Week 10 Flashcards
define a foetus
An unborn human, in-utero
Define a newly born infant
- The first minutes to hours following birth
* AV use ‘up to 24 hours’ as their definition
Define neonate?
• From birth up to 28 days of age
Define Infant?
• From birth up until 1 year of age
What is the normal newborn weight?
3.5 kg
What is the normal newborn blood volume?
80ml/kg
What is the normal newborn HR?
110-170
What is the normal newborn RR?
25-60
What is the normal newborn temp?
36.5-37.5
What is the normal newborn BGL?
2.6-3.2
When does the foetal heart begin beating?
4 weeks after fertilisation
what are the 4 shunts in the foetal cardiovascular system?
Ductus venosus
Foramen Ovale
Ductus arteriosus
Umbilical circulation
What does the ductus venosus do?
allows blood to pass from the umbilical vein to the right atrium. Closes at birth to become ligamentus venous
What does ductus arteriosis do?
allows blood to pass from pulmonary trunk to the aorta. Closes after borth to become the ligamentum arteriosum.
What is the ductus venosus?
- Narrow vessel with high velocity blood passing through
- Shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava
• Some blood oxygenates the liver –the rest pass through to the IVC • The degree of shunting in the fetus: • 30% at 20 weeks • which decreases to 18% at 32 weeks
What is the foramen ovale?
- Physiological defect in the atrial septum
- Allows blood to enter the left atrium from the right atrium
- In most individuals, the foramen ovalecloses at birth
- Oxygenated blood from the placenta travels through the umbilical cord to the right atrium of the fetal heart. As the fetal lungs are non-functional at this time, it is more efficient for the blood to bypass them
- It later forms the fossa ovalis in adulthood
What is the ductus arteriosus?
- A blood vessel connecting the main pulmonary artery to the proximal descending aorta
- Allows bulk of the blood from the right ventricle to bypass the foetus’slungs (at this stage is fluid filled and as we know doesn’t function)
- After birth it starts to constrict until it closes.
- In adults it becomes the ligamentum arteriosum
- Failure of the DA to close after birth results in a condition called patent ductus arteriosus (PDA) and the generation of a left-to-right shunt. If left uncorrected, patency leads to pulmonary hypertension and possibly congestive heart failure and cardiac arrhythmias.
What is the circulatory composition of the umbilical cord?
2 x umbilical arteries
1 x umbilical vein
What do the umbilical arteries do?
- Normally two umbilical arteries
- Carries de-oxygenated blood away from the neonate
- Branch from the internal iliac arteries
- Pressure normally 50mmHg
What does the umbilical vein do?
- Normally single umbilical vein
- Carries oxygenated and nutrient rich blood toward the neonate
- Connects to portal circulation where blood is shunted back to IVC via ductus venosus
- Pressure normally 20mmHg
What is the physiology of the foetal lungs?
- Fluid filled until birth (fluid production stops and is absorbed at birth)
- No air to breathe
- Lung almost completely deflated
- Leads to high PVR in lungs
- Surfactant production begins around 30 weeks gestation
- Surfactant production normally adequate by 35 weeks gestation
explain the process of gas exchange for the foetus?
- Before birth, all the oxygen used by the foetus diffuses across the placental membrane from the mother’s blood.
- The foetallungs do not function as a source of oxygen or as a route to excrete carbon dioxide.
- Blood flow to the lungs is minimal (~8%) so pulmonary vascular resistance is high.
- Foetal SpO2 is 40-60%.
Explain the physiology of the foetal nervous system
- Earliest system to begin developing and one of the last to complete
- Most reflexes present by 3-4 months of pregnancy
- Cerebral cortex development still relatively immature at birth
Explain the physiology of the foetal GIT
- Primitive gut is present by the end of the 4thweek of gestation
- Consists of foregut, midgut and hindgut –each of these eventually develop into all the organs we know an associated with the GIT system
- 2ndtrimester foetus begins to consume amniotic fluid
- 3rdtrimester foetus begins to form meconium which may be passed prior to birth
Explain the physiology of the foetal renal system
- 2ndtrimester foetus begin to excrete urine into the amnion
- Accounts for 70-80% of amniotic fluid at birth
- Kidney abnormalities may present as oligohydramnios (low amniotic fluid levels)