Reproduction in lower and higher animakls

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Human Reproduction

Human Male Reproductive System

The human male reproductive system consists of:

  • Testes
  • Accessory ducts
  • Accessory glands
  • External genitalia

I. Primary Sex Organs – Testes

a. Structure and Function

  • Testes are a pair of primary sex organs.
  • They are mesodermal in origin.
  • Their main function is the production of sperms.

b. Location

  • Testes are located outside the abdominal cavity in a pouch called the scrotum.

c. Development and Descent

  • Testes develop in the abdominal cavity during early foetal life.
  • Later, they descend into the scrotal sac through the inguinal canal.

d. Suspension

  • Testes are suspended in the scrotal sac by the spermatic cord.

e. Attachment

  • Testes are connected to the wall of the scrotum by a short fibromuscular band called the gubernaculum.

f. Shape and Size

  • Testes are oval in shape.
  • Approximate size:
    • Length: 4–5 cm
    • Width: 2–3 cm

g. Covering

  • The outermost covering of the testes is a fibrous membrane called the tunica albuginea.

II. Accessory Sex Organs

Accessory sex organs include:

  • Accessory ducts
  • Accessory glands

A. Accessory Ducts

1. Rete Testis

  • Seminiferous tubules of the testes form a network of tubules called the rete testis.
  • The rete testis opens into the vasa efferentia.

2. Vasa Efferentia

  • Vasa efferentia are 12–20 fine tubules.
  • They arise from the rete testis.
  • They carry sperms from the testes to the epididymis.

3. Epididymis

  • Epididymis is a long and highly coiled tube.
  • It is differentiated into:
    • Caput (upper part)
    • Corpus (middle part)
    • Cauda epididymis (lower part)
  • Sperms undergo maturation in the epididymis.

4. Vas Deferens

  • Each vas deferens travels upward into the abdominal cavity.
  • It loops over the ureter and opens into the urethra.
  • The vas deferens joins the seminal vesicle to form the ejaculatory duct.

5. Ejaculatory Ducts

  • Each ejaculatory duct passes through the prostate gland.
  • It opens into the urethra.

6. Urethra / Urogenital Duct

  • The urethra provides a common passage for urine and semen.
  • In males, the urethra is long and extends through the penis.
  • It opens outside through the urethral meatus or urethral orifice.

B. Accessory Glands

The accessory glands associated with the male reproductive system are:

  • Seminal vesicles (paired)
  • Prostate gland (unpaired)
  • Cowper’s glands / Bulbourethral glands (paired)

Functions of Accessory Glands

  • Protect gametes
  • Facilitate movement of sperms
  • Nourish sperms

III. External Genitalia

A. Penis

  • Penis is the male copulatory organ.
  • It is cylindrical and muscular.
  • It contains three bundles of erectile tissue:
    • Two lateral corpora cavernosa
    • One median corpus spongiosum

Glans Penis

  • The swollen tip of the penis is called the glans penis.

Foreskin / Prepuce

  • The glans penis is covered by a loose fold of skin called the foreskin or prepuce.

B. Scrotum

  • Scrotum is a loose pouch of pigmented skin located behind the penis.
  • It is divided into right and left scrotal sacs by a septum called the tunica dartos.

Functions of Scrotum

  • Maintains the testes at a temperature 2–3°C lower than body temperature.
  • This lower temperature is necessary for spermatogenesis.

Muscles Involved

  • Cremaster muscles and dartos muscles help move the testes closer to or away from the body.

Cryptorchidism

  • Failure of the testes to descend into the scrotum is called cryptorchidism.

Functions of Male Accessory Glands

I. Seminal Vesicles

  • Seminal vesicles are a pair of small fibromuscular pouches present on the posterior side of the urinary bladder.
  • They secrete an alkaline seminal fluid containing:
    • Fructose
    • Citric acid
    • Fibrinogen
    • Prostaglandins

Functions

  • About 60% of semen volume is formed by seminal fluid.
  • Fructose provides energy for sperm movement.
  • Fibrinogen helps in coagulation of semen after ejaculation.
  • Prostaglandins stimulate reverse peristalsis in the vagina and uterus, helping faster sperm movement toward the egg.

II. Prostate Gland

  • The prostate gland consists of 20–30 lobes.
  • It is located below the urinary bladder and surrounds the urethra.
  • It secretes a milky white alkaline fluid called prostatic fluid.

Composition

  • Contains:
    • Citric acid
    • Acid phosphatase
    • Various enzymes

Functions

  • Prostatic fluid forms about 30% of semen volume.
  • Acid phosphatase protects sperms from the acidic environment of the vagina.

III. Cowper’s Glands / Bulbourethral Glands

  • These are pea-sized glands located on either side of the membranous urethra.
  • They secrete a viscous alkaline mucus-like fluid.

Functions

  • Acts as a lubricant during copulation.

Semen

  • Semen is a viscous, alkaline, milky fluid ejaculated by the male reproductive system.
  • pH: 7.2–7.7
  • Volume per ejaculation: 2.5–4.0 mL
  • Contains approximately 400 million sperms.

Functions of Seminal Components

  • Fructose → Nourishes sperms
  • Calcium and bicarbonates → Neutralize acidity
  • Prostaglandins → Activate sperm movement

Path of Sperm

Seminiferous tubules → Rete testis → Vasa efferentia → Epididymis → Vas deferens → Ejaculatory duct → Urethra

Prostate Cancer

  • Prostate cancer is cancer of the prostate gland.
  • Men above 50 years of age with high daily fat consumption have a higher risk.

Symptoms of Prostate Cancer

Early stages usually show no symptoms. Advanced stages may show:

  • Weak or slow urinary stream
  • Frequent urination, especially at night
  • Blood in urine or semen
  • Erectile dysfunction (ED)
  • Pain in hips, back, chest or ribs
  • Weakness or numbness in legs or feet
  • Loss of bladder or bowel control
These symptoms are not specific only to prostate cancer and may occur in other conditions.

Histology of Testis

I. Coverings of Testis

Externally, the testis is covered by three layers:

a. Tunica Vaginalis

  • It is the outermost incomplete peritoneal covering.
  • Made up of connective tissue and epithelium.

b. Tunica Albuginea

  • It is the middle layer.
  • Formed by collagenous connective tissue.

c. Tunica Vasculosa / Vascularis

  • It is the innermost thin membranous vascular layer.

II. Internal Structure of Testis



  • Each testis is divided into about 200–300 testicular lobules by fibres from the tunica albuginea.
  • Each lobule contains 1–4 highly coiled seminiferous tubules.

Seminiferous Tubules

  • Each seminiferous tubule is internally lined by:
    • Stratified germinal epithelial cells (spermatogonia)
    • Large pyramidal Sertoli or sustentacular cells

Functions

  • Germinal epithelial cells undergo gametogenesis to form spermatozoa.
  • Sertoli cells provide nutrition to developing sperms.

Stages of Spermatogenesis

  • Primary spermatocyte (2n)
  • Secondary spermatocyte (n)
  • Spermatids (n)
  • Sperms (n)

Interstitial Cells (Leydig Cells)

  • Present between seminiferous tubules.
  • After puberty, these cells produce the androgen hormone testosterone.

Human Female Reproductive System

The human female reproductive system consists of internal genitalia and external genitalia.


Internal Genitalia

  • Ovaries
  • Oviducts / Fallopian tubes
  • Uterus
  • Vagina

External Genitalia

  • Collectively called the vulva or pudendum.
  • A pair of vestibular glands are associated with the external genitalia.
  • Mammary glands are also associated with the female reproductive system.

I. Ovaries

  • Ovaries are solid, oval or almond-shaped organs.
  • Size:
    • Length: 3 cm
    • Breadth: 1.5 cm
    • Thickness: 1 cm

Location

  • Situated in the upper lateral part of the pelvis near the kidneys.

Hormones Secreted

  • Oestrogen
  • Progesterone
  • Relaxin
  • Activin
  • Inhibin

Functions

  • Control menstrual cycle.
  • Support pregnancy and parturition.

II. Oviducts / Fallopian Tubes

  • They lie horizontally over the pelvic cavity.
  • Each tube is 10–12 cm long.
  • Internally lined by ciliated epithelium.

Functions

  • Carry the ovulated egg from ovary to uterus.

