Transcript Chapter 3 Anatomy Notes

Chapter 3: Cells
Humans have 75 – 100 trillion cells
 Cells are the structural and functional
units of the body
 The human body is 65% water
 The intracellular environment is found
within the cell, separated from the
external environment
 Cell lie in a supportive bath that surrounds
them and provides everything they need,
the extracellular environment

The Extracellular Environment
Water, dissolved gases, salts, food
particles, cell products
 Cell products are synthesized by the cell
and released into the extracellular
environment by a process called secretion
 Cell products include hormones, proteins,
vitamins
 Water + products + other substances =
ECF (extracellular fluid)
 The ECF is thick and syrupy
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The ECF
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2 types:
Plasma is found in blood vessels and the
chambers of the heart
Plasma is the liquid that helps transport and float
the cells of blood through the body
Interstitial fluid is found between the cells of the
body
Interstitial fluid provides a pathway between cells
Travel between some areas of the body is restricted
by dense strands of protein that form a Matrix
This matrix provides structural support
Intercellular Environment
 Compartments
of the external
cellular environment found between
adjacent cells
 When cells are close together, these
spaces may contain molecular
bridges
 The bridges connect cells and make
rapid chemical communication
possible
Intracellular Environment
Protoplasm
water, proteins, fats, carbohydrates,
nucleic acids, and electrolytes
 When these substances are organized and
the life processes are being carried out,
protoplasm is called---alive
 Intracellular fluid (ICF) is made up of
water + proteins + other chemicals
 Cell work takes place in the intracellular
environment, e.g. energy production,
energy storage, product synthesis
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Components of Protoplasm
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The plasma membrane-the barrier that
separates intracellular and extracellular
environments

Cytoplasm-a thick, gel-like fluid that
contains all the cell’s organelles

Nucleus-Large, oval-shaped structure that
regulates the cell’s activities
Cell Structure and Function
Human cells vary in size—all are
microscopic
 The human egg cell is ~1000 micrometers
 The human sperm cell is ~ 50
micrometers
 25, 400 micrometers = 1 inch
 Human cells vary widely in shape
 Variation in size and shape is a reflection
of the various roles different cells play in
the body

The Plasma Membrane
Envelops the cell completely
 Regulates movement of materials into and
out of the cell
 Helps maintain homeostasis
 Made up of approximately equal weights
of lipids (fats) and proteins plus a very
small amount of carbohydrates
 Barrier is not solid, it is called selectively
permeable
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Lipids in the Plasma Membrane
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Phospholipids and cholesterol
Phospholipids have a hydrophilic head (attracted
to water) and hydrophobic tails
(repels water)
Due to their opposite interactions with water,
phospholipid molecules form a double-layered
arrangement called the lipid bilayer
At body temperature, the plasma membrane is
liquid (like vegetable oil)
Cholesterol molecules lie in the lipid bilayer and
help provide stability
Proteins in the Plasma Membrane
Peripheral and Integral
 Peripheral are attached to the outside and
inside surfaces of the plasma membrane
 Integral proteins are partially or
completely embedded in the lipid bilayer
 Integral proteins serve as channels for
transport of materials passing through the
membrane
 These openings are called pores

Modifications to the Plasma Membrane
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Modifications in the structure of the plasma membrane
enable some cells to perform special functions

Cells that are close together and cannot move about have 4
Regions:
free surface – exposed to a lumen (open space)
lateral borders- adjacent to neighboring cells
basal surface – attached to a matrix of protein called the
basement membrane
These cells are in the digestive tract, liver, kidney, walls of
the blood vessels
The modifications usually occur at the free surface
Microvilli
Some cells have a free surface that is
extensively folded to form many tiny,
slender projections called microvilli
 Each microvillus is covered by the cell
membrane and has a small amount of
cytoplasm inside of it
 Microvilli are common in cells that absorb
materials, such as cells of the small
intestine, and in cells that release
materials, such as excretory cells in the
kidneys
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Cilia
Cilia are slender projections of the plasma
membrane that extend into a lumen
 They contain an organized arrangement of
proteins called microtubules
 Cilia move about in a coordinated, whiplike manner in order to move body fluids
 Cilia are common in cells of the
respiratory tract which is layered with
mucus
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Flagella
Another modification of the plasma
membrane
 A flagellum is normally a single, long
structure
 Flagella contain microtubules for strength
and stability
 Flagella whip about and provide propulsion
for cells such as sperm cells
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Crossing the Plasma Membrane
Different mechanisms for movement of
materials across the cell membrane are
classified by the nature of the energy that
powers their movement
 Passive—powered by kinetic energy ( a
force that causes molecules to move
randomly)
 Active— demand an input of energy from
the cell/ATP
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Diffusion: A Passive Process
Molecules move from areas of high
concentration to areas of low
concentration
 Molecules move on a concentration
gradient by kinetic energy
 An equal distribution of molecules is called
equilibrium
 Facilitated diffusion occurs when some
molecules bind with integral proteins in
the plasma membrane
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Osmosis: A Passive Process
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The movement of water molecules (only) across
a selectively permeable membrane from an area
of higher water concentration to an area of lower
water concentration
Isotonic Solutions have equal osmotic pressure
Cell is at equilibrium
Hypertonic solutions have more solutes outside
the cell than in (cell will dump water and shrink,
crenation)
Hypotonic solutions have less solutes outside the
cell than in (cell will take in water and swell,
hypertrophy)