Stem Cells | 干细胞

📚 Stem Cells | 干细胞

Stem cells are unspecialised cells that can divide repeatedly and differentiate into specialised cell types. In A-Level Biology, understanding stem cell potency, sources and applications is essential, especially in the context of cell differentiation, developmental biology and medical biotechnology.

干细胞是未特化的细胞，能够反复分裂并分化为特化的细胞类型。在 A-Level 生物课程中，理解干细胞的潜能、来源和应用至关重要，尤其是在细胞分化、发育生物学和医学生物技术方面。

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1. Definition and Key Features | 定义与关键特征

A stem cell is defined by two key properties: self-renewal and potency. Self-renewal means the cell can undergo many mitotic divisions while remaining undifferentiated. Potency refers to the range of cell types that a stem cell can produce by differentiation.

干细胞的定义基于两个关键特性：自我更新和分化潜能。自我更新是指细胞能够经历多次有丝分裂，同时保持未分化状态。分化潜能是指干细胞通过分化所能产生的细胞类型范围。

Unlike specialised cells such as neurons or erythrocytes, stem cells do not have a fixed terminal function. They provide a reservoir for growth, repair and replacement of damaged or worn-out cells throughout the life of an organism.

与神经元或红细胞等特化细胞不同，干细胞没有固定的终末功能。它们为生物体一生中的生长、修复以及受损或衰老细胞的替换提供储备。

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2. Potency Hierarchy | 潜能等级

Stem cells are classified by their potency. Totipotent stem cells can give rise to all cell types of an organism, including embryonic and extra-embryonic tissues. In mammals, the zygote and early morula cells are totipotent.

干细胞按潜能分类。全能干细胞能够产生生物体的所有细胞类型，包括胚胎和胚外组织。在哺乳动物中，受精卵和早期桑葚胚细胞是全能干细胞。

Pluripotent stem cells can differentiate into all cell types of the three germ layers (ectoderm, mesoderm and endoderm) but cannot form extra-embryonic structures such as the placenta. Embryonic stem cells from the inner cell mass of the blastocyst are pluripotent.

多能干细胞能够分化为三个胚层（外胚层、中胚层和内胚层）的所有细胞类型，但不能形成胎盘等胚外结构。来自囊胚内细胞团的胚胎干细胞是多能干细胞。

Multipotent stem cells can differentiate into a limited range of cell types, usually within one tissue or lineage. Haematopoietic stem cells in bone marrow are multipotent because they can form red blood cells, white blood cells and platelets.

专能干细胞通常只能分化为一个组织或谱系内的有限细胞类型。骨髓中的造血干细胞是专能干细胞，因为它们可以形成红细胞、白细胞和血小板。

Unipotent stem cells can produce only one differentiated cell type but retain the ability to self-renew. An example is the spermatogonial stem cell, which produces sperm cells.

单能干细胞只能产生一种分化细胞类型，但保留自我更新能力。一个例子是精原干细胞，它产生精子细胞。

Type	Potency	Examples
Totipotent	All embryonic + extra-embryonic cells	Zygote, early morula
Pluripotent	All body cells (three germ layers)	Embryonic stem cells, iPSCs
Multipotent	Several related cell types	Haematopoietic stem cells
Unipotent	One cell type	Spermatogonial stem cells

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3. Embryonic Stem Cells | 胚胎干细胞

Embryonic stem cells (ESCs) are obtained from the inner cell mass of a blastocyst, about five to six days after fertilisation. At this stage, the embryo is a hollow ball of cells, and the inner cell mass would normally develop into the fetus.

胚胎干细胞（ESC）取自受精后约五到六天的囊胚内细胞团。此时胚胎是一个中空的细胞球，内细胞团正常情况下将发育为胎儿。

ESCs are pluripotent and can divide indefinitely in culture while retaining the ability to differentiate into any cell type of the body. This makes them valuable for research into early development and for potential regenerative therapies.

