Endoderm: parts and development in gestation.

It is one of the most important parts of the human embryo, since it is the origin of the vital organs.

The development and growth of the human body is an extremely complex and fascinating process in which the different structures work with millimetric precision to give birth to the different organs and body systems.

One of these structures is the endodermone of these structures is the endoderm, a layer or stratum of tissue that we will talk about throughout this article. This layer is one of the oldest biological parts at the developmental level and gives rise to important vital organs such as those found in the digestive system.

What is the endoderm?

The endoderm refers to the innermost layer of tissue of the three layers that develop during embryonic growth in animals. of animals. These layers known as germinative layers are the ectoderm, which is the outermost layer, and the mesoderm or middle layer.

However, it is necessary to specify that not all species possess these three germinative layers. Depending on each animal group, embryonic cells may derive in two or three layers, forming diblastic and triblastic beings respectively. Even so, they all possess the endoderm layer, which is found below the rest.

In the case of the endoderm, it appears around the third week of gestation, being considered one of the oldest layers in the process of embryonic differentiation. In addition, it is from this layer of the endoderm that the endoderm is formed, it is from this layer of cells that many vital organs are born for the survival of the adult survival of the adult living being.

From this germinative layer, most of the most important internal organs are formed. Some of them are the alveoli housed in the lungs, the entire digestive tract as well as its secretory glands, the epithelia of some glands such as the thyroid or thymus, and finally some parts of the kidneys, bladder and urethra.

How does it develop?

During early embryonic development, the embryo consists of a single layer of cells. It then folds in on itself in a process called gastrulation, thanks to which the first cell layers are born. The first of these layers to appear is the endoderm.

Around the second week of gestation, a group of migrating cellular organisms slither into the cells of the hypoblast, an inner mass formed by cells of the endoderm.The hypoblast, an inner mass of cuboidal cells, becomes the final endodermal layer.

The next phase in the evolution of the embryo is called organogenesis. This is in charge of producing the corresponding changes in the embryonic layers and giving way to the formation of the appropriate organs and tissues.

As mentioned above, in the case of the endoderm, this will give rise to different organs of the digestive system. will give rise to different organs of the digestive and respiratory system, as well as to the envelope of the embryo.as well as the epithelial envelope of some parts of the organism. However, it is necessary to specify that these organs are not definitive structures but primitive limbs pending full development.

Types of endoderm

Following the differentiation of the embryonic body, the endoderm is divided into two parts that have their own characteristics. These parts are the embryonic endoderm and the extraembryonic endoderm. These two divisions are connected by a wide orifice that, later on, will become the umbilical cord..

1. Embryonic endoderm

The embryonic endoderm is the section of the endodermal layer that will give rise to the internal structures of the embryo, forming the primary gut. In addition, this embryonic layer works together with the mesodermal layer to form the notochord.. When this structure is fully developed, it is primarily responsible for emitting the signals necessary to enable cell migration and differentiation, a process that is extremely important in enabling the formation of organic structures such as the brain.

From this point on, the notochord and the endoderm carry out a parallel development in which the former generates a series of folds that will go on to form the cranial, caudal and lateral axes of the embryo; while the folds of the endoderm remain in the interior of the organism forming the intestinal tube.

2. Extraembryonic endoderm

The second division of the endoderm is the one that remains outside the embryo forming the well-known yolk sac.. This membranous attachment is connected to the embryo, supplying sufficient nutrients and oxygen, as well as disposing of metabolic waste.

However, this embryonic endoderm division does not remain until the end of embryonic development but usually disappears around the tenth week of gestation.

Sections of the intestinal tract

In the previous section it was mentioned that the embryonic endoderm gives rise to a structure called the intestinal tube. This structure can in turn be differentiated into different sections that can correspond to both the embryonic endoderm and the extraembryonic endoderm. These sections are:

1. cranial intestine.

Known as the cranial or interior intestineThis structure is located inside the skull of the embryo. During the early stages of development it forms the buccopharyngeal membrane, which gradually transforms into the pharynx. Next, the lower boundary forms a structure known as the respiratory tract.

Finally, the intestinal tract dilates to become what will eventually correspond to the stomach..

2. Caudal intestine

Located within the caudal fold, it is the precursor of the allantoic membrane.. An extraembryonic web that appears through the formation of folds located next to the yolk sac.

3. Midgut

Finally, the midgut is located between the cranial and caudal structures. Its extension dilates until it reaches the yolk sac through the umbilical cord. Thanks to it, the embryo is supplied with sufficient nutrients from the maternal organism to allow its proper and allow its correct development.

What organs does it develop into?

It has already been mentioned on multiple occasions that the endoderm is the primitive structure thanks to which a large part of the organs and structures of the body arise, a process known as organogenesisi.e. the birth of organs.

This process of development of the definitive organs usually takes place between the calf and the eighth week of management. However, it has been shown that identifiable organs can be observed in humans as early as the fifth week.

To be more specific, from the endodermal layer derive these structures:

• Yolk sac.
• Allantois.
• Respiratory tractspecifically the bronchi and pulmonary alveoli.
• Epithelium and connective tissue of tonsils, pharynx, larynx and trachea. As well as the epithelium of lungs and certain parts of the Gastrointestinal tract.
• Urinary bladder.
• Epithelium of the eustachian tubes, ear cavities, thyroid and parathyroid glands, thymus, vagina and urethra.
• Glands of the digestive systemspecifically of the gastrointestinal tract; as well as the liver, gall bladder and pancreas.