Endoderm

Triploblasty is a condition known as gastrula in which the primary germ cells are covered by three layers. The embryonic cell’s germ layer consists of three layers namely, Ectoderm Mesoderm and Endoderm. 

The ectoderm is the outermost layer during embryonic development. It gives rise to hair, nasal cavity, skin,  the sinuses, nails or hooves, the lens of the eye, the epithelial (surface, or lining, tissues) of sense organs, the anal canal, nervous tissue, and the mouth (including tooth enamel) and etc. 

The Mesoderm found between Endoderm and Ectoderm. It gives rise to skeletal muscles,  fallopian tube, blood vessels, bone, cartilage, smooth muscle, joints, endocrine glands, kidney cortex, testicles, connective tissue, urogenital organ, heart muscle, uterus, and blood cells from the spinal cord and lymphatic tissue.  

The Endodermal tissue is the innermost layer of the primitive germ cell. The definitive endoderm of embryonic cells is developed into the colon, the intestines, the stomach, the liver, the lungs, and the pancreas. 

Endoderm Definition

The endoderm germ layer of embryonic cells gives rise to tissues and organs. 

Except for the sponges, all the multicellular animals form two or three germ layers at the stage of gastrulation. The body with the presence of two or three embryonic germ layers is known as diploblasty or triploblasty respectively. In triploblasty, ectoderm, endoderm, mesoderm are seen while in diploblasty only ectoderm and endoderm are present.  The endoderm layer found in embryos of both vertebrates and invertebrates. This endoderm gives rise to various parts of the digestive tract, the lower respiratory tract..etc.  

Formation of Endoderm Layer

The embryo from a blastula covered with a single layer of cells is developed into the gastrula with multiple layers of cells. This process of embryonic development is known as gastrulation. 

These multiple layers developed during the gastrulation are known as germ layers. The cells are may develop into endoderm even at the early stage of the animal embryo.  

While observing the primitive endoderm cells in mice, it is noted that the surface of the blastula is adjacent to the blastocoel. The fluid-filled cavity in the early blastocyst is going to develop as an extra-embryonic membrane. There are two major subtypes in extraembryonic endoderm, they are visceral endoderm, which is a protective membrane around the egg, and parietal endoderm, which is going to form the Reichert’s membrane. 

Initially, the endoderm cells are located on the surface of the blastula and ultimately develop into an internal structure. During the process of gastrulation, the developing embryo cells are drastically rearranged and germ layers end up in the development of the right position.  

Functions of Endoderm 

During the process of invagination, the endoderm and mesoderm move inside the embryo and start developing the guts during the gastrulation process. As the cells move into the inner part of the embryo, the dorsal endoderm generates the line of cells along the mesoderm. The gap developed between the dorsal endoderm and the vegetal endoderm cells is a precursor of the gut cavity. The definitive endoderm will develop into the digestive tract, other organ systems like the respiratory system, digestive system, reproductive system… etc. 

[Image will be uploaded soon]

This image shows how the organs and glands are developed from the endodermal tissues. This shows the development of digestive and respiratory systems, and the thyroid, parathyroid, and thymus glands.

List of Organs Formed by Endoderm and Its Functions 

The definitive endoderm is developed into the organs listed below. 

1. Lungs

2. Liver

3. Pancreas

4. Female vagina

5. Colon

6. Stomach

7. Small Intestine

8. Thymus

9. Prostate

10. Thyroid

11. Cecum 

Lungs:  The pair of lungs are part of the respiratory system, which purifies the incoming air. A pair of lungs work together and help to breathe. It mainly helps to oxygenate the fresh air to the body through the blood and extracts the carbon dioxide from deoxygenated blood. 

Liver: The liver is mainly found in all vertebrates. It detoxifies various metabolites, and synthesizes proteins further, produces biochemicals necessary for digestion and growth.

Pancreas: The pancreas plays an important role in converting the food particles to energize the body cell. The pancreas produces two major functions. One is an exocrine function, which helps the digestive system. And another is an endocrine function, which regulates blood sugar. 

Female Vagina: It is part of the female reproductive system. The vagina is an elastic, soft flexible muscular canal. It connects the uterus to the outside world. 

Colon: It is part of the digestive system, which is known as the large intestine. It absorbs the salt and water from the food materials and promotes digestion.

Stomach: It breakdown the food by temporarily contracting and relaxing the stomach and promotes digestion.  It temporarily stores the food. 

Small Intestine: It is a continuous tube running from the stomach to anus. It absorbs essential nutrients and water from the food. 

Thymus: It produces white blood cells called T-lymphocytes. It plays a major part in improving the immune system. 

Prostate: It produces the fluid with the sperm cells from testicles. 

Thyroid: It is the most important hormonal gland. It plays an important role in growth and metabolism. 

Cecum: The cecum connects the small intestine and large intestine. It simply acts as a storage unit for chyme which it receives from the ileum.