PHYSIOLOGY OF PHYSIOLOGY OF THE NEWBORNTHE NEWBORN

Belen Amparo E. Velasco, M.D.Belen Amparo E. Velasco, M.D.

The fetus has a recognizable human form by the 12th week of development.

The vital organs are not sufficiently developed to sustain life outside the uterus until the seventh month. While in the womb, the fetus is especially susceptible to the effects of drugs, alcohol, and X rays.

"Human Fetus."Microsoft® Encarta® Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

CIRCULATORY SYSTEM

FETAL CIRCULATION

Presence of 3 shunts:

Patent foramen ovale

Patent ductus arteriosus

Patent ductus venosus

CIRCULATORY SYSTEMFETAL CIRCULATION

OXYGENATED BLOOD FROM MATERNAL BLOOD:

PLACENTA (Clearing house) Umbilical vein Ductus venosus liver hepatic veins Inferior vena cava Superior vena cava Right auricle foramen ovale left auricle left ventricle ascending aorta

CIRCULATORY SYSTEM

FETAL CIRCULATION

UNOXYGENATED BLOOD:

Right ventricle pulmonary artery lungs ductus arteriosus descending aorta

CIRCULATORY SYSTEM

CHANGES AT BIRTH ADULT TYPE OF CIRCULATION

Cessation of placental circulation

Physiologic closure of foramen ovale ( L atrial pressure)

Functional closure of patent ductus arteriosus (O2 content)

RESPIRATORY SYSTEM

FETAL LUNGS

Filled with respiratory (filtrate of plasma) fluid

Metabolic functions; Production of surfactant

Occasional gasps

RESPIRATORY SYSTEM

NEWBORN LUNGS

Possess all equipment necessary for respiration incl. chemoreceptors and baroreceptors

High negative intrathoracic pressure (10-70cms H2O)

Clearance of respiratory fluid with replacement by air

RESPIRATORY SYSTEM

NEWBORN LUNGS

Establishment of FRC to permit gas exchange even during expiration

Alveolar structure

Periodic breathing with apneic pauses in premies

GASTROINTESTINAL SYSTEM

FETAL GI SYSTEM

Swallowing as early as the 12th week of gestation

Absence of excretion via the GIT unless with sphincter relaxation during hypoxic event.

Accumulation of epithelial debris and conjugated bilirubin in small intestine

GASTROINTESTINAL SYSTEM

NEWBORN GI SYSTEM

Passage of meconium (mixture of epithelial debris & mucopolysaccharide with conjugated sbilirubin) within the 1st 24 hours transitional stools (greenish soft stools) in the next 4 days milk stools (normal pasty consistency and yellow color) Adequate levels of pancreatic enzymes except for amylase and lipase

RENAL SYSTEM

FETAL RENAL SYSTEM

Production of urine as early as 4th month Renal function (GFR, tubular mass and RPF) not reach adult levels till 2nd year of life

Glomerular filtration begins at about 9 weeks

RENAL SYSTEM

NEONATAL RENAL SYSTEM

Passage of dilute urine due to inability to concentrate urine adequately

Transient metabolic acidosis due to inadequate removal of acid ions, limited formation of NH3 for acid removal with minimum loss of base and overproduction of lactic and pyruvic acid.

RENAL SYSTEM

NEONATAL RENAL SYSTEM

6-10% physiologic weight loss (loss of body water)due to:

DiuresisExpulsion of meconiumWithholding of water and calories

CENTRAL NERVOUS SYSTEM

FETAL CNS

Rapid growth of fetal brain during last half of fetal life with peak near time of birth

Posture of late fetal flexion attitude

Generalized symmetric muscular activity

Simple & stereotyped response to various environmental and internal stimuli

CENTRAL NERVOUS SYSTEM

NEONATAL BRAIN

Soft spots on a baby’s head, called fontanels, are areas that have not yet hardened to bone.

The skull is subjected to great pressure as it passes through the birth canal. Were it inflexible, the tight squeeze might injure the brain.

Growth is complete by one year of age, and lines called sutures are visible where the plates fuse.

SPECIFIC REACTIONS:Moro reflexGrasp reactionTonic and righting reflexRooting, sucking, tongue retrusion and

swallowing reflexes

CENTRAL NERVOUS SYSTEM

RESPONSE TO STIMULI: Simple and stereotyped

SENSES:Regards moving objects & changing light

intensityHears loud sound

CENTRAL NERVOUS SYSTEM

ENDOCRINE SYSTEM

FETAL ENDOCRINE SYSTEM

The pituitary adrenal axis and thyroid gland function separately from that of the mother to ensure adequate growth of infant.

