The primary gut that forms during gastrulation in a developing embryo is known as the archenteron, the gastrocoel or the primitive digestive tube. It develops into the endoderm and mesoderm of an animal.

Formation in sea urchins

primary mesenchyme Mesenchymal stem cells (MSCs) also known as mesenchymal stromal cells or medicinal signaling cells are multipotent stromal cells that can differentiate into a variety of cell types, including osteoblasts (bone cells), chondrocytes (cartilage cel ...

cells detach from the

vegetal pole In developmental biology, an embryo is divided into two hemispheres: the animal pole and the vegetal pole within a blastula. The animal pole consists of small cells that divide rapidly, in contrast with the vegetal pole below it. In some cases, the ...

in the gastrula and enter the fluid filled cavity in the center (the

blastocoel The blastocoel (), also spelled blastocoele and blastocele, and also called cleavage cavity, or segmentation cavity is a fluid-filled or yolk-filled cavity that forms in the blastula during very early embryonic development. At this stage in mammal ...

), the remaining cells at the vegetal pole flatten to form a vegetal plate. This buckles inwards towards the blastocoel in a process called

invagination Invagination is the process of a surface folding in on itself to form a cavity, pouch or tube. In developmental biology, invagination is a mechanism that takes place during gastrulation. This mechanism or cell movement happens mostly in the vegeta ...

. The cells continue to be rearranged until the shallow dip formed by invagination transforms into a deeper, narrower pouch formed by the

gastrula Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst is reorganized into a multilayered structure known as the gastrula. ...

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

. This narrowing and lengthening of the archenteron is driven by

convergent extension Convergent extension (CE), sometimes called convergence and extension (C&E), is the process by which the tissue of an embryo is restructured to converge (narrow) along one axis and extend (elongate) along a perpendicular axis by cellular movement. ...

. The open end of the archenteron is called the blastopore. Protovsdeuterostomes

The

filopodia Filopodia (singular filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lame ...

—thin fibers formed by the mesenchyme cells, found in late gastrulation, contract to drag the tip of the archenteron across the blastocoel. The endoderm of the archenteron will fuse with the

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...

of the blastocoel wall. At this point gastrulation is complete, and the embryo has a functional digestive tube.

Similar formation process in other animals

The indentation that is actually formed is called the lip of the blastopore or the

dorsal lip The dorsal lip of the blastopore is a structure that forms during early embryonic development and is important for its role in organizing the germ layers. The dorsal lip is formed during early gastrulation as folding of tissue along the involuting ...

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

s and

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

, and the

primitive streak The primitive streak is a structure that forms in the early embryo in amniotes. In amphibians the equivalent structure is the blastopore. During early embryonic development, the embryonic disc becomes oval shaped, and then pear-shaped with the ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s and

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. Each is controlled by the dorsal lip, and

primitive node The primitive node (or primitive knot) is the organizer for gastrulation in most amniote embryos. In birds it is known as Hensen's node, and in amphibians it is known as the Spemann-Mangold organizer. It is induced by the Nieuwkoop center in am ...

(also known as Hensen's node), respectively. During gastrulation, the archenteron develops into the digestive tube, with the blastopore developing into either the mouth (

protostome Protostomia () is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryogenesis, embryonic development. This nature has since been discovered to be extremely variable among Pro ...

) or the anus ( deuterostome).

External links

Diagram
Animal developmental biology {{developmental-biology-stub