Parts of Fallopian Tube

i. Infundibulum

  • Funnel-shaped part having an opening called the ostium.
  • Surrounded by finger-like projections called fimbriae.
  • Cilia and fimbriae help transport the ovulated egg to the ostium.

ii. Ampulla

  • Middle long and straight part of the oviduct.
  • Site of fertilization.

iii. Isthmus / Cornua

  • The narrow distal part opening into the uterus.

III. Uterus / Womb

  • It is a hollow, muscular, pear-shaped organ.
  • Located above and behind the urinary bladder.

Size

  • Length: 7.5 cm
  • Breadth: 5 cm
  • Thickness: 2.5 cm

Functions

  • Provides site for implantation.
  • Supports gestation and parturition.
  • Provides site for placental formation.

Layers of Uterine Wall

i. Perimetrium

  • Outermost layer.

ii. Myometrium

  • Middle smooth muscular layer.
  • Contractions of this layer cause labour during parturition.

iii. Endometrium

  • Innermost layer made of stratified epithelium.
  • Richly supplied with blood vessels and uterine glands.
  • Provides nourishment to the developing foetus.

Parts of Uterus

i. Fundus

  • Upper dome-shaped part.
  • Common site of implantation.

ii. Body

  • Broad central part tapering downwards.

iii. Cervix

  • Narrow neck of the uterus.
  • About 2.5 cm long.
  • Extends into the vagina.

IV. Vagina

  • Vagina lies between the cervix and the vestibule.
  • It is 7–9 cm in length.

Structure

  • Internally lined by stratified non-keratinized mucosal epithelium.
  • Stores glycogen.

Vaginal Orifice

  • The opening of the vagina into the vestibule is called the vaginal orifice.
  • It is partially covered by the hymen.

Functions

  • Passage for menstrual flow.
  • Acts as a birth canal during parturition.

External Genitalia (Vulva)

The external genitalia include:

  • Vestibule
  • Labia minora
  • Clitoris
  • Labia majora
  • Mons pubis

Accessory Glands

1. Vestibular Glands / Bartholin’s Glands

  • Open into the vestibule.
  • Release lubricating fluid.

2. Mammary Glands

  • Accessory organs responsible for production and release of milk after parturition.

Structure of Mammary Glands in Human Female



  • Mammary glands are a pair of rounded structures present in the pectoral region from the 2nd to 6th rib.
  • They are modified sweat glands.

Structure

  • Each mammary gland contains fatty connective tissue and numerous lactiferous ducts.
  • The glandular tissue of each breast is divided into 15–20 mammary lobes.
  • Each lobe contains:
    • Alveolar glands
    • Lactiferous ducts

Milk Secretion Pathway

  • Alveolar glands secrete milk stored in the lumen of alveoli.
  • Alveoli open into mammary tubules.
  • Tubules of each lobe join to form mammary ducts.
  • Many mammary ducts join to form a wider mammary ampulla.
  • The mammary ampulla connects to the lactiferous duct.
  • Lactiferous ducts converge towards the nipple.

Areola

  • The nipple is surrounded by a dark brown circular area called the areola.
Note: Prolactin secreted by lactotropic cells is also referred to as luteotropic hormone or luteotropin.

External Genital Organs of Female Reproductive System

a. Vestibule

  • A median vertical depression enclosing the urethral and vaginal openings.

b. Labia Minora

  • Pair of thin folds situated inner to the labia majora.
  • Posteriorly merge to form the fourchette (frenulum).
  • Anteriorly form a hood-like covering around the clitoris.

c. Clitoris

  • A small conical sensitive projection located at the anterior end of labia minora.
  • Contains erectile tissues called corpora cavernosa.
  • Homologous to the penis.

d. Labia Majora

  • Pair of fleshy folds forming the boundary of the vulva.
  • Homologous to the scrotum.
  • Protect other external genital organs.
  • Enclose the urethral and vaginal openings.

e. Mons Pubis

  • Fleshy elevation above the labia majora.
  • The mons pubis and outer labia majora contain pubic hairs.

Histological Structure of Ovary in Human

The histological structure of the ovary shows the different stages of development of the oocyte in the ovary. Each ovary is differentiated into:

  • A central part called medulla
  • An outer part called cortex

i. Medulla

  • The medulla consists of loose connective tissue called stroma.
  • It contains:
    • Blood vessels
    • Lymph vessels
    • Nerve fibres

ii. Cortex

a. Germinal Epithelium

  • The cortex is externally covered by a layer of germinal epithelium.

b. Ovarian Follicles

  • The outer cortex is compact and granular.
  • It contains numerous tiny masses of cells called ovarian follicles.

c. Origin of Ovarian Follicles

  • Ovarian follicles develop from immature ova originating from primordial germ cells.
  • These primordial germ cells arise from the dorsal endoderm of the yolk sac.
  • During embryonic development, they migrate to the gonadal ridge and divide mitotically.
  • These cells are then called oogonia.

d. Formation of Primordial Follicles

  • As oogonia increase in size, they become surrounded by a layer of granulosa cells.
  • This forms the rudiment of ovarian follicles.
  • The ovary contains more than two million primordial follicles.

e. Structure of Primordial Follicle

  • Each primordial follicle contains:
    • A large primary oocyte (2n)
    • A single layer of flat follicular cells
  • The primary oocyte starts meiosis but gets arrested at Meiosis I.

Development of Ovarian Follicles

i. Primary Follicle

  • Primordial follicles grow into primary follicles.
  • Primary follicles possess multilayered cuboidal follicular cells.

ii. Secondary Follicle

  • Stromal cells form the theca around the follicle.
  • This stage is called the secondary follicle.

iii. Graafian Follicle

  • The secondary follicle grows into a mature Graafian follicle by addition of more follicular cells.

iv. Ovulation

  • During ovulation, the egg is released from the Graafian follicle.

v. Corpus Luteum

  • The remaining part of the follicle changes into a temporary endocrine gland called the corpus luteum.

vi. Corpus Albicans

  • If fertilization does not occur, the corpus luteum degenerates into a white scar called the corpus albicans.

Folliculogenesis

Folliculogenesis is the process of development of ovarian follicles.

  • It is a continuous process.
  • At any given time, the ovary contains follicles at different stages of development.

Atresia

The large-scale degeneration and destruction of primordial follicles during growth is called atresia.

Structure of Graafian Follicle


i. Definition

  • The Graafian follicle is a mature ovarian follicle.

ii. Secondary Oocyte

  • The secondary oocyte is located eccentrically (away from the centre).
  • It is surrounded by a non-cellular layer called the zona pellucida.
  • The zona pellucida is secreted by the vitelline membrane of the oocyte.

iii. Layers of Graafian Follicle

a. Theca Externa

  • Outermost protective fibrous covering.

b. Theca Interna

  • Inner cellular layer.
  • Produces the hormone oestrogen.

c. Membrana Granulosa

  • Inner layer formed by follicular cells.

iv. Discus Proligerus and Corona Radiata

  • Cells of membrana granulosa differentiate into:
    • Discus proligerus
    • Corona radiata

v. Cumulus Oophorus

  • The oocyte together with surrounding granulosa cells is called the cumulus oophorus.

vi. Antrum

  • A fluid-filled cavity called the antrum lies between the oocyte and membrana granulosa.
  • It contains a fluid called liquor folliculi.

Important Terms Related to Female Reproductive System

i. Menarche

  • Menarche is the first menstrual cycle in females.
  • It usually occurs between 10–14 years of age.

ii. Menopause

  • Menopause is the permanent cessation of menstrual cycles.
  • It generally occurs between 45–50 years of age.

iii. Reproductive Age

  • The period between menarche and menopause is called the reproductive age.
  • It is approximately 32 years.
  • During this period, a female produces about 416 eggs.

iv. Puberty

  • Puberty is the stage at which the reproductive system becomes functional.
  • Sex organs begin producing gametes and sex hormones.
  • Occurs at:
    • 12–15 years in males
    • 10–14 years in females

Menstrual Cycle

The menstrual cycle involves cyclic changes in the ovaries and female reproductive tract, mainly the uterus.

  • These changes occur under the influence of gonadotropins and ovarian hormones.
  • The cycle repeats approximately every 28 days.
  • A secondary oocyte is released mid-cycle from one of the ovaries.

