Later Development, Develop. Physiol., Dr. D. Penney
Table 3.01 - Changes during Development: The Cardiovascular System is the first to become Functional in Fetus.
|Uterine blood flow|
|Cardiac output (CO)||4500||6000|
|Heart Rate = 70 ---> 80 beats per minute; Stroke Volume = 64 ---> 71 ml |
- 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 embryo||65 beats/min. |
|45 days||125 beats/min. |
|9 weeks. ||175 beats/min. |
|15 weeks.||145 beats/min. |
|0.5 - 1.0||135-155 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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