Topic 2: Foetal Life Flashcards
What are the prenatal and infant life stages?
Prenatal period: - early foetal period (conception-20 weeks) - late foetal period (20-40 weeks) Infancy: - Neonatal period (birth-28 days) - Post neonatal period (29 days-1 year)
What are the three stages in the early foetal period?
- Fertilisation stage
- Blastogenesis stage
- Embryonic stage
Explain the fertilisation stage
Conception usually occurs in the fallopian tube within 48 hours of ovulation and is followed by rapid cell division. The resulting mass of cells enter the uterus where it attaches itself to the endometrial lining of the uterus within 5-7 days after ovulation. The outer cells of the blastocyst begin to arrange themselves into a functioning placental unit.
Explain the blastogenesis stage
This continues for about two weeks after fertilisation. During this time the cells separate into two distinct layers of cells: an inner cell mass which gives rise to the embryo and an outer layer of cells (trophoblast) which becomes the placenta.
Explain the embryonic stage
Complete by 60 days of gestation, and is the time during which the basic structures for all of the major organs and tissues develop. This is considered the critical stage of development, because the inner cells of the blastocyst differentiate into the three germinal layers which in turn develop into the major organ systems.
Explain the late foetal period
The foetal stage of gestation is the period of most rapid growth. Between 13-40 weeks of gestation, the weight increases nearly 500-fold, from 6g to 3000-3500g at birth. By 34-36 weeks of gestation, growth in foetal size is solely due to hypertrophy.
Explain the effects of energy and nutrient restriction on foetal growth
This depends on whether it occurs in early or late foetal growth. During the first two stages of foetal growth, the amount of energy needed to support foetal development is extremely small.
In contrast, the restricted availability of energy after the third month of gestation will not have any teratogenic effects, but could interfere with foetal growth. Nutrient requirements are the greatest in the last trimester of pregnancy.
What is the role of the placenta?
Provides the efficient transfer of oxygen and nutrients from the maternal circulation to the foetal circulation. It also disposes of metabolic waste products from the foetal to the maternal circulation.
How are nutrients transferred from the mother to the foetus?
From the maternal blood supply to the foetal blood supply by passive or simple diffusion, facilitated diffusion, active transport and pinocytosis,
What are the key changes in body composition during gestation?
- body water: reduces from 90% to 70% by term
- protein: accretion is relatively constant and increases linearly with weight, commencing at 25 weeks and increases until end of gestation.
- fat: accretion is low early in gestation and increases markedly late in gestation. Accretion commences at 25 weeks and increases until term.
What are the three nutritional influence outcomes on foetal growth?
- growth failure: maternal malnutrition can be one cause of growth failure that results in low birth weight
- nature of tissue effects: animals malnourished from restrictions of their mothers’ diet throughout most of gestation are characterised by reduced number and size of cells in the placenta, reduced brain cell number and head size
- influencing factors: the foetal consequences depend on the timing, severity and duration of the maternal dietary restriction. Reduction in the number of cells may be permanent if the restriction is maintained throughout the entire period of hyperplastic growth.
Explain intrauterine growth restriction (IUGR)
This term refers to foetal growth being inhibited and the foetus not attaining its genetic growth potential.