Hormones Regulating Menstrual Cycle

  • GnRH (Gonadotropin Releasing Hormone)
  • FSH (Follicle Stimulating Hormone)
  • LH (Luteinizing Hormone)
  • Oestrogen
  • Progesterone

Phases of Menstrual Cycle



The menstrual cycle is divided into four phases:

  • Menstrual phase
  • Proliferative phase
  • Ovulatory phase
  • Secretory (Luteal) phase

I. Menstrual Phase

  • The menstrual phase begins on the first day of menstruation.
  • Approximately 45–100 mL of blood is lost during this phase.
  • Duration: approximately 3–7 days (average 5 days).

Special Feature

  • Menstrual blood does not clot due to the presence of fibrinolysin.

Cause of Menstruation

  • Occurs when the ovulated egg is not fertilized.
  • The unfertilized egg is shed out along with menstruum.
  • This process is sometimes called the “funeral of the unfertilized egg.”

Changes During Menstrual Phase

a. Changes in Uterus

  • The endometrium breaks down due to prostaglandins.
  • This occurs because progesterone and oestrogen levels decrease.
  • The following are discharged through the vagina:
    • Blood
    • Tissue fluid
    • Mucus
    • Endometrial lining
    • Unfertilized oocyte
  • The endometrial lining becomes very thin (about 1 mm).

b. Changes in Ovary

  • During these five days, many primordial follicles develop into primary follicles.
  • A few develop further into secondary follicles under the influence of FSH.

II. Proliferative Phase / Follicular Phase / Post-Menstrual Phase

This phase occurs between the end of menstruation and ovulation.

  • Duration: Usually from the 5th to the 13th day of the menstrual cycle.
  • This phase is more variable in duration compared to other phases.

a. Changes in the Ovary

  • Out of 6–12 developing secondary follicles, generally only one develops into a mature Graafian follicle.
  • The remaining follicles degenerate through a process called atresia.
  • The development of follicles is stimulated by GnRH, which stimulates the release of FSH.
  • Developing secondary follicles secrete the hormone oestrogen.

b. Changes in the Uterus

  • The endometrium begins to regenerate due to increasing levels of oestrogen.
  • Regeneration involves:
    • Formation of endothelial cells
    • Development of endometrial (uterine) glands
    • Formation of blood vessel networks
  • The thickness of the endometrium increases to about 3–5 mm.

III. Ovulatory Phase

The ovulatory phase is the shortest phase of the menstrual cycle.

a. Changes in the Ovary

  • The mature Graafian follicle ruptures and releases the ovum (secondary oocyte) into the pelvic cavity.
  • Ovulation usually occurs on the 14th day of the menstrual cycle.
  • A rapid increase in LH secretion called the LH surge causes rupture of the mature follicle.
  • The LH surge occurs through a positive feedback mechanism.
  • Ovulation may be accompanied by mild or severe pain in the lower abdomen.

IV. Secretory Phase / Luteal Phase

This phase occurs between ovulation and the beginning of the next menstrual cycle.

  • It is the longest phase of the menstrual cycle.
  • Duration: Approximately 14 days (15th to 28th day).

1. Changes in the Ovary

i. Formation of Corpus Luteum

  • After ovulation, the remaining tissue of the Graafian follicle transforms into the corpus luteum under the influence of LH.

ii. Hormone Secretion

  • The corpus luteum secretes:
    • Progesterone
    • Small amounts of oestrogen
    • Inhibin

iii. Fertilization

  • The ovulated egg can be fertilized within 24 hours after ovulation.

iv. In Absence of Fertilization

  • The corpus luteum survives for about two weeks.
  • It then degenerates into a white scar called the corpus albicans.
  • In the absence of fertilization, the next menstrual cycle begins.

v. In Case of Fertilization

  • The embryo gets implanted in the uterus.
  • The developing embryo secretes human chorionic gonadotropin (hCG).
  • hCG prolongs the life of the corpus luteum and stimulates its secretory activity.
  • Presence of hCG in maternal blood and urine is an indicator of pregnancy.

2. Changes in the Uterus

i. Endometrial Changes

  • Under the influence of progesterone and oestrogen:
    • Endometrial glands enlarge
    • Become coiled
    • Begin uterine secretions

ii. Increased Vascularization

  • The endometrium becomes highly vascularized.
  • Its thickness increases to about 8–10 mm.

iii. Role of Inhibin

  • Inhibin inhibits the secretion of FSH.

iv. Importance

  • These uterine changes prepare the uterus for:
    • Fertilization
    • Implantation of the embryo

Significance of hCG (Human Chorionic Gonadotropin)

  • hCG extends the life of the corpus luteum and stimulates its secretory activity.
  • Presence of hCG in maternal blood and urine is an indicator of pregnancy.

Menstrual Cycle in Primates

Menstruation is observed in the following primates:

  • Humans – 28 day cycle
  • Orangutans – 29 day cycle
  • Gorillas – 30 day cycle
  • Chimpanzees – 37 day cycle

Hygiene Practices During Menstruation

The following hygiene practices should be followed during menstruation:

  • Keep the pubic area clean.
  • Change sanitary napkins every 4–5 hours.
  • Maintain personal hygiene to reduce the risk of infections.
  • Dispose used sanitary napkins properly.
  • Avoid using damp or dirty clothes.
  • Do not use sanitary napkins for a prolonged period.

Damp clothes and prolonged use of sanitary napkins provide an ideal environment for the growth of harmful bacteria and may lead to infections.

Why Do Women Experience Pain During Menstruation?

During menstruation, the endometrial lining of the uterus is shed.

  • The muscles of the uterus contract and relax irregularly to expel the endometrial lining along with blood through the vagina.
  • These contractions may cause mild discomfort or painful cramps known as dysmenorrhea.
  • Women with heavier menstrual flow may experience more severe pain.

Menstrual pain differs from person to person and is classified into:

i. Primary Dysmenorrhea

  • Common in women below 30 years of age.
  • May occur due to:
    • Genetic factors
    • Stress
  • Prostaglandins play an important role in causing pain during uterine contractions.

ii. Secondary Dysmenorrhea

  • Occurs due to factors other than normal uterine contractions.
  • Possible causes include:
    • Fibroids
    • Polyps
    • Endometriosis
    • Other reproductive health disorders
  • Use of intrauterine devices (IUDs) may also cause pain in some women.

Gametogenesis

Gametogenesis is the process of formation of gametes in sexually reproducing animals.

Spermatogenesis

9 to

Spermatogenesis is the process of formation of male gametes (sperms or spermatozoa) from the germinal epithelium of the testis.

Process of Spermatogenesis

a. Hormonal Initiation

  • At puberty, the hypothalamus begins secretion of GnRH (Gonadotropin Releasing Hormone).
  • GnRH stimulates the release of FSH (Follicle Stimulating Hormone).
  • FSH initiates spermatogenesis.

b. Germinal Epithelium

  • Each seminiferous tubule is lined by a single layer of cuboidal epithelial cells called the germinal epithelium.
  • These cells undergo spermatogenesis to form sperms.

Phases of Spermatogenesis

1. Multiplication Phase

  • Primordial germ cells (2n) undergo repeated mitotic divisions.
  • They produce numerous spermatogonia (2n).
  • Each spermatogonium contains 46 chromosomes.

2. Growth Phase

  • Some spermatogonia stop dividing and increase in size.
  • They develop into primary spermatocytes (2n).
  • This growth occurs due to accumulation of food materials.

3. Maturation Phase

This phase involves meiotic (reduction) division.

Meiosis I

  • Each primary spermatocyte undergoes the first meiotic division.
  • Two haploid secondary spermatocytes (n) are formed.
  • Each contains 23 chromosomes.

Meiosis II

  • Each secondary spermatocyte undergoes the second meiotic division.
  • Four haploid spermatids are produced.

Spermiogenesis

Spermatids are non-motile and non-functional.

  • They transform into functional spermatozoa by a process called spermiogenesis.

Changes During Spermiogenesis

  • Spermatids remain attached to each other and to Sertoli cells through cytoplasmic bridges.
  • Sperm heads remain attached to Sertoli cells while tails hang into the lumen of seminiferous tubules.
  • The length of the spermatid increases.
  • Centrioles rearrange into:
    • Primary centriole
    • Distal centriole
  • Mitochondria become spirally coiled.
  • The acrosome develops from the Golgi complex.

Structure of Human Sperm



Sperm is the male gamete. It is a motile, microscopic and elongated cell.

