Animal-Development

In sexually reproducing organisms males and females produce sex cells,known as gametes.These are swimming sperm in males and ova(eggs)in females.The sperm of human being专业英语tailacrosomeLesson eight第1页/共57页 在在有有性性繁繁殖殖过过程程中中，生生物物的的雄雄性性和和雌雌性性产产生生性性细细胞胞，称称配配子子。雄雄性性生生殖殖细细胞胞是是能能够游动的够游动的卵子卵子精子精子，雌性产生。The eggs of female专业英语Lesson eight第2页/共57页 The process of sperm production,spermatogenesis,takes place in testes.The sperm originate in gonial cells(spermatogonia)in the walls of seminiferous tubules.Spermatocytes produced by mitosis in spermatogonia divide meiotically to generate haploid spermatids.专业英语Lesson eight第3页/共57页 The mature sperm has a tail,a nucleus containing haploid chromosomes,and a front end with an acrosome,the storage site for enzymes that will aid fertilization.专业英语Lesson eight第4页/共57页 精子产生过程，即精子发生在睾丸中。精子精子产生过程，即精子发生在睾丸中。精子产生于输精管壁的性母细胞（精原细胞）。产生于输精管壁的性母细胞（精原细胞）。精原细胞经有丝分裂再减数分裂产生单倍精原细胞经有丝分裂再减数分裂产生单倍体精子细胞，即精母细胞。成熟精子有尾体精子细胞，即精母细胞。成熟精子有尾部，单倍体染色体组，头部有顶体，内部部，单倍体染色体组，头部有顶体，内部储存酶类，有助于受精。储存酶类，有助于受精。http:/ eight第5页/共57页 Ova,which are produced during oogenesis,are generated in gonial cells(oogonia)of the females ovaries.Oocytes then enter a stage of arrest in early meiosis.专业英语Lesson eight第6页/共57页 At a species-specific later point,a final ripening(ovulation)and the first meiotic division occur.A second meiotic division,followed by development of the embryo,takes place if the egg is fertilized.专业英语Lesson eight第7页/共57页 在卵子发生过程中，由卵巢中的性母细胞产在卵子发生过程中，由卵巢中的性母细胞产生。卵母细胞进入减数分裂的抑制阶段。第生。卵母细胞进入减数分裂的抑制阶段。第一次减数分裂产生一个成熟卵。如果卵被受一次减数分裂产生一个成熟卵。如果卵被受精，那么第二次减数分裂伴随胚胎的发育。精，那么第二次减数分裂伴随胚胎的发育。http:/ eight第8页/共57页 Eggs vary greatly in size from species to species and have complex structures.Virtually all developing animal ova are surrounded by helper cells,either follicle cells or nurse cells.Follicle 毛囊细胞毛囊细胞专业英语Lesson eight第9页/共57页 Depending on the species,eggs also store varying amounts of yolk,a reservoir of nutrients produced by digestive-gland cells in the mothers body.Finally,follicle cells or cells of the maternal oviduct provide protective coatings for the egg,including albumen(egg white)and various types of outer membranes and shells.专业英语Lesson eight第10页/共57页The egg of bird专业英语Lesson eight第11页/共57页物种间卵细胞的大小变化很大，并且有复物种间卵细胞的大小变化很大，并且有复杂的结构。实际上，所有发育过程中的卵杂的结构。实际上，所有发育过程中的卵都辅助细胞环绕，要么是滤泡细胞，要么都辅助细胞环绕，要么是滤泡细胞，要么是抚育细胞。因为物种的不同，卵黄贮备是抚育细胞。因为物种的不同，卵黄贮备也不同，即由母体消化腺细胞产生的营养也不同，即由母体消化腺细胞产生的营养储备。最后，滤泡或母体输卵管细胞产生储备。最后，滤泡或母体输卵管细胞产生保护性的卵膜，包括保护性的卵膜，包括清蛋白和各种外部膜清蛋白和各种外部膜及壳。及壳。专业英语Lesson eight第12页/共57页 Frog oocytes have served as model systems for studies of oocyte development.During maturation they produce huge numbers of ribosomes through gene amplification.Large quantities of mRNA may also be made and stored.蛙蛙卵母细胞卵母细胞是卵母细胞发育的系统研究模型。是卵母细胞发育的系统研究模型。在成熟过程中，通过基因扩在成熟过程中，通过基因扩 增产生大量的核糖体。同时增产生大量的核糖体。同时 也产也产 生和储备了大量的生和储备了大量的mRNA。专业英语Lesson eight第13页/共57页专业英语第14页/共57页 Fertilization unites male and female gametes and initiates development.In some species fertilization is external;in others(including most terrestrial animals)it takes place internally.