fetal and neonatal circulation hu

Question 1

4 shunts in fetal circulation:

• the placenta
• the ductus venosus
• foramen ovale
• ductus arteriosus
• gas exchange in fetus occurs in placenta
• lungs in fetus have high resistance to blood flow bc of hypoxia causing vaso constriction and they havent inhaled yet.
• Prostaglandin E2 mainitains a patent ductus arteriosus in fetus

Answer 1

-lungs largely non functional, liver only partally functional, so vessels help bypass these organs
-heart pumps blood through the placenta
-blood is oxygenated in placenta and passes though the umbilical vein back into baby. to bypass the liver, passes through the ductus venosus and then enters the inferior vena cava to the RA of the heart
-in human fetus, 40% of blood from RA flows through FORAMEN OVALE into LA. blood also enters RA from superior vena cava, but this is deoxygenated blood. moves into RV next.
3/4th of the blood from the RV is pumped through the DUCTUS ARTERIOSUS (pulmonary artery from RV to the descending aorta) into descending aorta. this is how the RV bypasses the lungs.
-so, both the right and the left ventricle pump into the descending aorta and their output is parallel and not in series (in series in adult).
-sum of both ventricles is the CCO== combined cardiac output
-a little bit of blood in RV passes through lungs and then enters the LA.
-blood in the descending aorta passes through the hypogastric arteries, into the 2 umbilical arteries, and then into placenta.

Question 2

oxygen partial pressure and saturation

Answer 2

-oxygenated blood from placenta is mixed w/ deoxygenated blood from the other organs of fetus. if it weren’t mixed, then some organs wouldn’t get oxygenated. shunts make sure the whole body gets some

Question 3

cardiopulmonary adjustments after birth

Answer 3

• baby loses placental circulation so has to breathe on its own
• dramatic increase in pulmonary blood flow when lungs inflate after breathing starts– less resistance to flow
• closure of ductus venosus, foramen ovale, and ductus arteriosus

Question 4

first breath triggered by mild hypoxia, hypercapnia, tactile stimuli, and cold skin

• hypoxia and hypercapnia lead to adults breathing more
• study also shows reduced umbilical flow and O2 trigger first breath also

Answer 4

• babys first inspiration is very hard. needs 60cm H2O to increase lung volume by 40 ml. adults need 2.5cm H2O to increase lung volume 500 ml.
• breathing gets easier once alveoli are open and type II alveolar pneumocytes deliver SURFACTANT to the air water interface
• respiratory distress syndrome is caused by deficiency of surfactant, seen in premature babies

Question 5

fetal to neonatal switch is accompanied by dramatic drop in pulmonary vascular resistance

Answer 5

• pulmonary vascular resistance goes down
• pulmonary blood flow goes up
• mean pulmonary arterial pressure goes down– bc of the fall in pulmonary vascular resistance
• primary event is fall in resisitance which occurs bc of
  1. pulmonary blood vessels no longer crushed,
  2. breathing increases PO2, which causes vasodilation
  3. local prostaglandins cause vsodilation
• pulmonary pressure goes down, even though the ductus arteriosus closes, which would have increased pressure bc if increased flow, but pressure goes down bc of less resisitance from the vasculature.

Question 6

4 jobs of the placenta:

1. acts as lungs for gas exchange
2. acts as GI tract for nutrition
3. acts as liver for nutrition and waste removal
4. acts as kidney for fluid and electrolyte balance and waste removal
   - placenta insufficiency causes type II intrauterine growth restriction
   - anything that messes with gas exchange can case asphyxia- O2 deficiency

Answer 6

• pregnancy assiciated with great increase in uterine blood flow and placental development
• fetal heartbeat starts 1 month after fertilization. HR goes from 65 to 140 bpm at birth
• at one month all organs formed and over next 2-3 months details happen
• Nervous system, kidneys, and liver need more than 9 months to fully develop

Question 7

intervillous space has a pool of maternal blood for gas exchange

Answer 7

• chorionic villus is the capillaries for gas exchange for fetus
• maternal blood is trapped in intervillous space, between the endometrium on maternal side and the villi on fetal side
• in mature placenta, spiral arteries from mother empty directly into intervillous space and looks like trees

