Later Development, Develop. Physiol., Dr. D. Penney




Table 3.01 - Changes during Development: The Cardiovascular System is the first to become Functional in Fetus.


Maternal Circulation:
3 mos.Term
Uterine blood flow
(ml/min.)
50500-750
Cardiac output (CO)45006000
Heart Rate = 70 ---> 80 beats per minute; Stroke Volume = 64 ---> 71 ml

Placenta:

- 60 fetal codyledons
- 20 maternal lobes formed by septa
- At term 50 x 106 villous capillaries
- Blood flow: intervillous space = 65 - 120 ml/100 g/min., fetal = 90 - 190 ml/min.

Fetal Cardiac Output:

- 235 - 525 ml/kg body wt./min. (changes brought about mainly through changes in heart rate)
.... by comparison, the resting cardiac output of an adult human is about 75 ml/kg body wt./min.
15 mm embryo65 beats/min.
45 days125 beats/min.
9 weeks. 175 beats/min.
15 weeks.145 beats/min.
0.5 - 1.0135-155 beats/min.

Fetal regulation:

- Vagal (vagus nerve) pathway and chemoreceptors on large vessels are present by 6 - 8 weeks
- Bradycardia is a response to maternal hypoxia
- Arterial blood pressure shows a steady rise with fetal growth.


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