专业英语Lesson eight第15页/共57页 The first contact of the sperm head with the eggs jelly coat triggers the acrosome reaction,in which enzymes are released to digest a hole through the eggs protective layers,and the plasma membrane of the sperm is brought into position to bind to the ovums surface.专业英语Lesson eight第16页/共57页 After fusion of the egg and sperm plasma membranes,the haploid male nucleus with its chromosomes moves into the egg cytoplasm.Fusion also triggers the eggs final meiotic reduction divisions.专业英语Lesson eight第17页/共57页 When sperm and egg nuclei unite,the two sets of chromosomes mingle to create a diploid set.The fertilized egg is now a zygote.专业英语Lesson eight第18页/共57页 雌雄配子结合作用称受精作用，发育开始。雌雄配子结合作用称受精作用，发育开始。某些物种中，是外部受孕；另一些物种，某些物种中，是外部受孕；另一些物种，包括大部分陆生动物，是内部受孕。当精包括大部分陆生动物，是内部受孕。当精子和卵子的胶状膜发生接触时，触发了顶子和卵子的胶状膜发生接触时，触发了顶体反应。释放多种酶而将卵保护膜消解出体反应。释放多种酶而将卵保护膜消解出一个洞。精子的原生质膜与卵子的表面连一个洞。精子的原生质膜与卵子的表面连接起来。精卵原生质膜融合后，单倍体雄接起来。精卵原生质膜融合后，单倍体雄性核进入卵细胞质。融合也触发了卵细胞性核进入卵细胞质。融合也触发了卵细胞最后的减数分裂。当精卵核结合时，两套最后的减数分裂。当精卵核结合时，两套染色体混合产生一个二倍体，即受精卵。染色体混合产生一个二倍体，即受精卵。专业英语第19页/共57页The moment of fertilizetion专业英语Lesson eight第20页/共57页 The eggs cortical reaction serves as a barrier to the entry of more than one sperm.Initially,there is a temporary change in the eggs electrical state,and the egg cell is activated.The final stage of the reaction,the rapid elevation of the fertilization membrane,prevents further sperm penetration.专业英语Lesson eight第21页/共57页 卵卵皮皮层层阻阻止止其其他他的的精精子子进进入入，充充当当壁壁垒垒作作用用。开开始始时时，卵卵电电位位发发生生暂暂时时变变化化，卵卵细细胞胞被被激激活活。反反应应最最后后阶阶段段，受受精精卵卵的的膜膜快快速速隆隆起，阻止更多精子进入。起，阻止更多精子进入。专业英语Lesson eight第22页/共57页 In some species fertilization is not necessary.Instead,parthenogenesis takes place:the egg is spontaneously activated and proceeds to normal embryonic development.对对某某些些物物种种而而言言，受受精精不不是是必必须须的的。孤孤雌雌生生殖殖，即即卵卵自自发发地地被被激激活活并并进进入入正正常常的的胚胚胎胎发发育育过过程程中。中。专业英语Lesson eight第23页/共57页 Cleavage,the major developmental event immediately following fertilization,is a special form of cell division(mitosis).Cleavage produces a blastula,a sheet of cells rounded into a sphere that in most species surrounds a cavity.专业英语Lesson eight第24页/共57页 In the process,the single-celled zygote is divided into many small cells,and yolk,mRNA,ribosomes,and other materials arc distributed to each cell in precise ways.The cells of the blastula,called blastomeres,also each receive a full diploid set of chromosomes.专业英语Lesson eight第25页/共57页 受精后，立即发生卵裂，细胞有丝分裂的特受精后，立即发生卵裂，细胞有丝分裂的特殊过程。卵裂产生一个囊胚，形成的细胞殊过程。卵裂产生一个囊胚，形成的细胞壁球形排列形成一个空腔。在这个过程中，壁球形排列形成一个空腔。在这个过程中，单细胞的受精卵分裂成许多小细胞，卵黄，单细胞的受精卵分裂成许多小细胞，卵黄，mRNA，核糖体和其他物质被精确分配到，核糖体和其他物质被精确分配到每个细胞中。这些囊胚细胞，称卵裂球，每个细胞中。这些囊胚细胞，称卵裂球，每个细胞都有一套二倍体染色体组。每个细胞都有一套二倍体染色体组。专业英语Lesson eight第26页/共57页15专业英语第27页/共57页The prevention to further sperm penetration.Implantation of fertilization专业英语Lesson eight第28页/共57页 There are different patterns of cleavage in different species.The amount of yolk present in the egg is a major factor in determining the pattern:in species having little yolk(such as mammals)the zygote cleaves completely through,forming cells that are roughly equivalent in size.专业英语Lesson eight第29页/共57页 In frogs,in which the egg has somewhat more yolk,cleavage proceeds more rapidly in regions of the embryo having less yolk.In bird eggs the yolk is so massive that cleavage divisions are restricted to a tiny area of cytoplasm.