How is the circulation of a fetus different from the circulation of a baby answers?

The fetus does not use its lungs to bring oxygen to the blood.

Without getting to wordy, I'll try to explain it simply on the differences between fetal circulation and newborn circulation.

In utero, the baby has an umbilical cord. All nutrients and exchanges are done by this. Because the baby cannot physically breathe air for oxygen exchange two shunts are used to by pass the lungs for oxygenation. Those two shunts are called the foramen ovale and the ductus arteriosus.

So, here are the steps of fetal circulation:

1. Mom passes oxygenated blood to the fetus through the placenta. Through the placenta it is carried through the umbilical cord to the liver and then there is a branch of 3.

2. At the branch in the liver, the oxygenated blood goes into the inferior and superior vena cava into the right atrium of the heart. This is where the foramen ovale comes in. The blood from the right atrium goes through the foramen ovale and directly into the left atrium.

3. After in the left atrium, it will pass into the aorta and through the body and will return.

In a newborn:

Once the umbilical is clamped off, this initiates the ductus arteriosus to snap close and build pressure in the left atrium and ventricle. Once the pressure has shifted from the right to the left, the foramen ovale will snap closed, as well. Then, the newborn will resume normal body circulation meaning the lungs will do the work.

The deoxygenated blood will enter through the vena cava, to the right atrium, to the left atrium, through the pulmonary artery and into the lungs. The lungs will do oxygen/co2 exchange and will send oxygenated blood back through the pulmonary vein. From the pulmonary vein it will go into the left atrium, to the left ventricle and out through the aorta and to the entire body.

I hope I was able to explain it to you well.

Answer and Explanation:  

The exposed example refers to a population that exhibits a logistic growth model. Population growth depends on density, the natality and mortality rate depends on the population size, which means that there is no independence between population growth and population density.

When a population grows in a limited space, density rises gradually and eventually affects the multiplication rate. The population's per capita growth rate decreases as population size increases. The population reaches a maximum point delimited by available resources, such as food or space. This point is known as the carrying capacity, K.

K is a constant that coincides with the size of the population at the equilibrium point when the natality rate and the mortality rate get qual to each other.

If the population size, N, is inferior to K (N<K) the population can still grow. When N approximates to K, the population´s growth speed decreases. When N=K, the population reaches equilibrium, and when N is superior to K (N>K) the population must decrease in size because there are not enough resources to maintain that size.  

The sigmoid curve represents the logistic growth model. At the beginning population grow slowly. In the exposed example this occurred when the small group of 10 foxes moved to the new environment, starting a new population. In the second stage, the population size increases rapidly. Probably this happened when foxes reached a number of 40 individuals. And finally, slow and gradually, the population reaches the equilibrium point, K, which depends on resource availability. This point belongs to the stage where food starts to become harder to find, and much of the living space is occupied.

As the foxes population in the exposed example is still growing but in a decreased rate, we could assume that this population is reaching its carrying capacity, but it is not there yet. This population is reaching the top of the sigmoid curve. N is approximating to K, and the population´s growth speed decreases.