🌸 Chapter 2
Human Reproduction
🔷 INTRODUCTION
- Humans reproduce sexually.
- The process involves the formation
and fusion of gametes — a male gamete (sperm) and a female
gamete (ovum).
- This fusion forms a zygote,
which develops into an embryo and finally into a new individual.
- The reproductive system in
males and females consists of:
- Primary sex organs (gonads)
- Accessory ducts
- Glands
- External genitalia
🧔 MALE REPRODUCTIVE SYSTEM
🔹 Location
- Present in the pelvic region.
- Consists of:
1.
A
pair of testes
2.
Accessory
ducts
3.
Accessory
glands
4.
External
genitalia
Diagrams:
🔹 1. Testes
- Each testis is oval (4–5
cm long, 2–3 cm wide).
- Enclosed by a fibrous
covering (tunica albuginea).
- Located outside the abdominal
cavity in a scrotal sac → provides lower temperature (2–2.5°C
below body temp) essential for spermatogenesis.
🧬 Internal structure:
- Each testis has about 250
testicular lobules.
- Each lobule contains 1–3
seminiferous tubules.
- Seminiferous tubules are sites of sperm
formation.
Inside seminiferous tubules:
- Spermatogenic cells
(spermatogonia)
→ produce sperm.
- Sertoli cells (nurse cells) → provide nutrition and
secrete inhibin (controls sperm production).
In the spaces between tubules:
- Interstitial cells (Leydig
cells)
→ secrete testosterone, responsible for:
- Development of secondary
sexual characters
- Stimulation of spermatogenesis
🔹 2. Duct System
Sperm travels through a network of ducts:
Seminiferous tubules → Rete testis →
Vasa efferentia → Epididymis → Vas deferens → Ejaculatory duct → Urethra
✳️ Functions:
- Rete testis: Network collecting sperm from
seminiferous tubules.
- Vasa efferentia: Carry sperm to epididymis.
- Epididymis: Long, coiled tube where sperm
mature and are stored.
- Vas deferens: Connects epididymis to
urethra.
- Ejaculatory duct: Formed by the union of vas
deferens and duct of seminal vesicle — passes through prostate gland to
join urethra.
- Urethra: Common passage for urine
and semen; opens at the tip of penis.
🔹 3. Accessory Glands
1.
Seminal
Vesicles
o Secrete an alkaline fluid
rich in fructose (energy for sperm), prostaglandins, and clotting
proteins.
2.
Prostate
Gland
o Secretes a slightly acidic fluid
containing enzymes and calcium ions — enhances sperm motility.
3.
Bulbourethral
(Cowper’s) Glands
o Secrete mucus that lubricates
the penis and neutralizes urine traces in urethra.
Semen = Sperm + Secretions from all glands
🔹 4. External Genitalia
- Penis → Organ of copulation.
- Contains erectile tissue
that fills with blood during arousal.
- Tip: Glans penis
covered by foreskin (prepuce).
- Scrotum → Protective sac maintaining
testicular temperature.
👩 FEMALE REPRODUCTIVE SYSTEM
🔹 Structure
- Lies in the pelvic region.
- Consists of:
1.
A
pair of ovaries
2.
A
pair of oviducts (fallopian tubes)
3.
A
uterus
4.
A
vagina
5.
External
genitalia
6.
Mammary
glands
🔹 1. Ovaries
- Primary female sex organs.
- Functions:
- Produce ova (eggs).
- Secrete female sex hormones
— estrogen and progesterone.
- Attached to pelvic wall and
uterus by ligaments.
- Each ovary is covered by germinal
epithelium and has two regions:
- Outer cortex (contains follicles in
various stages)
- Inner medulla (contains blood vessels,
nerves)
🔹 2. Fallopian Tubes
(Oviducts)
- Each tube is 10–12 cm long,
extending from ovary to uterus.
- Three parts:
1.
Infundibulum: Funnel-shaped part near ovary with fimbriae
that collect released ovum.
2.
Ampulla: Broad middle part — fertilization
occurs here.
3.
Isthmus: Narrow region that joins the
uterus.
🔹 3. Uterus (Womb)
- Pear-shaped, muscular organ for
embryo development.
- Layers of uterine wall:
- Perimetrium: Outer thin membrane.
- Myometrium: Middle thick muscle —
contracts during childbirth.
- Endometrium: Inner glandular layer —
undergoes cyclic changes during menstrual cycle and implantation.
🔹 4. Cervix & Vagina
- Cervix: Narrow neck between uterus and
vagina.
- Cervical canal: Opens into vagina forming birth
canal.
- Vagina: Muscular tube; receives penis
during intercourse and serves as passage for menstrual flow and
childbirth.
🔹 5. External Genitalia
(Vulva)
Includes:
- Mons pubis – fatty tissue above vulva.
- Labia majora – outer folds protecting
genital organs.
- Labia minora – inner folds.
- Clitoris – small sensitive erectile
organ.
🔹 6. Mammary Glands
- Present in both sexes,
functional in females.
- Each gland has 15–20 lobes
containing alveoli.
- Alveoli secrete milk → stored in ampulla
→ reaches lactiferous ducts → nipple.
- During pregnancy, estrogen
and progesterone help development; prolactin and oxytocin
help milk secretion and ejection.
