Lecture Topics

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Lecture Topics

• Protein Synthesis
• Mitosis
• Epithelial Tissue

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Nucleus

• Most cells have one nucleus.

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Nucleus

• Exceptions
• Skeletal muscle cells are multinucleated.
• Some cardiac muscle cells are binucleated.
• Mature rbc lack a nucleus.

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Nucleus

• Nuclear envelope a double membrane that
  surrounds the nucleus

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Nucleus

• Both layers of the membrane are lipid bilayers

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Nucleus

• Contains a dark spherical body called a nucleoli
  where rRNA are made.

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Nucleus

• The nucleoli assembles rRNA and proteins into
  ribosomes.

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Nucleus

• Ribosomes are exported into the cytosol and play
  a major role in protein synthesis (translation).

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Nucleus

• Contains chromsomes. Humans have 46.

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Nucleus

• 23 pairs of chromosomes
• 23 from mother
• 23 from father

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Nucleus

• All chromsomes are referred to as autosomes
  except one pair. In other words 22 of the pairs
  are autosomes.

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Nucleus

• The last or 23rd pair are referred to as the sex
  chromsomes.

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Nucleus

• The two chromosomes of each pair are called
  homologous chromosomes

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Nucleus

• Each Chromosome is a long molecule of DNA.

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Nucleus

• Each Chromosomes contain thousands of genes
  arranged in a single file.

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Nucleus

• Each gene is a segment of DNA

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Nucleus

• Each gene represents a protein

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Nucleus

• The DNA molecule resembles a spiral ladder called
  a double Helix.

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Nucleus

• Monomers of DNA are called nucleotides.

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Nucleus

• Each monomer or unit of DNA contains a 1.
  pentose sugar
• 2. phosphate group,
• 3. nitrogenous base.

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Nucleus

• There are four different nitrogenous bases
• Adenine
• Thymine
• Cytosine
• Guanine

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Nucleus

• Cytosine always pairs with Guanine

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Nucleus

• Thymine always pairs with Adenine

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Nucleus

• These bases are held together by hydrogen bonds.

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Nucleus

• DNA Template DNA Complementary
• A T
• T A
• G C
• C G
• A T
• T A

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Protein Synthesis

• Two major Parts
• 1. Transcription (takes place in nucleus)
• 2. Translation ( takes place in ribosomes in
  the cytosol)

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Protein Synthesis

• Basic order
• DNA ? mRNA ? Protein

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Protein Synthesis Transcription

• DNA molecules have a template strand and a
  complementary strand.

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Transcription

• In transcription an RNA strand is made from the
  DNA template strand.

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Transcription

• There are three different types of RNA that are
  transcribed mRNA, rRNA, tRNA

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Transcription

• RNA molecules are single stranded unlike DNA
  molecules

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Protein Synthesis Transcription

• At the beginning of a gene there is a DNA
  sequence called a promoter.

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Transcription

• This promoter tells RNA polymerase where to start
  transcription. RNA polymerase catalyzes
  transcription

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Transcription

• As the DNA molecule unzips, bases pair with the
  template strand of the DNA molecule and a
  complementary RNA strand is formed.

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Protein Synthesis Transcription

• RNA have adenine, guanine, and cytosine bases,
  but do not have thymine. Instead they have
  uracil.

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Transcription

• Cytosine, Guanine, and Thymine in the DNA
  template pair with Guanine, Cytosine, and Adenine
  in the RNA strand.

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Transcription

• Adenine in the DNA template pairs with uracil not
  thymine in RNA

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Protein Synthesis Transcription

• DNA Template RNA Strand
• A U
• T A
• G C
• C G
• A U
• T A

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Protein Synthesis Nucleus

• DNA Template DNA Complementary
• A T
• T A
• G C
• C G
• A T
• T A

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Protein Synthesis Transcription

• The terminator is a nucleotide sequence that
  specifies the end of the gene.

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Transcription

• RNA polymerase detaches itself from the
  transcribed RNA molecule and DNA strand.

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Transcription

• The transcribed mRNA molecule is referred to as
  pre mRNA.

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Transcription

• A DNA segment is a gene

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Transcription

• Genes codes for proteins
• DNA segment or Gene ? RNA ? Protein

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Transcription

• Not all parts of a gene code for a protein.

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Transcription

• A gene can be divided into introns and exons.

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Transcription

• Introns are the parts that dont code for a
  protein.

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Transcription

• Exons are the parts that do code for a protein.

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Transcription

• Pre mRNA contains exons and introns

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Protein Synthesis Transcription

• Introns are removed from the pre mRNA and the
  exons are spliced together by small nuclear
  ribonucleoproteins (snRNPs).

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Transcription

• The end product is a mRNA molecule that exits the
  nucleus through a nuclear pore.

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Transcription

• The mRNA travels through the cytosol until it
  reaches a ribosome where translation takes place.

