Download REPRODUCTION Reproduction is a process of production of new

REPRODUCTION
Reproduction is a process of production of new generations of ones own kind. It is one of
the basic characteristics of all living things. However it is not essential for the survival of
an individual i.e. an individual can live with out even this process.
The process of reproduction involves the transmission of genetic material from
one generation to the next. It enables a species to survive for longer periods.
Reproduction may occur asexually or sexually. A sexual reproduction is different
from sexual in a way that it does not involve the fusion of male and female gametes.
Unicellular organisms and simple multicellular organisms reproduce asexually where as
higher animals like fishes, mammals etc reproduce by sexual means.
REPRODUCTION IN HUMANS
Humans reproduce sexually. In humans male and female sex organs are present in
different individuals. Male has sex organs that can produce and transfer male gametes
called sperms and the females reproductive organs are meant to produce eggs, conceive
male gametes and hold the fo4etus during gestation period of 9 months. Reproduction in
humans involve gamete production, copulation, fertilization, implantation, gestation,
birth and growth.
Gametes
The reproductive cells produced by a male and a female are called gametes.
Male gametes
Male gametes are the single celled reproductive structures called sperms.
Structure of a sperm
A sperm is a tiny cell. It is about eight times smaller than an average animal cell.
It can be distinguished into three regions, head, neck and tail.
The head contains a nucleus surrounded by cytoplasm which extends to make a
tail. The structure of a normal sperm is shown in fig 1. Their function is to fuse with a
female egg to make a zygote.
Sperm foramtion
Sperm production starts in humans at the age of 11 to 13 years. The sperms are
produced by actively dividing cells of the seminiferous tubules of the testes. The inactive
sperms produced in the tewstes are stored in the epidydimis. During sexual intercourse
the peristalsis in the sperm duct passes them out. The sperms not ejaculated are broken
down and reabsorbed. Secretions of the prostae gland and seminal vesicles produce a
fluid medium for the movement and nutrients for the sperm. The secretions also contain
enzymes, which activate the sperms after they are deposited in the vagina. In the female
body the sperms can survive for 1 to 3 days however they are highly fertile for 12 to 24
hrs.
Female gametes
The female ovaries contain potential egg cells. These cells are produced during
the development of a female foetus. However they mature one every month from the
alternative ovaries between age of 11 to 14 years.
The egg cells released from the ovary is called secondary oocyte. It travells down the
oviduct and when nfuses with the sperm the second meiotic division completes and the
secondary oocyte divides into a large cell, ovum and a smaller one second polar body.
Gamete formationThe male gametes, called sperms are produced in the testes and the
female gametes, called ova( ovum: singular) are produced by the ovaries. Both the
formation of sperms and eggs involve meiosis. The meiosis reduces the number of
chromosomes to half.
An egg cell released from an ovary is shown below.
The secondary oocyte differes from an ovum that the secondary oocyte divides to
produce another polar body.
A sperm cell has the half the number of chromosomes so that it restores the diploid
number of chromosomes i.e. 46 in humans after fusion with the female egg cell that also
has the half the number of chromosomes. The pointed head of a sperm helps to penetrate
the membrane of the egg cell. The propelling movements of the tail move the sperm
clo9ser to the egg cell. The energy needed for the movement of the tail is provided in the
form of ATP by oxidation of glucose. Large number of mitochondri produce more ATP.
Sperm formation
Formation of sperms takes about 70 days and 120 million sperms are produced in
a day. Their production starts between the ages of 14 to 17 years in boys.
The lining of the semineferous tubules contain actively dividing cells. This layer
of cell’s called germinal layer divides repeatedly by mitosis to produce many layers of
cells. Each cell enlarges in size and undergoes meiosis. The first meiotic division
produces secondary spermatocytes, which divide by second meiotic division to produce
immature sperms, spermatids. The spermatids move towards the lumen of the
seminiferous tubules and are moulded into sperms between the infoldings of the sertoli
cells. The sperms produced are passed into and storen in the epidydimis.
Egg formation
As it is stated earlier that the potential egg cells are produced in females even
before their birth. These potential egg cells divide into primary oocytes by mitosis. The
primary oocytesundergoe meiosis and remain at prophase of first meiotic division
through out the child hood and one of them matures in graffian follicle every month after
puberty. It bursts to release a secondary oocyte.
