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Thecae
In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common area of dehiscence called the stomium. Larry Hufford, "The origin and early evolution of angiosperm stamens" i''The Anther: form, function, and phylogeny'' William G. D'Arcy and Richard C. Keating (editors), Cambridge University Press, 1996, 351pp, p.60, (from Google Books) Any part of a microsporophyll that bears microsporangia is called an anther. Most anthers are formed on the apex of a filament. An anther and its filament together form a typical (or filantherous) stamen, part of the male floral organ. The typical anther is bilocular, i.e. it consists of two thecae. Each theca contains two microsporangia, also known as pollen sacs. The microsporangia produce the microspores, which for seed plants are known as pollen grains. If the polle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anther01
The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament and an anther which contains microsporangia. Most commonly, anthers are two-lobed (each lobe is termed a locule) and are attached to the filament either at the base or in the middle area of the anther. The sterile (i.e. nonreproductive) tissue between the lobes is called the connective, an extension of the filament containing conducting strands. It can be seen as an extension on the dorsal side of the anther. A pollen grain develops from a microspore in the microsporangium and contains the male gametophyte. The size of anthers differs greatly, from a tiny fraction of a millimeter in ''Wolfia'' spp up to five inches (13 centimeters) in '' Canna iridiflora'' and ''Strelitzia nicolai''. The stamens in a flower are collectively called the an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pollen
Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male Conifer cone, cone to the female cone of gymnosperms. If pollen lands on a compatible pistil or female cone, it Germination, germinates, producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archaeology, and Forensic science, forensics. Pollen in plants is used for transferring Ploidy#Haploid and monoploid, haploid male genetic ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ovarian Follicle
An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. In humans, women have approximately 200,000 to 300,000 follicles at the time of puberty, each with the potential to release an egg cell (ovum) at ovulation for Human fertilization, fertilization. These eggs are developed once every menstrual cycle with around 300-400 being ovulated during a woman's reproductive lifetime. Structure Ovarian follicles are the basic units of female reproductive biology. Each of them contains a single oocyte (immature ovum or egg cell). These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single competent oocyte in humans. They also consist of granulosa cells and theca of follicle. Oocyte Once a month, one of the ovaries releases a mature egg (ovum), known as an oocyte. The nucleus of such an oocyte is called a ''germinal vesicle (see picture).' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corpus Luteum
The corpus luteum (Latin for "yellow body"; : corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is the remains of the ovarian follicle that has released a mature ovum during a previous ovulation. The corpus luteum is colored as a result of concentrating carotenoids (including lutein) from the diet and secretes a moderate amount of estrogen that inhibits further release of gonadotropin-releasing hormone (GnRH) and thus secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). A new corpus luteum develops with each menstrual cycle. Development and structure The corpus luteum develops from an ovarian follicle during the luteal phase of the menstrual cycle or oestrous cycle, following the release of a secondary oocyte from the follicle during ovulation. The follicle first forms a corpus hemorrhagicum before it beco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human Embryogenesis
Human embryonic development or human embryogenesis is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, the development of the human body entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form the single cell zygote and the germinal stage of development commences. Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages. At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. Human embryology is the study of this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skull
The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent parts: the neurocranium and the facial skeleton, which evolved from the first pharyngeal arch. The skull forms the frontmost portion of the axial skeleton and is a product of cephalization and vesicular enlargement of the brain, with several special senses structures such as the eyes, ears, nose, tongue and, in fish, specialized tactile organs such as barbels near the mouth. The skull is composed of three types of bone: cranial bones, facial bones and ossicles, which is made up of a number of fused flat and irregular bones. The cranial bones are joined at firm fibrous junctions called sutures and contains many foramina, fossae, processes, and sinuses. In zoology, the openings in the skull are called fenestrae, the most ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thecal Sac
