Human Reproduction Test 7

It is the opening of the archenteron in the gastrula that develops into the anus of some animals

The mesoderm germ layer forms in the embryos of triploblastic animals. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm.The formation of a mesoderm leads to the development of a coelom. 

In humans, ovum is released from the ovary in the secondary oocyte stage. The wall of the ovary gets ruptured to release the oocyte. In humans ovulation occurs about 14 days before the onset of the next menstruation. Ovulation is induced by LH.

A single-celled zygote will undergo multiple rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula, with a fluid-filled cavity in its center, called a blastocoel.

A graafian follicle can be defined structurally as a heterogeneous family of relatively large follicles (0.4 to 23 mm) characterized by a cavity or antrum containing a fluid called follicular fluid or liquor folliculi. The characteristic structural unit of all graafian follicle is the antrum. For this reason, the term antral follicle is used correctly as a synonym for graafian follicle. 

The embryo with 8 to 16 blastomeres is called a morula. Morula is the solid mass of cells and is mulberry like. Morula is a developmental stage between the zygote and blastocyst.

Centrolecithal Eggs
When the yolk is aggregated at the centre of the egg and the active cytoplasm remains in the peripheral layer around the yolk. These eggs are called centrolecithal eggs and are found in some Hydrozoa and in some insects. The yolk-free cytoplasm is found in many insects and the cleav­age is total in Collembola.

HCG (Human chorionic gonadotropic hormone) is the basis for pregnancy test. It is seen in the urine.

Internal fertilization is a type of fertilization in which there is union of an egg and sperm inside the body of a parent. Examples include reptiles, mammals, birds. Colostrum is the first form of milk that is produced by the mammary glands of mammals. It contains large numbers of IgA antibodies and lymphocytes that help protect the mucous membranes of the infant. Polyspermy is a condition in which egg has been fertilized by more than one sperm. It is prevented by depolarization of the egg plasma membrane after the entry of first sperm. This depolarization prevents the entry of additional sperms. The fertilized ovum enters the uterine cavity 3-4 days later. Implantation occurs almost 7 to 10 days after fertilization and 5 to 6 days after it has entered the uterine cavity.

Thus, the correct answer is 'Polyspermy is prevented by the chemical changes on the egg surface..'

The endoderm is the innermost of the three germ layers. Cells derived from the endoderm eventually form many of the internal linings of the body, including the lining of most of the gastrointestinal tract, the lungs, the liver, the pancreas and other glands that open into the gastrointestinal tract, and certain other organs, such as the upper urogenital tract and female vagina.