 50% each).
• They further divides by meiosis-II and produces
four spermatids (23 + x, 23 + x, 23 + y, 23 + y).
Multiplicative
stage
Growth
stage
Maturation
stage
Maturation
stage

26. (b) SPERMIOGENESIS OR SPERMATOLEOSIS
• Formation of sperm from spermatid is called Spermiogenesis. It involves following developments.
• Nucleus of spermatid move to one end, chromatin undergo condensation. Nucleus becomes light
in weight and aquires spindle shape.
• Many golgi vesicle collects above the nucleus. Few vesicles develops a granule inside them, this
granule is known as proacrosomal granules (proacroblast).
• All proacroblasts fuse with each other & form a large vesicle, which is known as acroblast.
Granule of acroblast is called as Acrosomal granules. Acroblast collects on the nucleus.
• Cytoplasm of spermatid moves backward, so plasma membrane shrinks & attach with acroblast &
nucleus and head of sperm is formed.
• Two centrioles of spermatid arrange in perpendicular manner, just below to nucleus. Distal
centriole produces axonema. All mitochondria of spermatid arranged spirally around the
Axonema. This arrangement form the middle part of sperm.
• Axonema elongates & tail of sperm is formed.

28. Hormonal Regulation of Spermiogenesis
• The hypothalamus releases gonadotropin-releasing hormone (GnRH)
• GnRH stimulates the anterior pituitary to secrete FSH and LH
• FSH causes sustentacular (Sertoli) cells to release androgen-binding protein (ABP)
• LH stimulates interstitial (Leydig) cells to release testosterone
• ABP binding of testosterone enhances spermatogenesis
• Feedback inhibition on the hypothalamus and pituitary results from rising levels of testosterone and
increased production of inhibin.
• Two types of hormones are secreted by sertoli cells-
• (A) AMH (anti mularian hormone) - This hormone inhibits development of female genital organs in
male embryo. Although some vestigeal female genital organs persist in male.
• Eg. (i) Seminal vesicle/uterus masculinus - it is a vestigeal of part oviduct (mularian duct).
• (ii) Prostatic utricle/vagina masculinus - it is a vestigeal part of vagina.
• (B) Inhibin hormone - It inhibits the secretion of FSH, and controls the production of sperms.
• Sertoli cells also produces androgen binding proteins.

29. Testosterone
• Synthesized from cholesterol
• Necessary for fetal development of male external genitalia
• Increased levels of testosterone at puberty are responsible for further growth of male genitalia and
for the development and maintenance of male secondary sex characteristics
• Stimulates protein synthesis and accounts for the greater muscular development of the male
• Is the basis of libido in both males and females
• Stimulates development of male secondary sexual characteristics including:
• -Appearance of pubic, axillary, and facial hair
• -Enhanced growth of the chest and deepening of the voice
• -Skin thickens and becomes oily
• -Bones grow and increase in density
• -Skeletal muscles increase in size and mass

31. Structure Of A Sperm
• A plasma membrane envelops the whole body of sperm.
• It is a microscopic structure composed of a head, neck, a middle piece and a tail.
• (1) Head - Head contains two structures (a) Acrosome (b) Nucleus.
• Acrosome is a vesicle like double membranous structure which has hydrolytic enzymes. These
are combinely known as spermlysin.
• These enzymes help in penetrat ion of egg.
• Mammalian acrosome has mainly hyaluronidase & proacrosine enzyme. Both are combinely
known as acrosomine.
• Proacrosine is an inactive enzyme, but when it comes in contact with egg, it converts into active
acrosine.
• These membranes of golgibody left on acrosome cap are called as Galea capitis. A space
between acrosome & nucleus is known as perforatorium.

32. • (2) Middle piece- Its anterior part is narrow & called as neck of sperm. It has two
centrioles.
• In middle piece many mitochondria are arranged spirally around to axonema. which
produce energy for the movement of tail that facilitate sperm motility essential for
fertilisation.
• This spiral sheath of mitochondria around the axonema is known Nebenkern
sheath.
• Basal part of head & middle piece has a thin layer of cytoplasm which is called as
Manchette.
• (3) Tail - It is a long flagellum, its basal body is distal centriole.
• In humans sperm formation is completed in 74 days.
• The human male in one ejaculation 4 ml semen have about 200 to 300 million
sperms during a coitus of which, for normal fertility, at least 60 per cent sperms must
have normal shape and size and for at least 40 per cent of them must show vigorous
motility.
• If sperm count is less = Oligospermia.
• If there are dead sperms = Necrospermia.
• If there are no sperm = Azoospermia.