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Question

• Why do introns exist if it is useless informaiton?

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Question

• If there are only 35,000 to 45,000 genes, why are
  there actually 500,000 to 1 million genes?

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Protein Synthesis Translation

• RNA stores genetic information in sets of three
  nucleotides called codons.

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Protein Synthesis Translation

• Each codon specifies a particular amino acid.

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Translation

• There are 64 codons and only 20 amino acids.

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Translation

• This means there are more than one codon for each
  amino acid. In other words, several codons
  specify for the same amino acid.

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Question

• Why this redundancy?

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Six Steps in Translation

1. The mRNA molecule binds to the small ribosomal
   subunit at the mRNA binding site.

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Translation

• 1. Then the initiator tRNA that contains the
  anticodon attaches to the mRNA codon.

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Translation

• 1. The tRNA contains the amino acid that
  corresponds to the codon.

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Translation

• The first codon of an mRNA strand is always AUG,
  therefore methionine is always the first amino
  acid in a protein.

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Translation Steps Cont.

1. The large ribosomal subunit attaches to the small
   ribosomal subunit-mRNA complex, creating a
   functional ribosome.

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Translation

• The initiator tRNA, with the amino acid
  methionine, are now in the P site of the
  ribosome.

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Translation

• 3. Now another tRNA with another amino acid
  attach to the second mRNA codon at the A site of
  the ribosome.

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Translation Steps Cont.

1. A component of the large ribosomal subunit
   catalyzes the formation of a peptide bond between
   methionine in the P site and the amino acid at
   the A site.

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Translation

• Then methionine detaches itself from the tRNA at
  the P site.

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Translation

• 5. The tRNA at the P site leaves.

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Translation

• 5. The ribosome shifts the mRNA strand by one
  codon. Now the tRNA that was in the A site is
  now in the P site.

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Translation

• 5. This allows another tRNA with an amino acid
  to attach to the codon at the A site. Steps 3
  through 5 occur repeatedly.

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Translation Steps Cont.

• 6. Protein synthesis stops when the ribosome
  reaches a stop codon at the A site.

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Translation

• 6. When a ribosome reaches a termination codon
  on the mRNA, the A site of the ribosome accepts a
  protein called a release factor instead of tRNA

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Translation

• 6. Release factor hydrolyzes the bond between
  the tRNA in the P site and last a.a. of the
  protein.

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Translation

• 6. Then the completed protein detaches from the
  final tRNA.

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Translation

• 6. After the tRNA leaves the P site the ribosome
  disassociates into small and large subunits.

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DNA Viruses

• In a DNA virus the, the virus uses the host cells
  machinery to replicate itself.

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DNA Viruses

• The virus is made up of a protein capsid with
  viral DNA inside.

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DNA Viruses

• It uses the host cells machinery and duplicates
  the DNA and makes new protein capsids via protein
  synthesis.

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RNA Viruses

• In RNA retroviruses like HIV, it is a little
  different from DNA viruses but same concept. It
  uses the host cells machinery to replicate
  itself.

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RNA Viruses

• The virus is made up of viral RNA surrounded by a
  protein capsid.

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RNA Viruses

• It forms a complementary DNA strand via reverse
  transcriptase.

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RNA Viruses

• After the DNA forms double strands, it then
  replicates more viral RNA via transcription

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RNA Viruses

• It also makes more capsid proteins via
  translation.

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10 minute Break

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Cell Division

• Interphase
• Mitosis
• Cytokinesis

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Interphase

• Our cells are in interphase 90 of the time.

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Interphase

• During this time the DNA, protein, and RNA are
  referred to as chromatin.

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Interphase

• The chromatin looks like a diffuse granular mass.

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Interphase

• There are three phases of interphase.

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3 Stages of Interphase

• G1 phase
• During this phase it duplicates most of its
  organelles.

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3 Stages of Interphase

• S phase
• Chromosomes duplicate during this stage. The
  duplicated chromosomes are attached at the
  centromere are referred to as chromatids.

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3 Stages Cont.

• G2
• Cell growth continues and enzymes and other
  proteins are synthesized.
• Some cells for example remain in the G1 stage
  forever for example nerve cells. They are said
  to be in the G0 stage

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4 Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromatin fibers condense and are now visible
  underneath the microscope as individual
  chromosomes.

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Prophase

• The chromosomes have been replicated and are
  attached to its double or sister chromatid by the
  centromere.

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Prophase

• Later in prophase mitotic spindle radiating from
  the centrioles attach to the kinetochore ( a
  protein complex outside the centromere).

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Prophase Cont.

• Nucleoli disappears
• Nuclear envelope disappears as well

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Metaphase

• The mitotic spindle aligns the centromeres of the
  chromatid pairs at the metaphase plate.

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Anaphase

• The centromeres split separting the two members
  of each chromatid pair, which move toward
  opposite poles of the cell.

