This presentation is a part of Class 12 Biology (NCERT) syllabus. Contents of the presentation is also important for NEET-UG aspirants.

1. HUMAN REPRODUCTION
PRESENTED BY,
PRAMATHESH KALITA
BIOLOGY FACYLTY
VIDYARTHI ECUCATIONS PVT. LTD.
GUWAHATI, ASSAM (INDIA)

2. Learning outcome
➢ Reproductive system in males and females
➢ Gametogenesis (Spermatogenesis and Oogenesis)
➢ Structure of sperm and ovum
➢ Menstrual cycle
➢ Fertilization
➢ Development of zygote
➢ Implantation
➢ Extra embryonic membranes
➢ Placenta
➢ Parturition
➢ Lactation

3. Human reproductive system
• Humans show prominent
sexual dimorphism.
• Males and females
different from each other
by a no. of primary and
secondary sex characters
Primary sex character
Present since BIRTH
Secondary sex character
Developed after
attaining PUBERTY

4. PRIMARY SEX ORGAN
SECONDARY SEX ORGAN
Produce gametes and
sex hormones
Play important role in
reproduction
Testis
Ovary

5. Male reproductive system
Primary sex organ:
➢ Testis:
• Male gonad, site for sperm (male
gamete) production.
• Each testis is oval, about 4-5 cm in
length and 2-3 in width.
• Suspended in scrotum by spermatic
cord.
• Outermost covering of testis is called
tunica albuginea (fibrous membrane)
• Each testis is divided into 200-300
compartments called testicular lobules.
• Each lobule contains 1-3 highly
convoluted seminiferous tubule, blood
vessels and nerves embedded in loose
connective tissue. Male reproductive system

6. ➢ Scrotum:
• Tiny bag like structure of pigmented
skin arising from lower abdominal wall
and hanging between the legs.
• Lowers the temperature of testes about
2-2.5º C than internal body
temperature, essential for production of
sperm.
• Divided into left and right scrotal sacs
by muscular partition called septum
scrota.
• Testis originates in abdominal cavity,
but during the 7 months of
development, descends into respective
scrotal sacs through inguinal canal.
• Cryptochidism/Undescended testis
(When testis remain in abdominal cavity
at the time of birth)
LS of Human testis

7. ➢ Seminiferous tubule:
• Structural and functional unit of testis.
• Each seminiferous tubule is lined by two
types of highly specialized cells
1. Sertoli cells/Nurse cells: Provide
nutrition to the developing germ cells
2. Germ cells: Produces spermatogonia
• Region outside seminiferous tubule is
called interstitial space, containing
blood vessel and masses of cells called
Leydig cells/Interstitial cells.
• Leydig cells synthesise and secrete
testicular hormone, androgen.
• Leydig cells are endocrine in function
thus regulate and maintain male sex
characteristics.
Seminiferous tubule

8. Secondary sex organ:
➢ Accessory Duct System:
• These ducts store and transport sperm
from testis to outside through urethra.
Tubuli recti Rete testis Vasa
efferentia Epididymis Vas
deferens Urethra
• Sperms undergo physiological
maturation acquiring increased motility
and fertilizing capacity (capacitation) in
epididymis.
• Urethra originates from urinary bladder
and extends through the penis to its
external opening called urethral
meatus. Urethra carries urine from
bladder and spermatozoa from
Cowper’s and prostate gland. Accessory Duct System

9. ➢ Accessory Glands:
• Prostate gland: Secrets milky, slightly
alkaline fluid that contains lipid,
enzyme, citric acid etc. Released during
ejaculation, helps in neutralize the
acidic medium of vagina, making sperm
more active to swim.
• Seminal vesicle: Secrete mucus and
watery alkaline fluid contains
fructose(energy source for sperm).
Prostaglandin stimulates uterine
contraction for sperm movement.
Clotting proteins form temporary clot
after ejaculation.
• Cowper’s/Bulbourethral gland: Secrete
mucus and an alkaline fluid into
urethra. Mucus helps in lubrication of
penis and urinary acid in urethra.
➢ Semen:
Secretion of accessory sex gland and
mucus are added to sperm to
form semen/ seminal fluid.
• It provides medium for
transmission of sperm
• Nourish and activate sperm to
keep them viable & motile.
External Genitalia:
Penis is the external copulatory
organ. Tissue at the tip of penis
(corpus spongiosum), which
enlarged to form highly sensitive
glans penis covered by foreskin

