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| A group of cells working together to perform a specific function |
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- epithelial
- connective
- muscle
- nerve
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Epithelial cells cover, line, and protect the body and its internal organs.
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Connective tissue is the framework of the body, it provides support and structure for the organs.
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Nerve tissue is composed of neurons and connective tissue cells referred to as neuroglia.
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Muscle tissues have the ability to contract or shorten. Muscle tissue is classified as voluntary muscle (skeletal muscles) or involuntary muscle (smooth muscle and cardiac muscle tissue).
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The cell is the basic unit of life and the building block of tissues and organs. Within the cell, each organelle has a specific function. The nucleus, which contains deoxyribonucleic acid (DNA), and ribosomes are important in the synthesis of proteins. Proteins include the enzymes that regulate all chemical reactions within the body.
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Mitosis is necessary for growth and repair. In this process, the DNA is duplicated and distributed evenly to two daughter cells.
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Meiosis is the special cell division that takes place in the gonads - the ovaries and testes. In the process of meiosis, the chromosome number is reduced from 46 to 23.Therefore, after an egg and sperm are united during fertilization, the resulting zygote has 23 pairs of homologous chromosomes, one in each pair from the egg and one from the sperm. When the zygote undergoes mitosis to begin to form an embryo, each cell will have the normal number of 46 chromosomes.
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The skin is the largest organ of the body. The skin consists of two layers: the epidermis (the outermost protective layer of dead keratinized epithelial cells) and the dermis (the underlying layer of connective tissue with blood vessels, nerve endings, and the associated skin structures). The dermis rests on the subcutaneous tissue that connects the skin to the superficial muscles.
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(the outermost protective layer of dead keratinized epithelial cells).The layers of the epidermis, from outer layer to inner layer, are the stratum corneum, the stratum lucidum , the stratum granulosum, and the innermost stratum germinativum (includes stratum basale and stratum spinosum), where mitosis occurs.Epidermal cells contain the protein pigment called melanin, which protects against radiation from the sun.
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- outer layer stratum corneum
- stratum lucideum
- stratum granulosum
- inner layer stratum germinativum
- stratum basale
- stratum spinosum
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The inner layer of the skin is the dermis, composed of fibrous connective tissue with blood vessels, sensory nerve endings, hair follicles, and glands.
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The most widely distributed sweat glands regulate body temperature by releasing a watery secretion that evaporates from the surface of the skin. This type of sweat gland is known as eccrine. The other sweat glands, mainly in the armpits and groin area, display apocrine secretion . This secretion contains bits of cytoplasm from the secreting cells. This cell debris attracts bacteria, and the presence of the bacteria on the skin results in body odor. The sebaceous glands release an oily secretion (sebum) through the hair follicles that lubricates the skin and prevents drying. Oil is produced by holocrine secretion, in which whole cells of the gland are part of the secretion. These glands are susceptible to becoming clogged and attracting bacteria , particularly during adolescence.
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include hair and nails. Both are composed of a strong protein called keratin.
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