vasculature of the neonate

Question 1

list the major vessels of fetal circulation

Answer 1

• from placenta via umbilical vein to liver via
• ductus venosus to
• ICV to right atrium in fetal heart via
• **foramen ovale **to left atrium to aortic arch, carotid, SVC back to RA
• back through ductus arteriosus to descending aorta
• umbilical arteries back to placenta

Question 2

explain how and why the fetal circulation differs from the adult

Answer 2

the how relates to circulatory shunts which are passages between 2 natural channels such as blood vessels
1. ductus venosus
2. foramen ovale
3. ductus arteriosus
WHY:
the placenta replaces many functions:
lungs and liver recieve nutrients from the placenta during growth rather than provide
- the lungs are collapsed, unecessary and have high resistance in the fetus
- the liver is not required to excrete waste as mothers liver does that for it. in later gestation starts to store glycogen for after birth
- developing organs and tissues are fragile and therefore blood pressure must be kept lower

Question 2

what is the function of the umbilical artery? identify it on the image below

Answer 2

delivers nutrients to the fetus

Question 2

what is the function of the umbilical arteries. identify them on the image

Answer 2

delivers blood back to the placenta

Question 3

what is the function of the urachus and identify it

Answer 3

fibrous remnant of allantois. was a canal that drains the urinary bladder of the fetus

Question 4

trace the path of the ductus venosus and explain the function of this structure

Answer 4

• creates low resistance pathway throughout liver
• from umbilical vein to caudal VC
• remember that ulbilical arteries (x2) got to placenta and umbilical vein goes to fetus
• ductus venosus allows 50% of blood to bypass the liver (since mothers liver does liver function so liver only needs supply of blood)
• DV streams blood to formaen ovale

NOT present in the fetal horse!, not a single shunt in the fetal pig

Question 5

what is the function of the formen ovale. identify and describe it on an image

Answer 5

• shunts oxygenated blood striaght through RA to LA
• pressure differences across FO keep it open in fetus
• patency maintained by high blood flow

Question 5

what is the function of the ductus arteriosus. describe it and identify it on the image blow

Answer 5

• shunts blood in pulmonary artery striaght to descending aorta
• pressure differential flow back to placenta
• allows equivalent ventricular musculature and vasculature

Question 5

explain the consequences of partuition upon the circulatory system and list all the major circulatory changes that occur

Answer 5

at birth, fetus must take over all fuctions of placenta
- respiration starts
- circulation now a closed system
- digestion begins
- needs to thermoregulate
- kidneys need to start excreting waste (bladder starts to fill)

shunts close:
- umbilical cord ligated as placenta detaches = no more blood from umbilical vein and ductus venosus sphincter contracts so blood is diverted through the liver via hepatic portal vein (remnant called ligamentum venosum
- lungs open, placenta gone = low pulmonary pressure and high systemic pressure. pressure differential causes septa of formane ovale to close together and fuse so blood is diverted to lungs via right ventricle. remnant is called fossa ovalis
- at first breath, pO2 increases and ductus arteriosus constricts. as blood flow moves to open lungs, pressure lowers in the lungs and increases in the body which helps to close ductus arteriosus. can take a while to close. remnant called ligamentum arteriosum

Question 6

describe the mechanisms that regulate changes in circulation at birth

Answer 6

• pressure changes secondary to lung inflation (paO2 increase)
• changes in hormones (cortisol, catecholamines, prostaglandins)
• vascular resistance changes
• tissue layers pushed together fuse and fibrose to become ligaments

Question 7

describe the timeframe of closure for the ductus venosus, foramen ovale and ductus arteriosus

Answer 7

Ductus venosus
- functional closure occurs within minutes due to improved pumonary clearance and no umbilical blood supply
- anatomic closure occurs within days

formaen ovale
- functional closure is relatively quick (hours)
- anatomic closure is relatively slow (weeks to years) with a small opening persisting in about 25% of animals

ductus arteriosus
- functional closure within minutes to hours
- anatomic closure may take 2-7 days
- if closure does not occur = ventricl septal defect= patent ductus arteriosus (relatively common, non life threatening but reduces efficiency of the heart

Question 8

what are the physiological changes that occur at the transition from fetal to neonatal life

Answer 8

• increased oxygenation
• hemoglobin alters from fetal to adult
• blood pressure increases
• enteral intake of nutrients (mouth)

Question 9

what is the name of the anatomic remnant of the internal umbilical arteries called

Answer 9

round ligaments of the bladder

Question 10

what is the anatomic remnant of the internal umbilical vein called

Answer 10

round ligament of the liver

Question 11

what is the anatomic remnant of the ductus venosus called

Answer 11

ligamentum venosum

Question 12

what is the anatomic remnant of the formane ovale called

Answer 12

fossa ovalis

Question 13

what is the anatomic remnant of the ductus arteriosus called

Answer 13

ligamentum arteriosum