Question:
Which layer develops first during embryonic development?
Which layer develops first during embryonic development?
Updated On: Aug 1, 2022
- ectoderm
- mesoderm
- endoderm
- both (b) & (c)
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The Correct Option is C
Solution and Explanation
Gastrulation results in the formation of three germ layers. In all triploblastic animals three germ layers are ectoderm, mesoderm and endoderm.
(i) Formation of Endoderm. The blastocyst (blastodermic vesicle) grows in size by absorbing food from the uterus. Some cells detach from the inner cell mass to form endoderm in the blastocoel. Endoderm differentiates into the primitive gut. The primitive gut differentiates into two portions at a later stage. One portion forms the gut tract and the other portion communicates with the gut of the embryo and is called the yolk sac.
(ii) Formation of Embryonic Disc. Just after the formation of endoderm, the remaining mass of cells of the inner cell mass is called embryonic disc.
(iii)Formation of Mesoderm. It starts after the formation of endoderm. Formation of mesoderm starts from the caudal margin of the embryonic disc by rapid proliferation of cells. The proliferated cells detach from the embryonic disc and form mesoderm. (iv)Formation of ectoderm. After the formation of mesoderm, the remaining cells of the embryonic disc form a layer, the ectoderm.
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Concepts Used:
Human Reproduction
Reproduction in human beings involves the fusion of male and female gametes that produces in their reproductive system.
Male Reproductive System:
The male reproductive system comprises:
- Testicles (testes): A pair of oval-shaped organs masked in a pouch known as the scrotum. They manage the production of sperms and the male hormone testosterone.
- Scrotum: It is a sac-like organ that hangs under the penis and behind it. It is the house of the testes, or testicles, and maintains a temperature that is needed for the production of sperm by it.
- Vas deferens: The sperms produced in testes are stored in a tube known as the epididymis. Here the sperms get matured and pass to the urethra via the muscular tube known as vas deferens.
- Accessory glands: This includes three glands, namely the prostate gland, seminal vesicles, and Cowper’s gland. The secretions from the mentioned three glands mix to form a fluid known as semen. Semen nourishes the sperm, raises the volume, and helps in lubrication.
- Penis: The penis is a cylindrical tube that serves as both an excretory organ, and a reproductive organ. It transfers sperms into the vagina during sexual intercourse.
Female Reproductive System:
The female reproductive system is active before, during, and after fertilization as well. It comprises the following parts:
- A pair of ovaries: A pair of ovaries produce and stores ovum in them. They also produce a female hormone known to be estrogen.
- Fallopian tubes (Oviducts): They are the area of fertilization. They connect both the ovaries with the uterus.
- Uterus: Uterus is the place of development for the embryo.
- Vagina: The part that connects the cervix to the external female body parts is called a vagina. It is the passage for the penis during coitus as well as a fetus during transfer.