Placenta

Placenta

Temporary organ facilitating nutrient exchange

Choriovitelline placenta

Early

Yolk sac

Fetal membrane facilitating early nutrient and gas exchange

Chorion

Outermost fetal membrane forming part of the placenta

Vitelline vessels

Blood vessels in the yolk sac enabling maternal-fetal exchange

Chorioallantoic placenta

Definitive placenta formed by fusion of the chorion and allantois

Allantois

Vascular fetal membrane involved in nutrient and waste exchange

Umbilical vessels

Connect the fetus to the placenta for nutrient and waste transport

Diffuse placenta

Villi evenly distributed across the entire chorion (horses and pigs)

Cotyledonary placenta

Villi grouped into cotyledons interfacing with maternal caruncles (ruminants)

Placentome

Structure formed by fetal cotyledon and maternal caruncle in ruminants

Zonary placenta

Villi arranged in a belt-like band around the chorion (carnivores)

Discoid placenta

Villi concentrated in a disc-like region (primates and rodents)

Epitheliochorial placenta

Six-layer barrier with intact maternal and fetal epithelium (horses

Synepitheliochorial placenta

Five-layer barrier with partial fusion of maternal and fetal epithelium (ruminants)

Endotheliochorial placenta

Four-layer barrier with maternal endothelium in contact with fetal trophoblast (carnivores)

Haemochorial placenta

Three-layer barrier with direct contact between maternal blood and fetal trophoblast (primates)

Microcotyledons

Specialized placental structures in horses for enhanced nutrient exchange

Marginal hematomas

Blood accumulations in carnivores' placenta providing iron to the fetus

Placental angiogenesis

Formation of blood vessels in the placenta for maternal-fetal exchange

Umbilical cord

Structure connecting the fetus to the placenta

Spiral arteries

Maternal vessels remodeled by the trophoblast to increase blood flow

Chorionic villi

Finger-like projections increasing placental surface area

Placental hormones

Include progesterone

Progesterone

Supports uterine quiescence and prevents preterm labor

Estrogen

Promotes uterine growth and vascularization

Relaxin

Softens pelvic ligaments and cervix in preparation for birth

Placental lactogens

Regulate maternal metabolism and promote mammary gland development

Human chorionic gonadotropin (hCG)

Maintains corpus luteum and supports pregnancy in primates

Equine chorionic gonadotropin (eCG)

Stimulates accessory corpora lutea in horses

Fetal waste elimination

Placenta removes fetal metabolic waste like CO2 and urea

Placental immune barrier

Protects fetus from maternal immune attack

Non-classical MHC molecules

Reduce maternal immune response against the fetus

Fas ligand (FasL)

Induces apoptosis in maternal immune cells approaching the placenta

Placental transport

Includes diffusion

Oxygen diffusion

Maternal-fetal oxygen exchange across the placental membrane

Glucose transport

Facilitated diffusion via GLUT1 transporters

Amino acid transport

Active transport for fetal protein synthesis

Calcium and iron transport

Essential for fetal bone mineralization and hematopoiesis

Placental disorders

Include placenta previa

Placental abruption

Premature separation of the placenta from the uterine wall

Placenta previa

Abnormal placental attachment near or over the cervix

Retained fetal membranes

Failure of placental detachment after birth (common in ruminants)

Intrauterine growth restriction (IUGR)

Impaired fetal growth due to placental dysfunction

Ultrasound monitoring

Used to assess placental health and detect abnormalities

Species-specific adaptations

Variations in placental structure and function across species

Horses' placenta

Diffuse with microcotyledons and persistent endometrial cups

Ruminants' placenta

Cotyledonary with specialized placentomes for nutrient exchange

Carnivores' placenta

Zonary with marginal hematomas for iron transfer

Primates' placenta

Discoid

Marsupials' placenta

Choriovitelline

Placental nutrient exchange

Essential for fetal growth and metabolic support

Clinical implications

Placental dysfunction linked to pregnancy loss and fetal abnormalities