10. Female reproductive system
Primary sex organ:
➢ Ovary:
• One pair of ovary produces female
gametes (ovum) and steroid hormones.
• Ovaries are almond shaped, lying in the
lower part of abdomen held to broad
ligament by double fold of peritoneum,
called mesovarium.
• 2-4 cm in length, connected by ovarian
ligament to uterus and by suspensory
ligament to lateral pelvic wall.
• Each ovary is covered by thin
epithelium enclosing ovarian stroma,
containing connective tissue, blood
vessels and mature follicles.
• Stroma is divided into Cortex and
Medulla.
Stroma contains many rounded
follicles called ovarian follicles,
which finally gives ovum.
Female pelvis showing
reproductive system

11. Secondary sex organ:
➢ Accessory Duct:
• Oviduct (Fallopian tube): Small tubes lying on either sides of uterus near
kidney. These tubes carry egg from ovary to uterus and also provides
appropriate environment for fertilization. It has four regions, i.e.
Infundibulum, Ampulla, Isthmus and the Uterine part.
• Infundibulum is broad, funnel shaped with motile finger like projections
called fimbriae. It helps in collection of ovum after ovulation.
• Ampulla is long, thin walled part, next to infundibulum where fertilization
takes place.
• Isthmus joins ampulla with uterus.
• Uterine part passes through uterine wall and communicates with uterine
cavity.
• Uterus is about 7.5 cm long and 5 cm wide, like an inverted pear in shape.
Supported by ligaments attached to pelvic wall. Lies between urinary bladder
and rectum. It composed of 3 layers of tissues

12. Outer perimetrium, Thin membranous
covering of uterus wall.
Middle myometrium, layer of smooth
muscle fibres, which contracts strongly
during delivery of the baby.
Inner endometrium, glandular layer with
blood vessels, undergoes cyclic
changes during menstrual cycle.
Uterus receives ovum from fallopian tube
and forms placenta for development
of foetus.
Cervix is the narrow entrance of uterus
into vagina. Cavity of cervix is called
cervical canal which along with vagina
forms birth canal.
Cervix has a strongest sphincter in its wall
and is normally blocked by plug of
mucus.
Vagina acts as receptacle for penis
during copulation, allowing
menstrual flow and serving as
birth canal during parturition. It
opens to exterior by an aperture
called vaginal orifice.
Female reproductive system

13. ➢ Accessory Glands:
• Bartholin’s gland: One pair on either
side of vaginal orifice. Small rounded
bodies correspond to Cowper’s gland of
male, secreting clear and viscous fluid
which serves as a lubricant during
copulation.
• Mammary gland: Paired structure.
Breasts are rounded, located over
pectoral muscle in front of thorax.
Glandular tissue of breast is divided
into 15-20 mammary lobes containing
mammary alveoli. Te cells of alveoli
secrete milk which is stored in cavities
of alveoli.
• Lactiferous sinuses store milk during
lactation. Mammary ducts join to form
mammary ampulla, connected to
lactiferous duct.
Mammary gland
External genitalia (Vulva):
Mons pubis, anterior most structure
Labia majora (boundary of vulva)
Labia minora (additional folds of
tissue)
Clitoris, erectile organ, homologous
to glans penis.
Hymen, membrane of vaginal orifice

14. Gametogenesis
Process of formation
and maturation of
haploid gametes from
the undifferentiated
diploid germ cells in
the gonads for sexual
reproduction is called
GAMETOGENESIS
Spermatogenesis
(Formation and
maturation of
SPERM)
Oogenesis
(Formation and
maturation of
EGG/OVUM)

15. Spermatogenesis
It is the process of formation and
maturation of spermatozoa/sperm
(n) inside testis, which originate
from primordial germ cell (PGC).
Process starts at puberty.
Phases:
1. Formation of spermatid
• Multiplication phase
• Growth phase
• Maturation phase
2. Spermiogenesis
3. Differentiation phase: Sperm
heads get embedded in sertoli cells
and are finally released from
seminiferous tubule by a process
of spermiation.

