Topic 2c: Fetal Development and Birth

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Fetal Development:

refinement of the already established organ systems and continued growth

Birth:

labor is triggered by oxytocin (hormone produced by the posterior pituitary gland); oxytocin causes uterine contractions

the cervix must dilate, which takes hours. The amnion ruptures during this stage

contractions continue, resulting in expulsion of the fetus

the umbilical cord is cut

the placenta is delivered at the last

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Cell specialization:

determination: irreversible commitment of a cell to a particular body function or cell lineage

triggered by morphogens

differentiation: cell exhibits the structure, function, and biochemistry of a specific cell lineage

4 tissue types (muscle, nervous, epithelial, connective)

cell communication is essential to cell development and specialization.

cell migration is also essential during the development process

neural crest cells in particular exhibit a lot of movement

improper movement or dysfunction in migration mechanisms can lead to development of diseases and disorders (tumors, intellectual disabilities, vascular disease, etc.)

movement mechanisms include: blebbing, cytoskeleton changes driving changes in cell shape, cytoplasmic displacement, use of motor proteins etc.

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Stem cells:

undifferentiated cells, can give rise to any cell lineage

potency of the cell determines the number of cell types it can differentiate into

totipotent: the first stem cells resulting from zygotic division, can differentiate into any cell type

pluripotent: have the ability to develop into >1 cell type, divide as it wants, however cannot form a complete organism on its own

multipotent: differentiate into any cell type within a given lineage

Stem cells also provide the capacity of regeneration:

incomplete regeneration: lost or damaged tissues are replaced with tissue that is NOT identical

complete regeneration: lost or damaged tissues are replaced with identical tissue

the liver has great regenerative capacity in comparison to other organs, such as the heart which has little to none. The kidneys also have moderate regenerative capabilities however are more susceptible to damage than the liver

scar tissue is evidence of incomplete regeneration

humans typically exhibit incomplete regeneration while other species like newts have the ability to regenerate completely as they retain greater numbers of stem cells

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Role of programmed cell death:

death of cell carried out by regulated processes

apoptosis: essential for normal embryonic development; ex: removing unneeded cells via apoptosis to form fingers and toes

autophagy: self-digestion of cellular contents using an autophagolysosome

Necrosis is a type of cell death that is not programmed, triggered by cell damage or trauma or infection; since it is uncontrolled, it can cause damage to nearby cells

necroptosis, a programmed form of necrosis can serve as a back-up to apoptosis

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Fetal Circulation:

https://www.chop.edu/conditions-diseases/fetal-circulation#:~:text=The%20fetal%20circulatory%20system%20uses,is%20still%20in%20the%20womb.

fetus receives oxygen, nutrients, and all materials needed for sustenance from blood vessels in umbilical cord, which is connected to placenta.

waste products and CO2 are sent back through the cord to mother's circulation for elimination.

this is because fetus does not have functional lungs or liver, and certain other organs while still in the womb

3 main shunts which keep blood in fetus from going to nonfunctional body parts:

foramen ovale: bypasses the lungs, moves blood from R atrium to L atrium

becomes the fossa ovalis in adults

ductus arteriosus: bypasses the lungs, moves blood from pulmonary artery to aorta

becomes the ligamentum arteriosum in adults

ductus venosus: bypasses the liver, moves blood from inferior vena cava into R atrium

NOT found in the heart

Fetal heart circulation:

oxygenated blood enters the fetal heart via R atrium --->

flows through foramen ovale into L atrium --->

from L atrium, passes into L ventricle, then aorta --->

from aorta, blood goes to heart muscle, brain, and arms --->

deoxygenated blood returns to R atrium via superior vena cava --->

from R atrium, goes into R ventricle --->

from R ventricle, it is shunted by ductus arteriosus into aorta, where it then goes to the placenta

Newborn circulation:

after birth, the umbilical cord is cut, so no oxygen or nutrients are coming through the placenta from the mother.

baby's first breath causes lungs to expand

alveoli are cleared with expansion of lungs, BP increases, and pulmonary pressures decrease

these events eliminate the need for the ductus arteriosus and it closes

pressure in L atrium increases and decreases in R atrium, stimulating the closure of the foramen ovale