Chapter Summary

Introduction to Cytology

1. Cells are the structural and functional units of the body. Cellular function is referred to as metabolism and the study of cells is referred to as cytology.
2. Cellular function depends on the specific membranes and organelles characteristic of each type of cell.
3. All cells have structural modifications that serve functional purposes.

Cellular Chemistry

1. Four elements (oxygen, carbon, hydrogen, and nitrogen) compose over 95% of the body's mass and are linked together to form inorganic and organic compounds.
2. Water is the most abundant inorganic compound in cells and is an excellent solvent.
1. Water is important in temperature control and hydrolysis.
2. Dehydration, a condition in which fluid loss exceeds fluid intake, may be a serious problem, especially in infants.

3. Electrolytes are inorganic compounds that form ions when dissolved in water.
1. The three classes of electrolytes are acids, bases, and salts.
2. Electrolytes are important in maintaining pH, in conducting electrical currents, and in regulating the activity of enzymes.

4. Proteins are organic compounds that may exist by themselves or be conjugated with other compounds.
1. Proteins are important structural components of the body and are necessary for cellular growth, repair, and division.
2. Enzymes and hormones are examples of specialized proteins.

5. Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen, with a 2:1 ratio of hydrogen to oxygen.
1. The carbohydrate group includes the starches and sugars.
2. Carbohydrates are the most abundant source of cellular energy.

6. Lipids are organic fats and fat-related substances.
1. Lipids are composed primarily of carbon, hydrogen, and oxygen.
2. Lipids serve as an important source of energy, form parts of membranes, and protect and insulate various parts of the body.

Cellular Structure

1. A cell is composed of a cell membrane, cytoplasm and organelles, and a nucleus.
2. The cell membrane, composed of phospholipid and protein molecules, encloses the contents of the cell and regulates the passage of substances into and out of the cell.
1. The permeability of the cell membrane depends on its structure, the size of the molecules, ionic charge, lipid solubility, and the presence of carrier molecules.
2. Cell membranes may be specialized with such structures as microvilli, sacs, and hair cells.

3. Cytoplasm refers to the material between the cell membrane and the nucleus. Nucleoplasm is the material within the nucleus. Protoplasm is a collective term for both the cytoplasm and nucleoplasm.
4. Organelles are specialized components within the cytoplasm of cells.
1. Endoplasmic reticulum provides a framework within the cytoplasm and forms a site for the attachment of ribosomes. It functions in the synthesis of lipids and proteins and in cellular transport.
2. Ribosomes are particles of protein and RNA that function in protein synthesis. The protein particles may be used within the cell or secreted.
3. The Golgi complex consists of membranous vesicles that synthesize glycoproteins and secrete lipids. The Golgi complex is extensive in secretory cells, such as those of the pancreas and salivary glands.
4. Mitochondria are membranous sacs that consist of outer and inner mitochondrial layers and folded membranous extensions of the inner layer called cristae. The mitochondria produce ATP and are called the "powerhouses" of a cell.
5. Lysosomes are spherical bodies that contain digestive enzymes. They are abundant in the phagocytic white blood cells.
6. Peroxisomes are enzyme-containing membranous sacs that are abundant in the kidneys and liver. Some of the enzymes in peroxisomes generate hydrogen peroxide, and one of them, catalase, breaks down excess hydrogen peroxide.
7. The centrosome is the dense area of cytoplasm near the nucleus that contains the centrioles. The paired centrioles play an important role in cell division.
8. Vacuoles are membranous sacs that function as storage chambers.
9. Fibrils and microtubules provide support in the form of a cytoskeleton.
10. Cilia and flagella are projections of the cell that have the same basic structure and that function in producing movement.

5. The cell nucleus is enclosed in a nuclear membrane that controls the movement of substances between the nucleoplasm and the cytoplasm.
1. The nucleoli are small bodies of protein and RNA within the nucleus that produce ribosomes.
2. Chromatin is a coiled fiber of protein and DNA that shortens to form chromosomes during cell reproduction.

Cell Cycle

1. The cell cycle consists of growth, synthesis, and mitosis.
1. Growth is the increase in cellular mass that results from metabolism. Synthesis is the production of DNA and RNA to regulate cellular activity. Mitosis is the splitting of the cell's nucleus and cytoplasm that results in the formation of two diploid cells.
2. Mitosis permits an increase in the number of cells (body growth) and allows for the replacement of damaged, diseased, or worn-out cells.

2. A DNA molecule is in the shape of a double helix. The structural unit of the molecule is a nucleotide, which consists of deoxyribose (sugar), phosphate, and a nitrogenous base.
3. Cell division consists of a division of the chromosomes (mitosis) and a division of the cytoplasm (cytokinesis). The stages of mitosis include prophase, metaphase, anaphase, and telophase.