A sperm is divided into four parts:

  • Head
  • Neck
  • Middle piece
  • Tail

i. Head

  • The sperm head is oval in shape.
  • It contains a haploid nucleus.
  • Above the nucleus is a cap-like structure called the acrosome.
  • The acrosome is formed from the Golgi body.

Enzymes Present in Acrosome

  • Hyaluronidase
  • Zona lysins
  • Corona penetrating enzymes

These enzymes help the sperm penetrate the coverings of the ovum during fertilization.

ii. Neck

  • The neck is a very short region.
  • It contains two centrioles:
    • Proximal centriole
    • Distal centriole

iii. Middle Piece

  • Contains an axial filament surrounded by 10–14 spiral turns of mitochondria called Nebenkern.
  • Mitochondria produce energy required for sperm movement.

iv. Tail

  • Long, slender and tapering part of the sperm.
  • Contains cytoplasm and a fine thread-like axial filament.
  • The axial filament arises from the distal centriole and extends throughout the tail.
  • The major part of the tail is surrounded by plasma membrane and is called the main piece.
  • The terminal part without plasma membrane is called the end piece.

Process of Oogenesis

Oogenesis is the process of formation of the haploid female gamete (ovum or egg) from the diploid germinal epithelium.

  • Oogenesis occurs in the ovaries.
  • It begins before the birth of the female baby.
  • The process involves both mitosis and meiosis.

Stages of Oogenesis

  • Multiplication phase
  • Growth phase
  • Maturation phase

i. Multiplication Phase

  • Primary germinal cells (PGCs) of the ovary undergo repeated mitotic divisions.
  • They form millions of oogonial cells or oogonia (2n).
  • This phase is completed during the embryonic stage of human females.

ii. Growth Phase

  • Some oogonia stop dividing and increase in size.
  • They develop into primary oocytes (2n).
  • Cell organelles such as:
    • Endoplasmic reticulum (ER)
    • Golgi apparatus
    • Mitochondria
    increase in number.

iii. Maturation Phase

  • The primary oocyte enters meiosis I and meiosis II.

Meiosis I

  • The diploid primary oocyte undergoes meiosis I to form two haploid daughter cells.
  • Due to unequal division of cytoplasm:
    • The larger cell becomes the secondary oocyte (n).
    • The smaller cell becomes the first polar body (n).
  • The first polar body usually degenerates and generally does not enter meiosis II.

Meiosis II

  • The secondary oocyte proceeds up to metaphase II.
  • Its division remains arrested at this stage.
  • The secondary oocyte is released during ovulation.
  • Meiosis II is completed only if fertilization occurs.

Completion of Meiosis II

  • This usually occurs in the ampulla of the fallopian tube during fertilization.
  • Two unequal daughter cells are formed:
    • A large ovum (n)
    • A small second polar body (n)

Fate of Secondary Oocyte

  • If fertilization does not occur, the secondary oocyte is shed off along with menstrual flow.
Note: The first polar body may enter meiosis II, but it usually degenerates and does not contribute to embryo formation.

Structure of Secondary Oocyte

The secondary oocyte is the unfertilized egg released during ovulation.

i. Size and Nature

  • It is non-cleidoic (without shell).
  • It is microlecithal (contains very little yolk).
  • Approximate size: 0.1 mm (100 microns).
  • It is a rounded, non-motile, haploid female gamete.

ii. Polarity

  • The side containing the germinal vesicle and first polar body is called the animal pole.
  • The opposite side is called the vegetal pole.

iii. Nucleus

  • The nucleus appears large and is called the germinal vesicle.
  • The true pronucleus forms during fertilization.

iv. Cytoplasm

  • The cytoplasm of the egg is called the ooplasm.
  • It lacks centrioles.

v. Egg Membranes

a. Vitelline Membrane

  • The egg membrane is called the vitelline membrane.

b. Zona Pellucida

  • A non-cellular glycoprotein membrane called zona pellucida surrounds the vitelline membrane.

c. Corona Radiata

  • Several radially elongated cells adhere to the zona pellucida forming the corona radiata.
  • These cells originate from the innermost granulosa cells.
  • They are held together by hyaluronic acid.

d. Perivitelline Space

  • A fluid-filled space between the vitelline membrane and zona pellucida is called the perivitelline space.
  • The first polar body lies within this space.

Process of Fertilization in Human

Fertilization is the fusion of haploid male and female gametes resulting in formation of a diploid zygote (2n).

  • Fertilization is internal.
  • It usually occurs in the ampulla of the fallopian tube.
  • The zygote later develops into an embryo within the uterus.

Mechanism of Fertilization

i. Movement of Sperm Towards Egg

  • After ejaculation, semen undergoes liquefaction and sperms become active.
  • Many sperms are destroyed in the vagina.
  • The remaining sperms undergo capacitation.

ii. Capacitation (5–6 Hours)

  • The acrosomal membrane becomes thin.
  • Calcium ions enter the sperm.
  • Sperm tails show rapid whip-like movements.
  • Sperms become highly active and move towards the uterus and oviducts.
  • Prostaglandins and vestibular secretions increase sperm motility.
  • Sperms swim at an average speed of 1.5–3 mm/min.
  • Contractions of the uterus and fallopian tubes aided by oxytocin also help sperm movement.

iii. Entry of Sperm into Egg

  • Out of millions of sperms, only one fertilizes the ovum.
  • The acrosome releases:
    • Hyaluronidase
    • Corona penetrating enzymes
    • Zona lysins
  • These enzymes help dissolve the corona radiata and zona pellucida.

Zona Pellucida Receptors

  • The zona pellucida contains receptor proteins:
    • ZP3
    • ZP2
  • These receptors bind with sperm proteins and aid fertilization.

Acrosome Reaction

  1. The sperm head touches the zona pellucida at the animal pole.
  2. The acrosome ruptures and releases lytic enzymes.
  3. A fertilization cone forms on the egg membrane.
  4. The sperm head contacts this cone causing depolarization.
  5. Plasma membranes of sperm and egg fuse.
  6. The sperm nucleus and centrioles enter the egg.
  7. A cortical reaction converts the vitelline membrane into a fertilization membrane.
  8. A distinct perivitelline space forms.
  9. This prevents entry of additional sperms (prevention of polyspermy).

iv. Activation of Ovum

  • Before fertilization, the ovum remains arrested at metaphase II.
  • Contact with the sperm activates completion of meiosis II.
  • The second polar body is formed.
  • The germinal vesicle organizes into the female pronucleus.

v. Fusion of Male and Female Pronuclei

  • The pronuclear membranes degenerate.
  • Chromosomes pair together.
  • Fusion of pronuclei forms the synkaryon.
  • This process is called:
    • Syngamy
    • Karyogamy
  • The diploid zygote is formed.
  • The proximal centriole from the sperm helps in spindle formation and cleavage of the zygote into blastomeres.

Significance of Fertilization

The significance of fertilization is as follows:

  • The secondary oocyte completes oogenesis and transforms into a mature ovum (n).
  • The diploid chromosome number is restored in the zygote by the process of syngamy.
  • The ovum lacks centrioles necessary for cell division. These centrioles are supplied by the sperm during fertilization.
  • Fertilization involves fusion of male and female gametes from two parents, resulting in genetic variation important for evolution.
  • The sex of the offspring is determined during fertilization.

Formation of Morula from Zygote

The zygote formed after fertilization undergoes repeated mitotic divisions to form an embryo.

I. Cleavage

Cleavage is the process of early mitotic divisions of the zygote resulting in formation of a multicellular structure.

Characteristics of Cleavage

  • There is no growth of daughter cells during cleavage.
  • The cells formed are called blastomeres.
  • As cleavage continues, the size of blastomeres decreases.
  • The metabolic rate increases as cell size decreases.
  • Subsequent cleavages occur faster than earlier ones.
  • Rapid DNA replication and high oxygen consumption are required.

II. Process of Cleavage in Humans

  • Human cleavage is holoblastic, meaning the entire zygote divides.
  • Cleavage is:
    • Radial
    • Indeterminate
  • The fate of each blastomere is not predetermined.

Stages of Cleavage



a. First Cleavage

  • The first cleavage is meridional (longitudinal).
  • Occurs about 30 hours after fertilization.
  • The zygote divides into two blastomeres, one slightly larger than the other.

b. Second Cleavage

  • The second cleavage is also longitudinal.
  • Occurs at right angles to the first cleavage.
  • Results in a 4-cell stage embryo.

c. Third Cleavage

  • The third cleavage is horizontal (equatorial).
  • Results in an 8-cell stage embryo.

d. Formation of Morula

  • As cleavage continues, the embryo moves towards the uterus.
  • By the end of the 4th day after fertilization, the embryo forms a solid ball of 16–32 cells.
  • This stage resembles a mulberry and is called the morula.

