how does the fetus get nutrients and gas exchange
through the mothers circulation
- oxygen, CO2 and nutrients are exchanged through the placenta via diffusion
when does the primitive heart begin to beat
22 days gestation
when does the fetal circulation begin
27-29 days of gestation
define the cardiovascular development during first 3 weeks
day 16: angiogenic clusters appear (tubules supply nutrition to growing embryo)
day 21: the heart is fully formed (tubes connect)
define what happens in the cardiovascular development during weeks 4-6
chamber development
day 22: heart begins to beat/bidirection blood flow begins
day 25: atrial separation begins with growth of septum primum ( later contributes to forming atrial septum )
day 28: ventricular separation starts./unidirectional blood flow begins
day 32: septum secundum starts to develop, reinforcing the divsion bw the atria
day 37: foramen ovale is complete ensuring that blood can bypass the nonfunctional fetal lungs
-fetal heart stabilizes around 95bpm
define what happens during the wk 7-8 of cardiovascular development
wk 7-8
heart has matured structurally
day 49:all chambers fully developed allowing the heart to function efficiently
day 56: heart valves complete their formation ensuring proper directional blood flow
-fetal heart is fully developed and cont to grow and strengthen
-circulation remains dependent on specialized fetal shunts until birth
what are the 3 layers central portion of the embryonic disk?
-endoderm (innermost layer)
-mesodem (middle layer)
-ectoderm (outermost layer)
define the endoderm layer
(innermost layer)
- makes up the respiratory system
1. respiratory tract
2.pharynx
3.lungs & epithelial lining
4.digestive tract
5.bladder
6.thyroid
7.liver
8.pancreas
define the mesoderm layer
( middle layer)
forms the cardiovascular system
1.heart & blood vessels
2.muscles
3.dermis
4.bones
5.connective tissue
6.lymphoid tissue
7.reproductive organs
define the ectoderm layer
(outermost layer)
1. central and peripheral nervous system
2. brain and spinal cord
3. hair
4.nail
5. epidermis
6.lens of the eyes
how does the fetal circulation differ from circulation after the infant is born
-external respiration by fetus does not occur w/in lungs
-mothers lungs and liver perform most of the metabolic function
how is fetal blood flow shunted around the liver and lungs
-O2 blood travels through placenta throught umbilical veins and directed past the liver and lungs via specialized fetal shunts
-ensures O2 rich blood reaches vital organs such as heart and brain
-bypassing liver and lungs facilitates pumping larger qaulities of blood to the placenta (gas,nutrients, waste exchange)
what are the 3 keys shunts that direct blood flow in the fetal circulation
- foramen ovale
-one way flap bw R.& L atria
-allows O2 rich blood bypass the R.vent to the L.atrium to pump to brain and upper body.
2.ductus arteriosus
-connects pulmonary artery to aorta
-most blood from R.Vent bypass the lungs, flows directly into the aorta and is distributed to lower body
3.ductus venosus
-shunts blood past liver
-O2 rich blood is shunted directly into the inferior vena cava allowing for rapid delivery to the heart and brain
what happens to the shunts at birth
once newborn takes first breath shunts begin to close as the lungs expand, pressure gradients shift and circulation transitions to independent postnatal pattern
define ductus venosus
-O2 blood from placenta to fetus through umbilical vein
-shunts 30-50% of O2 rich blood directly to inferior vena cava, by passing liver
-O2 rich blood mixes with O2 depleted venous blood and flows to the R.atrium
-blood entering the R.atrium contains highest Oxygen saturation
-once closed at birth becomes ligament venosum
define foramen ovale
-a small hole w/in the atrial septum, where blood from vena cava flows from the R.atrium to L.atrium and pumped into L.ventricle to the aorta supplying brain and heart, bypasses the lungs
-remainder of blood in R.atrium drains into the R.ventricle, blood is pumped into pulmonary artery to developing lungs ( 13-25%)
-remaining blood is directed to ductus arteriosus
define the difference of PVR in utero vs at birth
-PVR is high in utero=low lung volumes and pulmonary vasoconstriction
-at birth PVR drops increasing blood flow to the lungs, right pressure drops and rise in left atrial pressure causes foramen ovale to close
what happens after blood has been oxygenated through the placenta and directed through fetal shunts?
-blood from the pulmonary veins empties into the L.A and flows into the LV
-blood flows out the aortic valve and into ascending aorta
-ascending aorta supples the head,right arm,coronary circulation w/blood with highest oxygen content
define ductus arteriosus
-high PRV causes most of the blood flowing through the pulmonary artery R.vent to pass through a less resistance ductus arteriosus into the aorta
-blood w/in pulmonary artery bypasses the lungs and left heart
-R and L vent pump almost in parallel due to large qualities of blood required to flow to the placenta
-if fail to close after birth–>patent ductus arteriosus
what does fetal circulation ensure?
-deoxygentated blood from upper torso returns to R.Atrium via superior vena cava
-blood in the descending and abdominal aorta flows through common iliac arteries to two umbilical arteries and back to placenta for oxygenation
-17-20% of fetal cardiac output flows through the umbilical arteries up to 33% as fetus matures
-placenta contains as much as half of the fetal blood volume
steps of the fetal circulation
placenta–>umbilical vein–>ductus venous (bypass liver)–>inferior vena cava–>R.A–>3 directions: 1. (some goes through the forman ovale–L.A–L.V–Aorta–systemic circulation-umbilical arteries–back to placenta), 2nd: left over blood in R.A–R.V–pulmonary trunk–lungs-pulmonary veins–L.A–L.V-aorta-systemic circulation-umbilical arteries–placenta. 3. blood from R.A goes to Pulmonary trunk–ductus arteriosus-aorta-systemic circulation-umbilical arteries–placenta
define the transition to extrauterine life?
-clamping of umbilical vessels remove low pressure system of placenta from fetal circualtion
-PVR decreases and pulmonary flow increases
-inflation of lungs initiates gas exchange- dialates pulmonary arterioles
-pressure in R side decrease,pressure in L side increase
-foramen ovale flap closes due to pressure change
-increase pressure in aorta becomes greater than thepressure in pulmonary artery causing shunting through ductus arteriosus to decrease
-closer of the ductus arteriosus occurs as result of increased levels of PaO2
-constriction begins @ birth 20% w/in 25hrs, 80% w/in 48hrs, 100% w/in 96hr
