Development Of Fetus

DEVELOPMENT OF FETUS DEFINITION Conception: It is defined as the union of a single egg and sperm, marks the beginning of a pregnancy. The act of becoming pregnant, by the fertilization of an ovum. Foetal development After the embryonic period (8 weeks) and birth the developing human is called a foetus. FERTILIZATION :Following ovulation, the ovum passes into the uterine tube and is moved along towards the uterus. At this time cervix, under the influence of oestrogen, secretes a flow of alkaline mucus that attracts the spermatozoa. At intercourse about 300 million sperm are deposited in the posterior fornix of the vagina.Those that reach the loose cervical mucus survive to propel themselves towards the uterine tubes while the remainder are destroyed by the acid medium of the vagina. Only thousands reach the uterine tube where they meet the ovum, usually in the ampulla. During this journey, the sperm matures and is capable of releasing the enzyme hyaluronidase, which allows penetration of the zona pellucida and the cell membrane is sealed to prevent entry of any further sperm and the nuclei of the two cells fuse. The sperm and the ovum are known as the male and female gametes, and the fertilised ovum as the zygote. AMNIOTIC FLUID : Amniotic Fluidity is secreted by the amnion, especially the part covering the placenta and umbilical cord. Some fluid is exuded from maternal vessels in the decidua and also from fetal vessels in the placenta. It increases in amount weekly until there is approximately 800-1200 ml at term. It is a clear, pale straw colored fluid 99% water and 1% is dissolved solid matter. FUNCTIONS OF AMNIOTIC FLUID : 1. It distends the amniotic sac and allows for the growth and free movement of the foetus. 2. It maintenance of constant body temperature for the fetus and provides small amounts of nutrients. 3. It equalizes pressure and protects the fetus from jarring and injury.

4. It protects the placenta and umbilical cord from the pressure of uterine contractions during labour. PLACENTA: Placental development begins at third week of embryonic development and develops at site where embryo attaches to uterine wall FUNCTIONS OF PLACENTA: ➢

Produces 4 hormones necessary to maintain pregnancy

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Support fetus for respiration, nutrition, excretion

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Storage of glucose in the form of glycogen and reconverts to glucose and also store proteins, calcium and iron

Fetal sac: It consists of a double membrane, outer membrane is the chorion, which lies under the capsular deciduas and becomes closely adherent to the uterine wall. The inner membrane is the amion which contains the amniotic fluid. Choroin: It is a thick opaque, friable membrane derived from the trophoblast.It is continuous with the chorionic plate, which forms the base of the placenta. Amion: It is a smooth, tough, translucent membrane derived from the inner cell mass. It is thought to have a role in the formation of the amniotic fluid. UMBILICAL CORD: ➢

Develops from amnion Body stalk attaches embryo to yolk sac, fuses with embryonic portion of placenta

➢ Provides pathway from chorionic villi to embryo

➢ Contains two arteries and one vein ➢

Surrounded by Wharton’s jelly to protect vessels

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Wharton’s jelly: Specialized connective tissue protects blood

vessels Function of umbilical cord: Provides circulatory pathway to Embryo

Pre-embryonic stage The first two weeks following conception is called the preembryonic period. Embryonic development From the fourteenth day after conception through the eighth week of pregnancy the products of conception are referred to as the embryo.

Third week: The embryonic disc becomes elongated and pear-shaped, with a broad cephalic and a narrow caudal end.The ectoderm formed a long cylindrical tube for brain and spinal cord development.The gastrointestinal tract developed from the endoderm appears as another tube like structure communicating with the yolk sac. The most advanced organ is the heart. At 3 weeks, a single tubular heart forms outside the body cavity of the embryo and by the end of 28 days, it starts beating at regular rhythm and push its own primitive blood cells through the main blood vessels.