Peculiarities in the fetus:Maternal estrogenic effectsurinary 17-ketosteroids

PITUITARY GLAND

ENDOCRINE SYSTEM

NEONATAL ENDOCRINE SYSTEM

MATERNAL ESTROGENIC EFFECTS

Hypertrophied mammary glands

Witch milk

Mucoid to bloody vaginal discharge

ENDOCRINE SYSTEM

NEONATAL ENDOCRINE SYSTEM

NEONATAL OUTCOME IN MATERNAL DIABETES

Immaturity of lungs – Hyaline membrane disease

Hypoglycemia

Hypocalcemia

Anomalies: Ventricular septal hypertrophy Microcolon

HEMATOLOGIC SYSTEM

FETAL HEMATOPOIETIC SYSTEM

Erythropoietin: hormone produced in the glomerular tuft responsible for the production of RBC

Due to relative hypoxia of the fetus stimulating the bone marrow, the fetal hemoglobin is as high as 20g/dl

Blood formation as early as 3rd wk after conception:Mesodermal tissue in the 1st monthLiver in the 2nd monthMedullary spaces from the 6th month onward

HEMATOLOGIC SYSTEMNEOWBORN HEMATOPOIETIC SYSTEM

At birth, still with high hgb. Starts to drop on the 3rd day of life until a minimum of 10-12g/dl on the 2nd-3rd month of life – PHYSIOLOGIC ANEMIA - a result of the following:

in bone marrow activity in rate of hemolysishemodilution due to rapid expansion of blood volume

Normal blood volume ranging from 80-90ml/kg

WBC ranging from 10,000-30,000/mm3 with PMN predominance

IMMUNOLOGIC SYSTEMFETAL IMMUNE SYSTEM

Liver serves as the repository for lymphoid precursor cells during early intrauterine life.

T cell functions begin as early as 7 weeks

Circulating B cells are seen as early as 13 weeks. IgM antibodies are first to develop

IMMUNOLOGIC SYSTEM

NEWBORN IMMUNE SYSTEM

Considered completely developed immunological system but with inadequate antigenic stimulus

IMMUNOLOGIC SYSTEM

NEWBORN IMMUNE SYSTEM

Antibodies (maternal in origin) present – 7s or IgG antibodies

Tetanus antitoxinDiphtheria antitoxinSmallpox agglutininsAntistreptolysinToxoplasma antibodiesSalmonella H antibodiesRh blocking antibodies

IMMUNOLOGIC SYSTEMNEWBORN IMMUNE SYSTEM

Antibodies absent – 19s gammaglobulinsStreptococcus agglutininsH. influenza antibodiesBlood group isoagglutininsShigella antibodiesPoliomyelitis antibodiesSalmonella O antibodiesE. coli H and O antibodies

Less capacity to produce antibodies and lower ameboid and phagocytic activities of neonatal leukocytes susceptibility to infection esp of the preterm

T lymphocytes are specialized white blood cells that identify and destroy invading organisms such as bacteria and viruses. Some T lymphocytes directly destroy invading organisms, whereas other T lymphocytes regulate the immune system by directing immune responses.

Antibodies absent in the newborna.m EXCEPT:A. Streptococcus agglutininsB. H. influenza antibodiesC. Poliomyelitis antibodiesD. E. coli H and O antibodiesE. Tetanus antitoxin

Physiologic anemia:A. Increased RBC turnover due to hemolysisB. Decreased RBC turnover due to hyperoxiaC. Decreased blood volume expansionD. Increased erythropoietic activityE. Depressed bone marrow activity due to

hyperoxia

True of fetal circulation, EXCEPT:A. Ductus arteriosus shunts blood from pulmonary

artery to aortaB. Foramen ovale shunts blood from right to left

auricleC. Ductus arteriosus shunts blood from right to left

side of heartD. Foramen ovale shunts blood from left to right

auricleE. Oxygenated blood from placenta supplies upper

half of body

Physiologic weight loss due to:A. PolyuriaB. DiuresisC. Adequate caloric intakeD. Retention of meconiumE. Transient metabolic acidosis