33. • Sperms released from the seminiferous tubules, are transported by the accessory ducts.
• Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for
maturation and motility of sperms.
• The seminal plasma along with the sperms constitute the semen.
• The functions of male sex accessory ducts and glands are maintained by the testicular
hormones (androgens).

34. OOGENESIS• Oogenesis is initiated during the embryonic development stage
when a couple of million gamete mother cells (oogonia) are
formed within each fetal ovary; no more oogonia are formed
and added after birth.
• These cells start division and enter into prophase-I of the
meiotic division and get temporarily arrested at that stage, called
primary oocytes.
• Each primary oocyte then gets surrounded by a layer of
granulosa cells and then called the primary follicle (Figure 3.7).
• A large number of these follicles degenerate during the phase
from birth to puberty.
• Therefore, at puberty only 60,000-80,000 primary follicles are
left in each ovary.
• The primary follicles get surrounded by more layers of
granulosa cells and a new theca and called secondary follicles.
• The secondary follicle soon transforms into a tertiary follicle
which is characterised by a fluid filled cavity called antrum.
Secondary
follicle

35. • The theca layer is organised into an inner theca interna
and an outer theca externa.
• The primary oocyte within the tertiary follicle grows in
size and completes its first meiotic division.
• It is an unequal division resulting in the formation of a
large haploid secondary oocyte and a tiny first polar
body (Figure 3.8b).
• The secondary oocyte retains bulk of the nutrient rich
cytoplasm of the primary oocyte.
• The tertiary follicle further changes into the mature
follicle or Graafian follicle.
• The secondary oocyte forms a new membrane called
zona pellucida surrounding it.
• The Graafian follicle now ruptures to release the
secondary oocyte (ovum) from the ovary by the process
called ovulation.

36. OOGENESIS (only for information)
• Formation of ova in ovary is called oogenesis.
• It also have similar stages like sperm formation. i.e. (a) Multiplicative, (b) growth,
(c)maturation & differentiation.
• (A) Multiplicative stage :
• Under the influence of FSH the primordial germ cells regularly divides and produces couple
of million number of gamete mother cells (oogonia (2n)).
• This stage is completed in early embryonic stage in most of the mammals in which number
of developing egg cell increases. No more oogonia are formed and added after birth.
• (B) Growth Stage : Many changes occurs during growth phase in oogonia.
• All these changes are divided in two substages by Raven.
• (1) Previtellogenesis (2) Vitellogenesis

37. • (1) Previtellogenesis
• Karyoplasm increases in oogonia. DNA activity increases & DNA rapidly produces
(transcribes) different types of RNA. Due to these changes nucleus of egg become large in size.
The large nucleus of egg is now known as Germinal vesicle.
• The rate of protein synthesis in cytoplasm increases and different types of proteins and
enzymes are formed.
• Mitochondria, Golgibodies and ER arranges in a ring which surrounds to nucleus. This ring is
• known as Balbiani ring or vitelline ring.
• Vitelline membrane is formed by golgibody. Golgi bodies also produces cortical granules.
These are covered with unit membrane & filled by mucopolysaccharide. At the time of
fertilization cortical granules forms the fertilization membrane.
• A space is present between the plasma membrane and vitelline membrane, it is known as
perivitelline space. A fluid is filled in this space which is known as Perivitelline fluid.

38. • (2) Vitellogenesis
• Yolk is the stored food. It is stored for the use of future embryo.
• The yolk which is formed by liver is soluble and liquid. The mitochondria of egg, converts it
into insoluble and viscous form by the help of kinase enzymes. After growth stage primary
oocytes are formed.
• C) Maturation stage and Differentiation stage :
• The primary oocyte now undergo meiosis there occurs unequal meiosis.
• After meiosis-I one large secondary oocyte and small first polar body is formed.
• Secondary oocyte becomes quiescent (dormant) and it starts further division only after the
beginning of fertilization.
• Meiosis-II is also unequal.
• So finally one functional ovum and 3 polar bodies are formed.

