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Prostate Evolution In Monotreme Mammals
The monotremes (egg laying mammals) represent the order of extant mammals most distantly related to humans. The platypus (''Ornithorhynchus anatinus'') is indigenous to eastern Australia; the short-beaked echidna (''Tachyglossus aculeatus'') is indigenous to Australia and Papua New Guinea; whereas the long-beaked echidna (''Zaglossus bruijni'') is restricted to Papua New Guinea and Irian Jaya. Since monotremes exhibit characteristics common with both reptiles (e.g. presence of a cloaca) and therian mammals (e.g. mammary glands), they are of great interest for the study of mammalian evolution.Griffiths, M. (1968). Echidnas. Pergamon Press.Griffiths, M. (1978). The Biology of the Monotremes. Academic Press. Monotremes exhibit a combination of reptilian and mammalian characteristics Male monotremes are testicond (have intraabdominal testes) with the testes undergoing seasonal emergence during winter. The fully developed seminiferous tubules exhibit distinctly small stages of sper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monotreme
Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. In addition, they lay eggs rather than bearing live young, but, like all mammals, the female monotremes nurse their young with milk. Monotremes have been considered members of Australosphenida, a clade that contains extinct mammals from the Jurassic and Cretaceous of Madagascar, South America, and Australia, though this is disputed. The only surviving examples of monotremes are all indigenous to Australia and New Guinea, although there is evidence that they were once more widespread, as ''Monotrematum'' is known from the Paleocene of South America. The extant monotreme species are the platypus and four species of echidnas. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Platypus
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal Endemic (ecology), endemic to Eastern states of Australia, eastern Australia, including Tasmania. The platypus is the sole living representative or monotypic taxon of its Family (biology), family (Ornithorhynchidae) and genus (''Ornithorhynchus''), though a number of Fossil Monotremes, related species appear in the fossil record. Together with the four species of echidna, it is one of the five wikt:extant, extant species of monotremes, mammals that lay Egg (biology), eggs instead of giving birth to live young. Like other monotremes, it senses prey through electroreception, electrolocation. It is one of the few species of venomous mammals, as the male platypus has a spur (zoology), spur on the hind foot that delivers a Platypus venom, venom, capable of causing severe pain to humans. The unusual appearance of this egg-laying, duck-billed, beaver-t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Short-beaked Echidna
The short-beaked echidna (''Tachyglossus aculeatus''), also called the short-nosed echidna, is one of four living species of echidna and the only member of the genus ''Tachyglossus''. It is covered in fur and spines and has a distinctive snout and a specialized tongue, which it uses to catch its insect prey at a great speed. Like the other extant monotremes, the short-beaked echidna lays eggs; the monotremes are the only living group of mammals to do so. The short-beaked echidna has extremely strong front limbs and claws, which allow it to burrow quickly with great power. As it needs to be able to survive underground, it has a significant tolerance to high levels of carbon dioxide and low levels of oxygen. It has no weapons or fighting ability but repels predators by curling into a ball and deterring them with its spines. It lacks the ability to sweat and cannot deal with heat well, so it tends to avoid daytime activity in hot weather. It can swim if needed. The snout has m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long-beaked Echidna
The long-beaked echidnas (genus ''Zaglossus'') make up one of the two extant genera of echidnas, spiny monotremes that live in New Guinea; the other being the short-beaked echidna. There are three living species and one extinct species in this genus. The extinct species were present in Australia. Echidnas are one of the two types of mammals that lay eggs, the other being the platypus. The echidnas retain reptilian features such as egg-laying but display mammalian features such as fur and lactation. The Eastern species is listed as vulnerable, while Sir David's and western long-beaked echidna species are listed as Critically Endangered by the IUCN. Species ''Zaglossus attenboroughi'' * Habitat: known only from the Cyclops Mountains of Papua, Indonesia, New Guinea * Time: Holocene * Critically endangered Database entry includes justification for why this species is listed as critically endangered. ''Zaglossus bartoni'' * Habitat: on the central cordillera between the Paniai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theria
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. Characteristics Therian mammals give birth (''see viviparity'') to live young without a shelled egg. This is possible thanks to key proteins called syncytins which allow exchanges between the mother and its offspring through a placenta, even rudimental ones such as in marsupials. Genetic studies have suggested a viral origin of syncytins through the endogenization process. The marsupials and the placental mammals evolved from a common therian ancestor that gave live birth by suppressing the mother's immune system. While the marsupials continued to give birth to an underdeveloped fetus after a short pregnancy, the ancestors of placental mammals gradually evolved a prolonged pregnancy. Therian mammals no longer have the coracoid bone, con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spermatogenesis
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically (Meiosis I) into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa (sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells. Spermatozoa are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Efferent Ducts
