Flashcards in Chapter 3 - Embryogenesis Deck (45)
(Role in senescence)
Telomeres are the ends of chromosomes. They shorten during each round of DNA synthesis, eventually become too short and the cell is no longer able to replicate.
What is telomerase?
Expressed by germ cells, fetal cells, and tumor cells.
A reverse transcriptase that is able to synthesize the ends of chromosomes, preventing senescence.
(May play a role in the survival of cancer cells)
Fetal circulation via diffusion (at the placental barrier)
Preferred method for waste, glucose, amino acids and inorganic salts.
Diffusion requires a gradient - partial pressure of O2 is HIGHER in maternal blood than in fetal blood.
Additionally, Fetal hemoglobin (HbF) exhibits a GREATER affinity for O2 than maternal hemoglobin (HbA)
How does the immune protection of the fetus happen?
Crossing of antibodies across the placental membrane serves as a protective function.
How does the placenta act like an endocrine organ?
It produces hormones:
Human chorionic gonadotropin (hCG)
These maintain pregnancy.
ARTERY versus VEIN, correct biological definitions
ARTERY caries blood away from the heart.
VEIN carries blood toward the heart
Why is the oxygen concentration reversed in umbilical arteries and veins?
Because oxygenation happens at the PLACENTA not at the LUNGS
What is the purpose of the 3 fetal shunts ?
What are the 3 fetal shunts?
They direct blood away from organs that aren't being used yet (mainly the lungs and the liver) - ways for blood to bypass these
What is the foramen ovale?
One of the three fetal shunts.
Connects R atrium to L atrium. (Bypasses R ventricle - goes to L atrium and then through the aorta into the systemic circulation) this is also due to the pressure difference in the fetus: R side of heart has higher pressure than L. At birth the pressure reverses, closing the foramen ovale.
What is the ductus arteriosus?
One of the three fetal shunts.
Shunts leftover blood from the pulmonary artery to the aorta. The pressure diff between R and L sides if the heart push blood through this opening.
What is the ductus venosus?
One of the three fetal shunts (bypasses the liver)
Shunts blood returning from the placenta (via the umbilical vein) directly to the inferior vena cava. The liver still does receive some blood from smaller hepatic arteries.
What happens during the 1st trimester? (By week)
22 days: heart starts beating, followed by development of eyes, gonads, limbs, and liver.
Week 5 - 10mm long
Week 6 - 15mm long! (Double)
Week 7 - cartilaginous skeleton hardens into bone
Week 8 - most organs formed, brain fairly developed --> known as "fetus"
At end of 3rd month, about 9cm long
What happens during the 2nd trimester?
- lots of growth
- starts moving in the amniotic fluid
- face takes on human appearance
- fingers and toes elongate
- at the end of 6 months, about 30-36cm long
What happens during the 3rd trimester?
- Months 7 and 8: continued rapid growth and brain development
- Month 9: active transport of antibodies to the fetus; growth slows, less room for fetus to move.