16. Hormonal regulation of Spermatogenesis
Spermatogenesis increases due to
significant increase in GnRH level at
the age of puberty.
Increased GnRH acts at anterior
pituitary and stimulates the
secretion of LH & FSH.
LH acts on Leydig cells, stimulating the
synthesis of androgen hormone,
which in turn stimulate
spermatogenesis. Androgen also
helps in maintaining secondary sex
characters.
FSH acts on Sertoli cells, stimulates the
secretion of some factors for
spermiogenesis.

17. Structure of Sperm (Spermatozoa)
A mature sperm is a microscopic tadpole shaped
structure. It has following parts
1. Head: Flat, oval with large haploid nucleus and a
small anterior cap like structure called
acrosome. Acrosome is formed from golgi
complex. It contains hydrolytic enzyme that
helps sperm to penetrate egg membrane during
fertilization.
2. Neck: Contains proximal centriole (first cleavage
of zygote), distal centriole (axial filament of
sperm).
3. Middle piece: Cylindrical part, containing
mitochondria providing energy for the
movement of sperm.
4. Tail: Long, slender, tapering part which gives
motility to sperm.
Structure of sperm

18. Oogenesis
• It is the process of formation and
maturation of egg/ovum (n) inside
ovary, which originate from
primordial germ cell (PGC).
• Process begins before birth i.e.
during embryonic developmental
stage but completed only after
fertilization.
• Phases:
• Multiplication phase
• Growth phase
• Maturation phase

20. • Process of formation and
maturation of follicles.
Folliculogenesis

21. Structure of Ovum (Egg)
• The ovum is rounded, non-motile cell.
• In human, ovum is alecithal (yolk free).
• Having abundant cytoplasm (ooplasm)
with a large nucleus, called germinal
vesicle carrying nucleolus at the
centre.
Membranes of ovum-
1. Vitelline membrane: Innermost, thin,
transparent, non-cellular membrane.
Secreted by follicular cells of ovum.
2. Zona pellucida: Middle, thin,
transparent membrane. Secreted by
follicular cells of ovum.
3. Corona radiata: Outermost, thicker
membrane, formed by rapidly
elongated follicular cells of ovum.

22. • Its a reproductive cycle of physiological
changes that occur in human fertile
female.
• First menstruation is called menarche
(at the age of 9-14 yrs).
• Last menstruation is called menopause
(at the age of 45-50 yrs).
• One ovum get released during the
middle of each menstrual cycle.
• Cycle generally consists of 28 days, but
sometimes may be as short as 15-20
days or as long as 45-50 days.
• Abnormal cycle length for prolong
period leads to infertility.
Menstrual cycle

23. Phase 1: Menstrual
1. Days: 1st – 5th day.
2. Breakdown of endometrial lining.
3. Losses about 40 ml of blood & 35
ml of serous fluid.
Phases of menstrual cycle
Phase 2: Follicular
1. Days: 5th – 13th day.
2. Rebuilding of endometrial lining.
3. FSH starts elevating, large no. of
follicles stimulated to develop.
4. Finally a single will mature
enough, namely GRAAFIAN
FOLLICLE.
5. Other follicles degenerate by
ATRESIA, due to the absence of
FSH receptor.
Phase 3: Ovulatory
1. Days: 14th day.
2. On 12th day, Estradiol level
reaches to its peak, stimulated
the synthesis of LH from anterior
pituitary.
3. FSH level attains threshold level.
4. Ovulation takes place on 14th day
(Depending on LH:FSH)
Phase 4: Secretory/Luteal
1. Days: 15th – 28th day.
2. Corpus luteum forms from
ruptured GRAAFIAN follicle after
about 36 hours of ovulation.
3. Progesterone level increases