专业英语Lesson eight第30页/共57页 不同物种，卵裂方式不同。决定因素主要取不同物种，卵裂方式不同。决定因素主要取决于卵黄的含量。含有少量卵黄的物种决于卵黄的含量。含有少量卵黄的物种（例如哺乳动物），合子分裂得很彻底，（例如哺乳动物），合子分裂得很彻底，子细胞大致平均分裂。蛙卵，卵黄稍微多子细胞大致平均分裂。蛙卵，卵黄稍微多点，在胚胎的卵黄较少区域发育更快些。点，在胚胎的卵黄较少区域发育更快些。鸟卵卵黄很大，卵裂被限制在细胞质很小鸟卵卵黄很大，卵裂被限制在细胞质很小区域内。区域内。专业英语Lesson eight第31页/共57页 In many species the precise distribution to blastomeres of molecular determinants in the cytoplasm is crucial to proper development of different cell types in the embryo.In mammal and bird species the fate of cells is determined by the position of a cell late in cleavage.专业英语Lesson eight第32页/共57页 细胞质中分子遗传因素精确分配到卵裂球中，细胞质中分子遗传因素精确分配到卵裂球中，对许多物种而言，是发育成胚中不同类型对许多物种而言，是发育成胚中不同类型细胞关键所在。对哺乳动物和鸟类而言，细胞关键所在。对哺乳动物和鸟类而言，细胞的命运最终由细胞分裂后所处的位置细胞的命运最终由细胞分裂后所处的位置决定的。决定的。专业英语Lesson eight第33页/共57页 The rearrangement of the blastula into a three-dimensional organism with inner,middle,and outer layers occurs during gastrulation.The resulting gastrula consists of an outer ectoderm,an inner endoderm,and a mesoderm layer positioned between them.在原肠胚形成过程中，囊胚重新排列，形成包括在原肠胚形成过程中，囊胚重新排列，形成包括内层，中层，外层的三围组织。最终原肠胚由一内层，中层，外层的三围组织。最终原肠胚由一个外肠胚，内肠胚，和一个中肠胚构成。个外肠胚，内肠胚，和一个中肠胚构成。专业英语Lesson eight第34页/共57页The rearrangement of the blastula专业英语Lesson eight第35页/共57页 Each layer gives rise to specific tissues during embryonic development.A variation in gastrulation,involving the movement of cells into endodermal and mesodermal positions through the thickened primitive streak,arose in reptiles and can still be seen in bird and mammalian embryos,lending support to the theory that birds and mammals evolved from reptiles.专业英语Lesson eight第36页/共57页The picture of Gastrula 专业英语Lesson eight第37页/共57页 每个胚层产生特殊的胚胎组织。密实的原肠每个胚层产生特殊的胚胎组织。密实的原肠胚通过细胞运动进入内胚层和中胚层，爬胚通过细胞运动进入内胚层和中胚层，爬虫，鸟，哺乳动物的胚胎都如此。因此提虫，鸟，哺乳动物的胚胎都如此。因此提出这样的理论，鸟类和哺乳动物是由爬行出这样的理论，鸟类和哺乳动物是由爬行动物进化而来的。动物进化而来的。专业英语Lesson eight第38页/共57页 The organs and tissues of the embryo arise during organogenesis as cells inside the embryo and on its surface become specialized.Organogenesis actually includes two closely linked processes,morphogenesis and differentiation.专业英语Lesson eight第39页/共57页 During morphogenesis cells and cell populations change shape:an example is neurulation in vertebrate embryos,in which the edges of the flat neural plate fold upward and fuse,forming the beginnings of the hollow brain and spinal cord.专业英语Lesson eight第40页/共57页A transgenetic rates with the organs of ear 胚经过内部细胞和表面细胞特化后，器官胚经过内部细胞和表面细胞特化后，器官形成，发育成器官和组织。器官形成实质形成，发育成器官和组织。器官形成实质上包括两个联系紧密的过程，即形态发生上包括两个联系紧密的过程，即形态发生和分化。在形态发生期间，细胞和细胞群和分化。在形态发生期间，细胞和细胞群体形状发生改变：例如，脊椎动物的神经体形状发生改变：例如，脊椎动物的神经胚，扁平神经板的边缘向上折叠并融合，胚，扁平神经板的边缘向上折叠并融合，是中空大脑和脊髓神经形成的开端。是中空大脑和脊髓神经形成的开端。专业英语Lesson eight第41页/共57页 During differentiation cells mature so that they may perform separate functions.This maturation may include taking on a function-related shape,such as the long,spindly shape of skeletal-muscle cells.专业英语Lesson eight第42页/共57页 Cell differentiation also results in responsiveness-the ability of a cell to be regulated within the organism through the action of hormones,neurons,and other signals.