Cross section of the epithelium of a seminiferous tubule showing various stages of spermatocyte development

Spermatogenesis is the process by which male spermatogonia develop into mature spermatozoa. Spermatozoa are the mature male gametes, in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis. In mammals it occurs in the male testes and epididymis in a stepwise fashion, and for humans takes approximately 64 days. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age. The entire process can be broken up into several distinct stages, each corresponding to a particular type of cell: Image File history File links Gray1150. ... Image File history File links Gray1150. ... Types of epithelium In biology and medicine, epithelium is a tissue composed of a layer of cells. ... This article needs to be wikified. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... Schematic diagram of a sperm cell, showing the (1) acrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail) A sperm cell, or spermatozoon ( spermatozoa) (in Greek: sperm = semen and zoon = alive), is the haploid cell that is the male gamete. ... A gamete is a specialized germ cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Gametogenesis is the creation of gametes by meiotic division of gametocytes into various gametes. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in... Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ... Male Anatomy The epididymis is part of the human male reproductive system and is present in all male mammals. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Puberty refers to the process of physical changes by which a childs body becomes an adult body capable of reproduction. ...

A mature human Spermatozoon

Ploidy is the number of homologous sets of chromosomes in a biological cell. ... This article is about the biological chromosome. ... A chromatid forms one part of a chromosome after it has coalesced for the process of mitosis or meiosis. ... A Spermatogonium (plural: spermatogonia) is an intermediary male gametogonium (a kind of germ cell) in the production of spermatozoa. ... Spermatocytogenesis is the male form of gametocytogenesis. ... Mitosis is the process in which a cell duplicates its chromosomes to generate two identical cells. ... Spermatogenesis refers to the creation, or genesis, of sperm cells, which occurs in the male gonads or testes. ... it is the creation of spermatids from secondary spermatocytes through mitosis ... Not to be confused with miosis. ... Spermatogenesis refers to the creation, or genesis, of sperm cells, which occurs in the male gonads or testes. ... it is the creation of spermatids from secondary spermatocytes through mitosis ... Not to be confused with miosis. ... The term spermatid refers to the haploid male germ cell that results from secondary spermatocyte division. ... Spermiogenesis is the creation of a spermatozoon from a spermatid. ... A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ... Image File history File links Simplified_spermatozoon_diagram. ... Image File history File links Simplified_spermatozoon_diagram. ... A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ...

Purpose

Spermatogenesis produces mature male gametes, commonly called sperm but specifically known as spermatozoa, which are able to fertilize the counterpart female gamete, the oocyte, during conception to produce a single-celled individual known as a zygote. This is the cornerstone of sexual reproduction and involves the two gametes both contributing half the normal set of chromosomes (haploid) to result in a chromosomally normal (diploid) zygote. An oocyte or ovocyte is a female gametocyte or germ cell involved in reproduction. ... The term conception can refer to more than one meaning: Concept Fertilisation This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... It has been suggested that Biparental zygote be merged into this article or section. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ...

To preserve the number of chromosomes in the offspring, which differs between species, each gamete must have half the usual number of chromosomes present in other body cells. Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result. In humans, chromosomal abnormalities arising from incorrect spermatogenesis can result in Down Syndrome, Klinefelter's Syndrome, and spontaneous abortion. Most chromosomally abnormal zygotes will not survive for long after conception; however, plant reproduction is a little more robust, and viable new species may arise from cases of polyploidy. The hierarchy of scientific classification. ... Not to be confused with XYY syndrome or XXX syndrome. ... Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ...

Location

Spermatogenesis takes place within several structures of the male reproductive system. The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation. The seminiferous tubules of the testes are the starting point for the process, where stem cells adjacent to the inner tubule wall divide in a centripetal direction—beginning at the walls and proceeding into the innermost part, or lumen—to produce immature sperm. Maturation occurs in the epididymis and involves the acquisition of a tail and hence motility. The male reproductive system is a series of organs located outside of the body and around the pelvic region of a male. ... Male Anatomy The epididymis is part of the human male reproductive system and is present in all male mammals. ... Ejaculation is the ejecting of semen from the penis, and is usually accompanied by orgasm. ... This article needs to be wikified. ...

Stages

Spermatocytogenesis

Schematic diagram of Spermatocytogenesis

Main article: Spermatocytogenesis

Spermatocytogenesis is the male form of gametocytogenesis and results in the formation of spermatocytes possessing half the normal complement of genetic material. In spermatocytogenesis, a diploid spermatogonium divides mitotically to produce a diploid intermediate cell called a primary spermatocyte. Each primary spermatocyte duplicates its DNA and subsequently undergoes meiosis I to produce two haploid secondary spermatocytes. This division implicates sources of genetic variation, such as random inclusion of either parental chromosomes, and chromosomal crossover, to increase the genetic variability of the gamete. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Spermatocytogenesis is the male form of gametocytogenesis. ... Gametocytogenesis is the creation of gametocytes by mitosis of gametogonia. ... Spermatogenesis refers to the creation, or genesis, of sperm cells, which occurs in the male gonads or testes. ... A Spermatogonium (plural: spermatogonia) is an intermediary male gametogonium (a kind of germ cell) in the production of spermatozoa. ... Mitosis is the process in which a cell duplicates its chromosomes to generate two identical cells. ... Spermatogenesis refers to the creation, or genesis, of sperm cells, which occurs in the male gonads or testes. ... Not to be confused with miosis. ... Spermatogenesis refers to the creation, or genesis, of sperm cells, which occurs in the male gonads or testes. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but...