HUMAN REPRODUCTIVE ORGANS
The visible parts of the reproductive system are called genitalia. The organs that produce
reproductive cells are called gonads. In addition to these structures the reproductive
system consists of glands and ducts adapted for successful reproduction
Male reproductive organs
Testis
A pair of testis lie outside the abdominal cavity in a man, which are contained in a saclike scrotum hanged dowqn between the legs. This position proteccts the testis from
injurious. It also keeps the about 2 to 3 C lower than the body temperature. The lower
temperature of the testes favours the development of the sperms in the testes.
Structure of testis
Each testis consists of upto 900 coiled seminiferous tubules. Each tube is half a
meter long. The sperm formation takes place here.
Epidydimids
It is a coiled tube about six meters in lenghth. The sperms produced in the testes
are passed into the epidydimis where they are stored. The sperms that pass from testis to
epidydimis are non motile and non-fertile. After passing a day in the epidydimis they
become capable to move and fertilize but they remain inactive in the male reproductive
system. They become active after they are ejaculated. The secretions of the prostate and
seminal vessicles activate them.
Seminal vessicles
The seminal vessicles lie at the posterior wall of the urinary bladder close to the terminal
of sperm duct.
The seminal vessiicles secrete mucus and a watery alkaline fluids that contains
nutrients i.e. fructoose and prostaglandins
Each seminal vessicle empties its contents into the ejaculatory dict during the sexual
intercourse. The secretions of the seminal vessicles add to the bulk of the semen. The
fructose provide nutrition top the sperms and the prostaglandins help sperm to penetrate
the cervical mucus and causes reverse peristalsis in the walls of the uterus and fallopian
tubes to carry sperms towards the egg.
Prostate glands
The prostate gland encircles the urethra just inferior to the urinary bladder. It
secretes mucus and slighltly alkaline fluid, which is released during ejaculation. The
acidity of the vagina can greatly reduce the activity of sperms and even kill them. The
alkaline secretions neutralize the acidity of the vagina and greatky enhance the motility
and fertility of the sperms.
Penis
The penis is a part of the genitalia. It is a copuilatory organ of the male and is
desighned to transfer semen into the female reproductive system.
A penis consists of a long shaft. The tip of the penis is smooth and enlarged called
glans. The penis is covered with a membranous skin that continues over the glans is
called prepuce or foreskin. The shaft of the penis contains spongy tissue. It becomes erect
when the spongy tissue is engorged with blood during sexual excitement. The rigid, erect
and enlarged penis can be inserted into vagina during copulation. It can adequately
deposit the semen into vagina closer to cervix.
Cowper’s gland
There are tiny, pea shaped glands inferior to the prostate. They produce a thick,
clear, alkaline mucus that passes into the urethra. It washes remains of the urine out of the
urethra. It also neutralize the acidity in the urethra.Semen
Semen, which is ejaculated during the male sexual mact, is composed of the
following componbents.
Fluid medium
Sperms
The sperms make up about 10% and the secretions of the seminal vessicles are about
60%. About 30% of the fluid is added by the prostate gland. 15 to 30 minutes after the
semen is ejaculated the sperms beco0me active.
Female reproductive organs
External organs
The external oregans are called external genitalia. It includes vulva.
Vulva
Vulva consists of pubis, labium, clitoris, opening of urethra and vagina and the
vaginal gland
Pubis
Pubis bears the pubic hairs after puberty.
Labium
The vulva has two pairs of lip like folds of the skin. The outer ones are pigmented
and hairy called labium majora. It is comparable to scrotum in males. They enclose the
labium minora, which is hair free fold of skin.
Clitoris
It is a small structure, homologous to the male penis. It consists of highly
sensitive erectile tissue. During sexual intercourse it erects and when rubbed by the penis
produces feelings of pleasure and stimulates to reach a woman at sexual climax
Opening of the urethra
Posterior to the clitoris and opening of the urinary system is present. It does not
play any role in reproduction. In a male however there is a single opening of urethra
meant for passing urine as well as realeasin semen
Opening of the vagina
The opening of the vagina is partially closed by a membrane called hymen. This
opening is meant to recveive penis during sexual intercourse and releases the blood, dead
egg and shredded lining of the uterus during menses. It is an opening that also allows the
release of baby during birth and release of placenta, membranes, umblical cord etc after
birth.
Internal female organs
The internal organ include vagina, uterus, fallopian tubes also called oviducts or uterine
tubes, ovaries and the structures that hold them in the abdominal cavity.
