Placentation Flashcards
functions of placenta
- source of protein and steroid hormones
- metabolism, exchange of gas and waste productsion between mom and fetus
- selective barrier determines the nature of communication
- participates in the control of fetal growth, development, and parturition
nondeciduate/indeciduate/apposed placenta
- trophoblasts don’t significantly invade or destroy the endometrium
- virtually no loss of maternal tissue at parturition
- most domestic animals
deciduate or conjoined placenta
- trophoblasts invade and destroy superficial endometrium which responds by forming large, polygonal cells called decidual cells
- loss of maternal tissue and hemorrhage at parturition
choriovitelline placenta
- yolk sac wall (endoderm) fuses with chorion (trophophectoderm and mesoderm)
- little importance in domestic animals
Allantochorionic or Chorioallantoic placenta
- definitive form of placentation in higher mammals
- embryonic componet formed by fusion of the allantois and chorion
- extensive area of contact between embryonic placental component and endometrium - increased surface area achieved through folding of chorioallantois and the endometrial surface, formation of chorionic villi, and chorionic labyrinths
chorionic villi
- functional unit of the fetal placenta
- small, finger-like projections on the surface of the chorion
- increase surface area for attachment and exchange
- interdigitate with the vascular folding of the endometrial surface in farm animals
- penetrate directly into the endometrium in humans
cotyledon
placental unit, consisting of blood vessels and connective tissue, in cow
Carnucles
small, non-glandular areas in cow
placentome
- point where the fetal cotyledon and maternal carnucle meet in cotyledon placentas (ruminants)
- formed by fusion of fetal cotyledon
- increases in diameter during gestation
glycogen plaques
- on the surface of the chorion and amnion (in cows) aka verrucae
- squamous cell proliferations
diffuse placenta of mare characterized by
microcotyledons
microcotyledons
- discrete regions at the fetal/maternal interface
= inverted dome-like structures composed of chorionic cilli and their corresponding crypts
Endometrial Cups (Mare)
- develop between days 35-60 of pregnancy
- phagocyze and digest epithelial cells of the uterus
- produce eCG
eCG from endometrial cups
stimulates CL which secretes progesterone to break down the epithelial cells of the endometrium
Formation of Chorioallantoic Pouches
after the endometrial cups are detached, they either lay freely or become enclosed in a fold of allantochorionic tissue
Chorioallantoic Pouches are
invaginations into the allantois arranged in a circle around the umbilical cord
Hippomanes (in Mares)
- aka allantoic calculi
- float freely in the allantoic cavity
- unknown signifigance
Cervical Star (in Mares)
- outer chorionic surface of cervix is covered in microtyledon
- radiating bands where villi are not formed correspond to creases and visually look like a star, thus named “cervical star”
zonary placenta
- Bitch
- chorionic villi confined to girdle-like structure around the middle of the chorionic sac
- 3 zones: transfer zone, pigmented zone/paraplacenta, avascular allantochorion
Uteroverdin
refers to green pigment of dogs placenta
transfer zone
- on zonary placenta (bitch)
- region of nutrient exchange around chorion in the middle of conceptus
paraplacenta
- on zonary ploacenta (bitch)
- local region of maternal hemorrhage and necrosis
- may be important for iron transport
Avascular Allantochorion
- on zonary placenta (bitch)
- may be involved in the absoprtion of materials from the uterine lumen
discoid placenta of human
- characterized by disctinct disc containing chorionic villi that interface with the endometrium and provide region for gas, nutrient, and metabolic waste exchange
- chorionic tissue forms fetal-maternal interface
- pools of blood where metabolic exchange occurs
classifications of placenta based on morphology and areas of chorionic-villous attachment
- cotyledonary (ruminants)
- diffuse (mare, pig)
- zonary (dog, cat)
- discoid (primates, rodents)
folded placenta
- (plicae) macroscopic undulations in fetal tissues
- microscopic ridges (rugae in pigs, lamellae in carnivores) interlock with corresponding infolding (fossae) in endometrium
villous placenta
branched chorionic villous protusions interdigitate with corresponding maternal crypts (horse, ruminant, human)
maternal/fetal interface of sow
- folded type
- allantochorion develops intricate corrugations which interlock with folds and crevices of the endometrium to form the placenta
End Result= chorion is folded and lined with tall columnar epithelum, which projects into the areolar cavity and absorbs uterine secretions (+ iron transport)
maternal/fetal interface of bitch
- folded
- Placental Labyrinth (connective tissue and blood vessels)
- Junctional Zone (villious tips, maternal vessels, uterine secretions, cell debris)
- Glandular/Spongy Zone: hypertrophied uterine glands
maternal/fetal interface of cow and ewe/ bovine and ovine
- villous processes develop on the chorioallantoic membrane opposite to the caruncles
- as gestation proceeds primary villi form secondary and tertiary villi which fit into corresponding crypts in the caruncles
bovine carnucles are
convex, villi protrude toward the uterine lumen
ewe/ovine caruncles are
concave with broad attachments, chorionic tissue pushes inward to create space betwen the chorion and maternal caruncle
maternal/fetal interface in humans
- villious type
- consits of extraembryonic membranes, decidua, and placenta
maternal/fetal interphase of human after implantation occurs
- endometrium transforms into the decidua
- consists of 3 different regions: decidua basalis, capsularis, parietalis
- chorionic villi develop mostly in the decidua basalis (becomes major portion of the placenta)
Tissue layers at maternal/fetal interface
1) endometrial capillaries
2) endometrial interstitium
3) endometrial epithelium
4) chorionic epithelium
5) chorionic interstitium
6) chorionic capillaries
Types of placenta based upon the fetal/maternal interhemal barrier
- epitheliochorial
- syndesmorchorial
- endotheliochorial
- hemochorial
Epitheliochorial Placenta
- least intimate
- all 6 layers present
- both the endometrial epithelium and the epithelium of the chorionic villi are intact
- in mare and sow
Syndesmochorial Placenta
- endometrial epithelium erodes and then regrows
- causes matneral capillaries to be briefly exposed to the chorionic epithelium
- chorionic epithelium composed of two cells: mononuclear columnar cells, binucleate giant cells
binucleate giant cells
- migrate from the chorion to the endometrial epithelium in ruminants
- secrete estradiol, progesterone, placental lactogen and pregnancy specific protein-B
Endotheliochorial Placenta
- compete erosion of endometrial epithelium and underlying interstitium
- matneral capillaries directly exposed to epithelial cells of chorion
- chorionic epithelium packs around vessels on maternal side
Hemochorial Placenta
- highly intimate
- chorionic epithelium in direct apposition to maternal pools of blood
- nutrients and gases are exchanged directly from maternal blood and must move through only three tissue layers
the placenta regulates the exhcange between fetus and dam via
- simple diffusion (gases, water)
- gacilitated diffusion (glucose, amino acids)
- active transport (ions)
function of eCG
- stimulates primary CL to produce progesterone
- stimulates additional ovulations
- produces accessory CL
- promotes luteinization of antral follicles that don’t ovulate
- FSH-like actions when administered in species (other than mares) used to induce superovulation
Luteal-Placental Shift in Mares
1) Primary CL (from ovulation till day 40 of pregnancy)
2) Accessory CL
3) Placenta and CL (day 60-160)
4) Placenta (over 160 days)
5) Fetal Adrenal (last month)