Each cell division from a spermatogonium to a spermatid is incomplete; the cells remain connected to one another by bridges of cytoplasm to allow synchronous development. It should also be noted that not all spermatogonia divide to produce spermatocytes, otherwise the supply would run out. Instead, certain types of spermatogonia divide to produce copies of themselves, thereby ensuring a constant supply of gametogonia to fuel spermatogenesis.

Spermatidogenesis

Main article: Spermatidogenesis

Spermatidogenesis is the creation of spermatids from secondary spermatocytes. Secondary spermatocytes produced earlier rapidly enter meiosis II and divide to produce haploid spermatids. The brevity of this stage means that secondary spermatocytes are rarely seen in histological preparations. it is the creation of spermatids from secondary spermatocytes through mitosis ... The term spermatid refers to the haploid male germ cell that results from secondary spermatocyte division. ...

Spermiogenesis

Main article: Spermiogenesis

During spermiogenesis, the spermatids begin to grow a tail, and develop a thickened mid-piece, where the mitochondria gather and form an axoneme. Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation. The resultant tightly packed chromatin is transcriptionally inactive. The Golgi apparatus surrounds the now condensed nucleus, becoming the acrosome. One of the centrioles of the cell elongates to become the tail of the sperm. Spermiogenesis is the creation of a spermatozoon from a spermatid. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... An axoneme is the core scaffold of the eukaryotic cilia and flagella, which are projections from the cell made up of microtubules. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Protamine is a drug that reverses the anticoagulant effects of heparin by binding to it. ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Diagram of the endomembrane system in a typical eukaryote cell Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... In spermatozoa of many animals, the acrosome is an organelle that develops over the anterior half of the spermatozoons head. ... A centriole in biology is a barrel shaped microtubule structure found in most animal cells and algae though not frequently in plants. ...

Maturation then takes place, which removes the remaining unnecessary cytoplasm and organelles. The excess cytoplasm, known as residual bodies, is phagocytosed by surrounding Sertoli cells in the testes. The resulting spermatozoa are now mature but lack motility, rendering them sterile. The mature spermatozoa are released from the protective Sertoli cells into the lumen of the seminiferous tubule in a process called spermiation. It has been suggested that Cytoplast be merged into this article or section. ... In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. ... Phagocytosis (literally cell-eating) is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ... A Sertoli cell (a kind of sustentacular cell) is a nurse cell of the testes which is part of a seminiferous tubule. ... This article needs to be wikified. ...

The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells with the aid of peristaltic contraction. Whilst in the epididymis they acquire motility and become capable of fertilisation. However, transport of the mature spermatozoa through the remainder of the male reproductive system is achieved via muscle contraction rather than the spermatozoon's recently acquired motility. Male Anatomy The epididymis is part of the human male reproductive system and is present in all male mammals. ... In much of the digestive tract, muscles contract in sequence to produce a peristaltic wave which forces food (called bolus while in the esophagus and chyme below the esophagus) along the alimentary canal. ... The male reproductive system is a series of organs located outside of the body and around the pelvic region of a male. ...

Role of Sertoli cells

Labelled diagram of the organisation of Sertoli cells (red) and spermatocytes (blue) in the testis. Spermatids which have not yet undergone spermination are attached to the lumenal apex of the cell

Main article: Sertoli cell

At all stages of differentiation, the spermatogenic cells are in close contact with Sertoli cells which are thought to provide structural and metabolic support to the developing sperm cells. A single Sertoli cell extends from the basement membrane to the lumen of the seminiferous tubule, although the cytoplasmic processes are difficult to distinguish at the light microscopic level. Image File history File links Germinal_epithelium_testicle. ... Image File history File links Germinal_epithelium_testicle. ... A Sertoli cell (a kind of sustentacular cell) is a nurse cell of the testes which is part of a seminiferous tubule. ...

Sertoli cells serve a number of functions during spermatogenesis, they support the developing gametes in the following ways:

• Maintain the environment necessary for development and maturation via the blood-testis barrier
• Secrete substances initiating meiosis
• Secrete supporting testicular fluid
• Secrete androgen-binding protein, which concentrates testosterone in close proximity to the developing gametes
• Secrete hormones effecting pituitary gland control of spermatogenesis, particularly the polypeptide hormone, inhibin
• Phagocytose residual cytoplasm left over from spermiogenesis

The blood-testis barrier (abbreviated as BTB) is a barrier between the blood vessels and the seminiferous tubules of the animal testes. ... Androgen-binding protein (ABP) is a glycoprotein (beta-globulin) produced by the Sertoli cells in the seminiferous tubules of the testis that binds specifically to testosterone (T), dihydrotestosterone (DHT), and 17-beta-estradiol. ... Testosterone is a steroid hormone from the androgen group. ... Inhibin is a peptide that is an inhibitor of FSH synthesis and secretion and participates in the regulation of the menstrual cycle. ...