Vagina
It is about 10 cm in length and extends from vulva to the cervix. It serves as
copulatory organ and birth canal. It also permits passage of the menstrual flow.
Uterus
It is an inverted pear shaped organ. Its narrower end, cervix is situated downward
that open into the vagina. It is located between the urinary bladder and the rectum. Uterus
is the site for the implantation of the fertilized egg and also holds the embryo or foertus
during its development and growth.
FEMALE MENSTRUAL CYCLE
Females produce eggs regularly during a menstrual cycle or oestrous cycles. It completes
in about 28 days. The lenghth of menstrual cycle is h9ighly variable. It may be of 21 day
or 38 days.
The signs of sexual maturity in girls is the discharge of blood or menses from the
uterus via the vagina. It is the onset of the puberty. In the beginning the menstrual cycles
may be irregular but becomes regular after one to two years. The menstrual cycles
continue regularly every month from about 12 to 45 years of age except the periods of
pregnency. After the age of 45 the menses stop and this is the age when a woman can not
become mother. This end of menstrual cycles is called menopause. The menstrual cycle
can be divided into three stages.
Menstrual stage
From1 to 5 days of the cycle the blood, dead unfertilized egg and the sloughed off
lining of the uterus that was thickened to receive a fertilized egg for implantation, is
discharged via the vagina.
Proliferative stage
The thickening of the uterus lining takes place during this stage. The
endometrium is prepaired to receive a fertilized egg. The changes in the uterus lining
occur under the 9influence of oestrogen. This stage can be distinguished from 6 to 14
days. It starts with the end of the bleeding and ends with the ovulation.
Secretory stage
After the ovulation to the end of the menstrual cycle. Approximately 15 to 28
days. During this period the progesteron produced from the corpus luteum increases the
blood supply to the endometrium. It caus4es the glands in the endometrium to develop.
The glands increase in size and secrete nutrients to sustain a developing emryo, untill the
implantation occurs.
Ovulation
Another very important event occurs from days 13 to 15 is the ovulation. The
ovulation is the release of a single egg cell, the secondary oocyte from the graffian
follicle into the peritonial cavity.
The graffian follicle increases in size under the influence of LH (leutinizing
hormone). As the LH reaches its maximum concentration in the blood on the 13 day, it
causes the graffian follicle to increase further in size. The graffian follicle bursts on 14th
day, releasing the secondary oocyte.
Hormonal changes during menstrual cycle
After the menstrual stage ( menstration) lasts from first 4 to 5 days, the pituitary gland
secretes a hormene, FSH ( follicle stimulating hormone). It stimulates the ovaries to
develop an egg and to release certain hormones. The various hormones released during
the menstrual cycle and the changes taking place in the uterus and the ovary at the same
time are briefly explained below.
The FSH released, stimulate the development of the graffian follicle.
The developing graffian follicle secretes a female sex hormone oestrogen. Its
concentration increases in the first half of the menstrual cycle graduallly. It reaches at
maximum during the menstrual cycle from day 11 to day 13. The oestrogen effects the
uterus and pituitary gland.
in the uterus it stimulates repair and development of the lining of the uterus so it prepares
it for the possible implantation after the fertilization has occurred.
The secretion of oestrogen also inhibits the secretion of FSH so it prevents the
development of any other follicle and ensures the release of one egg only at a time.
The higher concentration of oestrogen triggeres the release of LH.
The concentration of LH reaches at maximum from day 11 to day 13. It causes the
ripening of the graffian follicle. At day 14 it bursts to release a secondary oocyte into the
funnel of the oviduct whose ciliated cells waft it into the tube. The LH stimulate the
development of the remainintg part of the graffian follicle to an endocrine gland called
carpus luteum, yellow body.
The corpus luteum produces anothe hormone progesterone along with oestrogen. The
progesterone maintains the thickening of the endometrium. It also inhibits the secretion
of LH and FSH
If fertilization does not occur, by unknown means, however, the corpus luteum
degenerates. The decline of the ovarian hormones in the blood causes the blood vessels in
the endometrium to kink and become spastic. It causes the menses to begin by 28th
daySEXUAL REPRODUCTION IN HUMANS
The sexual reproduction in humans involves
The sexual intercourse
Fertilization
Implantation
Gestation
Birth
Sexual intercourse
(Copulation)
The erect penis is the first sign of the sexual excitement in males. The sexual
excitement may be due to an inborn stimulus like filling up of the sexual organs with
secretions or an out born stimulus like messaging on the glans penis or the scrotum. The
psychic factor of the sexual excitement can not be ignored. Just thinking or dreaming
may even drive the sexual act to occur and culminate in ejaculation.
