L4 Fetal Nourishment and Development Flashcards
How long is the embryonic period?
Week 1 to 8
How long is the fetal period?
Week 9 to 38
What are the 3 stages of cell development?
Hyperplasia: increased cell division
Hyperplasia and Hypertrophy: cell division and cell growth
Hypertrophy: increased cell size
Explain the steps in fertilization (x4).
A sperm perforates the outer layer of the oocyte and breaches the plasma membrane of the oocyte. Enzymes in the acrosome on the sperm break down the zona pellucida.
Sperm enters the cytoplasm of the oocyte without its plasma membrane.
Zona pellucida now closes off and doesn’t allow any more sperm to enter.
What does fertilization trigger?
Sperm entering and first meiosis.
Explain the 4 stages that occur in week one of fetal development?
Where in the reproductive system do they occur?
Stage 1: fertilization > zygote
Stage 2: Zygote divides > 2cell > 4 cell > 8 cell > morula (16-32 cells). Both stages occur within the fallopian tube. Zona pellucida intact
Stage 3: Early blastocysts > late blastocyst
Stage 4: Implantation begins at about the 6th day
What is the main nutrient for the fertilized egg in week 1 and what is it supplied from?
Glycogen supplied by the uterine gland.
In stage 3 of week one of fertilization, what occurs?
A blastocyst cavity develops surrounded in the embryoblast, and then trophoblasts (outer layer).
The blastocyst then enters the uterus and the zona pellucida degenerates.
What occurs week 2 of fetal development?
Implantation - blastocyst is fully embedded in the endometrium and an inner cell mass forms the embryonic plate.
What occurs early in week 2 of fetal development?
Trophoblasts invade the endometrium and secrete proteolytic enzymes (break down proteins).
What is the syncytiotrophoblast?
Placental villi that originate from the trophoblast layer that invade the endometrium to establish circulation of nutrients between the mother and the fetus.
What happens late in week 2 of fertilization?
Inner cell mass becomes a flattened disk of 2 layers and the amniotic cavity develops.
The 2 layers are the epiblast layer and the hypoblast layer.
What is the epiblast layer (top)?
Forms late in week 2 of fertilization and give rise to the ectoderm and the mesoderm.
It is adjacent to the amniotic cavity.
What is the hypoblast?
Forms late in week 2 of fertilization and give rise to the endoderm. As this layer thickens it will develop into the cranial region.
What are the lacunar networks and when do they form?
They are spaces within the trophoblast that fill with maternal blood. It is how the trophoblast absorbs nutrients and oxygen to the embryonic disk. It marks the beginning of maternal-fetal circulation.
Occurs in week 2 of fertilization.
What are 3 main events that occur in week 3 of pregnancy?
Gastrulation
Neurulation
Cardiovascular system begins to develop.
What is gastrulation?
The formation of the 3 germ layers:
- Embryonic ectoderm
- Embryonic mesoderm
- Embryonic endoderm
Which germ layer gives rise to the epidermis, nails, teeth, teeth enamel, inner ear, retina, CNS, and PNS?
Embryonic ectoderm
Which germ layer gives rise to the epithelial lining of the respiratory, and GIT including the glands, and liver pancreas, and bladder?
Embryonic endoderm
Which germ layer gives rise to the muscle, connective tissue, skeleton, cardiovascular system including vessels, blood cells, and bone marrow, as well as the reproductive and excretory systems?
Embryonic mesoderm
The folding of the neural tube stems from what tissue and occurs during what week of pregnancy?
Ectoderm
Week 3
These structures come from the mesoderm and develop into the skeleton and musculature.
What week do they develop?
Somites
Week 3
What is the likely result if the neural plate forms improperly?
Misscarige
What is a coelum and when do they develop?
Spaces within the mesoderm that become body cavities. Develop in the 3rd week.
In what week of pregnancy does the following occur:
- development of blood vessels and blood cells from the mesoderm
- vessels and heart tubes are linked to allow for circulation of blood
- completion of the chorionic villi and the connecting stalk
Week 3
What is the most important event in the latter half of the embryonic period (4-8weeks)?
The folding in the longitudinal and transverse directions
Briefly explain embryonic folding.
The ectoderm folds downwards and encapsulates the entire embryonic tissue.
Cavities appear and the yolk sac is pinched.
