Transcript Marieb’s Human Anatomy and Physiology Marieb w Hoehn Chapter 3 Cells: The Living Units Lecture 5 Video Part II.

Marieb’s Human
Anatomy and Physiology
Marieb w Hoehn
Chapter 3
Cells: The Living Units
Lecture 5 Video Part II
1
Lecture Overview
• Part 1
– Specialization and differentiation of cells
– General characteristics of cells
– The cell membrane
• Part 2
– Movement of substances into and out of the cell
– Osmotic pressure and tonicity
• Part 3
– Overview of cellular organelles
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Movements Into and Out of the Cell
Passive (Physical) Processes
• require no cellular
energy
• simple diffusion
• facilitated diffusion
• osmosis
Active (Physiological) Processes
• require cellular energy
• active transport
• endocytosis
• exocytosis
• transcytosis
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Simple Diffusion
Figure from: Hole’s Human A&P, 12th edition, 2010
Solutes will evenly disperse in a solvent with time
by diffusion. This is the lowest energy state.
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Simple Diffusion
• movement of solute from regions of higher concentration to
regions of lower concentration (a physical process)
Figure from: Hole’s Human A&P, 12th edition, 2010
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Simple Diffusion and Concentration Gradient
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Where Would You Rather Be?
“Spread out, would ya!?”
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Facilitated Diffusion
• diffusion across a membrane with the help of a channel or
carrier molecule
• e.g, transport of
glucose across cell
membrane
BUT…still from a
region of higher
concentration to a
region of lower
concentration
Figure from: Hole’s Human A&P, 12th edition, 2010
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Factors Influencing Diffusion Rates
• Distance (shorter is faster)
• Gradient size (bigger difference in
concentration is faster)
In the body, diffusion
distances are
typically limited to a
maximum of about
125 µm
• Molecule size (smaller is faster)
• Temperature (warmer is faster)
• Electrical forces (repulsion is better)
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Diffusion and the Cell Membrane
Carrier/channel
proteins required
for all but fatsoluble molecules
and small
uncharged
molecules
oxygen, carbon
dioxide and other
lipid-soluble
substances diffuse
freely through the
membrane
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Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Osmosis
• movement of water (solvent) through a selectively permeable
membrane from regions of higher water concentration to
regions of lower water concentration
• *water always moves toward a higher concentration of solutes
A special case of
passive diffusion
Figure from: Hole’s
Human A&P, 12th
edition, 2010
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Osmotic Pressure/Tonicity
Osmotic Pressure – ability of osmosis to generate enough
pressure to move a volume of water
*Osmotic pressure increases as the number of nonpermeable
solutes particles increases
0.9% NaCl
• isotonic – same
5.0% Glucose
osmotic pressure as a
second solution
Figure from: Hole’s Human A&P, 12th edition, 2010
• hypertonic – higher
osmotic pressure
• hypOtonic – lower
osmotic pressure
Crenation
The O in
o
hyp tonic
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The Effect of Osmolarity on Cells
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Filtration
• smaller molecules are forced through porous membranes
• separates large from small molecules
• hydrostatic pressure; important in fluid movement
• molecules leaving blood capillaries
Think
‘sprinkler hose’
Figure from: Hole’s Human A&P, 12th edition, 2010
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Active Transport
• carrier molecules transport substances across a membrane from regions of
lower solute concentration to regions of higher concentration, i.e., against a
concentration gradient
• sugars, amino acids, sodium ions, potassium ions, etc.
Active transport
is a physiological
process since it
requires cellular
energy, e.g., ATP
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Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson
Transmembrane Potential
Dependent upon active transport
Cells maintain a
transmembrane
potential, with
the inside of the
cell membrane
being slightly
negative relative
to the outside
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
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Endocytosis
• cell engulfs a substance by forming a vesicle around the
substance
• three types
• pinocytosis – substance is mostly water
• phagocytosis – substance is a solid
• receptor-mediated endocytosis – requires the
substance to bind to a membrane-bound receptor
Figure from: Hole’s Human A&P, 12th edition, 2010
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Endocytosis
Figures from: Hole’s Human A&P, 12th edition, 2010
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Exocytosis
• reverse of endocytosis
• substances in a vesicle fuse with cell membrane
• contents released outside the cell
• release of neurotransmitters from nerve cells
Figure from: Hole’s Human A&P, 12th edition, 2010
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Transcytosis
• endocytosis followed by exocytosis
• transports a substance rapidly through a cell
• HIV crossing a cell layer
Figure from: Hole’s Human A&P, 12th edition, 2010
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