The sexual stimulus causes the dilation of arterioles in the penis. The arterial
blood flows into the spongy tisssue in the shaft of the penis. The flow of blood into the
erectile tissue and the higher presuure inside causes the penis to become hard and
elonngated.
The erect penis can easily be inserted into the vagina. thE movements of the penis
during the sexual intercourse stimulate the muscles in the scrotum and around the
epididymis and sperm duct to contract, the peristaltic wave pushes the sperms from the
testis along the sperm ducts to the urethra. The secretions from the seminal vessicles and
prostate gland are also released. The sperms are mixed with these secretions making the
semen. The filling of the urethra stimulates the penile muscles to contract and the
continuing peristalsis in the urethra pushes the semen out through the urethra. This
process is called ejaculation. And is the climax of the male sexual act called orgasm or
sexual orgasm. After sexual orgasm the sexual excitement diminishes and the erection
ceases.
The elongated, hard penis and the forceful ejacualtion help to deposit the semen
into the deepest recess of the vagina closer to the cervix.
Journey of sperms
Passage of sperms from testis to vagina
The sexual stimulus produces a reflex that causes the smooth muscles in the
epidydimis, sperm duct and urethra to contract and produce a peristaltic wave that pushes
the sperms from testis to the epididymis, sperm duct and urethra and then out of the
urethra called ejaculation.
Passage of sperms in the female body to the egg
Approximately 3 cubic cm of semen is deposited in the vagina close to the cervix.
The semen contains hundreds million of sperms. The sperms must travel a distance from
cervix to the fallopian tube, as shown in the diagram, to fertilize an egg. This travel in the
female body is aceived by these ways.
Uterine contractions
Movement of the cilia lining the uterus and fallopian tube.
Movements of the sperm by its tail.
The chemicals in the semen stimulate contractions in the walls of the vagina and uterus.
These contractions possibly squeeze the sperms upward. The cilia lining the uterus and
oviduct also propels the sperms to meet the egg passing down through the fallopian tube.
oNly a few thousan of the sperms succeed to reach at the opening of the oviduct. The tail
of the sperms propels them closer to the egg. If the secondary oocyte is present in the
oviduct, the sperms surround it. Thge sperms spend several hours in the genital tract to
become active. Unless they pass almost seven hours in the genital tract, they can not
fertilize an ovum.
Fertilization
Although several thousands of sperms may reach an egg but only one them enters
it. The sperms get closer to the egg by lashing their tails and reach the outer surface of the
zona pellucida. The head of the sperms produces an enzyme that makes an entry through
bthe zona pellucida. Once a sperm makes its entry through the zona pellucida, the
cytoplasm of the secondary oocytwe secretes a substance that hardens the zona pelloucida
making a protective layer that prevents entry of any other sperm.
Second meiotic division completes and secondary oocyte divides to make an
ovum. The nucleus of the sperm fuses with the nucleus of the ovum to form a zygote.
The fusion of male and a female nuclei to make a diploid cell known as zygote is
called fertilization.
After fertilization the zygote undergoes a successive mitototic division. The
zygote turns into a ball of cells and continues to pass down the oviduct.
Transport in the oviduct
After fertilization has occurred, it takes 3 to 4 days to a fertilized ovum to reach
the uterus. This transpoprt is brought about by the beating movements of the cilia lining
the oviduct. The weak muscular contractions in the walls of the fallopian tube also help
the egg/zygote to pass down.
Fig. Showing the process of fusion of male and female gametes.
1 the sperms are bumping
Into the jelly coat round the egg.
2 One of them penetrates
into the jelly.
3 The head of one sperm only enters into the cytoplasm. The tail remains
outside.Implantation
The delay during the passage of zygote down the oviduct enables few successive
cell divisions to occur and divide it into a ball of cells. This ball of cells(embryo) emeds
itself with in the endometrium on seventh day after fertoilization. This process is called
implantation.