The efferent ducts (or efferent ductules or ductuli efferentes or ductus efferentes or vasa efferentia) connect the rete testis with the initial section of the epididymis.Hess 2018 There are two basic designs for efferent ductule structure: * a) multiple entries into the epididymis, as seen in most large mammals. In humans and other large mammals, there are approximately 15 to 20 efferent ducts, which also occupy nearly one third of the head of the epididymis. * b) single entry, as seen in most small animals such as rodents, where by the 3–6 ductules merge into a single small ductule prior to entering the epididymis. The ductuli are unilaminar and composed of columnar ciliated and non-ciliated (absorptive) cells. The ciliated cells serve to stir the luminal fluids, possibly to help ensure homogeneous absorption of water from the fluid produced by the testis, which results in an increase in the concentration of luminal sperm. The epithelium is surrounded by a band of smooth mu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epididymides
The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is a single, narrow, tightly-coiled tube in adult humans, in length. It serves as an interconnection between the multiple efferent ducts at the rear of a testicle (proximally), and the vas deferens (distally). Anatomy The epididymis is situated posterior and somewhat lateral to the testis. The epididymis is invested completely by the tunica vaginalis (which is continuous with the tunica vaginalis covering the testis). The epididymis can be divided into three main regions: * The head ( la, caput). The head of the epididymis receives spermatozoa via the efferent ducts of the mediastinium of the testis at the superior pole of the testis. The head is characterized histologically by a thick epithelium with long stereocilia (described below) and a little smooth muscle. It is involved in absorbing fluid to make the sperm more concentrated. The concentrat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vas Deferens
The vas deferens or ductus deferens is part of the male reproductive system of many vertebrates. The ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. The vas deferens is a partially coiled tube which exits the abdominal cavity through the inguinal canal. Etymology ''Vas deferens'' is Latin, meaning "carrying-away vessel"; the plural version is ''vasa deferentia''. ''Ductus deferens'' is also Latin, meaning "carrying-away duct"; the plural version is ''ducti deferentes''. Structure There are two vasa deferentia, connecting the left and right epididymis with the seminal vesicles to form the ejaculatory duct in order to move sperm. The (human) vas deferens measures 30–35 cm in length, and 2–3 mm in diameter. The vas deferens is continuous proximally with the tail of the epididymis. The vas deferens exhibits a tortuous, convoluted initial/proximal section (which measures 2–3 cm in length). Distally, it forms ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulbourethral Gland
The bulbourethral glands or Cowper's glands (named for English anatomist William Cowper) are two small exocrine glands in the reproductive system of many male mammals (of all domesticated animals, they are absent only in dogs). They are homologous to Bartholin's glands in females. The bulbouretheral glands are responsible for producing a pre-ejaculate fluid called Cowper's fluid (known colloquially as ''pre-ejaculate'' or ''pre-cum''), which is secreted during sexual arousal, neutralizing the acidity of the urethra in preparation for the passage of sperm cells. Location Bulbourethral glands are located posterior and lateral to the membranous portion of the urethra at the base of the penis, between the two layers of the fascia of the urogenital diaphragm, in the deep perineal pouch. They are enclosed by transverse fibers of the sphincter urethrae membranaceae muscle. Structure The bulbourethral glands are compound tubulo-alveolar glands, each approximately the size of a pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution Of Descended Testes In Mammals
Mammals are the only animals in which the testes descend from their point of origin into a scrotum. Concurrently, mammals are the only class of vertebrates to evolve a prostate gland starting with prostate evolution in monotreme mammals. Testicular descent occurs to a variable degree in various mammals, ranging from virtually no change of position from the abdominal cavity (monotremes, elephants and hyraxes); through migration to the caudal end of the abdominal cavity (armadillos, whales and dolphins); migration just through the abdominal wall (hedgehogs, mole (animal), moles, Pinniped, seals); formation of a sub-anal swelling (pigs, rodents); to the development of pronounced scrota (primates, dogs, ruminants) in mammals.Setchell B.P. (1978). The Mammalian Testis. Cornell University Press, Ithaca, New York. Since descent of the testes into a scrotal pouch subjects the animal to enhanced risk of accidental damage and/or vulnerability from predators and rivals, presumably there must b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Figure 1
Figure 1 is a Toronto, Ontario-based online social networking service for healthcare professionals to post and comment on medical images. Figure 1 was founded in Toronto by Dr. Joshua Landy, Richard Penner and Gregory Levey. The platform launched in North America in May 2013 and is now available in more than 100 countries. The privately held company reports more than 1 million healthcare professionals use its app and website. Funding In 2013, Figure 1 launched with $2 million (CDN) in seed money, with Rho Canada Ventures and Version One Ventures led the investment. In 2015, the company added $5 million (USD) to its Series A financing round, which was led by Union Square Ventures, an early investor in Twitter, Tumblr, Etsy, and Kickstarter. This brings the total round to $9 million (USD). Reception Figure 1's content has been characterized as "gruesome". The app's founder said the "very colorful images" are what medics see every day. "It's a transparent view into a world y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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