خلية نطفية

Figure 1. The process of spermatogenesis as the cells progress from spermatogium, to primary spermatocytes, to secondary spermatocytes, to spermatids and to Sperm.

الخلية النطفية Spermatocytes are a type of male gametocyte in animals. They derive from immature germ cells called spermatogonia. They are found in the testis, in a structure known as the seminiferous tubules.[1] There are two types of spermatocytes, primary and secondary spermatocytes (Figure 1). Primary and secondary spermatocytes are formed through the process of spermatocytogenesis (Figure 3).[2]

Primary spermatocytes are diploid (2N) cells. After Meiosis I, two secondary spermatocytes are formed. Secondary spermatocytes are haploid (N) cells that contain half the number of chromosomes.[1]

All male animals produce spermatocytes, even hermaphrodites such as C. elegans, which exist as a male or hermaphrodite. In hermaphrodite C. elegans, sperm production occurs first and is then stored in the spermatheca. Once the eggs are formed, they are able to self-fertilize and produce up to 350 progeny.[3]

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النمو

Figure 2. Spermatogonia going through mitosis to form primary spermatocytes in Grasshopper testes.

At puberty, spermatogonia located along the walls of the seminiferous tubules within the testis will be initiated and start to divide mitotically, forming two types of A cells that contain an oval shaped nucleus with a nucleolus attached to the nuclear envelope; one is dark (Ad) and the other is pale (Ap), which can be seen in Figure 3. The Ad cells are spermatogonia that will stay in the basal compartment (outer region of the tubule); these cells are reserve spermatogonial stem cells that do not usually undergo mitosis. Type Ap are actively-dividing spermatogonial stem cells which begin differentiation to type B spermatogonia, which have round nuclei and heterochromatin attached to the nuclear envelope and the center of nucleolus.[4] Type B cells will move on to the adluminal compartment (towards the inner region of tubule) and become primary spermatocytes; this process takes about 16 days to complete.[2][5]

Figure 3. Schematic diagram of Spermatocytogenesis

The primary spermatocytes within the adluminal compartment will continue on to Meiosis I and divide into two daughters cells, known as secondary spermatocytes, a process which takes 24 days to complete. Each secondary spermatocyte will form two spermatids after Meiosis II.[1]

Although spermatocytes that divide mitotically and meiotically are sensitive to radiation and cancer, spermatogonial stem cells are not. Therefore, after termination of radiation therapy or chemotherapy, the spermatognia stems cells may re-initiate the formation of spermatogenesis.[6]

Figure 4. Hormones produced by the Pituitary gland. GnRH is secreted by the hypothalamus, which induces anterior pituitary to produce FSH and LH upon puberty.


دور الهرمونات

ملخص أنواع الخلايا

In the following table, ploidy, copy number and chromosome/chromatid counts listed are for a single cell, generally prior to DNA synthesis and division (in G1 if applicable). Primary spermatocytes are arrested after DNA synthesis and prior to division.[1][2]

Cell Type Ploidy/Chromosomes in human DNA copy number/Chromatids in human Process entered by cell Duration
spermatogonium (types Ad, Ap and B) germ cells diploid (2N) / 46 2C / 46 spermatocytogenesis (Mitosis) 16 days
primary spermatocyte male gametocyte diploid (2N) / 46 4C / 2x46 spermatocytogenesis (Meiosis I ) 24 days
secondary spermatocyte male gametocyte haploid (N) / 23 2C / 46 spermatidogenesis (Meiosis II ) A few hours
spermatids male gametid haploid (N) / 23 1C / 23 spermiogenesis 24 days
spermatozoids sperm haploid (N) / 23 1C / 23 spermiation 64 days (total)

فسيولوجيا

الضرر والتصليح والفشل

تحورات محددة

Figure 5. Wild-type spermatocyte progression compared to repro4 mutated spermatocytes.

تاريخ

Meiosis in Grasshopper testes (primary spermatocytes in zygotene, pachytene, prophase I).

An important discovery in the spermatogenesis process was the identification of the seminiferous epithelial cycle in mammals—work by C.P. Leblound and Y. Clermont in 1952 that studied the spermatogonia, spermatocyte layers and spermatids in rat seminiferous tubules. Another critical discovery was that of the hypothalamic-pituitary-testicular hormone chain, which plays a role in spermatogenesis regulation; this was studied by R. M. Sharpe in 1994.[7]


مقطع عرضي لـ tubule في خصية فأر. تكبير: X 250.
Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids (young spermatozoa).



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صور اضافية


See also

الهامش

  1. ^ أ ب ت ث Boron, Walter F., MD, Ph.D., Editor; Boulpaep, Emile L. (2012). "54". Medical physiology a cellular and molecular approach (Print) (Updated second ed.). Philadelphia: Saunders Elsevier. ISBN  978-1-4377-1753-2 .CS1 maint: Extra text: authors list (link) [صفحة مطلوبة]
  2. ^ أ ب ت Schöni-Affolter, Dubuis-Grieder, Strauch, Franzisk, Christine, Erik Strauch. "Spermatogenesis". Retrieved 22 March 2014.CS1 maint: Multiple names: authors list (link)
  3. ^ Riddle, DL; Blumenthal, T; Meyer, B.J.; et al., eds. (1997). "I, The Biological Model". C. elegans II (2nd ed.). Cold Spring Harbor. NY: Cold Spring Harbor Laboratory Press. Retrieved April 13, 2014.
  4. ^ Boitani, Carla; Di Persio, Sara; Esposito, Valentina; Vicini, Elena (2016-03-05). "Spermatogonial cells: mouse, monkey and man comparison". Seminars in Cell & Developmental Biology. 59: 79–88. doi:10.1016/j.semcdb.2016.03.002. ISSN 1096-3634. PMID 26957475.
  5. ^ Y, Clermont (1966). Renewal of spermatogonia in man. American Journal of Anatomy. pp. 509–524.
  6. ^ Tres, Abraham L. Kierszenbaum, Laura L. (2012). Histology and cell biology : an introduction to pathology (3rd ed.). Philadelphia, PA: Saunders. pp. Chapter 20. ISBN  9780323078429 .
  7. ^ خطأ استشهاد: وسم <ref> غير صحيح؛ لا نص تم توفيره للمراجع المسماة Spermatog history

وصلات خارجية