The thecal sac or dural sac is the membranous sheath (theca) or tube of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid which provides nutrients and buoyancy to the spinal cord. From the skull the tube adheres to bone at the foramen magnum and extends down to the second sacral vertebra where it tapers to cover over the filum terminale. Along most of the spinal canal it is separated from the inner surface by the epidural space. The sac has projections that follow the spinal nerves along their paths out of the vertebral canal which become the dural root sheaths. Clinical significance The lumbar cistern is part of the subarachnoid space. It is the space within the thecal sac which extends from below the end of the spinal cord (the conus medularis), typically at the level of the first to second lumbar vertebrae down to tapering of the dura at the level of the second sacral vertebra. The dura is pierced with a nee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Androgen
An androgen (from Greek ''andr-'', the stem of the word meaning ) is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes the embryological development of the primary male sex organs, and the development of male secondary sex characteristics at puberty. Androgens are synthesized in the testes, the ovaries, and the adrenal glands. Androgens increase in both males and females during puberty. The major androgen in males is testosterone. Dihydrotestosterone (DHT) and androstenedione are of equal importance in male development. DHT ''in utero'' causes differentiation of the penis, scrotum and prostate. In adulthood, DHT contributes to balding, prostate growth, and sebaceous gland activity. Although androgens are commonly thought of only as male Sex steroids, sex hormones, females also have them, but at lower levels: they function in libido and sexual arousal. An ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theca Of Follicle
The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become secondary follicles. The theca are divided into two layers, the theca interna and the theca externa. Theca cells are a group of endocrine cells in the ovary made up of connective tissue surrounding the follicle. They have many diverse functions, including promoting folliculogenesis and recruitment of a single follicle during ovulation. Theca cells and granulosa cells together form the stroma of the ovary. Androgen synthesis Theca cells are responsible for synthesizing androgens, providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures. Theca cells are responsible for the production of androstenedione, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graderia Subintegra, Helmdrade, Veldblomstappie, Faerie Glen NR, A
''Graderia'' is a genus of plants in the family Orobanchaceae, which is native to Africa and Socotra. It belongs to the tribe Buchnereae. It is a hemiparasitic taxon. Etymology ''Graderia'' is a taxonomic anagram derived from the name of the confamilial genus '' Gerardia''. The latter name is a taxonomic patronym honoring the English botanist John Gerard. Description Sometimes a suffrutex with stems growing from a woody rhizome. Leaves may be opposite or alternate. The solitary flowers appear in the axils, and have a five-lobed calyx and corolla. The flower is tubular with four stamens, in pairs of unequal length. Each stamen has two divergent, oblong and curved theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...e. The two-locular ovary has numerous ovules, and produces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tapetum (botany)
The tapetum is a specialised layer of nutritive cells found within the anther of flowering plants, located between the sporogenous tissue and the anther wall. Tapetum is important for the nutrition and development of pollen grains and a source of precursors for the pollen coat.P.L. Polowick, V.K. Sawhney 1993Differentiation of the Tapetum During Microsporogenesis in Tomato (Lycopersicon esculentum Mill.), with Special Reference to the Tapetal Cell Wall Annals of Botany, Volume 72, Issue 6, December 1993, Pages 595–605 The cells are usually bigger and normally have more than one nucleus per cell. As the sporogenous cells undergo mitosis, the nuclei of tapetal cells also divide. Sometimes, this mitosis is abnormal, which is why many cells of mature tapetum become multinucleated. Polyploidy and polyteny can also be seen sometimes. The tapetum's unusually large nuclear constitution helps it provide nutrients and regulatory molecules to the forming pollen grains. The following pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Somatic (biology)
In cellular biology, the term somatic is derived from the French somatique which comes from Ancient Greek σωματικός (sōmatikós, “bodily”), and σῶμα (sôma, “body”.) is often used to refer to the cells of the body, in contrast to the reproductive ( germline) cells, which usually give rise to the egg or sperm (or other gametes in other organisms). These somatic cells are diploid, containing two copies of each chromosome, whereas germ cells are haploid, as they only contain one copy of each chromosome (in preparation for fertilisation). Although under normal circumstances all somatic cells in an organism contain identical DNA, they develop a variety of tissue-specific characteristics. This process is called differentiation, through epigenetic and regulatory alterations. The grouping of similar cells and tissues creates the foundation for organs. Somatic mutations are changes to the genetics of a multicellular organism that are not passed on to its offspr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