🔷 GAMETOGENESIS
🧬 1. Spermatogenesis
- Formation of sperms in seminiferous
tubules.
- Begins at puberty (under testosterone
influence).
Steps:
1.
Spermatogonia
(2n) → divide mitotically → primary
spermatocytes.
2.
Primary
spermatocyte (2n)
→ Meiosis I → secondary spermatocytes (n).
3.
Secondary
spermatocyte
→ Meiosis II → spermatids (n).
4.
Spermatids
→ Spermatozoa (sperms)
(process called spermiogenesis).
5.
Spermiation: Release of mature sperm into lumen
of tubules.
🧬 Structure of Sperm
- Head: Contains nucleus (DNA) +
acrosome (enzymes like hyaluronidase).
- Neck: Connects head and middle
piece.
- Middle piece: Has mitochondria → energy for
motility.
- Tail: Helps in swimming.
Each ejaculation releases ~200–300 million sperms.
🧬 2. Oogenesis
- Formation of ova in ovaries.
- Begins before birth:
- Oogonia (2n) → divide → primary oocytes
(2n) → enter prophase I → remain arrested till puberty.
- After puberty, every month:
- One primary oocyte
completes Meiosis I → forms:
- Secondary oocyte (n) (large cell)
- First polar body (small)
- Secondary oocyte → begins Meiosis II → stops
at metaphase II.
- Meiosis II completes only
after fertilization.
🔷 MENSTRUAL CYCLE
- Cyclic changes in the endometrium
every 28–29 days.
- Starts at puberty (menarche)
and ends at menopause (~50 years).
🔹 Phases:
1.
Menstrual
Phase (Day 1–5):
o Breakdown of endometrium → bleeding.
o Low levels of estrogen and
progesterone.
2.
Follicular
(Proliferative) Phase (Day 6–14):
o FSH stimulates follicle growth →
secretes estrogen → endometrium thickens.
3.
Ovulation
(Day 14):
o LH surge causes rupture of Graafian follicle
→ ovum released into fallopian tube.
4.
Luteal
(Secretory) Phase (Day 15–28):
o LH transforms empty follicle → Corpus
luteum → secretes progesterone → maintains endometrium.
o If fertilization fails → corpus
luteum degenerates → progesterone drops → menstruation begins again.
🔷 FERTILIZATION &
IMPLANTATION
🔹 Fertilization
- Takes place in ampulla of fallopian
tube.
- Steps:
1.
Sperm
reaches ovum.
2.
Acrosomal
reaction: Enzymes
help sperm penetrate zona pellucida.
3.
Fusion
of sperm and ovum membranes.
4.
Formation
of zygote (2n) → restores diploid chromosome number.
🔹 Cleavage and Embryo
Formation
- Zygote divides by mitosis → 2-cell,
4-cell, 8-cell → morula (solid ball) → blastocyst (hollow
ball).
- Blastocyst has:
- Outer trophoblast: Forms placenta.
- Inner cell mass: Forms embryo.
🔹 Implantation
- Occurs about 6–7 days
after fertilization.
- Blastocyst embeds into endometrium
→ establishes physical and physiological connection with mother.
🔷 PREGNANCY
- Duration: ~9 months (280
days).
- Placenta forms a lifeline
between mother and fetus.
🔹 Placenta Functions:
- Supplies oxygen and
nutrients to fetus.
- Removes wastes.
- Produces hormones:
- hCG (Human Chorionic
Gonadotropin)
- hPL (Human Placental Lactogen)
- Estrogen & Progesterone (for pregnancy maintenance)
🔷 PARTURITION (Childbirth)
- Expulsion of the baby from the
mother’s uterus after gestation.
- Triggered by neuroendocrine
mechanism:
- Fetal ejection reflex → Oxytocin
released → Uterine contractions → Baby expelled.
- After childbirth, placenta
is expelled.
🔷 LACTATION
- After delivery, prolactin
stimulates milk production.
- Oxytocin causes milk ejection.
- Colostrum: First milk → rich in antibodies
(IgA) → provides immunity to newborn.
🔷 SUMMARY CHART
|
Process |
Site |
Key Hormone |
Key Event |
|
Spermatogenesis |
Testis |
Testosterone |
Formation of sperms |
|
Oogenesis |
Ovary |
FSH, LH |
Formation of ovum |
|
Fertilization |
Ampulla |
— |
Fusion of gametes |
|
Implantation |
Uterus |
Progesterone |
Embedding of blastocyst |
|
Pregnancy |
Uterus |
hCG, hPL |
Growth of fetus |
|
Parturition |
Uterus |
Oxytocin |
Delivery |
|
Lactation |
Mammary gland |
Prolactin, Oxytocin |
Milk production and ejection |
🧠KEY POINTS FOR NEET &
CBSE
1.
Spermatogenesis
starts at puberty under testosterone.
2.
Fertilization
→ ampulla region of oviduct.
3.
Corpus
luteum → progesterone secretion.
4.
Menstrual
cycle → average 28 days.
5.
hCG
→ pregnancy hormone detected in urine.
6.
Placenta
→ exchange organ.
7.
Colostrum
→ first milk, antibodies-rich.
8.
Ovulation
→ triggered by LH surge.
9.
Spermiation
→ release of sperm into tubule lumen.
10.
Implantation
→ 6th–7th day after fertilization.