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Anaphase

• Once separated, the chromatids are termed
  chromosomes.

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Anaphase

• The chromosomes appear V shaped because the
  centromeres lead the way as they are being pulled
  by the mitotic spindle.

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Telophase

• Most events are opposite of prophase

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Telophase

• Chromosome revert back to a chromatin like
  appearance.

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Telophase

• Nuclear envelope develops around each set of
  chromosomes.

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Telophase

• Nucleoli reappears

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Telophase

• Mitotic spindle disappears

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Telophase

• Cleavage furrow appears

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Cyokinesis

• The cytoplasm, organelles and the two nuclei are
  divided into two daughter cells.

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Tissues

• Epithelial Tissue
• Connective Tissue
• Muscle Tissue
• Nervous Tissue

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Epithelial Tissue

• Covers the external body surface (epidermis),
  lines cavities and tubules, and generally marks
  off our insides from our outsides

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Epithelial Tissue

• Contain cell junctions

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Epithelial Tissue

• Avascular

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Epithelial Tissue

• Contains nerve supply

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Epithelial Tissue

• High rate of mitotic division

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Cell junctions

• They are contact points between the cell
  membranes of tissue cells.
• Five types
• Tight Junctions
• Adherens Junctions
• Desmosomes
• Hemidesmosomes
• Gap Junctions

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Tight Junctions

• This prevents the passage of substances between
  cells.

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Adherens Junctions

• Helps epithelial surfaces resist separation

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Desmosomes

• Contribute to stability
• Prevent epidermal cells from separating under
  tension and cardiac muscle cells from pulling
  apart during contraction.

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Hemidesmosomes

• Anchor cells

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Gap Junctions

• Allows cells in tissues to communicate

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Epithelial Cell Surfaces

1. Apical Surface Faces the body surface, a body
   cavity, the lumen, or a tubular duct

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Epithelial Cell Surfaces

• 2. Lateral surfaces - Face adjacent cells.
  Contain cell junctions except hemidesmosomes

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Epithelial Cell Surfaces

• 3. Basal surface - Opposite of apical surface.
  Attaches to the basal lamina of the basement
  membrane, an extracellular layer

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Types of Epithelial Tissue

• Simple Squamous
• Simple Cuboidal
• Simple Columnar
• Ciliated Simple Columnar
• Stratified Squamous
• Stratified Cuboidal
• Stratified Columnar

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Types Cont.

• Transitional
• Pseudostratified columnar

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Simple Squamous

• Single layer of cells
• Scale like

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Simple Squamous

• Functions in filtration, diffusion, osmosis, and
  secretion

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Simple Squamous

• Lines heart, blood vessels, air sacs, glomerular
  capsule of kidneys, serous membranes

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Simple Cuboidal

• Single layer
• Cube Shaped

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Simple Cuboidal

• Function in secretion and absorption

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Simple Cuboidal

• Covers surface of ovary, lines kidney tubules and
  small ducts of glands (thyroid and pancreas)

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Simple Columnar epithelium

• Single layer
• Rectangular shaped
• Some contain goblet cells

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Simple Columnar epithelium

• Function in secretion and absorption

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Simple Columnar epithelium

• Lines G.I. tract from stomach to the anus,
  gallbladder

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Ciliated Simple Columnar

• Single layer
• Columnar shaped
• Some contains goblet cells
• Ciliated

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Ciliated Simple Columnar

• Function in moving mucus and other substances

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Ciliated Simple Columnar

• Uterine tubes, uterus, central canal of spinal
  cord

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Stratified Squamous

• Several Layers
• Scale like shaped

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Stratified Squamous

• Function in protection

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Stratified Squamous

• Superficial layer of the skin, lining of the
  mouth, esophagus, epiglottis, vagina, and tongue

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Stratified Cuboidal

• Several layers
• Square or cube shaped in apical layer

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Stratified Cuboidal

• Function in protection and some secretion and
  absorption

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Stratified Cuboidal

• Ducts of sweat glands, esophageal glands, and
  male urethra

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Stratified Columnar

• Several Layers
• Rectangular shaped in apical layer

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Stratified Columnar

• Function in protection and secretion

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Stratified Columnar

• Part of urethra, large excretory ducts of some
  glands (esophageal)

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Transitional Epithelium

• Several layer
• Scale to cube shaped

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Transitional Epithelium

• Function in permitting distention

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Transitional Epithelium

• Lines urinary bladders and portions of ureters
  and urethra

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Pseudostratified Columnar

• Not stratified

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Pseudostratified Columnar

• ciliated

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Pseudostratified Columnar

• Nucleus of cells are at different levels, all
  cells are attached to a basement
• membrane, but not all reach the surface

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Pseudostratified Columnar

• Function in secretion and movement of mucus

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Pseudostratified Columnar

• Trachea, epididymis, and part of male urethra

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