Physiology Block 3 Week 16 16 Fetal and Neonatal Development

Question 1

How does that placenta get most of the nutrition for the fetus?

Answer 1

Nutrients, waste products of metabolism, oxygen, and carbon dioxide pass through the placental membranes mainly by diffusion.

For the first few months after implantation, the placental membrane is thick and the surface area is small which limits diffusion. However, eventually the membranes thin and the surface area increases which greatly facilitates diffusion

Question 2

How is oxygenated blood carried to the fetal heart?

Answer 2

By the umbilical vein

Un/semi-oxygenated fetus blood enters through two umbilical arteries and then flows through capillaries of the villi before returning through a single umbilical vein.

The mother’s blood enters through uterine arteries into maternal sinuses that surround the villi and then returns through the uterine veins.

Question 3

Why for any PO2, the fetal blood has a higher content of oxygen?

Answer 3

There is a pressure different between the mother’s blood in the placental sinuses and the fetal capillaries the provides difference for diffusion to occur

1. Fetal Hb has higher affinity than adult (Left shifted)
2. Concentration of Hb in fetus is much greater than adult
3. Double-Bohr effect

Question 4

What is the Double Bohr effect?

Answer 4

Fetal blood entering the placenta has a high CO2 pressure; thus, as the CO2 diffuses into the maternal blood, the hemoglobin dissociation curve of the maternal blood shifts to the right. At the same time, the decrease in CO2 in the fetal blood shifts the dissociation curve of the fetus to the left.

Question 5

How is fetal circulatory system different than newborn?

Answer 5

During 4th week of pregnancy, the fetus’s heart begins to beat and pump blood through the placenta and through the fetus

1. oxygenated umbilical blood bypasses the liver through the ductus venosus into the inferior vena cava and the right atrium
2. (Bypass the Lungs) Most of this blood then passes directly into the left atrium through the foramen ovale and then to the left ventricle which distributes this blood primarily to the head and forelimbs.
3. (Bypass Lungs) Deoxygenated blood entering the fetal right atrium from the superior vena cava passes to the right ventricle to the pulmonary artery and then through the ductus arterious into the descending aorta to the umbilical arteries of the placenta for re- oxygenation.

***Placenta, not fetal lung, is organ of gas exchange

***L and R ventricles are parallel pumps

***pulmonary circulation has high resistance and low flow

Question 6

When is the cortical surge and what does it do?

Answer 6

Cortisol is low for about 30 weeks, increased just before labor, and peaks after delivery

1. Facilitate lung maturation–activate sodium pump to clear lung fluid
2. Increased beta receptor density
3. Gut maturation (digestive enzymes)
4. Maturation of thyroid
5. Catecholamine release from adrenal glands
6. Maturation of glucose metabolism in liver

Question 7

Catecholamine Surge

Answer 7

At birth

Increases BP
Helps adapt energy metabolism of glucose and fatty acids
Initiates thermogenesis from brown fat

Question 8

Why does a baby lose body weight the first few days after birth?

Answer 8

the infant uses its stored fats and proteins for metabolism which results in a decrease in body weight for the first few days after birth until the mother’s milk provides the needed nutrients

As a fetus, was getting nutrients by diffusion

Question 9

How does the lung clear fluid after birth?

Answer 9

The increase in cortisol, T4, and catecholamines at birth shut down the fluid secretion (critical for lung growth) and activate Na+, K+ and ATPase of airway epithelium to pump fluid into the interstitial space to be cleared by the vasculature or lymphatics

Question 10

What happens if there is an operative delivery?

Answer 10

Can results in retained lung fluid often resulting in poor oxygenation and tachypnea

Preterm infants without maturation of the Na+ transport system to clear lung fluid may also experience same problems

Missing the cortical and catecholamine surge

Question 11

What is the lung compliance like after birth?

Answer 11

The alveoli are collapsed at birth; thus, to counter the high surface tension, the first and second breaths require a high effort to inflate the collapsed lungs. However, by 40 minutes later, the compliance of the lung is nearly normal

over the first 30 minutes after birth, changes in the lungs and ventilatory control mechanisms change arterial blood gases and pH to near normal levels

Question 12

How does the lung develop over the last 1/3 of gestation?

Answer 12

the lung rapidly grows forming millions of alveoli and numerous generations of airways.

Surfactant lipid and lipophilic proteins are formed such that by term, type II cells in the fetal lung contain more surfactant than the adult lung.

Surfactant secretion into the alveoli begins with labor under control of catecholamines which stimulate beta receptors

ATP and alveolar stretch probably also stimulate secretion early after birth particularly after operative delivery, but over the first few weeks after birth, the secretion decreases to adult levels.

Question 13

What happens to arterial blood gasses and pH after birth?

Answer 13

the first few minutes after birth, arterial blood gases and pH change greatly to reach levels normal for neonates within 2 hours

the drop in pH after birth is due to an increase in lactic acid production (initially anaerobic state)

Question 14

What are cardiovascular adaptation at birth?

