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Cytology
Anatomy and Physiology | Tutorial Notes
Cytology
LEARNING OBJECTIVES
After study of today’s learning, the student will:
1.
Explain how cells differ from one another
2.
Describe the general characteristics of a composite cell
3.
Explain how the components of a cell’s membrane provides its function
4.
Describe each kind of cytoplasmic organelle and explain its function
5.
Describe the various cellular structures that are parts of the cytoskeleton and explain their functions.
6.
Describe the cell nucleus and its parts.
7.
Explain how substances move into and out of cells.
8.
Describe the cell cycle.
9.
Explain how a cell divides.
10.
Describe several controls of cell division.
11.
Explain how stem cells and progenitor cells make possible growth and repair of tissues.
12.
Explain how two differentiated cell types can have the same genetic information, but different
appearances and functions.
13.
Discuss apoptosis.
14.
Distinguish between apoptosis and necrosis
15.
Describe the relationship between apoptosis and mitosis.
TUTORIAL OUTLINE
I.
Size and Functions of Cells (see figure 3.1)
A.
B.
Size - of a cell is measured in micrometers (μm).
1.
red blood cell is about 7.5 μm in diameter
2.
human egg cell is about 140 μm in diameter
Differentiation – formation of specialized cells from unspecialized cells
1.
stem cell → hematopoietic stem cell → lymphoblast → lymphocyte
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II.
III.
IV.
V.
3 Parts of a Composite Cell (see figure 3.3)
A.
cell membrane: forms the boundary of the cell
B.
nucleus: contains genetic material (DNA)
C.
cytoplasm: organelles within the cell + fluid
1.
organelles: carry out specialized activities within the cell
2.
cytosol: fluid in which the organelles are suspended
Characteristics of the Cell Membrane
A.
The membrane maintains integrity of the cell
B.
The cell membrane is flexible and somewhat elastic (fluid mosaic)
C.
Selectively permeable: controls which substances move into and out of the cell
D.
signal transduction: process by which a cell receives and responds to messages from outside
the cell
3 components of the cell membrane
A.
Phospholipid Bilayer
B.
Membrane Proteins
C.
Cholesterol
Phospholipid bilayer
A.
hydrophilic “heads”
water-soluble heads face the fluid outside and inside the cell
extracellular fluid (ECF) – fluid outside the cell
intracellular fluid (ICF) – fluid inside the cell
B.
hydrophobic “tails”
water insoluble tails form the interior of the cell membrane
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C.
VI.
Permeability of phospholipid bilayer
1.
The membrane is permeable to small lipid-soluble molecules: O2, CO2, and steroids.
2.
The membrane is impermeable to water-soluble molecules: H2O, electrolytes, sugars,
proteins, amino acids
Membrane Proteins (see table 3.1)
A.
Integral Proteins: extend through the cell membrane
1.
Receptors: bind to specific molecules (ligands), triggering responses from within
the cell.
2.
Pores: aquaporins allow water through
3
Channels: selective to specific ions
4.
a.
Sodium channels – allow sodium through
b.
Potassium channels – allow potassium through
Carrier Proteins: bind specific substrates and transports them across the cell
membrane
a.
Glucose transporter
Transmembrane protein – integral protein with domains inside and outside the cell
B.
Peripheral Proteins: loosely bind to the surface of the cell membrane or to other
membrane proteins.
1.
VII.
CAMs Cellular Adhesion Molecules (CAM) guide cells to target cells
a.
selectin – provides traction on the surface of white blood cells
b.
integrin – guides white blood cells out of the capillaries into nearby damaged
tissue
Cholesterol
A.
Cholesterol helps maintain the integrity of the cell
B.
Cholesterol maintains the fluidity of the cell membrane
C.
Cholesterol helps anchor membrane proteins in place
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VII.
VII.
Cytoplasm
A.
Cytosol: fluid within the cell
B.
Cytoskeleton: framework of the cell
1.
Microtubules: rigid proteins that maintain shape of cell, and transport organelles
2.
Microfilaments: smaller proteins than microtubules, form meshwork of cell
3.
Intermediate filaments: form strong scaffolding that helps the cell form a barrier
Organelles (see table 3.2)
A.
Ribosomes: responsible for protein synthesis
B.
Rough Endoplasmic Reticulum (ER): responsible for protein synthesis
C.
Smooth Endoplasmic Reticulum (ER): responsible for lipid synthesis
D.
Vesicles: membranous sacs that transport substances within the cell
E.
Golgi Apparatus: modifies, packages, and ships proteins throughout the cell
F.
Mitochondria: “powerhouse” energy for the cell in the form of ATP
1.
outer mitochondrial membrane
2.
inner mitochondrial membrane
3.
cristae – folds of the inner mitochondrial membrane
4.
matrix – space within the mitochondria
G.
Lysosome: breaks down carbohydrates, proteins, and other organic molecules
H.
Peroxisome: detoxifies alcohol and other drugs. Breaks down lipids
I.
Centrosome: produces microtubules for the cell; produces spindle fibers during mitosis
1.
VII.
A centrosome consists of a pair of centrioles
J.
Cilia: move substances across the surface of a cell
K.
Flagellum: long extension that propels the cell (tail of a sperm)
L.
Nucleus: Contains the cell’s genetic information (chromatin)
Nucleus of the Cell (see figure 3.19)
A.
Chromatin: is composed of DNA and proteins
1.
Genes are the sequence of DNA that encode the instructions for protein synthesis
2.
During cell division, chromatin condenses into 46 chromosomes
B.
Nucleolus: site of ribosome production.
C.
Nuclear Envelope
1.
2 phospholipid bilayers form and outer and inner membrane
2.
Nuclear Pores: channel proteins that allow certain molecules into and out of the
nucleus
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VIII.
Movements into and out of the cell
A.
Diffusion (simple diffusion)
1.
Diffusion is the random movement from area of higher concentration to lower
concentration, until molecules become evenly distributed (diffuse).
2.
Concentration gradient is the difference in concentration across the cell membrane.
3.
Molecules move (diffuse) down their concentration gradient.
4.
Diffusional equilibrium: When distribution of molecules becomes uniform diffusion
ceases to occur
5.
Requirements for diffusion
a.
only small nonpolar molecules (CO2, O2, steroids) can diffuse across the cell
membrane
b.
a concentration gradient must exist across the cell membrane.
(i)
O2 tends to diffuse into the cells because intracellular [O2] is low,
since it is always being consumed during cell respiration.
(ii)
B.
C.
CO2 tends to diffuse out of the cells because it’s always being
produced during cell respiration
Facilitated Diffusion
1.
Facilitated diffusion is the diffusion of molecules through a channel or carrier protein.
2.
Facilitated diffusion transports small polar molecules into and out of the cell, including
H20, ions, glucose, and amino acids
3.
Movement is still down the concentration gradient (from higher to lower
concentration)
Osmosis
1.
Osmosis is the diffusion of only water across a semipermeable membrane.
2.
Water freely moves across the membrane, but solutes (salts, sugars, proteins,
amino acids, etc.) cannot cross the membrane.
3.
Water moves from an area of lower solute concentration into area of higher solute
concentration (water follows salts!)
http://upload.wikimedia.org/wikipedia/commons/6/62/0307_Osmosis.jpg
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4.
Tonicity: measures the relative solute concentration of a solution
(i)
(ii)
(iii)
isotonic: solution that has the same solute concentration as the cells

