Transcript The Cell

Human Anatomy,
First Edition
McKinley & O'Loughlin
Chapter 2 Lecture Outline:
The Cell: Basic Unit of Structure
and Function
1
The Cell
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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.
2-2
Common Characteristics of
Cells
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All cells perform the general functions
necessary to sustain life.
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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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4
Cells
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Most cells in the human body are between 1
micrometer (mm) and 100 mm in diameter.
Individual cells are usually observed by light
microscopy
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Subcellular structures are studied by electron
microscopy.
2-5
Plasma (Cell)
Membrane
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The plasma
membrane
forms the
outer, limiting
barrier
separating the
internal
contents of the
cell from
external
materials.
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Cytoplasm
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Cytoplasm is a general term for all
cellular contents located between the
plasma membrane and the nucleus.
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Nucleus
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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
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Requires the participation of specific
transport proteins that help specific
substances or molecules move across
the plasma membrane.
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Bulk Filtration
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Involves the diffusion of both solvents
and solutes together across the
selectively permeable membrane.
2-11
Active Transport
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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
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Active transport processes that move
ions across the membrane are called ion
pumps.
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ion pumps allow a cell to maintain its
internal concentrations of small molecules
or ions
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Bulk Transport - Exocytosis
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The means by which large molecules
are secreted from the cell is called
exocytosis.
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Bulk Transport - Endocytosis
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Endocytosis is a process whereby the cell acquires
materials from the extracellular fluid. (3 Forms)
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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
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Movement of substances along a
concentration gradient
ATP is not required
2-19
Organelles
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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
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Mitochondria are organelles with a
double membrane.
Produce large amounts of ATP.
Are called the “powerhouses” of the
cell.
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Ribosomes
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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
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Filamentous proteins form the
cytoskeleton, which helps give the cell
its shape and coordinates cellular
movements.
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microfilaments
intermediate filaments
microtubules
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Membranous Organelles
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Some organelles are surrounded by a
membrane.
They are called membrane-bound
organelles, or membranous organelles.
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Cilia and Flagella
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Appendages extending from the surface
of some cells.
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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
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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
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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
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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
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DNA is the genetic material housed
within the nucleus of the cell.
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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
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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
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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
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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
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Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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Tumor
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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
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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
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Cancer is the general term used to describe a
group of diseases characterized by various
types of malignant neoplasms.
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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
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Cancer cells lose control of their cell
cycle.
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they divide too frequently and grow out of
control
cancer cells lose contact inhibition
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they overgrow one another and lack the ability
to stop growing and dividing when they crowd
other cells
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Cancer Cells
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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.
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