DEVELOPMENT OF EMBRYO
Early nutrition of the embryo
Before fertilization the sperms obtain their nutrition from the seminal fluid that
contains carbohydrates, i.e fructose in it. The cytoplasm of the egg contains reserve
glycogen used for it. After fertilization, before implantation, the embryo obtains its
nutrition from the endometrial secretions called” uterine milk”.
After implantation the finger like projections called chorionic villi embedded in
the wall of the uterus absorb nutrition from the endometrium. It continues for at least 8
weeks untill the placenta develops.Pregnancy and placentaThe period of development
between fertilization and birth is called pregnency. Human pregnancy lasts for about nine
months. During that time the hormones released from the corpus luteum in the beginig
and from the placenta later on prevent the monthly occurrence of menstruation and
ovulation. The implantation ensures the presence of these hormones in the blood. Thus
implntation in its true sense, the origin of new life, called conception. If the implantation
fails pregnency can not be held.
Placenta
A placenta is a disc shaped organ with millions of tiny root like out growths
called villi or chorionic villi. it is unique organ in the females formed only during
pregnency and released out after birth. It is made from the contribution of tissues from
two individuals i.e. endometrium of the uterus of he mother and the tissue from
developing embryo. Its function is to allow exchange of materials between mother and
foetus.
Blood flow to and away from placenta
A placenta is connected with the foetus by a tube called the umblical cord. The
foetus’ heart pumps blood through two umblical arteries to the placenta where it flows
through capillaries in the placental villi. The capillaries join together and forem a broader
blood vessel, umblical vein that carries blood from placenta towards the enmbryo. The
u8mblical vein opens into the vena cava of the embryo that inturn empties into right
atrium of the embryo’s heart.Functions of placenta
The main function of the placenat is the exchange of substances between the
blood of the mother and that of the foetus.
Mechanism of exchange of substances
The chorionic villi increase the surface area for the exchange of substances. The
cell surface membranes of the cells in the walls of the chorionic villi further increase the
surface area for exchange of substances. The substances may be exchanged between the
blood of mother and the foetus by diffusion , osmosis, active transport and pinocytosis.
Exchange of useful substances
Water
Water can cross the placenta by osmosis.
Nutrients
Glucose, amino acids, lipid, minerals salts and vitamins from the mothers blood
can pass into the blood of the foetus. Most of these substances diffuse from mothers
blood out through the thin membrane between into the foetal blood. The minerals mainly
cross the placenta by active transport.
Respiratory gasses
Oxygen is needed for aerobic respiration and diffuses from the region of high
concentration from the mothers blood to the blood of foetus. The haemoglobin of the
foetus has higher affinity for oxygen than that of an adult so it increases the efficiency of
oxygen exchange. Carbon dioxid4e is a product of cellular respiration. It is carried from
the fetus to the placenta through umblical arteries. It diffuses from blood of foetus to the
blood of mother.
Excretory products
From Biological science
Embryonic development anbd extra embryonic membranes
Amnion
The amnion encases the young embryonic body. The space between the embryo and the
amnion is filled up with afluid, amniotic fluid.
Functions of amniotic fluid
It prevents the embryo from sudden temperature fluctuations.
It acts as a shock absorber and prevents an embryo from trauma.
During growth the embryo roles around in the womb, amniotic fluid provides buouancy
to it.
It provides lubrication and facilitates the movements of head through the birth canal
during birth.
Amniocentesis is technique that involves, taking samples of the amniotic fluid that
contains cells from the embryo and its studies for gender and predisposition for genetic
disorders.
Yolk sac
The yolk sac in humans has lost its functions, which was to pass nutrients to the
embryo after digesting the yolk mass.
Allontoise
The allontoise is a redumentary structure in humans. However in birds and
reptiles, it is repository for embryonic wastes.Development of the embryo
Fertilization results into the formation of a diploid cell called a zygote. It
undergoes repeated cell divisions to make an embryo. Almost the 100 celled embryo
embedds itself into the endometrium. Conception, the begining of the development of a
new individual takes place when this embedding is complete.
Six weeks after conception, the embryo is recognisably human and is called
foetus. The foetus normally completes a total of about 38 weeks, nine months of
development, before birth occurs. This period of development from conception till the
birth occurs, is the gestation period or pregnency.
The age of the unborn baby can be calculated from the first day of the mothers
last period. Calculate the age of the foetus on April 21, if the mothers last menses ended
on November 5.? The age you calculate is the menstrual age. The exact age of the unborn
should be calculated from the time of fertilization. However it is impossible to determine
the time of fertilization with accuracy.
