Fetal Nourishment and Development Flashcards
What are the major developmental periods?
- fertilization - day 1
- embryonic period - week 1 to 8
- fetal period - week 9-38
What are the critican periods of fetal development?
- hyperplasia
- hyperplasia and hypertrophy
- hypertrophy
Where does fertilization occur?
fallopian tubes
Process of fertilization
Sperm encounters the egg in the fallopian tube where the acrosome at the head contains enzymes allowing it to capacite the outer wall of the oocyte, break down the zona pellucida and sperm enters the cytoplasm of the oocyte leaving behind its plasma membrane.
What is the first division with fertilization?
first mitotic division occurs and the oocyte is now called a zygote containing half chromosomes from each parent
What are the stages of week 1?
Both occur within the fallopian tube
* stage 1: fertilization → zygote
* stage 2: zygote division
* stage 3: early blastocyst → late blastocyst
* stage 4: implantation begins
What provides nutrition during zygote division?
Zona pellucida stays intact, providing nutrition and protective glycoproteins as the cell divides
What is the blastocyst structure?
- blastocystic cavity
- embryoblast (inner cell mass)
- trophoblasts (outer layer)
What happens with the blastocyst?
The morula becomes blastocyst which enters the uterus and the zona pellucida degenerates since major nutrients will start coming from the thick endometrium layer with implantation
What provides nutrients in week 1?
Uterine secretions (mostly glycogen), trophoblasts and yolk sac helps transfer nutrients to fetus until circulation established
What is the major development of embryonic development week 2?
Implantation where blastocyst wil completely imbed in endometrium and inner cell mass forms the embryonic disc to establish nutrient circulation.
* Early week 2
* Later week 2
What occurs in early week 2?
syncytio-trophoblasts (outer layer of blastocyst) invades the endometrium via proteolytic enzymes
What occurs in later week 2?
Inner cell mass becomes a flattened disc of 2 layers and amniotic cavity develops
* epiblast layer is adjacent to amniotic cavity giving rise to ectoderm and mesoderm
* hypoblast layer is adjacent to blastocyst cavity and will. give rise to endoderm
What occurs with localized thickening of the hypoblast?
develop into the cranial region
How is nutrient circulation established in week 2?
development of lacunae in the trophoblasts form into lacunar networks
* fill with maternal blood from uterine capillaries so that absorption of nutrients, oxygen can go to embryonic disc
What are the main processes for embryonic development in week 3
- gastrulation
- neurulation
- cardiovascular system begins
What happens in early week 3?
gastrulation which is the formation of the 3 germ layers:
* embryonic ectoderm (outer)
* intra-embryonic mesoderm (middle)
* embryonic endoderm (inner)
What do the three layers lead to?
complex series of folding results in the human body
What does embryonic ectoderm lead to?
- epidermis, hair, nails, teeth enamel, retinal
- CNS, PNS
What does the embryonic endoderm lead to?
- epithelium lining of respiration and GI including glands
- epithelium of liver, pancreas, bladder
What does the embryonic mesoderm lead to?
- muscle, connective tissue, skeleton
- cardiovascular system including vessels, blood cells, bone marrow
- reproductive and exretatory systems
What happens later week 3?
- neurulation
- beginning of cardiovascular system
- development of body cavities
- placenta
What is neurulation?
folding of the neural tube which is early development of the nervous system from the ectoderm
What nutrient is important for neurulation?
Folate
How does cardiovascualr system begin?
- development of paired somites from mesoderm which develops into skeleton and musculature
- development of blood vessels and cells from mesoderm
- linkage of vessel and ‘heart tubes’ to allow circulation of blood
How are body cavities formed?
Development of coelom which are spaces within mesoderm which become the body cavities
* lungs, heart and GI tract
Placenta development in week 3
completion of chorionic villi and connecting stalk
Major processes of weeks 4-8 of embryonic development
beginning of all major internal and external structures
* most important events are folding in longitudinal and transverse direction which is controlled by precise, sequential gene regulation
Week 4 developments
- neural tube ends close (head and tail)
- development of forebrain, limb buds, internal ears, eye lens, pharyngeal region
- organ system development, especially cardiovascular (heart now pumps blood)
Week 5-6 developments
- rapid development of brain and facial features
- head growth much greater than trunk growth
DHA important here
Week 7-8 developments
- limb development including fingers and toes
- ossification of limbs
- GI tract formation
average length and weight of embryo at end of week 8
- length: 29 mm
- weight: 5-8g
What happens in the fetal period?
Exponential growth in weight, linea growth in length
* continued development of tissues and organs
* growth, changes in body proportions
* Accumulation of body fat
When does most accumulation of body fat occur?
week 29 (3.5%) → week 38 (16%)
Estimated changes in body composition of the fetus by time in pregnancy
most notable:
* protein 30 - 40 weeks
* fat 30 - 40 weeks
* iron 30-40 weeks
what is the nutritional significant of embryonic development?
nutrition quality
* tissue differentiation and development
fertilization to 8th week
What is the nutritional significance of fetal development?
nutrition quantity and quality
* growth, further differentiation and development
9th week to birth
What is the new embryo nourishment on day 9?
First connection between lacunae and maternal uterine capillaries
Major parts of the placenta
- Fetal part – chorionic villus (stem and branch villi)
- Maternal part – decidua (endometrium functional layer)
Development of placenta
third week: trophoblast begins to branch, fetal blood vessels develop, surface area increases with branching for more exchange of nutrients
* blood does not mix
What are the 3 functions of the placenta?
- endocrine (hormone) secretion
- metabolism
- transfer of nutrients/other substances
What are the major endocrine hormone secretions of the placenta?
- human chorionic gonadotropin (hCG)
- estrogen
- progestrone
- placental lactogen (also called human chorionic somatotropin)
What is hCG used for?
To detect pregnancy
What is synthesized for placenta early on?
- glycogen
- cholesterol
- fatty acids
What is transferred between the maternal → fetus via the plancenta?
- oxygen
- water and electrolytes
- CHO (glucose)
- amino acids
- lipids (FFA)
- vitamins
- minerals
- some hormones and antibodies
- drugs, ketones, carbon monoxide, viruses
What are the 4 mechanisms of placental transfer?
- simple diffusion
- facilitated diffusion
- active transport
- pinocytosis (endocytosis)
what is transferred via simple diffusion?
- water
- fatty acids
- ketones
- vit E
- sodium
- chloride
- gases
What is transferred via facilitated diffusion?
- glucose
- iron
- vit A
- vit D
What is transferred via active transport?
- AAs
- water soluble vitamins
- minerals
What is transported via pinocytosis?
larger proteins
* immunoglobulins
* albumin
* anti-bodies
placental transfer of glucose
- source: maternal plasma glucose
- transfer: facilitated diffusion
- control: placental metabolism, fetal glucose concentration
How much glucose does placenta take from maternal circulation?
30-40%
placental transfer of lipids
- Source: maternal plasma lipid (FFA & TG)
- Transfer: simple diffusion, facilitated diffusion
- Control: n-6 and n-3 fatty acids transferred throughout pregnancy, lipids for fetal adipose tissue transferred late in gestation (due to increased fetal utilization, larger gradient)
Placental transfer of AAs?
- Source: maternal free amino acids; metabolism and synthesis of amino acids in placenta
- transfer: active transport
- control: ncreases in placental surface area, placental blood flow, placental permeability, concentration of carrier proteins