Fourth week: The interval between date 21 and 32 is characterized by somite formation.Somites are a series of mesodermal blocks that forms on each of the midline of the embryo.The vertebras that form the spinal column develop from these somites.Arm and leg buds are not visible but tail bud is visible.By this time 4 pirs of pharyngeal pouches are developed.The first arch forms the lower jaw, second-the hyoid bone and the third and fourth-cartilage of the laynx.The primordia of the eye and ear are also present.By 30th day, the arm and leg buds become prominent and by day 35, they are well developed.

Fifth week: During the 5th week, the optic cups and lens vesicles of the eye are formed and nasal pits develop.Partitioning of the heart occurs.The embryo has marked C- shaped body with rudimentary tail and a large head folded over a protuberant trunk.The heart,circulatory system and brain show the most advanced development.The brain differentiates into 5 areas and 10 pairs of cranial nerves.

Sixth week: At 6 weeks, the head structures are more highly developed and the trunk is straighter.The upper and lower jaws are recognizable and the external nares are well developed.Trachea is well developed and lung formation begins.The upper lip is forced and the palate ear, and other post brachial body parts begin to develop.The arm begins to extend ventrally across the chest and both arms and legs have digits though webbed.The embryo has prominent tail, but begins to regress.Foetal circulation begins to establish and the liver begins to produce blood cells. Seventh week At the seventh week, the head of the embryo is rounded and nearly erect.The eyes shift from their original position to a forward location, grow closer and the eyelids begins to form.The formation of the palate is nearly completed and tongue develops.The gastrointestinal and genitourinary tracts undergo significant changes.Now, the rectal and urogenital passages which were blind ended pouch separate into two tubular structures.The beginnings of all external and internal structures are present. Eight week Embryo is approximately 3cm long and clearly resembles a human being.Face and features continue to develop and external genitalia appears but are not discernible and the rectal passage opens, with the anal membrane now perforated.The circulatory system through the umbilical cord is well established.Long bones begins to form and the large muscle develop and are capable of contracting.By the end of the embryonic period, all major organ systems and the external structures are almost completely established.

Fetal stage:The embryo is now called a fetus, an offspring.No further primordial forms and every structure is present as found in the fullterm neonate.The remaining gestational period is devoted to refinement of structures and organization and perfection of function. 9-12 weeks The fetus by 10 weeks reaches 5cm in length and weighs about 14gm.The large head comprises of almost half of the fetus entire size.The neck is distinct from the head and both are straighter.The face is well formed with nose nose protruding,the chin small and receding and the ear acquiring a more adult shape.The eyelids closes at about the 10th week and remain so till the 28th weeks. Some reflex movement of the lips suggestive of sucking reflex can be observed and tooth buds appear.The limbs are longer and slender with well formed digits.The legs are shorter and less developed.The urogenital tract completes development and well differentiated genitals appear and the kidney begins to produce.RBC are produced primarily by the liver and spontaneous movement of the fetus now occur. 13-16 weeks At 13 weeks,the fetus weigh 55-60 gm and is about 9cm.Lanugo hairs begins to develop.The skin is transparent and blood vessels are visible beneath it.More muscle tissue and body skeleton develops that holds the fetus more erect.Active movements are present and sucking motions, swallows amniotic fluid and produces meconium in the intestinal tract.Bronchial tubes branches out and the sweat glands develops.The liver and pancreas begin production of secretions. 17-20 weeks Growth is rapid during 17-20th week period.The fetus almost doubles in length and measures about 20 cm or 8 inch. Fetal weight also increases to 435-460 gm.Lanugo covers the entire body and subcutaneous deposits of brown fat make the skin less transparent.Nipples appear and the head fetus has nails on both the fingers and toes. Muscles are well developed and the fetus is active. Fetal movement ‘quickening’ is felt by the mother and the heart beat is audible. 21 -24 weeks The fetus reaches a length of 28cm and weighs about 780 gm.The hairs on the head grows longer and the eyebrows and eyelashes are well formed.The eye is structurally complete and the fetus has a reflex hand