Hormonal factors in the pregnancy
In the early pregnancy, the corpus luteum produces oestrogen and progesterone.
Its maintenance itself is under the control of a hormone released by the outer cells of the
embryo for the first 10 weeks, untill the placenta develops. Later on the placenta
produces oestrogen, progesterone and some other hormones. A a brief description of the
hormones involved during pregnancy is given below.
Chorionic gonadotropin
(Embryonic LH)
it is similar to leutinizing hormoone produced by the pituitary gland. Its very
important function is to prevent the degeneration of the corpus luteum. It also causes the
corpus luteum to secrete more oestrogen and progesteronme. These are very essential
hormnes during the pregnancy.
The chorionic gonadotropin hormone also stimulates the foetal testes to secrete a
hormone testosterone. Testosterone causes the growth of male sex organs. It also caus3es
the testes to descend into the scrotum.
Oestrogen/ Progestrone
The graph below shows the daily concentration of oestrogen and progesterone
during the pregnancy. Oestrogen is produced by the developing follicle before ovulation
and after ovulation, the cvorpus luteum fulfils this responsibilty. The corpus luteum
degenerates 2-3 months after conception. Meanwhile the placenta develops and produces
this hormone.
The oestrogen produced during menstrual cycle is released by developing follicle
and performs the following functions. It causes the growth and enlargement of the
primary sex organs. It brings about the proliferation of the ndometrium. It repairs the
endometrium and prepares oit for the implantation of a fertilized ovum.
In females it causes the development and growth of the breasts. It stimulates the
brteasts to grow and deeposit fats. The oestrogen and progesterone are also responsible
for the secondary sexual characteristics in females. One of the very imporatant functions
of the oestrogen and progesterone is inhibition of release of FSH by pituitary gland.
The placental oestrogen plays role similar to the ovarian oestrogen. The higher
concentration of oestrogen during pregnancy causes
Enlargement of the uterus
Enlargement of the breasts and growth of the breasts ductal structure
Enlargement of females external genitalia
It also bring about the widening of the pelvis and prepares it for the easier passage of the
foetus through the birth canal.Secondary sex characteristics
The bodies of the children undergoe extensive changes under the influence of
hormones. The changes turn the children into adults. This period of transition of children
into adults is called adolescence and the onset of primary sexual characteristics is called
puberty. This is accompanied by the development of scondary sexual characteristics.
Some of the physical changes which take place in the females include.
Development of subcutaneous fat
Development of breasts
Widening of hips
Slight deep-ing of the voice
Development of hairs under arms and in the pubic region.
Response of mothers body to the pregnancyThe most obvious response to the pregnency
in females is the increase in size of the various sex organs. The size of the uterus
increases significantly. The breasts almost double in size.
Normally the weight of the prgenent women increases. The increase of weight
may be partly due to the foetus and the amniotic fluid. The desire for food increases so
more food is eaten. It is drawn by the foetus from the mother’s blood and part is
converted to fats that are stored in the mother’s body.
The metabolic rate also increases. It may result into 5the overheating of the body
towards the end of the pregnency.
The increased demand for oxygen due to higher metabolism slightly increases the
breathing rate.
Care during pregnancy
A pregnant woman should rgularly be examined by the doctors. She should eat
the right kinds of food and avoid the activities that may harm her baby. She should also
take some kinds of exercises to keep herself fit and prepare herself for the birth of her
baby.
Nutrition during pregnancy
Harmful substances that a pregnant woman should avoid
Alcohol
Smoking
BIRTH
Approximately nine mon5ths after conception the baby is ready to be born. During the
last months of pregnancy, the uterus walls develop a thick layer of muscles. A baby
usually turn its body with in the uterus untill its head is directed downwards towards the
cervix. The downward head facilitates the delivery. Once the head is pushed out through
the vagina, the rest of the body follows it quickly.
The normal delivery becomes very difficult if the baby is positioned with head
other than downwards. Birth takes place in three stages. The entire process of the birth is
ub\nder the controll of the changes in concentration of hormones in the blood of mothers
towards the end of the term.
The level of progesteron falls as culmination of pregnancy occurs. Conversly the
oestrogen level rises in the blood. Another hormone that stimulates the contractions of
uterine muscles is the oxytocin. The contractions come every 20 minutes at first, but as
the birth approaches the become more frequent and powerful. This is the onset of the
labour.