Example: cells with 0.9% NaCl are placed in a solution of 0.9% NaCl

Water moves into and out of the cell at equal rates

Cells retain their normal shape
hypertonic: solution that has a higher solute concentration than the cells

Example: cells with 0.9% NaCl are placed in a solution of 2% NaCl

Net movement of water is out of the cell into the surrounding solution

Cells shrink as water leaves the cells
hypotonic: solution that has a lower solute concentration than the cells

Example: cells with 0.9% NaCl are placed in a solution of 0% NaCl

Net movement of water is into the cell from the surrounding solution

Cells swell as water enters the cell

Cell may burst (lyse)
http://commons.wikimedia.org/wiki/File%3AOsmotic_pressure_on_blood_cells_diagram.svg
D.
Filtration
1.
Solution is passed through a membrane, separating larger molecules from smaller
molecules
2.
Filtration requires a pressure gradient (eg. Hydrostatic pressure)
3.
In the body, filtration occurs across capillary walls, where water, electrolytes, and
other small particles are pushed into the interstitial space, leaving proteins and cells
within the capillary
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E.
F.
G.
H.
Active Transport
1.
Movement of molecules, through a carrier protein, from an area of lower
concentration into an area of higher concentration
2.
Requires energy (usually in the form of ATP)
3.
Movement is against the concentration gradient (from lower to higher concentration)
4.
Example includes sodium/potassium pump (Na+/K+ ATPase)
5.
Active transport moves electrolytes, sugars, amino acids, and protons (hydrogen ions)
across the cell membrane
Endocytosis
1.
Cell membrane surrounds and engulfs a substance, forming a vesicle within the cell
2.
Uses cellular energy
3.
Pinocytosis: endocytosis of a fluid
4.
Phagocytosis: endocytosis of a solid
5.
Receptor-mediated endocytosis: specific particles bind to receptors on the cell
membrane, triggering endocytosis of the particles
a.
allows cells to remove specific substances from their surroundings
b.
cells take up cholesterol via receptor-mediated endocytosis of particles of low
density-lipoproteins (LDL)
Exocytosis
1.
Substances within vesicles are released from the cell when the vesicle binds to the
cell membrane.
2.
Essentially the reverse of endocytosis
3.
Neurons communicate with other cells by releasing neurotransmitters via
exocytosis
Transcytosis
1.
Combination of endocytosis and exocytosis
2.
Cells selectively and quickly transport substances from one end of the cell to the
other
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The Cell Cycle: represents the changes that occur within a cell from the time it’s formed until it divides.
IX.
Interphase: period of cell growth and activity
A.
G1 Phase: Period of Cell growth and activity
1.
Restriction Checkpoint: Following G1 phase a restriction checkpoint determines
the fate of the cell. The Cell may:
o Continue in the cell cycle and prepare for cell division
o Remain specialized
o Undergo apoptosis: programmed cell death
X.
B.
S phase (DNA Synthesis): Cell replicates its DNA
C.
G2 Phase: Period of rapid cell growth and protein synthesis as the cell prepares for cell
division
Mitosis: Division of the chromosomes
A.
B.
C.
D.
XI.
Prophase:
1.
Chromatin condenses into chromosomes (Each replicated chromosome
contains 2 sister chromatids connected by a centromere)
2.
Centrosomes (2 centrioles) migrate to opposite poles and form spindle fibers
3.
Nuclear envelope breaks down
Metaphase:
1.
spindle fibers attach to the centromere of each replicated chromosome
2.
chromosomes align along the equatorial plate
Anaphase:
1.
spindle fibers separate sister chromatids (now called chromosomes again)
2.
chromosomes migrate to opposite poles
Telophase
1.
migration of chromosomes is complete
2.
chromosomes unwind back into chromatin
3.
nuclear envelope forms
Cytokinesis: Division of cytoplasm. Begins in anaphase and continues through telophase.
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