Answer 14

Cortisol and catecholamine = inc BP

No longer have blood flowing thru placenta = increased vascualr and cardiac resistance

Pulmonary vascular resistance decreases = blood flow increases

Foramen ovale closed and ductus arteriosus and venosus obliterated = double in cardiac output (ventricular output now in series)

Question 15

Why does pulmonary vascular resistance decrease and blood flow increase after birth?

Answer 15

a) the pulmonary vessels are no longer compressed by the fluid in the lungs
b) breathing increases PO2 which reduces vasoconstriction
c) local prostaglandins cause vasodilation.

Question 16

What is important about the FRC in neonates?

Answer 16

The functional residual capacity (FRC) of the neonate is about 50% of the adult in relation to body weight.

it is a source (or store) of oxygen and it minimizes the cyclic variation in arterial blood gases.

As a result of the FRC in neonates, they will have large cyclic variations in blood gases particularly when breathing is low and also, they will have more airway and alveoli collapsing which requires greater effort to reopen

Question 17

Why increases blood volume at birth?

Answer 17

Stripping the umbilical cord

The red cell count at birth is about 4 million/mm3 which transiently increases if the cord is stripped, but then the count decreases over the first 6.8 weeks of life

Question 18

What will result due to the liver function being insufficient during the first few weeks?

Answer 18

Liver function is insufficient to prevent plasma proteins and glucose from falling.

liver poorly conjugates bilirubin with glururonic acid for excretion into the bile–can result in jaundice

Question 19

Erythroblastosis fetalis

Answer 19

Baby inherits Rh-positive red cells from the father while the mother is Rh-negative. The mother becomes immunized against the Rh-positive factor in the fetal blood and her antibodies destroy fetal red blood cells releasing large amounts of bilirubin in the fetus causing jaundice.

Question 20

What results from the underdeveloped kidneys over the first few weeks?

Answer 20

acidosis, dehydration, and overhydration.

Question 21

Compared to an adult, how is the metabolic rate? How does this effect temperature?

Answer 21

The metabolic rate of the neonate in relation to body size is twice that of the adult,

Because the body surface area in relation to body mass is higher in the neonate, body temperature decreases and then is unstable for several days

Brown adipose tissue generates heat by uncoupling oxidative metabolism from ATP synthesis in the mitochondria which results in release of heat.

Question 22

Why is it important for babies to ingest milk?

Answer 22

the rapid ossification of bone requires adequate calcium from ingested milk and adequate vitamin D for calcium absorption from the gut.

Question 23

What would happen if the mother did not have sufficient iron in her diet?

Answer 23

The neonate may have low store of iron leading to anemia

Question 24

Why is ascorbic acid given?

Answer 24

Needed for formation of cartilage, bone, and other intercellular structures–not in milk

Question 25

Are neonates born with their own antibodies?

Answer 25

No, for the first month, they inherit their mother’s

Will form their own and by 12-20 months will be sufficient

Question 26

What if the mother had above normal androgen levels?

Answer 26

Masculinization of feta sexual organs (hermaphroditism)

Question 27

What if the mother had type I diabetes?

Answer 27

Leads to poor growth of the fetus and high rate of intrauterine and neonatal mortality

Question 28

What if the mother had type II diabetes?

Answer 28

Would result in a large baby (GH stimulated by increase in glucose)

Question 29

What if the mother had hyperthyroidism?

Answer 29

Neonate could have hypothyroidism leading to dwarfism

Question 30

What are causes of respiratory distress syndrome (RDS) of preterm babies?

Answer 30

Low Tidal Volume
FRC
Depressed/absent surfactant secretion

Question 31

What results from a surfactant deficient lung?

Answer 31

A surfactant deficient lung is characterized by collapsed air-spaces alternating with hyper-expanded areas, vascular congestions, and hyaline membranes composed of fibrin, cellular debris, red blood cells, neutrophils, and macrophages lining the alveoli which compromise gas exchange.

Question 32

What are problems with preterm babies?

Answer 32

Low TV
FRC
Absent/Little surfacant
Inadequate absorption of food
Immature liver--protein/glucose
Immature kidney--regulation of acid-base
Decreased gamma globulin by lymphoid system
Inadequate temperature regulation

Question 33

Adrenal deficiency at birth will cause all the following except:

reduced norepinephrine release at birth.
decrease in blood glucose levels compared to the fetus.
increased thermogenesis from brown fat.
below normal secretion of surfactant into the alveoli.
delayed clearance of fluid from the lung.

Answer 33

increased thermogenesis from brown fat.

Question 34

The greatest risk factor for developing surfactant deficiency syndrome is:

Epithelial injury caused by over-distention of alveoli.
Intrauterine infection.
Asphyxia during delivery of the infant.
Gestational age of

Answer 34

Gestational age of

Question 35

You are called to the Neonatal Intensive Care Unit to assess a child with respiratory distress. The infant was born at 28 weeks of gestation and has developed grunting, tachypnea, and low oxygen saturations. The diagnosis is respiratory distress syndrome. The most effective intervention to reverse the cause of this child’s respiratory distress would be to address which of the following:
	Increased alveolar surface tension
	Decreased lung compliance
	Pulmonary edema
	Increased pulmonary artery pressure
	Lung inflammation

Answer 35

Increased alveolar surface tension