Prenatal Development: Stages, Events & Fetal Growth

Prenatal development DR. ARNEL BAÑAGA SALGADO PsyD , FPM , CertHI , EdD , MAN , GD Psychology, LPT , CertEd , RN , BSN Professorial Lecturer 10 – Tenure Track Dr. Arnel Bañaga Salgado 1  Prenatal...

Prenatal development DR. ARNEL BAÑAGA SALGADO PsyD , FPM , CertHI , EdD , MAN , GD Psychology, LPT , CertEd , RN , BSN Professorial Lecturer 10 – Tenure Track Dr. Arnel Bañaga Salgado 1  Prenatal development  Prenatal development refers to the process in which a baby develops from a single cell after conception into an embryo and, later, a fetus Dr. Arnel Bañaga Salgado 2 Description  The average length of time for prenatal development to complete is 38 weeks from the date of conception.  During this time, a single-celled zygote develops in a series of stages into a full-term baby. Dr. Arnel Bañaga 3 The three primary stages of prenatal development The germinal stage The embryonic stage The fetal stage. Dr. Arnel Bañaga 4  Germinal stage Conception occurs when the female egg (ovum) is fertilized by the male sperm. Under normal circumstances, one egg is released from a woman's ovary approximately once a month during ovulation. Dr. Arnel Bañaga 5  The egg enters a fallopian tube, which guides the egg away from the ovary toward the uterus.  For fertilization to occur, a sperm must penetrate the tough outer membrane of the egg called the zona pellucida.  The genetic material of the sperm and egg then combine to form a single cell called a zygote, and the germinal stage of prenatal development Dr. Arnel Bañaga commences. 6 Dr. Arnel Bañaga 7 Fertilized egg 2 cell embryo Dr. Arnel Bañaga 8  A 4-cell embryo (day 2) An 8-cell embryo (day 3) Dr. Arnel Bañaga 9  ZYGOTE The zygote soon begins to divide rapidly in a process called cleavage, first into two identical cells called blastomeres, which further divide into four cells, then into eight, and so on.Dr. Arnel Bañaga 10  The group of dividing cells moves along the fallopian tube toward the uterus.  About sixty hours after fertilization, approximately sixteen cells have formed what is called a morula, still enclosed by the zona Dr. Arnel Bañaga 11 pellucida.  Three days after fertilization, the morula enters the uterus.  As cell division continues, a fluid-filled cavity called a blastocoele forms in the center of the group of cells, with the outer shell of cells called trophoblasts and an inner mass of cells called embryo-blasts or inner cell mass.  The zona pellucida disappears, and the morula becomes a blastocyst.  At this stage, the blastocyst consists of 200 to 300 cells and is ready for implantation. Dr. Arnel Bañaga 12 A blastocyst (day 5) Dr. Arnel Bañaga 13 Dr. Arnel Bañaga 14  Implantation  The process in which the blastocyst implants into the uterine wall occurs approximately six days after conception.  Hormones secreted from the mother's ovaries and a chemical secreted by the trophoblasts begin to prepare the uterine wall.  The blastocyst first adheres to the wall and then moves into the uterine tissue. Implantation marks the end of the germinal stage and the beginning of the embryonic stage Dr. Arnel Bañaga 15  Embryonic stage  The embryonic stage begins after implantation and lasts until eight weeks after conception.  Soon after implantation, the cells continue to divide rapidly, and clusters of cells begin to take on different functions (called differentiation). Dr. Arnel Bañaga 16 A process (gastrulation) leads to the formation of three distinct layers called germ layers: the ectoderm (outer layer), the mesoderm (middle layer), and the endoderm (inner layer) Each germ layer differentiates into different tissues and structures as the embryo develops. Dr. Arnel Bañaga 17 Dr. Arnel Bañaga 18 The ectoderm eventually forms skin, nails, hair, brain, nervous tissue and cells, nose, sinuses, mouth, anus, tooth enamel, and other tissues. The mesoderm develops into muscles, bones, heart, lungs, reproductive organs, lymphatic tissue, and other tissues. Dr. Arnel Bañaga 19  The endoderm forms the lining of the lungs, bladder, digestive tract, tongue, tonsils, and other organs.  The process of differentiation takes place over a period of weeks, with different structures forming simultaneously. Dr. Arnel Bañaga 20  Major events  Week 3: Beginning development of the brain, heart, blood cells, circulatory system, spinal cord, and digestive system.  Week 4: Beginning development of bones, facial structures, and limbs (presence of arm and leg buds); continuing development of the heart (which begins to beat), brain, and nervous tissue. Dr. Arnel Bañaga 21  Week 5: Beginning development of eyes, nose, kidneys, and lungs; continuing development of the heart (formation of valves), brain, nervous tissue, and digestive tract.  