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Proctodeum
A proctodeum is the back ectodermal part of an alimentary canal. It is created during embryogenesis by a folding of the outer body wall. It will form the lower part of the anal canal, below the pectinate line, which will be lined by stratified squamous non-keratinized (zona hemorrhagica) and stratified squamous keratinized (zona cutanea) epithelium. The junction between them is Hilton's white line The anocutaneous line, also called the Hilton white line or intersphincteric groove, is a boundary in the anal canal. Below the anocutaneous line, lymphatic drainage is to the superficial inguinal nodes. The anocutaneous line is slightly below t .... External links * Embryology of digestive system {{developmental-biology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anal Canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segment of the bowel, it functions to regulate release of excrement by two muscular sphincter complexes. The anus is the aperture at the terminal portion of the anal canal. Structure In humans, the anal canal is approximately long, from the anorectal junction to the anus. It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior slit. The canal is differentiated from the rectum by a transition along the internal surface from endodermal to skin-like ectodermal tissue. The anal canal is traditionally divided into two segments, upper and lower, separated by the pectinate line (also known as the dentate line): * upper zone (zona col ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pectinate Line
The pectinate line (dentate line) is a line which divides the upper two-thirds and lower third of the anal canal. Developmentally, this line represents the hindgut-proctodeum A proctodeum is the back ectodermal part of an alimentary canal. It is created during embryogenesis by a folding of the outer body wall. It will form the lower part of the anal canal The anal canal is the part that connects the rectum to the ... junction. It is an important anatomical landmark in humans, and several distinctions can be made based upon the location of a structure relative to this line: Additional images File:Rectoanal jxn.JPG, Microscopic cross section of the anorectal junction. File:Anorectum-en.svg , Anatomy of the anus and rectum File:Gray1078.png, Coronal section of rectum and anal canal. References External links * () {{Authority control Digestive system Anatomic Landmarks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Ectoderm
The surface ectoderm (or external ectoderm) forms the following structures: *Skin (only epidermis; dermis is derived from mesoderm) (along with glands, hair, and nails) *Epithelium of the mouth and nasal cavity and glands of the mouth and nasal cavity *Tooth enamel (as a side note, dentin and dental pulp are formed from ectomesenchyme which is derived from ectoderm (specifically neural crest cells and travels with mesenchmyal cells) *Epithelium of anterior pituitary *Lens, cornea, lacrimal gland, tarsal glands and the conjunctiva of the eye *Apical ectodermal ridge inducing development of the limb buds of the embryo. *Sensory receptors in epidermis See also *List of human cell types derived from the germ layers This is a list of cells in humans derived from the three embryonic germ layers – ectoderm, mesoderm, and endoderm. Cells derived from ectoderm Surface ectoderm Skin * Trichocyte * Keratinocyte Anterior pituitary * Gonadotrope * Corticotro ... References Exte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Germ Layer
A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three primary germ layers. Some animals, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Other animals such as bilaterians produce a third layer (the mesoderm) between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal’s tissues and organs through the process of organogenesis. History Caspar Friedrich Wolff observed organization of the early embryo in leaf-like layers. In 1817, Heinz Christian Pander discovered three primordial germ layers while studying chick embryos. Between 1850 and 1855, Robert Remak had further refined the germ cell layer (''Keimblatt'') concept, stating that the external, internal and middle layers form respectively the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alimentary Canal
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as feces. ''Gastrointestinal'' is an adjective meaning of or pertaining to the stomach and intestines. Most animals have a "through-gut" or complete digestive tract. Exceptions are more primitive ones: sponges have small pores ( ostia) throughout their body for digestion and a larger dorsal pore (osculum) for excretion, comb jellies have both a ventral mouth and dorsal anal pores, while cnidarians and acoels have a single pore for both digestion and excretion. The human gastrointestinal tract consists of the esophagus, stomach, and intestines, and i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryogenesis
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals. The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation is the formation of the three germ layers that will form all of the different parts of the body. Neurulation forms the nervous sys ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stratified Squamous Epithelium
A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface. In the deeper layers, the cells may be columnar or cuboidal. There are no intercellular spaces. This type of epithelium is well suited to areas in the body subject to constant abrasion, as the thickest layers can be sequentially sloughed off and replaced before the basement membrane is exposed. It forms the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina. In the epidermis of skin in mammals, reptiles, and birds, the layer of keratin in the outer layer of the stratified squamous epithelial surface ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hilton's White Line
The anocutaneous line, also called the Hilton white line or intersphincteric groove, is a boundary in the anal canal. Below the anocutaneous line, lymphatic drainage is to the superficial inguinal nodes. The anocutaneous line is slightly below the pectinate line and a landmark for the intermuscular border between internal and external anal sphincter muscles. The anocutaneous line represents the transition point from non-keratinized stratified squamous epithelium of the anal canal to keratinized stratified squamous epithelium of the anus and perianal skin. In live persons, the color of the line is white, hence the alternative name. It is named for John Hilton. See also *Anal canal *Dentate line *Hilton's Law Hilton's law, espoused by John Hilton in a series of medical lectures given in 1860–1862, is the observation that in the study of anatomy, the nerve supplying the muscles extending directly across and acting at a given joint not only supplies the ... References D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