First stage
The forceful contractions in the uterine muscles cause the amnion to break and
release the amniotic fluid. This is called the “show”. First a pinkish mucousy substance
that had closed the cervix during the pregnancy comes out. The amniotic fluid then
gushes or runs out slowly through the vagina. It lubricates the vagina or birh canal. The
opening of the cervix dilates about 10cm wide. This first stage is extremly painful.
Second stage
The muscular contractions continue and become more forceful. These
contractions run from upside downwards pushing the baby outward. The contractions in
the walls of the vagina and the abdominal muscles also assist to expel the baby out of the
uterus and down the vagina, usually head first. Once the head is born the hard work is
almost over because rest of the body follows much more easily. The lack of bony
structure in the head helps the head to be squeezed through the birth canal and facilitate
the birth. The sequence of events described above that lead to the birth of a baby is called
labour.
After leaving the mother, a baby takes its first braeth and usually begins crying.
The cryinmg of the baby establishes the regular breathing. When the baby is breathing
regularly the umblical cord is clamped at the two places and cut from inbetween. In a few
days, the remains of the umblical cord attached to the babies abdomen shrivel and falls
away, leaving in the abdominal wall a scar called the navel.
Third stage
Few minutes later the baby is born, placenta breaks from the walls of the uterus
and is pushed out of the uterus along with the extra embryonic membranes, blood and
umbilical cord. It is called after birth. The blood vessels supplying to placenta constrict
and limit the blood loss to 350cm.
Fetal circulation
In a developing fetus, the lungs and digestive system do not function. Instead all
the nutrients, excretory and gases exchange occurs through the placenta. Nutrients and
oxygen diffuse across the placenta barriers from mothers’ blood into fetal blood, and
carbondioxide and other excretory waste substances diffuse from foetal blood to the
mothers blood.
Foetal blood travels through the umbilical cord, which contains three blood
vessels; two smaller umbilical arteries and one larger ubilical vein.
The umbilical vein
It carries oxygenated blood, rich in nutrients from placenta to the foetus.
The umbilical arteries
They carry carbondioxide and metabolic wastes from the foetus to the placenta.
They transport blood away from the foetal heart. The two umbilical arteries wrap around
umbilical vein from naval of the foetus to their attachement at placenta. The circulatory
system of a foetus is shown below in the figure.
As the lungs are non-functional in a foetus, so the blood by passes them in a foetus. There
are two shunting mechanisms that ensure the blood bypasses the lungs.
Foramen ovale
Ductus arteriosus
Foramen ovale and ductus arteriosus
Foramen ovale is a flap like opening present in the wall separating the two atria.
The blood entering into the right atrium passes to the left atrium via this hole. Some of
the blood from the right atrium that flows inro the right ventricle is pumped out through
pulmonary artery. But it is returned to the atria via ductus arteriosus bypassing the lungs.
As the lungs are non-functional and collaps4ed, they provide high resistance to the flow
of blood in pulmonary artery, so the blood enters readily to the aorta via ductus
arteriosus.
Changes in the foetal circulation at birth
At birth the umbilical cord is tied and cut off. The constriction of the umbilical
arteries rises the blood pressure inside the right side of the heart. This change in the
pressure insisde the right atrium closes the small valve guarding the foramen ovale. It
prevents the short circulating of the blood from right atrium to the left atrium. The
inflation of the lungs also reduces the resistance to the blood flow through pulmonary
arteries, so blood does not return through ductus arteriosus. These changes in the foetal
circulation bring about the normal pulmonary circulation occur in addition to the normal
systemic circulation.
Care for the new born
The normal birth usually produces, healthy babies. The normal weight for the new
born is on average 8lbs. However, it greatly varies due to various factors. Some of the
factors are given below.
Mothers on poor diet during pregnancy
Physical health of the mother during pregnancy
Life style of the mother
The age of the mother
Placental development
Genetic predisposition
Multiple birthsThe hormones like, prolactin and oxytocin are released into the blood.
Towards the end of the term oestrogen stimulates development of breasts. Mammary
bglands in the breasts are prepared to secrete milk. Soon after the birth the baby sucks its
mother’s nipples. This sets the release of prolactin from the pituitary gland that causes the
mammary glands to rlease milk.