25. Hormonal regulation of Menstrual cycle

26. • Process of fusion of sperm (n) and ovum (n) to produce a
diploid zygote (2n) is called FERTILIZATION.
• Fertilization leads to development of new individual.
Mechanism of Fertilization:
1. Encounter of sperm with ovum: Male discharges seminal
fluid containing about 4000 million of sperms into female’s
vagina during coitus (insemination), but only about 100s of
sperm can reach the fallopian tube brought about by
swimming movement of sperm.
2. Contact of sperm with ovum: Sperm produces a chemical
substance called anti-fertilizin and ovum produces fertilizin.
Both these sunstances form a chemical lock.
Fertilization

27. Diagrammatic representation of mechanism of Fertilization

28. 3. Acrosomal reaction: Acrosome of the sperm releases
acrosomal granules, containing a lytic enzyme namely
SPERMLYSIN . This enzyme causes degeneration of plasma
membrane of the egg and forming an acrosomal tubule that
penetrate the egg envelop and fuses with egg membrane.
4. Activation of ovum: After the entry of sperm nucleus into
the egg, the egg cytoplasm bulges out forming a fertilization
cone. After that vitelline membrane get separated from inner
plasma membrane leading to the formation of fertilization
membrane. This membrane prevents polyspermy.
5. Migration of pronuclei, Amphimixis: Male and female nuclei
before union is called Pronuclei.
After the formation of fertilization membrane, both
pronuclei migrates towards each other forming a diploid
zygote. This fusion is known as Amphimixis.

29. Significance of Fertilization:
1. Restore diploid number of chromosome.
2. Initiates cleavage.
3. Results in determination of sex of an embryo.
4. Introduces variation.
Union of male and female gamete
(SYNGAMY)
Intermixing of their cytoplasm
(PLASMOGAMY)
Fusion of male & female pronuclei
(KARYOGAMY)
Intermixing of their chromosome
(AMPHIMIXIS)

30. Unicellular zygote undergoes changes one after another to form an
EMBRYO. Sequence of changes are
1. Cleavage:
• Term was given by Von Baer.
• Progressive sub-division of zygote by mitotic division.
• Newly formed cells are called blastomeres.
• 16 cell stage is called morula.
Embryonic development
Cleavage Mitosis
Newly formed cells are Blastomeres Newly formed cells are Daughter cells.
Interphase absent. Only S-phase present Interphase is long, G1, S, G2 phases present.

31. • On the basis of amount of yolk,
Cleavage is of two types
Complete/Holoblastic Incomplete/Meroblastic
Whole egg divides Doesn’t occur in the part
where yolk is present.
Occurs only in
cytoplasmic part.
Equal holoblastic &
Unequal holoblastic
Discoidal & Superficial
Blatomeres are same
size. Eg. Homolecithal/
Isolecithal (Other
mammamls).
Discoidal – Birds,
reptiles
Blastomeres are of
unequal sizes. Eg.
Mesolecithal (Human)
Superficial - Insect
Transformation of zygote into Morula

32. 2. Blastula:
• Cells arrange themselves
towards the surface forming a
ball of cells called BLASTULA,
having a cavity called
Blastocoel.
• Outer layer form Trophoblast
which get attached to uterine
endometrium.
• Inner cell mass forms
embryonal knob that get
differentiated as embryo.
• Blastula enlarges to form
Blastocyst.
Blastula

33. 3. Implantation:
• After the formation of
blatocyst, the trophoblast layer
get attached to inner
endometrium & inner cell mass
differentiated as embryo.
• After that uterine wall divide
rapidly and covers the
blastocyst. As a result of which
blastocyst becomes embedded
in the endometrium of the
uterus.
Implantation

34. 4. Gastrula:
• Process of conversion of
blastula into gastrula is called
Gastrulation.
• Single layered cells of blastula
gets converted into 3 layered
cells in embryonic stage known
as germinal layers, including
Ectoderm (outer)
Mesoderm (middle)
Endoderm (inner).
• Archenteron/gut cavity present.
• Cells show morphogenetic
movement. Gastrula

35. • Zygote Morula
(Cleavage)
• Morula Blastula
(Blastulation)
• Blastula Gastrula
(Gastrulation)