III. Structure of Morula



  • The morula contains two types of cells:
    • Smaller clear cells towards the outer side
    • Larger cells forming the inner cell mass
  • Cells are compactly arranged.
  • The zona pellucida remains around the embryo till the morula stage.
  • Therefore, there is no increase in overall size from zygote to morula.
  • The morula reaches the isthmus and enters the uterus by the end of the 4th day.
Note: The first cleavage begins about 24–30 hours after fertilization and completes nearly 6 hours later. By the end of the third day, the embryo reaches the 16-cell stage.

Site of Fertilization and Implantation

  • Fertilization usually occurs in the ampulla of the fallopian tube.
  • Implantation occurs in the endometrium of the uterus.

Why Implantation Occurs Only in the Uterus

  • The egg membrane secretes the zona pellucida.
  • The zona pellucida prevents exposure of sticky trophoblast cells before the embryo reaches the uterus.
  • This prevents implantation at abnormal sites.
  • The uterus has a rich blood supply necessary for implantation and development.
  • Progesterone and oestrogen prepare and maintain the endometrium for implantation.

Important Structures and Their Functions

i. Corpus Luteum

  • Releases progesterone, small amounts of oestrogen and inhibin.
  • Essential for establishing and maintaining pregnancy.

ii. Acrosome

  • Contains hydrolytic enzymes.
  • Helps the sperm penetrate the secondary oocyte during fertilization.

iii. Endometrium

  • Provides the site for implantation of the embryo.

iv. Sperm Tail

  • Responsible for movement of sperm from the vagina to the uterus for fertilization.

v. Fimbriae

  • Along with cilia, fimbriae help direct the non-motile egg towards the ostium of the fallopian tube.

Why Corpus Luteum Persists After Fertilization

  • After fertilization and implantation, the embryo secretes human chorionic gonadotropin (hCG).
  • hCG extends the life of the corpus luteum and stimulates its secretory activity.
  • The corpus luteum secretes:
    • Progesterone
    • Small amounts of oestrogen
    • Inhibin
  • These hormones are necessary for maintaining pregnancy.

Blastulation

Blastulation is the process of formation of a hollow multicellular blastocyst from the morula.

Process of Blastulation

  • The morula enters the uterus and floats in the uterine cavity for about 2–4 days.
  • The outer layer of morula cells forms the trophoblast.
  • Trophoblast cells absorb glycogen-rich uterine milk.
  • The blastocyst increases in size from about 0.15 mm to 0.30 mm.
  • Fluid enters the embryo forming the blastocyst cavity.
  • The outer flattened cells become trophoblast cells.
  • The inner larger cells form the inner cell mass or embryoblast.
  • The embryoblast develops into the embryo proper.
  • The inner cell mass remains attached to the trophoblast on one side.
  • Trophoblast cells in contact with the embryonal knob are called cells of Rauber.

Polarity of Blastocyst

  • The side containing the inner cell mass is called the embryonal end.
  • The opposite side is called the abembryonic end.

Ready for Implantation

  • By the end of the 7th day after fertilization, the blastocyst is fully formed.
  • It becomes ready for implantation and gastrulation.

Function of Zona Pellucida

  • The zona pellucida prevents implantation of the embryo at abnormal sites.
  • It keeps trophoblast cells covered until the embryo reaches the uterus.
  • After reaching the uterus, the zona pellucida ruptures allowing implantation.

Structure of Blastula



Blastula is the embryonic stage formed after the completion of blastulation.

  • It is a hollow ball of cells.

Characteristics of Blastula

  • After reaching the uterus, the blastula gets implanted in the uterine wall.
  • The outer trophoblast cells absorb glycogen-rich uterine milk.
  • The blastocyst increases in size from about 0.15 mm to 0.30 mm.
  • Fluid enters inside and forms the blastocyst cavity.
  • The outer flattened cells are called trophoblast cells.
  • Trophoblast cells help in absorption of nutrition for the developing embryo.
  • The larger inner cells form the inner cell mass or embryoblast.
  • The embryo proper develops from the embryoblast.
  • The inner cell mass remains attached to the trophoblast on one side only.
  • The trophoblast cells in contact with the embryonal knob are called cells of Rauber.

Polarity of Blastocyst

  • The side containing the inner cell mass is called the embryonal end.
  • The opposite side is called the abembryonic end.

Monozygotic, Dizygotic and Conjoined Twins

When two embryos develop simultaneously in the same uterus and two offspring are produced from the same pregnancy, they are called twins.

i. Monozygotic Twins



  • During early embryonic development (within 8 days after zygote formation), cells of a single embryo divide into two groups.
  • Each group develops into a separate embryo.
  • These twins are genetically identical.
  • They have:
    • Same appearance
    • Same gender

ii. Dizygotic Twins



  • Sometimes two oocytes are released from the ovary at the same time.
  • Each oocyte is fertilized by a different sperm.
  • Two separate zygotes are formed.
  • The embryos implant separately in the uterus.
  • Dizygotic twins are genetically different.
  • They may be:
    • Of the same gender
    • Of different genders

iii. Conjoined Twins (Siamese Twins)



  • In monozygotic twins, if embryonic separation occurs after about 13 days of zygote formation, incomplete separation may occur.
  • This results in formation of conjoined twins or Siamese twins.

Process of Gastrulation



Gastrulation is the process of formation of a gastrula from the blastocyst.

Main Events During Gastrulation

i. Differentiation of Blastomeres

  • Blastomeres differentiate to form three germ layers:
    • Ectoderm
    • Mesoderm
    • Endoderm

ii. Morphogenetic Movements

  • Cells undergo specific movements to reach their proper position in the embryo.

iii. Formation of Extraembryonic Membranes

a. Formation of Hypoblast

  • About the 8th day after fertilization, cells at the free end of the inner cell mass flatten and divide.
  • These cells are called hypoblasts or primitive endoderm.
  • They grow downward towards the blastocoel cavity.

b. Formation of Yolk Sac

  • The hypoblast forms a sac called the yolk sac.

c. Formation of Epiblast

  • The remaining cells of the inner cell mass are called epiblasts or primary ectoderm.
  • These cells remain in contact with the cells of Rauber.

d. Bilaminar Embryonic Disc

  • The hypoblast and epiblast together form a flat bilaminar embryonic disc.

e. Formation of Amniotic Cavity

  • Epiblast cells divide and arrange themselves around the amniotic cavity.
  • The roof of the amniotic cavity is lined by amniogenic cells.
  • These cells form the amnion.

f. Function of Amnion

  • Amnion is an extraembryonic membrane that surrounds and protects the embryo.

g. Position of Embryonic Disc

  • The bilaminar embryonic disc lies between:
    • The amniotic cavity
    • The yolk sac

iv. Process of Gastrulation Proper

  • Gastrulation occurs about 15 days after fertilization.
  • The bilaminar embryonic disc transforms into a trilaminar embryonic disc.
  • The trilaminar disc consists of:
    • Ectoderm
    • Mesoderm
    • Endoderm

Formation of Primitive Streak

  • Gastrulation begins with formation of the primitive streak.
  • A shallow groove appears on its surface called the primitive groove.
  • The primitive streak extends from posterior to anterior end of the embryo.

Blastopore

  • The anterior end of the primitive groove communicates with the yolk sac through an opening called the blastopore.
  • The blastopore later forms the anus.

Formation of Germ Layers

a. Formation of Endoderm

  • Cells of the epiblast move inward below the primitive streak through invagination.
  • Some invaginated cells displace the hypoblast and form the endoderm.

b. Formation of Ectoderm

  • The remaining epiblast cells form the ectoderm.

c. Formation of Mesoderm

  • A third layer called the mesoderm develops between ectoderm and endoderm.

Result of Gastrulation

  • The embryonic disc becomes trilaminar.
  • The three germ layers formed are:
    • Ectoderm
    • Mesoderm
    • Endoderm
  • Gastrulation is followed by organogenesis.