39. MENSTRUAL CYCLE
• Menstrual cycle is the cyclic changes in the reproductive tract of primate females e.g.
monkeys, apes and human beings.
• Menstruation is the periodic shedding of the endometrium of the uterus with bleeding.
• In healthy women, menstruation occurs at intervals of about 28 days.
• The first menstruation begins at puberty and is called menarche. Menarche is the starting
of menstruation in girls at about 13 years.
• In human beings, menstrual cycles ceases around 50 years of age; that is termed as
menopause.
• In human females, menstruation is repeated at an average interval of about 28/29 days, and
the cycle of events starting from one menstruation till the next one is called the menstrual
cycle.
• Cyclic menstruation is an indicator of normal reproductive phase and extends between
menarche and menopause.
• One ovum is released (ovulation) during the middle of each menstrual cycle.

40. • Menstrual cycle consists of three phases-
• (a) Menstrual Phase,
• (b) Proliferative Phase (follicular phase) and
• (c) Secretory Phase (luteal phase).
• (a) Menstrual Phase :- The cycle starts with the
menstrual phase, when menstrual flow occurs and it lasts
for 3-5 days.
• The menstrual flow results due to breakdown of
endometrial lining of the uterus and its blood vessels
which forms liquid that comes out through vagina.
• Menstruation only occurs if the released ouvm is not
fertilised.
• Lack of menstruation may be indicative of pregnancy.
• However, it may also be caused due to some other
underlying causes like stress, poor health etc.
MENSTRUAL CYCLE
Proliferative Phase
(follicular phase)-6 to14
Secretory Phase
(luteal phase).
15-28 days

41. • (b) Proliferative Phase (follicular phase)
• Proliferative phase (5th to 14th day) consists of growth of endometrium of uterus, fallopian
tube and vagina.
• In ovary, a Graafian follicle grows, matures and secretes estrogen during this phase.
• Endometrium of uterus regenerates through proliferation. These changes in the ovary and the
uterus are induced by changes in the levels of pituitary and ovarian hormones.
• The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase,
and stimulates follicular development as well as secretion of estrogens by the growing follicles.
• Both LH and FSH attain a peak level in the middle of cycle (about 14th day). Rapid secretion
of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of
Graafian follicle and thereby the release of ovum (ovulation).
MENSTRUAL CYCLE

42. (c) Secretory Phase (luteal phase 15-28 days)
• The subsequent 14 days in which corpus luteum is active is referred to as the secretory phase.
• The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of
the Graafian follicle transform as the corpus luteum.
• Progesterone secreted by corpus luteum is active during secretory phase, which is essential for
maintenance of the endometrium.
• The uterine endometrium and glands grow further during secretory phase.
• Such an endometrium is necessary for implantation of the fertilized ovum and other events of
pregnancy.
• At the end of secretory phase, corpus Interim degenerates in the ovary, progesterone secretion fails,
the overgrown uterine endometrium breaks down and menstruation takes place.
• During pregnanacy all events of the menstrual cycle stop and there is no menstruation. In the
absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the
endometrium leading to menstruation, marking a new cycle.

44. ESTROUS CYCLE
• The estrous cycle consists of cyclic changes in the female reproductive system of non-
primate mammals
• There is no menstruation at the end of estrous cycle.
• The estrogen level in blood increases resulting strong sex urge in the female. This is called
“period of heat”.
• The estrous cycles run only during the breeding season.
• The estrous cycles remain suspended in female during non-breeding season.
• The suspension of estrous cycles is called the state of anestrum.
• Those animals that have only a single estrous during the breeding season are called
monoestrous, e.g., Dog, fox, deer, bat, etc.
• The animals that have a recurrence of estrous during breeding season are called
polyestrous, e.g., Mouse, squirrel, cow, sheep, pig, horse, etc.

46. FERTILISATION AND IMPLANTATION
• During copulation (coitus) semen is released by the penis into the vagina (insemination).
• The phenomenon of sperm activation in female genital tract in mammals is known as
capacitation. It occurs in 5-6 hours. Finally sperms reach ampulla of oviduct & fuses to ovum.
• The motile sperms swim rapidly, pass through the cervix, enter into the uterus and finally reach
the junction of the isthmus and ampulla (ampullary-isthmic junction) of the fallopian tube.
• The ovum released by the ovary is also transported to the ampullary-isthmic junction where
fertilisation takes place.
• Fertilisation can only occur if the ovum and sperms are transported simultaneously to the
ampullaryisthmic junction.
• This is the reason why not all copulations lead to fertilisation and pregnancy.
• The process of fusion of a sperm with an ovum is called fertilisation.