Question 8

maternal and fetal O2 levels

Answer 8

• uterine artery has a PO2 of 100 mmHg and Hb saturation of 97.5%
• from uterine arteries blood enters the intervillous space. has PO2 of 30-35 and Hb saturation of 67%
• uterine vein has PO2 of 30, and Hb sat of 57%
• Umbilical vein has PO2 of 30 and Hb stat of 85. O2 saturation in umbilical vein equals uterine vein PO2. fetal blood Hb is higher though bc of higher affinity
• umbilical artery has PO2 of 23 and Hb of 60
• you ensure that baby gets sufficient O2 to body 3 ways:
  1. fetal hemoglobin has increased affinity
  2. fetus has increaed heartbeat so increased CO
  3. fetus has 50% higher fetal Hb content

Question 9

closure of the placental circulation increases pressure in the aorta

Answer 9

• at birth, circulating prostaglandin decreases, and prostaglandin causes dilation, so decrease in it causes constriction of umbilical cord
• the placenta receives 50% of the CCO combined cardiac output in fetus
• closing the placenta causes peripheral resistance to double, increasing the aortic and left ventricular pressure

Question 10

closure of the foramen ovale is caused by reversal of right left atrial pressure

Answer 10

• the increaed pulmonary circulation that was basically zero before causes an increase in venous return to heart
• decrease in right atrial pressure
• reversing this pressure where RA was high pressure before but now is less bc more pressure goes to LA pressure closes foramaen ovale
• fossa ovalis forms when permanent seal forms. failure to close is a patent foramen ovale

Question 11

closing the ductus venosus forces portal blood to perfuse the liver

Answer 11

• in fetus, alot of the blood from the portal vein enters the ductus venosus and bypasses the liver.
• 3 hrs after birth, ductus venosus shunt is completely occluded. it becomes the ligamentum venosum. happens by constriction of the vascular smooth muscle within the ductus venosus
• mechanism is increased PO2 and reduced prostagmandins
• failure of closure is portosystemic shunt

Question 12

closing the ductus arteriosus is mediated by changes in PO@ and prostaglandins

Answer 12

• a few hours after birth ductus arteriosus closes bc of constriction of the walls. thrombosis will obliterate the lumen ina month. becomes ligamentum arteriosum.
• mechanism:
  1. increased PO2.
  2. decreased circulating prostaglanins causes constriction
  3. bradykinin from the lungs involved

failure of closure leads to patent ductus arteriosus and would cause pulmonary hypertension, congestive heart failure, and cardiac arrythmias

Question 13

changes in circulation at birth in heart

1. closure of foramen ovale bc of change in pressure diff bw right and left atrium
2. closure of ductus arteriosus

Answer 13

• closure of the 2 shunts esablishes right and left circulatory systems
• foramen ovale closes when pressure of left atrium rises above pressure of right atrium bc of the decrease in pulmonary vasuclar ristance, foramen ovale flap pushes on the hole and seals shut eventually.
• as aortic pressure exceeds pressure in pulmonar yartery, blood flow through ductus arterisus reverse. well oxygenated aortic blood now flows through the ductus arteriosus and PO2 causes vasoconstriction of it, which closes the ductus arteriosus in a few hrs. falling prostaglandin levels also contribute.

Question 14

birth defects

Answer 14

• patent ductus arteriosus: small opening, and few symptoms besides a murmur. a larger hole would mean breathing difficulty, feeding poor, HR and sweating elevated, low weight. causes endocarditis risk as germs in blood adhere to valves, heart, or ductus where turbulence destroys smooth lining of vessels
• coarctation of aorta: smooth muscle of the ductus arteriosus invaded the descending aorta, so aorta contracts bc of the increaed O2 partial pressure. you get high BP in region perfused by the aorta above the constriction
• ventricular septal defects: hole in wall bw ventricles. small hole isn a problem and closes itslf. large hole causes probelems, first month, can cause congestive heart failure
• atrial septal defects: big hole would be blood moving from left atria to right, leading to volume overload of right heart. pulmonary hypertension, heart failure
• tetralogy of fallot:: 1. pulmonary stenosis- improper development of pulmonary valse
  2. dextroposition of aorta so it over rides the ventricular septum 3. right ventricular hypertrophy 4. ventricular septal defect—– all cause blue baby syndrome