专业英语Lesson eight第43页/共57页 在分化期间，细胞成熟，执行各自功能。成在分化期间，细胞成熟，执行各自功能。成熟包括功能相关的成型过程。例如，细长熟包括功能相关的成型过程。例如，细长的骨骼肌肉细胞。细胞分化也产生应答能的骨骼肌肉细胞。细胞分化也产生应答能力，即细胞受生物体内激素，神经和其他力，即细胞受生物体内激素，神经和其他信号的调控过程。信号的调控过程。专业英语Lesson eight第44页/共57页The nerve cells The muscle cells专业英语第45页/共57页 The embryos of land vertebrates are enclosed within four extraembryonic membranes that afford protection while still permitting the exchange of gases,nutrients,and other materials.脊脊椎椎动动物物的的胚胚胎胎被被4 4层层膜膜包包被被，起起保保护护作作用用，但仍能交换气体，营养和其他物质。但仍能交换气体，营养和其他物质。专业英语Lesson eight第46页/共57页专业英语第47页/共57页 Growth in embryos is largely due to an increase in the number of cells rather than to an increase in the size of individual cells.In many species the extent of embryonic growth is limited by the availability of food(yolk).专业英语Lesson eight第48页/共57页 In animals that develop entirely free of the maternal body,such as frogs and insects,the embryo give rise to a larval stage that can feed itself and later undergo metamorphosis to attain the adult stage.专业英语Lesson eight第49页/共57页 In many species the most spectacular growth phase takes place during the juvenile and adolescent phases of the life cycle.Actual growth generally stops once the organism reaches its typical adolescent phases of the life cycle.Actual growth generally stops once the organism reaches its typical adult size,although replacement of dead cells may continue.专业英语Lesson eight第50页/共57页 胚的生长很大程度取决于细胞数量的增加而胚的生长很大程度取决于细胞数量的增加而不是单个细胞大小的改变。在大多数物种中，不是单个细胞大小的改变。在大多数物种中，胚的生长是受卵黄的量限制的。在动物细胞胚的生长是受卵黄的量限制的。在动物细胞中，完全依赖于母体，例如蛙和昆虫，胚产中，完全依赖于母体，例如蛙和昆虫，胚产生幼虫状态，后来经历变态而进入成年状态。生幼虫状态，后来经历变态而进入成年状态。在许多物种中，在少年和青春期，发生特别在许多物种中，在少年和青春期，发生特别显著的生长。一旦细胞进入成年状态和成年显著的生长。一旦细胞进入成年状态和成年大小，生长就停止了，尽管新生细胞与死细大小，生长就停止了，尽管新生细胞与死细胞的替代不断发生。胞的替代不断发生。专业英语Lesson eight第51页/共57页 A special type of growth,regeneration of lost body parts,can take place in adults of some species.Prior to such regeneration cells in stump tissue undergo dedifferentiation.They lose their functional phenotype,divide rapidly,and generate a population of cells that will regenerate the lost part.专业英语Lesson eight第52页/共57页 Compensatory hypertrophy is a different,temporary growth response in which residual tissue increases in mass and cell number:cells undergo mitosis but do not dedifferentiate.专业英语Lesson eight第53页/共57页 一个特殊类型的生长，再生失去的部分躯体，一个特殊类型的生长，再生失去的部分躯体，发生在某些物种的成体中。在再生之前，发生在某些物种的成体中。在再生之前，残肢组织细胞经历了去分化过程。他们失残肢组织细胞经历了去分化过程。他们失去功能表型，快速分裂，产生细胞群来再去功能表型，快速分裂，产生细胞群来再生失去的部分。代偿式肥大是一个不同的，生失去的部分。代偿式肥大是一个不同的，暂时的生长应答过程，残余组织在体积和暂时的生长应答过程，残余组织在体积和细胞数量上增加：细胞经历了有丝分裂，细胞数量上增加：细胞经历了有丝分裂，但没有脱分化过程。但没有脱分化过程。专业英语Lesson eight第54页/共57页 Aging is an ongoing,time-dependent developmental process in which body parts deteriorate.Proposed causes include the degeneration of collagen(the fibrous proteins of the connective tissues)and limits on the number of times cells can divide.Other theories focus on a decline of the immune system or on the accumulation of lipofuscins(aging pigments).专业英语Lesson eight第55页/共57页 老化是一个持续过程，随时间发育，身体部老化是一个持续过程，随时间发育，身体部分恶化。可能原因包括胶质的退化（纤维分恶化。可能原因包括胶质的退化（纤维蛋白）和能分裂活细胞的限制。另外理论蛋白）和能分裂活细胞的限制。另外理论认为，老化是由免疫系统的免疫下降或脂认为，老化是由免疫系统的免疫下降或脂褐素的堆积造成的。褐素的堆积造成的。专业英语Lesson eight第56页/共57页 第57页/共57页