Embryo Histology

91. Resting mammary gland (HE) 92. Lactating mammary gland (HE) 93. Umbilical cord (HE) 94. Placenta (HE) 95. Chicken embryo (HE)

The mammary gland consists of 15 to 20 lobes,each of which is an individual conpound alveolar gland with its own lactiferous duct opening onto the surface of the nipple. The interlobar stroma is dense connective tissue and varying amount of fat.Within each lobe, similar interlobular connective tissue bands courses between lobules.

Dense interlobular connective tissue

lobule

Adipose tissue

In an inactive gland, connective tissue is aboundant and and glandular elements are minimal.

Interlobular connective tissue

lobule

Glandular tubules

Intralobular connective tissue

A lobule contains groups of small tubules lined with cuboidal or low columnar epithelium.These look like ducts and usually remain in this state as long as the gland is inactive.The tubules are embedded in loose cellular connective tissue, the intralobular connective tissue. Surrounding this is the dense interlobular connective tissue and fat.

lobules

Interlobular connective tissue

The mammary gland is fully developed in lactation. The lobules are filled with alveoli.Their lumens contain milk secretion. The amounts of the connective tissue stroma and adipose tissue, relative to the parenchyma decrease considerably.

Interlobular connective tissue

Lipid droplets

Milk secretion

Milk is produced by the epithelial cells of the alveoli and accumulates in their lumens and inside the lactiferous ducts.The secretory cells become low cuboidal and their cytoplasm contains spherical lipid droplets of various sizes.

One of the umbilical arteries

Wharton s jelly

Amniotic epithelium

The umbilical cord connects the embryo/fetus to the placenta.It is covered by simple cuboidal epithelium of the amnion.It contains the umbilical vessels:2 umbilical arteries and 1 umbilical vein.These vessels are embedded in Wharton s jelly (mucous tissue).

cells

The cells of the Wharton s jelly stain slightly basophilic.They have processes connecting with each other. The aboundant jellylike ground substance is rich in hyaluronic acid. The Wharton s jelly contains only a few fibers.

Base of villous stemm

Chorionic plate

Epithelium of the amnion

Chorionic villi

It consists of a fetal part formed by the chorion, and a maternal part, formed by the decidua basalis. Fetal portion (chorion): It consists of the chorionic plate and the chorionic villi arising from it.The chorionic villi may be either free or anchored to the decidua basalis.The surfaces of the villi are bathed with maternal blood (intervillous sace) from the lacunae of the basal decidua.

Chorionic villi

Decidua basalis

Intervillous space with maternal blood

The maternal portion comprises the basal plate or decidua basalis and its septal projections (placental septa) that form incomplete separations between individual cotyledons.

Intervillous space

Chorionic villi

Trophoblast of the chorion Chorionic plate

Chorionic villi

Intervillous space containing maternal blood

Branches of umbilical vessels with fetal blood

Intervillous space Fetal blood Extraembryonic connective tissue (mesenchyme) cytotrophoblast

Placental barrier

Syncytial trophoblasts

Neural tube Intermediate mesoderm /

somite

nephrogonotom

Intraembryonic coelom

notochord

ectoderm

Somatic mesoderm

endoderm Splanchnic mesoderm