Foetal Circulation

Question 1

Explain how foetal circulation is modified in comparison to adult circulation

Answer 1

• 3 by-passes to avoid liver/lungs
• by-pass of hepatic circulation
• by-pass of pulmonary circulation by foramen ovale and ductus arteriosus

Question 2

What surrounds and is contained in the umbilical cord?

Answer 2

• surrounded by fetal membrane and amnion

- contains Wharton’s jelly which contains 2 umbilical arteries and 1 umbilical vein

Question 3

What is the function of the umbilical vein?

Answer 3

carries oxygen and nutrient rich blood from the placenta

Question 4

What are the divisions of the umbilical vein?

Answer 4

• smaller branch to the liver (liver then has branch to IVC)

- larger branch: the ductus venosus which by-passes the liver to drain to IVC

Question 5

What order can blood be passed through the vessels from drainage to the IVC?

Answer 5

• right atrium to left atrium through foramen ovale
• to left ventricle
• to aorta

Question 6

What order can blood be passed through the vessels from drainage to the SVC?

Answer 6

• right atrium
• right ventricle
• pulmonary trunk
• ductus arteriosus (90%)
• aorta
• pulmonary trunk
• pulmonary arteries (10%)
• pulmonary veins
• left atrium, left ventricle
• aorta
  (blood is NOT oxygenated)

Question 7

Where does the blood in the aorta go?

Answer 7

• one third gets distributed around the abdomen, pelvis and lower limbs
• 2 thirds goes to placenta by internal iliac artery then to umbilical artery then placenta

Question 8

Explain the effect tying and cutting the umbilical cord has on postnatal circulation

Answer 8

• loss of blood flow through placenta
• increased systemic vascular resistance as blood must now be distributed in systemic circulation
• therefore increased aortic, left ventricular and left atrial pressure

Question 9

Explain the effect of the first breath on post natal circulation

Answer 9

• expansion of the lungs expands the before collapsed alveoli
• decreased pulmonary vascular resistance
• therefore reduced pulmonary arterial, right ventricular and right atrial pressures

Question 10

Explains what happens once pulmonary circulation is established upon the first breath

Answer 10

• blood from pulmonary circulation is returned to left atrium
• increases pressure in left atrium
• valve of foramen ovale is pushed rightward and closes
• becomes structurally closed in 4 months to become fossa ovalis

Question 11

What is patent foramen ovale?

Answer 11

• when foramen ovale doesn’t close
• usually asymptomatic
• can cause paradoxical emboli

Question 12

Explain how the obliteration of ductus arteriosus occurs

Answer 12

• occurs due to the systemic pressure changes to cause blood that normall flows through ductus arteriosus from pulmonary trunk to aorta to be reversed
• functionally closed after 1hr due to increased oxygen/decreased prostaglandin causing constriction of the vessel
• structural closure between 1-4 months by thickening of tunica intima to become ligamentum arteriosum

Question 13

Patent ductus arteriosus

Answer 13

• when ductus arteriosus isn’t obliterated
• due to pressure gradient blood flows back into pulmonary circulation
• results in pulmonary hypertension ad congestive cardiac failure

Question 14

Explain how obliteration of ductus venosus occurs

Answer 14

• blood flow through umbilical vein stops
• muscle wall of vessel contracts
• portal venous blood flows through hepatic sinuses
• occurs 1-3hrs after
• becomes ligamentum venosum

Question 15

Where can the ligamentum venosum be identified in adults?

Answer 15

Between caudate and left lobe of liver

Question 16

What does the umbilical vein become after birth?

Answer 16

• round ligament of the liver: ligamentum teres hepatis

Question 17

What does the umbilical arteries become after birth?

Answer 17

medial umbilical ligaments within medial umbilical folds

Question 18

Explain the development from a zygote to a morula

Answer 18

• 2 cell stage: 30hr
• 4 cell stage: 40hr
• morula (16 cell stage): 72hrs
  surrounded by zona pellucida which disappears after 4 days

Question 19

Explain the development from a morula to a blastocyst

Answer 19

• morula travels down fallopian tube, enters uterine cavity and implants on endometrium
• fluid accumulates in intracellular spaces
• spaces merge to form single cavity (blastocyst cavity)
• inner cell mass at one pole where cells will differentiate to form the primary germ layers in gastrulation

Question 20

Explain the development of a blastocyst

Answer 20

• day 8 inner cell mass differentiates into
• epiblast adjacent to amniotic cavity
• hypoblast adjacent to blastocyst cavity/primitive yolk sac
• layers form bilaminar disc
• cavity forms within epiblast to become amniotic cavity

Question 21

What side and region is the primitive streak found on the bilaminar disc?

Answer 21

• dorsal side

- caudal region

Question 22

Explain the formation of the trilaminar disc

Answer 22

• cells of epiblast begin to migrate through primitive streak and creates a third layer between epiblast and hypoblast
• epiblast differentiates to ectoderm
• hypoblast differentiates to endoderm
• middle layer becomes mesoderm

Question 23

Explain the events that occur in the trilaminar disc of a 17 day old embryo

Answer 23

• prenotochordal cells migrate through primitive streak to form notochordal plate in endoderm
• plate detaches from endoderm to form notochord
• activates signalling pathway for tissue differentiation and development
• events occur in cranial to caudal direction

Question 24

What does the mesoderm become?

Answer 24

divided into:

• paraxial mesoderm: somites and head mesenchyme
• intermediate mesoderm: urogenital system
• lateral plate mesoderm: walls of body cavities, serous membranes and circulatory system