Fetal and Neonatal Physiology Flashcards
As a general rule, how do you estimate Gestational Age?
Fertilization age + 2 weeks
Differentiate between Hyperplasia and Hypertrophy.
Hyperplasia: Increase in the NUMBER of cells
Hypertrophy: Increase in CELL SIZE
List the three phases of cell growth.
- Pure Hyperplasia
- Mix of Hyperplasia and Hypertrophy
- Pure Hypertrophy
What is the predominant type of growth associated with the placenta vs. the fetus?
Placenta: Hypertrophy
Fetus: Hyperplasia
When does the majority of growth in length and weight occur during a pregnancy?
Last Month of Gestation
Placental growth will increase linearly with Fetal growth until when?
Last 4 weeks before birth
Intrauterine Growth Restriction (IUGR) may occur as a result of what?
Decrease in Placental Reserve
Mothers who smoke during pregnancy tend to have small placentas and are at high risk of delivering a low birth weight baby!
Name some hormones that are going to STIMULATE fetal growth and how they work.
- Glucocorticoids: Promote the storage of glucose as GLYCOGEN in the fetal liver; INCREASES greatly during the final month of gestation because baby will not be able to receive nutrients from mother after birth.
- Insulin: DOES NOT cross the placenta; Contributes to the storage of glucose as glycogen (made by fetal liver); Near Term, fetal glucose metabolism becomes SENSITIVE to INSULIN
- Growth Hormone: Acts postnatally; Fetal Liver has relatively FEW GH receptors during pregnancy
- IGF-1 and IGF-2: Birth weight POSIVITELY correlates with IGF levels; mitogenic peptides
- Thyroid Hormones: BEFORE 2nd trimester, most of T4 in fetus is MATERNAL; Fetal production of TSH and T4 begins to increase in the 2nd trimester
When does the heart start beating?
4th week after fertilization
Initial BPM (65 bpm) & after birth (140 bpm)
Which organs are responsible for the development of RBCs in the fetus? What are the different structures of RBC production during Childhood vs. Adulthood?
0-2 Months: Yolk Sac
1-7 Months (2nd Trimester): Liver and Spleen
7 Months-Birth (3rd Trimester): Bone Marrow
Childhood and Early Adolescent: Tibia and Femur (still bone marrow)
Adult: Ribs, Sternum, Vertebra and Pelvis (still bone marrow)
What is the % reticulocytes in the fetus at term? How long do RBCs last in the fetus at term?
5% @ term (Adults = 0.5-1.5%)
Lives 80 days (Much shorter than in Adults)
When does Hemoglobin begin to form?
3rd week after Fertilization
What is Meconium composed of?
“EARLIEST Stool” in an infant; Composed of materials form when the Infant was still INSIDE of the mother
Swallowed Amniotic fluid and partly mucus, epithelial cells, and other residues of excretory products from the GI tract and glands
Iron accumulates rapidly in the developing fetus in which week? What is that iron used for? Where is it stored?
12th week
Used for formation of additional Hemoglobin
Stored in the Liver (about 1/3 of the iron in a fully developed fetus is stored here)
When does urine excretion in the fetus begin? Describe the function of the Fetal Kidney.
2nd Trimester
Functional development of the Kidney is not complete until the 1 month after birth
Fetal Kidney cannot regulate EC Volume, Acid-Base balance or Electrolyte balance (Controlled by the PLACENTA)
Why is it important to have inhibition of Respiration in a fetus?
- Prevents filling of the lungs with fluid and debris from Meconium
- HIGH resistance because there is no air in the uterus to breathe
What are two stimulants for breathing at birth?
- Aphyxiation during birth
2. Sudden drop in ambient temperature and cooling of skin
What can delay breathing at birth?
- Use of general anesthesia during delivery
- Prolonged labor
- Head Trauma
What are some causes of Hypoxia during delivery?
- Compression of umbilical cord
- Premature separation of placenta
- Excessive uterine contractions
- Excessive anesthsia of the mother
- Neonates have a higher tolerance for hypoxia than adults (Might take 8-10 minutes to cause damage)
Describe the physiology behind taking a first breath for a neonate.
