Transcript Placentation - Delta State University

Placentation
Embryonic development
• Pre-implantation
– Free-floating
• Endogenous reserves
• Nutrients from surrounding environment
– Histotropic
• Implantation and placentation
– Formation of intimate but temporary
relationship with uterus
• Provision of nutrients
• Protection
• Placenta
– Transient organ
• Metabolic interchange between maternal and fetal
systems
• Endocrine organ
– Production of steroids
– Production of protein hormones
– Composition
• Chorion (fetal compartment)
• Modified uterine endometrium (maternal
compartment)
• Contact between chorion and
endometrium
– Site of metabolic exchange
– Hormone production
Embryonic cellular differentiation
• Blastcyst
– Blastcoel
• Fluid-filled cavity
– Inner cell mass
• Develops into fetus and part of placenta
• Three distinct cell
– Ectoderm
– Mesoderm
– Endoderm
• Three embryonic cell layers
– Ectoderm
• Skin and hair
• Nerve tissue
• Part of chorion
– Mesoderm
• Muscles, bones, and organs
• Part of chorion and allantois
– Endoderm
• Inner lining of the GI tract
• Part of allantois and amnion
Origin of placenta
• Conceptus
– Embryo
– Extraembryonic menbrane
• Extraembryonic membranes
– Originate from trophoblasts
– 3 compartments
• Amnion (endoderm and ectoderm)
• Chorion (ectoderm and endoderm)
• Allantois (endoderm and mesoderm)
Composition of placenta
• Fetal component
– Chorionic villus
• Functional unit
• Small, finger-like projections on the surface of
chorion
• Used for classification of placenta
– Distribution
Chorionic villi distribution
• Diffuse
– Villi distributed over
the entire surface of
the chorion
• Pigs
– Horse placenta
• Specialized villi called
microcotyledons
(microzones)
• Formation of
endometrial cups (eCG
secretion)
• Cotyledonary
placenta
– Large discrete buttonlike structures
• Cotyledons
• Abundant blood supply
– Formation of
placentome
• Cotyledons (fetal)
• Caruncles (maternal)
• Zonary placenta
(dogs and cats)
– Broad zone of villi
• Exchange
– Pigmented zone
• Either end of the central
region of the zone
(blood clots)
– Transparent zone
• Distal ends
• Discord
– Humans and primates
– One or two distinctive
disks on the one end
of the placenta
Classification of placenta based on
microscopic appearance
• Number of placental layers separating the
fetal blood from maternal circulation
– Degree of intimacy
– Prefix=maternal endometerium
– Suffix=fetal membrane
– Ranges anywhere from one to seven layers
• Epitheliochorial placenta
– Least amount of contact
• Surface to surface contact
• No invasion of the uterine endometrium by chorion
• Pigs and horses
• Epitheliochorial placenta
– Some intimate between trophoblasts and endometrium
• Ruminants
– Syndesmochorial placenta
• Formation of binucleated giant cells
– Fusion of trophoblasts
– Invasion and fusion with endometrium (trinucleated cells)
• Endotheliochorial
placenta
– Complete erosion of
endometrial epithelium
and underlying
interstitium
– Exposure of maternal
capillaries to the
chorion
• Embryos separated
from actual maternal
circulation
• Hemochorial placenta
– Primates
• Actual contract between chorionic villi and maternal circulation
– Fetal circulation separated from maternal circulation by three tissue
layers
• Direct exchange of materials from maternal circulation
• Hemoendotherial placenta
– Most intimate contact
• Fetal circulation bathed in maternal blood
Exchange of materials
• Three methods
– Diffusion
• Small molecules
• Gases
– Facilitated diffusion
• Glucose
• Amino acids
– Active transport
• Ions (Na, K, Ca)
• Acts as a barrier
– Maternal proteins
• Hormones
• Exception
– Antibodies/immunoglobulins in hemochorial and
hemoendotherial placenta
– Lipids and fat-soluble vitamins
– Cannot prevent entrance of toxic materials and
infectious materials
• Alcohol, opium, and other drugs
– Birth defects (teratogenic agents)
• Virus and bacteria
Placental lactogen
• Some species
– Type of placentation
• Ruminants
• Humans
• Rodents
• Produced by fused
cells
– Syncytiotropoblast
– Binucleated/trinucleate
d cells
• Proteins related to
pituitary GH and
prolactin
– Close to GH in
humans
– Close to prolactin in
rodents
– 50-50 in cows
• Function
– Regulation of metabolism
• GH-like activity
– Much weaker than pituitary GH
– Development of mammary gland
• Prolactin-like activity
– Maintenance of CL function
• Rodents during early stage of pregnancy
• No known receptor(s) for placental
lactogen
– Interacts with GH receptor
– Interacts with prolactin receptor
• Pattern of secretion
– Different between
cattle and sheep
• Degree of fusion
between tropoblasts
and endometrium
• GH-Variant
– Human only
– Acts like GH
• Tissue growth
• Nutrient metabolism
– Affects function of insulin
• Pregnancy-induced diabetes
Placental steroidogenesis
• Cholesterol
– Lipoproteins from circulation
• No De Novo synthesis
• Progesterone
– Replace CL in some species
• Maintenance of pregnancy
• Precursor for fetal adrenal steroids
• Estrogens
– Limited production
• Limited 17a-hydroxylase activity
– Abundant in fetal adrenal gland
– Androgens from fetal adrenal gland
• Converted to estrogens in the placenta
– Production of estriol rather than estradiol
– Secretion of estrone
• Majority of placental estrogen in some species