Thursday, April 7, 2011

Teeth everywhere

On page 78 in Subin's book, he starts to describe the similarities in the formation of hair, feathers, breasts, and teeth. Using outside information, describe the process of each forming. Feel free to talk about the significance of all these exterior structures formed in similar ways.

Nikhil Pereira (nikhil.pereira3@gmail.com)

3 comments:

  1. Feathers are essential to helping birds survive and migrate, by not only controlling their body temperature as part of their integumentary system, but also by allowing birds to fly. Down feathers typically cover newborn birds, while adult birds have feathers. Birds have feather follicles which contains an underdeveloped contour feather inside. Down feathers are on top of each follicle, and as the bird grows, contour feathers will emerge, as the down feathers are pushed away until they rub off. The down feathers provide insulation for newborn birds, while adult feathers are more durable and assist in flight. Similar to hairs, feathers grow individually, rather than being connected as scales are. Each feather gets its own blood supply and is protected by a keratin sheath. These mechanisms are put in place because growing individual feathers is a greater energy investment than growing hair. Birds can move each of their feathers individually, allowing them to fine tune the speed and direction of their flight. Through history, feathers have become so essential to birds, that they will invest in feathers that can also provide them camouflage, so that they can hide from predators.

    Similarly, hair also forms in a follicle. As the epidermis thickens and cells grow in the dermis of the follicle, cells multiply in the dermal papilla, to form the hair. These cells are then pushed up, forming the hair we see on our head. Hair also contains keratin, as feathers do, protecting the hair from damage. Hairs also grow individually, each on their own cycle, and have the highest rate of mitosis, allowing hair to grow 1 cm per month.

    Breast development begins a few weeks after conception in the embryo. During this state, the mammary ridge begins to thicken. This initial development is the same in both males and females. While a child is still young, rudimentary mammary glands will develop, forming additional nipples or breasts. In females, at 6 months, column cells grow inward in each brease bud. These column cells hollow out, so that a rudimentary milk-duct system forms before birth. During puberty, the hormones progesterone and estrogen cause the breasts to further develop, by stimulating fat tissues to form. Myo-epithelial cells also form during puberty. These cells squeeze milk from the gland once a woman is pregnant to stimulate milk production.

    Teeth formation begins with the tooth bud, which forms in the ectoderm of the neural creast. Cells from the enamel organ give rise to ameloblases, which produce the outer enamel of the tooth. The dental papilla cells develop into ondontoblasts, which form dentin. Tooth pulp is formed by mesenchymal cells. In the dental follicle, the cementum of the tooth arises, and osteoblasts form the roots of the teeth.

    Sources:
    http://www.dnr.state.mn.us/young_naturalists/feathers/index.html
    http://www.loc.gov/rr/scitech/mysteries/grayhair.html
    http://www.youtube.com/watch?v=E7NzRBiXxWM
    http://www.aad.org/education-and-quality-care/medical-student-core-curriculum/hair-follicles
    University of Texas Medical Branch.

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  2. On page 78, Shubin states, "It turns out that exactly the same process underlies the development of all the structures that develop within skin: scales, hair, feathers, sweat glands, even mammary glands." Shubin makes this connection to show that although creatures today have all sorts of different skin structures, our evolution from a common ancestor is appparent because of the way these skin structures form.

    Birds developed feathers back in evolutionary history as a way to regulate body temperature and aid in flying, which was a selective advantage most likely because of the advantages of being able to migrate to suitable conditions and being able to spot prey from an aerial perspective. Like Anna mentioned, feathers grow out of follicles. As a feather begins to grow within a covering called a sheath, it develops its central shaft, color, and pattern. Then, "blood vessels nourish the growing feather until it is fully formed, then the blood vessels wither away. The sheath bursts open and falls off, or the bird removes the sheath with its beak" (http://www.dnr.state.mn.us/young_naturalists/feathers/index.html). Similarly to our hairs but unlike scales of a reptile, each feather grows individually so that the bird can place its feathers in the best position possible for flying, another selective advantage of having feathers.

    Like Anna pointed out, mammalian hair also grows from follicles. The hair develops in the epidermis, which moves down into the dermis. This downward growth forms a cap over some connective tissue, which is known as the papilla. Cells of this papilla multiply to form the hair (http://www.youtube.com/watch?v=E7NzRBiXxWM). As the cells grow away from the dermis, they are impregnated with the hard protein keratin, which feathers also have. Feathers and hairs both grow individually and in very similar manners, which indicates the common ancestor that birds and mammals have, but different environmental pressures caused the two groups to develop different selective advantages until they were unable to reproduce with one another.

    In the development of mammary glands, the proliferation of paired areas of epithelial cells in the epidermis of the thoracic region are seen. Similar to feathers and hairs, the column cells of females will grow downward in each breat bud. When these column cells hollow out, a rudimentary milk-duct system is able to form before birth (http://www.ana.ed.ac.uk/anatomy//mammbase/mamdev.html). This similar formation of this skin structure also points to evolution because of the selective advantages that these mammary glands have; for females, they are able to give passive immunity to their babies through their milk which better helps them survive and reproduce.

    Regarding the formation of teeth, Shubin says that the "key to tooth development is that an interaction between these two layers of tissue, an outer sheet of cells and an inner loose layer of cells, causes the tissue to fold and makes both layers secrete the molecules that build the organ" (78). Tooth formation, like Anna mentioned, begins with the tooth bud, which forms in the ectoderm of the neural crest. Ameloblases develop from cells of the enamel organ, and produce the outer enamel of the tooth. Then, as we saw specifically in hair devlopment, the papilla cells develop into ondontoblasts, which form dentin. Mesenchymal cells form tooth pulp, which, in the dental follicle, forms the cementum of the tooth (http://8e.devbio.com/article.php?ch=13&id=274). These similarities between the development of skin structures in all different creatures furthur supports evolution and the fact that all creatures came from a common ancestor.

    Hannah Kay (hgkay@aol.com)

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  3. I agree with what Anna and Hannah said about the formation feathers from follicles. Anna also mentioned that feathers have become useful to birds by allowing them to camouflage to hide from predators. Another important factor to consider when talking about feathers is the color. The color of the feather is very important for birds when mating. If the colors of the feathers look attractive to a female bird of the same species, then that bird will have an advantage of mating and reproducing. This is only true because birds, unlike some mammals, can see in color (1). The reason why birds can have colorful feathers is because of color pigments similar to ones found in plants that give them their color. Also, these feathers are similar to hair formation because they both originate from the follicle, and they both have the ability to molt and regenerate (2). That is very important in birds and all mammals with hair because these structures help the animal keep warm and if a certain part is destroyed, it can immediately be regenerated. Especially in birds, feathers need to be cared for as much as possible this is what allows the bird to stay warm and fly through the air. Interdependence in nature is present in the caring of feathers. In a recent study, it was found that birds and feather mites are in a symbiotic relationship. While the birds host these mites by giving them food and shelter, the mites eat all the oil and fungi keeping the feathers healthy and clean (3). Feathers are more than just a way to hide from predators.

    1. http://wings.avkids.com/Book/Animals/intermediate/birds-01.html
    2. http://www.ijdb.ehu.es/web/paper.php?doi=15272383
    3. http://www.dandydesigns.org/id34.html

    Benny Jeong
    bennyjeong218@gmail.com

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