Reproductive System of the Female Mammal Help
Introduction to Reproductive System of the Female Mammal
In order to achieve internal fertilization, the penis of the male must be inserted into the vagina (vah- JEYE -nah), a tapered “sheath” (vagin) that also serves as the birth canal. The vagina leads into the uterus or womb through a tiny hole in its neck-like cervix ( SIR -viks) (see Figure 20.5).
Attached to the top of the uterus are the right and left oviducts ( OH -vih-ducts) or “egg ducts.” The oviducts are alternately called the Fallopian (fah- LOH -pea-un) tubes in honor of their discoverer, the Italian anatomist, Gabriello Fallopio (fah- LOH -pea-oh). The oviducts (fallopian tubes) are a pair of slender egg ducts that carry ova towards the uterus.
The ova are released from the ovaries ( OH -var- eez ). There is both a right ovary and a left ovary, each named for their oval, whitish appearance, much like a chicken “egg” (ovari).
Internal Fertilization And The Female Reproductive Pathway
The key to internal fertilization, of course, is both ejaculation by the male and ovulation by the female. (You may want to review appropriate parts of Chapter 15, the glands, at this point.) Previously, we learned that increased secretion of luteinizing hormone was the usual trigger for ovulation. Basically, the LH (luteinizing hormone) dissolves and weakens the outer surface of the ovary, allowing a mature ovarian follicle to rupture and release an ovum.
The ovum is usually swept up into a nearby oviduct (Fallopian tube). Fertilization usually occurs in the first (outer) 1/3 of the oviduct. Fusion of sperm and ovum creates a zygote. As the zygote moves through the oviduct and towards the uterus, it undergoes a series of mitoses (my- TOH -seez).
Embryo Development Leading to Birth
The single-celled zygote becomes a solid mass of cells called a morula (mor- OO -luh), whose name comes from the Latin for “little mulberry.” The morula passes out of the oviduct and enters the body (main hollow cavity) of the uterus. Here it becomes a blastula ( BLAS -chew-lah), alternately called a blastocyst ( BLAS -toh-sist). The blastula (blastocyst) is a “little sprouter” (blastul) or “hollow sprouting bladder” (blastocyst) that embeds itself within the endometrium ( en -doh- ME -tree-um), the “inner” (endo-) epithelial lining of the “uterus” (metr).
After the blastula (blastocyst) implants itself into the uterine ( YOU -ter-in) wall, it starts a process of cellular differentiation (the cells becoming different from each other and specialized). This leads to a gastrula ( GAS -true-lah) or hollow “little stomach” (gastrul). As Figure 20.6 clearly displays, the gastrula gives rise to the three primary germ layers of the human embryo.
The gastrula does, indeed, have some of the same characteristics as a miniature version of the real stomach! Besides having a hollow interior, the gastrula (like the real stomach), has multiple layers of cells within its walls. These cell layers are technically called derms - various layers of “skin.”
The endoderm ( EN -doh- derm ), or “inner skin,” for instance, eventually creates much of the inner lining of the main body cavities in the mature adult. The mesoderm ( ME -so- derm ) – “middle skin” – differentiates to become bone and muscle tissue. And the ectoderm ( EK -toh- derm ) specializes to ultimately become much of the skin and nervous system. It is the skin and nervous system (Chapter 14), after all, that lies at or near the body surface, reacts to environmental stimuli, and communicates extensively about such stimuli.
To summarize the above information, we have:
THREE PRIMARY GERM LAYERS OF THE EMBRYO = Endoderm (“Inner skin”) + Mesoderm (“Middle skin”) + Ectoderm (“Outer skin”)
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