Fetal circulation year 1

• Fetal Circulation

  Temporary structures within fetal circulation facilitate passage of oxygen to fetus
• Temporary Structures of Fetal Circulation

  • Umbilical Vein
  • Ductus Venosus
  • Foramen Ovule
  • Ductus Arteriosus
  • Hypogastric Arteries
  • Umbilical Arteries
• Fetal Circulation – Step by Step

  1. Blood containing nutrients and oxygen flows from the placenta into the umbilical cord

  2. Flows first into the Umbilical Vein

  3. The Umbilical Vein goes to the liver where it gives off branches to the L lobe and receives the venous blood from the portal vein

  4. This mixed blood by-passes the liver via the Ductus Venosus to enter the Inferior Vena Cava

  5. The blood passes along the IVC till it reaches the R. Atrium of the heart. This blood mixes with blood returning from the SVC

  6. 75% of this mixed blood in the R. Atrium is diverted through an opening in the septum called the Foramen Ovale into the L. Atrium

  7. The remaining 25% of the blood is pumped into the R. Ventricle into Pulmonary Artery some will go to the lungs but most will go into the Ductus Arteriosus which by-passes the lungs to deliver blood to the Aortic arch

  8. The blood from the L. Atrium passes into L. Ventricle

  9. Blood enters Aorta and passes along it's branches to supply head, neck and arms first.

  10. Blood passes down the aorta giving branches off to all the main organs as it descends through the chest and abdomen

  11. The aorta divides into the iliac arteries which supply the lower limbs - the majority of the blood flow passes into the Hypogastric Arteries

  12. These arteries arise in the pelvis and pass through the umbilicus and enter the cord as the 2 Umbilical Arteries

  13. Returns blood flow to the placenta
• Oxygenation of fetal blood

  • When blood enters the fetal circulation from the placenta it is approx. 80% saturated with oxygen
  • As it circulates O2 transfers to the fetal tissue
  • When blood reaches the Hypogastric Arteries and the placenta, it is only about 15% saturated with O2
  • The whole cycle of circulation takes about 30 seconds!
• Transition to Extrauterine Life

  • The fetus grows in a quiet, dark, protected environment where the mother's placenta meets all physiological needs.
  • At birth, the fetus must adapt to extra-uterine life in order to exist.
  • Each individual baby will adapt at their own pace.
• Adaptation: Fetus to Infant

  1. Respiratory + cardiovascular transition from placental oxygenation to lung gas exchange occurs in stages:

  2. Phase 1: Completed within minutes after birth

  3. Phase 2: Changes in C.V. function continue > 10 days

  4. Liver function adapts almost immediately – this is vital to keep blood sugar levels within normal range
• Respiratory changes at birth

  1. Squeezing of thoracic wall during vaginal birth drains some of the lung fluid

  2. External stimuli assists baby in taking his first breaths

  3. Pulmonary vessels dilate with oxygen
• Respiration

  • In fetal life all oxygenation took place via the placenta
  • Lung fluid expelled due to chest compression at delivery
  • Surfactant reduces surface tension – prevents collapse
  • Oxygen decreases, CO2 increases – stimulates respiratory centre and baby breathes
  • Respiratory rate should be 40-60/min – can be irregular initially
• Haematological

  • High Hb at birth – excessive RBC – used to carry O2 in utero – no longer needed due to gas exchange in lungs
  • HbF present in large amounts – takes months to change to adult Hb
  • Excessive breakdown of HBF leads to jaundice (increased SBR levels)
  • Lack of Vit K & low Prothrombin levels therefore clotting decreases
• Temperature Control

  • Heat regulating centre immature in newborn
  • Heat lost by convection, radiation, evaporation + conduction
  • Stores of brown fat reduced
  • No shivering reflex
  • Adequate intake of glucose / calories essential
• Gastrointestinal

  • In utero, nutrients obtained via the placenta
  • Baby has to adapt after birth- suck, swallow, absorb + excrete
  • Should pass meconium within 24 – 48 hours
  • Changing stools indicate the presence + function of small and large bowel
• Renal

  • At term the kidneys are relatively immature
  • G.F.R. reduced - urine is very dilute initially
  • Large volume of water needed to excrete solutes – if the baby does not receive adequate fluids - can retain sodium and urea
  • Should pass urine within 24 hours - 3-4mls/ kg/ hour
  • Output should increase dramatically by one week of age
• Protection against Infection

  • Intact membranes and the placenta afford the fetus some protection against infection
  • During last trimester- transplacental transfer of IgG from mother to fetus
  • Soon after birth – becomes colonised by micro-organisms eg. Staphylococci on umbilicus + skin
  • Clinical infection occurs when there is overwhelming infection, and the immune system fails to cope
  • Breastfeeding provides more immunity for the baby from his mother
• Central Nervous System

  • Poor motor development at birth
  • Highly developed sensations – sight, hearing, touch, taste and smell
  • Newborn babies need to be touched gently , talked to, provided with sensory stimuli (skin-to-skin) and fed on demand