Why Is the Endoderm Essential in Embryonic Development?
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.
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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.
Lungs
Liver
Pancreas
Female vagina
Colon
Stomach
Small Intestine
Thymus
Prostate
Thyroid
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.
FAQs on Endoderm: Structure, Formation, and Functions
1. What is the endoderm and what is its primary role in embryonic development?
The endoderm is the innermost of the three primary germ layers in a developing embryo, formed during the process of gastrulation. Its primary role is to form the epithelial linings of the body's internal tubes, such as the digestive and respiratory tracts. It also gives rise to the functional parts of major glands like the liver and pancreas.
2. What are the key differences between the endoderm and the ectoderm?
The key differences between the endoderm and ectoderm relate to their position and the structures they form:
- Position: The endoderm is the innermost germ layer, while the ectoderm is the outermost germ layer.
- Developmental Fate: The endoderm primarily develops into the linings of the digestive and respiratory systems, liver, and pancreas. In contrast, the ectoderm develops into the skin, hair, nails, and the entire nervous system (brain and spinal cord).
3. How is the endoderm formed during the process of gastrulation?
The endoderm is formed during gastrulation, a critical phase of embryonic development. During this process, cells from the surface layer of the embryo (the epiblast) migrate inwards. These migrating cells displace the existing inner layer (the hypoblast) and establish a new, definitive inner layer, which is the embryonic endoderm. This process establishes the fundamental tube-within-a-tube body plan.
4. Which major organs and tissues are derived from the embryonic endoderm?
The endoderm is the precursor to several vital internal structures. Major derivatives include:
- The epithelial lining of the entire digestive tract, from the pharynx to the rectum.
- The epithelial lining of the respiratory tract, including the trachea, bronchi, and lungs.
- Major glands such as the liver, gallbladder, and pancreas.
- The thyroid, parathyroid, and thymus glands.
- The lining of the urinary bladder and parts of the urethra.
5. Why is the proper formation of the endoderm so critical for the digestive and respiratory systems?
The proper formation of the endoderm is critical because it establishes the foundational cellular blueprint for the digestive and respiratory systems. It doesn't just create a passive lining; it forms the primitive gut tube from which all associated organs bud and differentiate. Any errors in endoderm formation can lead to severe or fatal defects in the development of the lungs, stomach, intestines, liver, or pancreas, as these organs would lack the initial cell population required to form.
6. How does the endoderm interact with the mesoderm to form complex organs?
The formation of complex organs like the liver or pancreas is a cooperative process. The endoderm typically forms the functional epithelial tissues of the organ (the parenchyma), such as the hepatocytes in the liver or the acinar cells in the pancreas. The adjacent mesoderm (the middle germ layer) is induced by the endoderm to form the organ's supportive structures, including the connective tissue (stroma), blood vessels, and smooth muscle. This reciprocal signalling between the two layers is essential for proper organogenesis.
7. Is the endoderm in animals the same as the endodermis in plants?
No, they are functionally and structurally unrelated, despite the similar names. The animal endoderm is one of the three embryonic germ layers that gives rise to internal organs. The plant endodermis is a specialized cylinder of cells found in the root cortex that acts as a selective barrier, regulating the passage of water and minerals into the vascular system via the Casparian strip. They are an example of analogous terminology for entirely different biological structures.
8. What is the difference between definitive endoderm and extraembryonic endoderm?
The distinction lies in their developmental timing and ultimate fate. The extraembryonic endoderm (also known as the hypoblast or primitive endoderm) forms first and contributes to structures outside the embryo proper, like the yolk sac, which provides nourishment. The definitive endoderm (or embryonic endoderm) forms later during gastrulation, replacing the hypoblast. It is this definitive layer that gives rise to all the internal organs and linings within the embryo itself.