grip and by the end of the 6th month have startle reflex.The skin is reddish and wrinkled with little subcutaneous fat.The skin on the hand and feet are thickened with skin ridges on the palms and soles formed distinct footprints and fingerprints.The skin over the entire body is covered with a protective cheese-like fatty substance secreted by the sebaceous glands called vernix caseosa.The alveoli in the lung begins to develop. 25-28 weeks At 6 months, the fetus has appearance of a little old man.The skin is still wrinkled covered with vernix caseosa.The brain is rapidly developing and the nervous system is complete enough to provide some regulation of body functions.The eyelids open and close under neural control.In male fetus,the testes begins to descend into the scrotal sac.Respiratory and circulatory systems are sufficiently developed.28th week has been traditionally considered the earliest period of extra uterine viability.The lungs are still immature and the fetus requires intensive specialized care to survive.The fetus at 28 weeks is about 35-38cm long and weighs about 1250 gm.

29-32 weeks The fetus weighs about 2000 gm and measure about 38-43 cm by 32 weeks of age. If born during this time, the infant has about 60% chance of surviving with special care.The CNS has matured enough to direct rhythmic breathing and partially control body temperature. However the lungs are not fully matured and the bones are soft and flexible.The fetus begins storing minerals-iron, calcium and phosphorus.In male, the testicle are in the high inguinal canal. 33-36 weeks The body and extremities begins to fill out.The skin becomes less wrinkled.Lanugo hairs begins to disappear and the nails grow to reach the edge of the fingertips.By 36 weeks, the weigh is 2600- 2750 gm and 42-48 cm in length.The infant born at this age has good chance of survival but requires some special care. 37-40 weeks The fetus is considered full term at 38 weeks.The crown to heel length varies from 48-52 cm, with males longer than females.Males usually weigh more than female.The weigh at term is about 3000-3600 gm.The

skin is pink and smooth with a polished look and the only lanugo hair remaining is on the upper arms and shoulders.The head hair is coarse and about an inch long.Varnix casosa is present but varies in amount with heavier deposits in the creases and folds of skin.Good skin turgor and finger nails extend beyond the fingertips.The chest is prominent but smaller than the head and mammary glands begins to protrude in both sexes.The testes are in the scrotum or are palpable in the inguinal canals.As the fetus enlarges, amniotic fluid diminishes to about 500ml or less and the fetal body mass fills the uterine cavity.The fetus assumes a position of comfort or lie.Generally the head is pointed downward.The extremities and often the head are well flexed.After the 5th month, feeding patterns, sleeping and activity patterns become established.The fetus at term has its own body rhythms and individual style to response.

THE FOETAL CIRCULATION The umbilical vein carrying the oxygenated blood from the placenta, enters the fetus at the umbilicus and runs along the three margin of the falciform ligament of the liver, it gives off branches to the left lobe of the liver and receives the deoxygenated blood from the portal vein. The greater portion of the oxygenated blood, mixed with some portal venous blod, short circuits the liver through the ductus venosus to enter the inferior vena cava and thence to right atrium of the heart.The terminal part of the inferior vena cava also contains the deoxygenated blood from the caudal parts of the fetus below the diaphragm.The amount of such draining venous blood is not large enough to vitiate the pure blood from the ductus venosus to a great extent. In the right atrium, most of the blood(75%) is guided towards the foramen ovale by the valve if the inferior vena cava and crista dividens and passes into the left atrium.Here it is mixed with small