Milk is the baby’s only food for the first few months of life. Human milk contains
the right proportion of various nutrients for human babies. However it does not contain
iron in it. It is an essential mineral needed for the formation of haemoglobin. The foetus
uses the iron stored in its own body during the gestation period. Breast milk is the
balanced diet for early months of life. The baby can not take solid food at this stage due
to the various reasons.
has no teeth, so can not chew solid food
the gut is unable to digest it
Advantages of breast feeding
the milk produced for the first few days after birth is called clostrum. It is particularly
rich in antibodies and low in fat. It protects the baby against certain diseases, the mother
has already recovered.
The breast milk is available all the times and is at the normal body temperature.
It is usually free from bacteria, provided the breasts and nipples are properly washed and
air dried.
Mother’s milk is more easily dig4ested by the baby.
It is cheaper than the bottle feeding and readily available.
It also allows close contact between the mother and a baby, which is good fore both of
them, physically and emotionally.
It provides the right proportion of minerals for a baby.
Growth
Contraception
Contraception can be defined as ‘deliberately preventing pregnancy’. There are various
reasons for the contraception
Reasons for contraception
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Use of contraceptive methods
Using methods of contraception enables people to choose when they want
children and how many children do they want. This choice is called family planning or
borth control. The choice of the use of the contraceptive method depends upon various
factors. They are listed below.
The method used should be
reliable
acceptible to both of the parteners
comfortable and easy to use
harmless or lwess likely to cause harm.
In keeping with one’s religious and ethecal beleifs
The age of the couples and whether they require a short term, long term or permanent
contraception are other criteria for making a choice of the use of a contraceptive method.
However any of the contraceptive method used ensures that
Either the sperms do not reach to the egg or
Eggs are not produced or
Fertilized eggs are prevented from developing inside the uterus.
Methods of contraception
Methods of contraception can broadly be grouped into
Natural contraception
Physical contraception
Chemical contraception
Hormonal contraception
Surgical contraception
Natural contraception
There are two of natural contraception
abstinence
rhythmic method
Abstinence
It is possible for some of the couples or individuals not to have a sexual
intercourse at all. Avoiding the sexual intercourse at all is called abstinence.
It is common for nuns, monks and preists of certain religions. It is hundred
percent reliable.
Rhythm method
In this method the couples only avoid sexual intercourse during the fertilre period.
The sexual intercourse in the safe periods is less likely to result into pregnency. The risk
of pregnency depends upon, how accurately the fertile and safe periods are judged. Some
of the ways for working out the fertile and safe periods are given below.
Calender method
Ovulation normally occurs about half way between one menstrual cycle and the
next, usually between days 12 and 16 in a menstrual cycle.
By keeping the record of, when the last six or more periods started, the time of
ovulation can be calculated
Temperature method
Just after ovulation the body temperature rises slightly.
By recording the body temperature every day over several months, the woman
can work out , when the ovulation occurred and when is likely to occur in future.
Recommendations
The time of ovulation and the time between menstrual periods may vary,
particularly in the teenagers. And it is difficult to keep record of the temperature for very
long periods. So this makes the natural method difficult to use.
Withdrawal
The penis is withdrawn from vagina before ejaculation
Recommendation
This method is unreliable as small amounts of semen may leak before ejaculation.
It also requires much self discipline. It has higher failure rate.
Physical methodsUse of condoms
A condom is a thin rubber sheeth. It is unrolled over erect penis before sexual
intercourse. It prevents the release of semen into the vagina, so stops the sperms entering
into the vagina.
Recommendations
It is cheap and easily available. It is also easy to use and also protects from
STD’s. it disrupts the act of love making and may slip off or tear during sexual climax. It
is less reliable and the failure rate reduces with the experienced use.
Diaphragm
It is a flexible rubber cap, which fits over the cervix. It prevents the entry of
sperms into the uterus. It is available in various sizes and is inserted into the vagina
before sexual intercourse and should be left in place for 6 to 8 hrs after sexual
intercourse.
Recommendations
If the diaphragm is not of the right size, its use may be risky. It needs to be
regularly checked by the doctors whether it is of the right size. It can be fit into place by
the doctor or a training is needed to use it. It becomes very reliable if combined with a
chemical method.
IUD ( Intra uterine device)
It is a small copper or plastic wire that is inserted into the uterus by a doctor.
Surgical method
Vasectomy
Hormonal contraception
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