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Human sexual reproduction, to produce offspring, begins with fertilization. Successful reproduction typically involves sexual intercourse between a healthy, sexually mature and fertile male and female. [1] During sexual intercourse, sperm cells are ejaculated into the vagina through the penis, resulting in fertilization of an ovum to form a ...
The human female reproductive system is a series of organs primarily located inside the body and around the pelvic region of a female that contribute towards the reproductive process. The human female reproductive system contains three main parts: the vagina, which leads from the vulva , the vaginal opening, to the uterus; the uterus , which ...
The early embryo has 1–2 weeks in order to produce sufficient hCG in order to stabilize the endometrial lining to allow for blastocyst attachment. The dramatic increase in trophoblastic and corpus luteal hCG synthesis signals both blastocyst [5] and corpus luteal [6] production of P4, crucial for the maintenance of the endometrium.
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction.Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. [1]
By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce [1] and organisms only pass on 50% of their genes. [2]
The role of vitamins in nutrition was studied in the following decades. The first recommended dietary allowances for humans were developed to address fears of disease caused by food deficiencies during the Great Depression and the Second World War. [3] Due to its importance in human health, the study of nutrition has heavily emphasized human ...
As a result, the vast majority of human babies must rotate inside the birth canal in order to squeeze through the birthing canal and fit through the pelvic planes. This process is known as a rotational birth, and while it is not a process unique to humans, humans are unique in that nearly all human babies undergo this process out of necessity.
Another theory is that sexual reproduction originated from selfish parasitic genetic elements that exchange genetic material (that is: copies of their own genome) for their transmission and propagation. In some organisms, sexual reproduction has been shown to enhance the spread of parasitic genetic elements (e.g. yeast, filamentous fungi). [80]