Flashcards in Fetal - Neonatal Transition Physiology Deck (52)
What are the 5 stages of fetal lung development?
Embryonic stage: length and events.
- Implantation to 5 weeks
- trachea and bronchi formed
- evidence of 5 lobes
Psudoglandular phase: length and events
- 5-16 weeks
- airway branching up to 15 generations
- growth of cuboidal cell lining
Canalicular phase: length and events
- 16 - 24 weeks
- enlargement of the airways
- epithelium thins
- capillaries develop
Saccular phase: length and events
- 24-36 weeks
- basement membranes fuse to form the blood gas barrier
- type II pneumocytes start producing surfactant
Alveolar phase: length and events
- 36 weeks to 8-10 years
- capillaries bulge into terminal sacs
- formation of septae/crests
- increase in total SA
Compare and contrast between the histology of an immature and mature lung
- thick blood gas barrier
- poorly vascularized
- small area for gas exchange
- thin blood-gas barrier
- highly vascularized
- large area for gas exchange
How is fetal lung fluid formed? How much is formed/day ?
Ultrafiltration of pulmonary capillary blood and active secretion of chloride ions.
About 250-300ml is formed per day but slows in later pregnancy
What mechanisms exist to deal with fetal lung fluid at birth?
1. switch from Cl- secretion to Na+ absorption during labour
2. Vaginal squeeze forces fluid out of lungs
3. Clearance by capillaries and lymphatics as lungs distend and drive fluid into the interstitium
What are 4 radiological findings of an infant with TTN?
1. increased central vascular markings
3. Evidence of interstitial and pleural fluid
4. Prominent interlobar fissures
What is the rough % composition of surfactant ?
10% neutral lipids
What is RDS?
Respiratory Distress Syndrome.
- aka hyaline membrane disease
Surfactant deficiency (mainly in premies) results in poor lung compliance given the high alveolar surface tension.
Atelectasis then occurs and babies enter resp. distress due to inadequate ventilation, hypoxia and then acidosis.
What are fetal breathing movements?
Rhythmic contractions of the diaphragm lasting from 1-60 minutes.
- increase after maternal meals and at night
-related somewhat to melatonin concentration
What substances or situations can inhibit fetal breathing movements?
- acute/severe hypoxia
What 2 mechanisms allow for breathing to become regular at birth?
1. Sensory stimuli (touch, temp, auditory, and visual)
2. loss of placental inhibitor peptide
Describe the reversal of cardiovascular shunts that occurs at the time of birth?
1. First breath decreases PVR and increases blood flow to lungs
2. This causes a shift from R--> L shunting to normal circulation which mechanically closes the foramen ovale
3. Increasing PO2 stimulates closure of the DA along with decreases in PGE2
4. Ductus venosus closes due to constriction of the sphincter following a drop in blood flow through the umbilical sinus.
What are 3 benefits and 1 downside to delayed cord clamping?
1. higher Hb at 24-48 hours
2. Reduced iron deficiency at 3-6 months
3. Pre-term infant have lower rates of intraventricular hemorrhage
one downside is increased need for phototherapy for neonates with jaundice
What are the 5 criteria of the APGAR score?
1. Appearance (colour)
3. Grimace (response to stimulation)
4. Activity (muscle tone)
What are the possible ratings given for colour in the APGAR?
0: blue or pale
2: all pink
What are the possible ratings given for pulse rate on the APGAR?
1: <100 bmp
2: >100 bmp
What are the possible ratings given for response to stimulus in the APGAR?
2. sneeze or cough
What are the possible ratings given for activity on the APGAR?
1: some flexion
2: active motion
What are the possible ratings given for respiratory effort on the APGAR?
What is a normal HR for a newborn?
What are the 4 mechanisms of heat loss that the newborn is susceptible to?
What is the role of brown fat? where is it located?
Brown fat is mitochondria rich fat located around the viscera of the infant and is crucial for thermogenesis for the newborn.
Sympathetic stimulation triggers hydrolysis of triglycerides, release of FA + glycerol and the production of heat
Describe the features of fetal metabolism
1. Anabolism mainly
2. glucose, lactate, and amino acids are main substrates
3. Glucose is most important (70-80% of maternal levels)
Describe the metabolic changes that need to occur at the fetal - neonatal transition
1. switch from anabolic to catabolic state
2. fall in neonatal glucose levels once cord is cut.
3. rapid glycogenolysis from FFA, ketones, and lactate occurs to raise blood glucose + feeding
What is the definition of neonatal hypoglycaemia?