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MCB 135E Discussion
September 26, 2005
Mid-Term I Review
Monday
October 3rd
5-7 pm in 105 Northgate
Topic List
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Early Embryonic Stages
Placenta
Fetal Circulation
Nervous System Development
Terminology
• Germ Layer Theory
– Embryo’s Method of sorting out its parts
• Ectoderm – Outer covering of embryo
• Entoderm (Endoderm) – Lies under the ectoderm and forms
lining of the primitive gut cavity
• Mesoderm – Develops between ectoderm and entoderm
• Gastrulation – The process by which germ layers come
to occupy their characteristic positions
• Embryonic Stages – Phases of gastrulation; stages of
organ and tissue differentiation
Embryonic Stages
• Early Gastrulation
– Occurs at implantation when cells on ICM
arrange into the entoderm
– Remaining cells that are neither trophoblast or
entoderm become a plate containing the
progenitors of future ectodermal and
mesodermal cells
– Referred to as 2-layered embryo and
characterized by embryonic disc
Embryonic Stages
• Late Gastrulation (second phase)
– Segregation of mesoderm and notochord occurs
• Notochord will for primitive vertebral column
– Starts by end of second week and finishes by end of
third week
– 2-layered embryo becomes 3-layered embryo
– Primitive streak appears upon upper surface of
embryonic disc over which mesoderm spreads
– At conclusion of this process, upper layer of embryonic
disc becomes ectoderm
Germ Layers and Their Systems
• Ectoderm
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Epidermis and lining cells of glands
Appendages of skin
Nervous system
Posterior Pituitary
Chromafin organs - adrenal medulla
Anterior Pituitary
Some Epithelium
• Entoderm
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Epithelial lining of alimentary canal
Lining cells of glands that open to alimentary canal
Epithelium of most of the urinary bladder and urethra
Epithelium of prostate
• Mesoderm
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Remaining organs and tissues not made by Ectoderm or Entoderm
Connective tissue
Teeth
Musculature
Blood
Adrenal Cortex
Terminology
• Placenta
– Maternal-Fetal Membrane
• Villus
– small vascular process or protrusion
• Sinus
– recess, cavity or hollow space
• Cotyledon
– any one of the subdivisions of the uterine surface of a
discoidal placenta
Placenta Functions
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Gas Exchange
Nutrient Delivery
Antibody Delivery
Removal of Waste
Secretion of hormones
Placental Membranes
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Fetal
1. Yolk Sac
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Center of blood formation in early embryonal life
Facilitates transfer of nutrients from developing trophoblast
to embryo
2. Allantois
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Blood vessels develop around allantoic tube
Tube eventually fuses with chorion
By 6th week – 1 umbilical vein and 2 umbilical arteries
3. Amnion
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Membranous sac that surrounds embryo
Fluid fills amnion that has protective role throughout
pregnancy
Placental Membranes
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Maternal
1. Deciduas
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Highly modified uterine endometrium
2. Basalis
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Portion between ovum and uterine wall
3. Capsularis
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Region of decidua where ovum is embedded
4. Parietalis
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Lines remainder of uterus
Hormones of Pregnancy
• Endocrine Overview
• Hormones and their functions
• Hormone Synthesis
Functions
• Deliver Oxygen-rich blood and nutrients
from placenta to fetus
• Remove Carbon dioxide and metabolic
waste from fetus
• Umbilical Vein – PlacentaFetus
• Umbilical Arteries – Fetus  Placenta
Challenges and Adaptations
• Challenge
– Oxygen and Nutrients are less in umbilical vein
than in adult arteries
• Adaptations
– Establish priorities
– Establish specific structures to supply priorities
– Embryonal Hemoglobin
Specific Structures
1. Ductus Venosus
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Shunts Umbilical Vein to Inferior Vena Cava
2. Foramen Ovale
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Shunts between atria
Establishes high pressure in right side instead
of left
3. Ductus Arteriosus
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Shunts pulmonary artery to aorta
Nervous System
• Major Functions
– Communication with external/internal environment
– Regulation of…
• Major Components
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Neurons
Neuroglia
Mylenated nerve fibers
Microglia
Ground Substance
Blood Vessels and CSF
Neurulation
• N.S. – Arises from ectoderm on dorsal portion of
embryo
• 3-4 Weeks – Cells proliferate along middle plate
• 5-6 Weeks – Plate folds to form neural groove
• 6-7 Weeks – Groove closes into neural tube
– Brain develops from anterior portion
– Spinal cord develops from the posterior portion
Neural Epithelium
• Neuroblast
– Neuron
• Spongioblast
– Migratory Spongioblast
• Oligodendria
• Astrocytes
– Astrocytes
– Ependyma
Energy Sources
• Carbohydrates
– Primarily maternal
glucose
– Stored as glycogen
• Under influence of
glucocorticoids
• In fetus
– Insulin levels high
– Insulin sensitivity high
– Hypoglycemic
• Anaerobic Glycolysis
– Glyceraldehyde-PDehydrogenase
• Glycolitic enzyme
• High in postnatal brain
• During same period
the oxidative enzyme
– Succinic Dehydrogenase
– Much lower
Thyroid Hormone
• Functions
– Promotion of body growth
– Development of CNS through:
• Promotion of neorogenesis
• Promotion of myelination
• Promotion of brain metabolism
– Stimulates oxygen consumption in all cells
• Abnormalities
– Hypothyroidism
• Cretinism
• Short stature, low metabolic rate, skin changes
• Treatable if given Thyroxine at an early age
Thyroid Hormones
Functional Development
• Neuronal Connections
• Differential Development of N.S.
– Neurotransmitter activity in different brain regions
• Perinatal Behavior
– Reflexes
• Respiratory (17-24 weeks)
• Gastrointestinal (24th week)
• Startle (Presence of excessive activity after birth is an indicator
of delayed development of certain brain centers)
• Suckling - Postnatal
• Education
– Better educated appear to live longer with less disability
– Several pieces of evidence discussed for this in class