47. FERTILISATION• The process of fusion of a sperm with an ovum is
called fertilisation.
• During fertilisation, a sperm comes in contact with
the zona pellucida layer of the ovum (Figure 3.10) and
induces changes in the membrane that block the
entry of additional sperms.
• Thus, it ensures that only one sperm can fertilise an
ovum.
• The secretions of the acrosome help the sperm
enter into the cytoplasm of the ovum through the
zona pellucida and the plasma membrane.
• This induces the completion of the meiotic division
of the secondary oocyte.
• The second meiotic division is also unequal and
results in the formation of a second polar body
and a haploid ovum (ootid).
• Soon the haploid nucleus of the sperms and that of
the ovum fuse together to form a diploid zygote.

48. • (i) Sperms are produced and released in large amount : In humans 100 million
sperm/ml of semen are present. In one ejaculation 3 to 5 ml of semen are introduced
in female body at a time.
• (ii) Size of egg is very large as compaired to sperms : This increase the possiblities
of fusion. The size of egg about 0.1 mm while the sperm of human is of 60 .
• Fertilzin is found on the surface of egg. Antifertilizin are present on the surface of
sperms. It is a type of acidic protein. Fertilizin and antifertilizin are specific for each
species of animals (species specificity).
• By the reaction of both sperm and egg, both combine each other, this reaction is
known as agglutination.

49. GAMONS
• On the surface of egg and ova some hormones are also present. These hormones are known as
Gamons.
• Androgamones are found on surface of the sperms and Gyanogamones are found on the
surface of eggs.
• Androgamones are of two types –
• (i) Androgamone I – Conserves the energy of sperms, inactivates them.
• (ii) Androgamones II – Dissolves the viscous layers of egg and forms rough surface on the egg.
This helps in attachment.
• Gyanogamones are of two types – Present on egg surface
• (i) Gyanogamones I : When sperm reach to the surface of egg then the Gyanogamones I
neutrilize the androgamone I. Therefore sperm becomes more active.
• (ii) Gyanogamone II : This hormone makes the head of sperm viscous. And viscous sperm
head attaches strongly with rough surface of egg.

50. MONOSPERMY OR POLYSPERMY
• Generally only one sperm enters into a egg, this phenomenon is known as
Monospermy.
• Rarely more than one sperm enters in one egg, this phenomenon is known as
polyspermy.
• Polyspermy is of two types –
• (a) Pathological Polyspermy – All the nucleus of sperms fuse with nucleus of egg.
Egg degenerate and embryo do not develop.
• (b) Physiological polyspermy – Nucleus of only one sperm fuse with nucleus of the
egg and all the other sperms dies in cytoplasm of egg.
• The dead sperms in cytoplasm of egg are known as “merocyte”. It is commonly
found in polylecithal eggs of Reptiles, Aves, etc.

51. • The chromosome pattern in the human female is XX and that in the male is XY.
• Therefore, all the haploid gametes produced by the female (ova) have the sex
chromosome X whereas in the male gametes (sperms) the sex chromosome could be
either X or Y.
• 50 per cent of sperms carry the X chromosome while the other 50 per cent carry the Y.
• After fusion of the male and female gametes the zygote would carry either XX or XY
depending on whether the sperm carrying X or Y fertilised the ovum.
• The zygote carrying XX would develop into a female baby and XY would form a male
Sex determination of child

52. • Initial repeated mitosis divisions in zygote or
fertilized eggs are called as cleavage.
• The daughter cells formed by cleavage are
known as blastomeres.
• There is holoblastic ( Cleavage takes places in
whole egg) cleavage.
• The mitotic division starts as the zygote moves
through the isthmus of the oviduct called
cleavage towards the uterus (Figure 3.11) and
forms 2, 4, 8, 16 daughter cells called
blastomeres.
• The embryo with 8 to 16 blastomeres is called a
morula (Figure 3.11e).
• The morula continues to divide and transforms
into blastocyst (Figure 3.11g) as it moves further
into the uterus.
• The blastomeres in the blastocyst are arranged
into an outer layer called trophoblast and an
inner group of cells attached to trophoblast
called the inner cell mass.
IMPLANTATION

53. • The trophoblast layer then
gets attached to the
endometrium and the inner
cell mass gets differentiated as
the embryo.
• After attachment, the uterine
cells divide rapidly and covers
the blastocyst. As a result, the
blastocyst becomes embedded
in the endometrium of the
uterus (Figure 3.11h). This is
called implantation and it
leads to pregnancy.