- At birth, Alveoli are collapsed (due to surface tension of the amniotic fluid filling them)
- More than 25 mmHg negative inspiratory pressure is needed to overcome surface tension and to open the alveoli for the FIRST TIME
- 1st breathe of neonate can produce as much as 60 mmHg negative pressure in the intrapleural space and bring in 40 mL of AIR
- DEFLATION will require strong POSITIVE PRESSURE to overcome the viscous resistance in the BRONCHIOLES
- Less Negative and Positive PRESSURE is going to be need after the 1st breathe
- Breathing does not become completely normal until about 40 MIN after birth (minimum pressure is needed to both inflate and deflate the lung)
What is the molecule that is going to decrease surface tension in the alveoli? Which cell makes it? When does synthesis begin?
Surfactanct
TYPE II ALVEOLAR epithelial cells
Last Trimester
- Pressure needed to collapse the alveoli with SURFACTANT is nearly 4-5 times greater than that without srufactant!
Describe Respiratory Distress Syndrome.
- Common in Premature Infants and Infants with Diabetic Mothers
- Related to low levels of Surfactant Levels in the final trimester, resulting in COLLAPSED alveoli
- Development of Pulmonary Edema
List and describe the 4 unique shunts that are present in fetal circulation.
- Placenta
- Shunts blood away from the LOWER TRUNK and lowers the effective blood flow to all abdominal viscera including the kidneys
- Umbilical vein brings Oxygenated blood to the fetus (enters the ductus venosus) - Ductus Venosus
- Bypasses the LIVER (which is largely nonfunctional)
- Allows blood from the umbilical vein to enter the IVC directly - Foramen Ovale
- Hole in the septum dividing the atria located in the posterior aspect of the Right ATRIUM
- Blood with the highest O2 content enters the left ventricle
- “Right-to-left-Shunt”: Of 69% of the combined cardiac output that enters the right atrium through the IVC, About 27% shunts through the Foramen Ovale DIRECTLY to the Left Atrium
- PO2 in fetal right ventricle is somewhat LOWER than that in the Left ventricle because of mixing of Deoxygenated blood coming from SVC and Oxygenated blood from IVC - Ductus Arteriosus
- “Right-to-Left-shunt”
- Directs blood from the Pulmonary Artery to the Aorta
- Remains open due to active RELAXATION of Smooth Muscle mediated by Prostaglandins (PGE2)
Describe the pressure changes after birth on the RIGHT side of the heart.
- Pulmonary vascular resistance decrease due to Lung EXPANSION
- Local Prostaglandins cause vasodilation (This will INCREASE Pulmonary Blood Flow)
- Since the resistance to blood flow is reduced, there will reduce Pulmonary Arterial Pressure, Right Ventricular Pressure and Right Atrial Pressure
How does the the Foramen Ovale close?
Elevated Left Atrial Pressure and a DECREASE in RIGHT Atrial Pressure
How does the Ductus Arteriosus close?
Well-oxygenated blood will flow through the ductus arteriosus
- HIGH PO2 causes VASOCONSTRICTION which will functionally close the Ductus Arteriosus within a few hours
- Falling PROSTAGLANDIN levels contribute to the rapid closure of the ductus arteriosus
What happens with Patent Foramen Ovale?
Sustained Pulmonary Hypertension or Transient increases in Right-sided pressures (during bowel movement, coughing, or sneezing)
How do you treat Patent Ductus Arteriosis?
Prostaglandin ANTAGONISTS (IV indomethacin)
Describe changes in blood pressure after birth.
1st day after birth: 70/50 mmHg
Few Months: 90/60 mmHg
Adolescence: 115/70 mmHg
Describe the physiological state of the Neonate Liver.
- Poor conjugation of bilirubin, deficiency in forming plasma proteins and coagulation factors
- Infants use its stored fats and proteins until mother milk can be provided
- Physiological Hyperbilirubinemia during first 2 weeks of life
Describe the trend of Hemoglobin levels in neonates.
Fetal hemoglobin concentration in the blood will decrease after birth by approximately 3% per week
- Physical anemia @ 6-12 weeks of life
Describe the main changes in the immune system during the neonatal period.
- Neonate DOES NOT form antibodies of its own to a significant extent
- DECREASE in baby’s IgG by the end of the 1st month
- IgG is normal by age 12-20 Months
