Transcript Chapter 3 Cells and Tissues

Chapter 3
Cells and Tissues
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CELLS

Size and shape

Human cells vary considerably in size; all are microscopic
 Cells differ notably in shape

Composition

Cells contain cytoplasm—substance found only
in cells
 Organelles—specialized structures within the cytoplasm
 Cell interior—surrounded by plasma membrane
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CELLS (cont.)

Structural parts

Plasma membrane (Figure 3-1)
• Forms outer boundary of cell
• Composed of thin, two-layered membrane
of phospholipids
• Embedded with proteins
• Selectively permeable
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CELLS (cont.)

Cytoplasm (Figure 3-2)
• All cell substance from the nucleus to the plasma membrane
• Cytoskeleton—internal framework of cell


Made up of microfilaments and microtubules
Provides support and movement of cell and organelles
• Other cell parts

Ribosomes
– Made of two tiny subunits of mostly ribosomal RNA (rRNA)
– May attach to rough endoplasmic reticulum or lie free
in cytoplasm
– Manufacture enzymes and other proteins; often called
protein factories
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CELLS (cont.)
• Other cell parts (cont.)

Endoplasmic reticulum (ER)
– Network of connecting sacs and canals
– Carry substances through cytoplasm
– Rough ER collects, folds, and transports proteins made
by ribosomes
– Smooth ER synthesizes chemicals; makes new membrane

Golgi apparatus
– Group of flattened sacs near nucleus
– Collect chemicals into vesicles that move from the smooth
ER outward to the plasma membrane
– Called the chemical processing and packaging center

Mitochondria
– Composed of inner and outer membranous sacs
– Involved with energy-releasing chemical reactions
(cellular respiration)
– Often called power plants of the cell
– Each mitochondrion contains one DNA molecule
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CELLS (cont.)
• Other cell parts (cont.)
 Lysosomes
– Membrane-enclosed packets containing digestive enzymes
– Have protective function (eat microbes)
– Formerly thought to be responsible for apoptosis
(programmed cell death)
 Centrosome
– Microtubule-organizing region of the cytoskeleton near
the nucleus
– Centrioles—paired organelles that lie at right angles
to each other within the centrosome and function
in moving chromosomes during cell reproduction
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CELLS (cont.)

Other cell parts (cont.)
 Cell
extensions (Figure 3-3)
– Microvilli—short extensions of the plasma membrane that
increase surface area and produce slight movements that
enhance absorption by the cell
– Cilia—Hairlike extensions with inner microtubules found
on free or exposed surfaces of all cells; serve sensory
functions but some are also capable of moving together in
a wavelike fashion to propel mucus across a surface
– Flagella—single projections (much longer than cilia) that
act as “tails” of sperm cells
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CELLS (cont.)

Nucleus
• Controls cell because it contains most of the genetic
code (genome)—instructions for making proteins,
which in turn determine cell structure and function
• Component structures include nuclear envelope,
nucleoplasm, nucleolus, and chromatin granules
• DNA molecules become tightly coiled chromosomes
during cell division
• 46 nuclear chromosomes contain DNA, which
contains the genetic code
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CELLS (cont.)

Relationship of cell structure and function

Every human cell has a designated
function— some help maintain the cell;
others regulate life processes
 Specialized functions of a cell depend
on number and types of organelles
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MOVEMENT OF SUBSTANCE THROUGH
CELL MEMBRANES

Passive transport processes do not require added
energy and result in movement “down a concentration
gradient”

Diffusion (Figure 3-4)
• Substances scatter evenly throughout an available space, with
particles moving from high to low concentration and moving through
channels or carriers in a membrane to reach an equilibrium
(equality of concentration)
• Passive process—it is unnecessary to add energy to the system
• Osmosis is diffusion of water (when some solutes cannot cross
the membrane)
• Dialysis is diffusion of small solute particles

Filtration—movement of water and solutes caused
by hydrostatic pressure on one side of membrane
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MOVEMENT OF SUBSTANCE THROUGH
CELL MEMBRANES (cont.)

Active transport processes occur only in living cells; movement
of substances is “up the concentration gradient”; this requires energy
from ATP
 Ion pumps (Figure 3-5)
• An ion pump is a protein complex in the cell membrane
• Ion pumps use energy from ATP to move substances across cell
membranes against their concentration gradients
• Examples: sodium-potassium pump, calcium pump
• Some ion pumps work with other carriers so that glucose or amino
acids are transported along with ions

Phagocytosis and pinocytosis
• Phagocytosis (“cell eating”)—engulfs large particles in a vesicle
as a protective mechanism; destroys bacteria or debris from tissue
damage (Figure 3-6)
• Pinocytosis (“cell drinking”)—engulfs fluids or dissolved substances
into cells
• Both are active transport mechanisms because they require cell energy
(from ATP) to move the cytoskeleton in a way that engulfs material
and pulls it into the cell
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CELL REPRODUCTION

DNA structure

Large molecule shaped like a spiral staircase;
sugar (deoxyribose) and phosphate units compose
sides of the molecule; base pairs (adenine-thymine
or guanine-cytosine) compose “steps”
 Base pairings are always the same
(complementary base pairing), but the sequence
of base pairs differs in different DNA molecules
• A gene is a specific sequence of base pairs within
a DNA molecule
• Genes dictate formation of enzymes and other
proteins by ribosomes, thereby indirectly determining
a cell’s structure and functions; in short, genes
determine heredity (Figure 3-7)
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CELL REPRODUCTION (cont.)

