Anatomy of the Placenta

The Placenta

• Also known as the basal plate, attached next to the uterine wall, dark/dull red in color
• Mapped out into slightly elevated regions of about 18-20 lobes or cotyledon
• Cotyledons are separated by sulci/furrows and are made up of lobules with each containing a single villus with its branches
• Surface may be rough due to deposits of lime salt or calcium, especially at term

The Fetal Surface

• Also known as chorionic plate, faces the fetus in utero, bluish-gray in color
• Covered by the amnion, making it appear smooth and shiny
• Umbilical cord is usually inserted in the center with branches of umbilical vein and arteries radiating through it

The Membranes

• Two membranes: the amnion and the chorion
• Amnion: develops from the inner cell mass, tough, smooth, transparent, and shiny membrane
• Amnion covers the fetal surface of the placenta, continuous with the covering of the umbilical cord, and forms the amniotic sac containing amniotic fluids
• Chorion: develops from the trophoblast, rough, thick, fibrous, opaque, and friable
• Chorion is loosely attached to the uterine wall and continues with the edge of the placenta, aiding the uterus in initiating labor by reducing progesterone levels and increasing production of prostaglandins and oxytocin

Functions of the Placenta

Respiration

• Two umbilical arteries carry deoxygenated blood from the fetus to the placenta to be oxygenated by diffusion
• Oxygenated blood is carried by the umbilical vein to the fetus

Nutrition

• Amino acids, glucose, minerals (calcium, phosphorus, iron), vitamins, blood, and nerve cells cross the placenta to the fetus
• Nutrient transport is achieved through diffusion, osmosis, active transport, and endocytosis

Excretion

• Carbon dioxide, urea, uric acid, and bilirubin are eliminated from the fetus to maternal circulation

Storage

• The placenta metabolizes glucose, stores it in the form of glycogen for the fetus, and reconverts it to glucose and glycogen as needed

Endocrine

• Several hormones are produced by the placenta to aid in the advancement of pregnancy and the growth of the fetus
• Hormones produced by the placenta include hCG, hPL, progesterone, estrogen, and relaxin

The Umbilical Cord (Funis)

• Extends from the fetal umbilicus to the fetal surface of the placenta
• Length: about 50cm, considered short when it measures less than 40cm, diameter: about 1-2cm
• Contains one vein and two arteries surrounded and protected by jelly-like substance called Wharton's jelly
• Covered by the amnion, which is continuous with that of the covering of the placenta

Abnormalities of the Umbilical Cord (Funis)

• True Knot of the Cord: associated with long cord and increased amniotic fluid, may compromise circulation
• Velamentous Insertion of the Cord: abnormal insertion of the cord into the placenta

Abnormalities of the Placenta

Anatomical Abnormalities

• Placenta Succenturiate: a small extra lobe of placenta situated in the membranes and blood vessels connecting it to the main placenta
• Placenta Circumvallate: an opaque ring seen on the fetal surface, formed by a double layer of chorion and amnion that has undergone infraction
• Placenta Bipartita: the placenta is partly or wholly divided into two lobes, but there is only one cord
• Placenta Fenestrata: a hole in the placenta

Pathological Abnormalities

• Placenta Infarcts: suggest poor perfusion of the fetoplacental unit, where some areas in the placenta, such as the chorionic villi, die
• Placenta Accreta: the placenta adheres firmly to the uterine wall, failing to separate at the end of labor, and may require hysterectomy
• Hydatidiform Mole: a cystic degeneration of the chorionic villi, usually resulting in the fetus failing to develop
• Oedema of the Placenta: a large, pale, water-logged placenta associated with haemolytic disease of the newborn
• Calcareous Degeneration: deposit of calcium or lime salt in the placenta, believed to be associated with aging of the placenta