Endoderm folds in to form the foregut, midgut, and hindgut.
Eventually, forms and you can begin to see the beginning of a human body.
What generally happens in the 4th week of pregnancy?
- Neural tube ends close
- Development of forebrain, limb buds, internal ears, eye lens, pharyngeal region.
- Organ sysem development, especially cardiovascular (blood pumping)
What occurs in the 5-6 weeks of pregnancy?
- Rapid development of the brain and facial features.
- Head growth much greater than trunk growth,
What occurs during the 7-8 weeks of pregnancy?
- Limb development (fingers, and toes)
- Ossification of limbs
- GIT formation (not fully)
What in general occurs in the fetal period?
- Continued development of tissues and organs
- Growth, changes in body proportions
- Accumulation of body fat
What is the approximate body fat % at week 29 and week 38?
week 29 - 3.5%
week 38 - 16%
The most significant increase of iron content in the fetus occurs at what point in pregnancy?
between 30-40 weeks
104 - 278
The most significant increase in protein composition of a fetus occurs in what point during pregnancy?
20-40 weeks
22- 134 - 446
The most significant increase in fat composition of a fetus occurs in what point during pregnancy?
20 - 40 weeks
26- 66 - 525
At what point during pregnancy during pregnancy is the quality of nutrition the most important?
Fertilization - 8th week bc of tissue differentiation and development
When is the first connection between the lacunae and maternal uterine capillaries?
about day 9
What helps to transfer nutrients to the fetus until circulation is established?
Uterine secretions, trophoblasts and the yolk sac
What is the fetal part of the placenta?
Chorionic villus (stem and branch villi))
What is the maternal part of the placenta?
decidua (endometrium functional layer)
What part of the placental development increases the surface area for exchange of nutrients between mother and baby?
Branching villi
What part of the umbilical cord carry nutrients to the fetus and what carries it from the fetus?
To fetus - umbilical veins
From fetus - umbilical arteries
What are the 3 functions of the placenta?
- Endocrine secretion of the hCG, estrogen, progesterone, placental lactogen (aka. human chorionic somatotropin)
- Metabolism
- Transfer of nutrients/other substances
What hormone is released from trophoblasts and used in pregnancy tests to determine pregnancy?
hCG - human chorionic gonadatropin
At what point to progesterone, estradiol, and human placental lactogen peak in pregnancy?
At what point does human chorionic gonadatropin peak during pregnancy?
about 40 weeks
about 10 weeks
What nutrients can the placenta metabolize for the fetus in early pregnancy?
Glycogen, cholesterol, and fatty acids
What nutrients and toxins can a mother transfer to a fetus through the placenta (X14)?
- Oxygen
- Water
- Electrolytes
- CHO (glucose)
- Amino acids
- Lipids (ffa)
- Vitamins
- Minerals
- Some hormones (ie. thyroxine)
- Antibodies
- Drugs
- Ketones
- Carbon monoxide
- Viruses
What are the 4 mechanisms for placental transfer of nutrients?
Simple diffusion, facilitated diffusion, active transport, pinocytosis
What nutrients travel through the placenta by simple diffusion (X7)?
Water, fatty acids, ketones, vit.E, sodium, chloride, gases
What nutrients travel through the placenta by facilitated diffusion (X4)?
Glucose, iron, vit.A, and vit. D
What nutrients travel through the placenta through active transport (X4)?
amino acids, water soluble vitamins, minerals
What nutrients travel through the placenta through pinocytosis (X2)?
Immunoglobins, albumin
How is the transfer of glucose to from the mother to the fetus controlled?
Transfer occurs by facilitated diffusion.The placenta uses about 30-40% of the glucose taken from the maternal circulation so the control of glucose occurs by the placental metabolism and by the fetal glucose concentration.
How is the transfer of lipids from the mother to the fetus controlled?
Transferred by simple diffusion and by facilitated diffusion.
Omega-6 and omega-3 are transferred throughout pregnancy. Lipids for fetal adipose tissue is transferred in late gestation due to an increase in the gradient = utilization.
How is the transfer of amino acids from the mother to the fetus controlled?
The amino acids are sourced from the maternal free amino acids (synthesis of amino acids in the placenta).
Transferred by active transport.
As the placenta grows, there is an increase in the surface area for transfer - meaning there is more placental blood flow, placental permeability, and concentration of carrier proteins.