amount of venous blood returning from the lungs through the pulmonary veins.This left atrial blood is passed on through the mitral opening to the left ventricle. Remaining lesser amount of blood(25%) after reaching the right atrium via the superior and inferior vena cava passes through the tricuspid opening into the right ventricle. During ventricular systole, the left ventricular blood is pumped into the ascending and arch of aorta and distributed by their branches to the heart,head,neck,brain, and arms.The right ventricular blood with low oxygen content is discharged into the pulmonary trunk.Since the resistance in the pulmonary arteries during fetal life is very high, the main portion of the blood passes directly through the ductus arteriosus into the descending aorta by passing the lungs where it mixes with the blood from the proximal aortaThe mixed blood is distributed by the descending aorta and leaves the body by way of two umbilical arteries.The deoxygenated blood leaves the body by way of two umbilical arteries to reach the placenta where it is oxygenated and gets ready for recirculation.The mean cardiac output is comparatively high in fetus and is estimated to be 255ml per kkkg per minute. FETAL SKULL: It consists the delicate brain, which gives great pressure as the head passes through the birth canal. It is large in relation to the fetal body and in comparison with the mother’s pelvis; therefore some adaptation between skull and pelvis must take place during labour. Ossification: The bones of the fetal head originate in two different ways. The face is laid down in cartilage and is almost completely ossified at birth, the bones being fused together and firm. The bones of the vault are laid down in membrane and are much flatter and more pliable. They ossify from the centre outwards and this process is incomplete at birth leaving small gaps, which form the sutures and fontanelles.The ossification centre on each bone appears as a boss or protuberance.

BONES OF THE VAULT 1. The occipital bone 2. The two parietal bone

3. The two frontal bone

SUTURES AND FONTANELLES Sutures are cranial joints and are formed where two bones adjoin. 1. The lambdoidal suture: This suture separates the occipital bone from the two parietal bones. 2. The sagittal suture: This lies between the two parietal bones. 3. The coronal suture: This separates the frontal bones from the parietal bones, passing from one temple to the other. 4. The frontal suture: This runs between the two halves of the frontal bone. Fontanelles 1. The posterior fontanelle or lambda: This is situated at the junction of the lambdoidal and sagittal sutures. It is small, triangular in shape and can be recognised vaginally because a suture leaves from each of the three angles. It normally closes by 6 weeks of age. 2. The anterior fontanelle or bregma. This is found at the junction of the sagittal , coronal and frontal sutures .It is broad, kite shaped and recognisable vaginally because a suture leaves from each of the four corners. It measures 3-4 cm long and 1.52cm wide and normally closes by the time the child is 18 months old.

REGIONS AND LANDMARKS OF THE FOETAL SKULL The occiput: This region lies between the foramen magnum and the posterior fontanelle.The part below the occipital protuberance is known as the suboccipital region. The protuberance itself can be seen and felt as a prominent point on the posterior aspect of the skull The vertex: This is bounded by the posterior fontanelle, the two parietal eminences and the anterior fontanelle. Of the 96% of the babies born head first, 95% present of the vertex. The sinciput or brow: This extends from the anterior fontanelle and the coronal suture to the orbital ridges. The face: The face is small in the newborn baby. It extends from the orbital ridges and the root of the nose to the junction of the chin and the neck. The point between the eyebrows is known as the

glabella.The chin is termed the mentum and is an important landmark. DIAMETERS OF THE SKULL There are two transverse diameters Biparietal diameter: This is 9.5cm –the diameter between the two parietal eminences Bitemporal diameter: This is 8.2 cm –the diameter between the furthest points of the coronal suture at ht temples The remaining diameters described are anteroposterior or longitudinal Suboccipitobregmatic: This is 9.5cm –the diameter from below the occipital protuberance to the centre of the anterior fontanelle or bregma. Suboccipitofrontal: This is 10 cm –the diameter from below the occipital protuberance to the centre of the frontal suture. Occipitofrontal: This is 11.5 cm – the diameter from the occipital protuberance to the glabella. Mentovertical: This is 13.5cm –the diameter from the point of the chin to the highest point on the vertex, slightly nearer to the posterior than to the anterior fontanelle. Submentovertica: This is 11.5cm –the diameter from the point where the chin joins the neck to the highest point on the vertex. Submentobregmatic: This is 9.5cm –the diameter from the point where the chin joins the neck to the centre of the bregma.

SUBMITTED TO:MRS SUNDARAM HOD OBG NURSING P.I.O.N. SUBMITTED BY:MS DIMSEY .R.MARAK MSC NURSING1ST YEAR P.I.O.N