Fate of the Three Germ Layers



After gastrulation, the three germ layers develop into different tissues and organs. This process is called histogenesis.

i. Fate of Ectoderm

Ectoderm gives rise to:

  • Epidermis of skin
  • Hair
  • Nails
  • Sweat glands
  • Salivary glands
  • Mammary glands
  • Lacrimal glands
  • Sebaceous glands
  • Cornea
  • Lens
  • Retina
  • Conjunctiva
  • Nasal epithelium
  • Enamel of teeth
  • Internal and external ear
  • Foregut and hindgut epithelium
  • Adrenal medulla
  • Anterior and posterior pituitary
  • Pineal gland
  • Entire nervous system

ii. Fate of Mesoderm

Mesoderm forms:

  • All types of muscles (except iris and ciliary muscles)
  • Connective tissues
  • Dermis of skin
  • Adrenal cortex
  • Heart
  • Blood
  • Blood vessels
  • Lymphatic vessels
  • Middle ear
  • Dentine of teeth
  • Urinary and reproductive ducts
  • Gonads
  • Kidneys
  • Sclera and choroid of eye

iii. Fate of Endoderm

Endoderm develops into:

  • Epithelium of midgut
  • Glands of stomach and intestine
  • Tongue
  • Tonsils
  • Lungs
  • Trachea
  • Bronchi
  • Larynx
  • Urinary bladder
  • Vagina
  • Liver
  • Pancreas
  • Thyroid gland
  • Parathyroid gland
  • Thymus gland
  • Eustachian tube
  • Epithelium of urethra
  • Lining of middle ear

Pregnancy

Pregnancy is the condition of carrying one or more embryos in the uterus.



  • Pregnancy is also called gestation.
  • It refers to the period from fertilization of the egg until parturition.
  • The average duration of human pregnancy is:
    • 266 days from fertilization
    • Approximately 280 days counted from the LMP (Last Menstrual Period)
  • The period of pregnancy is divided into three trimesters of approximately three months each.
Note: The accepted clinical term is LMP (Last Menstrual Period).

First Trimester (Fertilization to 12th Week)

General Features



  • This period involves the most rapid and radical changes in both mother and embryo.
  • During the first 2–4 weeks, the embryo receives nutrients directly from the endometrium.

Changes in the Foetus



  • This is the major period of organogenesis.
  • By the end of the 8th week, most major organs are formed in a rudimentary form.
  • The embryo is now called a foetus.
  • The foetus is about 3 cm long by the end of the 8th week.
  • Arms, hands, fingers, feet and toes are formed.
  • The foetus can open and close its mouth and fists.
  • The central nervous system becomes functional.
  • Circulatory and excretory systems begin functioning.
  • Foetal movements begin, but cannot yet be felt by the mother.
  • Heartbeat can be detected from the 6th week.
  • By the end of the first trimester, the foetus measures about 7–10 cm in length.

Changes in the Mother



  • Progesterone levels increase significantly.
  • The menstrual cycle stops during pregnancy.
  • Rapid changes occur in the mother’s body.
  • High progesterone levels bring changes in the reproductive system.
  • The maternal part of the placenta develops.
  • The uterus enlarges gradually.
  • The mother may experience:
    • Morning sickness
    • Nausea
    • Vomiting
    • Mood swings

Second Trimester (13th to 26th Week)



Changes During the Second Trimester






  • This is the period of rapid growth of the foetus.
  • The uterus enlarges and pregnancy becomes externally visible.
  • The foetus becomes very active.
  • The foetus grows to about 30 cm in length.
  • Development of the brain continues.
  • Hormone levels stabilize as hCG levels decline.
  • The corpus luteum regresses.
  • The placenta completely takes over progesterone production to maintain pregnancy.
  • The mother can clearly feel foetal movements.
  • The head becomes covered with hair.
  • Eyebrows and eyelashes appear.
  • Pinnae of the ears become distinct.
  • The baby reaches about half the size of a newborn.

Third Trimester (27th Week to Parturition)



Changes During the Third Trimester





  • The foetus grows to about:
    • 3–4 kg in weight
    • 50 cm in length
  • The foetus can open its eyes.
  • There is rapid gain in body weight.
  • The growing uterus compresses and displaces the mother’s abdominal organs.
  • This may lead to:
    • Frequent urination
    • Digestive discomfort
    • Back muscle strain
  • By the end of the third trimester, the foetus becomes fully developed and ready for parturition.

Difference Between Embryo and Foetus



Embryo Foetus
Developing organism from fertilization up to the end of the 8th week. Developing organism from the beginning of the 3rd month until birth.
Organogenesis mainly occurs during this stage. Growth and maturation of organs occur during this stage.

Significance of Ultrasound (Sonography)

  • Ultrasound examination performed at 18–20 weeks helps observe the baby’s growth and position.
  • It helps estimate the expected date of delivery.
  • It is useful for monitoring normal foetal development.

Placenta

  • Placenta is a flattened, discoidal organ present in the uterus of a pregnant woman.
  • It forms a temporary structural and functional connection between maternal and foetal circulation.
  • Placenta is attached to:
    • The wall of the uterus
    • The baby through the umbilical cord
  • Placenta is the only organ formed from tissues of two different individuals:
    • Mother
    • Foetus

Parts of Placenta

i. Foetal Placenta

  • The foetal contribution to the placenta is formed by the chorionic villi.

ii. Maternal Placenta

  • The maternal contribution is formed from the uterine wall rich in blood supply.
  • Human placenta is therefore called haemochorial placenta.

Umbilical Cord

  • The umbilical cord contains three blood vessels:
    • Two umbilical arteries
    • One umbilical vein
  • The arteries carry blood from the foetus to the placenta.
  • The vein carries blood from the placenta back to the foetus.

Functions of Placenta

  • Supplies oxygen and nutrients to the foetus.
  • Transfers hormones and antibodies to the foetus.
  • Removes carbon dioxide and metabolic wastes from the foetus.

Placenta as an Endocrine Organ

Placenta also functions as a temporary endocrine gland.

Hormones Secreted by Placenta

  • hCG (Human Chorionic Gonadotropin)
  • Progesterone
  • Oestrogen
  • Relaxin
  • hPL (Human Placental Lactogen)

Important Points

  • Relaxin is secreted during the later stages of pregnancy.
  • hCG levels rise up to the end of the first trimester and then gradually decline.
  • By the end of the first trimester, progesterone production is mainly taken over by the placenta.
  • These hormones help in:
    • Foetal growth
    • Maintenance of pregnancy

Why Placenta is Called a Temporary Endocrine Gland

  • Placenta secretes hormones such as:
    • hCG
    • Progesterone
    • Oestrogen
  • These hormones are essential for maintaining pregnancy and supporting foetal development.
  • After childbirth, the placenta is expelled from the body.

Cord Blood and Cord Blood Banking

i. Cord Blood

Cord blood is the blood that remains in the umbilical cord and placenta after delivery.

Importance of Cord Blood

  • Cord blood is rich in stem cells.
  • These stem cells can develop into different types of blood cells.
  • They are used in treatment of diseases affecting blood and immune systems.

Diseases Treated Using Cord Blood Stem Cells

  • Leukemia
  • Certain cancers
  • Sickle cell anaemia
  • Some metabolic disorders

ii. Cord Blood Banking

Cord blood banking is the process of collecting, extracting and cryogenically preserving cord blood for future medical use.

  • The preserved stem cells may be used for treatment in future.

Hormones Produced Only During Pregnancy

  • hCG (Human Chorionic Gonadotropin)
  • hPL (Human Placental Lactogen)
  • Relaxin

Parturition

Parturition is the process of giving birth to a baby.

The physical activities involved during childbirth are collectively called labour.

Events Included in Labour

  • Uterine contractions
  • Abdominal contractions
  • Dilation of cervix
  • Passage of baby through the birth canal

Labour is accompanied by pain called labour pains.

Stages of Parturition

i. Dilation Stage

  • Uterine contractions begin from the upper part of the uterus.
  • The baby is pushed towards the cervix.
  • Contractions cause pain due to compression of blood vessels.
  • Oxytocin stimulates stronger uterine contractions through a positive feedback mechanism.
  • The head of the baby presses against the cervix.
  • The cervix and vagina gradually dilate.
  • This stage may last for several hours.
  • It usually ends with rupture of the amniotic sac (“water breaking”).

ii. Expulsion Stage

  • Uterine and abdominal contractions become very strong.
  • In normal delivery, the baby passes out through the cervix and vagina with the head first.
  • This stage generally lasts about 20–60 minutes.
  • After delivery, the umbilical cord is tied and cut near the baby’s navel.

iii. After Birth Stage

  • After delivery of the baby, strong uterine contractions continue.
  • The placenta separates from the uterine wall and is expelled out.
  • This expelled placenta is called the afterbirth.
  • This stage occurs within 10–45 minutes after delivery.
Note: The expulsion stage may last from 10 minutes to several hours, while afterbirth usually occurs within 5–30 minutes.