Influencing factors

The process of spermatogenesis is highly sensitive to fluctuations in the environment, particularly hormones and temperature. Testosterone is required in large local concentrations to maintain the process, which is achieved via the binding of testosterone by androgen binding protein present in the seminiferous tubules. Testosterone is also produced by interstitial cells, also known as Leydig cells, which preside adjacent to the seminiferous tubules. Norepinephrine A hormone (from Greek όρμή - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Androgen binding protein is a protein produced by the Sertoli cells in the seminiferous tubules that binds androgen hormones like testosterone. ... Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testes. ...

Seminiferous epithelium is sensitive to elevated temperature in humans and some other species, and will be adversely affected by temperatures exceeding 4°C - 5°C less than normal body temperature. Consequently, the testes are located outside the body in a sack of skin called the scrotum. Optimal temperature is maintained by the retraction and relaxation of the scrotum towards and away from the heat of the body depending on the environmental temperature. In some male mammals, the scrotum is a protuberance of skin and muscle containing the testicles. ...

Dietary deficiencies (such as vitamins B, E and A), anabolic steroids, metals (cadmium and lead), x-ray exposure, dioxin, alcohol, and infectious diseases will also adversely affect the rate of spermatogenesis. Anabolic steroids are a class of natural and synthetic steroid hormones that promote cell growth and division, resulting in growth of muscle tissue and sometimes bone size and strength. ... Dioxin is the common name for the group of compounds classified as polychlorinated dibenzodioxins (PCDDs). ...

Hormonal control

Hormonal control of spermatogenesis varies among species. In humans the mechanism are not completely understood, however it is known that initiation of spermatogenesis occurs at puberty due to the interaction of the hypothalamus, pituitary gland and Leydig cells. If the pituitary gland is removed, spermatogenesis can still be initiated by follicle stimulating hormone and testosterone. The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in a small, bony cavity (sella turcica) covered by a dural fold (sellar diaphragm) at the base of the brain. ... Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testes. ... Follicle stimulating hormone (FSH) is a hormone produced by gonadotropes in the anterior pituitary gland. ... Testosterone is a steroid hormone from the androgen group. ...

Follicle stimulating hormone stimulates both the production of androgen binding protein by Sertoli cells, and the formation of the blood-testis barrier. Androgen binding protein is essential to concentrating testosterone in levels high enough to initiate and maintain spermatogenesis, which can be 20-50 times higher than the concentration found in blood. Follicle stimulating hormone may initiate the sequestering of testosterone in the testes, but once developed only testosterone is required to maintain spermatogenesis. However, increasing the levels of follicle stimulating hormone will increase the production of spermatozoa by preventing the apoptosis of type A spermatogonia. The hormone inhibin acts to decrease the levels of follicle stimulating hormone. Androgen binding protein is a protein produced by the Sertoli cells in the seminiferous tubules that binds androgen hormones like testosterone. ... The blood-testis barrier (abbreviated as BTB) is a barrier between the blood vessels and the seminiferous tubules of the animal testes. ... Androgen binding protein is a protein produced by the Sertoli cells in the seminiferous tubules that binds androgen hormones like testosterone. ... A section of mouse liver showing an apoptotic cell indicated by an arrow // Apoptosis is a process of deliberate life relinquishment by a cell in a multicellular organism. ...

The Sertoli cells themselves mediate parts of spermatogenesis though hormone production. They are capable of producing the hormones estradiol and inhibin. The Leydig cells are also capable of producing estradiol in addition to their main product testosterone. Estradiol (17β-estradiol) (also oestradiol) is a sex hormone. ... Inhibin is a peptide that is an inhibitor of FSH synthesis and secretion and participates in the regulation of the menstrual cycle. ... Estradiol (17β-estradiol) (also oestradiol) is a sex hormone. ...

See also

• Folliculogenesis
• Germ cells
• Oogenesis
• Sertoli cells
• Sperm count

In biology, folliculogenesis refers to the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Oogenesis or rarely oögenesis is the creation of an ovum (egg cell). ... The Sertoli cell is the nurse cell of the testes. ... The sperm count is a measure of fertility in a man. ...

References

Year 2006 (MMVI) was a common year starting on Sunday (link displays full 2006 calendar) of the Gregorian calendar. ... is the 331st day of the year (332nd in leap years) in the Gregorian calendar. ...

External links

• Spermatogenesis - male reproductive physiology - Am Fam Physician 2000;62:1095.