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Spermatogenesis
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D013091 |
[The process of male germ cell development in which the haploid SPERMATIDS give rise to SPERMATOZOA by metamorphosis.
, The process of male germ cell development in which the euploid SPERMATOGONIA give rise to SPERMATOCYTES and then the haploid SPERMATIDS by MITOSIS and MEIOSIS.
, The process of germ cell development in the male from the primordial germ cells, through SPERMATOGONIA; SPERMATOCYTES; SPERMATIDS; to the mature haploid SPERMATOZOA.
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Spermatogenesis-Blocking Agents
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D013092 |
[Chemical substances which inhibit the process of spermatozoa formation at either the first stage, in which spermatogonia develop into spermatocytes and then into spermatids, or the second stage, in which spermatids transform into spermatozoa.
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Spermatogonia
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D013093 |
[Euploid male germ cells of an early stage of SPERMATOGENESIS, derived from prespermatogonia. With the onset of puberty, spermatogonia at the basement membrane of the seminiferous tubule proliferate by mitotic then meiotic divisions and give rise to the haploid SPERMATOCYTES.
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Spermatozoa
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D013094 |
[Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.
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Spermidine
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D013095 |
[A polyamine formed from putrescine. It is found in almost all tissues in association with nucleic acids. It is found as a cation at all pH values, and is thought to help stabilize some membranes and nucleic acid structures. It is a precursor of spermine.
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Spermidine Synthase
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D011436 |
[An enzyme that catalyzes the transfer of the propylamine moiety from 5'-deoxy-5'-S-(3-methylthiopropylamine)sulfonium adenosine to putrescine in the biosynthesis of spermidine. The enzyme has a molecular weight of approximately 73,000 kDa and is composed of two subunits of equal size.
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Spermine
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D013096 |
[A biogenic polyamine formed from spermidine. It is found in a wide variety of organisms and tissues and is an essential growth factor in some bacteria. It is found as a polycation at all pH values. Spermine is associated with nucleic acids, particularly in viruses, and is thought to stabilize the helical structure.
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Spermine Synthase
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D013097 |
[An enzyme that catalyzes the transfer of the propylamine moiety from 5'-deoxy-5'-S-(3-methylthiopropylamine)sulfonium adenosine to spermidine in the biosynthesis of spermine. It has an acidic isoelectric point at pH 5.0. EC 2.5.1.22.
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Sphaerotilus
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D042744 |
[A genus of gram-negative, sheathed, rod-shaped bacteria in the family COMAMONADACEAE. They are closely related to LEPTOTHRIX.
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Sphagnopsida
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D044003 |
[A plant genus of the family Sphagnaceae, order Sphagnales, subclass Sphagnidae, class SPHAGNOPSIDA.
, A class of BRYOPHYTA which is best known for Sphagnum forming PEAT bogs.
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Spheniscidae
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D046429 |
[The sole family in the order Sphenisciformes, comprised of 17 species of penguins in six genera. They are flightless seabirds of the Southern Hemisphere, highly adapted for marine life.
, An order of flightless BIRDS, comprised of one family SPHENISCIDAE.
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Sphenoid Bone
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D013100 |
[An irregular unpaired bone situated at the SKULL BASE and wedged between the frontal, temporal, and occipital bones (FRONTAL BONE; TEMPORAL BONE; OCCIPITAL BONE). Sphenoid bone consists of a median body and three pairs of processes resembling a bat with spread wings. The body is hollowed out in its inferior to form two large cavities (SPHENOID SINUS).
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Sphenoid Sinus
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D013101 |
[One of the paired air spaces located in the body of the SPHENOID BONE behind the ETHMOID BONE in the middle of the skull. Sphenoid sinus communicates with the posterosuperior part of NASAL CAVITY on the same side.
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Sphenoid Sinusitis
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D015524 |
[Inflammation of the NASAL MUCOSA in the SPHENOID SINUS. Isolated sphenoid sinusitis is uncommon. It usually occurs in conjunction with other paranasal sinusitis.
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Sphenopalatine Ganglion Block
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D059387 |
[Method of treating pain associated with the sphenopalatine ganglion located in the PTERYGOPALATINE FOSSA, posterior to the middle nasal turbinate. The transnasal approach involves application of suitable local anesthetic to the mucous membrane overlying the ganglion.
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Sphenostylis
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D031303 |
[A plant genus of the family FABACEAE that contains LECTINS and raffinose oligosaccharides.
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Spherocytes
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D013102 |
[Small, abnormal spherical red blood cells with more than the normal amount of hemoglobin.
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Spherocytosis, Hereditary
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D013103 |
[A group of familial congenital hemolytic anemias characterized by numerous abnormally shaped erythrocytes which are generally spheroidal. The erythrocytes have increased osmotic fragility and are abnormally permeable to sodium ions.
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Spheroids, Cellular
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D018874 |
[Spherical, heterogeneous aggregates of proliferating, quiescent, and necrotic cells in culture that retain three-dimensional architecture and tissue-specific functions. The ability to form spheroids is a characteristic trait of CULTURED TUMOR CELLS derived from solid TUMORS. Cells from normal tissues can also form spheroids. They represent an in-vitro model for studies of the biology of both normal and malignant cells. (From Bjerkvig, Spheroid Culture in Cancer Research, 1992, p4)
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Spheroplasts
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D013104 |
[Cells, usually bacteria or yeast, which have partially lost their cell wall, lost their characteristic shape and become round.
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