Week 6: Beginning development of hands, feet, and digits; continuing development of brain, heart, and circulation system. Dr. Arnel Bañaga 22  Week 7: Beginning development of hair follicles, nipples, eyelids, and sex organs (testes or ovaries); first urine formation in the kidneys and first evidence of brain waves. Dr. Arnel Bañaga 23  Week 8: Facial features are more distinct, internal organs are well developed, the brain can signal for muscles to move, heart development ends, and external sex organs begin to form.  By the end of the embryonic stage, all essential external and internal structures have been formed. The embryo is now referred to as a fetus. Dr. Arnel Bañaga 24  Fetal stage  Prenatal development is most dramatic during the fetal stage.  When an embryo becomes a fetus at eight weeks, it is approximately 3 centimeters (1.2 inches) in length from crown to rump and weighs about 3 grams (0.1 ounce).  By the time the fetus is considered full-term at 38 weeks gestation, he or she may be 50 centimeters (20 inches) or 3.3 kilograms (7.3 pounds).  Although all of the organ systems were formed during embryonic development Dr. Arnel Bañaga 25  MAJOR EVENTS  Weeks 10 to 13 (8th to 11th week of development)  The fetus reaches a length of 8 cm (3.2 inches).  The head comprises nearly half of the fetus' size.  The face is well-formed  The eyelids close and will not reopen until about the 28th week.  Tooth buds, which will form the baby teeth, appear.  The limbs are long and thin.  The fetus can make a fist with its fingers.  Genitals appear well differentiated.  Red blood cells are produced in the liver. Dr. Arnel Bañaga 26  Weeks 14 to 17 (12th to 15th week of development)  The fetus reaches a length of about 15 cm (6 inches).  A fine hair called lanugo develops on the head.  Fetal skin is almost transparent.  More muscle tissue and bones have developed, and the bones become harder.  The fetus makes active movements.  Sucking motions are made with the mouth.  Meconium is made in the intestinal tract.  The liver and pancreas produce fluid secretions. Dr. Arnel Bañaga 27  Week 20 (18th week of development)  The fetus reaches a length of 20 cm (8 inches).  Lanugo covers the entire body.  Eyebrows and eyelashes appear.  Nails appear on fingers and toes.  The fetus is more active with increased muscle development.  "Quickening" usually occurs (the mother can feel the fetus moving).  The fetal heartbeat can be heard with a stethoscope. Dr. Arnel Bañaga 28  Week 24 (22nd week of development)  The fetus reaches a length of 28 cm (11.2 inches).  The fetus weighs about 725 g (1 lb 10 oz).  Eyebrows and eyelashes are well formed.  All of the eye components are developed.  The fetus has a hand and startle reflex.  Footprints and fingerprints continue forming. Dr. Arnel Bañaga 29   Week 28 (26th week of development)  The fetus reaches a length of 38 cm (15 inches).  The fetus weighs about 1.2 kg (2 lb 11 oz).  The brain develops rapidly.  The nervous system develops enough to control some body functions.  The eyelids open and close. Dr. Arnel Bañaga 30  The cochleae are now developed, though the myelin sheaths in the neural portion of the auditory system will continue to develop until 18 months after birth.  The respiratory system, while immature, has developed to the point where gas exchange is possible.  A baby born prematurely at this time may survive, but the possibilities for complications and death remain high. Dr. Arnel Bañaga 31  Weeks 32 (30th week of development)  The fetus reaches a length of about 38-43 cm (15-17 inches).  The fetus weighs about 2 kg (4 lb 6 oz).  The amount of body fat rapidly increases.  Rhythmic breathing movements occur, but lungs are not fully mature.  Thalamic brain connections, which mediate sensory input, form.  Bones are fully developed, but are still soft and pliable.  The fetus begins storing iron, calcium, and phosphorus. Dr. Arnel Bañaga 32  Week 36 (34th week of development)  The fetus reaches a length of about 40-48 cm (16-19 inches).  The fetus weighs about 2.5 to 3 kg (5 lb 12 oz to 6 lb 12 oz).  Lanugo begins to disappear.  Body fat increases.  Fingernails reach the end of the fingertips.  a baby born at 36 weeks has a high chance of survival but may require medical interventions. Dr. Arnel Bañaga 33 Weeks 37 to 40 (35th to 38th week of development)  The fetus is considered full-term at the 37th week of gestational age.  It may be 48 to 53 cm (19 to 21 inches) in length.  The lanugo is gone except on the upper arms and shoulders.  Fingernails extend beyond fingertips.  Small breast buds are present on both sexes.  Head hair is now coarse and thickest. Dr. Arnel Bañaga 34 Dr. Arnel Bañaga 35 Dr. Arnel Bañaga 36