Testes And Male Tract Notes
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Testes and male tract Male strategy
-males mate opportunistically from puberty to old age- testis produces large number of active spermatozoa continuously
-this requires continuous division of stem cells- the development of 1 spermatazoon takes more than days Structure of testis
-Made of seminiferous tubules &
-Seminiferous tubules: 3 stages, increase in number of cells by mitosis, reduction in the number of chromosomes by meisosis, production of mature sperm from spermatids by spermiogenesis
-Interstitum: Leydig cells, Blood, nerves, lymph vessels Function: Production of spermatozoa, male sex hormones Development: Expression of SRY protein within somatic support cells of the XY gonad differentiate into sertoli cells and envelop into germ cells
-7th week: sertoli cells with interstitial cells of the gonad, organise to form testis cords
-Puberty: testis cords become canalised (hole) and differentiate into semineferous tubules. Adjacent to the mesonephros, sertoli cells organise into a set of thin walled
ducts called rete testis- these connect the semineferous tubules with mesonephric tubules
-the mesonephric duct develops into the epididymis, spermatic ducts/vasa deferens, seminal vesicles Epididymis: continued maturation of released spermatozoa, it is a single long and very coiled tube Vas deferens: transports spermatozoa, stores them in its ampulla, contracts in response to NA/ATP stimulation
-coelomic epithelium, separated from testis cords by an intervening layer of connective tissue called tunica albuginea Spermatogenesis
-Primordial germ cells migrate into the gonad during embryogenesis- these cells immature germ cells/spermatogonia - migratory pathway important- teratoma 3 months postnatal- differentiate into type A spermatogonia (diploid)
-At puberty and continuing throughout life, spermatogonia lie next to the basement membrane of stratified epithelial lining of seminiferous tubules- divide mitoticallydiploid complement of 46 chromosomes-After puberty: Further mitosis into spermatogonia B (committed sperm cell) and replenishes stem cell pool, spermatogonia a Meiosis
-Spermatogonia undergo meiosis: Primordial germ cells contain 23 pairs of chromosomes
- primary spermatocytes undergo meiosis 1 to form secondary spermatocytes Meiosis 1:
-DNA replication, converts diploid cell from 2N to 4N- marks the beginning of spermatogenesis, spermatogonium is called the primary spermatocyte
-Prophase: chromosomes condense into double stranded structures, homologous pairing centromere to centromere to form a structure called chiasma (4 chromatids, two centromeres, two chromosomes)
-chiasma formation makes it possible for two homologous chromosomes to exchange segments of DNA by crossing over- recombination of genetic material between maternal and paternal chromosomes is random- increases the genetic variability of gametes
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