test 3 part 2 Flashcards
In the fetus, some organs do not function until birth
Lungs
Kidneys
GI Tract
Fetus obtains oxygen and nutrients via
diffusion from the
maternal blood.
Wastes and CO2 are eliminated via
diffusion into the maternal blood
Exchange occurs via the placenta
Inside the uterus
Attached to baby via the umbilical cord
Umbilical Artery
carries deoxygenated blood AWAY from the fetus to the placenta
Carries wastes and CO2
LOW O2 Content!
Umbilical Vein
carries oxygenated blood from the placenta to the fetus
Carries nutrients and O2
HIGH O2 Content
Fetal Capillaries
Umbilical arteries and veins branch into these capillaries located inside the intervillous spaces in the placenta.
Intervillous Spaces
Spaces filled with maternal blood from uterine arterioles. Drained by Uterine veins.
The Placenta
The placenta communicates with the mother’s cardiovascular system via uterine blood vessels.
Wastes diffuse out of the capillaries into the intervillous spaces containing maternal blood in the placenta.
Nutrients travel from mother’s blood vessels to the intervillous space via uterine arteries.
Diffuse from the intervillous spaces into the fetal capillaries
The concentration of hemoglobin in fetal blood is about 50% higher than maternal blood
Fetal hemoglobin has a greater affinity for oxygen than maternal blood
Can carry 30-35% more oxygen.
THERE IS NO DIRECT MIXING OF MATERNAL AND FETAL BLOOD!!!
The Placenta - Function
Exchange of gases – CO2, O2, CO
Accomplished via diffusion
20-30mL O2/min extracted
Short interruption in blood flow can be fatal to fetus
Depends on delivery not rate of diffusion
Exchange Nutrients/ Electrolytes
Amino Acids, Free Fatty Acids, Carbohydrates, Vitamins
Exchange is rapid and increases as pregnancy increases
Placental circulation has a very low resistance (They flow into pools)
Transfer of Maternal Antibodies
Immunoglobulins – Primarily IgG transported from mother to fetus providing passive immunity
Newborns produce own IgG, but don’t reach adult levels until about age 3 (get antibodies from breast milk)
Hormone Production
Umbilical Blood Vessels
Blood passes from the fetus to the placenta via 2 umbilical arteries
Branch of the internal iliac arteries
Sat ~58%
Oxygenated blood (sat ~80%) returns from the placenta via 1 umbilical vein
Goes to the liver of the fetus where it divides into 2 branches
Joins hepatic portal vein -> Liver (1/3)
Ductus Venosus -> IVC (2/3)
Sphincter mechanism in ductus that controls blood flow through the liver
In the IVC, oxygenated blood via the ductus venosus meets deoxygenated blood from the lower body
Sat falls to about 67%
Fetal Lungs
Filled with fetal lung fluid
Not used to oxygenate blood
This liquid increases the pulmonary vascular resistance to blood flow
Most fetal blood does not go from the RV to the lungs
Instead, it passes through the Foramen Ovale
Hole between the Right and Left Atria.
Blood entering from the IVC is guided toward the foramen ovale to the Left Atrium.
In the LA, blood mixes with the very small amount of blood returning from the pulmonary veins
Goes to the LV
LV pumps the oxygenated blood into the aorta
Perfuses the brain and myocardium
Getting highest O2 content available
Fetal blood returning to the heart from the SVC
bypasses the Foramen Ovale and enters the RA
Goes to the RV and pumped to the PA
Pulmonary Vascular Resistance is so high that 95% of this blood bypasses the pulmonary arteries
Travels across the ductus arteriosus to the descending aorta
Ductus arteriosus connects PA and Aorta
Perfuses fetal tissues
At the common iliac branch to the internal and external iliacs
Part of that blood flowing systemically will flow through the internal iliacs to the umbilical artery
Will go to the placenta for nutrient/waste exchange
The only fetal vessel to carry fully oxygenated blood is the umbilical vein
Blood entering the aorta from the LV and perfusing the head and heart has a higher oxygen content than the blood perfusing the rest of the body.
Transition to Neonatal Circulation
At birth, the Pulmonary, Renal and Digestive Systems start to function.
There are 3 shunts present in the fetal circulation that normally close after birth:
Ductus Arteriosus
Foramen Ovale
Ductus Venosus