Genetic code

Genetic information—stored in base-pair
sequences on genes; expressed through protein
synthesis
 RNA molecules and protein synthesis
• DNA—contained in cell nucleus
• Protein synthesis—occurs in cytoplasm, thus genetic
information must pass from the nucleus to the
cytoplasm
• Process of transferring genetic information from
nucleus to cytoplasm where proteins are produced
requires completion of transcription and translation
(Figure 3-8)
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CELL REPRODUCTION (cont.)

Genetic code (cont.)

Transcription
• Double-stranded DNA separates to form messenger RNA
(mRNA)
• Each strand of mRNA duplicates a particular gene
(base-pair sequence) from a segment of DNA
• mRNA molecules pass from the nucleus to the cytoplasm
where they direct protein synthesis in ribosomes and ER

Translation
• Involves synthesis of proteins in cytoplasm by ribosomes
• Requires use of information contained in mRNA
• Codon—a series of three nucleotide bases that act as
a code for specific amino acid
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CELL REPRODUCTION (cont.)

Cell division—reproduction of cell involving division
of the nucleus (mitosis) and the cytoplasm

Two daughter cells result from the division
 Interphase—period when cell is not actively dividing
 DNA replication—process by which each half of a DNA
molecule becomes a whole molecule identical to the
original DNA molecule; precedes mitosis
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CELL REPRODUCTION (cont.)

Mitosis—process in cell division that distributes
identical chromosomes (DNA molecules) to each new
cell formed when the original cell divides; enables cells
to reproduce their own kind; makes heredity possible
(Figure 3-9)
• Prophase—first stage





Chromatin granules become organized
Chromosomes (pairs of linked chromatids) appear
Centrioles move away from nucleus
Nuclear envelope disappears, freeing genetic material
Spindle fibers appear
• Metaphase—second stage


Chromosomes align across center of cell
Spindle fibers attach to each chromatid
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CELL REPRODUCTION (cont.)

Mitosis (cont.)
• Anaphase—third stage
Centromeres break apart
 Separated chromatids are called chromosomes
 Chromosomes are pulled to opposite ends of cell
 Cleavage furrow develops at end of anaphase
• Telophase—fourth stage
 Cell division is completed
 Nuclei appear in daughter cells
 Nuclear envelope and nucleoli appear
 Cytoplasm is divided (cytokinesis)
 Daughter cells become fully functional

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CELL REPRODUCTION (cont.)

Results of cell division
• Two identical cells result from cell division,
growing tissues or replacing old damaged cells
• Differentiation—process by which daughter cells
can specialize and form different kinds of tissue
• Abnormalities of mitotic division can produce
benign or malignant neoplasms
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TISSUES (Tables 3-5 through 3-7)

Epithelial tissue

Covers body and lines body cavities
 Cells packed closely together with little matrix
 Classified by shape of cells (Figure 3-10)
• Squamous
• Cuboidal
• Columnar
• Transitional
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TISSUES (cont.)

Epithelial tissue (cont.)

Also classified by arrangement of cells into one
or more layers: simple or stratified
 Simple squamous epithelium—single layer
of scalelike cells adapted for transport
(e.g., absorption) (Figure 3-11)
 Stratified squamous epithelium—several layers
of closely packed cells specializing in protection
(Figure 3-12)
 Simple columnar epithelium—tall, column-like
cells arranged in a single layer; contain
mucus-producing goblet cells; specialized
for absorption (Figure 3-13)
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TISSUES (cont.)

Epithelial tissue (cont.)

Stratified transitional epithelium—up to 10 layers
of roughly cuboidal-shaped cells that distort to
squamous shape when stretched; found in body
areas that stretch, such as urinary bladder
(Figure 3-14)
 Pseudostratified epithelium—single layer of
distorted columnar cells; each cell touches
basement membrane
 Simple cuboidal epithelium—single layer of
cubelike cells often specialized for secretory
activity; may secrete into ducts, directly into blood,
and on body surface (Figure 3-15)
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TISSUES (cont.)

Connective tissue



Most abundant and widely distributed tissue in body, with many
different types, appearances, and functions
Relatively few cells in intercellular matrix
Types
• Areolar (loose connective) tissue—fibrous glue (fascia) that holds organs
•
•
•
•
•
•
together; collagenous and elastic fibers, plus a variety of cell types
Adipose (fat) tissue—lipid storage, metabolism regulation; brown fat
produces heat (Figure 3-16)
Reticular tissue—delicate net of collage fibers, as in bone marrow
Dense fibrous tissue—bundles of strong collagen fibers; example
is tendon (Figure 3-17)
Bone tissue—matrix is calcified; functions as support and protection
(Figure 3-18)
Cartilage tissue—matrix is consistency of gristle-like gel; chondrocyte
is cell type (Figure 3-19)
Blood tissue—matrix is fluid; functions are transportation and protection
(Figure 3-20)
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TISSUES (cont.)

Muscle tissue (Figures 3-21 to 3-23)

Types
• Skeletal muscle tissue—attaches to bones; also
called striated or voluntary; control is voluntary;
striations apparent when viewed under a microscope
(Figure 3-21)
• Cardiac muscle tissue—also called striated
involuntary; composes heart wall; ordinarily cannot
control contractions (Figure 3-22)
• Smooth muscle tissue—also called nonstriated
(visceral) or involuntary; no cross striations; found
in blood vessels and other tube-shaped organs
(Figure 3-23)
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TISSUES (cont.)

Nervous tissue (Figure 3-24)

Function—rapid communication between body
structures and control of body functions
 Neurons
• Conduction cells
• All neurons have cell body and two types of
processes: axon and dendrite
 Axon (one) carries nerve impulse away from
cell body
 Dendrites (one or more) carry nerve impulse
toward cell body
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