Hormonal Control of Parturition

Parturition is regulated by a complex neuroendocrine mechanism.

Hormonal Events During Parturition

  • Signals from the fully developed foetus and placenta initiate mild uterine contractions.
  • The oestrogen to progesterone ratio increases towards the end of pregnancy.
  • The number of oxytocin receptors in uterine muscles also increases.
  • This leads to powerful contractions of the uterine myometrium.

Role of Foetus

  • The fully developed foetus secretes:
    • ACTH (Adrenocorticotropic Hormone)
    • Corticosteroids from the adrenal gland
  • These stimulate release of oxytocin from the mother’s pituitary gland.
  • Oxytocin acts on uterine muscles and causes strong contractions leading to childbirth.

Role of Progesterone and Oestrogen

  • Labour does not begin until the inhibitory effect of progesterone on uterine contractions decreases.
  • Towards the end of pregnancy, oestrogen levels rise sharply.
  • Oestrogen counteracts progesterone inhibition.
  • High oestrogen levels:
    • Increase oxytocin receptors
    • Promote formation of gap junctions in uterine muscles

Role of ACTH and Cortisol

  • Increased corticotropin-releasing hormone stimulates the anterior pituitary.
  • The anterior pituitary secretes ACTH.
  • ACTH stimulates the foetal adrenal gland to produce:
    • Cortisol
    • Adrenal androgens
  • The placenta converts adrenal androgens into oestrogen.

Lactation

Lactation is the process by which the mammary glands of the female begin producing milk after childbirth.

  • Prolactin is the hormone responsible for milk production.
  • Oxytocin is responsible for milk ejection or the let-down reflex.
  • Both hormones are essential for successful lactation.

Colostrum

Colostrum is a sticky yellowish fluid secreted by the mammary glands soon after childbirth.

Composition of Colostrum

  • Rich in proteins
  • Contains lactose
  • Contains maternal antibodies such as IgA
  • Has low fat content

Importance of Colostrum

  • The antibodies present in colostrum help develop immunity in the newborn baby.
  • It protects the baby during the period when the infant’s immune system is still immature.

Why Mother's Milk is Safest for the Newborn

A newborn baby has very weak immunity and requires proper nourishment for healthy growth and development.

Mother’s milk is considered the safest food for a newborn because:

  • It contains essential nutrients such as:
    • Fatty acids
    • Lactose
    • Amino acids
    • Minerals
    • Vitamins
    • Water
  • These nutrients help in:
    • Digestion
    • Brain development
    • Growth of the baby
  • Colostrum and breast milk contain antibodies that strengthen the baby’s immune system.
  • Mother’s milk also contains white blood cells (WBCs) that protect the baby from infections.
  • Breastfeeding reduces the risk of contamination associated with bottle feeding.
  • Improperly sterilized bottles and unboiled milk may contain harmful microbes.
  • Formula feeding and bottle feeding may increase the chances of diarrhoea and infections in newborns.

Weaning

The gradual replacement of mother’s milk with solid food is called weaning.

Reproductive Health

Reproductive health refers to the total well-being of an individual in all aspects of reproduction.

  • It includes:
    • Physical well-being
    • Emotional well-being
    • Behavioral well-being
    • Social well-being

Goals of the Reproductive and Child Healthcare (RCH) Programme

The major goals of the RCH programme are:

  • To create awareness among people about various aspects related to reproduction.
  • To provide healthcare facilities for maintaining reproductive health.
  • To support the development of a reproductively healthy society.
  • To improve major health indicators such as:
    • Reducing total infertility rate
    • Reducing infant mortality rate (IMR)
    • Reducing maternal mortality rate (MMR)

Ways to Achieve the Goals of the RCH Programme

  • Introduction of sex education in schools to:
    • Provide correct information
    • Remove myths and misconceptions
    • Create awareness about safe and hygienic sexual practices
    • Educate about sexually transmitted diseases (STDs) and AIDS
    • Provide knowledge regarding reproductive organs and adolescence-related problems
  • Government and non-government organizations should use:
    • Audio-visual media
    • Print media
    to spread awareness regarding reproductive health.
  • Educating people about:
    • Birth control measures
    • Prenatal care
    • Postnatal care
    • Importance of breastfeeding
  • Creating awareness about:
    • Population explosion
    • Sex abuse
    • Sex-related crimes
    • Other social evils
  • Creating awareness regarding the legal ban on amniocentesis for sex determination.
  • Promoting child immunization programmes.
  • Educating couples to reduce infant and maternal mortality rates.

Contraceptives

Contraceptives are birth control methods that deliberately prevent fertilization and avoid unwanted pregnancies.

Features of an Ideal Contraceptive

  • Should be easily available.
  • Should be user-friendly.
  • Should effectively prevent unwanted pregnancy.
  • Should have no or minimal side effects.

Methods of Birth Control

Contraceptive methods are broadly classified into:

  • Temporary methods
  • Permanent methods

I. Temporary Methods

1. Natural Method / Safe Period / Rhythm Method

  • This method avoids sexual intercourse during the fertile period.
  • A week before and a week after menstruation are considered relatively safe periods.
  • This method is based on the fact that ovulation generally occurs around the 14th day of the menstrual cycle.

Drawback

  • High chances of failure.

2. Coitus Interruptus (Withdrawal Method)

  • The male withdraws the penis from the vagina before ejaculation.
  • This helps avoid insemination.

Drawback

  • Pre-ejaculatory fluid may contain sperms and can cause fertilization.

3. Lactational Amenorrhea

  • This method is based on the absence of ovulation during intense breastfeeding after childbirth.
  • As long as the mother fully breastfeeds the baby, chances of conception are greatly reduced.

Drawback

  • Possibility of failure exists.

4. Chemical Methods (Spermicides)

  • Foams, tablets, creams and jellies are inserted into the vagina before intercourse.
  • These chemicals immobilize or kill sperms.

Drawback

  • May cause allergic reactions.
  • Failure rate is possible.

5. Mechanical / Barrier Methods

These methods prevent physical meeting of sperm and ovum.

a. Condom

  • A thin rubber sheath used to cover the penis during intercourse.
  • Prevents entry of semen into the female reproductive tract.
  • Helps prevent pregnancy and sexually transmitted diseases (STDs).
  • Has no major side effects.
  • Should be discarded after single use.
  • Nirodh is a widely used condom brand in India.

b. Diaphragm, Cervical Caps and Vaults

  • Rubber devices used by females.
  • Inserted into the reproductive tract to cover the cervix.
  • Prevent entry of sperms into the uterus.

c. Intra-Uterine Devices (IUDs)

IUDs are plastic or metal devices inserted into the uterus by trained medical personnel.

Types of IUDs

  • Lippes Loop
  • Copper-releasing IUDs:
    • Cu-T
    • Cu-7
    • Multiload 375
  • Hormone-releasing IUDs:
    • LNG-20
    • Progestasert

i. Lippes Loop

  • A plastic double “S” shaped loop.
  • Stimulates macrophages in the uterus.
  • Macrophages increase phagocytosis of sperms.

ii. Copper-Releasing IUDs

  • Reduce sperm motility and fertilizing capacity.

iii. Hormone-Releasing IUDs

  • Make the uterus unsuitable for implantation.
  • Make the cervix hostile to sperms.
  • Provide long-term contraception.

Drawbacks of IUDs

  • Spontaneous expulsion
  • Occasional bleeding
  • Risk of infection

6. Oral Contraceptive Pills

  • Contain progesterone and oestrogen hormones.
  • Prevent ovulation and release of eggs.
  • Also alter cervical mucus to block sperm entry.

Saheli

  • A non-steroidal oral contraceptive pill developed in India.
  • Taken once a week.
  • Included in the National Family Welfare Programme.