54. PREGNANCY AND EMBRYONIC DEVELOPMENT
• After implantation, finger-like
projections appear on the trophoblast
called chorionic villi which are
surrounded by the uterine tissue and
maternal blood.
• The chorionic villi and uterine tissue
become interdigitated with each other
and jointly form a structural and
functional unit between developing
embryo (foetus) and maternal body
called placenta (Figure 3.12).

55. • The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of
carbon dioxide and excretory/waste materials produced by the embryo. The placenta is
connected to the embryo through an umbilical cord which helps in the transport of substances
to and from the embryo. Placenta also acts as an endocrine tissue and produces several
hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL),
estrogens, progestogens, etc. hCG, hPL and relaxin are produced in women only during
pregnancy.
• Human chorionic gonadotropin ( hCG) is a hormone produced by the placenta after
implantation. The presence of hCG is detected in some pregnancy tests ( HCG pregnancy strip
tests ).
• hPL, also known as human chorionic somatomammotropin, (a mouthful) is yet another
hormonal helper that prepares your breasts for lactation.
• In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary.
• Relaxin relaxes the body's muscles, joints, and ligaments. Not surprisingly, the effect centers on
the joints of the pelvis, allowing them to stretch during delivery. It also softens and lengthens
the cervix and helps relax smooth muscles in the uterus and elsewhere throughout the body.

56. • In addition, during pregnancy the levels of other hormones like estrogens, progestogens,
cortisol, prolactin, thyroxine, etc., are increased several folds in the maternal blood.
• Increased production of these hormones is essential for supporting the fetal growth,
metabolic changes in the mother and maintenance of pregnancy.
• Role of placenta :
• (i) Placenta acts as filter.
• (ii) Soluble inorganic, organic nutrients, hormones, antibodies against diphtheria, small
pox, scarlet fever, measles can pass through it.
• (iii) It helps in respiration, excreation.
• (iv) It produces - Human chorionic gonadotropin (HCG). HCG favours growth of
corpus leuteum.
• (v) Relaxin that helps in parturation by softening connective tissue of pubic symphysis.
• (vi) The umbilical cord connects foetus to placenta.

57. • Immediately after implantation, the inner cell mass (embryo) differentiates into an outer
layer called ectoderm and an inner layer called endoderm.
• A mesoderm soon appears between the ectoderm and the endoderm.
• These three layers give rise to all tissues (organs) in adults.
• It needs to be mentioned here that the inner cell mass contains certain cells called stem
cells which have the potency to give rise to all the tissues and organs.
• The human pregnancy lasts 9 months.

59. EMBRYO DEVELOPMENT
• In human beings, after one month of pregnancy, the embryo’s heart is formed.
• The first sign of growing foetus may be noticed by listening to the heart sound carefully
through the stethoscope.
• By the end of the second month of pregnancy, the foetus develops limbs and digits.
• By the end of 12 weeks (first trimester), most of the major organ systems are formed, for
example, the limbs and external genital organs are well-developed.
• The first movements of the foetus and appearance of hair on the head are usually observed
during the fifth month.
• By the end of 24 weeks (second trimester), the body is covered with fine hair, eye-lids
separate, and eyelashes are formed.
• By the end of nine months of pregnancy, the foetus is fully developed and is ready for
delivery.

60. PARTURITION
• The average duration of human pregnancy is about 9 months which is called the gestation period.
• Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus.
This process of delivery of the foetus (childbirth) is called parturition.
• Parturition is induced by a complex neuroendocrine mechanism.
• The signals for parturition originate from the fully developed fetus and the placenta which induce mild
uterine contractions called foetal ejection reflex.
• This triggers release of oxytocin from the maternal pituitary.
• Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates
further secretion of oxytocin.
• The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in
stronger and stronger contractions.
• This leads to expulsion of the baby out of the uterus through the birth canal – parturition. Soon after
the infant is delivered, the placenta is also expelled out of the uterus.

61. LACTATION
• The mammary glands of the female undergo differentiation during pregnancy and starts
producing milk towards the end of pregnancy by the process called lactation.
• This helps the mother in feeding the newborn.
• The milk produced during the initial few days of lactation is called colostrum which contains
several antibodies absolutely essential to develop resistance for the new-born babies.
• It is rich in calories and protein. It have various antibodies. It provides passive immunity to
newborn. Milk secretion is regulated by prolactin high level of oxytosin stimulate prolactin
production.
• Breast-feeding during the initial period of infant growth is recommended by doctors for
bringing up a healthy baby.
• Inhibitory peptide : It is present in milk. If milk remains in mammory glands (breasts) this
accumulated peptide inhibits milk production.

62. THANK
YOU