36. Extra Embryonic Membranes:
• Yolk sac: Its main function is to absorb nutritive food from
uterine wall & to supply to the foetus which help the embryo to
settle in proper position.
• Amnion: After about 8 weeks of fertilization, amnion is
completely incorporated into connecting stalk which finally forms
umbilical cord. Embryo at this stage is called foetus, hanging in
amniotic fluid. It provides watery environment to the foetus for
movement as well as protecting the foetus from mechanical
injury.
• Chorion: From trophoblast several finger like projections develop
namely chorionic villi, gets attached to uterine endometrium. It
helps in respiration and excretion of developing foetus.
• Alantois: It connects embryo with placenta & provide
respiratory supply to the embryo.

38. Placenta
• It is a structure formed by the fusion of extra embryonic
membranes of foetus with uterine endometrium for the
purpose of physiological exchange of materials between
mother and foetus.
Function of Placenta:
1. It facilitates the supply of oxygen and nutrients to the
embryo.
2. It also facilitates removal of carbon dioxide and waste
materials produced by foetus.
3. Placenta is connected to the embryo through umbilical cord
which helps in transport of substances to and from the
embryo.

39. • Placenta acts as an important endocrine tissue as it produces
no. of hormones necessary for continuity of pregnancy as well
as normal development of the foetus.
Placental hormone:
1. Human chorionic gonadotropin (hCG):
• Stimulates ovary as well as anterior pituitary hormones &
thus maintaining estrogen and progesteron concentration.
2. Estrogen:
• Promotes development of mammary gland.
• Helps in enlargement of pregnant uterus.
3. Progesteron:
• Decreases contractibility and prevents pre mature release of
foetus.

40. 4. Human chorionic
somatotropin (hCS):
• Known as Plcental
lactogen.
• Promotes growth and
development of mammary
gland.
5. Relaxin:
• It inhibits ovulation.
• Promotes growth and
development of mammary
gland.

41. • In humans, pregnancy casts for 9 months (gestation period).
• After 1 month of pregnancy, foetus heart formed.
• By the end of 2nd month, foetus develops limbs and digits.
• By the end of 12 weeks, major organ system and external
genitalia are well developed.
• During 5th month, first movement of foetus and appearance of
hair can be observed.
• By the end of 24 weeks (Second trimester), body covered with
fine hairs, eyelids get separate and eyelashes are formed.
• By the end of 9 months, foetus becomes fully developed and
is ready for delivery.
Changes in Embryo

44. • Vigorous contraction of uterus at
the end of pregnancy causes
expulsion or delivery of the foetus,
known as Parturition.
• Its a complex neuro-endocrine
mechanism.
• Signal for parturition originates
from the fully developed foetus &
the placenta which induce mild
uterine contraction called foetal-
ejection reflex.
• Oxytocin is the main hormone that
promotes uterine contraction
causing expulsion of the baby.
Parturition

45. Role of estrogen & progesteron during parturition:
• Progesteron inhibits uterine contractibility during pregnancy,
thereby helping to prevent the pre mature release of foetus.
• Estrogen has tendency to increase uterine contractibility.
• Levels of both hormones almost same upto 7th month of
pregnancy. But from 7th month onwards, estrogen secretion
continues to increase while progesteron secretion remains
constant or even decreases slightly.
• Estrogen:Progesteron increases which is responsible for
increased contractibilty of uterus causing parturition.
• Relaxin hormone, secreted by placenta and pregnant uterus
relaxes pubic symphysis (joint between pelvic girdle). So more
space available for foetus to move out.

46. • It involves synthesis of milk, its
transport through alveolar cell
membrane and finally released from
mammary gland.
• Main function of lactation is to
provide nutrition and develop innate
immunity to the younger ones.
• Prolactin is the major hormone that
initiates milk synthesis. Its
concentration generally increases in
blood from 5th week of pregnancy till
the birth of the baby.
• 1st milk produced after child birth is
called colostrum (rich in higher
amount of WBCs and antibody IgA.
Lactation
Composition of Human
milk:
Constituent Percentage
Water 87.4%
Fat 4.3%
Lactose 6.8%
Milk protein
(Casein) 0.9%
Other proteins 0.6%