Side Effects

  • Nausea
  • Weight gain
  • Breast tenderness
  • Slight bleeding between menstrual cycles

7. Birth Control Implants

  • Thin rod-like implants placed under the skin of the upper arm.
  • Examples:
    • Implanon
    • Explanon
  • Contain progesterone and oestrogen.
  • Act similarly to oral pills.
  • Prevent pregnancy for 3–4 years.

II. Permanent Methods (Sterilization)

1. Vasectomy

  • Permanent contraceptive method in males.
  • A small part of the vas deferens is cut and tied.
  • Prevents transport of sperms.

2. Tubectomy

  • Permanent contraceptive method in females.
  • A small part of the fallopian tube is cut and tied.
  • Prevents movement of ova and sperms.

Importance of Sterilization

  • These methods permanently prevent pregnancy by blocking gamete transport.

Tubectomy

Tubectomy is a permanent method of birth control used in women.

  • It is a highly effective contraceptive method.
  • However, reversal of tubectomy is difficult and often unsuccessful.
  • In this procedure:
    • A small part of the fallopian tube is removed, or
    • The fallopian tube is tied.
  • The procedure may be performed:
    • Through a small incision in the abdomen, or
    • Through the vagina.
  • Tubectomy blocks gamete transport and prevents pregnancy.
  • This method may be chosen to:
    • Prevent future pregnancies
    • Delay pregnancy
    • Maintain spacing between pregnancies

Why Removal of Gonads is Not Considered a Contraceptive Method

  • Contraceptive methods are generally designed to temporarily prevent fertilization.
  • Many contraceptive methods are reversible.
  • Examples include:
    • Natural methods
    • Mechanical methods
    • Chemical methods
    • Oral contraceptives
    • Surgical sterilization methods
  • Removal of gonads permanently eliminates reproductive function and therefore is not considered a standard contraceptive option.

Medical Termination of Pregnancy (MTP)

Medical Termination of Pregnancy (MTP) refers to the intentional or voluntary termination of pregnancy before full term.

  • It is also called:
    • Induced abortion
  • MTP may be necessary in:
    • Unwanted pregnancies
    • Cases of defective foetal development
  • MTP is considered safer during the first trimester of pregnancy.

MTP Act, 1971

  • The Government of India legalized MTP through the MTP Act, 1971.
  • The Act was introduced with strict conditions to prevent misuse.
  • The main objective of the Act is:
    • To reduce illegal abortions
    • To reduce maternal mortality associated with unsafe abortions

MTP Amendment Act, 2017

  • The Medical Termination of Pregnancy (Amendment) Act, 2017 was enacted under Section 3 of the MTP Act, 1971.
  • According to the Act, consent of only the pregnant woman is required for termination of pregnancy.

Conditions for MTP

Pregnancy may be terminated:

  • Within the first 12 weeks of pregnancy.
  • Between 12 and 20 weeks under specific medical conditions.

A registered medical practitioner must certify that continuation of pregnancy may:

  • Risk the life of the pregnant woman.
  • Cause grave physical or mental health issues.
  • Lead to severe abnormalities in the child.

Amniocentesis

Amniocentesis is a diagnostic procedure in which amniotic fluid containing foetal cells is collected using a hollow needle under ultrasound guidance.

Uses of Amniocentesis

  • Detection of defective foetal development.
  • Study of chromosomes to identify genetic abnormalities in the foetus.

Misuse of Amniocentesis

  • Amniocentesis may be misused for determination of the sex of the unborn child.
  • Sex determination through amniocentesis is legally prohibited in India.

Sexually Transmitted Diseases (STDs)

Diseases or infections transmitted through sexual intercourse are called:

  • Sexually Transmitted Diseases (STDs)
  • Venereal Diseases (VDs)
  • Reproductive Tract Infections (RTIs)

Common venereal diseases include:

  • Syphilis
  • Gonorrhoea

Syphilis

i. Causative Agent

  • Treponema pallidum (Bacterium)

ii. Incubation Period

  • Approximately 3–4 weeks

iii. Site of Infection

  • Mucous membranes of:
    • Genital region
    • Rectal region
    • Oral region

iv. Symptoms

  • Formation of a primary lesion called chancre at the site of infection.
  • Chancre commonly appears on the external genitalia.
  • Other symptoms include:
    • Skin rashes
    • Mild fever
    • Inflamed joints
    • Hair loss
    • Paralysis
    • Degenerative changes in heart and brain

v. Preventive Measures

  • Sex education and awareness.
  • Maintaining sexual hygiene.
  • Avoiding sexual contact with unknown or multiple partners.
  • Using condoms during intercourse.

vi. Treatment

  • Antibiotic therapy using Penicillin.

Gonorrhoea

Causative Agent

  • Gonorrhoea is caused by the bacterium Neisseria gonorrhoeae.

Site of Infection

The bacteria generally infect the mucous membranes of:

  • Urinogenital tract
  • Rectum
  • Throat
  • Eyes

Incubation Period

  • In males: Symptoms usually appear within 2–4 days after exposure.
  • In females: Symptoms usually appear within 7–21 days after exposure.

Symptoms of Gonorrhoea

i. Symptoms in Males

  • Partial blockage of urethra and reproductive ducts.
  • Pus discharge from the penis.
  • Pain and burning sensation during urination.
  • Arthritis.

ii. Symptoms in Females

  • Pelvic inflammation.
  • Inflammation of urinary tract.
  • Sterility.
  • Arthritis.

Effects on Newborns

Children born to infected mothers may suffer from:

  • Gonococcal ophthalmia
  • Gonococcal vulvovaginitis

Treatment

  • Antibiotic: Cefixime

Preventive Measures

  • Maintain sexual hygiene.
  • Use condoms during sexual intercourse.
  • Avoid sexual contact with unknown or multiple partners.

Sexually Transmitted Diseases (STDs)

Common sexually transmitted diseases include:

  • Chlamydiasis
  • Herpes
  • Genital warts
  • Trichomoniasis
  • Hepatitis-B
  • AIDS

Important Note

  • Except Hepatitis-B, genital herpes and HIV infection, most other STDs are completely curable if detected and treated early.

Infertility

Infertility is the inability to conceive naturally after one year of regular unprotected sexual intercourse.

Causes of Infertility

Causes may be:

  • Physical
  • Congenital
  • Disease-related
  • Immunological
  • Psychological

Common Causes

In Females

  • PCOS (Polycystic Ovary Syndrome)
  • Hormonal imbalance
  • Endometriosis

In Males

  • Low sperm count
  • Small penis size

Assisted Reproductive Technologies (ART)

Infertile couples can be assisted to conceive through special techniques called Assisted Reproductive Technologies (ART).

i. IVF (In Vitro Fertilization)

  • Fertilization occurs outside the body under laboratory conditions.
  • The egg and sperm are combined in a test tube or glass dish.
  • A zygote is formed and allowed to develop into an early embryo.
  • The embryo (up to 8 blastomeres) is then transferred into the fallopian tube or uterus.

ii. ZIFT (Zygote Intra Fallopian Transfer)

  • Used when the fallopian tubes are blocked.
  • The egg is removed from the ovary and fertilized outside the body.
  • The zygote is then transferred into the fallopian tube.

iii. GIFT (Gamete Intra Fallopian Transfer)

  • Used when the upper part of the oviduct is blocked.
  • A donor ovum is transferred into the fallopian tube.
  • Ova and sperms are introduced into the oviduct where fertilization occurs naturally.
  • The success rate is about 30%.

iv. ICSI (Intra Cytoplasmic Sperm Injection)

  • A single sperm is directly injected into the cytoplasm of an ovum under laboratory conditions.

v. Artificial Insemination (AI)

  • Used when the male partner has a very low sperm count.
  • Sperms are collected and artificially introduced into the cervix of the female.
  • Fertilization occurs inside the body (in vivo).

vi. IUI (Intra Uterine Insemination)

  • Similar to artificial insemination.
  • Sperms are directly introduced into the uterus.

Sperm Bank

A sperm bank or semen bank is a facility that collects, stores and supplies human sperms or semen.

  • The semen is donated by healthy males called sperm donors.
  • Sperms are preserved through cryopreservation at very low temperatures.

Adoption

Adoption is a legal process through which a couple or a single parent acquires the rights and responsibilities of raising a child as their own.

  • The adoptive parent must be:
    • Medically fit
    • Financially capable of caring for the child
  • A person must generally be at least 21 years old to adopt.
  • There is no fixed legal upper age limit for adoption.

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