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Human Anatomy, First EditionMcKinley & O'Loughlin

Chapter 2 Lecture Outline: The Cell: Basic Unit of Structure and Function

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The Cell Cells are the structural and functional

units of all living organisms. They are the building blocks of the

human body. An adult human body contains about 75

trillion cells. Each cell type in the body performs

specific functions.

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Common Characteristics of Cells All cells perform the general

functions necessary to sustain life. Obtain nutrients and other materials

essential for survival from its surrounding fluids.

Dispose of the wastes they produce Shape and integrity Cell division

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Cells Most cells in the human body are

between 1 micrometer (mm) and 100 mm in diameter.

Individual cells are usually observed by light microscopy Subcellular structures are studied by

electron microscopy.

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Plasma (Cell) Membrane The plasma

membrane forms the outer, limiting barrier separating the internal contents of the cell from external materials.

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Cytoplasm Cytoplasm is a general term for all

cellular contents located between the plasma membrane and the nucleus.

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Nucleus The nucleus is the cell’s control

center. It controls protein synthesis and

directs the functional and structural characteristics of the cell.

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Facilitated Diffusion Requires the participation of

specific transport proteins that help specific substances or molecules move across the plasma membrane.

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Bulk Filtration Involves the diffusion of both

solvents and solutes together across the selectively permeable membrane.

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Active Transport Movement of a substance across a plasma

membrane against a concentration gradient. Materials must be moved from an area of low

concentration to an area of high concentration. requires cellular energy in the form of ATP

(adenosine triphosphate) and sometimes a transport protein as well

ATP is continually synthesized by mitochondria

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Ion Pumps Active transport processes that

move ions across the membrane are called ion pumps. ion pumps allow a cell to maintain its

internal concentrations of small molecules or ions

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Bulk Transport - Exocytosis The means by which large

molecules are secreted from the cell is called exocytosis.

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Bulk Transport - Endocytosis Endocytosis is a process whereby the cell

acquires materials from the extracellular fluid. (3 Forms)

phagocytosis occurs when membrane extensions, termed pseudopodia, engulf a particle and internalize it into a vacuole

pinocytosis is the incorporation of droplets of extracellular fluid into the cell in small vesicles

receptor-mediated endocytosis is when receptors with specific molecules bound to them aggregate within the membrane, and then an invagination forms around them to create a cytoplasmic vesicle

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Passive Transport Movement of substances along a

concentration gradient ATP is not required

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Organelles Organelles are complex, organized

structures with unique, characteristic shapes.

Each type of organelle performs a different function for the cell.

Collectively, the specialized functions of all organelles are essential for normal cellular structure and activities.

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Mitochondria Mitochondria are organelles with a

double membrane. Produce large amounts of ATP. Are called the “powerhouses” of

the cell.

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Ribosomes Ribosomes are very small, dense

granules that are responsible for protein production (synthesis).

Each ribosome has a small and a large subunit.

The small subunit is about one-half the size of the large subunit.

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The Cytoskeleton Filamentous proteins form the

cytoskeleton, which helps give the cell its shape and coordinates cellular movements. microfilaments intermediate filaments microtubules

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Membranous Organelles Some organelles are surrounded

by a membrane. They are called membrane-bound

organelles, or membranous organelles.

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Cilia and Flagella Appendages extending from the

surface of some cells. Cilia usually occur in large numbers;

they work together to move materials or fluids along the surface of a cell.

Flagella are longer than cilia, and usually occur as single appendages.

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The Nucleus The nucleus is the central core, or

the control center, of cellular activities.

Usually, it is the largest structure within the cell and appears as a single spherical or oval structure.

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The Nucleus The nucleus is enclosed by a

double membrane structure called the nuclear envelope.

The nuclear envelope controls the entry and exit of materials between the nucleus and the cytoplasm.

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Nucleolus The cell nucleus may contain one

or more usually spherical, darkstaining bodies called nucleoli.

Nucleoli are responsible for making the small and the large subunits or ribosomes.

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Chromatin and DNA DNA is the genetic material housed

within the nucleus of the cell. DNA is a polymer of nucleotides

(sugar, phosphate, nitrogen base) in the shape of a double helix.

Strands of DNA and histone proteins associate within the nucleus to form chromatin.

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Insert Figure 2.18

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Chromosome The chromosome is the most

organized level of genetic material. Each chromosome contains a

single, long molecule of DNA and associated proteins.

Chromosomes become visible only when the cell is dividing.

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The Cell Cycle The life cycle of the cell is called

the cell cycle. New cells must be made

continuously in order for an organism to grow and replace its damaged cells.

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Mitosis and Meiosis There are two types of cell

division. Mitosis is the cell division process

that takes place in somatic cells. Sex cells undergo a cell division

process called meiosis.

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Mitosis Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

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Tumor Normal tissue development

exhibits a balance between cell division and cell death.

If this balance is upset and cells multiply faster than they die, abnormal growth results in a new cell mass that is called a neoplasm, or tumor.

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Cancer Benign neoplasms usually grow slowly and are

confined within a connective tissue capsule. Cells within these tumors dedifferentiate—that

is, they revert to a less specialized state, and cause an increase in their own vascular supply to support their growth.

These tumors are usually not lethal, but they have the potential to become life-threatening if they compress brain tissue, nerves, blood vessels, or airways.

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Cancer Cancer is the general term used to

describe a group of diseases characterized by various types of malignant neoplasms. unencapsulated contain cells that dedifferentiate increase their vascular supply grow rapidly spread easily to other organs by way of the

blood or lymph (metastasis)

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Cancer Cancer cells lose control of their

cell cycle. they divide too frequently and grow

out of control cancer cells lose contact inhibition

they overgrow one another and lack the ability to stop growing and dividing when they crowd other cells

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Cancer Cells

Exhibit dedifferentiation and revert to an earlier, less specialized developmental state.

Produce chemicals that cause local blood vessel formation resulting in increased blood vessels in the developing tumor (angiogenesis).

Have the ability to squeeze into any space (invasiveness) permitting them to leave their place of origin and travel elsewhere in the body.

Acquire the ability to metastasize—that is, spread to other organs in the body.