胚胎干细胞是多能干细胞，在培养中能够无限分裂，同时保持分化为身体任何细胞类型的能力。这使得它们在早期发育研究和潜在的再生疗法中具有重要价值。

However, obtaining ESCs involves destruction of the embryo, which raises ethical concerns. The inner cell mass cells are removed before the embryo can implant, so some people view this as ending a potential human life.

然而，获取胚胎干细胞涉及破坏胚胎，这引发了伦理问题。内细胞团细胞在胚胎着床前被取出，因此有些人认为这终结了一个潜在的人类生命。

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4. Adult Stem Cells | 成体干细胞

Adult stem cells, also called somatic stem cells, are found in various tissues of the body, including bone marrow, skin, gut epithelium, brain and muscle. They are usually multipotent or unipotent and function in tissue maintenance and repair.

成体干细胞，也称为体干细胞，存在于身体的多种组织中，包括骨髓、皮肤、肠上皮、大脑和肌肉。它们通常是专能或单能干细胞，功能是维持和修复组织。

Haematopoietic stem cells in bone marrow are the best-studied adult stem cells. They continuously produce blood cells and are used in bone marrow transplants to treat leukaemia and other blood disorders.

骨髓中的造血干细胞是研究最深入的成体干细胞。它们持续产生血细胞，并用于骨髓移植以治疗白血病和其他血液疾病。

Adult stem cells are less controversial than embryonic stem cells because they can be harvested from the patient’s own body. However, they are less flexible in their differentiation potential and can be difficult to isolate and grow in large numbers.

成体干细胞比胚胎干细胞的争议小，因为它们可以从患者自身体内获取。然而，它们的分化潜能较小，且难以分离和大量培养。

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5. Induced Pluripotent Stem Cells | 诱导多能干细胞

Induced pluripotent stem cells (iPSCs) are adult somatic cells that have been genetically reprogrammed to an embryonic-like pluripotent state. This is achieved by introducing specific transcription factors such as Oct4, Sox2, Klf4 and c-Myc.

诱导多能干细胞（iPSC）是通过基因重编程使其回到类似胚胎多能状态的成体体细胞。这一过程通过导入特定转录因子（如 Oct4、Sox2、Klf4 和 c-Myc）实现。

iPSCs avoid the ethical problems associated with embryo destruction because they are derived from adult cells such as skin fibroblasts. They also allow patient-specific cell lines to be produced, which may reduce immune rejection in future therapies.

诱导多能干细胞避免了与破坏胚胎相关的伦理问题，因为它们来源于皮肤成纤维细胞等成体细胞。它们还可以制备患者特异性细胞系，这在未来治疗中可能减少免疫排斥。

Nevertheless, the reprogramming process carries risks such as incomplete differentiation, genetic mutations and the potential to form teratomas. These risks must be controlled before iPSCs can be used safely in clinical medicine.

然而，重编程过程存在风险，如分化不完全、基因突变以及形成畸胎瘤的可能性。在 iPSC 安全用于临床医学之前，必须控制这些风险。

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6. Sources and Ethical Considerations | 来源与伦理考量

Human stem cells can be obtained from several sources: embryonic stem cells from IVF surplus embryos, fetal tissue, umbilical cord blood, adult tissues, and induced pluripotent stem cells reprogrammed from the patient.

人类干细胞可以从多种来源获取：来自体外受精剩余胚胎的胚胎干细胞、胎儿组织、脐带血、成体组织，以及从患者重编程得到的诱导多能干细胞。

The use of embryonic stem cells is ethically debated because it involves the destruction of a blastocyst. Some argue that the blastocyst has the potential to develop into a person and should be protected. Others argue that the benefits of treating severe diseases outweigh the moral concerns.

胚胎干细胞的使用在伦理上存在争议，因为它涉及破坏囊胚。一些人认为囊胚有发育成人的潜能，应受到保护。另一些人则认为治疗严重疾病的好处大于道德顾虑。

Umbilical cord blood and adult stem cells raise fewer ethical objections because no embryo is destroyed. Cord blood can be collected after birth and stored for potential future use, although the number

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